Citation
Clover residue effectiveness in reducing orthophosphate sorption on ferric-hydroxide coated soil

Material Information

Title:
Clover residue effectiveness in reducing orthophosphate sorption on ferric-hydroxide coated soil
Creator:
Easterwood, George William, 1955-
Publication Date:
Language:
English
Physical Description:
ix, 155 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Dissertations, Academic -- Soil Science -- UF
Soil Sciences thesis Ph. D
Soil absorption and adsorption -- Effect of clover on ( lcsh )
Soil solutions ( lcsh )
City of Madison ( local )
Clover ( jstor )
Soil science ( jstor )
Adsorption ( jstor )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1987.
Bibliography:
Includes bibliographical references (leaves 148-154).
Additional Physical Form:
Also available online.
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by George William Easterwood.

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University of Florida
Holding Location:
University of Florida
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The University of Florida George A. Smathers Libraries respect the intellectual property rights of others and do not claim any copyright interest in this item. This item may be protected by copyright but is made available here under a claim of fair use (17 U.S.C. §107) for non-profit research and educational purposes. Users of this work have responsibility for determining copyright status prior to reusing, publishing or reproducing this item for purposes other than what is allowed by fair use or other copyright exemptions. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder. The Smathers Libraries would like to learn more about this item and invite individuals or organizations to contact the RDS coordinator (ufdissertations@uflib.ufl.edu) with any additional information they can provide.
Resource Identifier:
021065735 ( ALEPH )
17886201 ( OCLC )

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Full Text














CLOVER RESIDUE EFFECTIVENESS IN REDUCING ORTHOPHOSPHATE SORPTION ON FERRIC-HYDROXIDE
COATED SOIL














By

GEORGE WILLIAM EASTERWOOD
















A DISSERTATION PRESENTED TO
THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE
OF DOCTOR OF PHILOSOPHY






UNIVERSITY OF FLORIDA


1987
































Dedicated with love to B.J.















ACKNOWLEDGEMENTS

With the help of various individuals, both friends and family. I was encouraged to pursue a doctoral degree. They directed me in obtaining the best education possible, and guided me to a more fulfilled life, both philosophically and intellectually.

I am deeply indebted to Dr. J. B. Sartain, my major professor, who painstakingly helped mold me intellectually. He shared with me his values, work ethic, and extensive knowledge as professor and friend. I am very fortunate to have a Supervisory Committee of scientists who display avant garde concepts. Dr. J. G. A. Fiskell, Dr. J. J. Street, Dr. E. A. Hanlon, Dr. W. G. Harris, and Dr. S. H. West are men of enlightnment and inspiration. In my opinion, I have had a Supervisory Committee that excelled in knowledge, guidance, and helpfulness. I am sincerely grateful to these gentlemen for their help and accessibility despite rigorous schedules.

I truly thank my mother and father for their encouragement in pursuing the doctoral degree. My parents, who so long ago gave me gifts of direction, self discipline, and character development by





iii









emulation, anchored by a spirit of love, aided me more than they will ever know.

During the third year of my pursuit of a doctorate, I endured a bitter disappointment that almost devastated me. Miss Betty Jean (B.J.) Cross, my former fiancee, passed from this life. She endured the rigors of graduate school with me and was always supportive. This beautiful lady, both physically and spiritually. shall always be in my memory. It is to her, that this work is dedicated.








































iv


















TABLE OF CONTENTS

ACKNOWLEDGMENTS. ........................*ii

ABSTRACT ........................................... vii

CHAPTERS

I INTRODUCTION .........................................1

II LITERATURE REVIEW.............................4

Effect of Iron Oxides on Soil Chemical
Properties ....................... .. ..........4
Present Management Practices for Reduction
of P Fixation ................................9
Decompositional Products of Organic
Materials... ...................13
Organic Anion and Iron Mineral Interactions...... .................................. ..............17
Organo-Mineral Reactions Affecting P
Fixation............. ............................20

III ORGANIC ADSORPTION EXPERIMENT................25

Introduction..... ...... ......................25
Materials and Methods ........................26
Results and Discussion.......................33
Conclusions..................................45

IV PHOSPHATE AND ORGANIC AMENDMENT EXPERIMENT...50

Introduction.......... ......................50
Materials ........................ ............51
Methods.... ....... .................. .......52
Incubation Study ...........................52
Glasshouse Study........................... 52
Surface Charge............................... 55
SEM Study .............. ..................56
Results and Discussion..........................56
Incubation Study............................56
Glasshouse Study........................... 65
Surface Charge............................111
SEM Study................................. 118
Conclusions.................................121




V











V FERTILIZER COATING AND PLACEMENT EXPERIMENT.125

Introduction.. ................ ........... .......125
Materials and Methods ...... ................126
Results and Discussion...................... 129
Conclusions.................................. 140

VI SUMMARY AND CONCLUSIONS.......................145

BIBLIOGRAPHY............................................... 148

BIOGRAPHICAL SKETCH ........... ....................155




















































vi
















Abstract of Dissertation Presented to the Graduate
School of the University of Florida in Partial
Fulfillment of the Requirements for the Degree of
Doctor of Philosophy


CLOVER RESIDUE EFFECTIVENESS IN REDUCING
ORTHOPHOSPHATE SORPTION ON FERRIC-HYDROXIDE COATED SOIL

By

GEORGE WILLIAM EASTERWOOD August, 1987

Chairman: Dr. J. B. Sartain Major Department: Soil Science Department

Laboratory research suggests that organic acids bind to iron-mineral surfaces, reducing P fixation. Experiments were conducted to determine 1) maximal clover residue adsorption, 2) P fixation capacity of Fe(OH)3 treated topsoil and goethite coated subsoil amended with clover, 3) clover residue effectiveness in relation to maize yield and extractable P levels, and 4) surface charge with P, clover, and P and clover applications to Fe(OH)3 treated soils.

Amorphous iron-hydroxide (Fe(OH)3) precipitate was applied to Orangeburg soil (fine, loamy, siliceous, thermic Typic Paleudult) at rates of 0 and 5.6 g Fe as Fe(OH)3. White clover (Trifloium repens) was grown hydroponically in Hoagland's solution.




vii









Maximum clover residue adsorption occurred at pH 6.3 with Fe(OH)3 addition. Without Fe(OH)3 application, adsorption was dependent on solution ionic strength.

Clover applications decreased P adsorption within each sampling time (30, 60, 90 d) for Orangeburg soil with synthetic Fe(OH)3 and Orangeburg subsoil containing goethite but increased P fixation without Fe(OH)3 application.

A glasshouse experiment was conducted to measure maize yield, P uptake and extractable P levels. Two crops of maize were grown 50 d each prior to P refertilization for the third crop. An increase of 350% in maize yield with increases in P uptake and extractable P levels was observed with clover and P applications compared to P fertilization only, on Fe(OH)3 treated soils within cropping periods. A second experiment was conducted to determine effectiveness of coating diammonium phosphate (DAP) with clover to reduce P fixation around fertilizer microsites. Point placement of fertilizer and granules was superior to mixing fertilizer and clover to soil as measured by yield, P uptake, and extractable P levels. Granules were superior to point placement in increasing P uptake and extractable P levels on Orangeburg + Fe(OH)3 soil.








Viii










Surface charge studies indicated negative shifts in Zero Point of Charge (ZPC) with P and clover applications. A ZPC of 4.7, the pK of carboxyl groups, was observed with clover addition. Mechanisms of ionic complexation by organic functional groups and organic ligand exchange appeared to exist from these observations. Experimental observations indicate that applications of clover to Fe(OH)3 treated soils enhanced crop production.









































ix
















CHAPTER I
INTRODUCTION



In the soil environment, chemical processes favor equilibrium status of minerals although equilibrium is seldom obtained (Kittrick, 1977). Rain, however, dilutes the soil solution and promotes dissolution of mineral phases thereby increasing the soil solution activity of certain ionic species. Partial desorption of ions bound to the exchange complex also buffers the soil system. Conversely, drought may increase soilsolution ionic concentration until it is supersaturated, resulting in precipitation of a solid phase. Changes within the soil chemical environment can promote mineralogical transformations. Each of these processes, as described by Lindsay (1979), over time produce minerals possessing greater resistance to weathering. Iron-oxide formation is indicative of highly-weathered soils (Schwertmann and Taylor, 1977). Iron oxide or hydroxide minerals may exist as an independent solid phase in soils where sufficient Fe oxide concentrations exist or occur in association with the clay fraction (Carroll, 1958). In either case, iron oxides could effect surface chemistry by coating clay minerals (Stevensen, 1982).


1






2


Phosphorus (P) fixation, which is reduction of soil solution phosphate by Fe minerals, may occur by adsorption to the solid phase or precipitation reactions from the solubility products (Chu et al., 1962). Adsorption may occur as a mono- or binuclear covalent bonding to the Fe mineral (Hingston et al., 1974). Binuclear adsorption is irreversible in that desorption is negligible. Iron ionic species may reduce P availability below pH 5.5 through precipitation reactions. If the solution species of Fe and H2PO4 reach saturation with respect to the solubility product of strengite (FePO4 2H20), precipitation can result (Lindsay, 1979).

Present management practices for reduction of P

fixation include either P as an amendment, or use of a low input strategy which includes proper placement, less costly P sources, and soil amendments such as lime or silicates (Sanchez and Uehara, 1980). Another management practice that could possibly reduce P fixation would be to apply an organic amendment to the soil. Humic and fulvic acids covalently bind to Fe mineral surfaces (Parfitt et al., 1977) and reduce net positive charge (Moshi et al., 1974). Complexation of solution Fe or Al may occur by bonding ionically to the organic functional groups (Deb and Datta, 1967).

Less costly management practices of applying crop residue possibly could substantially increase agronomic





3


yield on high P-fixing soils. To test this hypothesis experimental objectives are 1) to assess the effectiveness of organic amendment on Fe(OH)3-treated soil which can be measured by dry-matter yield, P uptake, and extractable P levels.

2) to determine the effectiveness of organic coating on fertilizer phosphate granules in relation to dry matter yield, P uptake, and extractable P levels.















CHAPTER II
LITERATURE REVIEW



Effect of Iron Oxides on Soil Chemical Properties

Iron oxides can exist as independent minerals in soils where significant concentrations of these oxides have accumulated (Schwertmann, 1959), or can occur in association with the clay fraction (Carroll, 1958). Follett (1965) studied the retention of amorphous ferric hydroxide in association with kaolinite, quartz, and gibbsite. He observed that the amorphous material reacted immediately with kaolinite on basal plane surfaces. Smaller amounts of amorphous ferric hydroxide were adsorbed on finely ground quartz and an insignificant amount to gibbsite. At the experimental pH of 5,

which would create a net positive charge on the amorphous colloid, adsorption to negatively charged kaolinite could occur. If ferric hydroxides existed in sufficient amounts to coat soil particles, the surface

chemical properties would approach that of the ferric hydroxide (Stevensen, 1982).











4






5


Surface Chargg of Iron Oxides

Surface charge of Fe oxides is pH dependent as

shown in the following model (Parks and deBruyn, 1962):

Charge (+) Charge (0) Charge (-)

OH2 + OH2 0 OH

OH OH

Fe A Fe Fe C

H+ H+

OH2 OH OH

Adsorption or desorption of H+ creates either a positive, neutral or negative charge on the oxide surface. As a pH-dependent charge is developed, an anion or cation (A or C ion model) is attracted to and satisfies the electrostatic charge according to the law of electroneutrality in the outer diffuse electric double layer. This type of adsorption is termed nonspecific adsorption or ionic bonding (Schwertmann and

Taylor, 1977).

A stronger adsorption bond is produced when ions penetrate the coordination shell of the Fe atom on the oxide surface and exchange their OH and OH20 ligands. A covalent bond is produced between the anion and oxide and is termed specific adsorption (Stevensen, 1982). Phosphate Fixation by Iron Oxides

Soils rich in Fe oxides, such as some Utisols and Oxisols of the tropics, are known for their low availability of phosphate (Kamprath, 1967; Fox and Kamprath,






6


1970). In most cases, high P content is associated with high Fe content in the soil such that Fe minerals are thermodynamically sinks for P (Taylor and Schwertmann, 1974).

Mechanisms of P fixation by Fe oxides are by precipitation and/or adsorption reactions (Chu et al., 1962). Under acidic soil conditions, the ionic activities of solution species of Fe and H2PO4 may reach saturation with respect to the solubility product of strengite (FePO4 2H20) (Lindsay, 1979). Concurrently, precipitation of strengite at low pH would occur (Lindsay and Moreno, 1960). Progressively less phosphate is precipitated as the pH is increased (Struthers and Sieling, 1950).

Specific adsorption of phosphate is another mechanism of reducing plant-available P. Hingston et al. (1974) found differences in surface-charge values of goethite after phosphate addition while measuring P adsorption. They postulated that the difference in charge was due to either mononuclear or binuclear adsorption of phosphate as shown in the following schematic:





7



OH2 -2 OH2 -1

Fe 0O Fe



0 0 P +OH

OH \ 00

Fe Fe

OH2 OH2

Reversibly adsorbed P Irreversibly adsorbed P

Wann and Uehara (1978) determined that phosphate addition to Fe-oxide-rich Oxisols lowered the ZPC and increased surface charge density at any pH above the ZPC. They suggested phosphate as an amendment to increase cation exchange capacity. Parfitt et al. (1975) confirmed the binuclear coordination of phosphate adsorption in goethite using infrared spectroscopic analysis. Increasing surface area of major soil Fe oxides was observed in which amorphous ferric hydroxide > lepidocrocite > goethite > hematite. Phosphorus adsorption also increased with increasing mineral surface area.

Kinetics

Hsu (1965) studied phosphate fixation with soils possessing Fe and Al oxides. He observed a two-stage reaction rate in which P was fixed rapidly within a few minutes or hours and a slower rate with increasing time. Adsorption of P to Fe oxides is postulated to be





8


a first order relationship after 48 hours of reaction time (Ryden et al., 1977) such as:


[A) = K[A]
t

when A, t, and K represent phosphate concentrations, time, and a constant, respectively (Bohn et al., 1985). Differences in reaction rates were attributed to mineral and solution Fe and Al (Hsu, 1965). He also stated that in principle, there was no difference between precipitation and adsorption reactions. He noted that whether a Fe6(OH)12(H2PO 4)6 or Fe54(OH)144(H2P04)18 compound is formed is irrelevant since the chemical reaction is the same.

Desorption is also an extremely complex phenomenon. If the enthalpies of the mononuclear and binuclear Fe phosphate complexes are similar, the binuclear adsorption would exhibit greater stability (Hingston et al., 1974) due to an increase in entropy (Martell and Calvin, 1952). Slow release of phosphate from Fe oxides has been attributed to a ring-forming, binuclear phosphate adsorption (Atkinson et al., 1972). Phosphorus Fixation by Organic Components

During the decomposition of organic materials in acidic soils, organic functional groups can form a stable complex with Fe or Al in solution (Deb and Datta, 1967). Humic acids extracted from acid soils usually have a high Al and Fe content (Greenland,






9


1965). Phosphate adsorption may occur on organic material by cation bridging to Fe and Al. Bloom (1981) determined that P is strongly adsorbed by Al-saturated peat within the pH range of 3.2 to 6.0. He postulated that the mechanism of fixation was an adsorption of orthophosphate to trivalent complexed Al followed by the precipitation of amorphous Al-hydroxy-phosphate such as A1(OH)2H2P04. The strength of phosphate adsorption by this mechanism was less than that for an Al-permanent charge resin but greater than that on a weight basis of organic matter obtained from an Andept soil.

Present Management Practices for Reduction of P Fixation

There are at present two management alternatives for favorable P fertility on acidic soils (Sanchez and Uehara, 1980). One is a high input strategy utilizing P as an amendment and the other is a more economical low input strategy. Each method will be discussed. Phosphorus as an Amendment

Fox and Kamprath (1970) determined that 95% of the maximum yield could be obtained when the fertilizer rate was adjusted such that 0.2 ug P/ml existed in the soil solution as determined by adsorption isotherms on acidic soils. To obtain that concentration, 700 kg P/ha were added. Ten y after the initial experiment, the residual efficiency which is fertilizer P effectiveness in crop production over time, ranged from






10


28 to 50%. It was noted that soil properties affected the residual effectiveness. Kamprath (1967) found that previously applied high rates of P fertilizer oxisols resulted in increased yield 9 y later and that supplemental P application greatly increased yield.

Fox and Kamprath (1970) also determined that the P fixation capacity of acidic soils was reduced by high rates of initial P applications. It took less application of P. with increasing rates of initial P application, to maintain 0.2 ug P/ml in the soil solution after 10 y.

An increase in cation exchange capacity (CEC) was accomplished by phosphate addition. As stated previously, adsorption of phosphate to Fe-oxide-coated soils increased the net negative charge of the colloid and thereby the CEC (Wann and Uehara, 1978).

High applications of P may also increase the soil pH. In acidic soils, soil-solution Al and Fe may be precipitated, thus reducing their activity (Lindsay, 1979). Stoop (1974) observed that ammonium phosphate addition increased acidic soil pH due to a decrease in anion exchange capacity.

Low Input Strategy

An alternative to the costly applications of

massive rates of P would be the low input strategy of increased P fertilization efficiency by improving placement, using cheaper sources of P. and decreasing P









fixation through various amendments (Sanchez and

Uehara, 1980).

Placement

Placement of fertilizer P can have an effect on yield. Kamprath (1967) obtained similar yields of maize by banding 22 kg P/ha for 7 y (154 kg P/ha) as compared with an initial application of 350 kg P/ha. Yost et al. (1979) observed that banding was inferior to broadcast applications to a high-P fixing Oxisol in Brazil, with very low levels of extractable P. The best methodology for high P fixing soils probably is an initial broadcast of P fertilizer with small annual bandings of P fertilizer (Sanchez and Uehara, 1980). P Sources

Lower cost phosphate fertilizers such as phosphate rock may substitute for higher cost more soluble phosphate sources. Reactivity, as determined by the absolute citrate solubility (Lehr and McClellan, 1972) of the rock source, determines its effectiveness on acidic soils. The initial relative agronomic effectiveness of rock sources as compared to soluble superphosphate was observed by Hammond (1978) to be 79 to 94% for high, 41 to 65% for medium and 27 to 40% for low reactivity rock sources. He also observed an increase in the calculated relative agronomic effectiveness values for rock sources during subsequent cropping resulting from the slow-release characteristics of the source. Phosphate






12


rock may also produce a liming effect when there is a slow-carbonate release from highly-reactive rock

(Easterwood, 1982).

Soil Amendments

Soil amendments may aid in reducing P fixation.

The addition of lime reduced P fixation as measured by adsorption isotherms of Oxisols (Mendez and Kamprath, 1978), Ultisols (Woodruff and Kamprath. 1965), and Andepts (Truong et al., 1974). The pH of these soils was below pH 5.2 initially. With an increase in soil pH, the soil-solution Fe and Al activity was reduced (Lindsay, 1979). Although liming may reduce P fixation, the orthophosphate adsorption mechanism can still be operable (Parfitt et al., 1975).

Addition of silicate salts may also reduce P fixation. The silicate anion may replace phosphate on oxide surfaces (Silva, 1971). Roy et al. (1971) observed a decrease of 47% in P fixation on an Ultisol, 41% on an Oxisol, and 9% on an Inceptisol when 500 mg
-1
Si kg as calcium silicate was added to these soil

oxides.

Another management practice that could possibly

reduce P fixation is the addition of organic matter to soils. Sanchez and Uehara (1980) state that organic radicles could block exposed hydroxyls on surfaces of Fe and Al oxides. They noted that topsoils with the






13


same mineralogy as subsoils fix considerably less P due to the organic content in the topsoil.

Decomposition Products of Organic Materials

A synopsis of previous research of the chemical nature of soil organic compounds was compiled by Greenland (1965). Component properties of the humicacid, fulvic-acid, and humin fractions were obtained from his publication and are reported below. Humic Acids

Humic acids are composed of amino acids and

phenolic compounds combined to form high molecular weight polymers (20,000 to 30,000). This component of organic matter is soluble in alkali and precipitated by acids. Research data indicate that humic acids at low pH have a spherical configuration. As the pH of the environment around the polymer is increased, the molecular compound increases in charge and becomes more flattened due to reduction in H bonding. Titration curves indicate a large number of acidic groups, of which about half possess a negative charge in the pH range of 5.0 to 7.0.

Fulvic Acids

Fulvic acids are more heterogenous than humic

acids. Fractionation of fulvic acids reveals that the principle components are phenolic materials similar to humic acids but with lower molecular weight. Up to 30% of the fulvic acid may consist of polysaccharides which






14


also may form polymers. Polymers appear to be large, linear, flexible molecules having less carboxyl groups than in humic acids.

Humins

Humins are organic compounds which are irreversibly bound to the mineral part of the soil. It appears that humins have a lower carbon content compared to humic acids possibly from less aromatic compounds adsorbed to the mineral surface. These compounds appear to possess resistance against microbial degradation.

Clover Humification: Rate, Products, and Functional Groups

To assess the humification process, the degradation of clover (Trifolium repens) will be discussed. Topics of discussion for this section were obtained from Kononava (1966).

Plant residue decomposition is accomplished by a

variety of soil microorganisms whose speciation depends on the chemical composition of the plants and soil environmental conditions. Microbes oxidize the plant material which loses its stability resulting in a

decrease in weight and volume. During humification, plant residues became brown in color and, if enough water is present, an aqueous solution of humic substances may be formed.






15


Rate of Decomposition

First signs of humification of clover leaves

appear within 2 to 4 d with the first appearance of

humic substances 2 wk after inoculation. The following

observations were recorded:


Clover leaves. A microscopic examination of
different sections of tissue humification enabled
us to distinguish the following stages of
humification:

1) A darkening of the leaves 3 to 4 days after the start of the experiment; this appears to be
brought about the action of oxidizing enzymes in
the tissues and also by the activity of mold fungi
which form a weft on the leaf surfaces.

2) In the following 7 to 8 days. the development
of an enormous number of different bacteria and
protozoa is observed in the leaf tissues. The
number of bacteria is so great that in some
sections the tissues are completely filled with
them. A gradual disappearance (like "dissolving")
of the cell walls of the epidermis,
particularly noticeable in young leaves, is
observed from a microscopic examination of the
leaf surface. At the same time, bacteria, found
after isolation to be cellulose myxobacteria have
penetrated into the interior of the epidermal
cells.

3) These bacteria, which are at first colorless, later group themselves into slimy masses, become
brown in color, and completely fill the cell.
After some time, the bacteria mass in the cells
undergoes lysis and is converted into a brown liquid which seeps out of the cell (Kononova,
1966. p.147)

Total humification of clover leaves took about 3

wk. Weight loss was 50 to 70% of the original

material.





16


Degradation Products

Decomposition rate is influenced by the ease of

metabolism of the organic substrate and the percentage of slowly-metabolizable compounds. On a percentage basis of dry ash-fee material before humification, clover leaves contained 23% organic-soluble substances (i.e. benzene-ethanol), 3% starch, 8% hemicellulose, 15% cellulose, 22% protein, and 4% lignin. After the humification reactions, the residue, expressed as a percentage of dry ash-free material, contained 16% substances extracted by organic solvent, 0% starch, 6% hemicellulose, 13% cellulose, 34% protein, and 16% lignin. Comparisons of chemical composition of humified and non-humified residues suggests that the percentage of material extracted with ethanol-benzene, starch, and cellulose decrease greatly during humification. Humus has a larger percentage of protein and lignin than non-humified clover since the previous components are easily metabolized. The most stable substance was lignin whose content decreased very little. Type and Distribution of Functional Groups

Clover leaves contain 57% C, 6% H, 32% 0, and 5% N on a dry weight basis. Configural arrangement of these elements into organic functional groups determines the reactivity of the compound or polymer. Humic substances formed from clover tend to be acidic in nature due to the reactivity of their functional groups






17


releasing H+ as the pK value is reached. On a percentage basis of dry ash-free material, plant residue contains 9% carboxylic, 8% alcoholic-OH, 6% phenolic-OH, and 3% methoxy functional groups producing the high reactivity of humified organic material. Inorganic P Released From Clover Decomposition

During the decomposition of clover, inorganic

phosphate may be mineralized. Lockett (1938) postulated that P was mineralized and assimilated into microbial lipids and nucleoproteins. Later P became available upon disintergration of microbial cells. He determined that, after decomposition, 59% of the total P was in organic form and 41% in inorganic form. He obtained similar results as those observed by Kononava (1961).

Organic Anion and Iron Mineral Interactions

Unlike cation bridging of organic anions to clays (Evans and Russell, 1959), the mechanism of humic and fulvic-acid anion bonding to Fe minerals is by specific adsorption or ligand exchange (Parfitt et al., 1977). The process is not sensitive to electrolyte concentrations, although it is sensitive to pH since the adsorption maximum inflection point occurs near the pH corresponding to the pK of the acid species, which is usually carboxylic and near pH 5.0 (Greenland, 1971). He reported a very strong bond between oxide and humic molecules since most functional groups of the organic







18


acid participate in the adsorption and their distribution was throughout the organic molecules. Greater surface area of the humic acid, at or above the pK value, allows stronger adsorption to the oxide.

Reduction of available functional groups may occur as cations are complexed from the soil solution (Zunino and Martin, 1977). Complexation is very effective in reducing Fe or Al in solution due to the stability of the complex (Deb and Datta, 1967). They found that the stability of the complex is so great that functional groups are rendered inactive with respect to further interactions with hydrous oxides. Bloom and McBride (1979) did research on the complexing ability of metal

ions with humic acids. They observed that humic acids bind with most divalent metal ions, with the exception
2+
of Cu, as hydrated species. Also, they observed that humic acids exhibit a strong affinity for trivalent
3+
ions. The Al ion is likely bound to three carboxyl groups, but the case of the mono- and divalent species adsorption from solution cannot be ruled out (Bloom and McBride, 1979). Bloom (1979) observed the titration behavior of Al-saturated organic matter. He observed that, as the pH of the material is increased, the OH would most likely form Al(OH)2+ on the organic-matter exchange sites. As the pH is increased until the activity of (A3+) (OH-)3 is exceeded, precipitation of amorphous Al(OH)3 would be induced. Acid addition on







19


the other hand results in release of Al3+ ions into solution as H+ ions bind to functional groups at adsorption sites.

Freshly humified clover material adsorption on

allophane was studied by Inoue and Wada (1968). They found that newly humified clover possessed a greater capacity for adsorption than humic substances extracted from soils. Possible inactivation of functional groups due to ion complexation was suggested as the reason for the reduction in adsorption (Greenland, 1971). Preferential adsorption of high molecular weight (1,500 to 10,000) decomposition products was observed on allophane (Inoue and Wada, 1968).

Different ideas exist in the literature concerning the stability of Fe-organo mineral complexes. Levashkevich (1966) determined that humic acids form more stable bonds with Al-hydroxide gels than with Fehydroxide gels which he stated had a lower capacity for adsorption. Greenland (1971) stated that a very strong bond would be formed between the oxide and humic molecule if several carboxyl or other groups participated. Schwertmann (1966) stated that the transformation of amorphous ferric hydroxide to a crystalline Fe mineral may be halted due to the bonding of organic ligands to the mineral. Schwertmann and Fischer (1973) determined that ferric-hydroxide surface area would be reduced by organic-ligand adsorption.





20


The following relationship was observed: S(m2/g) = 76.6 16.4(%C) + 9.56(%Fe) where n=17 and r=0.94.

This relationship suggests strong covalent bonding between Fe hydroxide and organic anions. Parfitt et al. (1977) determined that fulvic acid is adsorbed on goethite surfaces by ligand exchange at the pH of 66.5. Parfitt and Russell (1977) determined that mononucleate species, such as benzoate and 2,4-D, had a low-binding constant and were easily desorbed from goethite surfaces. Binuclear species such as oxalic acid were strongly adsorbed on the goethite surface. Appelt et al. (1975a) measured the adsorption of benzoate, p-OH benzoate, salicylate, and phthalate on Andept soils from Chile. They observed that monoprotic adsorption was by anion exchange whereas diprotic adsorption was by anion and ligand exchange.

Organo- Mineral Reactions Affecting P Fixation Possible Mechanisms

Mechanisms relating to reduction in P fixation on Fe oxides by organic amendments are not clearly delineated in the literature. Singh and Jones (1976) stated that inorganic P from the decomposition of organic residues would possibly supply sufficient P to reduce P fixation such that added P would be in a stable form. They stated that an organic residue must contain at least 0.3% P. otherwise added P would be immobilized.






21


Conversely, Datta and Goswami (1962), utilizing 32p tracer techniques, came to different conclusions. The following excerpt is from their paper:

The increase in the uptake of total P was
again due to a greater uptake of soil and not
fertilizer P, except in red soil, where
the uptake of both soil and fertilizer P
increased. It is, however, expected that, though organic matter itself has contributed towards the
amount of soil P, it is considered to bear very little in relation to such a large increase in
total uptake (p 236).

Singh and Jones (1976) also stated that P adsorption could be lowered by blocking adsorption sites with decomposition products from organic matter. Bhat and Bouyer (1968), utilizing 32P studies, found that the addition of organic matter to ferruginous tropical soils lowered P-fixation capacity and isotopicallydilutable P was also greater. Initial soil pH was 6.6. Datta and Nagar (1968) using 32P studies determined that the uptake of fertilizer P was decreased substantially by organic addition in all their experimental soils except red soils where there was a slight increase in fertilizer P uptake rather than P uptake from organic and soil P. Initial soil pH of this red soil was also 6.6.

Datta and Nagar (1968) suggested that the mechanism of organic acid production could solubilize certain insoluble phosphates present in the soil. This explanation was given due to large amounts of soil





22


rather than fertilizer P uptake on all experimental soils except the red soil.

Deb and Datta (1967) stated that organic anions in acidic medium are very effective in complexing Fe and/or Al in solution. They observed reduction of Fe and Al activity preventing precipitation as insoluble phosphate compounds.

Observations

Conclusions relating to the reduction of P fixation by organic addition by previous researchers are mixed. Appelt et al., (1975b) found that the adsorption of benzoate, p-OH benzoate, salicylate, phthalate, and humic and fulvic acids extracted from the surface soil of a Typic Dystrandepts did not block P adsorption sites on subsurface samples of that soil. Soil pH values ranged from 4.8 to 5.4. High extractable Al levels were observed. In their studies no characterization of the organic material relating to sesquioxide ash and P fixation capacity was given. Yuan (1980) studied the adsorption of phosphate and hot water-extractable soil organic matter on acidic soils and synthetic Al silicates. He found that pretreatment of organic material had no effect on an Eutrandept: a slight effect on a Haplaquod, and partial reduction of P fixation on a Paleudult. He observed that organic material adsorption was increased by an increase in the rate of material applied, but the amounts of P retained






23


by the soils were constant suggesting that adsorption sites for P and organic material were different.

Greenland (1971) determined that organo-mineral

studies should be performed utilizing pure mineral and organic materials. He determined that previous reactions may block adsorption sites on hydrous oxides. Also, organic functional groups could be rendered inactive by metal complexation.

Nagarajah et al., (1970) evaluated the competitive adsorption of polygalcturonate (a root exudate with atomic weight of approximately 25,000) on synthetic goethite. At pH 4.0, polygalcturonate decreased phosphate adsorption by chelation of Fe or adsorption on the goethite surface as determined in their experiments. Hashimoto and Takayama (1971) reported that humic acid, nitrohumic acid, and nitrohumate salts inhibited P fixation on a synthetically prepared goethite, ferric hydroxide, and ferrous orthosilicate, but not by lepidocrocite or amorphous Fe oxide hydrate. Manojlevic (1965) conducted laboratory studies with humic acid derived from dung and manure on high-Pfixing soils. Humic acids decreased P fixation from granular superphosphate which was in contact with the soil for 4 mo. Moshi et al., (1974) measured phosphate adsorption from two profiles (one cultivated and one under forest environment) of Kikuyu red clay from Kenya. He reported that surface-adsorbed organic






24


components reduced the positive charge on the soil surface. They found a linear correlation (p>.01) between increasing percentage of organics and reduction of positive charge. Phosphate adsorption at pH 5.0 was reduced by the presence of organic matter. They also observed a linear correlation (p>.01) between a decrease of phosphate adsorption and increasing C%. Hinga (1973), also obtained similar results on Kenya soils.















CHAPTER III
ORGANIC ADSORPTION EXPERIMENT Introduction

The mechanisms of humic and fulvic anion bonding to Fe minerals ares by specific adsorption or ligand exchange (Parfitt et al., 1977). The process is not sensitive to electrolyte concentration, although it is sensitive to pH since adsorption maximum occurs near the pH corresponding to the pK of the acid species, usually carboxylic, near pH 5.0 (Greenland, 1971). He found that a very strong bond was formed between oxides and humic molecules since most functional groups of the organic acid participated in the adsorption. Schwertmann (1966) stated that the transformation of amorphous ferric hydroxide to a more crystalline Fe mineral may be stopped due to the bonding of organic liquids to the mineral. Parfitt et al. (1977) determined that fulvic acid is adsorbed on goethite surfaces by ligand exchange within the pH range of 6 to 6.5.

The objectives for the organic adsorption experiment were as follows: 1) To determine pH for maximum clover decompositional product adsorption and 2) To determine time required for transformation of amorphous Fe(OH)3 to a crystalline phase in relation to clover application.

25






26


Materials and Methods

Soil

An Orangeburg series soil (fine, loamy, siliceous, thermic, Typic Paleudult) was obtained from the Agricultural Research and Education Station near Quincy, FL. Two portions of the profile under forest environment were sampled. The surface soil, devoid of organic litter, was obtained corresponding to the A horizon.

This sandy soil was to be the matrix for Fe(OH)3 addition. Subsurface B horizon samples were obtained of the corresponding soil profile. Characterization

Both samples were characterized physically, mineralogically, and chemically. Particle size distribution was determined by the methodology of Day (1965) for the clay fraction and sieving to determine sand and silt fractions. Pretreatment with H202 oxidized organic components.

Mineralogical characterization included identification of clay fraction minerals. Pretreatment included removal of organic matter with H202 and free Fe oxides with citrate-bicarbonate-dithionite extraction (CDB). Free iron oxide and Al concentrations in CDB extracts were determined using atomic adsorption spectrophotometry (Kunze, 1965).

Chemical characterization included cation exchange capacity by the summation method as described by






27


Chapman 1965). Organic carbon was determined by dichromate-oxidation techniques (Walkley and Black, 1934). Soil pH was determined in a 1:1 ratio of soil to water (McLean, 1982). Phosphorus fixation was determined by methodology of Fassbender and Igue (1967) in which 5 g of soil were placed into a centrifuge bottle with 100 mL of 100 mg P/L solution. The bottle was shaken for 6 hours at 180 excursions/min. Separation between solution and solid phase was accomplished through millipore filtering (.2 u). Extracts were analyzed for P using methodology described by Murphy and Riley (1962). Results are given in Tables 3-1 and 3-2. Fe(OH)3 Synthesis

Amorphous ferric hydroxide was prepared by potentiometrically titrating 2 M Fe(NO3)3 with 6 M KOH to pH

8.1 (ZPC). Equivalent concentrations of both reagents were used in precipitating the Fe(OH)3 (Fig 3-1). To remove the soluble KNO3 formed, approximately 2 L of deionized water was filtered through 250 g of precipitate resulting in negligible concentrations of K+ and NO3 A suspension of Fe(OH)3 in H20 was prepared with a concentration of approximately 1 M as Fe(OH)3. Rates of 0 and 5.6 g Fe as Fe(OH)3 were applied to Orangeburg surface soil by complete mixing.





28



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I I -- I
to I I I
10 I l I
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29







o, q o
11 1









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32


Clover Production

White clover (Trifolium repens) was grown hydroponically to insure organic functional groups did not contain high sesquioxide ash contents. Hydroponic solution possessed ionic concentrations of 10-3 M P 10-22 M K. 10-1.8 M NO3, 10-2.3 M Ca. 10-2.7 M Mg, 10
2.7 -3.5
M S04, 10 M Fe, with micronutrient concentrations of 0.5 ug B/ml, 0.5 ug Mn/ml, 0.05 ug Zn/ml, and

0.02 ug Cu/ml (Hoagland and Arnon, 1938). Solutions were continually aerated and replaced biweekly. Clover biomass was harvested every 40 d and the material was then dried and ground to pass a 2- mm sieve.

Liming Curve and Organic Adsorption Measurements

To determine the maximum organic adsorption to

Orangeburg topsoil, an incubation study was initiated in which 50 g samples were treated with or without 5.6 g Fe as Fe(0H)3, plus or minus 3.15 g/kg dried and ground clover, at CaCO3 rates of 0, 0.5, 1.0, 1.5, and 2.0 cmol CaCO3/kg soil. Reagent grade CaCO3 was mixed with soil and incubated for 2 w at 250C and 8% moisture on a weight basis. Dried and ground clover was then applied and allowed to decompose for 30 d. Duplicate samples were prepared.

Organic anion extraction was performed by extracting 10 g of soil with 20 mL of 0.01 M NaCI and shaking for 30 min (Stevenson, 1982). Samples were centrifuged and aliquot decanted. Electrical conductivity of each






33


aliquot was measured prior to increase of solution pH to pH 7.0 with 0.1 M NaOH for adsorption measurements of humic and fulvic acids at 465 nm (Chen et al., 1977). Soil pH was measured in water (1:1 ratio)

(McLean. 1982).

Crystallization of Fe(OH)3

Solid Fe(OH)3 and Fe(OH)3 associated with the clay fraction of Orangeburg soil were monitored over a 6 mo period for crystal formation. Both samples were subjected to wetting and drying cycles over time. X-ray diffraction (XRD) techniques were employed using Cu K radiation to monitor changes. Differential scanning calorimetry (DSC) techniques were also employed.

Results and Discussion


Organic Adsorption Experiment


Study of organic adsorption on soil solids can produce confounding results in impure systems due to previous reactants on solid surfaces or inactivity of organic functional groups due to ion complexation (Greenland, 1971). For this reason, pure phases were prepared for study. Amorphous ferric hydroxide was applied to the Orangeburg sandy soil which was the matrix for the mineral addition. Follett (1965) observed that ferric hydroxide reacts with basal-plane surfaces of kaolinite, which is the primary clay mineral in the Orangeburg soil. Since Orangeburg soil is







34


acidic (pH 4.9), a liming curve after Fe(OH)3 application was essential to determine pH for maximal organic adsorption. Also the pH of the soil must be greater than the dissociation constant of the organic acid (pH > 5.0) to activate organic anions (Greenland, 1971). Clover rates were similar to residue rates added to the soil for cover crop production.

Results from the incubation study with respect to treatment are given in Fig. 3-2 to 3-9. Organic adsorption relationships produced by changes in pH are given in Fig. 3-2 to 3-5 and adsorption relationships with change in ionic strength are given in Fig. 3-6 3-9. Numbers in parenthesis in these figures are soil pH values. Ionic strength was calculated to be the total ionic strength of solution minus the ionic strength of the 0.01 M NaCl solution. Total ionic strength was calculated by the following equation:



u = 0.013 EC



where 0.013 is a constant and EC is electrical conductivity expressed in millimhos cm-2 (Griffin and Jurinak, 1973).

Stevenson (1982) stated that organic adsorption to clay surfaces was sensitive to changes in ionic strength. The mechanism of adsorption is by ionic








35






















0.6

0


o 0.5
o




U
r


u < 0.4
U





5 0.3
E Cp
Ln



S0.2

o .0

m S0.1







5.0 6.0 6.6

pH



Fig. 3-2 Effect of Soil pH on Organic Release From
Orangeburg Topsoil.






36











*

0.6


0

-0.5
o




S0.4
U
.,
E 00.3
E



0.2


o
rif


0.)
U



00.1




5.0 6.0 6.8

pH Fig. 3-3 Clover Decompositional Product Adsorption
to Orangeburg Topsoil as Influenced by
Soil pH.





37

















0 .H

o 0.08


0.07
o
u 0.06 0.05
E


0.03
4r.





0.02
u C





o 0.01
.=0

5 6 7 8 pH


Fig. 3-4 Effect of Soil pH on Organic Release From
Orangeburg Topsoil + Fe(OH)3.






38


















0 o
g 0.08
o
= 0.07


u 0.06
U
0.05

0.04


S0.03
Lt
-It
0.02

o
c 0.01





pH


Fig. 3-5 Clover Decompositional Product Adsorption
to Orangeburg Topsoil + Fe(OH)3 as
Influenced by Soil pH.






39


bonding. Similar results were obtained from the treatments of Orangeburg soil without Fe hydroxide addition. Increasing lime rates increased soil pH from 4.9 to 6.7 (Figs 3-2 and 3-3) but also increased solution ionic strength due to increased Ca2+ activity (Figs 3-6 and 3-7). Calcium does not form a strong complex between negatively charged clay and humic acid, but is effective as a bridge between ions (Stevenson, 1982). Greenland (1971) observed that organic matter bound to

clay through Ca2+ cation bridging was easily displaced by monovalent ions such as NH4+ or Na+. Increases in pH increase negative charges on mineral surfaces (Kaolinite) and therefore cation exchange capacity. Near pH 6.2, less organic anions were extracted by NaCl. Possibly Na+ and Ca2+ ions increased exchangeable Al3+ or Fe3+ levels. Aluminum and Fe at low concentrations could reduce organic anions by flocculation (Stevenson, 1982). Results are inconclusive above pH

6.2.

Stevenson (1982) also stated that organic adsorption to hydrous oxides occurred by ligand exchange or covalent bonding. Only anions that bind strongly to oxide surfaces could replace organic anions. This mechanism is insensitive to solution ionic strength but highly sensitive to pH. Salt solution extraction did not affect organic adsorption. Results in Fig. 3-4, 35, 3-8, and 3-9 support this mechanisms organic






40

















0.5

o (6.2)

o 0.4





U
(6.0)



o 0.2

S (5.4)
L(6.5)

V0.1





0.0 .004 .008 .012 .016 .02 .024

Ionic Strength


Fig. 3-6 Effect of Solution Ionic Strength on
Organic Release From Orangeburg Topsoil.






41













0.6 (6.2)

0.6



3 0.5
o



"U 0.4
U
S* 9(6.2)

0.3 0(5.6)

E -.7
f0.2

a

0 (6.7) *(6.2)
a 0.1





0 .004 .008 .012 .016 .02 .024

Ionic Strength


Fig. 3-7 Clover Decompositional Product Adsorption
to Orangeburg Topsoil as Influenced by
Solution Ionic Strength.





42
















S0.08 0.07



E 0.05
-00 (7.51) o 0.04 0 (7.09)

S0.03
.= (6.4)
'0.02
a, (6.8)




< 0 .004 .008 .012 .016 .02 .024 Ionic Strength



Fig. 3-8 Effect of Organic Release From Orangeburg
Topsoil + Fe(OH) as Influenced by
Solution Ionic Sirength.






43














0
S0.08
0
Ul

a 0.07 0(7.0)
r (7.5)*
0(7.2)
u 0.06
o 0 (5.6)
0.05

0.04 (6.3)

E
r 0.03

1- 0.02
U
a 0.01

0 A S A
< 0 .004 .008 .012 .016 .02 .024 Ionic Strength


Fig. 3-9 Clover Decompositional Product Adsorption
to Orangeburg Topsoil + Fe(OH) as
Influenced by Solution Ionic Sirength.







44


covalent bonding. Organic adsorption was not affected by ionic strength as seen in Fig. 3-8 and 3-9 but was greatly affected by changes in soil pH (Fig. 3-4 and 35). Ionic strength ranged from 0.016 to 0.022 units whereas pH changes within small ranges of ionic strength greatly affected adsorption measurements. As pH increases above pH 5.0. organic anions are formed. However, Fe(OH)3 possessed a variable charged surface so that increases in pH could reduce net positive charge and adsorption sites on mineral surface thereby resulting in reduced adsorption. Maximal organic adsorption occurred at pH 6.3 with residue amendment. It is also important to observe the effectiveness of organic adsorption of the Fe(OH)3 treated soil compared to untreated soil. Several orders of magnitude of adsorption exist in the binding capacity, making the Fe(OH)3-treated soil an excellent sorbant system for organic anions.

Crystallization of Fe(OH)

Changes in crystallization of Fe(OH)3 affects surface area and reactive sites for organic anion and P adsorption. Mineralogy of solid phase Fe(OH)3 and Fe(OH)3 treated Orangeburg soil were observed over a 6 m period. Solid Fe(OH)3 endured wetting and drying cycles whereas Fe(OH)3 treated soil with and without clover amendment was under a cropping system. At no time during the 6 m period did the solid Fe(OH)3






45


exhibit crystallinity as observed by XRD or DSC methodologies. The same result was obtained for the Fe(OH)3 treated soil. Differential Scanning Calorimetric plots of Orangeberg soil + Fe(OH)3 clay fractions without clover amendment and with clover amendment are given in Fig 3-10 and 3-11, respectively. No Fe mineral endotherm was observed. However, endotherms for both gibbsite and kaolinite, were observed.


Conclusions

Adsorption study observations in conjunction with previous research suggested that Fe(OH)3 treated soil exhibited covalent bonding of organic anions whereas treatments without Fe(OH)3 exhibited ionic bonding via cation bridging. Maximum adsorption of organic constituents occurred at pH 6.3 on the Fe(OH)3 treated soil with clover amendment compared to pH 6.2 for Fe(OH)3 untreated soil. After 6 m of investigation, solid Fe(OH)3 and soil Fe(OH)3 remained in an amorphous state.


































0


04
O C


















0







0
.r









0









-I
CO c00








O





0








47










































)






0)








CD 00


(DaslrwNJ mOJ P






































0o



4









o0
- .





0 i







*H
CYH


(O)








0
r

coo


wn a














C60
- H W 'a cz 0 < 2









49



















































0) C)




C14


















mola juE
















CHAPTER IV
PHOSPHATE AND ORGANIC AMENDMENT STUDY Introduction

Reduction of plant available phosphorus in acidic soils causing an agronomic yield reduction has plagued man for many years. The problem is produced by reactions of phosphates with Fe and Al hydroxides, aluminosilicates and/or the ions released from dissolution of these minerals (Chu et al., 1962; Lindsay, 1979; Fox, 1974; Hingston et al., 1974).

A possible management alternative for reducing P sorption could be addition of organic amendments. Moshi et al., (1974) measured phosphate adsorption from two profiles (one cultivated and one under forest environment) of Kikuyu red clay from Kenya. They reported that surface-adsorbed organic components reduced the positive charge on mineral surfaces. There was a high statistical linear correlation between increasing percentage organic carbon and reducing positive charge. Since positive charge was reduced, phosphate adsorption at pH 5.0 was reduced by the presence of organic matter. Hinga (1973) obtained similar results on Kenya soils. Yuan (1980) found that pretreatment with organic material resulted in partial reduction of P fixation on a Paleudult.


50






51


Mechanisms producing reduction in P fixation might include 1) release of P for organic components, 2) blockage of P-adsorption sites with decompositional products from organic amendment, 3) complexation of solution Al and Fe by organic functional groups, and 4) solubilization of fertilizer reaction products such as dicalcium phosphate (DAP) by acidity produced from the humification process (Singh and Jones, 1976). The objectives of this study are to assess the effectiveness of clover addition to highly-weathered soils in reducing P fixation as measured by dry matter plant yield, P uptake, extractable P levels, and changes in surface charge on soil colloids.

Materials

Soil

An Orangeburg topsoil as described in Chapter 3

was used in the clover amendment experiment. Amorphous Fe(OH)3 was prepared and applied as described by previous methodology. The soil was limed to pH 6.3 utilizing the liming curve developed during preliminary experimentation, and incubated for 2 wk at 25 C at 10% moisture on a weight basis. Dried and ground clover was then completely mixed with predetermined treatments and incubated for 30 d prior to fertilizer addition.






52


Clover

White clover was grown hydroponically to insure reactivity of organic functional groups. Hydroponic methodology is described in Chapter 3. Fertilizer

Pots used in the glasshouse study contained 3 kg of soil on a dry weight basis. Fertilizer applications (N, P, K, Mg) were adjusted by treatment assuming 50% mineralization from clover application. Total nutrient addition included 100 mg N/kg as NH4NO3, 140 mg K/kg as KC1. Diammonium phosphate was applied at rates equivalent to 0, 50, and 100 mg P/kg. Supplemental nutrient addition to pots included 19.8 mg Mg as MgSO4'7H20, 11.4 mg Zn as ZnSO 47H20, 5.09 mg Ca as CaS04'5H20 and

1.2 mg B as Na2B207 10H20.

Methods

Incubation Study

To investigate soil P retention, an incubation study was conducted with three soils. These were Orangeburg, Orangeburg + 5.6 g Fe/kg as Fe(OH)3, and Orangeburg subsoil. Each soil was amended with dried and ground clover at rates of 0, 1.58, and 3.16 g/kg over times of 30, 60, 90 d. Each soil had been previously limed to pH 6.3 and incubated for 2 w. Soil P retention was determined at each time interval by shaking 5 g of sieved soil with 100 ml of solution containing 100 mg P/L as K2PO4 for 6 h (Fassbender and






53


Igue, 1967) in duplicate. After shaking, aliquots were filtered through a 0.2 um membrane filter disk and analyzed for orthophosphate (Murphy and Riley, 1962). Phosphorus fixation was determined by subtraction. Soil pH at each time interval was determined in a 1:1 soil to water suspension. Analysis of variance was performed on the split plot design utilizing time as a main plot with soil and clover addition as subplots.

Glasshouse Study

A 3 X 2 X 3 factorial experiment using 0, 50, and 100 mg P/kg soil, 0 and 5.6 g Fe/kg as Fe(OH)3 and 0, 1.58 and 3.15 g clover/kg in split-split plot design with three replications was conducted in a glasshouse. Phosphate addition was the main plot with Fe(OH)3 addition as the sub plot, and clover addition the sub-sub

plot. Two crops of Zea mays L. were grown for 50 d each to determine initial and residual effectiveness of fertilizer. Treatments were limed and refertilized with previous rates before initiation of a third crop. Variables measured include dry matter yield, uptake of P. Ca, Mg and K, Al and Fe concentrations within plant tissue. Soil measurements included Truog and Bray 2 extractable P levels, soil pH, and organic C levels. Plant samples were analyzed in the following manner:

0.10 g of dried and ground tissue, passing a 1 mm sieve, was placed in a 50 mL beaker and oxidized in a muffle furnace at 4500C. The ash was further digested






54


with 3 M HNO3, evaporated to dryness on a hotplate, with removal of excess HNO3 by placing each beaker into the muffle furnace at 45000C for 10 m. After cooling, 25 mL of 5 M HC1 were added to the beaker, placed on a hotplate and evaporated to dryness to completely oxidize plant material. After cooling, 1 mL of 5 M HC1 was placed in the beaker with water and diluted to a final volume of 50 mL. Ionic concentrations of Ca. Mg, K, Al, and Fe were determined by Inductively Coupled Argon Plasma spectrophotometry. Plant P concentrations were determined by methodology described by Murphy and Riley (1962).

Soils were sampled after each maize crop. Soil pH was determined in 1:1 soil to water ratio (McLean. 1982). Organic C levels were determined by methodology

described by Walkley and Black (1934).

Since reaction products of DAP are CaHPO *2H20.

CaHPO 4, and colloidal ferric phosphate with Orangeburg soil, proper extractants needed to be chosen for extraction of these phases. Ballard (1974) compared various extractant effectiveness on a variety of phosphate reaction products as independent solid phases and those phases mixed with soil. In his research Truog reagent (0.001 M H2S04 + 3 g (NH4)2S04) extracted 100% of P applied as dicalcium phosphate (DCP) as a solid phase and 98% DCP mixed with Leon fine sand. Only 2% of P applied as colloidal ferric phosphate (CFP) as a







55


solid and mixed with Leon fine sand was extracted. Bray 2 (.03 M NH4F + 0.1 M HCI) extracted 98% P from CFP and CFP mixed with Leon fine sand. Sequential extractions for P were performed with Truog and Bray 2 solutions. Extraction methodology was as follows: 2 g of soil were placed in a centrifuge tube with 25 ml of Truog reagent. Samples were shaken at 180 excursions per minute for 30 m and centrifuged. Aliquots were filtered through Whatman #42 filter paper. Soil samples were again extracted with Bray 2 solution. Twenty mL of extractant were added to the soil sample and shaken for 1 m. Aliquots were immediately filtered through Whatman #42 filter paper. Soil P concentrations were determined by methodology described by Murphy and Riley (1962).

Surface Charge

To determine net electric charge and ZPC of 1)

Fe(OH)3 treated soil, 2) Fe(OH)3 treated soil + 100 mg P/kg, 3) Fe(OH)3 treated soil + 3.15 g clover/kg, and 4) Fe(OH)3 treated soil + 100 mg P/kg + 3.15 g clover/kg, potentiometric titrations were performed. Samples were obtained after the first cropping period of the glasshouse experiment. Methodology described by Laverdiere and Weaver (1977) was performed in which 10 g of sample were weighed into 250 mL beakers with addition of 100 mL either 0.01, 0.1 or 1.0 M NaC1. Samples were allowed to equilibriate for 60 m and pH was






56


determined. Soil suspensions were titrated with 0.02 M HC1 under continuous stirring. Salt solutions without soil were also titrated as a baseline for charge determination by subtracting H+ concentrations of blank titrations at a given pH from H+ concentrations of the soil suspension.

SEM Study

Clay fractions from 1) Orangeburg + Fe(OH)3 + P, and 2) Orangeburg + Fe(OH)3 + P + 3.15 g clover/kg for study under the scanning electron microscope were obtained by sieving the soil through a 300-mesh sieve, washing with water at pH 10, and collecting the aliquot. The clay-silt suspensions were centrifuged for 5 m at 1500 RPM. Gravimetric determinations of clay in suspension was performed. Samples were diluted by factors of 2, 3, 5 and 10, applied on a carboncoated stub, and magnified within ranges of 450X to 10,000X.

Results and Discussion

Incubation Study

An incubation study was developed to determine

effects of time, soil, and clover amendment relating to P fixation capacity of the soil. As shown in Table 41, a triple order interaction was obtained. Phosphate fixation capacity was affected by times of 30, 60, or 90 d of incubation, clover application at rates of 0,

1.58 and 3.15 g/kg and the type of soil matrix.







57


Table 4-1. Effect of Experimental Parameters on
P Retention Capacity

Source df Mean Square p>F



Time 2 279999 0.0001

REP 1 2759 0.39

Error a 2 1245

Soil 2 550367 0.0001

Clover 2 3058 0.44 Soil X Time 4 11426 0.03 Clover X Time 4 13726 0.02 Soil X Clover 4 11474 0.03

Soil X Clover

X Time 8 13491 0.01

Error b 24 3611






58


Since a triple order interaction was obtained, response surface equations were developed for each soil over clover application rates at each time of comparison. Equations are given in Table 4-2. Graphs of results at each time interval are given in Fig. 4-1 through 4-3.

Orangeburg Topsoil

Orangeburg topsoil is a sandy soil (85% sand, with iron concretions (0.31%)). Increasing rates of application of clover increased P fixation capacity after 30 d. After decomposition of clover, organic functional groups were available for reaction with soil components. Calcium can be bound ionically to organic functional groups (Bloom and McBride, 1979) thereby attaching orthophosphate to organic components and reducing P concentration in solution. With clover addition there was an increase in soil pH from 6.4 to 6.7. Differences in pH could also be induced by precipitation of DCP.

After 60 d of incubation, there was a slight increase in soil pH from 6.4 to 6.7 without clover treatment. Increased P fixation was also noted possibly due to the formation of a calcium phosphate precipitate. Clover-amended treatments decreased P fixation capacity, although it remained higher than the 0 clover application rate. Singh and Jones (1976) reported decreases in P fixation capacity of organic






59


Table 4-2. Response Surface Equations Relating P
Fixation Capacity of Soils With Clover
Addition Over Time.
Correlation
Time (d) Response Surface Equation Coefficient Orangeburg

30 P fix = 196 81 clover + 69 clover2 r2 = 0.71 60 P fix = 202 6 clover + 8 clover2 r2 = 0.49 90 P fix = 274 + 252 clover 76 clover2 r2 = 0.67

Orangeburg + 5.6 g Fe
2 2
30 P fix = 986 467 clover + 111 clover r2 = 0.83
2 2
60 P fix = 240 + 107 clover 36 clover r2 = 0.78 90 P fix = 517 + 72 clover 21 clover2 r2 = 0.29 Orangeburg Subsoil

30 P fix = 936 177 clover + 41 clover2 r2 = 0.30 60 P fix = 684 130 clover + 26 clover2 r2 = 0.99
2 2
90 P fix = 810 116 clover + 33 clover r = 0.83






60













700



-500

400

300

--- -" 200

100


Orangeburg Subsoil Orangeburg + Fe(OH)3 Orangeburg Topsoil

0 1.58 3.15
Clover Applied g/kg




Fig. 4-1 Phosphate Fixation Capacity of Soils
Amended With Various Clover Rates After
30 Days of Incubation.






61














600

60 Days



--- 400















Das f Incub--~aion.---- 300 : 200






-0 .-..... .. Orangeburg Subsoil Orangeburg + Fe(OH)3 Orangeburg Topsoil

0 1.58 3.15
Clover Applied g/kg



Fig. 4-2 Phosphate Fixation Capacity of Soils
Amended With Various Clover Rates After 60
Days of Incubation.





62














800

90 03
700

-: 5 600



00


------- ---2
.00




-------- 0O



Orangeburg Subsoil Z Orangeburg + Fe(OH)3 ._._.... ,Orangeburg Topsoil

0 1.58 3.15
Clover Applied g/kg



Fig. 4-3 Phosphate Fixation Capacity of soils
Amended With Various Clover Rates After 90
Days of Incubation.






63


treated soils after 30 d incubation due to P mineralization from organic substrates. Mineralization of P from microbial populations may have produced this result.

After 90 d of incubation, there was a slight decrease of soil pH from 6.6 to 6.3 without clover treatment. Increased P fixation was observed compared to 30 and 60 d incubation periods. The 3.15 g/kg clover treatment remained stable with respect to P fixation data from 60 d incubation time. However the 1.58 g/kg clover treatment increased soil P fixation capacity.

Orangeburg Topsoil + Fe(OH)3

After 30 d of incubation, treatments receiving

clover applications possessed lower P fixation capacities than did treatments without clover application. Treatments receiving 1.58 g/kg clover had a lower P fixation capacity than 3.15 g clover/kg. Possibly decompositional products of clover were bound to the iron hydroxide surface as was the case in the clover amendment experiments of blocking positive charged sites available for P fixation. Soil pH ranged from 6.5 to 7.2 so that acid forming ions of Al, Fe, and Mn were not available for precipitation or ionically binding orthophosphate to organic components. Precipitation of calcium phosphates at pH 7.2 from the 3.15 g clover/kg






64


soil treatment may have occurred thereby increasing P fixation capacity for that treatment.

After 60 d of incubation, total P fixation of all treatments was reduced, possibly due to P mineralization from microbes and clover residues. Decreasing P fixation with increasing clover application was observed. Soil pH also increased possibly due to a selfliming effect of Fe3+ to Fe2+ with hydroxyl release from water applications reducing net positive charge and P-fixation capacity.

After 90 d of incubation, P fixation capacity was increased to near initial levels. Clover-amended treatments, although lower in P-fixation capacity than unamended treatments, did not produce substantial Pfixation reduction as was noted initially. Orangeburg Subsoil

Orangeburg subsoil contains 34% material in the

clay-size fraction with kaolinite as the dominant clay mineral. The clay surface is coated with goethite which is 1.3% of the total weight of the soil. Orangeburg subsoil results are similar to those obtained from Orangeburg + Fe(OH)3 but clover application has less effect in reducing P fixation. Clover application at 30 d reduced P-fixation slightly compared to untreated soil. Greater total surface area of goethite with Orangeburg subsoil compared to Fe(OH)3






65


applied to Orangeburg topsoil reduced clover-amendment effectiveness.

At 60 d of incubation, similar trends of reduction in P fixation capacity with increased soil pH were observed. Clover amendments lowered P fixation capacity compared to treatments without clover.

At 90 d, the effectiveness of the clover amendment was negligible.

Glasshouse Study

A glasshouse study was conducted to determine

clover amendment effectiveness in reducing P fixation in relation to crop production. Three crops of maize were grown for 50 d each. Results from experimental parameters from each cropping period will be discussed. Crop 1

Yield

Dry matter yield was affected by P rate, Fe(OH)3 addition, and clover application as determined by a triple-order interaction. As seen in Table 4-3 and Fig. 4-4. without application of P, no difference in yield was obtained with clover applications on the Fe(OH)3 treated soil. Ferric hydroxide provided a sink for indigenous soil P to be bound as well as P available from mineralization of clover. Without Fe(OH)3 addition, yield was increased from clover applications with P additions. This effect could have been from clover functional groups binding







66



Table 4-3 Yield Response Surface Equations Obtained
From the First Cropping Period.

Clover applied Correlation g/kg Response Surface Equation Coefficient P = 0 mg/kg

0 Y = 0.97 0.07 Fe r2 = 0.61

1.58 Y = 0.73 0.04 Fe r2 = 0.18 3.15 Y = 3.17 0.48 Fe r2 = 0.68 P = 50 mg/kg

0 Y = 2.07 0.22 Fe r = 0.73

1.58 Y = 2.13 0.20 Fe r2 = 0.52 3.15 Y = 5.43 0.61 Fe r2 = 0.63 P = 100 mg/kg
2
0 Y = 6.57 0.88 Fe r = 0.95

1.58 Y = 3.37 0.17 Fe r = .18 3.15 Y = 5.37 0.20 Fe r2 = 0.25





67



.0

Ro



3.0
0





O0














----- 3.15
15





A"" Fe Applied g/kg


Fig. 4-4 Plant Dry Weight Yield Affected by Fe(OH)3
and Clover Application at the 0 mg/kg P
Rate During the First Cropping Period.






68


to Al or Fe ions from solution reducing precipitation of indigenous soil P. Although no differences in soil pH were observed, the pH of both soils had dropped to 5.2 which would increase Al and Fe activity in solution. Also, this effect may have been produced by P released from clover mineralization. Initially, P fertilizer was added (7.0 mg P/kg) to the clover control and 3.5 mg P/kg to the 1.58 g clover/kg treatment since the literature suggests that approximately 50% of organic P is released as orthophosphate

(Lockett, 1938). Application of 3.58 g clover/kg was equivalent to adding 14 mg/P kg soil. Possibly release of P from clover later in the cropping period resulted in enhanced yield rather than immediate solubilization of fertilizer P.

Application of 50 mg P/kg increased plant yield compared to that without P. Fe(OH)3 again decreased plant yield. However, increasing application rates of clover increased plant yield on Fe(OH)3 treated soil (Table 4-3 and Fig. 4-5). It appeared that P was more available on Fe(OH)3 treated soils due to blockage of P adsorption sites by organic ligands from clover application. Increase in yield of treatments without Fe(OH)3 addition may have been produced by binding Al and Fe by organic ligands. Doubling of dry matter yield from clover addition of 3.18 g





69







0.0


P=50

.0



0
.0 o













1.0





3.15


1.58





Fe Applied g/kg



Fig. 4-5 Plant Dry Weight Yield Affected by Fe(OH)3
and Clover Applications at the 50 mg/kg P Rate During the First Cropping Period.






70


clover/kg soil could not have been produced solely by P release at the rate of 7.0 mg P/kg) .

Applications of 100 mg P/kg increased dry weight yield compared to the 50 mg P/kg rate (Table 4-3 and Fig. 4-6). Ferric hydroxide treatments decreased maize yield but an incremental increase in yield was observed

with increasing clover applications. Yield was more than tripled when clover was applied at 3.15 g clover/kg soil. Phosphorus availability appeared to be greater due to clover pretreatment. Results agree with the previous incubation study relating to P availability with Fe(OH)3 treatment in acidic (pH 5.2) ranges.

Greater yield was obtained without clover application if Fe(OH)3 was not introduced into the soil system. Cation bridging of P to organic functional groups may have produced this result. P uptake

Phosphorus uptake by maize plants was affected by amount of P or Fe(OH)3 applied. Increasing P rates increased P in plants while addition of Fe(OH)3 reduced P uptake. With increasing rates of clover applied (Table 4-4 and Fig. 4-7, 4-8 and 4-9), enhanced P uptake was obtained. Mechanisms relating to clover amendment effectiveness were not determined. Yield data appears to relate well to P uptake observations. Binding of Fe or Al by organic functional groups or





71







S o 1 1 *w el C4 Cr 1 O a l II II II

0 ol P p 4 1








0







co I

I I P
0 I I






+
l 1 I I
0 4 41














wl

m Ia w I
I












- I


1 -t 04 S0I '-4 < I oI I











0 w 0 a I O I I








o I 0 0 0 H I o >


- MI o a *



e 1e






72




7.0


P=10
0.0













co
2.0


0
-4 .0



S3.0
00


.0b8o.0




0















Fe Applied g/kg



Fig. 4-6 Plant Dry Weight Yield Affected by Fe(OH)
and Clover Applications at the 100 mg/kg
Rate During the First Cropping Period.





73








3.0












0








so


















Fe Applied g/pot



Fig. 4-7 Phosphorus Uptake by Maize as Affected by
Fe(OH)3 and P Application at the 0 g/kg
Clover Rate During the First Cropping
Period.





74











5.0





3.0





3.o







2.100
















50






Fe Applied g/pot




Fig. 4-8 Phosphorus Uptake by Maize as Affected by
Fe(OH)3 and P Application at the 1.58 g/kg
Clover Rate During the First Cropping
Period.






75














.O
.0



5.0







3 .o .o











-- ----.. D





o0




U.u0 Fe Applied g/kg


Fig. 4-9 Phosphorus Uptake by Maize as Affected by
Fe(OH)3 and P application at the 3.15 g/kg
Clover Rate During the First Cropping
Period.







76


bonding of organic ligands to Fe(OH)3 surfaces would explain the results obtained. Truog Extractable P

A reaction product of DAP is dicalcium phosphate (Lindsay, 1959). Truog reagent is a good extractant for this phase (Ballard, 1974). Preliminary extraction with Truog reagent produced an Fe-clover interaction. Addition of Fe(OH)3 reduced Truog extractable P levels drastically (Fig. 4-10, 4-11 and 4-12). Without clover application, P addition of 100 mg/kg slightly increased Truog P levels which would apply to the dicalcium phosphate fraction. Inconclusive results were obtained with Fe(OH)3 treated soils regardless of rate of P application. Without Fe(OH)3 application, increases in Truog extractable P resulted from clover application at increasing P rates (Table 4-5). Previous mechanisms, discussed above appeared to have produced these effects.

Bray 2 Extractable P

Orthophosphate adsorption to iron mineral surfaces reduces plant available P. Bray 2 extraction is a good method for determining slightly soluble or desorbable P reaction products. Bray 2 extractable P was affected by main effects of P rate, Fe(OH)3 amendment, and







77





o 1.

m l o\
-4dri **
W441 0 0 0 .0 0 o o
I I II II ol o ol u N N I
0 1 1
o 1 1
I I




07
c) eMW
I o > Ol-- o o I



o al 1> a o l A .1 WI0

zII o


w l o o


*W cc 1 I 0 0 I


I I *. o e4 m 0 04 0









II I



a I



E-4o






78



6.0

P 0

5.0




4.0
00



0 1.58 3.3.0




















0 1.58 3.15 @
Clover Applied g/kg



Fig. 4-10 Truog Extractable P Levels as Affected by
Clover and Fe(OH)3 Applications at the 0
mg/kg P Rate During the First Cropping
Period.






79






9.0

P=50



4.0





- -5.0


4.0


.3.0



--- -- -- .0





0.0
-- -- -------_E-.0


5.6 e

0 1.58 3.15
Clover Applied g/kg


Fig. 4-11 Truog Extractable P Levels as Affected by
Clover and Fe(OH)3 Applications at the 50
mg/kg P Rate During the First Cropping
Period.






80








16.0

P=100,
14.0



12.0


1_0.0 o0 8.0





6.0



4.0



2.0


S 0.0
0.0




0 1.58 3.15 4
Clover Applied g/kg


Fig. 4-12 Truog Extractable P Levels as Affected by
Clover and Fe(OH) Applications at the
100 mg/kg P Rate ;uring the First
Cropping Period.







81


clover application, as shown in Table 4-6. With increasing P rates, significant increases were observed in Bray 2 extractable P levels probably from adsorption to the iron mineral surface. Binuclear adsorption would reduce extractable P results due to the stability of the adsorption bond and the irreversible nature of the adsorption. Clover amendments increased extractable P availability. Possible mechanisms of organic ligand adsorption, Al and Fe complexation, P release for clover and/or acid humification processes solubilizing calcium phosphates, could increase extractable P concentrations. Organic Carbon

No significance with respect to organic carbon levels was found with clover pretreatment. Further monitoring of this experimental parameter was terminated.

Crop 2

A second maize crop, grown for 50 d, was initiated to determine residual treatment effectiveness in relation to experimental parameters. Yield

Plant dry weight yield was influenced by previous Fe(OH)3 and clover applications (Table 4-7). Main plot

effects did not show increase in yield from previous






82



Table 4-6 Main Effects of P, Fe(OH) and Clover
Affecting Bray 2 Extractasle P Levels From
the First Cropping Period.

P Aapplied Bray 2 Contrast p>F (mg/kg) Extractable P


0 9.86
0 vs others 0.01 50 20.01
50 vs 100 0.01 100 27.84

Fe Applied (g/kg)

0 26.06
0 vs 5.6 0.05
5.6 12.41


Clover Applied (g/kg)

0 14.56
0 vs others 0.01
1.58 18.13
1.58 vs 3.15 0.01
3.15 25.02






83


DAP application due to fixation mechanisms. Ferrichydroxide decreased dry weight yield fourfold. Clover addition increased yield with each increasing rate of application. Since P was a limiting factor, clover applications apparently increased P reaction product

availability. Release of P from clover should have subsided long before termination of the second cropping period. Yield was not likely to be reduced from Al or Fe toxicity at pH values of the soil. Although differences in Al and Fe levels within plant tissue existed (Table 4-8) with respect to Fe(OH)3 treatment, Al and Fe levels were not at toxic concentrations. P Uptake

Phosphorus uptake by maize was affected by Fe(OH)3 addition (Table 4-9). The Fe(OH)3 provided a sink for P adsorption. Also as seen in Table 4-10, soil pH had dropped to 5.0 such that Al3+ and Fe3+ could be in solution reducing P availability from precipitation reactions. Aluminum and Fe ions were present in soil solution as determined by plant uptake of these ions. Addition of Fe(OH)3 resulted in a fourfold decrease in P uptake.

Truog Extractable P

Truog extractable P was affected by an interaction of Fe(OH)3 and clover. Increasing levels of clover






84


Table 4-7 Main Effects of Fe(OH)3 and Clover
Treatments on Plant Yield During the Second
Cropping Period.

Fe applied
(g/kg) Yield (g/pot) Contrast p>F


0 2.17
0 vs. 5.6 0.01
5.6 0.53


Clover applied
(glkg)

0 0.85
0 vs. others 0.01
1.58 1.35
1.58 vs 3.15 0.01
3.15 1.85







85


Table 4-8 Main Effect of Fe(OH) Addition on Al and Fe Concentrations in lant Tissue After the
Second Cropping Period.

Al Fe Contrast p>F

----- mg/kg---Plus Fe(OH) 131 133 Plus vs Minus 0.01 Minus Fe(OH)3 83 83






Table 4-9 Main Effect of Fe(OH) Treatment on Plant P
Uptake During the Second Cropping Period.


Fe (g/kg) P uptake mean Contrast p>F mg P/Pot

0 2.15
0 vs 5.6 0.01
5.6 0.57







Table 4-10 Main Effect of Fe(OH) Treatment on Soil
pH After Two Cropping Periods.


Fe (g/kg) pH mean Contrast p>F


0 5.12
0 vs 5.6 0.01
5.6 4.95






86


increased Truog P, as Fe(OH)3 produced a reduction in P at each P application rate (Table 4-11). As the pH of the soil decreased, solubilization of indigenous soil P, or P from fertilizer reaction products increased producing measurable levels of Truog extractable P which is a P form readily available to plants. Without

Fe(OH)3 addition, increasing levels of Truog P were obtained with increasing clover rates, without added P. This same observation (Fig. 4-13) was also noted during the first cropping period. Reduction in Truog extractable P on Fe(OH)3 treated soil without P addition with increasing clover rates may be explained by P utilized for plant growth. Increased maize yields were

obtained with increasing clover application rates, which would lower Truog P levels. Similar observations were obtained at the 50 mg P/kg rate (Fig. 4-14) and the 100 mg P/kg rate (Fig. 4-15) with the exception that Truog extractable P levels also increased with increasing rate of P application.

Bray 2 Extractable P

Bray 2 extractable P levels were affected by interaction of P and Fe(OH)3. Extractable P was increased with increasing P rates but decreased with Fe(OH)3 additions. Extractable P levels were increased





87





o 41

W(*MI a 1 4 W
o I 9 MI II II II


o
to I 001





,) 1 > M I I




I I 4
I
W I I



0 W
I o



> 11 91 w 9 el > > 0
0 I o o








I, :31 ,l > ol ;0 C > l I 0 I 0 u

U I I e I 1
1 1 II






0
0 1 1 a







W I co Wj vl o l



0 1 ,I a)



Ol 0 -:
M I r I I





oq
I 0 I 0








I w
i c 00 ,
0 H 0
0 + m I ol E-4 *


100
















v41






88


with increasing clover rates (Table 4-12 and Fig. 4-16, 4-17, and 4-18). Increases of Bray 2 extractable P from Fe(OH)3 untreated soil compared to that for Crop 1 may have been produced by precipitation of Fe or Al phosphates with decreasing soil pH. Reversion of a calcium phosphate to a Fe or Al phosphate possessing greater stability would increase Bray 2 levels. Change in Bray 2 extractable P may be due to blockage of P fixation sites by organic ligands reducing the irreversible binuclear P adsorption. Crop 3

A third crop was grown for 50 d to determine

clover effectiveness over time in increasing dry weight yield, P uptake, and Truog and Bray 2 extractable P. Each treatment was again limed to pH 6.3 utilizing the liming curve described in Chapter 3. Constant fertilizer amounts were applied. Rates of 0, 50, and 100 mg P/kg as DAP were applied to appropriate treatments. Yield

Dry matter yield was influenced by interaction of P with Fe(OH)3 applications. (Table 4-13). Increasing rates of P increased dry weight yield (Fig. 4-19, 4-20 and 4-21). Observations of increases in yield on

Fe(OH)3 treated soil with increasing clover applications suggested that organic functional groups were bonded to Fe mineral surfaces, thereby reducing P






89



Table 4-12 Response Surface Equations of Bray 2
Extractable P Levels After the Second
Cropping Period.
Correlation
Response Surface Equation Coefficient


Clover Applied (0 g/kg)

Bray P = 9.28 + .28 P .85 Fe .04 P Fe r2 = .96

Clover Applied (1.58 g/kg)

Bray P = 16.99 + .24 P 2.13 Fe .02 P Fe r2 = .97

Clover Applied (3.15 g/kg)

Bray P = 23.19 + .22 P 2.62 Fe .02 P Fe r2 = .96





90








7.0

P=O
0.0


5.0


4.0


3.0














0 1.58 3.15






0 mg/kg P Rate During the Second Cropping
2.0






0.0
0.0

5.6 eb

0 1.58 3.15 qo
Clover Applied g/kg


Fig. 4-13 Truog Extractable P Levels as Affected by
Clover and Fe(OH)3 Applications at the
0 mg/kg P Rate During the Second Cropping





91









8.0

P=50
7.0


6.0


5.0


4.0


3.0 "X


2.0





S... 0.0
.-- o.o

------ 5.6 .,b

0 1.58 3.15
Clover Applied g/kg




Fig. 4-14 Truog Extractable P Levels as Affected by
Clover and Fe(OH)3 Applications at the
50 mg/kg P Rate During the Second Cropping
Period.




Full Text
133
fertilizer with incremental clover additions.
Treatment effects may be explained by enhanced P uptake
due to placement of P fertilizer material. Lack of
differences in yield on the two soils possibly
indicates that the P rate of 75 mg/kg may have been too
high. Since P uptake was different due to soils, it
should follow that yield would be different by soil as
it was by treatment. However, since P was not a
limiting factor, optimal plant uptake of P across soils
was obtained.
Calcium, Mg, and K uptake by corn followed closely
to P treatment yield. Increased dry matter yield
resulted in increased Ca, Mg, and K uptake but these
elements in plant tissue were not interpreted as being
deficient. Aluminum and Fe concentrations did not
approach toxic levels in the plant during the first
cropping period.
Crop 2
Soil pH values for both soils dropped from the
limed pH values of 6.3 to the indigenous values of A.7
and 5.2 (Table 5-3) for Orangeburg + FeCOH)^ and
Orangeburg subsoil, respectively, over the two cropping
periods. Although A1 and Fe were never at toxic concen
trations within the tissue, the percentage of P within
tissue was lower (< 0.1%) in Crop 2 than the first crop.


106
1.58
Clover Applied g/kg
3.15
Fig. 4-24 Truog Extractable P Levels as Affected by
Clover and Fe(OH), Applications at the
100 mg/kg P Rate During the Third
Cropping Period.
Truog Extractable P mg/kg


33
aliquot was measured prior to increase of solution pH
to pH 7.0 with 0.1 M NaOH for adsorption measurements
of humic and fulvic acids at 465 nm (Chen et al.,
1977). Soil pH was measured in water (1:1 ratio)
(McLean, 1982).
Crystallization of Fe(OH)^
Solid Fe(0H)g and Fe(0H)g associated with the clay
fraction of Orangeburg soil were monitored over a 6 mo
period for crystal formation. Both samples were sub
jected to wetting and drying cycles over time. X-ray
diffraction (XRD) techniques were employed using Cu K
radiation to monitor changes. Differential scanning
calorimetry (DSC) techniques were also employed.
Results and Discussion
Organic Adsorption Experiment
Study of organic adsorption on soil solids can
produce confounding results in impure systems due to
previous reactants on solid surfaces or inactivity of
organic functional groups due to ion complexation
(Greenland, 1971). For this reason, pure phases were
prepared for study. Amorphous ferric hydroxide was
applied to the Orangeburg sandy soil which was the
matrix for the mineral addition. Follett (1965)
observed that ferric hydroxide reacts with basal-plane
surfaces of kaolinite, which is the primary clay min
eral in the Orangeburg soil. Since Orangeburg soil is


122
Fig. 4-34 Scanning Electron Micrograph (10.000X)
of an Aggregate From Orangeburg + Fe(OH)
Clay Fraction Amended With 3.15 g Clover/kg
From the First Cropping Period.


56
determined. Soil suspensions were titrated with 0.02 M
HC1 under continuous stirring. Salt solutions without
soil were also titrated as a baseline for charge
determination by subtracting H+ concentrations of blank
titrations at a given pH from H+ concentrations of the
soil suspension.
SEM Study
Clay fractions from 1) Orangeburg + FeCOH)^ + P
and 2) Orangeburg + Fe(0H)g + P + 3.15 g clover/kg for
study under the scanning electron microscope were
obtained by sieving the soil through a 300mesh sieve,
washing with water at pH 10, and collecting the
aliquot. The clay-silt suspensions were centrifuged
for 5 m at 1500 RPM. Gravimetric determinations of
clay in suspension was performed. Samples were diluted
by factors of 2, 3, 5 and 10, applied on a carbon-
coated stub, and magnified within ranges of 450X to
10,000X.
Results and Discussion
Incubation Study
An incubation study was developed to determine
effects of time, soil, and clover amendment relating to
P fixation capacity of the soil. As shown in Table 4-
1, a triple order interaction was obtained. Phosphate
fixation capacity was affected by times of 30, 60, or
90 d of incubation, clover application at rates of 0,
1.58 and 3.15 g/kg and the type of soil matrix.



PAGE 1

CLOVER RESIDUE EFFECTIVENESS IN REDUCING ORTHOPHOSPHATE SORPTION ON FERRIC-HYDROXIDE COATED SOIL By GEORGE WILLIAM EASTERWOOD A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1987

PAGE 2

Dedicated with love to B.J.

PAGE 3

ACKNOWLEDGEMENTS With the help of various individuals, both friends and family, I was encouraged to pursue a doctoral degree. They directed me in obtaining the best education possible, and guided me to a more fulfilled life, both philosophically and intellectually. T am deeply indebted to Dr. J. B. Sartain, my major professor, who painstakingly helped mold me intellectually. He shared with me his values, work ethic, and extensive knowledge as professor and friend. I am very fortunate to have a Supervisory Committee of scientists who display avant garde concepts. Dr. J. G. A. Fiskell, Dr. J. J. Street, Dr. E. A. Hanlon, Dr. W. G. Harris, and Dr. S. H. West are men of enlightnment and inspiration. In my opinion, I have had a Supervisory Committee that excelled in knowledge, guidance, and helpfulness. I am sincerely grateful to these gentlemen for their help and accessibility despite rigorous schedules. I truly thank my mother and father for their encouragement in pursuing the doctoral degree. My parents, who so long ago gave me gifts of direction, self discipline, and character development by iii

PAGE 4

emulation, anchored by a spirit of love, aided me more than they will ever know. During the third year of my pursuit of a doctorate, I endured a bitter disappointment that almost devastated me. Miss Betty Jean (B.J.) Cross, my former fiancee, passed from this life. She endured the rigors of graduate school with me and was always supportive. This beautiful lady, both physically and spiritually, shall always be in my memory. It is to her, that this work is dedicated. iv

PAGE 5

TABLE OF CONTENTS ACKNOWLEDGMENTS iii AB STRACT vii CHAPTERS I INTRODUCTION 1 II LITERATURE REVIEW 4 Effect of Iron Oxides on Soil Chemical Properties A Present Management Practices for Reduction of P Fixation 9 Decompositional Products of Organic Materials 13 Organic Anion and Iron Mineral Interactions 17 Organo-Mineral Reactions Affecting P Fixation 20 III ORGANIC ADSORPTION EXPERIMENT 25 Introduction 25 Materials and Methods 26 Results and Discussion 33 Conclusions 45 IV PHOSPHATE AND ORGANIC AMENDMENT EXPERIMENT. .. 5 0 Introduction 50 Materials 51 Methods. 52 Incubation Study 52 Glasshouse Study ...52 Surface Charge 55 SEM Study 56 Results and Discussion 56 Incubation Study 56 Glasshouse Study 65 Surface Charge Ill SEM Study 118 Conclusions 121 V

PAGE 6

V FERTILIZER COATING AND PLACEMENT EXPERIMENT. 1 25 Introduction 125 Materials and Methods 126 Results and Discussion 129 Conclusions 140 VI SUMMARY AND CONCLUSIONS 145 BIBLIOGRAPHY 148 BIOGRAPHICAL SKETCH 155 vi

PAGE 7

Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy CLOVER RESIDUE EFFECTIVENESS IN REDUCING ORTHOPHOSPHATE SORPTION ON FERRIC-HYDROXIDE COATED SOIL By GEORGE WILLIAM EASTERWOOD August, 1987 Chairman: Dr. J. B. Sartain Major Department: Soil Science Department Laboratory research suggests that organic acids bind to iron-mineral surfaces, reducing P fixation. Experiments were conducted to determine 1) maximal clover residue adsorption, 2) P fixation capacity of FeCOH)^ treated topsoil and goethite coated subsoil amended with clover, 3) clover residue effectiveness in relation to maize yield and extractable P levels, and A) surface charge with P, clover, and P and clover applications to Fe(OH)^ treated soils. Amorphous iron-hydroxide (FeCOH)^) precipitate was applied to Orangeburg soil (fine, loamy, siliceous, thermic Typic Paleudult) at rates of 0 and 5.6 g Fe as FeCOH)^. White clover (Trif]^oi.um repens) was grown hy dr opon ic al ly in Hoagland's solution. Vll

PAGE 8

Maximum clover residue adsorption occurred at pH 6.3 with FeCOH)^ addition. Without Fe(0H)3 application, adsorption was dependent on solution ionic strength. Clover applications decreased P adsorption within each sampling time (30, 60, 90 d) for Orangeburg soil with synthetic FeCOH)^ and Orangeburg subsoil containing goethite but increased P fixation without FeCOH)^ appl icat ion. A glasshouse experiment was conducted to measure maize yield, P uptake and extractable P levels. Two crops of maize were grown 50 d each prior to P refertilization for the third crop. An increase of 350% in maize yield with increases in P uptake and extractable P levels was observed with clover and P applications compared to P fertilization only, on FeCOH)^ treated soils within cropping periods. A second experiment was conducted to determine effectiveness of coating diammonium phosphate (DAP) with clover to reduce P fixation around fertilizer microsites. Point placement of fertilizer and granules was superior to mixing fertilizer and clover to soil as measured by yield, P uptake, and extractable P levels. Granules were superior to point placement in increasing P uptake and extractable P levels on Orangeburg + Fe(0H)_ soil. viii

PAGE 9

Surface charge studies indicated negative shifts in Zero Point of Charge (ZPC) with P and clover applications. A ZPC of 4.7, the pK of carboxyl groups, was observed with clover addition. Mechanisms of ionic compl exat ion by organic functional groups and organic ligand exchange appeared to exist from these observations. Experimental observations indicate that applications of clover to FeCOH)^ treated soils enhanced crop production. ix

PAGE 10

CHAPTER I INTRODUCTION In the soil environment, chemical processes favor equilibrium status of minerals although equilibrium is seldom obtained (Kittrick, 1977). Rain, however, dilutes the soil solution and promotes dissolution of mineral phases thereby increasing the soil solution activity of certain ionic species. Partial desorption of ions bound to the exchange complex also buffers the soil system. Conversely, drought may increase soilsolution ionic concentration until it is supersaturated, resulting in precipitation of a solid phase. Changes within the soil chemical environment can promote mineral ogical transformations. Each of these processes, as described by Lindsay (1979), over time produce minerals posseeeing greater resistance to weathering. Iron-oxide formation is indicative of highly-weathered soils (Schwertmann and Taylor, 1977). Iron oxide or hydroxide minerals may exist as an independent solid phase in soils where sufficient Fe oxide concentrations exist or occur in association with the clay fraction (Carroll, 1958). In either case, iron oxides could effect surface chemistry by coating clay minerals (Stevensen, 1982). 1

PAGE 11

2 Phosphorus (P) fixation, which is reduction of soil solution phosphate by Fe minerals, may occur by adsorption to the solid phase or precipitation reactions from the solubility products (Chu et al 1962). Adsorption may occur as a monoor binuclear covalent bonding to the Fe mineral (Kingston et al 197A). Binuclear adsorption is irreversible in that desorption is negligible. Iron ionic species may reduce P availability below pH 5.5 through precipitation reactions. If the solution species of Fe and H^PO^" reach saturation with respect to the solubility product of strengite (FePO^ ZH^O) precipitation can result (Lindsay, 1979). Present management practices for reduction of P fixation include either P as an amendment, or use of a low input strategy which includes proper placement, less costly P sources, and soil amendments such as lime or silicates (Sanchez and Uehara, 1980). Another management practice that could possibly reduce P fixation would be to apply an organic amendment to the soil. Humic and fulvic acids covalently bind to Fe mineral surfaces (Parfitt et al 1977) and reduce net positive charge (Moshi et al 197 A). Complexation of solution Fe or Al may occur by bonding ionically to the organic functional groups (Deb and Datta, 1967). Less costly management practices of applying crop residue possibly could substantially increase agronomic

PAGE 12

3 yield on high P-fixing soils. To test this hypothesis experimental objectives are 1) to assess the effectiveness of organic amendment on Fe (OH) treated soil which can be measured by dry-matter yield, P uptake, and extractable P levels. 2) to determine the effectiveness of organic coating on fertilizer phosphate granules in relation to dry matter yield, P uptake, and extractable P levels.

PAGE 13

CHAPTER II LITERATURE REVIEW Effect o f Iron Oxides on Soil Chemical Properties Iron oxides can exist as independent minerals in soils where significant concentrations of these oxides have accumulated ( Schwertmann, 1959), or can occur in association with the clay fraction (Carroll, 1958). Follett (1965) studied the retention of amorphous ferric hydroxide in association with kaolinite, quartz, and gibbsite. He observed that the amorphous material reacted immediately with kaolinite on basal plane surfaces. Smaller amounts of amorphous ferric hydroxide were adsorbed on finely ground quartz and an insignificant amount to gibbsite. At the experimental pH of 5, which would create a net positive charge on the amorphous colloid, adsorption to negatively charged kaolinite could occur. If ferric hydroxides existed in sufficient amounts to coat soil particles, the surface chemical properties would approach that of the ferric hydroxide (Stevensen, 1982). 4

PAGE 14

5 Surface Charge of Iron Oxides Surface charge of Fe oxides is pH dependent as shown in the following model (Parks and deBruyn, 1962): Charge (+) 0H„ Charge (0) Fe OH, OH. OH Fe H OH Charge (-) OH OH Fe \ OH Adsorption or desorption of H^ creates either a positive, neutral or negative charge on the oxide surface. As a pH-dependent charge is developed, an anion or cation (A or C^ ion model) is attracted to and satisfies the electrostatic charge according to the law of electroneutrality in the outer diffuse electric double layer. This type of adsorption is termed nonspecific adsorption or ionic bonding (Schwertmann and Taylor, 1977). A stronger adsorption bond is produced when ions penetrate the coordination shell of the Fe atom on the oxide surface and exchange their OH and 0H2 ligands. A covalent bond is produced between the anion and oxide and is termed specific adsorption (Stevensen, 1982). Phosphate Fixation by Iron Oxides Soils rich in Fe oxides, such as some Utisols and Oxisols of the tropics, are known for their low availability of phosphate (Kamprath, 1967; Fox and Kamprath,

PAGE 15

6 1970). In most cases, high P content is associated with high Fe content in the soil such that Fe minerals are thermodynamically sinks for P (Taylor and Schwertmann, 1974). Mechanisms of P fixation by Fe oxides are by precipitation and/or adsorption reactions (Chu et al 1962). Under acidic soil conditions, the ionic activities of solution species of Fe and H2P0^ may reach saturation with respect to the solubility product of strengite (FePO^'2H20) (Lindsay, 1979). Concurrently, precipitation of strengite at low pH would occur (Lindsay and Moreno, 1960). Progressively less phosphate is precipitated as the pH is increased (Struthers and Sieling, 1 950) Specific adsorption of phosphate is another mechanism of reducing pi antavail abl e P. Kingston et al.(197A) found differences in surface-charge values of goethite after phosphate addition while measuring P adsorption. They postulated that the difference in charge was due to either mononuclear or binuclear adsorption of phosphate as shown in the following s chematic :

PAGE 16

7 OH. Fe. 0 — PZIO i Fe OH OH, -2 + 0H Reversibly adsorbed P Irreversibly adsorbed P Wann and Uehara (1978) determined that phosphate addition to Fe-oxide-rich Oxisols lowered the ZPC and increased surface charge density at any pH above the ZPC. They suggested phosphate as an amendment to increase cation exchange capacity. Parfitt et al. (1975) confirmed the binuclear coordination of phosphate adsorption in goethite using infrared spectroscopic analysis. Increasing surface area of major soil Fe oxides was observed in which amorphous ferric hydroxide > lepidocrocite > goethite > hematite. Phosphorus adsorption also increased with increasing mineral surface area. Kinetics Hsu (1965) studied phosphate fixation with soils possessing Fe and Al oxides. He observed a two-stage reaction rate in which P was fixed rapidly within a few minutes or hours and a slower rate with increasing time. Adsorption of P to Fe oxides is postulated to be

PAGE 17

8 a first order relationship after 48 hours of reaction time (Ryden et al 1977) such as: [A] = K[A] t when A, t, and K represent phosphate concentrations, time, and a constant, respectively (Bohn et al 1985) Differences in reaction rates were attributed to mineral and solution Fe and Al (Hsu, 1965). He also stated that in principle, there was no difference between precipitation and adsorption reactions. He noted that whether a Fe^ (OH) 2 (^2^A^ 6 ^ Fe^^(OH) j^^^(H2P0^) compound is formed is irrelevant since the chemical reaction is the same. Desorption is also an extremely complex phenomenon. If the enthalpies of the mononuclear and bin uclear Fe phosphate complexes are similar, the binuclear adsorption would exhibit greater stability (Kingston et al 1974) due to an increase in entropy (Kartell and Calvin, 1952). Slow release of phosphate from Fe oxides has been attributed to a ring-forming, binuclear phosphate adsorption (Atkinson et al 1972) Phosphorus Fixation by Organic Components During the decomposition of organic materials in acidic soils, organic functional groups can form a stable complex with Fe or Al in solution (Deb and Datta, 1967). Humic acids extracted from acid soils usually have a high Al and Fe content (Greenland,

PAGE 18

9 1965). Phosphate adsorption may occur on organic material by cation bridging to Fe and Al Bloom (1981) determined that P is strongly adsorbed by Al-saturated peat within the pH range of 3.2 to 6.0. He postulated that the mechanism of fixation was an adsorption of orthophosphate to trivalent complexed Al followed by the precipitation of amorphous Al-hy droxy-phosphate such as Al (OH) 2 H^PO^. The strength of phosphate adsorption by this mechanism was less than that for an Al-permanent charge resin but greater than that on a weight basis of organic matter obtained from an Andept soil Present Management Practices for Reduction of P Fixation There are at present two management alternatives for favorable P fertility on acidic soils (Sanchez and Uehara, 1980). One is a high input strategy utilizing P as an amendment and the other is a more economical low input strategy. Each method will be discussed. Phosphorus as an Amendment Fox and Kamprath (1970) determined that 95% of the maximum yield could be obtained when the fertilizer rate was adjusted such that 0.2 ug P/ml existed in the soil solution as determined by adsorption isotherms on acidic soils. To obtain that concentration, 700 kg P/ha were added. Ten y after the initial experiment, the residual efficiency which is fertilizer P effectiveness in crop production over time, ranged from

PAGE 19

10 28 to 50%. It was noted that soil properties affected the residual effectiveness. Kamprath (1967) found that previously applied high rates of P fertilizer oxisols resulted in increased yield 9 y later and that supplemental P application greatly increased yield. Fox and Kamprath (1970) also determined that the P fixation capacity of acidic soils was reduced by high rates of initial P applications. It took less application of P, with increasing rates of initial P application, to maintain 0.2 ug P/ml in the soil solution after 10 y. An increase in cation exchange capacity (CEC) was accomplished by phosphate addition. As stated previously, adsorption of phosphate to Fe-oxide-coated soils increased the net negative charge of the colloid and thereby the CEC (Wann and Uehara, 1978). High applications of P may also increase the soil pH. In acidic soils, soilsolution Al and Fe may be precipitated, thus reducing their activity (Lindsay, 1979). Stoop (197A) observed that ammonium phosphate addition increased acidic soil pH due to a decrease in anion exchange capacity. Low Input Strategy An alternative to the costly applications of massive rates of P would be the low input strategy of increased P fertilization efficiency by improving placement, using cheaper sources of P, and decreasing P

PAGE 20

11 fixation through various amendments (Sanchez and Uehara, 1 980) PI acement Placement of fertilizer P can have an effect on yield. Kamprath (1967) obtained similar yields of maize by banding 22 kg P/ha for 7 y (15A kg P/ha) as compared with an initial application of 350 kg P/ha. Yost et al (1979) observed that banding was inferior to broadcast applications to a high-P fixing Oxisol in Brazil, with very low levels of extractable P. The best methodology for high P fixing soils probably is an initial broadcast of P fertilizer with small annual bandings of P fertilizer (Sanchez and Uehara, 1980). P Sources Lower cost phosphate fertilizers such as phosphate rock may substitute for higher cost more soluble phosphate sources. Reactivity, as determined by the absolute citrate solubility (Lehr and McClellan, 1972) of the rock source, determines its effectiveness on acidic soils. The initial relative agronomic effectiveness of rock sources as compared to soluble superphosphate was observed by Hammond (1978) to be 79 to 94% for high, 41 to 65% for medium and 27 to 40% for low reactivity rock sources. He also observed an increase in the calculated relative agronomic effectiveness values for rock sources during subsequent cropping resulting from the slow-release characteristics of the source. Phosphate

PAGE 21

12 rock may also produce a liming effect when there is a slow-carbonate release from highlyreactive rock (Easterwood, 1982). Soil A mendments Soil amendments may aid in reducing P fixation. The addition of lime reduced P fixation as measured by adsorption isotherms of Oxisols (Mendez and Kamprath, 1978), Ultisols (Woodruff and Kamprath, 1965), and Andepts (Truong et al 197 A). The pH of these soils was below pH 5.2 initially. With an increase in soil pH, the 6 oilsol ut i on Fe and Al activity was reduced (Lindsay, 1979) Although liming may reduce P fixation, the orthophosphate adsorption mechanism can still be operable (Parfitt et al 1975). Addition of silicate salts may also reduce P fixation. The silicate anion may replace phosphate on oxide surfaces (Silva, 1971). Roy et al (1971) observed a decrease of 47% in P fixation on an Ultisol, 41% on an Oxisol, and 9% on an Inceptisol when 500 mg Si kg ^ as calcium silicate was added to these soil oxi de s Another management practice that could possibly reduce P fixation is the addition of organic matter to soils. Sanchez and Ueha ra (1980) state that organic radicles could block exposed hydroxyls on surfaces of Fe and Al oxides. They noted that topsoils with the

PAGE 22

13 same mineralogy as subsoils fix considerably less P due to the organic content in the topsoil. Decomposition Products of Organic Materials A synopsis of previous research of the chemical nature of soil organic compounds was compiled by Greenland (1965). Component properties of the humicacid, fulvic-acid, and humin fractions were obtained from his publication and are reported below. Humic Acids Humic acids are composed of amino acids and phenolic compounds combined to form high molecular weight polymers (20,000 to 30,000). This component of organic matter is soluble in alkali and precipitated by acids. Research data indicate that humic acids at low pH have a spherical configuration. As the pH of the environment around the polymer is increased, the molecular compound increases in charge and becomes more flattened due to reduction in H bonding. Titration curves indicate a large number of acidic groups, of which about half possess a negative charge in the pH range of 5.0 to 7.0. Fulvic Acids Fulvic acids are more heterogenous than humic acids. Fractionation of fulvic acids reveals that the principle components are phenolic materials similar to humic acids but with lower molecular weight. Up to 30% of the fulvic acid may consist of polysaccharides which

PAGE 23

14 also may form polymers. Polymers appear to be large, linear, flexible molecules having less carboxyl groups than in humic acids. Humins Humins are organic compounds which are irreversibly bound to the mineral part of the soil. It appears that humins have a lower carbon content compared to humic acids possibly from less aromatic compounds adsorbed to the mineral surface. These compounds appear to possess resistance against microbial degr adati on. Clover Humif ication; Rate, Products, and Functional Groups To assess the humification process, the degradation of clover ( Trif ol ium repens ) will be discussed. Topics of discussion for this section were obtained from Kononava (1966). Plant residue decomposition is accomplished by a variety of soil microorganisms whose speciation depends on the chemical composition of the plants and soil environmental conditions. Microbes oxidize the plant material which loses its stability resulting in a decrease in weight and volume. During humification, plant residues became brown in color and, if enough water is present, an aqueous solution of humic substances may be formed.

PAGE 24

15 Rate of Decomposition First signs of humif ication of clover leaves appear within 2 to 4 d with the first appearance of humic substances 2 wk after inoculation. The following observations were recorded: Clover leaves, A microscopic examination of different sections of tissue humification enabled us to distinguish the following stages of humification: 1) A darkening of the leaves 3 to A days after the start of the experiment; this appears to be brought about the action of oxidizing enzymes in the tissues and also by the activity of mold fungi which form a weft on the leaf surfaces. 2) In the following 7 to 8 days, the development of an enormous number of different bacteria and protozoa is observed in the leaf tissues. The number of bacteria is so great that in some sections the tissues are completely filled with them. A gradual disappearance (like "dissolving") of the cell walls of the epidermis, particularly noticeable in young leaves, is observed from a microscopic examination of the leaf surface. At the same time, bacteria, found after isolation to be cellulose myxobacteria have penetrated into the interior of the epidermal eel Is 3) These bacteria, which are at first colorless, later group themselves into slimy masses, become brown in color, and completely fill the cell. After some time, the bacteria mass in the cells undergoes lysis and is converted into a brown liquid which seeps out of the cell (Kononova, 1966. p. 147) Total humification of clover leaves took about 3 wk. Weight loss was 50 to 70% of the original material

PAGE 25

16 Degradation Products Decomposition rate is influenced by the ease of metabolism of the organic substrate and the percentage of si owly-metabol iz abl e compounds. On a percentage basis of dry ash-fee material before humif ication, clover leaves contained 23% organic-soluble substances (i.e. benz ene-ethanol) 3% starch, 8% hemicellulose, 15% cellulose, 22% protein, and A% lignin. After the humification reactions, the residue, expressed as a percentage of dry ash-free material, contained 16% substances extracted by organic solvent, 0% starch, 6% hemicellulose, 13% cellulose, 3 4% protein, and 16% lignin. Comparisons of chemical composition of humified and non-humified residues suggests that the percentage of material extracted with ethanol-benz ene starch, and cellulose decrease greatly during humification. Humus has a larger percentage of protein and lignin than non-humified clover since the previous components are easily metabolized. The most stable substance was lignin whose content decreased very little. Type and Distribution of Functional Groups Clover leaves contain 57% C, 6% H. 3 2% 0, and 5% N on a dry weight basis. Configural arrangement of these elements into organic functional groups determines the reactivity of the compound or polymer. Humic substances formed from clover tend to be acidic in nature due to the reactivity of their functional groups

PAGE 26

17 releasing as the pK value is reached. On a percentage basis of dry ash-free material, plant residue contains 9% carboxylic, 8% al cohol ic-OH, 6% phenolic-OH, and 3% methoxy functional groups producing the high reactivity of humified organic material. Inorganic P Released From Clover Decomposition During the decomposition of clover, inorganic phosphate may be mineralized. Lockett (1938) postulated that P was mineralized and assimilated into microbial lipids and nucl eoproteins. Later P became available upon dieintergration of microbial cells. He determined that, after decomposition, 59% of the total P was in organic form and 41% in inorganic form. He obtained similar results as those observed by Rononava (1961) Organic Anion and Iron Mineral Interactions Unlike cation bridging of organic anions to clays (Evans and Russell, 1959), the mechanism of humic and fulvic-acid anion bonding to Fe minerals is by specific adsorption or ligand exchange (Parfitt et al 1977). The process is not sensitive to electrolyte concentrations, although it is sensitive to pH since the adsorption maximum inflection point occurs near the pH corresponding to the pK of the acid species, which is usually carboxylic and near pH 5.0 (Greenland, 1971). He reported a very strong bond between oxide and humic molecules since most functional groups of the organic

PAGE 27

18 acid participate in the adsorption and their distribution was throughout the organic molecules. Greater surface area of the humic acid, at or above the pK value, allows stronger adsorption to the oxide. Reduction of available functional groups may occur as cations are complexed from the soil solution (Zunino and Martin, 1977). Complexation is very effective in reducing Fe or Al in solution due to the stability of the complex (Deb and Datta, 1967). They found that the stability of the complex is so great that functional groups are rendered inactive with respect to further interactions with hydrous oxides. Bloom and McBride (1979) did research on the complexing ability of metal ions with humic acids. They observed that humic acids bind with most divalent metal ions, with the exception 2 + of Cu as hydrated species. Also, they observed that humic acids exhibit a strong affinity for trivalent 3 + ions. The Al ion is likely bound to three carboxyl groups, but the case of the monoand divalent species adsorption from solution cannot be ruled out (Bloom and McBride, 1979). Bloom (1979) observed the titration behavior of Al-saturated organic matter. He observed that, as the pH of the material is increased, the OH 2 + would most likely form Al(OH) on the organic-matter exchange sites. As the pH is increased until the 3 + — 3 activity of (Al ) (OH ) is exceeded, precipitation of amorphous A1(0H)„ would be induced. Acid addition on

PAGE 28

19 3 + the other hand results in release of Al ions into solution as H"*" ions bind to functional groups at adsorption sites. Freshly humified clover material adsorption on allophane was studied by Inoue and Wada (1968). They found that newly humified clover possessed a greater capacity for adsorption than humic substances extracted from soils. Possible inactivation of functional groups due to ion complexation was suggested as the reason for the reduction in adsorption (Greenland, 1971). Preferential adsorption of high molecular weight (1,500 to 10,000) decomposition products was observed on allophane (Inoue and Wada, 1968). Different ideas exist in the literature concerning the stability of Fe-organo mineral complexes. Levashkevich (1966) determined that humic acids form more stable bonds with Al-hydroxide gels than with Fehydroxide gels which he stated had a lower capacity for adsorption. Greenland (1971) stated that a very strong bond would be formed between the oxide and humic molecule if several carboxyl or other groups participated. Schwertmann (1966) stated that the transformation of amorphous ferric hydroxide to a crystalline Fe mineral may be halted due to the bonding of organic ligands to the mineral. Schwertmann and Fischer (1973) determined that ferric-hydroxide surface area would be reduced by organic-1 igand adsorption.

PAGE 29

20 The following relationship was observed: S(m^/g) = 76.6 16.A(%C) + 9.56(%Fe) where n=17 and r=0.94. This relationship suggests strong covalent bonding between Fe hydroxide and organic anions. Parfitt et al. (1977) determined that fulvic acid is adsorbed on goethite surfaces by ligand exchange at the pH of 66.5. Parfitt and Russell (1977) determined that mononucleate species, such as benzoate and 2,4-D, had a low-binding constant and were easily desorbed from goethite surfaces. Binuclear species such as oxalic acid were strongly adsorbed on the goethite surface. Appelt et al (1975a) measured the adsorption of benzoate, p-OH benzoate, salicylate, and phthalate on Andept soils from Chile. They observed that monoprotic adsorption was by anion exchange whereas diprotic adsorption was by anion and ligand exchange. OrganoMineral Reactions Affecting P Fixation Possible Mechanisms Mechanisms relating to reduction in P fixation on Fe oxides by organic amendments are not clearly delineated in the literature. Singh and Jones (1976) stated that inorganic P from the decomposition of organic residues would possibly supply sufficient P to reduce P fixation such that added P would be in a stable form. They stated that an organic residue must contain at least 0.3% P, otherwise added P would be immobilized.

PAGE 30

21 Conversely, Datta and Goswami (1962), utilizing P tracer techniques, came to different conclusions. The following excerpt is from their paper: The increase in the uptake of total P was again due to a greater uptake of soil and not fertilizer P, except in red soil, where the uptake of both soil and fertilizer P increased. It is, however, expected that, though organic matter itself has contributed towards the amount of soil P, it is considered to bear very little in relation to such a large increase in total uptake (p 236) Singh and Jones (1976) also stated that P adsorption could be lowered by blocking adsorption sites with decomposition products from organic matter. Bhat and 3 2 Bouyer (1968), utilizing P studies, found that the addition of organic matter to ferruginous tropical soils lowered P-fixation capacity and isotopicallydilutable P was also greater. Initial soil pH was 6.6. 3 2 Datta and Nagar (1968) using P studies determined that the uptake of fertilizer P was decreased substantially by organic addition in all their experimental soils except red soils where there was a slight increase in fertilizer P uptake rather than P uptake from organic and soil P. Initial soil pH of this red soil was also 6.6. Datta and Nagar (1968) suggested that the mechanism of organic acid production could solubilize certain insoluble phosphates present in the soil. This explanation was given due to large amounts of soil

PAGE 31

22 rather than fertilizer P uptake on all experimental soils except the red soil. Deb and Datta (1967) stated that organic anions in acidic medium are very effective in complexing Fe and/or Al in solution. They observed reduction of Fe and Al activity preventing precipitation as insoluble phosphate compounds. Observations Conclusions relating to the reduction of P fixation by organic addition by previous researchers are mixed. Appelt et al., (1975b) found that the adsorption of benzoate, p-OH benzoate, salicylate, phthalate, and humic and fulvic acids extracted from the surface soil of a Typic Dystrandepts did not block P adsorption sites on subsurface samples of that soil. Soil pH values ranged from A. 8 to 5.4. High extractable Al levels were observed. In their studies no characterization of the organic material relating to sesquioxide ash and P fixation capacity was given. Yuan (1980) studied the adsorption of phosphate and hot water-extractable soil organic matter on acidic soils and synthetic Al silicates. He found that pretreatment of organic material had no effect on an Eutrandept: a slight effect on a Haplaquod, and partial reduction of P fixation on a Paleudult. He observed that organic material adsorption was increased by an increase in the rate of material applied, but the amounts of P retained

PAGE 32

23 by the soils were constant suggesting that adsorption sites for P and organic material were different. Greenland (1971) determined that organo-mineral studies should be performed utilizing pure mineral and organic materials. He determined that previous reactions may block adsorption sites on hydrous oxides. Also, organic functional groups could be rendered inactive by metal compl exa t i on. Nagarajah et al (1970) evaluated the competitive adsorption of polygalcturonate (a root exudate with atomic weight of approximately 25,000) on synthetic goethite. At pH 4.0, polygalcturonate decreased phosphate adsorption by chelation of Fe or adsorption on the goethite surface as determined in their experiments. Hashimoto and Takayama (1971) reported that humic acid, nitrohumic acid, and nitrohumate salts inhibited P fixation on a synthetically prepared goethite, ferric hydroxide, and ferrous orthosilicate, but not by lepidocrocite or amorphous Fe oxide hydrate. Manojlevic (1965) conducted laboratory studies with humic acid derived from dung and manure on high-Pfixing soils. Humic acids decreased P fixation from granular superphosphate which was in contact with the soil for A mo. Moshi et al (1974) measured phosphate adsorption from two profiles (one cultivated and one under forest environment) of Kikuyu red clay from Kenya. He reported that surface-adsorbed organic

PAGE 33

2A components reduced the positive charge on the soil surface. They found a linear correlation (p>.01) between increasing percentage of organics and reduction of positive charge. Phosphate adsorption at pH 5.0 was reduced by the presence of organic matter. They also observed a linear correlation (p>.01) between a decrease of phosphate adsorption and increasing C% Hinga (1973), also obtained similar results on Kenya soils.

PAGE 34

CHAPTER III ORGANIC ADSORPTION EXPERIMENT Introduction The mechanisms of humic and fulvic anion bonding to Fe minerals ares by specific adsorption or ligand exchange (Parfitt et al.. 1977). The process is not sensitive to electrolyte concentration, although it is sensitive to pH since adsorption maximum occurs near the pH corresponding to the pK of the acid species, usually carboxylic, near pH 5.0 (Greenland, 1971). He found that a very strong bond was formed between oxides and humic molecules since most functional groups of the organic acid participated in the adsorption. Schwertmann (1966) stated that the transformation of amorphous ferric hydroxide to a more crystalline Fe mineral may be stopped due to the bonding of organic liquids to the mineral. Parfitt et al. (1977) determined that fulvic acid is adsorbed on goethite surfaces by ligand exchange within the pH range of 6 to 6.5. The objectives for the organic adsorption experiment were as follows: 1) To determine pH for maximum clover decompositional product adsorption and 2) To determine time required for transformation of amorphous Fe(0H)2 to a crystalline phase in relation to clover appl ication. 25

PAGE 35

26 Materials and Methods Soil An Orangeburg series soil (fine, loamy, siliceous, thermic, Typic Paleudult) was obtained from the Agri~ cultural Research and Education Station near Quincy, FL Two portions of the profile under forest environment were sampled. The surface soil, devoid of organic litter, was obtained corresponding to the A horizon. This sandy soil was to be the matrix for FeCOH)^ addition. Subsurface B horizon samples were obtained of the corresponding soil profile. Chara c terization Both samples were characterized physically, mineralogically, and chemically. Particle size distribution was determined by the methodology of Day (1965) for the clay fraction and sieving to determine sand and silt fractions. Pretreatment with ^2^2 organic component s Mineral ogical characterization included identification of clay fraction minerals. Pretreatment included removal of organic matter with H2O2 and free Fe oxides with ci trate-bicarbonate-dithionite extraction (CDB). Free iron oxide and Al concentrations in CDB extracts were determined using atomic adsorption spectrophotometry (Kunze, 1965). Chemical characterization included cation exchange capacity by the summation method as described by

PAGE 36

27 Chapman 1965). Organic carbon was determined by dichromate-oxidation techniques (Walkley and Black, 193A). Soil pH was determined in a 1:1 ratio of soil to water (McLean, 1982). Phosphorus fixation was determined by methodology of Fassbender and Igue (1967) in which 5 g of soil were placed into a centrifuge bottle with 100 mL of 100 mg P/L solution. The bottle was shaken for 6 hours at 180 excursions/min. Separation between solution and solid phase was accomplished through millipore filtering (.2 u) Extracts were analyzed for P using methodology described by Murphy and Riley (1962). Results are given in Tables 3-1 and 3-2. Fe(OH)^ Synthesis Amorphous ferric hydroxide was prepared by potentiometrically titrating 2 M VeitiO^)^ with 6 M KOH to pH 8.1 (ZPC). Equivalent concentrations of both reagents were used in precipitating the Fe(0H)2 ^^^^ 3-1). To remove the soluble KNO^ formed, approximately 2 L of deionized water was filtered through 250 g of precipitate resulting in negligible concentrations of and NO^ A suspension of Fe(0H)2 in was prepared with a concentration of approximately 1 M as Fe(0H)2. Rates of 0 and 5.6 g Fe as Fe(0H)2 were applied to Orangeburg surface soil by complete mixing.

PAGE 37

1 1 i col 1 ^ 1 X 1 C O 1 i o o 1 < •H HI 1 1 4-1 fa 1 + 00 K ,i~, CO Ext O CO • o tH CO CD • U r-l % o o N •H / — ^ O '-v a W 0) • CM 4-) • Q) 0) 4-) CD CO a cl IT CS OO 1 CO • on c •H r-l o x> ^ CX o 4-1 u •H M Id C 4J CD o o c CD (U •H •H O •H nd in ^ 1 4-1 -W CJ 4-1 0) CO 0) Id u 0) ID Id • 4-1 V4 Id 4J o o 1-1 4-1 U U G 0) o 0) M W •H Id JS X! 4-> SK O >> 00 V4 TP^ H 1 H 1 00 O te 01 te te < rH CO al ni 4-> N -H in CD M o o <-lO lU u •H 4J CQ 4-) X PQ i-l iH < •H a O CD U3 U + 3 'H < + + Eh s O" O + + +

PAGE 38

a o •H 4-1 0) •H 00 OO a o o CO &4 •ri o a 3 W t>4 M 3 Xi 0) O0| c Q) M O W o o 4->{ Ql I §1 t\ l N •H U > to c CO 10 00 CO CO 00 ID + w Q) CO CO 0) M o (0 u 4-1 + + + 4J 1-1 •a CJ < 0) iH 0 I 4J 1 0| I I0| I Ml I M I 00 SI 1^ •H C •H 0) 4J N -rl 4J CO t4 Xi CO ^ OO 0) 4-1 0) C 4-1 •H -H J3 <4J 0) o CO 3 -H -if O C O tH O CM O CO o VO CO o o ^ Q) .CM •p • O 00 c ac O 0.5C U w CO a o o c •rl O 4-1 "rl V 4J <0 U •H I 0) U Id U 0) c o •H •rl H W •O ^ H I I 0) y CM 4-' < r-( CO O U H <-C0 •^i m •ri z + + + + +

PAGE 39

o in cn E -H O D •H cr 4-1 (U C -H 0) iH O •<-{ I •H

PAGE 40

31

PAGE 41

32 Clover Production White clover ( Trif ol ium repens ) was grown hydroponically to insure organic functional groups did not contain high sesquioxide ash contents. Hydroponic —3 solution possessed ionic concentrations of 10 M P, 10"^*^ M K. lO"-^*^ M NO^, lO""^*^ M Ca. 10~^'^ M Mg, 10~ 2 7 -3 5 M SO, 10 M Fe, with micr onutrient concentra— 4 — tions of 0.5 ug B/ml, 0.5 ug Mn/ml, 0.05 ug Zn/ml, and 0.02 ug Cu/ml (Hoagland and Arnon, 1938). Solutions were continually aerated and replaced biweekly. Clover biomass was harvested every 40 d and the material was then dried and ground to pass a 2mm sieve. Liming Curve and Organic Adsorption Measurements To determine the maximum organic adsorption to Orangeburg topsoil, an incubation study was initiated in which 50 g samples were treated with or without 5.6 g Fe as FeCOH)^, plus or minus 3.15 g/kg dried and ground clover, at CaCO^ rates of 0, 0.5, 1.0, 1.5, and 2.0 cmol CaCO^/kg soil. Reagent grade CaCO^ was mixed with soil and incubated for 2 w at 25C and 8% moisture on a weight basis. Dried and ground clover was then applied and allowed to decompose for 30 d. Duplicate samples were prepared. Organic anion extraction was performed by extracting 10 g of soil with 20 mL of 0.01 M NaCl and shaking for 30 min (Stevenson, 1982). Samples were centrifuged and aliquot decanted. Electrical conductivity of each

PAGE 42

33 aliquot was measured prior to increase of solution pH to pH 7.0 with 0.1 M NaOH for adsorption measurements of humic and fulvic acids at 465 nm (Chen et al 1977). Soil pH was measured in water (1:1 ratio) (McLean, 1982). Crystallization of Fe(OH)g Solid Fe(0H)2 and Fe(0H)2 associated with the clay fraction of Orangeburg soil were monitored over a 6 mo period for crystal formation. Both samples were subjected to wetting and drying cycles over time. X-ray diffraction (XRD) techniques were employed using Cu K radiation to monitor changes. Differential scanning calorimetry (DSC) techniques were also employed. Results and Discussion Organic Adsorption Experiment Study of organic adsorption on soil solids can produce confounding results in impure systems due to previous reactants on solid surfaces or inactivity of organic functional groups due to ion complexation (Greenland, 1971). For this reason, pure phases were prepared for study. Amorphous ferric hydroxide was applied to the Orangeburg sandy soil which was the matrix for the mineral addition. Follett (1965) observed that ferric hydroxide reacts with basal-plane surfaces of kaolinite, which is the primary clay mineral in the Orangeburg soil. Since Orangeburg soil is

PAGE 43

34 acidic (pH A. 9), a liming curve after FeCOH)^ application was essential to determine pH for maximal organic adsorption. Also the pH of the soil must be greater than the dissociation constant of the organic acid (pH > 5.0) to activate organic anions (Greenland, 1971). Clover rates were similar to residue rates added to the soil for cover crop production. Results from the incubation study with respect to treatment are given in Fig. 3-2 to 3-9. Organic adsorption relationships produced by changes in pH are given in Fig. 3-2 to 3-5 and adsorption relationships with change in ionic strength are given in Fig. 3-6 3-9. Numbers in parenthesis in these figures are soil pH values. Ionic strength was calculated to be the total ionic strength of solution minus the ionic strength of the 0.01 M NaCl solution. Total ionic strength was calculated by the following equation: u = 0.013 EC where 0.013 is a constant and EC is electrical conduc_2 tivity expressed in millimhos cm (Griffin and Jurinak. 1973). Stevenson (1982) stated that organic adsorption to clay surfaces was sensitive to changes in ionic strength. The mechanism of adsorption is by ionic

PAGE 44

35 5.0 6.0 6.6 PH Fig. 3-2 Effect of Soil pH on Organic Release From Orangeburg Topsoil.

PAGE 45

36 0.6 0.5 c o H 4-> D iH O m c •H o •H i a: 0.3 'e c m ""0.2 m u c CO u lo.i 5.0 6.0 pH 6.8 Fig. 3-3 Clover Decompositional Product Adsorption to Orangeburg Topsoil as Influenced by Soil pH.

PAGE 46

37 c o o 0.08 ^ 0.07I•H o
PAGE 47

38 c o 0.08 0.07 •a a 0.06 < 0.05 3 ^ 0.04 o I 0.03 in 0.02 0.01 pH Fig. 3-5 Clover Decompositional Product Adsorption to Orangeburg Topsoil + FeCOH)^ as Influenced by Soil pH.

PAGE 48

39 bonding. Similar results were obtained from the treatments of Orangeburg soil without Fe hydroxide addition. Increasing lime rates increased soil pH from 4.9 to 6.7 (Figs 3-2 and 3-3) but also increased solution ionic 2 + strength due to increased Ca activity (Figs 3-6 and 3-7). Calcium does not form a strong complex between negatively charged clay and humic acid, but is effective as a bridge between ions (Stevenson, 1982). Greenland (1971) observed that organic matter bound to 2 + clay through Ca cation bridging was easily displaced by monovalent ions such as NH^"*^ or Na"*^. Increases in pH increase negative charges on mineral surfaces (Kaolinite) and therefore cation exchange capacity. Near pH 6.2, less organic anions were extracted by + 2 + NaCl. Possibly Na and Ca ions increased exchange3+ 3 + able Al or Fe levels. Aluminum and Fe at low concentrations could reduce organic anions by flocculation (Stevenson, 1982). Results are inconclusive above pH 6.2. Stevenson (1982) also stated that organic adsorption to hydrous oxides occurred by ligand exchange or covalent bonding. Only anions that bind strongly to oxide surfaces could replace organic anions. This mechanism is insensitive to solution ionic strength but highly sensitive to pH Salt solution extraction did not affect organic adsorption. Results in Fig. 3-4, 35, 3-8, and 3-9 support this mechanisms organic

PAGE 49

AO Fig. 3-6 Effect of Solution Ionic Strength on Organic Release From Orangeburg Topsoil.

PAGE 50

Al 0.6 • (6.2) e o 0.5 o e •H •a •[j OA •< u •H E 3 • (6.2) 0.3 ^(5.6) E C in 0.2 u c (0 o S 0.1 (6.7) • •(6.2) • I • • 0 .004 .008 .012 .016 .02 .024 Ionic Strength Fig. 3-7 Clover Decompositional Product Adsorption to Orangeburg Topsoil as Influenced by Solution Ionic Strength.

PAGE 51

42 c o in •hO.07 h ^0.06 u 10.05 0 0.04 B c in 0.03 0.02 0) o c S 0.01 o m < • (7.51) • (7.09) : (^•^^V5.7) (6.8) .004 .008 .012 .016 .02 .024 Ionic Strength Fig. 3-8 Effect of Organic Release From Orangeburg Topsoil + Fe(OH). as Influenced by Solution Ionic Strength.

PAGE 52

43 G O (7.5) •(7.0) •(7.2) • (5.6) •(6.3) .004 .008 .012 .016 .02 .024 Ionic Strength Fig, 3-9 Clover De c omp o E i t ional Product Adsorption to Orangeburg Topsoil + Fe(OH)_ as Influenced by Solution Ionic Strength.

PAGE 53

44 covalent bonding. Organic adsorption was not affected by ionic strength as seen in Fig. 3-8 and 3-9 but was greatly affected by changes in soil pH (Fig. 3-4 and 35). Ionic strength ranged from 0.016 to 0.022 units whereas pH changes within small ranges of ionic strength greatly affected adsorption measurements. As pH increases above pH 5.0, organic anions are formed. However, FeCOH)^ possessed a variable charged surface so that increases in pH could reduce net positive charge and adsorption sites on mineral surface thereby resulting in reduced adsorption. Maximal organic adsorption occurred at pH 6.3 with residue amendment. It is also important to observe the effectiveness of organic adsorption of the FeCOH)^ treated soil compared to untreated soil. Several orders of magnitude of adsorption exist in the binding capacity, making the Fe (OH) 2 t r eat e d soil an excellent sorbant system for organic anions. Crystallization of Fe(OH)^ Changes in crystallization of Fe(0H)2 affects surface area and reactive sites for organic anion and P adsorption. Mineralogy of solid phase Fe(0H)2 and Fe(0H)2 treated Orangeburg soil were observed over a 6 m period. Solid Fe(0H)2 endured wetting and drying cycles whereas Fe(0H)2 treated soil with and without clover amendment was under a cropping system. At no time during the 6 m period did the solid Fe(OH)„

PAGE 54

A5 exhibit crystallinity as observed by XRD or DSC methodologies. The same result was obtained for the FeCOH)^ treated soil. Differential Scanning Calorimetric plots of Orangeberg soil + FeCOH)^ clay fractions without clover amendment and with clover amendment are given in Fig 3-10 and 3-11, respectively. No Fe mineral endotherm was observed. However, endotherms for both gibbsite and kaolinite, were observed. Conclusions Adsorption study observations in conjunction with previous research suggested that FeCOH)^ treated soil exhibited covalent bonding of organic anions whereas treatments without FeCOH)^ exhibited ionic bonding via cation bridging. Maximum adsorption of organic constituents occurred at pH 6.3 on the FeCOH)^ treated soil with clover amendment compared to pH 6.2 for FeCOH)^ untreated soil. After 6 m of investigation, solid FeCOH)^ and soil FeCOH)^ remained in an amorphous state.

PAGE 55

o c o 4-1 -H O -P -H u M on Q) /-V S X •H O M ^ O
PAGE 56

47 (oas/fui) Moxi

PAGE 57

M 0) o AO r-\ o U p 1 nd CO g •H O M O r-l to U th •H c •H c I-H c •H CO O o CO CO do i-H H CO •H OO P U • c 3 c
PAGE 58

49

PAGE 59

CHAPTER IV PHOSPHATE AND ORGANIC AMENDMENT STUDY Introduction Reduction of plant available phosphorus in acidic soils causing an agronomic yield reduction has plagued man for many years. The problem is produced by reactions of phosphates with Fe and Al hydroxides, aluminosilicates and/or the ions released from dissolution of these minerals (Chu et al., 1962; Lindsay, 1979; Fox, 197A; Kingston et al 197A). A possible management alternative for reducing P sorption could be addition of organic amendments. Moshi et al., (197A) measured phosphate adsorption from two profiles (one cultivated and one under forest environment) of Kikuyu red clay from Kenya. They reported that surface-adsorbed organic components reduced the positive charge on mineral surfaces. There was a high statistical linear correlation between increasing percentage organic carbon and reducing positive charge. Since positive charge was reduced, phosphate adsorption at pH 5.0 was reduced by the presence of organic matter. Hinga (1973) obtained similar results on Kenya soils. Yuan (1980) found that pretreatment with organic material resulted in partial reduction of P fixation on a Paleudult. 50

PAGE 60

51 Mechanisms producing reduction in P fixation might include 1) release of P for organic components, 2) blockage of P-adsorption sites with decompositional products from organic amendment. 3) complexation of solution Al and Fe by organic functional groups, and 4) solubilization of fertilizer reaction products such as dicalcium phosphate (DAP) by acidity produced from the humification process (Singh and Jones. 1976). The objectives of this study are to assess the effectiveness of clover addition to highly-weathered soils in reducing P fixation as measured by dry matter plant yield, P uptake, extractable P levels, and changes in surface charge on soil colloids. Materials Soil An Orangeburg topsoil as described in Chapter 3 was used in the clover amendment experiment. Amorphous Fe(0H)2 was prepared and applied as described by previous methodology. The soil was limed to pH 6.3 utilizing the liming curve developed during preliminary experimentation, and incubated for 2 wk at 25C at 10% moisture on a weight basis. Dried and ground clover was then completely mixed with predetermined treatments and incubated for 30 d prior to fertilizer addition.

PAGE 61

52 CI ov er White clover was grown hy dr oponical ly to insure reactivity of organic functional groups. Hydroponic methodology is described in Chapter 3. Fertilizer Pots used in the glasshouse study contained 3 kg of soil on a dry weight basis. Fertilizer applications (N, P, K, Mg) were adjusted by treatment assuming 50% mineralization from clover application. Total nutrient addition included 100 mg N/kg as NH^NOg 140 mg K/kg as KCl. Diammonium phosphate was applied at rates equivalent to 0. 50. and 100 mg P/kg. Supplemental nutrient addition to pots included 19.8 mg Mg as MgSO^*7H20. 11. A mg Zn as ZnSO^*7H20. 5.09 mg Ca as CaSO^*5H20 and 1.2 mg B as Na2B207 1 OH2O Methods Incubation Study To investigate soil P retention, an incubation study was conducted with three soils. These were Orangeburg, Orangeburg + 5.6 g Fe/kg as FeCOH)^. and Orangeburg subsoil. Each soil was amended with dried and ground clover at rates of 0, 1.58, and 3.16 g/kg over times of 30, 60, 90 d. Each soil had been previously limed to pH 6.3 and incubated for 2 w. Soil P retention was determined at each time interval by shaking 5 g of sieved soil with 100 ml of solution containing 100 mg P/L as K^PO^ for 6 h (Fassbender and

PAGE 62

53 Igue, 1967) in duplicate. After shaking, aliquots were filtered through a 0.2 um membrane filter disk and analyzed for orthophosphate (Murphy and Riley, 1962). Phosphorus fixation was determined by subtraction. Soil pH at each time interval was determined in a 1:1 soil to water suspension. Analysis of variance was performed on the split plot design utilizing time as a main plot with soil and clover addition as subplots. Glasshouse Study A 3 X 2 X 3 factorial experiment using 0, 50, and 100 mg P/kg soil. 0 and 5.6 g Fe/kg as FeCOH)^ and 0, 1.58 and 3.15 g clover/kg in split-split plot design with three replications was conducted in a glasshouse. Phosphate addition was the main plot with FeCOH)^ addition as the sub plot, and clover addition the sub-sub plot. Two crops of Zea mays L. were grown for 50 d each to determine initial and residual effectiveness of fertilizer. Treatments were limed and refertilized with previous rates before initiation of a third crop. Variables measured include dry matter yield, uptake of P, Ca, Mg and K, Al and Fe concentrations within plant tissue. Soil measurements included Truog and Bray 2 extractable P levels, soil pH, and organic C levels. Plant samples were analyzed in the following manner: 0.10 g of dried and ground tissue, passing a 1 mm sieve, was placed in a 50 mL beaker and oxidized in a muffle furnace at A50C. The ash was further digested

PAGE 63

54 with 3 M HNO^ evaporated to dryness on a hotplate, with removal of excess HNO^ by placing each beaker into the muffle furnace at A50C for 10 m. After cooling, 25 mL of 5 M HCl were added to the beaker, placed on a hotplate and evaporated to dryness to completely oxidize plant material. After cooling, 1 mL of 5 M HCl was placed in the beaker with water and diluted to a final volume of 50 mL. Ionic concentrations of Ca, Mg, K, Al, and Fe were determined by Inductively Coupled Argon Plasma spectrophotometry. Plant P concentrations were determined by methodology described by Murphy and Riley (1962). Soils were sampled after each maize crop. Soil pH was determined in 1 : 1 soil to water ratio (McLean, 1982). Organic C levels were determined by methodology described by Walkley and Black (1934). Since reaction products of DAP are CaHP0^'2H20, CaHPO^, and colloidal ferric phosphate with Orangeburg soil, proper extractants needed to be chosen for extraction of these phases. Ballard (1974) compared various extractant effectiveness on a variety of phosphate reaction products as independent solid phases and those phases mixed with soil. In his research Truog reagent (0.001 M H^SO^ + 3 g (NH^)2S0^) extracted lOOZ of P applied as dicalcium phosphate (DCP) as a solid phase and 98% DCP mixed with Leon fine sand. Only 2% of P applied as colloidal ferric phosphate (CFP) as a

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55 solid and mixed with Leon fine sand was extracted. Bray 2 (.03 M NH^F + 0.1 M HCl) extracted 9 8% P from CFP and CFP mixed with Leon fine sand. Sequential extractions for P were performed with Truog and Bray 2 solutions. Extraction methodology was as follows: 2 g of soil were placed in a centrifuge tube with 25 ml of Truog reagent. Samples were shaken at 180 excursions per minute for 30 m and centrifuged. Aliquots were filtered through Whatman #42 filter paper. Soil samples were again extracted with Bray 2 solution. Twenty mL of extractant were added to the soil sample and shaken for 1 m. Aliquots were immediately filtered through Whatman #42 filter paper. Soil P concentrations were determined by methodology described by Murphy and Riley (1962). Surface Charge To determine net electric charge and ZPC of 1) FeCOH)^ treated soil. 2) Fe(0H)3 treated soil + 100 mg P/kg. 3) Fe(0H)2 treated soil + 3.15 g clover/kg. and 4) Fe(0H)2 treated soil + 100 mg P/kg + 3.15 g clover/kg, potentiometric titrations were performed. Samples were obtained after the first cropping period of the glasshouse experiment. Methodology described by Laverdiere and Weaver (1977) was performed in which 10 g of sample were weighed into 250 mL beakers with addition of 100 mL either 0.01, 0.1 or 1.0 M NaCl. Samples were allowed to equilibriate for 60 m and pH was

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56 determined. Soil suspensions were titrated with 0.02 M HCl under continuous stirring. Salt solutions without soil were also titrated as a baseline for charge determination by subtracting H"^ concentrations of blank titrations at a given pH from H"^ concentrations of the soil suspension. S EM Study Clay fractions from 1) Orangeburg + FeCOH)^ + P. and 2) Orangeburg + FeCOH)^ + P + 3.15 g clover/kg for study under the scanning electron microscope were obtained by sieving the soil through a 300-mesh sieve, washing with water at pH 10, and collecting the aliquot. The clay-silt suspensions were centrifuged for 5 m at 1500 RPM. Gravimetric determinations of clay in suspension was performed. Samples were diluted by factors of 2, 3, 5 and 10, applied on a carboncoated stub, and magnified within ranges of A50X to 10,000X. Results and Discussion Incubation Study An incubation study was developed to determine effects of time, soil, and clover amendment relating to P fixation capacity of the soil. As shown in Table A1, a triple order interaction was obtained. Phosphate fixation capacity was affected by times of 30, 60, or 90 d of incubation, clover application at rates of 0, 1.58 and 3.15 g/kg and the type of soil matrix.

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57 Table A-1. Effect of Experimental Parameters on P Retention Capacity Source df Mean Square p>F Time 2 27 9999 U UUU 1 REP 1 Error a 2 1 245 Soil 2 c c r\ o 7 5 5 03 0/ u • u U U X CI over 2 3058 0.44 Soil X Time 4 11426 0.03 Clover X Time 4 13726 0.02 Soil X Clover 4 11474 0.03 Soil X Clover X Time 8 13491 0.01 Error b 24 3611

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58 Since a triple order interaction was obtained, response surface equations were developed for each soil over clover application rates at each time of comparison. Equations are given in Table 4-2. Graphs of results at each time interval are given in Fig. 4-1 through 4-3. Orangeburg Topsoil Orangeburg topsoil is a sandy soil (85% sand, with iron concretions (0.31%)). Increasing rates of application of clover increased P fixation capacity after 30 d. After decomposition of clover, organic functional groups were available for reaction with soil components. Calcium can be bound ionically to organic functional groups (Bloom and McBride, 1979) thereby attaching orthophosphate to organic components and reducing P concentration in solution. With clover addition there was an increase in soil pH from 6.4 to 6.7. Differences in pH could also be induced by precipitation of DCP. After 60 d of incubation, there was a slight increase in soil pH from 6.4 to 6.7 without clover treatment. Increased P fixation was also noted possibly due to the formation of a calcium phosphate precipitate. CI overamended treatments decreased P fixation capacity, although it remained higher than the 0 clover application rate. Singh and Jones (1976) reported decreases in P fixation capacity of organic

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59 Table 4-2. Response Surface Equations Relating P Fixation Capacity of Soils With Clover Addition Over Time. Correlation Time (d) Response Surface Equation Coefficient Orangeburg 30 P fix = 196 81 clover + 2 6 9 clover r^ = 0 .71 60 P fix = 202 6 c 1 ov e r + 2 8 clover 2 r = 0 .49 90 P fix = 274 + 252 clover 76 clover^ 2 r = 0 .67 Orangeburg + 5.6 g Fe 30 P fix 986 467 clover 2 + 111 clover 2 r 0 .83 60 P fix 240 + 107 clover 2 36 clover 2 r 0 .78 90 P fix 517 + 72 clover 2 21 clover r2 0 .29 Orangeburg Subs oil 30 P fix 936 177 clover 2 + 41 clover 2 r 0 .30 60 P fix 684 130 clover 2 + 26 clover 2 r 0 .99 90 P fix 810 116 clover 2 + 33 clover 2 r 0 .83

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60 0 1.58 3.15 Clover Applied g/kg Fig. A-1 Phosphate Fixation Capacity Amended With Various Clover 30 Days of Incubation. of Soils Rates After

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61 0 1.58 3.15 Clover Applied g/kg Fig. A-2 Phosphate Fixation Capacity Amended With Various Clover Days of Incubation. of Soils Rates After 60

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62 0 1.58 3.15 Clover Applied g/kg Fig. 4-3 Phosphate Fixation Capacity of soils Amended With Various Clover Rates After 90 Days of Incubation.

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63 treated soils after 30 d incubation due to P mineralization from organic substrates. Mineralization of P from microbial populations may have produced this r esul t After 90 d of incubation, there was a slight decrease of soil pH from 6.6 to 6.3 without clover treatment. Increased P fixation was observed compared to 30 and 60 d incubation periods. The 3.15 g/kg clover treatment remained stable with respect to P fixation data from 60 d incubation time. However the 1.58 g/kg clover treatment increased soil P fixation capacity Orangeburg Topsoil + Fe(OH)^ After 30 d of incubation, treatments receiving clover applications possessed lower P fixation capacities than did treatments without clover application. Treatments receiving 1.58 g/kg clover had a lower P fixation capacity than 3.15 g clover/kg. Possibly decompositional products of clover were bound to the iron hydroxide surface as was the case in the clover amendment experiments of blocking positive charged sites available for P fixation. Soil pH ranged from 6.5 to 7.2 so that acid forming ions of Al, Fe, and Mn were not available for precipitation or ionically binding orthophosphate to organic components. Precipitation of calcium phosphates at pH 7.2 from the 3.15 g clover/kg

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64 soil treatment may have occurred thereby increasing P fixation capacity for that treatment. After 60 d of incubation, total P fixation of all treatments was reduced, possibly due to P mineralization from microbes and clover residues. Decreasing P fixation with increasing clover application was observed. Soil pH also increased possibly due to a self3 + 2 + liming effect of Fe to Fe with hydroxyl release from water applications reducing net positive charge and P-fixation capacity. After 90 d of incubation, P fixation capacity was increased to near initial levels. Clover-amended treatments, although lower in P-fixation capacity than unamended treatments, did not produce substantial Pfixation reduction as was noted initially. Orangeburg Subsoil Orangeburg subsoil contains 34% material in the clay-size fraction with kaolinite as the dominant clay mineral. The clay surface is coated with goethite which is 1.3% of the total weight of the soil. Orangeburg subsoil results are similar to those obtained from Orangeburg + FeCOH)^ but clover application has less effect in reducing P fixation. Clover application at 30 d reduced P-fixation slightly compared to untreated soil. Greater total surface area of goethite with Orangeburg subsoil compared to Fe(OH)„

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65 applied to Orangeburg topsoil reduced cl ov eramendment effect ivenesE. At 60 d of incubation, similar trends of reduction in P fixation capacity with increased soil pH were observed. Clover amendments lowered P fixation capacity compared to treatments without clover. At 90 d, the effectiveness of the clover amendment was negligible. G lasshouse Study A glasshouse study was conducted to determine clover amendment effectiveness in reducing P fixation in relation to crop production. Three crops of maize were grown for 50 d each. Results from experimental parameters from each cropping period will be discussed. Crop 1 Yield Dry matter yield was affected by P rate, FeCOH)^ addition, and clover application as determined by a triple-order interaction. As seen in Table 4-3 and Fig. A-4, without application of P, no difference in yield was obtained with clover applications on the FeCOH)^ treated soil. Ferric hydroxide provided a sink for indigenous soil P to be bound as well as P available from mineralization of clover. Without FeCOH)^ addition, yield was increased from clover applications with P additions. This effect could have been from clover functional groups binding

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66 Table A-3 Yield Response Surface Equations Obtained From the First Cropping Period. Clover applied Correlation g/kg Response Surface Equation Coefficient P = 0 mg/kg 0 Y = 0.97 0.07 Fe r^ = 0.61 1.58 Y = 0.73 0.04 Fe r^ = 0.18 3.15 Y = 3.17 0.A8 Fe r^ = 0.68 P = 50 mg/kg 0 Y = 2.07 0.22 Fe r^ = 0.73 1.58 Y = 2.13 0.20 Fe r^ = 0.52 3.15 Y = 5. A3 0.61 Fe r^ = 0.63 P = 100 mg/kg 0 Y = 6.57 0.88 Fe = 0.95 1.58 Y = 3.37 0.17 Fe r^ = .18 3.15 Y = 5.37 0.20 Fe = 0.25

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67 Fig. A-A Plant Dry Weight Yield Affected and Clover Application at the 0 Rate During the First Cropping by FeCOH)^ mg/kg P Period.

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68 to Al or Fe ions from solution reducing precipitation of indigenous soil P. Although no differences in soil pH were observed, the pH of both soils had dropped to 5.2 which would increase Al and Fe activity in solution. Also, this effect may have been produced by P released from clover mineralization. Initially, P fertilizer was added (7.0 mg P/kg) to the clover control and 3.5 mg P/kg to the 1.58 g clover/kg treatment since the literature suggests that approximately 50% of organic P is released as orthophosphate (Lockett, 1938). Application of 3.58 g clover/kg was equivalent to adding 14 mg/P kg soil. Possibly release of P from clover later in the cropping period resulted in enhanced yield rather than immediate solubilization of fertilizer P. Application of 50 mg P/kg increased plant yield compared to that without P. FeCOH)^ again decreased plant yield. However, increasing application rates of clover increased plant yield on FeCOH)^ treated soil (Table 4-3 and Fig. 4-5). It appeared that P was more available on Fe(0H)2 treated soils due to blockage of P adsorption sites by organic ligands from clover application. Increase in yield of treatments without Fe(0H)2 addition may have been produced by binding Al and Fe by organic ligands. Doubling of dry matter yield from clover addition of 3.18 g

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69 Fe Applied g/kg Fig. A-5 Plant Dry Weight Yield Affected by Fe(OH) and Clover Applications at the 50 mg/kg P Rate During the First Cropping Period.

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70 clover/kg soil could not have been produced solely by P release at the rate of 7.0 mg P/kg) Applications of 100 mg P/kg increased dry weight yield compared to the 50 mg P/kg rate (Table A-3 and Fig. A-6). Ferric hydroxide treatments decreased maize yield but an incremental increase in yield was observed with increasing clover applications. Yield was more than tripled when clover was applied at 3.15 g clover/kg soil. Phosphorus availability appeared to be greater due to clover pretreatment Results agree with the previous incubation study relating to P availability with FeCOH)^ treatment in acidic (pH 5.2) ranges. Greater yield was obtained without clover application if FeCOH)^ was not introduced into the soil system. Cation bridging of P to organic functional groups may have produced this result. P uptake Phosphorus uptake by maize plants was affected by amount of P or FeCOH)^ applied. Increasing P rates increased P in plants while addition of FeCOH)^ reduced P uptake. With increasing rates of clover applied (Table A-4 and Fig. 4-7, 4-8 and 4-9), enhanced P uptake was obtained. Mechanisms relating to clover amendment effectiveness were not determined. Yield data appears to relate well to P uptake observations. Binding of Fe or Al by organic functional groups or

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c 4J o c •rl 0) CM 4J a o •H 60 II II II c u •H CM o. o o u u U O o (0 u g o IC 0) 0) 0) c •rl K (d o cu o CO o o o o 1 o CO C (U 1 o (a 1 •H c 0> 4J o in Q) fn 01 •rl o [14 4J • SO W (d o cs 3 o M 1 o 1 CO CM o (0 o lO <• o to (4 o Q) CO f CO c 0) o o CO o p< o CO n o 0) OS CO II II II ft) o 60 O rH cn a) H o

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Fig. A-6 Plant Dry Weight Yield Affected by Fe(OH) and Clover Applications at the 100 mg/kg Rate During the First Cropping Period.

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73 Fe Applied g/pot Fig. 4-7 Phosphorus Uptake by Maize as Affected by Fe(OH)and P Application at the 0 g/kg Clover Rate During the First Cropping Period.

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74 Fe Applied g/pot Fig. A-8 Phosphorus Uptake by Maize as Affected by Fe(OH), and P Application at the 1.58 g/kg Clover Rate During the First Cropping Period.

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75 Fe Applied g/kg Fig. A-9 Phosphorus Uptake by Maize as Affected by FeCOH)^ and P application at the 3.15 g/kg Clover Rate During the First Cropping Period.

PAGE 85

76 bonding of organic ligands to FeCOH)^ surfaces would explain the results obtained. Truog Extractable P A reaction product of DAP is dicalcium phosphate (Lindsay, 1959). Truog reagent is a good extractant for this phase (Ballard, 1974). Preliminary extraction with Truog reagent produced an Fe-clover interaction. Addition of Fe(0H)2 reduced Truog extractable P levels drastically (Fig. 4-10, 4-11 and 4-12) Without clover application, P addition of 100 mg/kg slightly increased Truog P levels which would apply to the dicalcium phosphate fraction. Inconclusive results were obtained with Fe(0H)2 treated soils regardless of rate of P application. Without Fe(0H)2 application, increases in Truog extractable P resulted from clover application at increasing P rates (Table 4-5). Previous mechanisms, discussed above appeared to have produced these effects. Bray 2 Extractable P Orthophosphate adsorption to iron mineral surfaces reduces plant available P. Bray 2 extraction is a good method for determining slightly soluble or desorbable P reaction products. Bray 2 extractable P was affected by main effects of P rate, Fe(OH), amendment, and

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C 4J| o CI •P -rll u| rH -HI 0) M-l >^ IM M 01 O O o e o at cr 0) u o s w O 0) m o • o I u > o o n • o + CO o I in o • CO II eo o :3 M H m o II S o m a; •H iH ft ft < o a> in o • o I u o o + 0) o o in II eo zi o h 00 o II A! a o o 0) ft <: u 0) > o 01 o I u > o o 0) Ut ON o 1 o • II cu eo 3 o u H

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0 1.58 3.15 <^ Clover Applied g/kg ig. 4-10 Truog Extractable P Levels as Affected by Clover and FeCOH)^ Applications at the 0 mg/kg P Rate During the First Cropping Period.

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79 Clover Applied g/kg Fig. A-11 Truog Extractable P Levels as Affected by Clover and Fe(OH), Applications at the 50 mg/kg P Rate During the First Cropping Period.

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0 1.58 3.15 Clover Applied g/kg Fig. 4-12 Truog Extractable P Levels as Affected by Clover and Fe(OH)^ Applications at the 100 mg/kg P Rate During the First Cropping Period.

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81 clover application, as shown in Table A-6. With increasing P rates, significant increases were observed in Bray 2 extractable P levels probably from adsorption to the iron mineral surface. Binuclear adsorption would reduce extractable P results due to the stability of the adsorption bond and the irreversible nature of the adsorption. Clover amendments increased extractable P availability. Possible mechanisms of organic ligand adsorption, Al and Fe compl exati on, P release for clover and/or acid humification processes solubilizing calcium phosphates, could increase extractable P concentrations. Organic Carbon No significance with respect to organic carbon levels was found with clover pr etreatment Further monitoring of this experimental parameter was terminated. Crop 2 A second maize crop, grown for 50 d, was initiated to determine residual treatment effectiveness in relation to experimental parameters. Yield Plant dry weight yield was influenced by previous FeCOH)^ and clover applications (Table A-7). Main plot effects did not show increase in yield from previous

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82 Table A-6 Main Effects of P. Fe(OH)„ and Clover Affecting Bray 2 Extractaole P Levels From t he First Cropping Period. P Aapplied (mg/k g) Bray 2 Extractable P Contrast p>F 0 9 .86 50 20.01 100 27.84 Fe Applied (g/kg) 0 vs others 0.01 50 vs 100 0.01 0 5.6 26.06 12. Al 0 vs 5.6 0.05 C lover Applied (g/kg) 0 1.58 3 .15 14.56 18.13 25 .02 0 vs others 0.01 1.58 vs 3.15 0.01

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83 DAP application due to fixation mechanisms. Ferrichydroxide decreased dry weight yield fourfold. Clover addition increased yield with each increasing rate of application. Since P was a limiting factor, clover applications apparently increased P reaction product availability. Release of P from clover should have subsided long before termination of the second cropping period. Yield was not likely to be reduced from Al or Fe toxicity at pH values of the soil. Although differences in Al and Fe levels within plant tissue existed (Table 4-8) with respect to FeCOH)^ treatment, Al and Fe levels were not at toxic concentrations. P Uptake Phosphorus uptake by maize was affected by FeCOH)^ addition (Table A-9). The Fe(0H)2 provided a sink for P adsorption. Also as seen in Table 4-10, soil pH had 3+ 3 + dropped to 5.0 such that Al and Fe could be in solution reducing P availability from precipitation reactions. Aluminum and Fe ions were present in soil solution as determined by plant uptake of these ions. Addition of Fe(0H)2 resulted in a fourfold decrease in P uptake. Truog Extractable P Truog extractable P was affected by an interaction of Fe(OH)and clover. Increasing levels of clover

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84 Table A-7 Main Effects of FeCOH)^ and Clover Treatments on Plant Yield During the Second Cropping Period. Fe applied (g/kg) Yield (g/pot) Contrast p>F 0 5.6 2.17 0.53 0 vs 5.6 0.01 Clover applied (g/kg) 0 1.58 3.15 0.85 1.35 1.85 0 vs. others 0.01 1.58 vs 3.15 0.01

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85 Table 4-8 Main Effect of Fe(OH)Addition on Al and Fe Concentrations in Plant Tissue After the Second Cropping Period. Al Fe Contrast p>F mg/kg Plus Minus FeCOH)^ 131 133 Plus vs Minus Fe(0H)3 83 83 0.01 Table 4-9 Main Effect of FeCOH)^ Treatment on Plant P Uptake During the Second Cropping Period. Fe (g/kg) P uptake mean Contrast mg P/Pot p>F 0 2.15 0 vs 5.6 5.6 0.57 0.01 Table 4-10 Main Effect of FeCOH)^ Treatment pH After Two Cropping Periods. on Soil Fe (g/kg) pH mean Contrast p>F 0 5.6 5.12 4.95 0 vs 5.6 0.01

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86 increased Truog P, as FeCOH)^ produced a reduction in P at each P application rate (Table 4-11). As the pH of the soil decreased, solubilization of indigenous soil P, or P from fertilizer reaction products increased producing measurable levels of Truog extractable P which is a P form readily available to plants. Without FeCOH)^ addition, increasing levels of Truog P were obtained with increasing clover rates, without added P. This same observation (Fig. 4-13) was also noted during the first cropping period. Reduction in Truog extractable P on Fe(0H)2 treated soil without P addition with increasing clover rates may be explained by P utilized for plant growth. Increased maize yields were obtained with increasing clover application rates, which would lower Truog P levels. Similar observations were obtained at the 50 mg P/kg rate (Fig. 4-14) and the 100 mg P/kg rate (Fig. 4-15) with the exception that Truog extractable P levels also increased with increasing rate of P application. Bray 2 Extractable P Bray 2 extractable P levels were affected by interaction of P and Fe(0H)2. Extractable P was increased with increasing P rates but decreased with Fe(OH)„ additions. Extractable P levels were increased

PAGE 96

c o •H U (0 •HI 1 r-l •rlj c 1 0) >4-l o 1 V4 M-l u 1 U 9) 0) 1 O O CO 1 U U 0) .a (U 4-> < U 0) > 0) ij 1 ^ CD 4-1 U 1 C| o| 4-1 •H| +J| 0)1 9| 00 ctI O Ul 3 1 M o 3 ta CO C O 0) •H 01 4-) a 0) o cx ca u a> Pi 4) O 0) O •H M U 3 0) CO 0) xo c G •H o (X p< n o 0) Pi y-l 1 0) VO VO Ov All ^1 ai rH o o o vO o u > O 00 CM 9) 1X4 o 00 CS II 00 o u Eh CM oq Ail ^1 m I o| ml 0)1 CM o ta 00 o u > o 0) ta vO O 00 o 3 H Ai 0(1 a o o (U •H i-l O. u o 0) ta ov o > o vO o + Q) ta cs o I IT) 11 ta 00 o 3 u

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88 with increasing clover rates (Table 4-12 and Fig. 4-16, 4-17, and 4-18). Increases of Bray 2 extractable P from FeCOH)^ untreated soil compared to that for Crop 1 may have been produced by precipitation of Fe or Al phosphates with decreasing soil pH. Reversion of a calcium phosphate to a Fe or Al phosphate possessing greater stability would increase Bray 2 levels. Change in Bray 2 extractable P may be due to blockage of P fixation sites by organic ligands reducing the irreversible binuclear P adsorption. Crop 3 A third crop was grown for 50 d to determine clover effectiveness over time in increasing dry weight yield, P uptake, and Truog and Bray 2 extractable P. Each treatment was again limed to pH 6.3 utilizing the liming curve described in Chapter 3. Constant fertilizer amounts were applied. Rates of 0, 50, and 100 mg P/kg as DAP were applied to appropriate treatments. Yield Dry matter yield was influenced by interaction of P with FeCOH)^ applications. (Table 4-13). Increasing rates of P increased dry weight yield (Fig. 4-19, 4-20 and 4-21). Observations of increases in yield on Fe(0H)2 treated soil with increasing clover applications suggested that organic functional groups were bonded to Fe mineral surfaces, thereby reducing P

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89 Table 4-12 Response Surface Equations of Bray 2 Extractable P Levels After the Second Cr opping Period. Correlation Response Surface Equation Coefficient Clover Applied (0 g/kg) Bray P = 9.28 + .28 P .85 Fe .04 P Fe r^ = .96 Clover Applied (1.58 g/kg) Bray P = 16.99 + .24 P 2.13 Fe .02 P Fe r^ = .97 Clover Applied (3.15 g/kg) Bray P = 23.19 + .22 P 2.62 Fe .02 P Fe r^ = .96

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90 Fig. A-13 Truog Extractable P Levels as Affected by Clover and FeCOH)^ Applications at the 0 mg/kg P Rate During the Second Cropping

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91 Clover Applied g/kg Fig. A-IA Truog Extractable P Levels as Affected by Clover and FeCOH)^ Applications at the 50 mg/kg P Rate During the Second Cropping Pe r i od

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92 Clover Applied g/kg Fig. 4-15 Troug Extractable P Levels as Affected by Clover and Fe(OH)_ Applications at the 100 mg/kg P Rate During the Second Cropping Period.

PAGE 102

P Applied mg/kg ig. A-16 Bray 2 Extractable P Levels as Affected by P and Fe(OH)„ Applications at the 0 g/kg Clover Rate During the Second Cropping Pe riod

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94 P Applied mg/ha Fig. 4-17 Bray 2 Extractable P Levels as Affected by P and Fe(OH)_ Applications at the 1.58 g/kg Clover Rate During the Second Cropping Period.

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P Applied mg/kg g. A-18 Bray 2 Extractable P Levels as Affected by P and Fe(OH), Applications at the 3.15 g/kg Clover Rate During the Second Cropping Period.

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96 Table 4-13 Response Surface Equations of P and FeCOH)^ Across Clover Application Rates in Relation to Dry Weight Yield After the Third Cropping. Corel ation Response Surface Equation Coefficient Yield Yield Yield Clover Applied (0 g/kg) 2 ,33 + .09 P + .12 Fe .01 P*Fe r = .76 Clover Applied (1.58 g/kg) .88 + .06 P + .04 Fe .01 P*Fe r^ = .52 Clover Applied (3.15 g/kg ) 2.28 + .05 P .23 Fe .002 P*Fe r^ = .53

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P Applied mg/kg 4-19 Plant Dry Weight Yield as Affected by and Fe(OH)^ Applications at the 0 g/kg Clover Rate During the Third Cropping Period.

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P Applied mg/kg g. A-20 Plant Dry Weight Yield as Affected by P and Fe(OH), Applications at the 1.58 g/kg Clover Rate During the Third Cropping Period.

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99 P Applied rag/kg Fig. A-21 Plant Dry Weight Yield as Affected by P and Fe(OH) Applications at the 3.15 g/kg Clover Rate During the Third Cropping Period.

PAGE 109

100 adsorption sites. At the 100 mg P/kg rate, addition of 3.15 g clover/kg increased yield 600% compared to treatments without clover addition. This effect was produced after an initial clover application and two previous cropping periods on the same soil. Stability exists in the effect produced by clover application on FeCOH)^ treated soil, whatever the mechanism. Without FeCOH)^ application, mixed results were obtained with P and clover application. At 50 mg P/kg, yield was increased with increasing clover addition but at 100 mg P/kg, yield was decreased with increasing clover rate of application. P Uptake A second application of fertilizer P masked the clover effect with respect to P uptake. As seen in Table A-IA, P uptake was affected by main effects of P and FeCOH)^ application. Increased rates of P application increased P uptake whereas addition of FeCOH)^ decreased P uptake. Soil pH Since the soil was limed before the third cropping period, reversion of soil pH to its natural state had not fully occurred. Differences in soil pH had developed with respect to FeCOH)^ addition (Table A-15), but pH had not decreased to a state that would promote further extensive P fixation from Al or Fe

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101 Table 4-14 Main Effects of P and FeCOH)^ Relating to Plant P Upt a ke From the Thirfl Cropping. P uptake mg/pot Contrast £_>. ^ P Applied (mg/kg) 0 1.27 50 3.42 100 8.01 Fe Applied (g/kg) 0 6.14 5.6 2.33 0 VE others 0.01 50 vs 100 0.01 0 vs 5 6 0.01

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102 release into the soil solution or as sites for P retention. Truog Extractable P Truog extractable P levels were affected by an interaction of FeCOH)^ with clover (Table A-16). Without FeCOH)^ addition, Truog extractable P levels increased with increasing P rates and clover additions. (Fig. A-22, 4-23 and A-24) With Fe(0H)2 addition. Truog P levels were increased with clover application compared to without clover application. The Fe(0H)2 addition reduced Truog P levels at each P and clover rate. Variability in Truog P levels on Fe(0H)2 treated soils may result from differences in P taken up by plants causing reduction extractable P levels. Bray 2 Extractable P Bray 2 extractable P levels were affected by P rates, Fe(0H)2 addition, and clover application rates as a triple-order interaction (Table A-17). Increases in extractable P were linear with increasing clover applications (Fig. A-25, A-26, and A-27) and also with increasing P rates. The Fe(0H)2 applications reduced extractable P levels significantly. Although increases in extractable P were obtained with clover application on Fe(OH)^ treated soil, increases were not as great

PAGE 112

103 1 1 (4 CO 0 0) a 0) •H •H •H 4-1 • 4-* a OS Cd 1— 1 •rl o •H Q) M-l u C M m u o O 01 (U yN • •rl pL4 0 0 Oi o 4-) 0 u 0) 60 U C •H 'rl T-4 a p. a O .a -l 4-> 60 *0 C Dl U •H CD U CQ ,13 O H Q 4J vD t-l CO • O 0) to as u-i < lO 0) U 4-* U) 4-1 ta c c > 0) U Q) o > 0) o O 4-1 r-l M-l O 4J O COO) Q) W 3 CT O O &4 M 4-) 0) 01 OJ 60 (J C CO •H >4-l cd •M O 4J CO o 00 3 PB c/a V • • a u Pi O 4-> 0) •rl M (0 on — \ a) 0 P3 3 60 ft O o CO V |xl 3 0) 0) U 0) H U m (0 o o MH 4-1 i-l 4-> 3 C u w O 0) •H 14-1 0) 4-> M-l • CO 0) Cd "O C rH o O 0) C -H CO •H u la a) 0) 0) c 60 ^y tr, •c r-> Q) 1 •H vO 1 -aiH (X O lO 01 a. rH O o CO o u 01 o o CM 0) CS 00 •* II CM 60 O 3 H 601 •ii| ^1 act a o •0 0) •H rH ft ft o 00 m II 00 o 9 U H CM u 01 o 0) 60 60 a o o •0 0) •H rH ft ft < u o rH U 1^ 0) 00 10 60 o 3 u Eh

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104 0 1.58 3.15 Clover Applied g/kg Fig. A-22 Truog Extractable P Levels as Affected by Clover and FeCOH)^ Applications at the 0 mg/kg P Rate During the Third Cropping Period.

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Clover Applied g/kg ig. A-23 Truog Extractable P Levels as Affected by Clover and FeCOH)^ Applications at the 50 mg/kg P Rate During the Third Cropping Period.

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0 1.58 3.15 ^'^'^ Clover Applied g/kg g. A-24 Truog Extractable P Levels as Affected by Clover and Fe(OH) Applications at the 100 mg/kg P Rate During the Third Cropping Period.

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107 Table A-17 Regression Equations of FeCOH)^ and Clover Application in relation to of Bray 2 Extractable P Levels After the Third Cropping. Clover added Correlation ( g /kg ) Re gression E qu ations Coef f icient P Applied ( 0 mg/kg) 0 Bray P = 8.92 .84 Fe 1.58 Bray P = 13.42 .90 Fe 3.15 Bray P = 20.52 2.21 Fe P Ap p lied (50 mg /kg) 0 Bray P = 32.92 3.76 Fe 1.58 Bray P = 39.60 4.73 Fe 3.15 Bray P = 42.53 3.73 Fe P Applied (100 mg/kg) 0 Bray P = 59.8 6.07 Fe 1.58 Bray P = 66.91 6.29 Fe 3.15 Bray P = 69.87 5.89 Fe r2 = .95 2 r = : .41 r2 = = .95 2 r = = .97 2 r = : .98 2 r = : .96 2 r = = .96 2 r = = .99 2 r = : .98

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108 Clover Applied g/kg Fig. A-25 Bray 2 Extractable P Levels as Affected by Clover and FeCOH)^ Applications at the 0 mg/kg P Rate During the Third Cropping Period.

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109 Fig. A-26 Bray 2 Extractable P Levels as Affected by Clover and Fe(OH), Applications at the 50 mg/kg P Rate During the Third Cropping Period.

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110 Fig. A-27 Bray 2 Extractable P Levels as Affected by Clover and Fe(OH) Applications at the 100 mg/kg P Rate During the Third Cropping Period.

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Ill with clover application as measured during other cropping periods with previous P application before cropping. Surface Char g e Study Since differences in yield, P uptake, Truog extractable P and Bray 2 extractable P existed on FeCOH)^ treated soils with respect to P and clover addition, potentiometric titrations relating to variations in net electric surface charge and ZPC were determined. Addition of FeCOH)^ to kaolinite, the main clay component of Orangeburg soil, creates greater positive surface charge with reduced cation exchange capacity (Dixon, 1977). Experimental objectives included qualification and quantification of surface charge properties of Orangeburg soil samples treated with FeCOH)^ with applications of P. clover, and P and clover, from the glasshouse study. Orangeburg + Fe(OH) g Zero points of titration occur at pH values of 5.2 to 5.4 (Fig. A-28) to Fe(0H)2 treated Orangeburg topsoil. Since this treatment had been used in the glasshouse experiment, reversion of soil pH from 6.3 to 5. A had occurred. A ZPC value was obtained at pH 4.0. Kaolinite, the major clay mineral in the Orangeburg soil, possesses ZPC values near this pH. Surface charge of 1.0 cmol(+)/kg soil is probably produced by

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112 NaCl NaCl NaCl Fig. A-28 Surface Properties of Orangeburg Topsoil + FeCOH)^ as Determined by Po t en t i ome t r ic Titration

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113 FeCOH)^ addition which increases net positive charge. However, the integrity of the kaolinite surface should not have been totally lost after addition of 5.6 g Fe/kg as FeCOH)^. Orangeburg + Fe(OH)^ + p Orthophosphate binds covalently to FeCOH)^ mineral surfaces releasing OH^" and OH ligands and produces a surface with greater net negative charge (Hingston et al., 197A) This reaction lowers the pH of the ZPC ( Schwertmann and Taylor, 1977). From the results shown in Fig. A-29, a decrease in ZPC pH from A.O to 3.5 had occurred suggesting covalent bonding of P to the iron mineral surface. Increase in positive charge (2 cmol(+)/kg soil) indicates that H^ adsorption possibly occurs on a more negatively charged surface produced by orthophosphate specific adsorption with lowering of kaolinite ZPC. Orangeburg + Fe(OH)^ + Clover Humic and fulvic acids from clover are decompositional products that possess mainly carboxyl functional groups (Kononava, 1961). Disassociation constants for humic acid are near pH 5.0 (Greenland, 1971) which is close to the acetic acid (H^C20) disassociation constant (4.75) (Weast, 1973). Titration of Orangeburg soil + Fe(0H)2 clover addition produced a ZPC at pH A. 70 with 0.01 and 0.1 M NaCl additions. Binding of soluble Al and Fe by carboxyl groups may have occurred.

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Fig. A-29 Surface Properties of Orangeburg Topsoil + FeCOH)^ amended with 100 mg P/kg as Determined by Potentiometr ic Titration.

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115 The 1.0 M NaCl plot did not intersect with other plots possibly due to mass action of Na replacing Al or Fe from the carboxyl group and producing acidity upon hydration, requiring less H"*^ from the titration. The ZPC values from previous plots were not at pH 4.70 indicating surface properties produced from clover application (Fig. 4-30) A second ZPC was produced at pH 3.8. Since organic functional groups bind covalently to iron minerals, partial reduction of kaolinite ZPC at pH 4.0 may have been produced by organic ligands binding to FeCOH)^ on the kaolinite surface. Increased negative charge for adsorption and reducing pH at the ZPC would result. With clover addition, positive charge was increased to 2.5 cmol (+)/kg compared to 1.0 and 2.0 cmol (+)/kg for Orangeburg + FeCOH)^ and plus P addition, respectively. Orangeburg + Fe(OH)g With P and Clover Addition Addition of P and clover produced surface properties similar to clover addition alone. A ZPC value was obtained at pH 4.75 (Fig. 4-31) which is similar to carboxyl disassociation constants. If Al or Fe had been released into solution with increasing additions, acidity from Al or Fe hydration could lower the ZPC of 1 M NaCl to pH 4.50. However, this pH may be an artifact of the titration from precipitation of

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116 Fig. A-30 Surface Properties of Orangeburg Topsoil + FeCOH)^ with 3.15 g/kg Applications as Determined by Potentiometric Titration.

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117 Fig. A-31 Surface Properties of Orangeburg Topsoil + FeCOH)^ With 100 mg/kg P and 3.15 g/kg Clover Applications as Determined by Potentiometric Titration.

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118 insoluble phosphates. A second ZPC of 3.5 with orthophosphate addition was not found. However a ZPC at pH 3.9 suggested presence of adsorption of P or organic components to FeCOH)^ surfaces. Implications are that functional groups of clover bonded with Al and Fe ions in addition to adsorbing on Fe mineral surfaces. If this is the accurate mechanism, P would possess greater plant availability with clover addition. Results by yield, P uptake, and soil test methods such as Truog and Bray 2 extractable P indicate greater P availability with clover application. Surface properties confirm differences were produced by clover applications. SEM Study Orangeburg +Fe(0H)2 + 100 mg P/kg soil with and without clover additions (3.15 g/kg) were placed on C coated Al stubs at varying clay concentrations. Samples containing 1600, 800, 533 and 320 mg clay/L were oo concentrated to notice any difference between treatments. When samples were diluted to 160 mg clay/L in deionized water, differences in aggregation were observed. Greater clay dispersion (Fig. A-32) without clover pretreatment was observed compared to increased aggregation with clover pretreatment (Fig. A-33).

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119 Fig. 4-32 Scanning Electron Micrograph (A50X) of Orangeburg + FeCOH)^ Clay Fraction (160 mg clay/L) From the First Cropping Period.

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120 Fig. A-33 Scanning Electron Micrograph (A50X) of Orangeburg + Fe(OH)Clay Fraction (160mg clay/L Amended With 3.15 g Clover/kg From the First Cropping Period.

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121 Whether this relationship was produced from segregating clay fractions or existed previously in the soil is unknown. Much care was taken to isolate clay fractions with minimal reagent addition. A close up view of an aggregate magnified lO.OOOX, from a clover pretreatment sample is shown in Fig. 4-3A. High molecular weight humic acids contain numerous functional groups (Inoue and Wada, 1968) which can bind to FeCOH)^ surfaces, thereby reducing soil surface area. (Schwertmann and Fisher, 1973). Clay fraction surface area could be reduced if aggregation of clay particles had occurred. Concl usi on s Incubat xon studxes indicated that P fixation is reduced with clover pretreatment on soils containing sesquioxide minerals. Orangeburg topsoil +Fe(0H)2 Orangeburg subsoil, coated with goethite, had lowered P fixation capabilities after receiving clover application. Increased P fixation capacity was observed on Orangeburg topsoil without FeCOH)^ application with increasing clover rates. At 60 d of incubation, P fixation capacity was reduced on all treatments after possible P mineralization of clover, and increase in pH reducing net positive charge on soil mineral surfaces. After 90 d, P fixation capacity had returned to near initial levels as pH decreased. Phosphorus fixation

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122 00101 20KU 0.5U Fig. A-3A Scanning Electron Micrograph (lO.OOOX) of an Aggregate From Orangeburg + Fe(OH)Clay Fraction Amended With 3.15 g Clover7kg From the First Cropping Period.

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123 capacity of the Orangeburg soil without FeCOH)^ addition was probably produced by cation bridging of orthophosphate to organic functional groups. However, P fixation on FeCOH)^ treated soil and goethite in Orangeburg subsoil was reduced by organic anion specific adsorption. Crop production benefited from clover application. During the first two croppings of the glasshouse experiment, clover applications increased greater plant yield, P uptake, and extractable P levels. Without FeCOH)^ addition, cation bridging of P to organic components would have greater plant availability than a precipitation product of an insoluble Fe or Al phosphate as the soil pH decreased over time. With FeCOH)^ applications, complexation of soluble Fe and Al and/or organic ligand adsorption to FeCOH)^ surfaces may have increased yield, P uptake and extractable P levels. After ref ert il iz at ion of the third crop, P uptake for soil amended with clover was not significant according to treatment. However yield and extractable P levels increased with clover applications. Clover effectiveness in reducing P fixation persisted long after the time span for nutrient mineralization. Mechanisms of cation bridging and organic ligand adsorption appear to exist, confirmed data obtained from the surface charge and SEM study. Surface charge studies indicate a negative shift in ZPC values from P and clover applications, indicative of

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124 ligand exchange reactions. Soil treatments with clover addition had ZPC values of 4.7, near pK values for carboxyl groups. The main functional group in humic acids from clover decomposition is carboxyl groups which can complex acid forming ions in the soil solution. Scanning electron microscopy appeared to show greater aggregation of the clay fraction with clover amendment, possibly indicating ligand exchange.

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CHAPTER V FERTILIZER COATING AND PLACEMENT EXPERIMENT Introduction After application of water-soluble P fertilizer, P moves very slowly from the point of placement such that the orthophosphate is generally immobile in acid soils (Tisdale and Nelson, 1975). Distribution of fertilizer P, due to its immobility, is generally less than 1% of the total soil volume (Lindsay, 1959). Immobility of fertilizer P is due to rapid reaction with soil components and metastable precipitation products of diammonium phosphate (DAP) whose dissolution pH is 7.98, are dicalcium phosphate dihydrate (DCPD) and Etruvite (NH^MgPO^ 6H2O) (Lindsay, 1959). Orthophosphate ions from the dissolution of fertilizer or solubilization of reaction products may form stable secondary products such as varisite, strengite, hydroxyapatite, or fluorapatite (Lindsay, 1979) or be specifically adsorbed on hydrous oxide mineral surfaces (Kingston et al., 197A). Organic matter addition to soils which contain Fe and Al oxides has reduced net positive surface charge and orthophosphate adsorption in acidic environments (Moshi et al., 197A). Organic addition may also reduce solution Al (Bloom and McBride, 1979) or Fe activity 125

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126 (Deb and Datta, 1967). Other observations produced evidence that organic functional groups bonded covalently to Fe mineral surfaces or ionically complexed Fe or Al solution species (Greenland, 1971). Clover decompositional products contain high percentages of organic functional groups (Kononava, 1961) capable of reaction with sesquiozide minerals or dissolution products above pH 5 (Greenland, 1971). Studies of freshly humified clover adsorption to allophane (Inoue and Wanda, 1968) exhibited the effectiveness of organic adsorption to mineral surfaces. The objective of the fertilizer coating experiment was to assess the effectiveness of coating granules of DAP with dried and ground clover as measured by dry matter production, P uptake, and extractable P levels. Materials and Methods Soil An Orangeburg series topsoil + 5.6 g Fe as Fe(0H)2 and subsoil corresponding to the Bt horizon as characterized in Tables 3—1 and 3—2 of Chapter 3 were used in the fertilizer coating experiment. Ferric hydroxide was prepared and applied by the same methodology described in Chapter 3. The soil was limed to pH 6.3 utilizing the liming curve developed in preliminary experimentation and incubated for 2 wk.

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127 Fertilizer Addition Pots contained 2 kg of soil on a dry weight basis. The source of phosphate fertilizer applied was DAP with an application rate of 75 mg P/kg soil to all treatments. Variation in method of applications was the experimental treatment. Fertilizer was either completely mixed with the soil or applied by point placement. Point placement methodology consisted of placing one-half of the fertilizer rate (37.5 mg P/kg) at two positions spaced 4 cm from pot boundary along the diameter fo the pot at a space of 6 cm.. Depth of placement was 6 cm. Clover-coated fertilizer granules were prepared by mixing small increments of Elmer's glue with dried and ground clover material until all material was bound together. Dried and ground clover was placed in a spherical paraffin mold with 37.5 mg P/kg as DAP placed in the center of the granule. Fertilizer granules were coated with 0.25, 0.50, 0.75 and 1.0 g of dried and ground clover with granule diameters ranging from 9 to 13 mm. CI over— coated granule placement in the soil was the same methodology as that of the point placement. Uniform fertilizer addition included 150 mg N/kg soil as NH^NOg, 150 mg K/kg soil as KCl, and a secondary and micronutrient solution containing 19.8 mg Mg

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128 as MgSO^'TH^O, 11. A mg Zn as ZnSO^*7H20, 5.09 mg Cu as CUSO^'SH^O and 1.2 mg B as Na2B207 1 OH^O. Fertilizer application was adjusted to a constant rate by treatment assuming 50% mineralization of clover nutrients. Experimental Design Eight fertilizer treatments applied to two soils and replicated three times were set in a randomized complete block (RGB) design. Fertilizer treatments were applied to Orangeburg subsoil and Orangeburg topsoil + 5.6 g Fe/kg as FeCOH)^. Each soil received P fertilizer at a rate of 75 mg P/kg soil as DAP. Treatments were 1) Completely mixed soil without clover, 2) Completely mixed soil with 1.58 g clover/kg, 3) Completely mixed soil with 3.16 g clover/kg. A) 2 granules coated with 0.25 g clover, 5) 2 granules coated with 0.50 g clover, 6) 2 granules coated with 0.75 g of clover, 7) 2 granules coated with 1.00 g clover, and 8) 2 point placements (uncoated DAP with same placement as granules. Statistical analysis of the factorial experiment in RGB design data was performed utilizing the Statistical Analysis System. Mean separation was made using the single degree of freedom orthogonal contrast technique. Methods Two crops of maize were grown for 50 d to assess the initial and residual effectiveness of the

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129 fertilizer treatments. Only top growth above the soil surface was analyzed during the first cropping period. The soil was not disturbed other than replanting the second crop. Soil and plant samples were analyzed after the second cropping period. Plant samples were analyzed by previously described methods. Soils were sampled after the second cropping period. Completely mixed soil samples were obtained as well as samples around the granules or point placement. Fertilizer residue was discarded but soil samples were taken up to 2 cm distance from point or granule placement. Bulk samples from granule or point placement treated soil, after soil near granules had been removed, were compared to completely mixed samples as well as soil 2 cm from granules. Soil samples were analyzed for Truog end Bray 2 extractable P and pH. Results and Discussion Crop 1 Orangeburg subsoil contained 0.8A% Fe as goethite coating clay mineral surfaces. Orangeburg topsoil was sandy containing Fe concretions with a citratedithionite-bicarbonate extraction concentration of 0.31% of the soil. Addition of amorphous FeCOH)^ (5.6 g/kg) to the topsoil increased the Fe content to a

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130 total of 0.87%. Extractable Fe contents of both soils were equivalent, but as different mineral solid phases. Phosphorus uptake by corn was affected by soil type and placement of fertilizer (Table 5-1). Greater P uptake was obtained with Orangeburg subsoil than topsoil + FeCOH)^ for the granule and point placement applications. This observation appears contradictory since from characterization data, the subsoil fixed 800 mg P/kg while the FeCOH)^ treated topsoil fixed only 6A0 mg P/kg. Goethite has less surface per unit weight than FeCOH)^ (Parfitt et al 1975). Within the point placement and clover coated granule microsite, greater adsorptive surface would be available for P fixation on the FeCOH)^ treated soil since the fertilizer reacts with approximately 1% of total soil volume (Lindsay, 1959) resulting in greater P fixation by Fe(0H)2 treated soil. Results are inconclusive for the completely mixed treatments. Unlike previous experimentation, time for decomposition of clover prior to fertilizer addition. Clover and fertilizers were applied on the same day. Lack of response to clover addition may be due to lack of time for decomposition before fertilizer addition. Fertilizer placement as a

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131 Table 5-1. Soil and Treatment Effects on P Uptake From the First Cropping Pe riod. Treatment Clover Orangeburg + Orangeburg Applied Fe(OH)„ Subsoil P Uptake mg P/po t Completely Mixed (CM) g/kg 0 9.63 11.97 1.58 10.77 8.27 3.15 11.87 10.97 Granule (G) g/granule 1) 0.25 27.07 29.60 2) 0.50 29.50 31. A3 3) 0.75 29.80 30.13 A) 1.00 27. AO 29.57 Point Placement (PP) 0 2A.03 33.07 Contrasts p>F Orangeburg + Fe(0H)_ vb Orangeburg Subsoil 0.01 CM vs PP 0.01 0.01 G vs PP 0.01 NS G(3) vs G(1,2.A) NS NS

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132 granule or point placement exhibited greater superiority of P uptake and yield than complete mixing. Complete mixing of fertilizer to soil exposed a greater volume of soil to the fertilizer. Reduction in plant available fertilizer due to reaction with a greater volume of soil components reduced fertilizer effectiveness. Apparently, reduction in P uptake by corn due to complete mixing of the DAP was from reaction of fertilizer P with larger soil volumes. No differences in P uptake effectiveness by individual granule treatments on either soil were observed, however, clover coated granules were superior in increasing P uptake to fertilizer point placement on the Orangeburg + FeCOH)^ treated soil. Theoretically, clover decompositional products should reduce positive charge near the granule microsite before dissolution of DAP, making the orthophosphate fraction more readily available for plant uptake. Also, dissolution pH of DAP (7.98) would depress Fe and Al activity as well as reduce pH-dependent positive charge near microsites. Amorphous ferric hydroxide treated soil or goethite in the Orangeburg subsoil had no effect on the dry weight yield of the first corn crop. Treatment effects due to placement of 75 mg P/kg affected dry matter yield production. As shown in Table 5-2. granules and point placement were superior in dry weight yield production compared to complete mixing of

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133 fertilizer with incremental clover additions. Treatment effects may be explained by enhanced P uptake due to placement of P fertilizer material. Lack of differences in yield on the two soils possibly indicates that the P rate of 75 mg/kg may have been too high. Since P uptake was different due to soils, it should follow that yield would be different by soil as it was by treatment. However, since P was not a limiting factor, optimal plant uptake of P across soils was obtained. Calcium, Mg, and K uptake by corn followed closely to P treatment yield. Increased dry matter yield resulted in increased Ca, Mg, and K uptake but these elements in plant tissue were not interpreted as being deficient. Aluminum and Fe concentrations did not approach toxic levels in the plant during the first cropping period. Crop 2 Soil pH values for both soils dropped from the limed pH values of 6.3 to the indigenous values of A. 7 and 5.2 (Table 5-3) for Orangeburg + FeCOH)^ and Orangeburg subsoil, respectively, over the two cropping periods. Although Al and Fe were never at toxic concentrations within the tissue, the percentage of P within tissue was lower (<0.1%) in Crop 2 than the first crop.

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134 Table 5-2 Effect of Treatment on Maize Dry Matter Y ield From the First Cropping Period. Treatment Clover Applied Yield g/pot Completely Mixed (CM) g/kg 0 12.07 1.58 12.05 3.15 13.05 Granule (G) g/ granul e 1) 0.25 21.97 2) 0.50 22.82 3) 0.75 22.77 4) 1.00 21.50 Point Placement (PP) 0 21.42 Contrasts p >F CM vs PP 0.01 G vs PP NS G (2) vs G(1.3.4) NS

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135 Decrease in pH increased sesquioxide ionic activity and reduced P availability. There was no apparent difference between pH of completely mixed soil and soil near granules or spot placement. Truog extractable P levels of granule treatments were different with respect to soil. Greater concentrations of extractable P were found in the soil around granule placement with Orangeburg subsoil resulting in increased dry mater yield and P uptake than with Orangeburg topsoil + FeCOH)^ (Table 5-4). This observation confirmed the hypothesis that greater adsorptive surfaces would be available for P adsorption on the FeCOH)^ treated soil instead of goethite for granule and point placement. Truog extractable P levels from soil near fertilizer granules were also affected by treatment (Table 55). There was no difference between extractable P levels from granule fertilizers or point placement resulting in lack of response in plant yield and P uptake for the two plant growth periods. The highest Truog extractable P results within granule treatments came from DAP granules coated with 0.50 g clover. However, yield was not increased comparatively to other granules or point placement treatments during either

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136 Table 5-3 Effect of Soil and Fertilizer Placement on Soil pH After the Second Cropping Period. Treatment Contrast p>F Completely Mix ed Orangeburg + Fe(OH) Orangeburg Subsoil A. 67 Topsoil ve Subsoil 0.01 5 .24 Granul e Orangeburg + FeCOH)^ 4.68 Orangeburg Subsoil 5.23 Topsoil vs Subsoil 0.01 Table 5-4. Truog Extractable P Levels on Granule Samples as Affected by Soil After the Second Cropping Period. Treatment T ruog P levels Contrast p >F mg/kg Orangeburg + FeCOH)^ 7.05 Topsoil vs Subsoil 0.05 Orangeburg subsoil 17.22

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137 cropping period. Phosphorus uptake from granule treatments was superior to point placement on Orangeburg + Fe soil during the first cropping. Soil around the granule or point placement possessed greater concentrations of Truog extractable P than soil from the completely mixed treatments. Completely mixing fertilizer with soil increases the volume of soil capable of reducing fertilizer availability. This trend was observed throughout the duration of the experiment. Truog extractable P levels by soil and treatment were indicative of plant yield and P uptake measurements since Truog levels denoted highly available P to plants. Bray P 2 extractable P levels were affected by treatment and followed the same trends as the Truog extractable P results (Table 5-6). Completely mixed treatments were less effective than granule or point placement of fertilizer. There was no difference between granule or point placement methodologies. Granules coated with 0.5 g clover appeared more effective in supplying P than other granules manuf actur ed. Reduced P availability reduced plant yield by onehalf if one compares the first to the second crop.

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138 Table 5-5. Effect of Treatment on Granule Truog Extractable P Levels After the Second Crop ping Period. T reatment Clover Applied Tr uog P Completely Mixed (CM) g/k g mg P/kg 0 6.10 1.58 5.98 3.15 6.10 Granule (G) g/ gr anul e 1) 0.25 10.28 2) 0.50 25.60 3) 0.75 19.63 A) 1.00 18.08 Point Placement (P P) 0 24.85 Contrast p>F CM vs PP 0.01 Gran vs PP NS Gran (2) vs Gran (1,3,4) 0.05

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139 Table 5-6 Effect of Granule Treatments on B ray 2 Extractable P Levels After the Second Cropping Period. Treatment Clover Applied ij L ay ^ L Completely Mixed (CM) g/kg mo P / Ic CT 0 20.58 1.58 22.08 3.15 19.50 Granule (G) g/Gran • 1) 0. 25 38.37 2) 0. 25 63.48 3) 0.75 52.63 4) 1.00 47.65 Point Placement (PP) 0 60.60 Contrast p>F CM vs PP 0.01 Gran vs PP NS Gran (2) vs Gran (1.3,4) 0.05

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lAO Reduced P availability also induced a soil and treatment interaction in which the P in Orangeburg subsoil was more available to plants as determined by plant P uptake (Table 5-7) than P from Orangeburg topsoil + FeCOH)^. Differences in P uptake produced a soil and treatment interaction in which yield was greater on Orangeburg subsoil than Orangeburg + FeCOH)^ treated soil (Table 5-8). Similar trends observed during the first cropping period occurred for the second cropping period. Point placement and granules were superior in producing yield and increasing P uptake to completely mixed placement methodologies. Loss of effectiveness of the 0.5 g clover coated granule in increasing P uptake on Orangeburg topsoil + Fe(0H)2 noted only during the second plant growth period. Conclusion s Point placement of fertilizer and clover coated granules were superior to completely mixing fertilizer and clover to the soil, as measured by corn yield, P uptake, Truog extractable P and Bray P 2 extractable levels of soil P. There was no difference in experimentation variables between point or granule placement of fertilizers except increased P uptake on Orangeburg topsoil + Fe(0H)2 ^^^ring the first cropping period. Lack of differences in yield between granule and point

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141 Table 5-7 Soil and Treatment Effect on P uptake From the Seco nd Cropping Perio d Treatment Clover Orangeburg + Orangeburg Applied FeCOH)^ Subsoil P uptake mg/pot Completely Mixed (CM) g/kg 0 2.17 2.88 1.58 2.69 3.29 3.15 2.40 3 .20 GranulpfG) o/cranule 1 ) 0.25 3 .66 9.44 2) 0.50 4.39 9.38 3 ) 0 7 5 4.16 7.98 4) 1 00 5.12 8.11 Point Placement (PP) 0 4.71 9.01 Contrast B p>F Orangeburg + Fe(OH)„ vs Orangeburg subsoil 0.01 CM vs PP 0.01 0.01 G vs PP NS NS G (2) vs G (1.3.4) NS G (1) vs G(2.3,4) NS

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1A2 Table 5-8. Soil and Treatment Effects on Yield from the Se c on d Cropping Period. Treatment Clover Orangeburg + Orangeburg Applied Fe(OH)Subsoil Yield g/Pot Completely Mixed (CM) g/kg 0 2.67 3.60 1.58 3.07 4.50 3.15 3.27 4.27 Granule (G) g/ gr anul e 1) 0.25 5.06 10.33 2) 0.50 6.67 9.40 3) 0.75 5.07 9.13 4) 1.00 6.50 11.43 Point Placement (PP) 0 7.07 9.93 Contrast s p>F Orangeburg + FeCOH)^ vs Orangeburg Subsoxl 0.01 CM vs PP 0.01 0.01 G vs PP NS NS G(2) vs G(1.3,4) NS G(4) vs G (1,2.3) NS

PAGE 152

143 placements during this period may have been produced by the fertilizer rate of 75 mg P/kg soil as a concentrated point on the Orangeburg soil + FeCOH)^ resulting in sufficient P for plant growth. Of the granules manufactured and applied, the 0.50 g clover coating rate produced the best results only on Orangeburg + FeCOH)^ treated soil, as measured by Truog and Bray P 2 extractable P levels. Possibly coating thickness was related to time of P release during microbial degradation which induced increased response to applied P. No difference between granule and point placement was observed on Orangeburg subsoil. Differences between soils included pH, Truog extractable P levels, P uptake, and yield from the second cropping period. The pH of 4.7 of the Orangeburg topsoil + FeCOH)^ which would increase Al and Fe solution activity and increase net positive charge on Fe mineral surface reducing P availability. Reduction in P uptake and yield from the second cropping period are indicative of these types of changes. Changes over time were not as dramatic on Orangeburg subsoil. After liming and fertilizer P application, no differences in yield with respect to soils was observed during the first cropping period. However, as the two soils reverted to their natural status, a difference in yield with respect to soils was observed from a soil by treatment interactions during the second cropping

PAGE 153

144 period. Truog P measured after the second cropping period was substantially lower in Orangeburg topsoil + FeCOH)^ than in the subsoil. Phosphorus deficiency in maize plants was also observed on the Orangeburg topsoil during the second cropping period. Applications of P fertilizers to high-P fixing soils should be by band or point placement of fertilizer. If the sequioxide mineral in the soil possesses a high surface area, consideration to coating the P source material with an organic material may be favorable for increasing P uptake by a crop.

PAGE 154

CHAPTER VI SUMMARY AND CONCLUSIONS Incubation study results indicate that P fixation is reduced with clover pretreatment on soils containing sesquioxide minerals. Orangeburg topsoil + FeCOH)^ and Orangeburg subsoil coated with goethite, had reduced P fixation capacities with increasing clover application rates. Increased amounts of P were fixed in Orangeburg topsoil without FeCOH)^ applications with increasing clover rates. At 60 d of incubation, P fixation capacity was reduced for all treatments. Possibly P mineralization from clover and pH increase reduced net positive charge on soil mineral surfaces. After 90 d, P fixation capacity had returned to near initial levels as soil pH decreased. Phosphorus fixation capacity by the Orangeburg soil without FeCOH)^ addition probably was produced by cation bridging of orthophosphate by organic functional groups. However, P fixation on FeCOH)^ treated soil and soil with goethite was reduced by organic adsorption mechanisms. Throughout the duration of the first glasshouse experiment, pretreatment with clover induced greater plant yield, increased P uptake except during the third cropping period, and extractable P levels. Dry weight yields averaged 350% higher with clover application than without clover 145

PAGE 155

146 addition on FeCOH)^ treated soil. Soil FeCOH)^ remained in an amorphous state throughout the 180 d of cropping. Without FeCOH)^ addition, cation bridging of P to organic functional groups would have resulted in greater plant P availability than a precipitation product of an insoluble Fe or Al phosphate. With FeCOH)^ application, complexation of solution Fe and Al and/or organic ligand coordination to FeCOH)^ surfaces mayhave effectively increased plant yield, P uptake, and extractable P levels. After P r ef ert il iz a t ion of the third crop, P uptake across clover levels was not significant according to treatment, but yield and extractable P levels increased with clover rate of application. Clover effectiveness in reducing P fixation remained long after clover nutrients were mineralized. Mechanisms of ionic compl exations by organic functional groups and organic ligand adsorption appear to exist from data obtained from the surface charge. Surface charge studies indicate a negative shift in ZPC values with P and clover application, indicative of ligand exchange reactions. Carboxyl groups can complex acid forming ions from soil solutions. Scanning electron microscopy appears to reveal a greater aggregation of the clay fractions with clover amendment. A second glasshouse experiment was conducted to determine effectiveness of coating DAP with clover. If complete mixing of clover with the soil induced a

PAGE 156

147 positive response in lowering P fixation, clover amendments should reduce P fixation around P fertilizer microsites. Point placement of fertilizer and clovercoated granules were superior to completely mixing fertilizer and clover ino the soil, as measured by dry matter yield, P uptake, and extractable P levels. Clover granules were somewhat superior to point placement in increasing P uptake on Orangeburg + FeCOH)^ during initial cropping. Of the granules manufactured, the 0.5 g-clover coating produced the best results of extractable P levels on Orangeburg + FeCOH)^ treated soil When management is considering practices for crop production on highly-weathered acidic soils possessing Fe mineral coatings, management practices using an organic material such as a legume residue to be incorporated into the soil should be considered because increases in crop production with minimal input and less fertilizer costs may be obtained. In the near future, organic coatings of P fertilizer material may increase yields on highly weathered soils. Research reported herein tried to bridge the gap between laboratory results and plant growth studies. It appeared that theories developed from laboratory results would explain effectiveness of fertilizer for plant growth with clover application.

PAGE 157

BIBLIOGRAPHY Appelt. H. N. T. Coleman, and P. F. Pratt. 1975a. Interactions between organic compounds, minerals and ions in volcanic ash derived soils: I. Adsorption of benzoate. p-OH benzoate, salicylate, and phthalate ions. Soil Sci. Am. Proc. 39:623627 Appelt, H. N. T. Coleman, and P. F. Pratt. 1975b. Interactions between organic compounds, minerals and ions in volcanic ash derived soils: II. Effects of organic compounds on the adsorption of phosphate. Soil Sci. Am. Proc. 39:628-630. Atkinson, R. J., A. M. Posner, and J. P. Quirk. 1972. Kinetics of heterogenous isotopic exchange reactions. Exchange of phosphate at the alphaFeOOH aqueous solution interface. J. Inorg. Nucl. Chem. 34:2201-2211. Ballard, R. 1974. Extractabil ity of reference phosphates by soil test reagents in absence and presence of soils. Soil and Crop Sci. Soc. Fla. Proc. 33:169-174. Bhat, K. K. S. and S. Bouyer. 1968. Effect of organic matter on the isotopically exchangeable phosphorus on some types of tropical soils, p. 299-313. I^n Isotopes and Radiation in Soil Organic-Matter Studies. Proc. Symp. lAEA/FAO, Vienna. 1968. Bloom, P. R. 1979. Titration behavior of aluminum organic matter. Soil Sci. Soc. Am. J. 43:815-817. Bloom, P. R. 1981. Phosphorus adsorption by an aluminum peat complex. Soil Sci. Soc. Am. J. 45 : 267-272. Bloom, P. R. and M. B. McBride. 1979. Metal ion binding and exchange with hydrogen ions in acid washed peat. Soil Sci. Soc. Am. J. 43:687-692. Bohn, H. L. B. L. McNeal, and G. A. O'Connor. 1985. Soil Chemistry. John Wiley and Sons, New York. 148

PAGE 158

149 Carroll, D. 1958. Role of clay minerals in the transportation of iron. Geochemica et Cosmochimica Acta, 14:1-28. Chapman, H. D. 1965. Total exchangeable bases, p 902904. In Methods of Soil Analysis, Part 1. Am. Soc. Ag. Inc., Madison, WI. Chen, Y. N. Senesi, and M. Schnitzer. 1977. Information provided on humic substances by E4/E6 ratios. Soil Sci. Soc. Am. J. 41:352-358. Chu, C. R. W. W. Moschler, and G. W. Thomas. 1962. Rock phosphate transformations in acid soils. Soil Sci. Soc. Am. J 26:476-478. Datta, N. P., and N. N. Goswami. 1962. Transformations of organic matter in relation to the availability of nutrients to plants, p 223-238. In^ Isotopes and Radiation in Soil Organic Matter Studies. Proc. Symp. IAEA/FAG, Vienna. Datta, N. P., and B. R. Nagar. 1968. Studies on the decomposition of organic matter in soil in relation to its maintenance and the availability of nutrients to plants, and on the origin and structure of humic acids, p 287-296. In Isotopes and Radiation in Soil Organic-Matter Studies. Proc. Symp. lAEA/FAO, Vienna. Day, P. R. 1965. Particle fractionation and particle size analysis. P 532-543. In Methods of Soil Analysis. Part 1. Am. Soc. Ag., Inc., Madison, WI. Deb, D. L. and N. P. Datta. 1967. Effect of associating anions on phosphorus retention in soil: II. Under variable anion concentration. Plant Soil 26 (3) : 43 2-444. Dixon, J. B. 1977. Kaolinite and serpentine minerals, p 357-398. In Minerals in Soil Environments. SSSA. Madison, WI. Easterwood, G. W. 1982. Liming effect of cabonate apatites. Master's thesis. University of Florida. Evans, L. T. and E. W. Russell. 1959. The adsorption of humic and fulvic acids by clays. J. Soil Sci. 10(1):119-132.

PAGE 159

150 Fassbender. H. W. and Y. K. Igue. 1967. Comparacion de methodos radiometricos y col orimetricos en estudios sobre retencion y transof rmaci on de fosfatos enBuelo. Turialba 17:284-287. Follett, E. A. C. 1965. The retention of amorphous colloidal ferric hydroxide by kaolinites. J. Soil Sci. 16:334-341. Fox, R. L. and E. J. Kamprath. 1970. Phosphate sorption isotherms for evaluating the phosphate requirements of soils. Soil Sci. Soc. Am. Proc. 34:902-907. Greenland, D. J. 1965. Interactions between clays and organic compounds in soils. Part II. Adsorption of soil organic compounds and its effect on soil properties. Soils Fert. 28:521-531. Greenland, D. J. 1971. Interactions between humic and fulvic acids and clays. Soil Sci. 1 1 1 ( 1 ) : 3 4-41 Hammond, L. L. 1978. Agronomic measurements of phosphate rock effectiveness. p 147-173. In International Fertilizer Development Center, Seminar on Phosphate Rock for Direct Application, Muscle Shoals, Ala. Hashimoto, Y., and H. Takayama. 1971. Inhibiting effect of nitrohumates and on phosphorus fixation in soil. VII. Inhibiting effect using synthesized iron compounds as the fixation materials. J. Sci. Soil 42(l):37-43. Hinga, G. 1973. Phosphate sorption capacity in relation to properties of several types of Kenya soil. East Afr. Agri. For. J. 38:400-404. Kingston, F. J., A. M. Posner, and J. P. Quirk. 1974. Anion adsorption by goethite and gibbsite. II. Desorptions of anions from hydrous oxide surfaces. J. Soil Sci. 25 (1): 16-26. Hoagland, D. R. and D. I. Arnon. 1938. Growing plants without soil by the water-culture method. Univ. of Gal. Ag. Exp. Ssta. Berkeley, CA. Circular 347. Hsu, P. H. 1965. Fixation of phosphate by aluminum and iron in acidic soils. Soil Sci. 9 9 ( 6 ) : 3 9 8-40 2 Inoue, T. and K. Wada. 1968. Adsorption of humified clover extracts by various clays. Trans. 9th Int. Congr. Soil Sci., Adelaide, 3:289-298.

PAGE 160

151 Kamprath, E. J. 1967. Residual effects of large applications of phosphorus on high fixing soils. Agron. J. 59:25-27. Kittrick, J. A. 1977. Mineral equilibria and the soil system. p 1-2A. In Minerals in Soil Environments. Soil Sci Soc Am., Inc. Madison, WI. Kononova, M. M. 1966. Soil Organic Matter. 2nd Edition Pergamon Press, Oxford. Kunze, E. W. 1965. Pretreatment for Mineralogical Analysis, p 574-576. In Methods of Soil Analysis, Part 1. American Society of Agronomy, Inc., Madison, WI. Laverdiere, M. R. and R. M. Weaver. 1977. Charge characteristics of spodic horizons. Soil Sci. Soc. Am. J. Al:505-510. Lehr, J. R. and G. H. McClellan. 1972. A laboratory scale for evaluating phosphate rocks for direct applications. TVA Bull. Y-A3 Levashkevich, G. A. 1966. Interactions of humic acid with iron and aluminum hydroxides. Soviet Soil Sci. A:422-A27. Lindsay, W. L. 1959. Behavior of water soluble phosphate. _In Proc. Tenth Annual Fertilzier Conference in the Pacific Northwest. Tacoma, WA. Lindsay, W. L. 1979. Chemical Equilibria in Soils. John Wiley and Sons, New York. Lindsay, W. L., and E. C. Moreno. 1960. Phosphate phase equilibria in soils. Soil. Sci. Soc. Am. Proc. 24:177-182. Lockett, J. L. 1938. Nitrogen and phosphorus changes in the decomposition of rye and clover at different stages of growth. Soil Sci. A5:13-2A. Manojlevic, S. 1965. Study of the role of humic acid in the fixation of soluble phosphorus in soil. Soil Fert. 29:37-41. Martell, A. E., and M. Calvin. 1952. Chemistry of the Metal Chelate Compounds. Prentice-Hall, Englewood Cliffs, NJ..

PAGE 161

152 McLean, E. 0. 1982. Soil pH and lime requirement, p 199-22A. ^n Methods of Soil Analysis. Part 2. Am. Soc. Agron. Inc., Madison, WI. Mendez, J., and E. J. Kamprath. 1978. Liming of Latosols and the effect on P response. Soil Sci. Soc. Am. J. 41:86-88. Moshi, A. 0., A. Wild, and D. J. Greenland. 1974. Effect of organic matter on the charge and phosphate adsorption characteristics of Kikuyu red clay from Kenya. Geoderma 11:275-285. Murphy, J., and J. P. Riley. 1962. A modified solution method for determination of phosphate in natural waters. Anal. Chim. Acta 27:31-36. Nagarajah, S. A. M. Posner, and J. P. Quirk. 1970. Competitive adsorption of phosphate with polyglacturonate and other organic anions and oxide surfaces. Nature 228:83-84. Parfitt, R. L., R. J. Atkinson, and R. St. C. Smert. 1975. The mechanism of phosphate fixation by iron oxides. Soil Sci. Soc. Am. Proc. 39:837-841. Parfitt, R. L. A. R. Eraser, and V. C. Farmer. 1977. Adsorption in hydrous oxides. III. Fulvic acid and humic acid on goethite, gibbsite and imogolite J. Soil Sci. 28:289-296. Parfitt, R. L. and J. D. Russell. 1977. Adsorption of hydrous oxides. IV. Mechanisms of adsorption of various ions on goethite. J. Soil Sci. 28:297305. Parks, G. A., and P. L. de Bruyn. 1962. The zero point of charge of oxides. J. Phys. Chem. 66:967-973. Roy, A. C. M. Y. Ali, R. L. Fox, and J. A. Silva. 1971. Influence of calcium silicate on phosphate solubility and availability in Hawaiian Latosols. Proc. Int. Symp. Soil Fert. Eval. (New Delhi) 1:757-765. Ryden, J. C., J. R. McLaughlin, and J. K. Syers. 1977. Time-dependent sorption of phosphate by soils and hydrous ferric oxides. J. Soil Sci. 28:585-595. Sanchez, P. A., and G. Uehara. 1980. Management considerations for acid. In The Role of Phosphorus in Agriculture. ASA, CSSA, and SSA. Madison, WI.

PAGE 162

153 Schwertmann, U. 1959. Mine r al ogi s che und chemische unter suchungen an eisenoxyden in boden und sedimenten. Neues Jb. Miner. Abk. 93:67-86. Schwertmann, U. 1966. Inhibitory effect of soil organic matter on the crystallization of amorphous ferric hydroxide. Nature. 212:645-646. Schwertmann, U., and W. R. Fisher. 1973. Natural amorphous ferric hydroxide. Geoderma 10:237-247. Schwertmann, U. and R. M. Taylor. 1977. Iron oxides. p 145-181. Tn Minerals in Soil Environments. SSSA. Madison, WI. Silva, J. A. 1971. Possible mechanisms for crop response to silicate applications. Proc. Int. Symp. Soil Pert. Eval. (New Delhi) 1:805-814. Singh, B. B., and J. P. Jones. 1976. Phosphorus sorption and desorption characteristics of soil as affected by organic residues. Soil Sci. Soc. Am. J. 40:389-394. Stevenson, F. J. 1982. Humus Chemistry. John Wiley and Sons, NY. Stoop, W. A. 1974. Interactions between phosphate adsorption and cation adsorption by soils and implications for plant nutrition. PhD. Thesis. Univ of Hawaii, Honolulu. 203 p. (Diss. Abstr. 755042) University Microfilms, Ann Arbor, Michigan. Struthers, P. H. and D. H. Sieling. 1950. Effect of organic anions in phosphate precipitation by iron and aluminum as influenced by pH. Soil Sci. 69:205-213. Taylor, R. M. and U. Schwertmann. 1974. The association of phosphorus with iron in ferruginous soil concretions. Aust. J. Soil Res. 12:133-145. Tisdale, S. L. and W. L. Nelson. 1975. Soil Fertility and Fertilizers. Third Edition. Macmillan Publishing Company, NY. Trong, B. R. Bertrand, S. Burdin, and J. Pichot. 1974. Contribution a I'etude du phosphore dan les sols derives de roches volcaniques de I'elle de la Reunion (Mascaregnes ) Action due carbonate et du silicate de calcium. Agron. Trop. (France) 29:663674.

PAGE 163

154 Walkley, A., and I. A. Black. 1934. An examination of the Degtjareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Sci. 37:3=29-38. Wann, S. S., and G. Uehara. 1978. Surface charge manipulation of constant surface potential soil colloids: I. Relation to sorbed phosphorus. Soil Sci. Soc. Am. J. 42:565-570. Weast, R. C. 1973. Handbook of Chemistry and Physics. CRC Press, Cleveland, OH. Woodruff, J. R. and E. J. Kamprath. 1965. Phosphorus adsorption maximum as measured by the Langmuir isotherm and its relationship to phosphorus availability. Soil Sci. Soc. Am. Proc. 29:148150. Yost, R. S. E. J. Kamprath, E. Lobato, and G. C. Naderman, Jr. 1979. Phosphorus response of corn on an Oxisol as influenced by rates of placement. Soil Sci. Soc. Am. J. 43:388-343. Yuan, T. L. 1980. Adsorption of phosphate and water extractable soil organic material by synthetic aluminum silicates and acid soils. Soil Sci. Soc. Am. J. 44:951-955. Zunino, H. and J. P. Martin. 1977. Metal-binding organic macr omol o cul e s in soil: 1. Hypothesis interpreting the role of soil organic matter in the translocation of metal ions from rocks to biological systems. Soil Sci. 1 23 ( 2) : 65-7 6

PAGE 164

BIOGRAPHICAL SKETCH George William Easterwood was born on April 8, 1955, in Sheffield, Alabama. He was reared in a rural area whose economy was based largely on agriculture. He attended and graduated from Cherokee Vocational High School in Cherokee, Alabama, in 1973. He then attended the University of North Alabama where he obtained a B.S. degree in zoology with a minor in chemistry in 1977. After graduation, he was employed at the International Fertilizer Development Center (IFDC) in Muscle Shoals, Alabama, for 3 years. During this period, he developed an interest in agricultural research and entered the University of Florida in 1980 under the directorship of Dr. J. J. Street. After graduation with a master's degree in 1982, he returned to IFDC for a year. In 1984, he returned to the University of Florida to pursue a Ph.D. degree in soil science under the directorship of Dr. J. B. Sartain. 155

PAGE 165

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly p^re s ent a t ion and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Ph il o s ophy J. G. A. Fiskell Professor of Soil Science Science E. A. Hanlon Assistant Professor of Soil Science

PAGE 166

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. This dissertation was submitted to the Graduate Faculty of the College of Agriculture and to the Graduate School and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. W. G. Harris Assistant Professor of Soil Science S. H. West Professor of Agronomy August, 1987 Dean, Graduate School


127
Fertilizer Addition
Pots contained 2 kg of soil on a dry weight basis.
The source of phosphate fertilizer applied was DAP with
an application rate of 75 mg P/kg soil to all treat
ments. Variation in method of applications was the
experimental treatment. Fertilizer was either com
pletely mixed with the soil or applied by point place
ment. Point placement methodology consisted of placing
one-half of the fertilizer rate (37.5 mg P/kg) at two
positions spaced 4 cm from pot boundary along the diam
eter fo the pot at a space of 6 cm.. Depth of place
ment was 6 cm.
Clover-coated fertilizer granules were prepared by
mixing small increments of Elmer's glue with dried and
ground clover material until all material was bound
together. Dried and ground clover was placed in a
spherical paraffin mold with 37.5 mg P/kg as DAP placed
in the center of the granule. Fertilizer granules were
coated with 0.25, 0.50, 0.75 and 1.0 g of dried and
ground clover with granule diameters ranging from 9 to
13 mm. Clover-coated granule placement in the soil was
the same methodology as that of the point placement.
Uniform fertilizer addition included 150 mg N/kg
soil as NH^NO^, 150 mg K/kg soil as KC1, and a sec
ondary and micronutrient solution containing 19.8 mg Mg


10
28 to 50%. It was noted that soil properties affected
the residual effectiveness. Kamprath (1967) found that
previously applied high rates of P fertilizer oxisols
resulted in increased yield 9 y later and that supple
mental P application greatly increased yield.
Fox and Kamprath (1970) also determined that the P
fixation capacity of acidic soils was reduced by high
rates of initial P applications. It took less applica
tion of P, with increasing rates of initial P applica
tion, to maintain 0.2 ug P/ml in the soil solution
after 10 y.
An increase in cation exchange capacity (CEC) was
accomplished by phosphate addition. As stated previ
ously, adsorption of phosphate to Fe-oxide-coated soils
increased the net negative charge of the colloid and
thereby the CEC (Wann and Uehara, 1978).
High applications of P may also increase the soil
pH. In acidic soils, soil-solution A1 and Fe may be
precipitated, thus reducing their activity (Lindsay,
1979). Stoop (1974) observed that ammonium phosphate
addition increased acidic soil pH due to a decrease in
anion exchange capacity.
Low Input Strategy
An alternative to the costly applications of
massive rates of P would be the low input strategy of
increased P fertilization efficiency by improving
placement, using cheaper sources of P, and decreasing P


124
ligand exchange reactions. Soil treatments with clover
addition had ZPC values of 4.7, near pK values for car
boxyl groups. The main functional group in humic acids
from clover decomposition is carboxyl groups which can
complex acid forming ions in the soil solution. Scan
ning electron microscopy appeared to show greater ag
gregation of the clay fraction with clover amendment,
possibly indicating ligand exchange.


131
Table 5-1. Soil and Treatment Effects on P Uptake From
the First Cropping Period.
Treatment
Clov er
Applied
Orangeburg
Fe(OH)
P
m£
+ Orangeburg
Subs oil
Uptake
P/pot
Completely Mixed
(CM) g/kg
0
9.63
11.97
1.58
10.77
8.27
3.15
11.87
10.97
Granule (G)
g/granule
1) 0.25
27.07
29.60
2) 0.50
29.50
31.43
3) 0.75
29.80
30.13
4) 1.00
27.40
29.57
Point Placement
(PP) 0
24.03
33.07
Contrasts p > F
Orangeburg + Fe(OH)_ vs
Orangeburg Subsoil
0.01
CM vs PP
0.01
0.01
G vs PP
0.01
NS
G(3) vs G(1,2,4)
NS
NS


59
Table 4-2
Time (d)
Response Surface Equations Relating P
Fixation Capacity of Soils With Clover
Addition Over Time.
Response Surface Equation
Correlation
Coefficient
Orangeburg
30
P
f ix
=
196
-
81 clover +
69 clover
z
r
=
0.71
60
P
f ix
=
202
-
6 clover +
8 clover2
2
r
=
0.49
90
P
f ix
=
274
+
252 clover
2
- 76 clover
2
r
=
0.67
Orangeburg +
5.6 g Fe
30
P
f ix
=
986
-
467 clover
+ 111 clover2
2
r
=
0.83
60
P
f ix
=
240
+
107 clover
2
- 36 clover
2
r
=
0.78
90
P
f ix
=
517
+
72 clover -
21 clover2
r2
=
0.29
Orangeburg
Subsoil
30
P
f ix
=
936
-
177 clover
2
+ 41 clover
2
r
=
0.30
60
P
fix
=
6 84
-
130 clover
2
+ 26 clover
2
r
=
0.99
90
P
f ix

810
_
116 clover
2
+ 33 clover
2
r

0.83


139
Table 5-6 Effect of Granule Treatments on Bray 2
Extractable P Levels After the Second
Cropping Period.
Treatment
Clover Applied
Bray
Completely Mixed
(CM)
g/kg
mg P/kg
0
20.58
1.58
22.08
3.15
19.50
Granule (G)
g/Gran
1)
0.25
38.37
2)
0.25
63.48
3)
0.75
52.63
4)
1.00
47.65
Point Placement
(PP)
0
60.60
Contrast
p > F
CM vs PP
Gran vs PP
Gran (2) vs Gran (1,3,4)
0.01
NS
0.05


63
treated soils after 30 d incubation due to P mineral
ization from organic substrates. Mineralization of P
from microbial populations may have produced this
result.
After 90 d of incubation, there was a slight
decrease of soil pH from 6.6 to 6.3 without clover
treatment. Increased P fixation was observed compared
to 30 and 60 d incubation periods. The 3.15 g/kg
clover treatment remained stable with respect to P fix
ation data from 60 d incubation time. However the 1.58
g/kg clover treatment increased soil P fixation
capacity.
Orangeburg Topsoil + Fe(OH)^
After 30 d of incubation, treatments receiving
clover applications possessed lower P fixation capaci
ties than did treatments without clover application.
Treatments receiving 1.58 g/kg clover had a lower P
fixation capacity than 3.15 g clover/kg. Possibly de-
compositional products of clover were bound to the iron
hydroxide surface as was the case in the clover amend
ment experiments of blocking positive charged sites
available for P fixation. Soil pH ranged from 6.5 to
7.2 so that acid forming ions of Al, Fe, and Mn were
not available for precipitation or ionically binding
orthophosphate to organic components. Precipitation of
calcium phosphates at pH 7.2 from the 3.15 g clover/kg


CHAPTER I
INTRODUCTION
In the soil environment, chemical processes favor
equilibrium status of minerals although equilibrium is
seldom obtained (Kittrick, 1977). Rain, however,
dilutes the soil solution and promotes dissolution of
mineral phases thereby increasing the soil solution
activity of certain ionic species. Partial desorption
of ions bound to the exchange complex also buffers the
soil system. Conversely, drought may increase soil-
solution ionic concentration until it is
supersaturated, resulting in precipitation of a solid
phase. Changes within the soil chemical environment
can promote mineralogical transformations. Each of
these processes, as described by Lindsay (1979), over
time produce minerals possessing greater resistance to
weathering. Iron-oxide formation is indicative of
highly-weathered soils (Schwertmann and Taylor, 1977).
Iron oxide or hydroxide minerals may exist as an
independent solid phase in soils where sufficient Fe
oxide concentrations exist or occur in association with
the clay fraction (Carroll, 1958). In either case,
iron oxides could effect surface chemistry by coating
clay minerals (Stevensen, 1982).
1


Absorbance (445 nm) of Humic Acid in Solution
35
0.6
0.5
0.4
0.3
0.2
0.1
5.0
Fig. 3-2
t 6^6
pH
Effect of Soil pH on Organic Release From
Orangeburg Topsoil.


86
increased Truog P, as FeCOH)^ produced a reduction in P
at each P application rate (Table 4-11). As the pH of
the soil decreased, solubilization of indigenous soil
P, or P from fertilizer reaction products increased
producing measurable levels of Truog extractable P
which is a P form readily available to plants. Without
Fe(OH)g addition, increasing levels of Truog P were
obtained with increasing clover rates, without added P.
This same observation (Fig. 4-13) was also noted during
the first cropping period. Reduction in Truog
extractable P on FeiOH)^ treated soil without P addi
tion with increasing clover rates may be explained by P
utilized for plant growth. Increased maize yields were
obtained with increasing clover application rates,
which would lower Truog P levels. Similar observations
were obtained at the 50 mg P/kg rate (Fig. 4-14) and
the 100 mg P/kg rate (Fig. 4-15) with the exception
that Truog extractable P levels also increased with
increasing rate of P application.
Bray 2 Extractable P
Bray 2 extractable P levels were affected by
interaction of P and Fe(0H)3> Extractable P was
increased with increasing P rates but decreased with
Fe(OH)3 additions. Extractable P levels were increased


Table 4-11 Response Surface Equations of Truog Extractable P Levels After the Second
Cropping Period.
Response Surface Equation
Correlation
Coefficient
P Applied (0 mg/kg)
2
Truog P = 2.48 + .05 Fe + .28 clover .06 Fe clover r = .36
P Applied (50 mg/kg)
2
Truog P = 5.06 .45 Fe + .41 clover .08 Fe clover r = .96
P Allied (lop mg/kg)
2
Truog P = 7.75 0.92 Fe + 0.61 clover 0.09 Fe clover r = .96
oo


64
soil treatment may have occurred thereby increasing P
fixation capacity for that treatment.
After 60 d of incubation, total P fixation of all
treatments was reduced, possibly due to P mineraliza
tion from microbes and clover residues. Decreasing P
fixation with increasing clover application was ob
served. Soil pH also increased possibly due to a self-
3 + 2 +
liming effect of Fe to Fe with hydroxyl release
from water applications reducing net positive charge
and P-fixation capacity.
After 90 d of incubation, P fixation capacity was
increased to near initial levels. Cl over-amended
treatments, although lower in P-fixation capacity than
unamended treatments, did not produce substantial P-
fixation reduction as was noted initially.
Orangeburg Subsoil
Orangeburg subsoil contains 34% material in the
clay-size fraction with kaolinite as the dominant clay
mineral. The clay surface is coated with goethite
which is 1.3% of the total weight of the soil.
Orangeburg subsoil results are similar to those
obtained from Orangeburg + FeCOH)^ but clover applica
tion has less effect in reducing P fixation. Clover
application at 30 d reduced P-fixation slightly com
pared to untreated soil. Greater total surface area of
goethite with Orangeburg subsoil compared to Fe(OH)^


32
Clover Production
White clover (Trifolium repens) was grown hydro-
ponically to insure organic functional groups did not
contain high sesquioxide ash contents. Hydroponic
_3
solution possessed ionic concentrations of 10 M P,
10-2*2 M K, 10-1,8 M N03, lO"2*3 M Ca, 10_2'7 M Mg, 10~
2 7 -3 5
M SO., 10 M Fe, with micronutrient concentra-
A
tions of 0.5 ug B/ml, 0.5 ug Mn/ml, 0.05 ug Zn/ml, and
0.02 ug Cu/ml (Hoagland and Arnon, 1938). Solutions
were continually aerated and replaced biweekly. Clover
biomass was harvested every A0 d and the material was
then dried and ground to pass a 2- mm sieve.
Liming Curve and Organic Adsorption Measurements
To determine the maximum organic adsorption to
Orangeburg topsoil, an incubation study was initiated
in which 50 g samples were treated with or without 5.6
g Fe as Fe(0H)3> plus or minus 3.15 g/kg dried and
ground clover, at CaCO^ rates of 0, 0.5, 1.0, 1.5, and
2.0 cmol CaCO^/kg soil. Reagent grade CaCO^ was mixed
with soil and incubated for 2 w at 25C and 8% moisture
on a weight basis. Dried and ground clover was then
applied and allowed to decompose for 30 d. Duplicate
samples were prepared.
Organic anion extraction was performed by extract
ing 10 g of soil with 20 mL of 0.01 M NaCl and shaking
for 30 min (Stevenson, 1982). Samples were centrifuged
and aliquot decanted. Electrical conductivity of each


26
Materials and Methods
Soil
An Orangeburg series soil (fine, loamy, siliceous,
thermic, Typic Paleudult) was obtained from the Agri
cultural Research and Education Station near Quincy,
FL. Two portions of the profile under forest environ
ment were sampled. The surface soil, devoid of organic
litter, was obtained corresponding to the A horizon.
This sandy soil was to be the matrix for FeCOH)^ addi
tion. Subsurface B horizon samples were obtained of
the corresponding soil profile.
Characterization
Both samples were characterized physically, miner-
alogically, and chemically. Particle size distribution
was determined by the methodology of Day (1965) for the
clay fraction and sieving to determine sand and silt
fractions. Pretreatment with ^2^2 organic
component s.
Mineralogical characterization included identifi
cation of clay fraction minerals. Pretreatment
included removal of organic matter with H C>2 ant* free
Fe oxides with citrate-bicarbonate-dithionite extrac
tion (CDB). Free iron oxide and A1 concentrations in
CDB extracts were determined using atomic adsorption
spectrophotometry (Kunze, 1965).
Chemical characterization included cation exchange
capacity by the summation method as described by


BIBLIOGRAPHY
Appelt, H., N. T. Coleman, and P. F. Pratt. 1975a.
Interactions between organic compounds, minerals
and ions in volcanic ash derived soils: I.
Adsorption of benzoate, p-OH benzoate, salicylate,
and phthalate ions. Soil Sci. Am. Proc. 39:623-
627 .
Appelt, H., N. T. Coleman, and P. F. Pratt. 1975b.
Interactions between organic compounds, minerals
and ions in volcanic ash derived soils: II.
Effects of organic compounds on the adsorption of
phosphate. Soil Sci. Am. Proc. 39:628-630.
Atkinson, R. J., A. M. Posner, and J. P. Quirk. 1972.
Kinetics of heterogenous isotopic exchange
reactions. Exchange of phosphate at the alpha-
FeOOH aqueous solution interface. J. Inorg. Nucl.
Chem. 34:2201-2211.
Ballard, R. 1974. Extractability of reference
phosphates by soil test reagents in absence and
presence of soils. Soil and Crop Sci. Soc. Fla.
Proc. 33:169-174.
Bhat, K. K. S., and S. Bouyer. 1968. Effect of organic
matter on the isotopically exchangeable phosphorus
on some types of tropical soils, p. 299-313. _In
Isotopes and Radiation in Soil Organic-Matter
Studies. Proc. Symp. IAEA/FA0, Vienna. 1968.
Bloom, P. R. 1979. Titration behavior of aluminum
organic matter. Soil Sci. Soc. Am. J. 43:815-817.
Bloom, P. R. 1981. Phosphorus adsorption by an
aluminum peat complex. Soil Sci. Soc. Am. J.
45 : 267-272.
Bloom, P. R., and M. B. McBride. 1979. Metal ion
binding and exchange with hydrogen ions in acid
washed peat. Soil Sci. Soc. Am. J. 43:687-692.
Bohn, H. L., B. L. McNeal, and G. A. O'Connor. 1985.
Soil Chemistry. John Wiley and Sons, New York.
148


144
period. Truog P measured after the second cropping
period was substantially lower in Orangeburg topsoil +
FeCOH)^ than in the subsoil. Phosphorus deficiency in
maize plants was also observed on the Orangeburg
topsoil during the second cropping period.
Applications of P fertilizers to high-P fixing
soils should be by band or point placement of fertil
izer. If the sequioxide mineral in the soil possesses
a high surface area, consideration to coating the P
source material with an organic material may be favor
able for increasing P uptake by a crop.


108
Fig. 4-25 Bray 2 Extractable P Levels as Affected by
Clover and Fe(OH)3 Applications at the
0 mg/kg P Rate During the Third Cropping
Period.
Bray 2 Extractable P mg/kg


Fig. 3-10 Differential Scanning Calorimetry Plot of
Orangeburg Topsoil With FeCOH)^ Addition.


81
clover application, as shown in Table 46. With in
creasing P rates, significant increases were observed
in Bray 2 extractable P levels probably from adsorption
to the iron mineral surface. Binuclear adsorption
would reduce extractable P results due to the stability
of the adsorption bond and the irreversible nature of
the adsorption. Clover amendments increased ex
tractable P availability. Possible mechanisms of
organic ligand adsorption, A1 and Fe complexation, P
release for clover and/or acid humification processes
solubilizing calcium phosphates, could increase
extractable P concentrations.
Organic Carbon
No significance with respect to organic carbon
levels was found with clover pretreatment. Further
monitoring of this experimental parameter was termi
nated.
Crop 2
A second maize crop, grown for 50 d, was initiated
to determine residual treatment effectiveness in
relation to experimental parameters.
Yield
Plant dry weight yield was influenced by previous
FeCOH)^ and clover applications (Table 4-7). Main plot
effects did not show increase in yield from previous


123
capacity of the Orangeburg soil without FeCOH)^
addition was probably produced by cation bridging of
orthophosphate to organic functional groups. However,
P fixation on FeCOH)^ treated soil and goethite in
Orangeburg subsoil was reduced by organic anion
specific adsorption. Crop production benefited from
clover application. During the first two croppings of
the glasshouse experiment, clover applications
increased greater plant yield, P uptake, and ex
tractable P levels. Without FeCOH)^ addition, cation
bridging of P to organic components would have greater
plant availability than a precipitation product of an
insoluble Fe or A1 phosphate as the soil pH decreased
over time. With FeiOH)^ applications, complexation of
soluble Fe and A1 and/or organic ligand adsorption to
FeCOH)^ surfaces may have increased yield, P uptake and
extractable P levels. After refertilization of the
third crop, P uptake for soil amended with clover was
not significant according to treatment. However yield
and extractable P levels increased with clover applica
tions. Clover effectiveness in reducing P fixation
persisted long after the time span for nutrient miner
alization. Mechanisms of cation bridging and organic
ligand adsorption appear to exist, confirmed data
obtained from the surface charge and SEM study. Sur
face charge studies indicate a negative shift in ZPC
values from P and clover applications, indicative of


Absorbance (445 nm) of Humic Acid in Solution
40
Ionic Strength
Fig. 3-6
Effect of Solution Ionic Strength on
Organic Release From Orangeburg Topsoil.


93
Fig. 4-16 Bray 2 Extractable P Levels as Affected by
P and Fe(OH) Applications at the 0 g/kg
Clover Rate During the Second Cropping
Period.
Bray 2 Extractable P mg/kg


92
Clover Applied g/kg
Fig. 4-15 Troug Extractable P Levels as Affected by
Clover and Fe(OH) Applications at the
100 mg/kg P Rate During the Second Cropping
Period.
Truog Extractable P mg/kg


132
granule or point placement exhibited greater superior
ity of P uptake and yield than complete mixing. Com
plete mixing of fertilizer to soil exposed a greater
volume of soil to the fertilizer. Reduction in plant
available fertilizer due to reaction with a greater
volume of soil components reduced fertilizer effective
ness. Apparently, reduction in P uptake by corn due to
complete mixing of the DAP was from reaction of fertil
izer P with larger soil volumes.
No differences in P uptake effectiveness by indi
vidual granule treatments on either soil were observed,
however, clover coated granules were superior in
increasing P uptake to fertilizer point placement on
the Orangeburg + Fe(OH)g treated soil. Theoretically,
clover decompositional products should reduce positive
charge near the granule microsite before dissolution of
DAP, making the orthophosphate fraction more readily
available for plant uptake. Also, dissolution pH of
DAP (7.98) would depress Fe and A1 activity as well as
reduce pH-dependent positive charge near microsites.
Amorphous ferric hydroxide treated soil or
goethite in the Orangeburg subsoil had no effect on the
dry weight yield of the first corn crop. Treatment
effects due to placement of 75 mg P/kg affected dry
matter yield production. As shown in Table 5-2, gran
ules and point placement were superior in dry weight
yield production compared to complete mixing of


15
Rate of Decomposition
First signs of humification of clover leaves
appear within 2 to 4 d with the first appearance of
humic substances 2 wk after inoculation. The following
observations were recorded:
Clover leaves. A microscopic examination of
different sections of tissue humification enabled
us to distinguish the following stages of
humification:
1) A darkening of the leaves 3 to 4 days after
the start of the experiment; this appears to be
brought about the action of oxidizing enzymes in
the tissues and also by the activity of mold fungi
which form a weft on the leaf surfaces.
2) In the following 7 to 8 days, the development
of an enormous number of different bacteria and
protozoa is observed in the leaf tissues. The
number of bacteria is so great that in some
sections the tissues are completely filled with
them. A gradual disappearance (like "dissolving)
of the cell walls of the epidermis,
particularly noticeable in young leaves, is
observed from a microscopic examination of the
leaf surface. At the same time, bacteria, found
after isolation to be cellulose myxobacteria have
penetrated into the interior of the epidermal
cells.
3) These bacteria, which are at first colorless,
later group themselves into slimy masses, become
brown in color, and completely fill the cell.
After some time, the bacteria mass in the cells
undergoes lysis and is converted into a brown
liquid which seeps out of the cell (Kononova,
1966. p.147)
Total humification of clover leaves took about 3
wk. Weight loss was 50 to 70% of the original
material.


98
P Applied mg/kg
Fig. 4-20 Plant Dry Weight Yield as Affected by P
and Fe(OH), Applications at the 1.58 g/kg
Clover Rate During the Third Cropping
Period.
Dry Weight Yield g/pot


110
Fig. 4-27 Bray 2 Extractable P Levels as Affected by
Clover and Fe(OH)~ Applications at the
100 mg/kg P Rate During the Third Cropping
Period.
Bray 2 Extractable P mg/kg


Temperature (Deg C)
vO


Absorbance (445 nm) of Humic Acid in Solution
41
Ionic Strength
Fig. 3-7 Clover Decompositional Product Adsorption
to Orangeburg Topsoil as Influenced by
Solution Ionic Strength.


Surface charge studies indicated negative shifts
in Zero Point of Charge (ZPC) with P and clover appli
cations. A ZPC of 4.7, the pK of carboxyl groups, was
observed with clover addition. Mechanisms of ionic
complexation by organic functional groups and organic
ligand exchange appeared to exist from these observa
tions. Experimental observations indicate that appli
cations of clover to Fe(OH)3 treated soils enhanced
crop production.
IX


136
Table 5-3 Effect of Soil and Fertilizer Placement on
Soil pH.After the Second Cropping Period.
Treatment£H Contrast p >F
Completely Mixed
Orangeburg
Orangeburg
+ F e(OH)3
Subsoil
4.67
Topsoil vs
5.24
Subsoil
0.01
Granule
Orangeburg
Orangeburg
+ F e(OH)3
Subsoil
4.68
Topsoil vs
5.23
Sub soil
0.01
Table 5-4. Truog Extractable P Levels on Granule
Samples as Affected by Soil After the
Second Cropping Period.
Treatment Truog P levels Contrast
p >F
mg/kg
Orangeburg
+ F e(OH)3 7.05
Topsoil vs Subsoil
0.05
Orangeburg
subsoil 17.22


13
same mineralogy as subsoils fix considerably less P due
to the organic content in the topsoil.
Decomposition Products of Organic Materials
A synopsis of previous research of the chemical
nature of soil organic compounds was compiled by
Greenland (1965). Component properties of the humic-
acid, fulvic-acid, and humin fractions were obtained
from his publication and are reported below.
Humic Acids
Humic acids are composed of amino acids and
phenolic compounds combined to form high molecular
weight polymers (20,000 to 30,000). This component of
organic matter is soluble in alkali and precipitated by
acids. Research data indicate that humic acids at low
pH have a spherical configuration. As the pH of the
environment around the polymer is increased, the molec
ular compound increases in charge and becomes more
flattened due to reduction in H bonding. Titration
curves indicate a large number of acidic groups, of
which about half possess a negative charge in the pH
range of 5.0 to 7.0.
Fulvic Acids
Fulvic acids are more heterogenous than humic
acids. Fractionation of fulvic acids reveals that the
principle components are phenolic materials similar to
humic acids but with lower molecular weight. Up to 30%
of the fulvic acid may consist of polysaccharides which


137
cropping period. Phosphorus uptake from granule
treatments was superior to point placement on
Orangeburg + Fe soil during the first cropping. Soil
around the granule or point placement possessed greater
concentrations of Truog extractable P than soil from
the completely mixed treatments. Completely mixing
fertilizer with soil increases the volume of soil
capable of reducing fertilizer availability. This
trend was observed throughout the duration of the
experiment. Truog extractable P levels by soil and
treatment were indicative of plant yield and P uptake
measurements since Truog levels denoted highly
available P to plants.
Bray P 2 extractable P levels were affected by
treatment and followed the same trends as the Truog
extractable P results (Table 5-6). Completely mixed
treatments were less effective than granule or point
placement of fertilizer. There was no difference
between granule or point placement methodologies.
Granules coated with 0.5 g clover appeared more
effective in supplying P than other granules
manuf actured.
Reduced P availability reduced plant yield by one-
half if one compares the first to the second crop.


Absorbance (445 nm) of Humic Acid in Solution
43
Ionic Strength
Fig. 3-9
Clover Decompositional Product Adsorption
to Orangeburg Topsoil + Fe(OH)_ as
Influenced by Solution Ionic Strength.


53
Igue, 1967) in duplicate. After shaking, aliquots were
filtered through a 0.2 urn membrane filter disk and
analyzed for orthophosphate (Murphy and Riley, 1962).
Phosphorus fixation was determined by subtraction.
Soil pH at each time interval was determined in a 1:1
soil to water suspension. Analysis of variance was
performed on the split plot design utilizing time as a
main plot with soil and clover addition as subplots.
Glasshouse Study
A 3 X 2 X 3 factorial experiment using 0, 50, and
100 mg P/kg soil, 0 and 5.6 g Fe/kg as Fe(OH)^ and 0,
1.58 and 3.15 g clover/kg in split-split plot design
with three replications was conducted in a glasshouse.
Phosphate addition was the main plot with FeiOH)^ addi
tion as the sub plot, and clover addition the sub-sub
plot. Two crops of Zea mays L. were grown for 50 d
each to determine initial and residual effectiveness of
fertilizer. Treatments were limed and refertilized
with previous rates before initiation of a third crop.
Variables measured include dry matter yield, uptake of
P, Ca, Mg and K, A1 and Fe concentrations within plant
tissue. Soil measurements included Truog and Bray 2
extractable P levels, soil pH, and organic C levels.
Plant samples were analyzed in the following manner:
0.10 g of dried and ground tissue, passing a 1 mm
sieve, was placed in a 50 mL beaker and oxidized in a
muffle furnace at A50C. The ash was further digested


147
positive response in lowering P fixation, clover
amendments should reduce P fixation around P fertilizer
microsites. Point placement of fertilizer and clover-
coated granules were superior to completely mixing fer
tilizer and clover ino the soil, as measured by dry
matter yield, P uptake, and extractable P levels.
Clover granules were somewhat superior to point place
ment in increasing P uptake on Orangeburg + FeCOH)^
during initial cropping. Of the granules manufactured,
the 0.5 g-cl over coating produced the best results of
extractable P levels on Orangeburg + FeCOH)^ treated
soil.
When management is considering practices for crop
production on highly-weathered acidic soils possessing
Fe mineral coatings, management practices using an
organic material such as a legume residue to be incor
porated into the soil should be considered because
increases in crop production with minimal input and
less fertilizer costs may be obtained. In the near
future, organic coatings of P fertilizer material may
increase yields on highly weathered soils. Research
reported herein tried to bridge the gap between labora
tory results and plant growth studies. It appeared
that theories developed from laboratory results would
explain effectiveness of fertilizer for plant growth
with clover application.


7
Milliequivalents Oil
u>


Ill
with clover application as measured during other crop
ping periods with previous P application before crop
ping.
Surface Charge Study
Since differences in yield, P uptake, Truog
extractable P and Bray 2 extractable P existed on
Fe(OH)g treated soils with respect to P and clover
addition, potentiometric titrations relating to varia
tions in net electric surface charge and ZPC were
determined. Addition of Fe(OH)g to kaolinite, the main
clay component of Orangeburg soil, creates greater
positive surface charge with reduced cation exchange
capacity (Dixon, 1977). Experimental objectives in
cluded qualification and quantification of surface
charge properties of Orangeburg soil samples treated
with FeCOH)^ with applications of P, clover, and P and
clover, from the glasshouse study.
Orangeburg + Fe(OH)^
Zero points of titration occur at pH values of 5.2
to 5.A (Fig. 4-28) to FeiOH)^ treated Orangeburg top
soil. Since this treatment had been used in the
glasshouse experiment, reversion of soil pH from 6.3 to
5.A had occurred. A ZPC value was obtained at pH A.O.
Kaolinite, the major clay mineral in the Orangeburg
soil, possesses ZPC values near this pH. Surface
charge of 1.0 cmol(+)/kg soil is probably produced by


51
Mechanisms producing reduction in P fixation might
include 1) release of P for organic components, 2)
blockage of P-adsorption sites with decompositional
products from organic amendment, 3) complexation of
solution A1 and Fe by organic functional groups, and 4)
solubilization of fertilizer reaction products such as
dicalcium phosphate (DAP) by acidity produced from the
humification process (Singh and Jones, 1976). The
objectives of this study are to assess the effective
ness of clover addition to highly-weathered soils in
reducing P fixation as measured by dry matter plant
yield, P uptake, extractable P levels, and changes in
surface charge on soil colloids.
Materials
Soil
An Orangeburg topsoil as described in Chapter 3
was used in the clover amendment experiment. Amorphous
FetOH)^ was prepared and applied as described by previ
ous methodology. The soil was limed to pH 6.3 utiliz
ing the liming curve developed during preliminary
experimentation, and incubated for 2 wk at 25C at 10%
moisture on a weight basis. Dried and ground clover
was then completely mixed with predetermined treatments
and incubated for 30 d prior to fertilizer addition.


CLOVER RESIDUE EFFECTIVENESS IN REDUCING
ORTHOPHOSPHATE SORPTION ON FERRIC-HYDROXIDE
COATED SOIL
By
GEORGE WILLIAM EASTERWOOD
A DISSERTATION PRESENTED TO
THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE
OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1987


116
PH
Fig. 4-30 Surface Properties of Orangeburg Topsoil
+ FeCOH)^ with 3.15 g/kg Applications as
Determined by Potentiometric Titration.


91
Fig. A-14 Truog Extractable P Levels as Affected by
Clover and FeCOH)^ Applications at the
50 mg/kg P Rate During the Second Cropping
Period.
Truog Extractable P mg/kg


23
by the soils were constant suggesting that adsorption
sites for P and organic material were different.
Greenland (1971) determined that organo-mineral
studies should be performed utilizing pure mineral and
organic materials. He determined that previous reac
tions may block adsorption sites on hydrous oxides.
Also, organic functional groups could be rendered inac
tive by metal complexation.
Nagarajah et al., (1970) evaluated the competitive
adsorption of polygalcturonate (a root exudate with
atomic weight of approximately 25,000) on synthetic
goethite. At pH 4.0, polygalcturonate decreased phos
phate adsorption by chelation of Fe or adsorption on
the goethite surface as determined in their experi
ments. Hashimoto and Takayama (1971) reported that
humic acid, nitrohumic acid, and nitrohumate salts
inhibited P fixation on a synthetically prepared
goethite, ferric hydroxide, and ferrous orthosilicate,
but not by lepidocrocite or amorphous Fe oxide hydrate.
Manojlevic (1965) conducted laboratory studies with
humic acid derived from dung and manure on high-P-
fixing soils. Humic acids decreased P fixation from
granular superphosphate which was in contact with the
soil for 4 mo. Moshi et al., (1974) measured phosphate
adsorption from two profiles (one cultivated and one
under forest environment) of Kikuyu red clay from
Kenya. He reported that surface-ads orbed organic


69
"O ETTET
Fe Applied g/kg
Fig. 4-5 Plant Dry Weight Yield Affected by Fe(OH)3
and Clover Applications at the 50 mg/kg
P Rate During the First Cropping Period.
Dry Weight Yield g/pot


66
Table 4-3 Yield Response Surface Equations Obtained
From the First Cropping Period.
Clover applied
g/kg
Response Surface Equation
Correlation
Coef ficient
P = 0
mg/kg
0
Y
= 0.97
- 0.07
Fe
2
r
=
0.61
1.58
Y
= 0.73
- 0.04
Fe
2
r
=
0.18
3.15
Y
= 3.17
- 0.48
Fe
2
r
=
0.68
P = 50
mg/kg
0
Y
= 2.07
- 0.22
Fe
2
r
=
0.73
1.58
Y
= 2.13
- 0.20
Fe
2
r
=
0.52
3.15
Y
= 5.43
- 0.61
Fe
2
r
=
0.63
P = 100 mg/kg
0
Y
= 6.57
- 0.88
Fe
2
r
=
0.95
1.58
Y
= 3.37
- 0.17
Fe
2
r
=
.18
3.15
Y
= 5.37
- 0.20
Fe
2
r
=
0.25


99
Fig. 4-21 Plant Dry Weight Yield as Affected by P
and Fe(OH), Applications at the 3.15 g/kg
Clover Rate During the Third Cropping
Period.
Dry Weight Yield g/pot


19
3 +
the other hand results in release of A1 ions into
solution as H+ ions bind to functional groups at
adsorption sites.
Freshly humified clover material adsorption on
allophane was studied by Inoue and Wada (1968). They
found that newly humified clover possessed a greater
capacity for adsorption than humic substances extracted
from soils. Possible inactivation of functional groups
due to ion complexation was suggested as the reason for
the reduction in adsorption (Greenland, 1971). Prefer
ential adsorption of high molecular weight (1,500 to
10,000) decomposition products was observed on allo
phane (Inoue and Wada, 1968).
Different ideas exist in the literature concerning
the stability of Fe-organo mineral complexes. Lev-
ashkevich (1966) determined that humic acids form more
stable bonds with Al-hydroxide gels than with Fe-
hydroxide gels which he stated had a lower capacity for
adsorption. Greenland (1971) stated that a very strong
bond would be formed between the oxide and humic
molecule if several carboxyl or other groups partici
pated. Schwertmann (1966) stated that the transforma
tion of amorphous ferric hydroxide to a crystalline Fe
mineral may be halted due to the bonding of organic
ligands to the mineral. Schwertmann and Fischer (1973)
determined that ferric-hydroxide surface area would be
reduced by organic-ligand adsorption.


22
rather than fertilizer P uptake on all experimental
soils except the red soil.
Deb and Datta (1967) stated that organic anions in
acidic medium are very effective in complexing Fe
and/or A1 in solution. They observed reduction of Fe
and A1 activity preventing precipitation as insoluble
phosphate compounds.
Observations
Conclusions relating to the reduction of P fixa
tion by organic addition by previous researchers are
mixed. Appelt et al., (1975b) found that the
adsorption of benzoate, p-OH benzoate, salicylate,
phthalate, and humic and fulvic acids extracted from
the surface soil of a Typic Dystrandepts did not block
P adsorption sites on subsurface samples of that soil.
Soil pH values ranged from A.8 to 5.4. High
extractable Al levels were observed. In their studies
no characterization of the organic material relating to
sesquioxide ash and P fixation capacity was given.
Yuan (1980) studied the adsorption of phosphate and hot
water-extractable soil organic matter on acidic soils
and synthetic Al silicates. He found that pretreatment
of organic material had no effect on an Eutrandept: a
slight effect on a Haplaquod, and partial reduction of
P fixation on a Paleudult. He observed that organic
material adsorption was increased by an increase in the
rate of material applied, but the amounts of P retained


101
Table 4-14 Main Effects of P and Fe(OH), Relating to
Plant P Uptake From the Third Cropping.
P uptake
mg/pot
Contrast
p > F
P Applied (mg/kg)
0
1.27
0
vs others
0.01
50
3.42
50
vs 100
0.01
100
8.01
Fe Applied (g/kg)
0
6.14
0
vs 5.6
0.01
5.6
2.33


154
Walkley, A., and I. A. Black. 1934. An examination of
the Degtjareff method for determining soil organic
matter and a proposed modification of the chromic
acid titration method. Soil Sci. 37:3=29-38.
Wann, S. S., and G. Uehara. 1978. Surface charge
manipulation of constant surface potential soil
colloids: I. Relation to sorbed phosphorus. Soil
Sci. Soc. Am. J. 42:565-570.
Weast, R. C. 1973. Handbook of Chemistry and Physics.
CRC Press, Cleveland, OH.
Woodruff, J. R., and E. J. Kamprath. 1965. Phosphorus
adsorption maximum as measured by the Langmuir
isotherm and its relationship to phosphorus
availability. Soil Sci. Soc. Am. Proc. 29:148-
150.
Yost, R. S., E. J. Kamprath, E. Lobato, and G. C.
Naderman, Jr. 1979. Phosphorus response of corn
on an Oxisol as influenced by rates of placement.
Soil Sci. Soc. Am. J. 43:388-343.
Yuan, T. L. 1980. Adsorption of phosphate and water
extractable soil organic material by synthetic
aluminum silicates and acid soils. Soil Sci. Soc.
Am. J. 44:951-955.
Zunino, H., and J. P. Martin. 1977. Metal-binding
organic macromolocules in soil: 1. Hypothesis
interpreting the role of soil organic matter in
the translocation of metal ions from rocks to
biological systems. Soil Sci. 123 ( 2): 65-76.


84
Table 4-7 Main Effects of FeCOH)^ and Clover
Treatments on Plant Yield During the Second
Cropping Period.
Fe applied
(g/kg)
Yield (g/pot)
Contrast
p > F
0
2.17
0 vs. 5.6
0.01
5.6
0.53
Clover applied
(g/kg)
0
0.85
0 vs. others
0.01
1.58
1.35
1.58 vs 3.15
0.01
3.15
1.85


3
yield on high P-fixing soils. To test this hypothesis
experimental objectives are 1) to assess the
effectiveness of organic amendment on Fe(OH)treated
soil which can be measured by dry-matter yield, P
uptake, and extractable P levels.
2) to determine the effectiveness of organic coat
ing on fertilizer phosphate granules in relation to dry
matter yield, P uptake, and extractable P levels.


Heat Flow (mJ/sec)
-2.0
I. ,1 > .... mA
130 250 490 610
Temperature (Deg C)


128
as MgSO^VH^O, 11.A mg Zn as ZnSO^^H^O, 5.09 mg Cu as
CUSO^5H^O and 1.2 mg B as Na2B20y'1OH^O. Fertilizer
application was adjusted to a constant rate by treat
ment assuming 50% mineralization of clover nutrients.
Experimental Design
Eight fertilizer treatments applied to two soils
and replicated three times were set in a randomized
complete block (RCB) design. Fertilizer treatments
were applied to Orangeburg subsoil and Orangeburg
topsoil + 5.6 g Fe/kg as Fe(0H)g. Each soil received P
fertilizer at a rate of 75 mg P/kg soil as DAP.
Treatments were 1) Completely mixed soil without
clover, 2) Completely mixed soil with 1.58 g clover/kg,
3) Completely mixed soil with 3.16 g clover/kg, 4) 2
granules coated with 0.25 g clover, 5) 2 granules
coated with 0.50 g clover, 6) 2 granules coated with
0.75 g of clover, 7) 2 granules coated with 1.00 g
clover, and 8) 2 point placements (uncoated DAP with
same placement as granules.
Statistical analysis of the factorial experiment
in RCB design data was performed utilizing the Statis
tical Analysis System. Mean separation was made using
the single degree of freedom orthogonal contrast tech
nique.
Methods
Two crops of maize were grown for 50 d to assess
the initial and residual effectiveness of the


146
addition on Fe(OH)g treated soil. Soil FeCOH)^ re
mained in an amorphous state throughout the 180 d of
cropping. Without FeCOH)^ addition, cation bridging of
P to organic functional groups would have resulted in
greater plant P availability than a precipitation prod
uct of an insoluble Fe or A1 phosphate. With Fe(OH)^
application, complexation of solution Fe and A1 and/or
organic ligand coordination to Fe(OH)^ surfaces may
have effectively increased plant yield, P uptake, and
extractable P levels. After P refertilization of the
third crop, P uptake across clover levels was not sig
nificant according to treatment, but yield and
extractable P levels increased with clover rate of
application. Clover effectiveness in reducing P fixa
tion remained long after clover nutrients were mineral
ized. Mechanisms of ionic complexations by organic
functional groups and organic ligand adsorption appear
to exist from data obtained from the surface charge.
Surface charge studies indicate a negative shift in ZPC
values with P and clover application, indicative of
ligand exchange reactions. Carboxyl groups can complex
acid forming ions from soil solutions. Scanning elec
tron microscopy appears to reveal a greater aggregation
of the clay fractions with clover amendment.
A second glasshouse experiment was conducted to
determine effectiveness of coating DAP with clover. If
complete mixing of clover with the soil induced a


CHAPTER II
LITERATURE REVIEW
Effect of Iron Oxides on Soil Chemical Properties
Iron oxides can exist as independent minerals in
soils where significant concentrations of these oxides
have accumulated (Schwertmann, 1959), or can occur in
association with the clay fraction (Carroll, 1958).
Follett (1965) studied the retention of amorphous
ferric hydroxide in association with kaolinite, quartz,
and gibbsite. He observed that the amorphous material
reacted immediately with kaolinite on basal plane sur
faces. Smaller amounts of amorphous ferric hydroxide
were adsorbed on finely ground quartz and an insignifi
cant amount to gibbsite. At the experimental pH of 5,
which would create a net positive charge on the amor
phous colloid, adsorption to negatively charged
kaolinite could occur. If ferric hydroxides existed in
sufficient amounts to coat soil particles, the surface
chemical properties would approach that of the ferric
hydroxide (Stevensen, 1982).
4


143
placements during this period may have been produced by
the fertilizer rate of 75 mg P/kg soil as a
concentrated point on the Orangeburg soil + Fe(OH)^
resulting in sufficient P for plant growth.
Of the granules manufactured and applied, the 0.50
g clover coating rate produced the best results only on
Orangeburg + FeCOH)^ treated soil, as measured by Truog
and Bray P 2 extractable P levels. Possibly coating
thickness was related to time of P release during
microbial degradation which induced increased response
to applied P. No difference between granule and point
placement was observed on Orangeburg subsoil.
Differences between soils included pH, Truog
extractable P levels, P uptake, and yield from the
second cropping period. The pH of 4.7 of the Orange
burg topsoil + FeCOH)^ which would increase A1 and Fe
solution activity and increase net positive charge on
Fe mineral surface reducing P availability. Reduction
in P uptake and yield from the second cropping period
are indicative of these types of changes. Changes over
time were not as dramatic on Orangeburg subsoil. After
liming and fertilizer P application, no differences in
yield with respect to soils was observed during the
first cropping period. However, as the two soils
reverted to their natural status, a difference in yield
with respect to soils was observed from a soil by
treatment interactions during the second cropping


80
0 1.58 3.15
Clover Applied g/kg
Fig. 4-12 Truog Extractable P Levels as Affected by
Clover and Fe(OH), Applications at the
100 mg/kg P Rate During the First
Cropping Period.
Truog Extractable P mg/kg


126
(Deb and Datta, 1967). Other observations produced
evidence that organic functional groups bonded cova
lently to Fe mineral surfaces or ionically complexed Fe
or A1 solution species (Greenland, 1971).
Clover decompositional products contain high
percentages of organic functional groups (Kononava,
1961) capable of reaction with sesquioxide minerals or
dissolution products above pH 5 (Greenland, 1971).
Studies of freshly humified clover adsorption to allo-
phane (Inoue and Wanda, 1968) exhibited the effective
ness of organic adsorption to mineral surfaces.
The objective of the fertilizer coating experiment
was to assess the effectiveness of coating granules of
DAP with dried and ground clover as measured by dry
matter production, P uptake, and extractable P levels.
Materials and Methods
Soil
An Orangeburg series topsoil + 5.6 g Fe as FetOH)^
and subsoil corresponding to the Bt horizon as charac
terized in Tables 3-1 and 3-2 of Chapter 3 were used in
the fertilizer coating experiment. Ferric hydroxide
was prepared and applied by the same methodology
described in Chapter 3. The soil was limed to pH 6.3
utilizing the liming curve developed in preliminary
experimentation and incubated for 2 wk.


141
Table 5-7 Soil and Treatment Effect on P uptake From
the Second Cropping Period
Treatment
Clov er
Applied
Orangeburg
Fe(0H)3
P uptak
+ Orangeburg
Subsoil
e mg/pot
Completely Mixed
(CM) g/kg
0
2.17
2.88
1.58
2.69
3.29
3.15
2.40
3.20
Granule(G)
g/granule
1) 0.25
3.66
9.44
2) 0.50
4.39
9.38
3) 0.75
4.16
7.98
4) 1.00
5.12
8.11
Point PIacement(PP) 0
4.71
9.01
Contrasts
p > f
Orangeburg + FeCOH)^ vs Orangeburg subsoil 0.01
CM vs PP 0.01
G vs PP NS
G (2) vs G (1.3,4) NS
G (1) vs G(2,3,4)
0.01
NS
NS


55
solid and mixed with Leon fine sand was extracted.
Bray 2 (.03 M NH^F + 0.1 M HC1) extracted 98% P from
CFP and CFP mixed with Leon fine sand. Sequential
extractions for P were performed with Truog and Bray 2
solutions. Extraction methodology was as follows: 2 g
of soil were placed in a centrifuge tube with 25 ml of
Truog reagent. Samples were shaken at 180 excursions
per minute for 30 m and centrifuged. Aliquots were
filtered through Whatman #42 filter paper. Soil sam
ples were again extracted with Bray 2 solution. Twenty
mL of extractant were added to the soil sample and
shaken for 1 m. Aliquots were immediately filtered
through Whatman #42 filter paper. Soil P concentra
tions were determined by methodology described by
Murphy and Riley (1962).
Surface Charge
To determine net electric charge and ZPC of 1)
FeiOH)^ treated soil, 2) FeiOH)^ treated soil + 100 mg
P/kg, 3) FeiOH)^ treated soil + 3.15 g clover/kg, and
4) FeiOH)^ treated soil + 100 mg P/kg + 3.15 g
clover/kg, potentiometric titrations were performed.
Samples were obtained after the first cropping period
of the glasshouse experiment. Methodology described by
Laverdiere and Weaver (1977) was performed in which 10
g of sample were weighed into 250 mL beakers with addi
tion of 100 mL either 0.01, 0.1 or 1.0 M NaCl. Samples
were allowed to equilibriate for 60 m and pH was


97
Fig. 4-19 Plant Dry Weight Yield as Affected by P
and Fe(OH), Applications at the 0 g/kg
Clover Rate During the Third Cropping
Period.
Dry Weight Yield g/pot


16
Degradation Products
Decomposition rate is influenced by the ease of
metabolism of the organic substrate and the percentage
of siowly-metabolizable compounds. On a percentage
basis of dry ash-fee material before humification,
clover leaves contained 23% organic-soluble substances
(i.e. benzene-ethanol), 3% starch, 8% hemicellu ose,
15% cellulose, 22% protein, and 4% lignin. After the
humification reactions, the residue, expressed as a
percentage of dry ash-free material, contained 16%
substances extracted by organic solvent, 0% starch, 6%
hemicellulose, 13% cellulose, 34% protein, and 16%
lignin. Comparisons of chemical composition of humi
fied and non-humified residues suggests that the per
centage of material extracted with ethanol-benzene,
starch, and cellulose decrease greatly during humifica
tion. Humus has a larger percentage of protein and
lignin than non-humified clover since the previous com
ponents are easily metabolized. The most stable sub
stance was lignin whose content decreased very little.
Type and Distribution of Functional Groups
Clover leaves contain 57% C, 6% H, 32% 0, and 5% N
on a dry weight basis. Configural arrangement of these
elements into organic functional groups determines the
reactivity of the compound or polymer. Humic sub
stances formed from clover tend to be acidic in nature
due to the reactivity of their functional groups


21
3 2
Conversely, Datta and Goswami (1962), utilizing P
tracer techniques, came to different conclusions. The
following excerpt is from their paper:
The increase in the uptake of total P was
again due to a greater uptake of soil and not
fertilizer P, except in red soil, where
the uptake of both soil and fertilizer P
increased. It is, however, expected that, though
organic matter itself has contributed towards the
amount of soil P, it is considered to bear very
little in relation to such a large increase in
total uptake (p 236).
Singh and Jones (1976) also stated that P adsorp
tion could be lowered by blocking adsorption sites with
decomposition products from organic matter. Bhat and
3 2
Bouyer (1968), utilizing P studies, found that the
addition of organic matter to ferruginous tropical
soils lowered P-fixation capacity and isotopically-
dilutable P was also greater. Initial soil pH was 6.6.
Datta and Nagar (1968) using P studies determined
that the uptake of fertilizer P was decreased substan
tially by organic addition in all their experimental
soils except red soils where there was a slight
increase in fertilizer P uptake rather than P uptake
from organic and soil P. Initial soil pH of this red
soil was also 6.6.
Datta and Nagar (1968) suggested that the mecha
nism of organic acid production could solubilize
certain insoluble phosphates present in the soil. This
explanation was given due to large amounts of soil


118
insoluble phosphates. A second ZPC of 3.5 with or
thophosphate addition was not found. However a ZPC at
pH 3.9 suggested presence of adsorption of P or organic
components to Fe(OH)g surfaces.
Implications are that functional groups of clover
bonded with A1 and Fe ions in addition to adsorbing on
Fe mineral surfaces. If this is the accurate mecha
nism, P would possess greater plant availability with
clover addition. Results by yield, P uptake, and soil
test methods such as Truog and Bray 2 extractable P
indicate greater P availability with clover applica
tion. Surface properties confirm differences were
produced by clover applications.
SEM Study
Orangeburg +Fe(0H)2 + 100 mg P/kg soil with and
without clover additions (3.15 g/kg) were placed on C
coated A1 stubs at varying clay concentrations. Sam
ples containing 1600, 800, 533 and 320 mg clay/L were
oo concentrated to notice any difference between
treatments. When samples were diluted to 160 mg clay/L
in deionized water, differences in aggregation were
observed. Greater clay dispersion (Fig. 4-32) without
clover pretreatment was observed compared to increased
aggregation with clover pretreatment (Fig. 4-33).


11
fixation through various amendments (Sanchez and
Uehara, 1980).
PIacement
Placement of fertilizer P can have an effect on
yield. Kamprath (1967) obtained similar yields of
maize by handing 22 kg P/ha for 7 y (154 kg P/ha) as
compared with an initial application of 350 kg P/ha.
Yost et al. (1979) observed that banding was inferior
to broadcast applications to a high-P fixing Oxisol in
Brazil, with very low levels of extractable P. The
best methodology for high P fixing soils probably is an
initial broadcast of P fertilizer with small annual
bandings of P fertilizer (Sanchez and Uehara, 1980).
P Sources
Lower cost phosphate fertilizers such as phosphate
rock may substitute for higher cost more soluble phos
phate sources. Reactivity, as determined by the abso
lute citrate solubility (Lehr and McClellan, 1972) of
the rock source, determines its effectiveness on acidic
soils. The initial relative agronomic effectiveness of
rock sources as compared to soluble superphosphate was
observed by Hammond (1978) to be 79 to 94% for high, 41
to 65% for medium and 27 to 40% for low reactivity rock
sources. He also observed an increase in the calcu
lated relative agronomic effectiveness values for rock
sources during subsequent cropping resulting from the
slow-release characteristics of the source. Phosphate


Dedicated with love to B.J


6
1970). In most cases, high P content is associated
with high Fe content in the soil such that Fe minerals
are thermodynamically sinks for P (Taylor and
Schwertmann, 1974).
Mechanisms of P fixation by Fe oxides are by pre
cipitation and/or adsorption reactions (Chu et al.,
1962). Under acidic soil conditions, the ionic activi
ties of solution species of Fe and H^PO^ may reach
saturation with respect to the solubility product of
strengite (FePO^^H^O) (Lindsay, 1979). Concurrently,
precipitation of strengite at low pH would occur
(Lindsay and Moreno, 1960). Progressively less phos
phate is precipitated as the pH is increased (Struthers
and Sieling, 1950).
Specific adsorption of phosphate is another mecha
nism of reducing pi ant-available P. Hingston et
al.(1974) found differences in surface-charge values of
goethite after phosphate addition while measuring P
adsorption. They postulated that the difference in
charge was due to either mononuclear or binuclear
adsorption of phosphate as shown in the following
schematic:


CHAPTER III
ORGANIC ADSORPTION EXPERIMENT
Introduction
The mechanisms of humic and fulvic anion bonding
to Fe minerals ares by specific adsorption or ligand
exchange (Parfitt et al., 1977). The process is not
sensitive to electrolyte concentration, although it is
sensitive to pH since adsorption maximum occurs near
the pH corresponding to the pK of the acid species,
usually carboxylic, near pH 5.0 (Greenland, 1971). He
found that a very strong bond was formed between oxides
and humic molecules since most functional groups of the
organic acid participated in the adsorption.
Schwertmann (1966) stated that the transformation of
amorphous ferric hydroxide to a more crystalline Fe
mineral may be stopped due to the bonding of organic
liquids to the mineral. Parfitt et al. (1977) deter
mined that fulvic acid is adsorbed on goethite surfaces
by ligand exchange within the pH range of 6 to 6.5.
The objectives for the organic adsorption experi
ment were as follows: 1) To determine pH for maximum
clover decompositional product adsorption and 2) To
determine time required for transformation of amorphous
Fe(0H)g to a crystalline phase in relation to clover
application.
25


CHAPTER VI
SUMMARY AND CONCLUSIONS
Incubation study results indicate that P fixation
is reduced with clover pretreatment on soils containing
sesquioxide minerals. Orangeburg topsoil + FeCOH)^ and
Orangeburg subsoil coated with goethite, had reduced P
fixation capacities with increasing clover application
rates. Increased amounts of P were fixed in Orangeburg
topsoil without FeCOH)^ applications with increasing
clover rates. At 60 d of incubation, P fixation
capacity was reduced for all treatments. Possibly P
mineralization from clover and pH increase reduced net
positive charge on soil mineral surfaces. After 90 d,
P fixation capacity had returned to near initial levels
as soil pH decreased. Phosphorus fixation capacity by
the Orangeburg soil without FeCOH)^ addition probably
was produced by cation bridging of orthophosphate by
organic functional groups. However, P fixation on
FeCOH)^ treated soil and soil with goethite was reduced
by organic adsorption mechanisms. Throughout the dura
tion of the first glasshouse experiment, pretreatment
with clover induced greater plant yield, increased P
uptake except during the third cropping period, and
extractable P levels. Dry weight yields averaged 350%
higher with clover application than without clover
145


73
4-J
O
CL
O0
TO
1
a.
a.
Fig. 4-7 Phosphorus Uptake by Maize as Affected by
Fe(OH) and P Application at the 0 g/kg
Clover Rate During the First Cropping
Period.


153
Schwertmann, U. 1959. Mineralogische und chemische
untersuchungen an eisenoxyden in boden und
sedimenten. Neues Jb. Miner. Abk. 93:67-86.
Schwertmann, U. 1966. Inhibitory effect of soil
organic matter on the crystallization of amorphous
ferric hydroxide. Nature. 212:645-646.
Schwertmann, U., and W. R. Fisher. 1973. Natural
amorphous ferric hydroxide. Geoderma 10:237247.
Schwertmann, U., and R. M. Taylor. 1977. Iron oxides.
p 145-181. _In Minerals in Soil Environments. SSSA.
Madison, WI.
Silva, J. A. 1971. Possible mechanisms for crop
response to silicate applications. Proc. Int.
Symp. Soil Fert. Eval. (New Delhi) 1:805-814.
Singh, B. B., and J. P. Jones. 1976. Phosphorus
sorption and desorption characteristics of soil as
affected by organic residues. Soil Sci. Soc. Am.
J. 40:389-394.
Stevenson, F. J. 1982. Humus Chemistry. John Wiley
and Sons, NY.
Stoop, W. A. 1974. Interactions between phosphate
adsorption and cation adsorption by soils and
implications for plant nutrition. PhD. Thesis.
Univ of Hawaii, Honolulu. 203 p. (Diss. Abstr. 75-
5042) University Microfilms, Ann Arbor, Michigan.
Struthers, P. H., and D. H. Sieling. 1950. Effect of
organic anions in phosphate precipitation by iron
and aluminum as influenced by pH. Soil Sci.
69:205-213.
Taylor, R. M., and U. Schwertmann. 1974. The
association of phosphorus with iron in ferruginous
soil concretions. Aust. J. Soil Res. 12:133-145.
Tisdale, S. L., and W. L. Nelson. 1975. Soil Fertility
and Fertilizers. Third Edition. Macmillan
Publishing Company, NY.
Trong, B., R. Bertrand, S. Burdin, and J. Pichot. 1974.
Contribution a l'etude du phosphore dan les sols
derives de roches volcaniques de l'elle de la
Reunion (Mascaregnes). Action due carbonate et du
silicate de calcium. Agron. Trop. (France) 29:663-
674.


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83
DAP application due to fixation mechanisms. Ferric-
hydroxide decreased dry weight yield fourfold. Clover
addition increased yield with each increasing rate of
application. Since P was a limiting factor, clover
applications apparently increased P reaction product
availability. Release of P from clover should have
subsided long before termination of the second cropping
period. Yield was not likely to be reduced from A1 or
Fe toxicity at pH values of the soil. Although differ
ences in A1 and Fe levels within plant tissue existed
(Table 4-8) with respect to Fe(OH)g treatment, A1 and
Fe levels were not at toxic concentrations.
P Uptake
Phosphorus uptake by maize was affected by FeiOH)^
addition (Table 4-9). The FeiOH)^ provided a sink for
P adsorption. Also as seen in Table 4-10, soil pH had
3+ 3 +
dropped to 5.0 such that A1 and Fe could be in so
lution reducing P availability from precipitation
reactions. Aluminum and Fe ions were present in soil
solution as determined by plant uptake of these ions.
Addition of Fe(OH)^ resulted in a fourfold decrease in
P uptake.
Truog Extractable P
Truog extractable P was affected by an interaction
of FeiOH)^ and clover. Increasing levels of clover


CHAPTER V
FERTILIZER COATING AND PLACEMENT EXPERIMENT
Introduction
After application of water-soluble P fertilizer, P
moves very slowly from the point of placement such that
the orthophosphate is generally immobile in acid soils
(Tisdale and Nelson, 1975). Distribution of fertilizer
P, due to its immobility, is generally less than 1% of
the total soil volume (Lindsay, 1959). Immobility of
fertilizer P is due to rapid reaction with soil
components and metastable precipitation products of
diammonium phosphate (DAP), whose dissolution pH is
7.98, are dicalcium phosphate dihydrate (DCPD) and
struvite (NH^MgPO^'H^O) (Lindsay, 1959). Orthophos
phate ions from the dissolution of fertilizer or solu
bilization of reaction products may form stable sec
ondary products such as varisite, strengite, hydroxyap
atite, or fluorapatite (Lindsay, 1979) or be specifi
cally adsorbed on hydrous oxide mineral surfaces
(Hingston et al., 197A).
Organic matter addition to soils which contain Fe
and A1 oxides has reduced net positive surface charge
and orthophosphate adsorption in acidic environments
(Moshi et al., 197A) Organic addition may also reduce
solution A1 (Bloom and McBride, 1979) or Fe activity
125


I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
W. G. Harris
Assistant Professor of Soil
Science
I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
S. H. West
Professor of Agronomy
This dissertation was submitted to the Graduate Faculty
of the College of Agriculture and to the Graduate
School and was accepted as partial fulfillment of the
requirements for the degree of Doctor of Philosophy.
August, 1987
Dean, Graduate School


142
Table 5-8. Soil and Treatment Effects on Yield from
the Second Cropping Period.
Treatment
Clov er
Applied
Orangeburg
Fe(OH)3
+
Yield
g/Pot
Orangeburg
Subsoil
Completely
Mixed(CM)
£/k£
0
2.67
3.60
1.58
3.07
4.50
3.15
3.27
4.27
Granule(G)
g/gr anule
1)
0.25
5.06
10.33
2)
0.50
6.67
9.40
3)
0.75
5.07
9.13
4)
1.00
6.
50
11.43
Point Placement(PP)
0
7 .
07
9.93
Contrasts
p > F
Orangeburg + FeCOH)^ vs
Orangeburg Subsoil
CM vs PP 0.01
G vs PP NS
G(2) vs G(l,3,4) NS
G(4) vs G (1.2.3)
0.01
NS
NS
0.01


89
Table 4-12 Response Surface Equations of Bray 2
Extractable P Levels After the Second
Cropping Period.
Correlation
Response Surface Equation Coefficient
Clover Applied (0 g/kg)
Bray P = 9.28 + .28 P .85 Fe .04 P Fe
Clover Applied (1.58 g/kg)
Bray P = 16.99 + .24 P 2.13 Fe .02 P Fe
Clover Applied (3.15 g/kg)
.96
2
r
.97
2
r
Bray P = 23.19 + .22 P 2.62 Fe
.02 P Fe
.96


Absorbance (445 nm) of Humic Acid in Solution
38
pH
Fig. 3-5 Clover Deconpositional Product Adsorption
to Orangeburg Topsoil + FeiOH)^ as
Influenced by Soil pH.


14
also may form polymers. Polymers appear to be large,
linear, flexible molecules having less carboxyl groups
than in humic acids.
Humins
Humins are organic compounds which are irre
versibly bound to the mineral part of the soil. It
appears that humins have a lower carbon content com
pared to humic acids possibly from less aromatic com
pounds adsorbed to the mineral surface. These com
pounds appear to possess resistance against microbial
degradation.
Clover Humification: Rate, Products, and Functional
Groups
To assess the humification process, the degrada
tion of clover (Trifolium repens) will be discussed.
Topics of discussion for this section were obtained
from Kononava (1966).
Plant residue decomposition is accomplished by a
variety of soil microorganisms whose speciation depends
on the chemical composition of the plants and soil
environmental conditions. Microbes oxidize the plant
material which loses its stability resulting in a
decrease in weight and volume. During humification,
plant residues became brown in color and, if enough
water is present, an aqueous solution of humic sub
stances may be formed.


60
Clover Applied g/kg
Phosphate Fixation Capacity
Amended With Various Clover
30 Days of Incubation.
ig. 4-1
of Soils
Rates After


152
McLean, E. 0. 1982. Soil pH and lime requirement, p
199-224. ^n Methods of Soil Analysis. Part 2. Am.
Soc. Agron., Inc., Madison, WI.
Mendez, J., and E. J. Kamprath. 1978. Liming of
Latosols and the effect on P response. Soil Sci.
Soc. Am. J. 41:86-88.
Moshi, A. 0., A. Wild, and D. J. Greenland. 1974.
Effect of organic matter on the charge and
phosphate adsorption characteristics of Kikuyu red
clay from Kenya. Geoderma 11:275-285.
Murphy, J., and J. P. Riley. 1962. A modified solution
method for determination of phosphate in natural
waters. Anal. Chim. Acta 27:31-36.
Nagarajah, S., A. M. Posner, and J. P. Quirk. 1970.
Competitive adsorption of phosphate with
polyglacturonate and other organic anions and
oxide surfaces. Nature 228:83-84.
Parfitt, R. L., R. J. Atkinson, and R. St. C. Smert.
1975. The mechanism of phosphate fixation by iron
oxides. Soil Sci. Soc. Am. Proc. 39:837-841.
Parfitt, R. L., A. R. Fraser, and V. C. Farmer. 1977.
Adsorption in hydrous oxides. III. Fulvic acid
and humic acid on goethite, gibbsite and imogolite
J. Soil Sci. 28:289-296.
Parfitt, R. L., and J. D. Russell. 1977. Adsorption of
hydrous oxides. IV. Mechanisms of adsorption of
various ions on goethite. J. Soil Sci. 28:297-
305.
Parks, G. A., and P. L. de Bruyn. 1962. The zero point
of charge of oxides. J. Phys. Chem. 66:967-973.
Roy, A. C., M. Y. Ali, R. L. Fox, and J. A. Silva.
1971. Influence of calcium silicate on phosphate
solubility and availability in Hawaiian Latosols.
Proc. Int. Symp. Soil Fert. Eval. (New Delhi)
1:757-765.
Ryden, J. C., J. R. McLaughlin, and J. K. Syers. 1977.
Time-dependent sorption of phosphate by soils and
hydrous ferric oxides. J. Soil Sci. 28:585-595.
Sanchez, P. A., and G. Uehara. 1980. Management
considerations for acid. ^n The Role of
Phosphorus in Agriculture. ASA, CSSA, and SSA.
Madison, WI.


ACKNOWLEDGEMENTS
With the help of various individuals, both friends
and family, I was encouraged to pursue a doctoral
degree. They directed me in obtaining the best
education possible, and guided me to a more fulfilled
life, both philosophically and intellectually.
I am deeply indebted to Dr. J. B. Sartain, my
major professor, who painstakingly helped mold me
intellectually. He shared with me his values, work
ethic, and extensive knowledge as professor and friend.
I am very fortunate to have a Supervisory Committee of
scientists who display avant garde concepts. Dr. J. G.
A. Fiskell, Dr. J. J. Street, Dr. E. A. Hanlon, Dr. W.
G. Harris, and Dr. S. H. West are men of enlightnment
and inspiration. In my opinion, I have had a
Supervisory Committee that excelled in knowledge,
guidance, and helpfulness. I am sincerely grateful to
these gentlemen for their help and accessibility
despite rigorous schedules.
I truly thank my mother and father for their
encouragement in pursuing the doctoral degree. My
parents, who so long ago gave me gifts of direction,
self discipline, and character development by
iii


105
1.58
Clover Applied g/kg
ig. 4-23 Truog Extractable P Levels as Affected by
Clover and FeCOH)^ Applications at the
50 mg/kg P Rate During the Third
Cropping Period.
Truog Extractable P mg/kg


79
1.58
Clover Applied g/kg
Fig. 4-11 Truog Extractable P Levels as Affected by
Clover and Fe(OH), Applications at the 50
mg/kg P Rate During the First Cropping
Period.
Truog Extractable P mg/kg


V FERTILIZER COATING AND PLACEMENT EXPERIMENT.125
Introduction 125
Materials and Methods 126
Results and Discussion 129
Conclusions 140
VI SUMMARY AND CONCLUSIONS 145
BIBLIOGRAPHY 148
BIOGRAPHICAL SKETCH 155
vi


Table 4-4 Phosphorus Uptake Response Surface Equations Obtained From First Cropping
Period.
Clover applied Correlation
g/kg Response Surface Equation Coefficient
0 P uptake = .004 + 0.06 P + 0.05 Fe 0.01 P*Fe r2 = .91
1.58 P uptake = .37 + .04 P .02 Fe .003 P*Fe r2 = .74
3.15 P uptake = 1.90 + .05 P .26 Fe .004 P*Fe r2 = .72


67
o
O.
oo
TJ
I
H
>~
SZ
CD
U
Q
Fig. A-A Plant Dry Weight Yield Affected by FeCOH)^
and Clover Application at the 0 mg/kg P
Rate During the First Cropping Period.


134
Table 5-2 Effect of Treatment on Maize Dry Matter
Yield From the First Cropping Period.
Treatment Clover Applied Yield g/pot
Completely Mixed(CM)
0
12.07
1.58
12.05
3.15
13.05
Granule (G) g/granule
1)
0.25
21.97
2)
0.50
22.82
3)
0.75
22.77
4)
1.00
21.50
Point Placement (PP)
0
21.42
Contrasts p >F
CM vs PP 0.01
G vs PP NS
G (2) vs GU.3.4) NS


95
Fig. A18 Bray 2 Extractable P Levels as Affected by
P and FeCOH), Applications at the 3.15 g/kg
Clover Rate During the Second
Cropping Period.
Bray 2 Extractable P mg/kg


130
total of 0.87%. Extractable Fe contents of both soils
were equivalent, but as different mineral solid phases.
Phosphorus uptake by corn was affected by soil
type and placement of fertilizer (Table 5-1). Greater
P uptake was obtained with Orangeburg subsoil than
topsoil + FeiOH)^ for the granule and point placement
applications. This observation appears contradictory
since from characterization data, the subsoil fixed 800
mg P/kg while the FeCOH)^ treated topsoil fixed only
640 mg P/kg. Goethite has less surface per unit weight
than FeiOH)^ (Parfitt et al., 1975). Within the point
placement and clover coated granule microsite, greater
adsorptive surface would be available for P fixation on
the Fe(0H)g treated soil since the fertilizer reacts
with approximately 1% of total soil volume (Lindsay,
1959) resulting in greater P fixation by FeiOH)^
treated soil. Results are inconclusive for the com
pletely mixed treatments. Unlike previous experimenta
tion, time for decomposition of clover prior to
fertilizer addition. Clover and fertilizers were
applied on the same day. Lack of response to clover
addition may be due to lack of time for decomposition
before fertilizer addition. Fertilizer placement as a


20
The following relationship was observed:
S(m^/g) = 76.6 16.4(%C) + 9.56(%Fe) where n=17 and
r=0.94.
This relationship suggests strong covalent bonding
between Fe hydroxide and organic anions. Parfitt et
al. (1977) determined that fulvic acid is adsorbed on
goethite surfaces by ligand exchange at the pH of 6-
6.5. Parfitt and Russell (1977) determined that
mononucleate species, such as benzoate and 2,4-D, had a
low-binding constant and were easily desorbed from
goethite surfaces. Binuclear species such as oxalic
acid were strongly adsorbed on the goethite surface.
Appelt et al. (1975a) measured the adsorption of ben
zoate, p-OH benzoate, salicylate, and phthalate on
Andept soils from Chile. They observed that monoprotic
adsorption was by anion exchange whereas diprotic
adsorption was by anion and ligand exchange.
Organo- Mineral Reactions Affecting P Fixation
Possible Mechanisms
Mechanisms relating to reduction in P fixation on
Fe oxides by organic amendments are not clearly delin
eated in the literature. Singh and Jones (1976) stated
that inorganic P from the decomposition of organic
residues would possibly supply sufficient P to reduce P
fixation such that added P would be in a stable form.
They stated that an organic residue must contain at
least 0.3% P, otherwise added P would be immobilized.


12
rock may also produce a liming effect when there is a
siow-carbonate release from highly-reactive rock
(Easterwood, 1982).
Soil Amendments
Soil amendments may aid in reducing P fixation.
The addition of lime reduced P fixation as measured by
adsorption isotherms of Oxisols (Mendez and Kamprath,
1978), Ultisols (Woodruff and Kamprath, 1965), and
Andepts (Truong et al., 1974). The pH of these soils
was below pH 5.2 initially. With an increase in soil
pH, the soil-solution Fe and Al activity was reduced
(Lindsay, 1979). Although liming may reduce P fixa
tion, the orthophosphate adsorption mechanism can still
be operable (Parfitt et al., 1975).
Addition of silicate salts may also reduce P fixa
tion. The silicate anion may replace phosphate on
oxide surfaces (Silva, 1971). Roy et al. (1971) ob
served a decrease of 47% in P fixation on an Ultisol,
41% on an Oxisol, and 9% on an Inceptisol when 500 mg
Si kg ^ as calcium silicate was added to these soil
oxides.
Another management practice that could possibly
reduce P fixation is the addition of organic matter to
soils. Sanchez and Uehara (1980) state that organic
radicles could block exposed hydroxyls on surfaces of
Fe and Al oxides. They noted that topsoils with the


138
Table 5-5. Effect of Treatment on Granule Truog
Extractable P Levels After the Second
Cropping Period.
Treatment
Clover Applied
Truog P
Completely Mixed
(CM)
¡Jlz
mg P/kg
0
6.10
1.58
5.98
3.15
6.10
Granule (G)
g/granule
1)
0.25
10.28
2)
0.50
25.60
3)
0.75
19.63
A)
1.00
18.08
Point Placement(PP)
0
24.85
Contrast
p>F
CM vs PP
0.01
Gran vs PP
NS
Gran (2) vs
Gran (1
.3,4)
0.05


129
fertilizer treatments. Only top growth above the soil
surface was analyzed during the first cropping period.
The soil was not disturbed other than replanting the
second crop. Soil and plant samples were analyzed
after the second cropping period.
Plant samples were analyzed by previously de
scribed methods.
Soils were sampled after the second cropping
period. Completely mixed soil samples were obtained as
well as samples around the granules or point placement.
Fertilizer residue was discarded but soil samples were
taken up to 2 cm distance from point or granule place
ment. Bulk samples from granule or point placement
treated soil, after soil near granules had been
removed, were compared to completely mixed samples as
well as soil 2 cm from granules.
Soil samples were analyzed for Truog and Bray 2
extractable P and pH.
Results and Discussion
Crop 1
Orangeburg subsoil contained 0.84% Fe as goethite
coating clay mineral surfaces. Orangeburg topsoil was
sandy containing Fe concretions with a citrate-
dithionite-bicarbonate extraction concentration of
0.31% of the soil. Addition of amorphous FeCOH)^ (5.6
g/kg) to the topsoil increased the Fe content to a


68
to Al or Fe ions from solution reducing precipitation
of indigenous soil P. Although no differences in soil
pH were observed, the pH of both soils had dropped to
5.2 which would increase A1 and Fe activity in solu
tion. Also, this effect may have been produced by P
released from clover mineralization. Initially, P fer
tilizer was added (7.0 mg P/kg) to the clover control
and 3.5 mg P/kg to the 1.58 g clover/kg
treatment since the literature suggests that approxi
mately 50% of organic P is released as orthophosphate
(Lockett, 193 8). Application of 3.58 g clover/kg was
equivalent to adding 14 mg/P kg soil. Possibly release
of P from clover later in the cropping period resulted
in enhanced yield rather than immediate solubilization
of fertilizer P.
Application of 50 mg P/kg increased plant yield
compared to that without P. FetOH)^ again decreased
plant yield. However, increasing application
rates of clover increased plant yield on Fe(0H)g
treated soil (Table 4-3 and Fig. 4-5). It appeared
that P was more available on FeiOH)^ treated soils due
to blockage of P adsorption sites by organic ligands
from clover application. Increase in yield of treat
ments without FeiOH)^ addition may have been produced
by binding A1 and Fe by organic ligands. Doubling of
dry matter yield from clover addition of 3.18 g


58
Since a triple order interaction was obtained, re
sponse surface equations were developed for each soil
over clover application rates at each time of compari
son. Equations are given in Table 4-2. Graphs of
results at each time interval are given in Fig. 4-1
through 4-3.
Orangeburg Topsoil
Orangeburg topsoil is a sandy soil (85% sand, with
iron concretions (0.31%)). Increasing rates of applica
tion of clover increased P fixation capacity after 30
d. After decomposition of clover, organic functional
groups were available for reaction with soil
components. Calcium can be bound ionically to organic
functional groups (Bloom and McBride, 1979) thereby
attaching orthophosphate to organic components and
reducing P concentration in solution. With clover
addition there was an increase in soil pH from 6.4 to
6.7. Differences in pH could also be induced by pre
cipitation of DCP.
After 60 d of incubation, there was a slight
increase in soil pH from 6.4 to 6.7 without clover
treatment. Increased P fixation was also noted possi
bly due to the formation of a calcium phosphate precip
itate. Clover-amended treatments decreased P fixation
capacity, although it remained higher than the 0 clover
application rate. Singh and Jones (1976) reported
decreases in P fixation capacity of organic


52
Clov er
White clover was grown hydroponically to insure
reactivity of organic functional groups. Hydroponic
methodology is described in Chapter 3.
Fertilizer
Pots used in the glasshouse study contained 3 kg
of soil on a dry weight basis. Fertilizer applications
(N, P, K, Mg) were adjusted by treatment assuming 50%
mineralization from clover application. Total nutrient
addition included 100 mg N/kg as NH^NO^ 140 mg K/kg as
KC1. Diammonium phosphate was applied at rates equiva
lent to 0, 50, and 100 mg P/kg. Supplemental nutrient
addition to pots included 19.8 mg Mg as MgS0^*7H20,
11.4 mg Zn as ZnSO^'/H^O, 5.09 mg Ca as CaSO^'SH^O and
1.2 mg B as Na2B27* 1OH2O.
Methods
Incubation Study
To investigate soil P retention, an incubation
study was conducted with three soils. These were
Orangeburg, Orangeburg + 5.6 g Fe/kg as FeiOH)^, and
Orangeburg subsoil. Each soil was amended with dried
and ground clover at rates of 0, 1.58, and 3.16 g/kg
over times of 30, 60, 90 d. Each soil had been previ
ously limed to pH 6.3 and incubated for 2 w. Soil P
retention was determined at each time interval by
shaking 5 g of sieved soil with 100 ml of solution con
taining 100 mg P/L as I^PO^ for 6 h (Fassbender and


65
applied to Orangeburg topsoil reduced cl over-amendment
effectiveness.
At 60 d of incubation, similar trends of reduction
in P fixation capacity with increased soil pH were
observed. Clover amendments lowered P fixation capac
ity compared to treatments without clover.
At 90 d, the effectiveness of the clover amendment
was negligible.
Glasshouse Study
A glasshouse study was conducted to determine
clover amendment effectiveness in reducing P fixation
in relation to crop production. Three crops of maize
were grown for 50 d each. Results from experimental
parameters from each cropping period will be discussed.
Crop 1
Yield
Dry matter yield was affected by P rate, FeCOH)^
addition, and clover application as determined by a
triple-order interaction. As seen in Table 4-3 and
Fig. 4-4, without application of P, no difference in
yield was obtained with clover applications on the
Fe(0H)g treated soil. Ferric hydroxide provided a sink
for indigenous soil P to be bound as well as P
available from mineralization of clover. Without
FeCOH)^ addition, yield was increased from clover
applications with P additions. This effect could have
been from clover functional groups binding


Fig. 4-33 Scanning Electron Micrograph (450X) of
Orangeburg + FeCOH)^ Clay Fraction (160mg
clay/L Amended With 3.15 g Clover/kg
From the First Cropping Period.


61
Clover Applied g/kg
Phosphate Fixation Capacity
Amended With Various Clover
Days of Incubation.
Fig. 4-2
of Soils
Rates After 60
P fixed mg/kg


CLOVER RESIDUE EFFECTIVENESS IN REDUCING
ORTHOPHOSPHATE SORPTION ON FERRIC-HYDROXIDE
COATED SOIL
By
GEORGE WILLIAM EASTERWOOD
A DISSERTATION PRESENTED TO
THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE
OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1987

Dedicated with love to B.J

ACKNOWLEDGEMENTS
With the help of various individuals, both friends
and family, I was encouraged to pursue a doctoral
degree. They directed me in obtaining the best
education possible, and guided me to a more fulfilled
life, both philosophically and intellectually.
I am deeply indebted to Dr. J. B. Sartain, my
major professor, who painstakingly helped mold me
intellectually. He shared with me his values, work
ethic, and extensive knowledge as professor and friend.
I am very fortunate to have a Supervisory Committee of
scientists who display avant garde concepts. Dr. J. G.
A. Fiskell, Dr. J. J. Street, Dr. E. A. Hanlon, Dr. W.
G. Harris, and Dr. S. H. West are men of enlightnment
and inspiration. In my opinion, I have had a
Supervisory Committee that excelled in knowledge,
guidance, and helpfulness. I am sincerely grateful to
these gentlemen for their help and accessibility
despite rigorous schedules.
I truly thank my mother and father for their
encouragement in pursuing the doctoral degree. My
parents, who so long ago gave me gifts of direction,
self discipline, and character development by
iii

emulation, anchored by a spirit of love, aided me more
than they will ever know.
During the third year of my pursuit of a doctor
ate, I endured a bitter disappointment that almost dev
astated me. Miss Betty Jean (B.J.) Cross, my former
fiancee, passed from this life. She endured the rigors
of graduate school with me and was always supportive.
This beautiful lady, both physically and spiritually,
shall always be in my memory. It is to her, that this
work is dedicated.
IV

TABLE OF CONTENTS
ACKNOWLEDGMENTS iii
ABSTRACT vii
CHAPTERS
I INTRODUCTION 1
II LITERATURE REVIEW 4
Effect of Iron Oxides on Soil Chemical
Properties 4
Present Management Practices for Reduction
of P Fixation 9
Decompositional Products of Organic
Material s 13
Organic Anion and Iron Mineral Interac
tions 17
Organo-Mineral Reactions Affecting P
Fixation 20
III ORGANIC ADSORPTION EXPERIMENT 25
Introduction 25
Materials and Methods 26
Results and Discussion 33
Conclusions 45
IV PHOSPHATE AND ORGANIC AMENDMENT EXPERIMENT...50
Introduction 50
Materials ....51
Methods.... 52
Incubation Study 52
Glasshouse Study 52
Surface Charge 55
SEM Study 56
Results and Discussion 56
Incubation Study 56
Glasshouse Study 65
Surface Charge Ill
SEM Study 118
Conclusions 121
v

V FERTILIZER COATING AND PLACEMENT EXPERIMENT.125
Introduction 125
Materials and Methods 126
Results and Discussion 129
Conclusions 140
VI SUMMARY AND CONCLUSIONS 145
BIBLIOGRAPHY 148
BIOGRAPHICAL SKETCH 155
vi

Abstract of Dissertation Presented to the Graduate
School of the University of Florida in Partial
Fulfillment of the Requirements for the Degree of
Doctor of Philosophy
CLOVER RESIDUE EFFECTIVENESS IN REDUCING
ORTHOPHOSPHATE SORPTION ON FERRIC-HYDROXIDE
COATED SOIL
By
GEORGE WILLIAM EASTERWOOD
August, 1987
Chairman: Dr. J. B. Sartain
Major Department: Soil Science Department
Laboratory research suggests that organic acids
bind to iron-mineral surfaces, reducing P fixation.
Experiments were conducted to determine 1) maximal
clover residue adsorption, 2) P fixation capacity of
Fe(OH)g treated topsoil and goethite coated subsoil
amended with clover, 3) clover residue effectiveness in
relation to maize yield and extractable P levels, and
4) surface charge with P, clover, and P and clover
applications to Fe(OH)3 treated soils.
Amorphous iron-hydroxide (FeCOH)^) precipitate was
applied to Orangeburg soil (fine, loamy, siliceous,
thermic Typic Paleudult) at rates of 0 and 5.6 g Fe as
FeiOH)^. White clover (Tr i^l^o ium tepens) was grown
hydroponically in Hoagland's solution.
Vll

Maximum clover residue adsorption occurred at pH
6.3 with F e (0 H) ^ addition. Without F e (0 H) g applica
tion, adsorption was dependent on solution ionic
strength.
Clover applications decreased P adsorption within
each sampling time (30, 60, 90 d) for Orangeburg soil
with synthetic FeCOH)^ and Orangeburg subsoil contain
ing goethite but increased P fixation without FeiOH)^
application.
A glasshouse experiment was conducted to measure
maize yield, P uptake and extractable P levels. Two
crops of maize were grown 50 d each prior to P refer
tilization for the third crop. An increase of 350% in
maize yield with increases in P uptake and extractable
P levels was observed with clover and P applications
compared to P fertilization only, on FeCOH)^ treated
soils within cropping periods. A second experiment was
conducted to determine effectiveness of coating
diammonium phosphate (DAP) with clover to reduce P fix
ation around fertilizer microsites. Point placement of
fertilizer and granules was superior to mixing fertil
izer and clover to soil as measured by yield, P uptake,
and extractable P levels. Granules were superior to
point placement in increasing P uptake and extractable
P levels on Orangeburg + Fe(OH)^ soil.
viii

Surface charge studies indicated negative shifts
in Zero Point of Charge (ZPC) with P and clover appli
cations. A ZPC of 4.7, the pK of carboxyl groups, was
observed with clover addition. Mechanisms of ionic
complexation by organic functional groups and organic
ligand exchange appeared to exist from these observa
tions. Experimental observations indicate that appli
cations of clover to Fe(OH)3 treated soils enhanced
crop production.
IX

CHAPTER I
INTRODUCTION
In the soil environment, chemical processes favor
equilibrium status of minerals although equilibrium is
seldom obtained (Kittrick, 1977). Rain, however,
dilutes the soil solution and promotes dissolution of
mineral phases thereby increasing the soil solution
activity of certain ionic species. Partial desorption
of ions bound to the exchange complex also buffers the
soil system. Conversely, drought may increase soil-
solution ionic concentration until it is
supersaturated, resulting in precipitation of a solid
phase. Changes within the soil chemical environment
can promote mineralogical transformations. Each of
these processes, as described by Lindsay (1979), over
time produce minerals possessing greater resistance to
weathering. Iron-oxide formation is indicative of
highly-weathered soils (Schwertmann and Taylor, 1977).
Iron oxide or hydroxide minerals may exist as an
independent solid phase in soils where sufficient Fe
oxide concentrations exist or occur in association with
the clay fraction (Carroll, 1958). In either case,
iron oxides could effect surface chemistry by coating
clay minerals (Stevensen, 1982).
1

2
Phosphorus (P) fixation, which is reduction of
soil solution phosphate by Fe minerals, may occur by
adsorption to the solid phase or precipitation
reactions from the solubility products (Chu et al.,
1962). Adsorption may occur as a mono- or binuclear
covalent bonding to the Fe mineral (Hingston et al.,
1974). Binuclear adsorption is irreversible in that
desorption is negligible. Iron ionic species may
reduce P availability below pH 5.5 through
precipitation reactions. If the solution species of Fe
and H^PO^ reach saturation with respect to the
solubility product of strengite (FePO^*2H2O),
precipitation can result (Lindsay, 1979).
Present management practices for reduction of P
fixation include either P as an amendment, or use of a
low input strategy which includes proper placement,
less costly P sources, and soil amendments such as lime
or silicates (Sanchez and Uehara, 1980). Another man
agement practice that could possibly reduce P fixation
would be to apply an organic amendment to the soil.
Humic and fulvic acids covalently bind to Fe mineral
surfaces (Parfitt et al., 1977) and reduce net positive
charge (Moshi et al., 1974). Complexation of solution
Fe or Al may occur by bonding ionically to the organic
functional groups (Deb and Datta, 1967).
Less costly management practices of applying crop
residue possibly could substantially increase agronomic

3
yield on high P-fixing soils. To test this hypothesis
experimental objectives are 1) to assess the
effectiveness of organic amendment on Fe(OH)treated
soil which can be measured by dry-matter yield, P
uptake, and extractable P levels.
2) to determine the effectiveness of organic coat
ing on fertilizer phosphate granules in relation to dry
matter yield, P uptake, and extractable P levels.

CHAPTER II
LITERATURE REVIEW
Effect of Iron Oxides on Soil Chemical Properties
Iron oxides can exist as independent minerals in
soils where significant concentrations of these oxides
have accumulated (Schwertmann, 1959), or can occur in
association with the clay fraction (Carroll, 1958).
Follett (1965) studied the retention of amorphous
ferric hydroxide in association with kaolinite, quartz,
and gibbsite. He observed that the amorphous material
reacted immediately with kaolinite on basal plane sur
faces. Smaller amounts of amorphous ferric hydroxide
were adsorbed on finely ground quartz and an insignifi
cant amount to gibbsite. At the experimental pH of 5,
which would create a net positive charge on the amor
phous colloid, adsorption to negatively charged
kaolinite could occur. If ferric hydroxides existed in
sufficient amounts to coat soil particles, the surface
chemical properties would approach that of the ferric
hydroxide (Stevensen, 1982).
4

5
Surface Charge of Iron Oxides
Surface charge of Fe oxides is pH dependent as
shown in the following model (Parks and deBruyn, 1962):
Charge (+) Charge (0) Charge (-)
Adsorption or desorption of H+ creates either a
positive, neutral or negative charge on the oxide
surface. As a pH-dependent charge is developed, an
anion or cation (A or C+ ion model) is attracted to
and satisfies the electrostatic charge according to the
law of electroneutrality in the outer diffuse electric
double layer. This type of adsorption is termed non
specific adsorption or ionic bonding (Schwertmann and
Taylor, 1977).
A stronger adsorption bond is produced when ions
penetrate the coordination shell of the Fe atom on the
oxide surface and exchange their OH and OH^0 ligands.
A covalent bond is produced between the anion and oxide
and is termed specific adsorption (Stevensen, 1982).
Phosphate Fixation by Iron Oxides
Soils rich in Fe oxides, such as some Utisols and
Oxisols of the tropics, are known for their low avail
ability of phosphate (Kamprath, 1967; Fox and Kamprath,

6
1970). In most cases, high P content is associated
with high Fe content in the soil such that Fe minerals
are thermodynamically sinks for P (Taylor and
Schwertmann, 1974).
Mechanisms of P fixation by Fe oxides are by pre
cipitation and/or adsorption reactions (Chu et al.,
1962). Under acidic soil conditions, the ionic activi
ties of solution species of Fe and H^PO^ may reach
saturation with respect to the solubility product of
strengite (FePO^^H^O) (Lindsay, 1979). Concurrently,
precipitation of strengite at low pH would occur
(Lindsay and Moreno, 1960). Progressively less phos
phate is precipitated as the pH is increased (Struthers
and Sieling, 1950).
Specific adsorption of phosphate is another mecha
nism of reducing pi ant-available P. Hingston et
al.(1974) found differences in surface-charge values of
goethite after phosphate addition while measuring P
adsorption. They postulated that the difference in
charge was due to either mononuclear or binuclear
adsorption of phosphate as shown in the following
schematic:

7
OH
2
-2
-1
Fe
OP0
O
/
)
\
Fe
/
O
O
O
o
p
+ OH
OH
O
O
Fe
Fe
\
OH2
Reversibly adsorbed P
Irreversibly adsorbed P
Wann and Uehara (1978) determined that phosphate
addition to Fe-oxide-rich Oxisols lowered the ZPC and
increased surface charge density at any pH above the
ZPC. They suggested phosphate as an amendment to in
crease cation exchange capacity. Parfitt et al. (1975)
confirmed the binuclear coordination of phosphate
adsorption in goethite using infrared spectroscopic
analysis. Increasing surface area of major soil Fe
oxides was observed in which amorphous ferric hydroxide
> 1epidocrocite > goethite > hematite. Phosphorus
adsorption also increased with increasing mineral sur
face area.
Kinetics
Hsu (1965) studied phosphate fixation with soils
possessing Fe and Al oxides. He observed a two-stage
reaction rate in which P was fixed rapidly within a few
minutes or hours and a slower rate with increasing
time. Adsorption of P to Fe oxides is postulated to be

8
a first order relationship after 48 hours of reaction
time (Ryden et al., 1977) such as:
[A] = K[A]
when A, t, and K represent phosphate concentrations,
time, and a constant, respectively (Bohn et al., 1985)
Differences in reaction rates were attributed to min
eral and solution Fe and Al (Hsu, 1965). He also
stated that in principle, there was no difference
between precipitation and adsorption reactions. He
noted that whether a Fe^(OH)^^(HjPO^)6 or
Fe^^(OH)^^^(H2PO^)jg compound is formed is irrelevant
since the chemical reaction is the same.
Desorption is also an extremely complex phe
nomenon. If the enthalpies of the mononuclear and bin
uclear Fe phosphate complexes are similar, the binu-
clear adsorption would exhibit greater stability
(Hingston et al., 1974) due to an increase in entropy
(Martell and Calvin, 1952). Slow release of phosphate
from Fe oxides has been attributed to a ring-forming,
binuclear phosphate adsorption (Atkinson et al., 1972)
Phosphorus Fixation by Organic Components
During the decomposition of organic materials in
acidic soils, organic functional groups can form a
stable complex with Fe or Al in solution (Deb and
Datta, 1967). Humic acids extracted from acid soils
usually have a high Al and Fe content (Greenland

9
1965). Phosphate adsorption may occur on organic mate
rial by cation bridging to Fe and A1. Bloom (1981)
determined that P is strongly adsorbed by Al-saturated
peat within the pH range of 3.2 to 6.0. He postulated
that the mechanism of fixation was an adsorption of
orthophosphate to trivalent complexed A1 followed by
the precipitation of amorphous Al-hydroxy-phosphate
such as A1(OH)^*H^PO^. The strength of phosphate
adsorption by this mechanism was less than that for an
Al-permanent charge resin but greater than that on a
weight basis of organic matter obtained from an Andept
soil.
Present Management Practices for Reduction of P
Fixation
There are at present two management alternatives
for favorable P fertility on acidic soils (Sanchez and
Uehara, 1980). One is a high input strategy utilizing
P as an amendment and the other is a more economical
low input strategy. Each method will be discussed.
Phosphorus as an Amendment
Fox and Kamprath (1970) determined that 95% of the
maximum yield could be obtained when the fertilizer
rate was adjusted such that 0.2 ug P/ml existed in the
soil solution as determined by adsorption isotherms on
acidic soils. To obtain that concentration. 700 kg
P/ha were added. Ten y after the initial experiment,
the residual efficiency which is fertilizer P
effectiveness in crop production over time, ranged from

10
28 to 50%. It was noted that soil properties affected
the residual effectiveness. Kamprath (1967) found that
previously applied high rates of P fertilizer oxisols
resulted in increased yield 9 y later and that supple
mental P application greatly increased yield.
Fox and Kamprath (1970) also determined that the P
fixation capacity of acidic soils was reduced by high
rates of initial P applications. It took less applica
tion of P, with increasing rates of initial P applica
tion, to maintain 0.2 ug P/ml in the soil solution
after 10 y.
An increase in cation exchange capacity (CEC) was
accomplished by phosphate addition. As stated previ
ously, adsorption of phosphate to Fe-oxide-coated soils
increased the net negative charge of the colloid and
thereby the CEC (Wann and Uehara, 1978).
High applications of P may also increase the soil
pH. In acidic soils, soil-solution A1 and Fe may be
precipitated, thus reducing their activity (Lindsay,
1979). Stoop (1974) observed that ammonium phosphate
addition increased acidic soil pH due to a decrease in
anion exchange capacity.
Low Input Strategy
An alternative to the costly applications of
massive rates of P would be the low input strategy of
increased P fertilization efficiency by improving
placement, using cheaper sources of P, and decreasing P

11
fixation through various amendments (Sanchez and
Uehara, 1980).
PIacement
Placement of fertilizer P can have an effect on
yield. Kamprath (1967) obtained similar yields of
maize by handing 22 kg P/ha for 7 y (154 kg P/ha) as
compared with an initial application of 350 kg P/ha.
Yost et al. (1979) observed that banding was inferior
to broadcast applications to a high-P fixing Oxisol in
Brazil, with very low levels of extractable P. The
best methodology for high P fixing soils probably is an
initial broadcast of P fertilizer with small annual
bandings of P fertilizer (Sanchez and Uehara, 1980).
P Sources
Lower cost phosphate fertilizers such as phosphate
rock may substitute for higher cost more soluble phos
phate sources. Reactivity, as determined by the abso
lute citrate solubility (Lehr and McClellan, 1972) of
the rock source, determines its effectiveness on acidic
soils. The initial relative agronomic effectiveness of
rock sources as compared to soluble superphosphate was
observed by Hammond (1978) to be 79 to 94% for high, 41
to 65% for medium and 27 to 40% for low reactivity rock
sources. He also observed an increase in the calcu
lated relative agronomic effectiveness values for rock
sources during subsequent cropping resulting from the
slow-release characteristics of the source. Phosphate

12
rock may also produce a liming effect when there is a
siow-carbonate release from highly-reactive rock
(Easterwood, 1982).
Soil Amendments
Soil amendments may aid in reducing P fixation.
The addition of lime reduced P fixation as measured by
adsorption isotherms of Oxisols (Mendez and Kamprath,
1978), Ultisols (Woodruff and Kamprath, 1965), and
Andepts (Truong et al., 1974). The pH of these soils
was below pH 5.2 initially. With an increase in soil
pH, the soil-solution Fe and Al activity was reduced
(Lindsay, 1979). Although liming may reduce P fixa
tion, the orthophosphate adsorption mechanism can still
be operable (Parfitt et al., 1975).
Addition of silicate salts may also reduce P fixa
tion. The silicate anion may replace phosphate on
oxide surfaces (Silva, 1971). Roy et al. (1971) ob
served a decrease of 47% in P fixation on an Ultisol,
41% on an Oxisol, and 9% on an Inceptisol when 500 mg
Si kg ^ as calcium silicate was added to these soil
oxides.
Another management practice that could possibly
reduce P fixation is the addition of organic matter to
soils. Sanchez and Uehara (1980) state that organic
radicles could block exposed hydroxyls on surfaces of
Fe and Al oxides. They noted that topsoils with the

13
same mineralogy as subsoils fix considerably less P due
to the organic content in the topsoil.
Decomposition Products of Organic Materials
A synopsis of previous research of the chemical
nature of soil organic compounds was compiled by
Greenland (1965). Component properties of the humic-
acid, fulvic-acid, and humin fractions were obtained
from his publication and are reported below.
Humic Acids
Humic acids are composed of amino acids and
phenolic compounds combined to form high molecular
weight polymers (20,000 to 30,000). This component of
organic matter is soluble in alkali and precipitated by
acids. Research data indicate that humic acids at low
pH have a spherical configuration. As the pH of the
environment around the polymer is increased, the molec
ular compound increases in charge and becomes more
flattened due to reduction in H bonding. Titration
curves indicate a large number of acidic groups, of
which about half possess a negative charge in the pH
range of 5.0 to 7.0.
Fulvic Acids
Fulvic acids are more heterogenous than humic
acids. Fractionation of fulvic acids reveals that the
principle components are phenolic materials similar to
humic acids but with lower molecular weight. Up to 30%
of the fulvic acid may consist of polysaccharides which

14
also may form polymers. Polymers appear to be large,
linear, flexible molecules having less carboxyl groups
than in humic acids.
Humins
Humins are organic compounds which are irre
versibly bound to the mineral part of the soil. It
appears that humins have a lower carbon content com
pared to humic acids possibly from less aromatic com
pounds adsorbed to the mineral surface. These com
pounds appear to possess resistance against microbial
degradation.
Clover Humification: Rate, Products, and Functional
Groups
To assess the humification process, the degrada
tion of clover (Trifolium repens) will be discussed.
Topics of discussion for this section were obtained
from Kononava (1966).
Plant residue decomposition is accomplished by a
variety of soil microorganisms whose speciation depends
on the chemical composition of the plants and soil
environmental conditions. Microbes oxidize the plant
material which loses its stability resulting in a
decrease in weight and volume. During humification,
plant residues became brown in color and, if enough
water is present, an aqueous solution of humic sub
stances may be formed.

15
Rate of Decomposition
First signs of humification of clover leaves
appear within 2 to 4 d with the first appearance of
humic substances 2 wk after inoculation. The following
observations were recorded:
Clover leaves. A microscopic examination of
different sections of tissue humification enabled
us to distinguish the following stages of
humification:
1) A darkening of the leaves 3 to 4 days after
the start of the experiment; this appears to be
brought about the action of oxidizing enzymes in
the tissues and also by the activity of mold fungi
which form a weft on the leaf surfaces.
2) In the following 7 to 8 days, the development
of an enormous number of different bacteria and
protozoa is observed in the leaf tissues. The
number of bacteria is so great that in some
sections the tissues are completely filled with
them. A gradual disappearance (like "dissolving)
of the cell walls of the epidermis,
particularly noticeable in young leaves, is
observed from a microscopic examination of the
leaf surface. At the same time, bacteria, found
after isolation to be cellulose myxobacteria have
penetrated into the interior of the epidermal
cells.
3) These bacteria, which are at first colorless,
later group themselves into slimy masses, become
brown in color, and completely fill the cell.
After some time, the bacteria mass in the cells
undergoes lysis and is converted into a brown
liquid which seeps out of the cell (Kononova,
1966. p.147)
Total humification of clover leaves took about 3
wk. Weight loss was 50 to 70% of the original
material.

16
Degradation Products
Decomposition rate is influenced by the ease of
metabolism of the organic substrate and the percentage
of siowly-metabolizable compounds. On a percentage
basis of dry ash-fee material before humification,
clover leaves contained 23% organic-soluble substances
(i.e. benzene-ethanol), 3% starch, 8% hemicellu ose,
15% cellulose, 22% protein, and 4% lignin. After the
humification reactions, the residue, expressed as a
percentage of dry ash-free material, contained 16%
substances extracted by organic solvent, 0% starch, 6%
hemicellulose, 13% cellulose, 34% protein, and 16%
lignin. Comparisons of chemical composition of humi
fied and non-humified residues suggests that the per
centage of material extracted with ethanol-benzene,
starch, and cellulose decrease greatly during humifica
tion. Humus has a larger percentage of protein and
lignin than non-humified clover since the previous com
ponents are easily metabolized. The most stable sub
stance was lignin whose content decreased very little.
Type and Distribution of Functional Groups
Clover leaves contain 57% C, 6% H, 32% 0, and 5% N
on a dry weight basis. Configural arrangement of these
elements into organic functional groups determines the
reactivity of the compound or polymer. Humic sub
stances formed from clover tend to be acidic in nature
due to the reactivity of their functional groups

17
releasing H+ as the pK value is reached. On a percent
age basis of dry ash-free material, plant residue con
tains 9% carboxylic, 8% alcoholic-OH, 6% phenolic-OH,
and 3% methoxy functional groups producing the high
reactivity of humified organic material.
Inorganic P Released From Clover Decomposition
During the decomposition of clover, inorganic
phosphate may be mineralized. Lockett (1938) postu
lated that P was mineralized and assimilated into
microbial lipids and nucleoproteins. Later P became
available upon disintergration of microbial cells. He
determined that, after decomposition, 59% of the total
P was in organic form and 41% in inorganic form. He
obtained similar results as those observed by Kononava
(1961).
Organic Anion and Iron Mineral Interactions
Unlike cation bridging of organic anions to clays
(Evans and Russell, 1959), the mechanism of humic and
fulvic-acid anion bonding to Fe minerals is by specific
adsorption or ligand exchange (Parfitt et al., 1977).
The process is not sensitive to electrolyte concentra
tions, although it is sensitive to pH since the adsorp
tion maximum inflection point occurs near the pH corre
sponding to the pK of the acid species, which is usu
ally carboxylic and near pH 5.0 (Greenland, 1971). He
reported a very strong bond between oxide and humic
molecules since most functional groups of the organic

18
acid participate in the adsorption and their distribu
tion was throughout the organic molecules. Greater
surface area of the humic acid, at or above the pK
value, allows stronger adsorption to the oxide.
Reduction of available functional groups may occur
as cations are complexed from the soil solution (Zunino
and Martin, 1977). Complexation is very effective in
reducing Fe or A1 in solution due to the stability of
the complex (Deb and Datta, 1967). They found that the
stability of the complex is so great that functional
groups are rendered inactive with respect to further
interactions with hydrous oxides. Bloom and McBride
(1979) did research on the complexing ability of metal
ions with humic acids. They observed that humic acids
bind with most divalent metal ions, with the exception
2 +
of Cu as hydrated species. Also, they observed that
humic acids exhibit a strong affinity for trivalent
3 +
ions. The A1 ion is likely bound to three carboxyl
groups, but the case of the mono- and divalent species
adsorption from solution cannot be ruled out (Bloom and
McBride, 1979). Bloom (1979) observed the titration
behavior of Al-saturated organic matter. He observed
that, as the pH of the material is increased, the OH
would most likely form A1(0H) on the organic-matter
exchange sites. As the pH is increased until the
activity of (A1 )(OH ) is exceeded, precipitation of
amorphous AliOH)^ would be induced. Acid addition
on

19
3 +
the other hand results in release of A1 ions into
solution as H+ ions bind to functional groups at
adsorption sites.
Freshly humified clover material adsorption on
allophane was studied by Inoue and Wada (1968). They
found that newly humified clover possessed a greater
capacity for adsorption than humic substances extracted
from soils. Possible inactivation of functional groups
due to ion complexation was suggested as the reason for
the reduction in adsorption (Greenland, 1971). Prefer
ential adsorption of high molecular weight (1,500 to
10,000) decomposition products was observed on allo
phane (Inoue and Wada, 1968).
Different ideas exist in the literature concerning
the stability of Fe-organo mineral complexes. Lev-
ashkevich (1966) determined that humic acids form more
stable bonds with Al-hydroxide gels than with Fe-
hydroxide gels which he stated had a lower capacity for
adsorption. Greenland (1971) stated that a very strong
bond would be formed between the oxide and humic
molecule if several carboxyl or other groups partici
pated. Schwertmann (1966) stated that the transforma
tion of amorphous ferric hydroxide to a crystalline Fe
mineral may be halted due to the bonding of organic
ligands to the mineral. Schwertmann and Fischer (1973)
determined that ferric-hydroxide surface area would be
reduced by organic-ligand adsorption.

20
The following relationship was observed:
S(m^/g) = 76.6 16.4(%C) + 9.56(%Fe) where n=17 and
r=0.94.
This relationship suggests strong covalent bonding
between Fe hydroxide and organic anions. Parfitt et
al. (1977) determined that fulvic acid is adsorbed on
goethite surfaces by ligand exchange at the pH of 6-
6.5. Parfitt and Russell (1977) determined that
mononucleate species, such as benzoate and 2,4-D, had a
low-binding constant and were easily desorbed from
goethite surfaces. Binuclear species such as oxalic
acid were strongly adsorbed on the goethite surface.
Appelt et al. (1975a) measured the adsorption of ben
zoate, p-OH benzoate, salicylate, and phthalate on
Andept soils from Chile. They observed that monoprotic
adsorption was by anion exchange whereas diprotic
adsorption was by anion and ligand exchange.
Organo- Mineral Reactions Affecting P Fixation
Possible Mechanisms
Mechanisms relating to reduction in P fixation on
Fe oxides by organic amendments are not clearly delin
eated in the literature. Singh and Jones (1976) stated
that inorganic P from the decomposition of organic
residues would possibly supply sufficient P to reduce P
fixation such that added P would be in a stable form.
They stated that an organic residue must contain at
least 0.3% P, otherwise added P would be immobilized.

21
3 2
Conversely, Datta and Goswami (1962), utilizing P
tracer techniques, came to different conclusions. The
following excerpt is from their paper:
The increase in the uptake of total P was
again due to a greater uptake of soil and not
fertilizer P, except in red soil, where
the uptake of both soil and fertilizer P
increased. It is, however, expected that, though
organic matter itself has contributed towards the
amount of soil P, it is considered to bear very
little in relation to such a large increase in
total uptake (p 236).
Singh and Jones (1976) also stated that P adsorp
tion could be lowered by blocking adsorption sites with
decomposition products from organic matter. Bhat and
3 2
Bouyer (1968), utilizing P studies, found that the
addition of organic matter to ferruginous tropical
soils lowered P-fixation capacity and isotopically-
dilutable P was also greater. Initial soil pH was 6.6.
Datta and Nagar (1968) using P studies determined
that the uptake of fertilizer P was decreased substan
tially by organic addition in all their experimental
soils except red soils where there was a slight
increase in fertilizer P uptake rather than P uptake
from organic and soil P. Initial soil pH of this red
soil was also 6.6.
Datta and Nagar (1968) suggested that the mecha
nism of organic acid production could solubilize
certain insoluble phosphates present in the soil. This
explanation was given due to large amounts of soil

22
rather than fertilizer P uptake on all experimental
soils except the red soil.
Deb and Datta (1967) stated that organic anions in
acidic medium are very effective in complexing Fe
and/or A1 in solution. They observed reduction of Fe
and A1 activity preventing precipitation as insoluble
phosphate compounds.
Observations
Conclusions relating to the reduction of P fixa
tion by organic addition by previous researchers are
mixed. Appelt et al., (1975b) found that the
adsorption of benzoate, p-OH benzoate, salicylate,
phthalate, and humic and fulvic acids extracted from
the surface soil of a Typic Dystrandepts did not block
P adsorption sites on subsurface samples of that soil.
Soil pH values ranged from A.8 to 5.4. High
extractable Al levels were observed. In their studies
no characterization of the organic material relating to
sesquioxide ash and P fixation capacity was given.
Yuan (1980) studied the adsorption of phosphate and hot
water-extractable soil organic matter on acidic soils
and synthetic Al silicates. He found that pretreatment
of organic material had no effect on an Eutrandept: a
slight effect on a Haplaquod, and partial reduction of
P fixation on a Paleudult. He observed that organic
material adsorption was increased by an increase in the
rate of material applied, but the amounts of P retained

23
by the soils were constant suggesting that adsorption
sites for P and organic material were different.
Greenland (1971) determined that organo-mineral
studies should be performed utilizing pure mineral and
organic materials. He determined that previous reac
tions may block adsorption sites on hydrous oxides.
Also, organic functional groups could be rendered inac
tive by metal complexation.
Nagarajah et al., (1970) evaluated the competitive
adsorption of polygalcturonate (a root exudate with
atomic weight of approximately 25,000) on synthetic
goethite. At pH 4.0, polygalcturonate decreased phos
phate adsorption by chelation of Fe or adsorption on
the goethite surface as determined in their experi
ments. Hashimoto and Takayama (1971) reported that
humic acid, nitrohumic acid, and nitrohumate salts
inhibited P fixation on a synthetically prepared
goethite, ferric hydroxide, and ferrous orthosilicate,
but not by lepidocrocite or amorphous Fe oxide hydrate.
Manojlevic (1965) conducted laboratory studies with
humic acid derived from dung and manure on high-P-
fixing soils. Humic acids decreased P fixation from
granular superphosphate which was in contact with the
soil for 4 mo. Moshi et al., (1974) measured phosphate
adsorption from two profiles (one cultivated and one
under forest environment) of Kikuyu red clay from
Kenya. He reported that surface-ads orbed organic

24
components reduced the positive charge on the soil sur
face. They found a linear correlation (p>.01) between
increasing percentage of organics and reduction of pos
itive charge. Phosphate adsorption at pH 5.0 was
reduced by the presence of organic matter. They also
observed a linear correlation (p>.01) between a
decrease of phosphate adsorption and increasing C%.
Hinga (1973), also obtained similar results on Kenya
soils.

CHAPTER III
ORGANIC ADSORPTION EXPERIMENT
Introduction
The mechanisms of humic and fulvic anion bonding
to Fe minerals ares by specific adsorption or ligand
exchange (Parfitt et al., 1977). The process is not
sensitive to electrolyte concentration, although it is
sensitive to pH since adsorption maximum occurs near
the pH corresponding to the pK of the acid species,
usually carboxylic, near pH 5.0 (Greenland, 1971). He
found that a very strong bond was formed between oxides
and humic molecules since most functional groups of the
organic acid participated in the adsorption.
Schwertmann (1966) stated that the transformation of
amorphous ferric hydroxide to a more crystalline Fe
mineral may be stopped due to the bonding of organic
liquids to the mineral. Parfitt et al. (1977) deter
mined that fulvic acid is adsorbed on goethite surfaces
by ligand exchange within the pH range of 6 to 6.5.
The objectives for the organic adsorption experi
ment were as follows: 1) To determine pH for maximum
clover decompositional product adsorption and 2) To
determine time required for transformation of amorphous
Fe(0H)g to a crystalline phase in relation to clover
application.
25

26
Materials and Methods
Soil
An Orangeburg series soil (fine, loamy, siliceous,
thermic, Typic Paleudult) was obtained from the Agri
cultural Research and Education Station near Quincy,
FL. Two portions of the profile under forest environ
ment were sampled. The surface soil, devoid of organic
litter, was obtained corresponding to the A horizon.
This sandy soil was to be the matrix for FeCOH)^ addi
tion. Subsurface B horizon samples were obtained of
the corresponding soil profile.
Characterization
Both samples were characterized physically, miner-
alogically, and chemically. Particle size distribution
was determined by the methodology of Day (1965) for the
clay fraction and sieving to determine sand and silt
fractions. Pretreatment with ^2^2 organic
component s.
Mineralogical characterization included identifi
cation of clay fraction minerals. Pretreatment
included removal of organic matter with H C>2 ant* free
Fe oxides with citrate-bicarbonate-dithionite extrac
tion (CDB). Free iron oxide and A1 concentrations in
CDB extracts were determined using atomic adsorption
spectrophotometry (Kunze, 1965).
Chemical characterization included cation exchange
capacity by the summation method as described by

27
Chapman 1965). Organic carbon was determined by
dichromate-oxidation techniques (Walkley and Black,
1934). Soil pH was determined in a 1:1 ratio of soil to
water (McLean, 1982). Phosphorus fixation was deter
mined by methodology of Fassbender and Igue (1967) in
which 5 g of soil were placed into a centrifuge bottle
with 100 mL of 100 mg P/L solution. The bottle was
shaken for 6 hours at 180 excursions/min. Separation
between solution and solid phase was accomplished
through millipore filtering (.2 u). Extracts were ana
lyzed for P using methodology described by Murphy and
Riley (1962). Results are given in Tables 3-1 and 3-2.
Fe(OH)^ Synthesis
Amorphous ferric hydroxide was prepared by poten-
tiometrically titrating 2 M Fe(N03)3 with 6 M KOH to pH
8.1 (ZPC). Equivalent concentrations of both reagents
were used in precipitating the Fe(0H)3 (Fig 3-1). To
remove the soluble KN03 formed, approximately 2 L of
deionized water was filtered through 250 g of precipi
tate resulting in negligible concentrations of K+ and
N03 A suspension of Fe(0H)3 in H30 was prepared with
a concentration of approximately 1 M as Fe(0H)3# Rates
of 0 and 5.6 g Fe as Fe(0H)3 were applied to Orangeburg
surface soil by complete mixing.

Table 3-1 Characterization Data of Orangeburg Surface Soil
Mineralogy
Particle
Size
pH (H20) 0C
CDB +
P Fixation
sand silt
cl ay
1 : 1
%
Fe A1
%
-Fe(OH) +Fe(OH)-
mg/kg
Kaolinite
Quartz
Gibbsit e
14 ^ intergrade
85 1.2
13.8
4.9 1.36
0.31 0.08
190 640
Extractable Bases++
Ca Mg Na K Extractable Acidity+++
cmol (+)/kg
0.77 0.32 0.04 0.04 5.70
+ Citrate-dithionite-bicarbonate
++ NH.OAc (1M) extraction (pH 7.0)
+ + + BaC^-TEA extraction (pH 8.2)
K>
00

Tab]L e !3- 2 Characterization Data of_Oraneburg_Subsoil
Mineralogy
Particle Size pH (H^O)
OC
CDB +
P Fixation
sand silt clay 1:1
%
Fe A1
%
mg/kg
Kaolinite
Quartz
Gibbsit e
14 intergrade
Goethite
Ca Mg Na K Extractable Acidity+++
Cmol (+)/kg
57.6
8.6
33.8
5.1
0.40 0.84 0.11
800
Extractable Bases++
0.70 0.86 0.03 0.04
6.21
+ Citrate-dithionite-bicarbonate
++ NH.OAc (1M) extraction (pH 7.0)
+++ BaCl^-TEA extraction (pH 8.2)

Potentiometric Titration of 450
Mil1iequival ents Fe as F e(NO)^ With KOH.
Fig. 3-1

7
Milliequivalents Oil
u>

32
Clover Production
White clover (Trifolium repens) was grown hydro-
ponically to insure organic functional groups did not
contain high sesquioxide ash contents. Hydroponic
_3
solution possessed ionic concentrations of 10 M P,
10-2*2 M K, 10-1,8 M N03, lO"2*3 M Ca, 10_2'7 M Mg, 10~
2 7 -3 5
M SO., 10 M Fe, with micronutrient concentra-
A
tions of 0.5 ug B/ml, 0.5 ug Mn/ml, 0.05 ug Zn/ml, and
0.02 ug Cu/ml (Hoagland and Arnon, 1938). Solutions
were continually aerated and replaced biweekly. Clover
biomass was harvested every A0 d and the material was
then dried and ground to pass a 2- mm sieve.
Liming Curve and Organic Adsorption Measurements
To determine the maximum organic adsorption to
Orangeburg topsoil, an incubation study was initiated
in which 50 g samples were treated with or without 5.6
g Fe as Fe(0H)3> plus or minus 3.15 g/kg dried and
ground clover, at CaCO^ rates of 0, 0.5, 1.0, 1.5, and
2.0 cmol CaCO^/kg soil. Reagent grade CaCO^ was mixed
with soil and incubated for 2 w at 25C and 8% moisture
on a weight basis. Dried and ground clover was then
applied and allowed to decompose for 30 d. Duplicate
samples were prepared.
Organic anion extraction was performed by extract
ing 10 g of soil with 20 mL of 0.01 M NaCl and shaking
for 30 min (Stevenson, 1982). Samples were centrifuged
and aliquot decanted. Electrical conductivity of each

33
aliquot was measured prior to increase of solution pH
to pH 7.0 with 0.1 M NaOH for adsorption measurements
of humic and fulvic acids at 465 nm (Chen et al.,
1977). Soil pH was measured in water (1:1 ratio)
(McLean, 1982).
Crystallization of Fe(OH)^
Solid Fe(0H)g and Fe(0H)g associated with the clay
fraction of Orangeburg soil were monitored over a 6 mo
period for crystal formation. Both samples were sub
jected to wetting and drying cycles over time. X-ray
diffraction (XRD) techniques were employed using Cu K
radiation to monitor changes. Differential scanning
calorimetry (DSC) techniques were also employed.
Results and Discussion
Organic Adsorption Experiment
Study of organic adsorption on soil solids can
produce confounding results in impure systems due to
previous reactants on solid surfaces or inactivity of
organic functional groups due to ion complexation
(Greenland, 1971). For this reason, pure phases were
prepared for study. Amorphous ferric hydroxide was
applied to the Orangeburg sandy soil which was the
matrix for the mineral addition. Follett (1965)
observed that ferric hydroxide reacts with basal-plane
surfaces of kaolinite, which is the primary clay min
eral in the Orangeburg soil. Since Orangeburg soil is

34
acidic (pH 4.9), a liming curve after FeCOH)^ applica
tion was essential to determine pH for maximal organic
adsorption. Also the pH of the soil must be greater
than the dissociation constant of the organic acid (pH
> 5.0) to activate organic anions (Greenland, 1971).
Clover rates were similar to residue rates added to the
soil for cover crop production.
Results from the incubation study with respect to
treatment are given in Fig. 3-2 to 3-9. Organic ad
sorption relationships produced by changes in pH are
given in Fig. 3-2 to 3-5 and adsorption relationships
with change in ionic strength are given in Fig. 3-6 -
3-9. Numbers in parenthesis in these figures are soil
pH values. Ionic strength was calculated to be the
total ionic strength of solution minus the ionic
strength of the 0.01 M NaCl solution. Total ionic
strength was calculated by the following equation:
u = 0.013 EC
where 0.013 is a constant and EC is electrical conduc-
_ £
tivity expressed in millimhos cm (Griffin and
Jurinak, 1973).
Stevenson (1982) stated that organic adsorption to
clay surfaces was sensitive to changes in ionic
strength. The mechanism of adsorption is by ionic

Absorbance (445 nm) of Humic Acid in Solution
35
0.6
0.5
0.4
0.3
0.2
0.1
5.0
Fig. 3-2
t 6^6
pH
Effect of Soil pH on Organic Release From
Orangeburg Topsoil.

Absorbance (445 nm) of Humic Acid in Solution
36
0.6
0.5
0.4
0.3
0.2
5.0
6.0
6.8
pH
Fig. 3-3
Clover Decompositional Product Adsorption
to Orangeburg Topsoil as Influenced by
Soil pH.

Absorbance (445 nm) of Humic Acid in Solution
37
pH
Fig. 3-4 Effect of Soil pH on Organic Release From
Orangeburg Topsoil + FeCOH)^.

Absorbance (445 nm) of Humic Acid in Solution
38
pH
Fig. 3-5 Clover Deconpositional Product Adsorption
to Orangeburg Topsoil + FeiOH)^ as
Influenced by Soil pH.

39
bonding. Similar results were obtained from the treat
ments of Orangeburg soil without Fe hydroxide addition.
Increasing lime rates increased soil pH from 4.9 to 6.7
(Figs 3-2 and 3-3) but also increased solution ionic
strength due to increased Ca activity (Figs 3-6 and
3-7). Calcium does not form a strong complex between
negatively charged clay and humic acid, but is effec
tive as a bridge between ions (Stevenson, 1982).
Greenland (1971) observed that organic matter bound to
2 +
clay through Ca cation bridging was easily displaced
by monovalent ions such as NH^ + or Na+. Increases in
pH increase negative charges on mineral surfaces
(Kaolinite) and therefore cation exchange capacity.
Near pH 6.2, less organic anions were extracted by
+ 2 +
NaCl. Possibly Na and Ca ions increased exchange-
3 + 3 +
able A1 or Fe levels. Aluminum and Fe at low con
centrations could reduce organic anions by flocculation
(Stevenson, 1982). Results are inconclusive above pH
6.2.
Stevenson (1982) also stated that organic adsorp
tion to hydrous oxides occurred by ligand exchange or
covalent bonding. Only anions that bind strongly to
oxide surfaces could replace organic anions. This mech
anism is insensitive to solution ionic strength but
highly sensitive to pH. Salt solution extraction did
not affect organic adsorption. Results in Fig. 3-4, 3-
5, 3-8, and 3-9 support this mechanisms organic

Absorbance (445 nm) of Humic Acid in Solution
40
Ionic Strength
Fig. 3-6
Effect of Solution Ionic Strength on
Organic Release From Orangeburg Topsoil.

Absorbance (445 nm) of Humic Acid in Solution
41
Ionic Strength
Fig. 3-7 Clover Decompositional Product Adsorption
to Orangeburg Topsoil as Influenced by
Solution Ionic Strength.

Absorbance (445 nm) of Humic Acid in Solution
42
Ionic Strength
Fig. 3-8 Effect of Organic Release From Orangeburg
Topsoil + Fe(OH)_ as Influenced by
Solution Ionic Strength.

Absorbance (445 nm) of Humic Acid in Solution
43
Ionic Strength
Fig. 3-9
Clover Decompositional Product Adsorption
to Orangeburg Topsoil + Fe(OH)_ as
Influenced by Solution Ionic Strength.

44
covalent bonding. Organic adsorption was not affected
by ionic strength as seen in Fig. 3-8 and 39 but was
greatly affected by changes in soil pH (Fig. 3-4 and 3-
5). Ionic strength ranged from 0.016 to 0.022 units
whereas pH changes within small ranges of ionic
strength greatly affected adsorption measurements. As
pH increases above pH 5.0, organic anions are formed.
However, FeCOH)^ possessed a variable charged surface
so that increases in pH could reduce net positive
charge and adsorption sites on mineral surface thereby
resulting in reduced adsorption. Maximal organic
adsorption occurred at pH 6.3 with residue amendment.
It is also important to observe the effectiveness of
organic adsorption of the FeCOH)^ treated soil compared
to untreated soil. Several orders of magnitude of
adsorption exist in the binding capacity, making the
Fe(OH)^-treated soil an excellent sorbant system for
organic anions.
Crystallization of Fe(OH)^
Changes in crystallization of FeiOH)^ affects sur
face area and reactive sites for organic anion and P
adsorption. Mineralogy of solid phase FeiOH)^ and
FeiOH)^ treated Orangeburg soil were observed over a 6
m period. Solid FeiOH)^ endured wetting and drying
cycles whereas FeiOH)^ treated soil with and without
clover amendment was under a cropping system. At no
time during the 6 m period did the solid FeiOH)^

45
exhibit crystallinity as observed by XRD or DSC method
ologies. The same result was obtained for the FeCOH)^
treated soil. Differential Scanning Calorimetric plots
of Orangeberg soil + FeCOH)^ clay fractions without
clover amendment and with clover amendment are given in
Fig 3-10 and 3-11, respectively. No Fe mineral en-
dotherm was observed. However, endotherms for both
gibbsite and kaolinite, were observed.
Conclusions
Adsorption study observations in conjunction with
previous research suggested that FeCOH)^ treated soil
exhibited covalent bonding of organic anions whereas
treatments without FeCOH)^ exhibited ionic bonding via
cation bridging. Maximum adsorption of organic con
stituents occurred at pH 6.3 on the FeCOH)^ treated
soil with clover amendment compared to pH 6.2 for
Fe(0H)g untreated soil. After 6 m of investigation,
solid FeCOH)^ and soil FeCOH)^ remained in an amorphous
state.

Fig. 3-10 Differential Scanning Calorimetry Plot of
Orangeburg Topsoil With FeCOH)^ Addition.

Heat Flow (mJ/sec)
-2.0
I. ,1 > .... mA
130 250 490 610
Temperature (Deg C)

Fig. 3-11 Differential Scanning Calorimetry Plot of
Orangeburg Topsoil with FeCOH)^ and Clover
Addition.

Temperature (Deg C)
vO

CHAPTER IV
PHOSPHATE AND ORGANIC AMENDMENT STUDY
Introduction
Reduction of plant available phosphorus in acidic
soils causing an agronomic yield reduction has plagued
man for many years. The problem is produced by reac
tions of phosphates with Fe and A1 hydroxides, alumi
nosilicates and/or the ions released from dissolution
of these minerals (Chu et al., 1962; Lindsay, 1979;
Fox, 1974; Hingston et al., 1974).
A possible management alternative for reducing P
sorption could be addition of organic amendments.
Moshi et al., (1974) measured phosphate adsorption from
two profiles (one cultivated and one under forest envi
ronment) of Kikuyu red clay from Kenya. They reported
that surface-adsorbed organic components reduced the
positive charge on mineral surfaces. There was a high
statistical linear correlation between increasing per
centage organic carbon and reducing positive charge.
Since positive charge was reduced, phosphate adsorption
at pH 5.0 was reduced by the presence of organic
matter. Hinga (1973) obtained similar results on Kenya
soils. Yuan (1980) found that pretreatment with
organic material resulted in partial reduction of P
fixation on a Paleudult.
50

51
Mechanisms producing reduction in P fixation might
include 1) release of P for organic components, 2)
blockage of P-adsorption sites with decompositional
products from organic amendment, 3) complexation of
solution A1 and Fe by organic functional groups, and 4)
solubilization of fertilizer reaction products such as
dicalcium phosphate (DAP) by acidity produced from the
humification process (Singh and Jones, 1976). The
objectives of this study are to assess the effective
ness of clover addition to highly-weathered soils in
reducing P fixation as measured by dry matter plant
yield, P uptake, extractable P levels, and changes in
surface charge on soil colloids.
Materials
Soil
An Orangeburg topsoil as described in Chapter 3
was used in the clover amendment experiment. Amorphous
FetOH)^ was prepared and applied as described by previ
ous methodology. The soil was limed to pH 6.3 utiliz
ing the liming curve developed during preliminary
experimentation, and incubated for 2 wk at 25C at 10%
moisture on a weight basis. Dried and ground clover
was then completely mixed with predetermined treatments
and incubated for 30 d prior to fertilizer addition.

52
Clov er
White clover was grown hydroponically to insure
reactivity of organic functional groups. Hydroponic
methodology is described in Chapter 3.
Fertilizer
Pots used in the glasshouse study contained 3 kg
of soil on a dry weight basis. Fertilizer applications
(N, P, K, Mg) were adjusted by treatment assuming 50%
mineralization from clover application. Total nutrient
addition included 100 mg N/kg as NH^NO^ 140 mg K/kg as
KC1. Diammonium phosphate was applied at rates equiva
lent to 0, 50, and 100 mg P/kg. Supplemental nutrient
addition to pots included 19.8 mg Mg as MgS0^*7H20,
11.4 mg Zn as ZnSO^'/H^O, 5.09 mg Ca as CaSO^'SH^O and
1.2 mg B as Na2B27* 1OH2O.
Methods
Incubation Study
To investigate soil P retention, an incubation
study was conducted with three soils. These were
Orangeburg, Orangeburg + 5.6 g Fe/kg as FeiOH)^, and
Orangeburg subsoil. Each soil was amended with dried
and ground clover at rates of 0, 1.58, and 3.16 g/kg
over times of 30, 60, 90 d. Each soil had been previ
ously limed to pH 6.3 and incubated for 2 w. Soil P
retention was determined at each time interval by
shaking 5 g of sieved soil with 100 ml of solution con
taining 100 mg P/L as I^PO^ for 6 h (Fassbender and

53
Igue, 1967) in duplicate. After shaking, aliquots were
filtered through a 0.2 urn membrane filter disk and
analyzed for orthophosphate (Murphy and Riley, 1962).
Phosphorus fixation was determined by subtraction.
Soil pH at each time interval was determined in a 1:1
soil to water suspension. Analysis of variance was
performed on the split plot design utilizing time as a
main plot with soil and clover addition as subplots.
Glasshouse Study
A 3 X 2 X 3 factorial experiment using 0, 50, and
100 mg P/kg soil, 0 and 5.6 g Fe/kg as Fe(OH)^ and 0,
1.58 and 3.15 g clover/kg in split-split plot design
with three replications was conducted in a glasshouse.
Phosphate addition was the main plot with FeiOH)^ addi
tion as the sub plot, and clover addition the sub-sub
plot. Two crops of Zea mays L. were grown for 50 d
each to determine initial and residual effectiveness of
fertilizer. Treatments were limed and refertilized
with previous rates before initiation of a third crop.
Variables measured include dry matter yield, uptake of
P, Ca, Mg and K, A1 and Fe concentrations within plant
tissue. Soil measurements included Truog and Bray 2
extractable P levels, soil pH, and organic C levels.
Plant samples were analyzed in the following manner:
0.10 g of dried and ground tissue, passing a 1 mm
sieve, was placed in a 50 mL beaker and oxidized in a
muffle furnace at A50C. The ash was further digested

54
with 3 M HNO^, evaporated to dryness on a hotplate,
with removal of excess HNO^ by placing each beaker into
the muffle furnace at 450C for 10 m. After cooling,
25 mL of 5 M HC1 were added to the beaker, placed on a
hotplate and evaporated to dryness to completely
oxidize plant material. After cooling, 1 mL of 5 M HC1
was placed in the beaker with water and diluted to a
final volume of 50 mL. Ionic concentrations of Ca, Mg,
K, Al, and Fe were determined by Inductively Coupled
Argon Plasma spectrophotometry. Plant P concentrations
were determined by methodology described by Murphy and
Riley (1962).
Soils were sampled after each maize crop. Soil pH
was determined in 1:1 soil to water ratio (McLean,
1982). Organic C levels were determined by methodology
described by Walkley and Black (1934).
Since reaction products of DAP are CaHPO^^H^O,
CaHPO^, and colloidal ferric phosphate with Orangeburg
soil, proper extractants needed to be chosen for
extraction of these phases. Ballard (1974) compared
various extractant effectiveness on a variety of phos
phate reaction products as independent solid phases and
those phases mixed with soil. In his research Truog
reagent (0.001 M H2S04 + 3 g (NH4)2S04) extracted 100%
of P applied as dicalcium phosphate (DCP) as a solid
phase and 98% DCP mixed with Leon fine sand. Only 2%
of P applied as colloidal ferric phosphate (CFP) as a

55
solid and mixed with Leon fine sand was extracted.
Bray 2 (.03 M NH^F + 0.1 M HC1) extracted 98% P from
CFP and CFP mixed with Leon fine sand. Sequential
extractions for P were performed with Truog and Bray 2
solutions. Extraction methodology was as follows: 2 g
of soil were placed in a centrifuge tube with 25 ml of
Truog reagent. Samples were shaken at 180 excursions
per minute for 30 m and centrifuged. Aliquots were
filtered through Whatman #42 filter paper. Soil sam
ples were again extracted with Bray 2 solution. Twenty
mL of extractant were added to the soil sample and
shaken for 1 m. Aliquots were immediately filtered
through Whatman #42 filter paper. Soil P concentra
tions were determined by methodology described by
Murphy and Riley (1962).
Surface Charge
To determine net electric charge and ZPC of 1)
FeiOH)^ treated soil, 2) FeiOH)^ treated soil + 100 mg
P/kg, 3) FeiOH)^ treated soil + 3.15 g clover/kg, and
4) FeiOH)^ treated soil + 100 mg P/kg + 3.15 g
clover/kg, potentiometric titrations were performed.
Samples were obtained after the first cropping period
of the glasshouse experiment. Methodology described by
Laverdiere and Weaver (1977) was performed in which 10
g of sample were weighed into 250 mL beakers with addi
tion of 100 mL either 0.01, 0.1 or 1.0 M NaCl. Samples
were allowed to equilibriate for 60 m and pH was

56
determined. Soil suspensions were titrated with 0.02 M
HC1 under continuous stirring. Salt solutions without
soil were also titrated as a baseline for charge
determination by subtracting H+ concentrations of blank
titrations at a given pH from H+ concentrations of the
soil suspension.
SEM Study
Clay fractions from 1) Orangeburg + FeCOH)^ + P
and 2) Orangeburg + Fe(0H)g + P + 3.15 g clover/kg for
study under the scanning electron microscope were
obtained by sieving the soil through a 300mesh sieve,
washing with water at pH 10, and collecting the
aliquot. The clay-silt suspensions were centrifuged
for 5 m at 1500 RPM. Gravimetric determinations of
clay in suspension was performed. Samples were diluted
by factors of 2, 3, 5 and 10, applied on a carbon-
coated stub, and magnified within ranges of 450X to
10,000X.
Results and Discussion
Incubation Study
An incubation study was developed to determine
effects of time, soil, and clover amendment relating to
P fixation capacity of the soil. As shown in Table 4-
1, a triple order interaction was obtained. Phosphate
fixation capacity was affected by times of 30, 60, or
90 d of incubation, clover application at rates of 0,
1.58 and 3.15 g/kg and the type of soil matrix.

57
Table 4-1. Effect of Experimental Parameters on
P Retention Capacity
Source
df
Mean Square
p > F
Time
2
279999
0.0001
REP
1
2759
0.39
Error a
2
1245
Soil
2
550367
0.0001
Clov er
2
3058
0.44
Soil X Time
4
11426
0.03
Clover X Time
4
13726
0.02
Soil X Clover
4
11474
0.03
Soil X Clover
X Time
8
13491
0.01
Error b
24
3611

58
Since a triple order interaction was obtained, re
sponse surface equations were developed for each soil
over clover application rates at each time of compari
son. Equations are given in Table 4-2. Graphs of
results at each time interval are given in Fig. 4-1
through 4-3.
Orangeburg Topsoil
Orangeburg topsoil is a sandy soil (85% sand, with
iron concretions (0.31%)). Increasing rates of applica
tion of clover increased P fixation capacity after 30
d. After decomposition of clover, organic functional
groups were available for reaction with soil
components. Calcium can be bound ionically to organic
functional groups (Bloom and McBride, 1979) thereby
attaching orthophosphate to organic components and
reducing P concentration in solution. With clover
addition there was an increase in soil pH from 6.4 to
6.7. Differences in pH could also be induced by pre
cipitation of DCP.
After 60 d of incubation, there was a slight
increase in soil pH from 6.4 to 6.7 without clover
treatment. Increased P fixation was also noted possi
bly due to the formation of a calcium phosphate precip
itate. Clover-amended treatments decreased P fixation
capacity, although it remained higher than the 0 clover
application rate. Singh and Jones (1976) reported
decreases in P fixation capacity of organic

59
Table 4-2
Time (d)
Response Surface Equations Relating P
Fixation Capacity of Soils With Clover
Addition Over Time.
Response Surface Equation
Correlation
Coefficient
Orangeburg
30
P
f ix
=
196
-
81 clover +
69 clover
z
r
=
0.71
60
P
f ix
=
202
-
6 clover +
8 clover2
2
r
=
0.49
90
P
f ix
=
274
+
252 clover
2
- 76 clover
2
r
=
0.67
Orangeburg +
5.6 g Fe
30
P
f ix
=
986
-
467 clover
+ 111 clover2
2
r
=
0.83
60
P
f ix
=
240
+
107 clover
2
- 36 clover
2
r
=
0.78
90
P
f ix
=
517
+
72 clover -
21 clover2
r2
=
0.29
Orangeburg
Subsoil
30
P
f ix
=
936
-
177 clover
2
+ 41 clover
2
r
=
0.30
60
P
fix
=
6 84
-
130 clover
2
+ 26 clover
2
r
=
0.99
90
P
f ix

810
_
116 clover
2
+ 33 clover
2
r

0.83

60
Clover Applied g/kg
Phosphate Fixation Capacity
Amended With Various Clover
30 Days of Incubation.
ig. 4-1
of Soils
Rates After

61
Clover Applied g/kg
Phosphate Fixation Capacity
Amended With Various Clover
Days of Incubation.
Fig. 4-2
of Soils
Rates After 60
P fixed mg/kg

62
Clover Applied g/kg
Phosphate Fixation Capacity
Amended With Various Clover
Days of Incubation.
Fig. 4-3
of soils
Rat es After 90

63
treated soils after 30 d incubation due to P mineral
ization from organic substrates. Mineralization of P
from microbial populations may have produced this
result.
After 90 d of incubation, there was a slight
decrease of soil pH from 6.6 to 6.3 without clover
treatment. Increased P fixation was observed compared
to 30 and 60 d incubation periods. The 3.15 g/kg
clover treatment remained stable with respect to P fix
ation data from 60 d incubation time. However the 1.58
g/kg clover treatment increased soil P fixation
capacity.
Orangeburg Topsoil + Fe(OH)^
After 30 d of incubation, treatments receiving
clover applications possessed lower P fixation capaci
ties than did treatments without clover application.
Treatments receiving 1.58 g/kg clover had a lower P
fixation capacity than 3.15 g clover/kg. Possibly de-
compositional products of clover were bound to the iron
hydroxide surface as was the case in the clover amend
ment experiments of blocking positive charged sites
available for P fixation. Soil pH ranged from 6.5 to
7.2 so that acid forming ions of Al, Fe, and Mn were
not available for precipitation or ionically binding
orthophosphate to organic components. Precipitation of
calcium phosphates at pH 7.2 from the 3.15 g clover/kg

64
soil treatment may have occurred thereby increasing P
fixation capacity for that treatment.
After 60 d of incubation, total P fixation of all
treatments was reduced, possibly due to P mineraliza
tion from microbes and clover residues. Decreasing P
fixation with increasing clover application was ob
served. Soil pH also increased possibly due to a self-
3 + 2 +
liming effect of Fe to Fe with hydroxyl release
from water applications reducing net positive charge
and P-fixation capacity.
After 90 d of incubation, P fixation capacity was
increased to near initial levels. Cl over-amended
treatments, although lower in P-fixation capacity than
unamended treatments, did not produce substantial P-
fixation reduction as was noted initially.
Orangeburg Subsoil
Orangeburg subsoil contains 34% material in the
clay-size fraction with kaolinite as the dominant clay
mineral. The clay surface is coated with goethite
which is 1.3% of the total weight of the soil.
Orangeburg subsoil results are similar to those
obtained from Orangeburg + FeCOH)^ but clover applica
tion has less effect in reducing P fixation. Clover
application at 30 d reduced P-fixation slightly com
pared to untreated soil. Greater total surface area of
goethite with Orangeburg subsoil compared to Fe(OH)^

65
applied to Orangeburg topsoil reduced cl over-amendment
effectiveness.
At 60 d of incubation, similar trends of reduction
in P fixation capacity with increased soil pH were
observed. Clover amendments lowered P fixation capac
ity compared to treatments without clover.
At 90 d, the effectiveness of the clover amendment
was negligible.
Glasshouse Study
A glasshouse study was conducted to determine
clover amendment effectiveness in reducing P fixation
in relation to crop production. Three crops of maize
were grown for 50 d each. Results from experimental
parameters from each cropping period will be discussed.
Crop 1
Yield
Dry matter yield was affected by P rate, FeCOH)^
addition, and clover application as determined by a
triple-order interaction. As seen in Table 4-3 and
Fig. 4-4, without application of P, no difference in
yield was obtained with clover applications on the
Fe(0H)g treated soil. Ferric hydroxide provided a sink
for indigenous soil P to be bound as well as P
available from mineralization of clover. Without
FeCOH)^ addition, yield was increased from clover
applications with P additions. This effect could have
been from clover functional groups binding

66
Table 4-3 Yield Response Surface Equations Obtained
From the First Cropping Period.
Clover applied
g/kg
Response Surface Equation
Correlation
Coef ficient
P = 0
mg/kg
0
Y
= 0.97
- 0.07
Fe
2
r
=
0.61
1.58
Y
= 0.73
- 0.04
Fe
2
r
=
0.18
3.15
Y
= 3.17
- 0.48
Fe
2
r
=
0.68
P = 50
mg/kg
0
Y
= 2.07
- 0.22
Fe
2
r
=
0.73
1.58
Y
= 2.13
- 0.20
Fe
2
r
=
0.52
3.15
Y
= 5.43
- 0.61
Fe
2
r
=
0.63
P = 100 mg/kg
0
Y
= 6.57
- 0.88
Fe
2
r
=
0.95
1.58
Y
= 3.37
- 0.17
Fe
2
r
=
.18
3.15
Y
= 5.37
- 0.20
Fe
2
r
=
0.25

67
o
O.
oo
TJ
I
H
>~
SZ
CD
U
Q
Fig. A-A Plant Dry Weight Yield Affected by FeCOH)^
and Clover Application at the 0 mg/kg P
Rate During the First Cropping Period.

68
to Al or Fe ions from solution reducing precipitation
of indigenous soil P. Although no differences in soil
pH were observed, the pH of both soils had dropped to
5.2 which would increase A1 and Fe activity in solu
tion. Also, this effect may have been produced by P
released from clover mineralization. Initially, P fer
tilizer was added (7.0 mg P/kg) to the clover control
and 3.5 mg P/kg to the 1.58 g clover/kg
treatment since the literature suggests that approxi
mately 50% of organic P is released as orthophosphate
(Lockett, 193 8). Application of 3.58 g clover/kg was
equivalent to adding 14 mg/P kg soil. Possibly release
of P from clover later in the cropping period resulted
in enhanced yield rather than immediate solubilization
of fertilizer P.
Application of 50 mg P/kg increased plant yield
compared to that without P. FetOH)^ again decreased
plant yield. However, increasing application
rates of clover increased plant yield on Fe(0H)g
treated soil (Table 4-3 and Fig. 4-5). It appeared
that P was more available on FeiOH)^ treated soils due
to blockage of P adsorption sites by organic ligands
from clover application. Increase in yield of treat
ments without FeiOH)^ addition may have been produced
by binding A1 and Fe by organic ligands. Doubling of
dry matter yield from clover addition of 3.18 g

69
"O ETTET
Fe Applied g/kg
Fig. 4-5 Plant Dry Weight Yield Affected by Fe(OH)3
and Clover Applications at the 50 mg/kg
P Rate During the First Cropping Period.
Dry Weight Yield g/pot

clover/kg soil could not have been produced solely by P
release at the rate of 7.0 mg P/kg) .
Applications of 100 mg P/kg increased dry weight
yield compared to the 50 mg P/kg rate (Table 4-3 and
Fig. 4-6). Ferric hydroxide treatments decreased maize
yield but an incremental increase in yield was observed
with increasing clover applications. Yield was more
than tripled when clover was applied at 3.15 g
clover/kg soil. Phosphorus availability appeared to be
greater due to clover pretreatment. Results agree with
the previous incubation study relating to P availabil
ity with Fe(OH)^ treatment in acidic (pH 5.2) ranges.
Greater yield was obtained without clover application
if Fe(OH)^ was not introduced into the soil system.
Cation bridging of P to organic functional groups may
have produced this result.
P uptake
Phosphorus uptake by maize plants was affected by
amount of P or FetOH)^ applied. Increasing P rates
increased P in plants while addition of FetOH)^ reduced
P uptake. With increasing rates of clover applied
(Table 4-4 and Fig. 4-7, 4-8 and 4-9), enhanced P
uptake was obtained. Mechanisms relating to clover
amendment effectiveness were not determined. Yield
data appears to relate well to P uptake observations.
Binding of Fe or A1 by organic functional groups or

Table 4-4 Phosphorus Uptake Response Surface Equations Obtained From First Cropping
Period.
Clover applied Correlation
g/kg Response Surface Equation Coefficient
0 P uptake = .004 + 0.06 P + 0.05 Fe 0.01 P*Fe r2 = .91
1.58 P uptake = .37 + .04 P .02 Fe .003 P*Fe r2 = .74
3.15 P uptake = 1.90 + .05 P .26 Fe .004 P*Fe r2 = .72

72
Plant Dry Weight Yield Affected by Fe(OH)
and Clover Applications at the 100 mg/kg
Rate During the First Cropping Period.
Fig. 4-6
Dry Weight Yield g/pot

73
4-J
O
CL
O0
TO
1
a.
a.
Fig. 4-7 Phosphorus Uptake by Maize as Affected by
Fe(OH) and P Application at the 0 g/kg
Clover Rate During the First Cropping
Period.

74
o
o.
oo
E
(0

co
tm S3
Fe Applied g/pot
Fig. 4-8 Phosphorus Uptake by Maize as Affected by
Fe(OH), and P Application at the 1.58 g/kg
Clover Kate During the First Cropping
Period.

75
o
a.
\
oo
E
cu
co
U
Q.
"O O'
Fe Applied g/kg
Fig. 4-9 Phosphorus Uptake by Maize as Affected by
FeCOH)^ and P application at the 3.15 g/kg
Clover Rate During the First Cropping
Period.

76
bonding of organic ligands to Fe(OH)^ surfaces would
explain the results obtained.
Truog Extractable P
A reaction product of DAP is dicalcium phosphate
(Lindsay, 1959). Truog reagent is a good extractant
for this phase (Ballard, 1974). Preliminary extraction
with Truog reagent produced an Fe-clover interaction.
Addition of Fe(OH)3 reduced Truog extractable P levels
drastically (Fig. 4-10, 4-11 and 4-12). Without clover
application, P addition of 100 mg/kg slightly increased
Truog P levels which would apply to the dicalcium phos
phate fraction. Inconclusive results were obtained
with Fe(0H)g treated soils regardless of rate of P ap
plication. Without Fe(0H)g application, increases in
Truog extractable P resulted from clover application at
increasing P rates (Table 4-5). Previous mechanisms,
discussed above appeared to have produced these
effects.
Bray 2 Extractable P
Orthophosphate adsorption to iron mineral surfaces
reduces plant available P. Bray 2 extraction is a good
method for determining slightly soluble or desorbable P
reaction products. Bray 2 extractable P was affected
by main effects of P rate, Fe(0H)3 amendment, and

Table 4-5 Truog Extractable P Levels Determined After the First Cropping Period
Response Surface Equation
Correlation
Coefficient
P Applied (0 mg/kg)
Truog P = 3.05 0.43 Fe + 0.30 clover 0.05 Fe clover
P Applied (50 mg/kg)
Troug P = 5.43 1.00 Fe + 0.46 clover -0.05 Fe clover
P Applied (100 mg/kg)
Troug P = 7.02 0.99 Fe + 1.07 clover -0.21 Fe clover
r2 =0.40
r2 =0.95
r2 =0.78

78
Fig. 4-10 Truog Extractable P Levels as Affected by
Clover and Fe(OH) Applications at the 0
mg/kg P Rate During the First Cropping
Period.
Truog Extractable P mg/kg

79
1.58
Clover Applied g/kg
Fig. 4-11 Truog Extractable P Levels as Affected by
Clover and Fe(OH), Applications at the 50
mg/kg P Rate During the First Cropping
Period.
Truog Extractable P mg/kg

80
0 1.58 3.15
Clover Applied g/kg
Fig. 4-12 Truog Extractable P Levels as Affected by
Clover and Fe(OH), Applications at the
100 mg/kg P Rate During the First
Cropping Period.
Truog Extractable P mg/kg

81
clover application, as shown in Table 46. With in
creasing P rates, significant increases were observed
in Bray 2 extractable P levels probably from adsorption
to the iron mineral surface. Binuclear adsorption
would reduce extractable P results due to the stability
of the adsorption bond and the irreversible nature of
the adsorption. Clover amendments increased ex
tractable P availability. Possible mechanisms of
organic ligand adsorption, A1 and Fe complexation, P
release for clover and/or acid humification processes
solubilizing calcium phosphates, could increase
extractable P concentrations.
Organic Carbon
No significance with respect to organic carbon
levels was found with clover pretreatment. Further
monitoring of this experimental parameter was termi
nated.
Crop 2
A second maize crop, grown for 50 d, was initiated
to determine residual treatment effectiveness in
relation to experimental parameters.
Yield
Plant dry weight yield was influenced by previous
FeCOH)^ and clover applications (Table 4-7). Main plot
effects did not show increase in yield from previous

82
Table 4-6 Main Effects of P, Fe(OH) and Clover
Affecting Bray 2 Extractable P Levels From
the First Cropping Period.
P Aapplied
Bray 2
Contrast
p > F
(mg/kg)
Extractable P
0
9.86
0
vs others
0.01
50
20.01
50
vs 100
0.01
100
27.84
Fe Applied
(fc/kg)
0
26.06
0
vs 5.6
0.05
5.6
12.41
Clover Applied (g/kg)
0
14.56
0 vs others
0.01
1.58
18.13
1.58 vs 3.15
0.01
3 .15
25.02

83
DAP application due to fixation mechanisms. Ferric-
hydroxide decreased dry weight yield fourfold. Clover
addition increased yield with each increasing rate of
application. Since P was a limiting factor, clover
applications apparently increased P reaction product
availability. Release of P from clover should have
subsided long before termination of the second cropping
period. Yield was not likely to be reduced from A1 or
Fe toxicity at pH values of the soil. Although differ
ences in A1 and Fe levels within plant tissue existed
(Table 4-8) with respect to Fe(OH)g treatment, A1 and
Fe levels were not at toxic concentrations.
P Uptake
Phosphorus uptake by maize was affected by FeiOH)^
addition (Table 4-9). The FeiOH)^ provided a sink for
P adsorption. Also as seen in Table 4-10, soil pH had
3+ 3 +
dropped to 5.0 such that A1 and Fe could be in so
lution reducing P availability from precipitation
reactions. Aluminum and Fe ions were present in soil
solution as determined by plant uptake of these ions.
Addition of Fe(OH)^ resulted in a fourfold decrease in
P uptake.
Truog Extractable P
Truog extractable P was affected by an interaction
of FeiOH)^ and clover. Increasing levels of clover

84
Table 4-7 Main Effects of FeCOH)^ and Clover
Treatments on Plant Yield During the Second
Cropping Period.
Fe applied
(g/kg)
Yield (g/pot)
Contrast
p > F
0
2.17
0 vs. 5.6
0.01
5.6
0.53
Clover applied
(g/kg)
0
0.85
0 vs. others
0.01
1.58
1.35
1.58 vs 3.15
0.01
3.15
1.85

85
Table 4-8 Main Effect of Fe(OH) Addition on A1 and
Fe Concentrations in Plant Tissue After the
Second Cropping Period,
A1 Fe Contrast p>F
mg/kg
Plus Fe(OH) 131 133
Plus vs Minus 0.01
Minus Fe(OH)3 83 83
Table 4-9 Main Effect of Fe(OH)^ Treatment on Plant P
Uptake During the Second Cropping Period.
Fe (g/kg) P uptake mean Contrast p>F
mg P/Pot
0
5.6
2.15
0.57
0vs5.6 0.01
Table 4-10 Main Effect of FeCOH)^ Treatment on Soil
pH After Two Cropping Periods.
Fe (g/kg) pH mean Contrast
p > F
0
5.12
5.6
4.95
0 vs 5.6
0.01

86
increased Truog P, as FeCOH)^ produced a reduction in P
at each P application rate (Table 4-11). As the pH of
the soil decreased, solubilization of indigenous soil
P, or P from fertilizer reaction products increased
producing measurable levels of Truog extractable P
which is a P form readily available to plants. Without
Fe(OH)g addition, increasing levels of Truog P were
obtained with increasing clover rates, without added P.
This same observation (Fig. 4-13) was also noted during
the first cropping period. Reduction in Truog
extractable P on FeiOH)^ treated soil without P addi
tion with increasing clover rates may be explained by P
utilized for plant growth. Increased maize yields were
obtained with increasing clover application rates,
which would lower Truog P levels. Similar observations
were obtained at the 50 mg P/kg rate (Fig. 4-14) and
the 100 mg P/kg rate (Fig. 4-15) with the exception
that Truog extractable P levels also increased with
increasing rate of P application.
Bray 2 Extractable P
Bray 2 extractable P levels were affected by
interaction of P and Fe(0H)3> Extractable P was
increased with increasing P rates but decreased with
Fe(OH)3 additions. Extractable P levels were increased

Table 4-11 Response Surface Equations of Truog Extractable P Levels After the Second
Cropping Period.
Response Surface Equation
Correlation
Coefficient
P Applied (0 mg/kg)
2
Truog P = 2.48 + .05 Fe + .28 clover .06 Fe clover r = .36
P Applied (50 mg/kg)
2
Truog P = 5.06 .45 Fe + .41 clover .08 Fe clover r = .96
P Allied (lop mg/kg)
2
Truog P = 7.75 0.92 Fe + 0.61 clover 0.09 Fe clover r = .96
oo

88
with increasing clover rates (Table 4-12 and Fig. 4-16,
4-17, and 4-18). Increases of Bray 2 extractable P
from Fe(OH)^ untreated soil compared to that for Crop 1
may have been produced by precipitation of Fe or A1
phosphates with decreasing soil pH. Reversion of a
calcium phosphate to a Fe or A1 phosphate possessing
greater stability would increase Bray 2 levels. Change
in Bray 2 extractable P may be due to blockage of P
fixation sites by organic ligands reducing the
irreversible binuclear P adsorption.
Crop 3
A third crop was grown for 50 d to determine
clover effectiveness over time in increasing dry weight
yield, P uptake, and Truog and Bray 2 extractable P.
Each treatment was again limed to pH 6.3 utilizing the
liming curve described in Chapter 3. Constant fertil
izer amounts were applied. Rates of 0, 50, and 100 mg
P/kg as DAP were applied to appropriate treatments.
Yield
Dry matter yield was influenced by interaction of
P with FeCOH)^ applications. (Table 4-13). Increasing
rates of P increased dry weight yield (Fig. 4-19, 4-20
and 4-21). Observations of increases in yield on
Fe(0H)g treated soil with increasing clover applica
tions suggested that organic functional groups were
bonded to Fe mineral surfaces, thereby reducing P

89
Table 4-12 Response Surface Equations of Bray 2
Extractable P Levels After the Second
Cropping Period.
Correlation
Response Surface Equation Coefficient
Clover Applied (0 g/kg)
Bray P = 9.28 + .28 P .85 Fe .04 P Fe
Clover Applied (1.58 g/kg)
Bray P = 16.99 + .24 P 2.13 Fe .02 P Fe
Clover Applied (3.15 g/kg)
.96
2
r
.97
2
r
Bray P = 23.19 + .22 P 2.62 Fe
.02 P Fe
.96

90
Clover Applied g/kg
Fig. 4-13 Truog Extractable P Levels as Affected by
Clover and FeCOH)^ Applications at the
0 mg/kg P Rate During the Second Cropping
4
Truog Extractable P mg/kg

91
Fig. A-14 Truog Extractable P Levels as Affected by
Clover and FeCOH)^ Applications at the
50 mg/kg P Rate During the Second Cropping
Period.
Truog Extractable P mg/kg

92
Clover Applied g/kg
Fig. 4-15 Troug Extractable P Levels as Affected by
Clover and Fe(OH) Applications at the
100 mg/kg P Rate During the Second Cropping
Period.
Truog Extractable P mg/kg

93
Fig. 4-16 Bray 2 Extractable P Levels as Affected by
P and Fe(OH) Applications at the 0 g/kg
Clover Rate During the Second Cropping
Period.
Bray 2 Extractable P mg/kg

94
Fig. 4-17 Bray 2 Extractable P Levels as Affected by
P and Fe(OH)_ Applications at the 1.58 g/kg
Clover Rate During the Second
Cropping Period.
Bray 2 Extractable P mg/kg

95
Fig. A18 Bray 2 Extractable P Levels as Affected by
P and FeCOH), Applications at the 3.15 g/kg
Clover Rate During the Second
Cropping Period.
Bray 2 Extractable P mg/kg

96
Table 4-13 Response Surface Equations of P and FeCOH)^
Across Clover Application Rates in Relation
to Dry Weight Yield After the Third
Cropping.
Corelation
Response Surface Equation Coefficient
Yield
= .33
Cl over
+ .09 P
Applied (0 g/kg)
+ .12 Fe .01 P*Fe
r2 = .76
Yield
= .88
Clov er
+ .06 P
Applied (1.58 g/kg)
+ .04 Fe .01 P*Fe
r2 = .52
Yield
= 2.28
Clov er
+ .05 P
Applied (3.15 g/kg)
- .23 Fe .002 P*Fe
r2 = .53

97
Fig. 4-19 Plant Dry Weight Yield as Affected by P
and Fe(OH), Applications at the 0 g/kg
Clover Rate During the Third Cropping
Period.
Dry Weight Yield g/pot

98
P Applied mg/kg
Fig. 4-20 Plant Dry Weight Yield as Affected by P
and Fe(OH), Applications at the 1.58 g/kg
Clover Rate During the Third Cropping
Period.
Dry Weight Yield g/pot

99
Fig. 4-21 Plant Dry Weight Yield as Affected by P
and Fe(OH), Applications at the 3.15 g/kg
Clover Rate During the Third Cropping
Period.
Dry Weight Yield g/pot

100
adsorption sites. At the 100 mg P/kg rate, addition of
3.15 g clover/kg increased yield 600% compared to
treatments without clover addition. This effect was
produced after an initial clover application and two
previous cropping periods on the same soil. Stability
exists in the effect produced by clover application on
Fe(0H)3 treated soil, whatever the mechanism. Without
FeCOH)^ application, mixed results were obtained with P
and clover application. At 50 mg P/kg, yield was
increased with increasing clover addition but at 100 mg
P/kg, yield was decreased with increasing clover rate
of application.
P Uptake
A second application of fertilizer P masked the
clover effect with respect to P uptake. As seen in
Table 4-14, P uptake was affected by main effects of P
and FeCOH)^ application. Increased rates of P applica
tion increased P uptake whereas addition of FeCOH)^
decreased P uptake.
Soil pH
Since the soil was limed before the third cropping
period, reversion of soil pH to its natural state had
not fully occurred. Differences in soil pH had devel
oped with respect to Fe(0H)3 addition (Table 4-15), but
pH had not decreased to a state that would promote
further extensive P fixation from A1 or Fe

101
Table 4-14 Main Effects of P and Fe(OH), Relating to
Plant P Uptake From the Third Cropping.
P uptake
mg/pot
Contrast
p > F
P Applied (mg/kg)
0
1.27
0
vs others
0.01
50
3.42
50
vs 100
0.01
100
8.01
Fe Applied (g/kg)
0
6.14
0
vs 5.6
0.01
5.6
2.33

102
release into the soil solution or as sites for P reten
tion.
Truog Extractable P
Truog extractable P levels were affected by an
interaction of FeCOH)^ with clover (Table 4-16). With
out FeCOH)^ addition, Truog extractable P levels in
creased with increasing P rates and clover additions.
(Fig. 4-22, 4-23 and 4-24). With FeiOH)^ addition,
Truog P levels were increased with clover application
compared to without clover application. The Fe(0H)g
addition reduced Truog P levels at each P and clover
rate. Variability in Truog P levels on Fe(OH)g treated
soils may result from differences in P taken up by
plants causing reduction extractable P levels.
Bray 2 Extractable P
Bray 2 extractable P levels were affected by P
rates, FeiOH)^ addition, and clover application rates
as a triple-order interaction (Table 4-17). Increases
in extractable P were linear with increasing clover ap
plications (Fig. 4-25, 4-26, and 4-27) and also with
increasing P rates. The FeiOH)^ applications reduced
extractable P levels significantly. Although increases
in extractable P were obtained with clover application
on FeiOH)^ treated soil, increases were not as great

Table 4-15 Main Effect
Period.
of Fe(0H)g Relating to Soil pH
Changes During
the Third Cropping
Fe Applied (g/kg)
pH
Contrast
p > F
0
6.20
0 vs 5.6
0.01
5.6
5.28
Table 4-16 Response Surface Equations of Fe(0H)g and Clover Acrosss
in Relation to Truog Extractable P Levels After the Third
P Application Rates
Cropping Period.
Response Surface Equation
Correlation
Coeffiecient
P Applied (0 mg/kg)
Truog P =
3.48 .12 Fe + .20 clover -.03 Fe clover
r2 = .59
P Applied (50 mg/kg)
2
Truog P = 7.75 -.28 Fe + .57 clover .10 Fe clover r =.36
P Applied (100 mg/kg)
2
Truog P = 14.54 -1.87 Fe + ,77clover .10 Fe clover r = .98
o
oo

104
1.58
Clover Applied g/kg
3.15
Fig. 4-22 Truog Extractable P Levels as Affected by
Clover and FeCOH)^ Applications at the
0 mg/kg P Rate During the Third Cropping
Period.
Truog Extractable P mg/kg

105
1.58
Clover Applied g/kg
ig. 4-23 Truog Extractable P Levels as Affected by
Clover and FeCOH)^ Applications at the
50 mg/kg P Rate During the Third
Cropping Period.
Truog Extractable P mg/kg

106
1.58
Clover Applied g/kg
3.15
Fig. 4-24 Truog Extractable P Levels as Affected by
Clover and Fe(OH), Applications at the
100 mg/kg P Rate During the Third
Cropping Period.
Truog Extractable P mg/kg

107
Table 4-17 Regression Equations of FeCOH)^ and
Clover Application in relation to of Bray 2
Extractable P Levels After the Third
Clover added
(fc/kg)
Regression Equations
Correlation
Coef ficient
P Applied (0 mg/kg)
0
Bray
P = 8.92 .84 Fe
r2
=
.95
1.58
Bray
P = 13.42 .90
Fe
2
r
=
.41
3.15
Bray
P = 20.52 2.21
Fe
r2
=
.95
P Applied (50 mg/kg)
0
Bray
P = 32.92 3.76
Fe
2
r
=
.97
1.58
Bray
P = 39.60 4.73
Fe
2
r
=
.98
3.15
Bray
P = 42.53 3.73
Fe
2
r
=
.96
P Applied (100 mg/kg)
0
Bray
P = 59.8 6.07
Fe
2
r
=
.96
1.5 8
Bray
P = 66.91 6.29
Fe
2
r
=
.99
3.15
Bray
P = 69.87 5.89
Fe
2
r
=
.98

108
Fig. 4-25 Bray 2 Extractable P Levels as Affected by
Clover and Fe(OH)3 Applications at the
0 mg/kg P Rate During the Third Cropping
Period.
Bray 2 Extractable P mg/kg

109
Clover Applied g/kg
Fig. 4-26 Bray 2 Extractable P Levels as Affected by
Clover and Fe(OH) Applications at the
50 mg/kg P Rate During the Third Cropping
Period.
Bray 2 Extractable P mg/kg

110
Fig. 4-27 Bray 2 Extractable P Levels as Affected by
Clover and Fe(OH)~ Applications at the
100 mg/kg P Rate During the Third Cropping
Period.
Bray 2 Extractable P mg/kg

Ill
with clover application as measured during other crop
ping periods with previous P application before crop
ping.
Surface Charge Study
Since differences in yield, P uptake, Truog
extractable P and Bray 2 extractable P existed on
Fe(OH)g treated soils with respect to P and clover
addition, potentiometric titrations relating to varia
tions in net electric surface charge and ZPC were
determined. Addition of Fe(OH)g to kaolinite, the main
clay component of Orangeburg soil, creates greater
positive surface charge with reduced cation exchange
capacity (Dixon, 1977). Experimental objectives in
cluded qualification and quantification of surface
charge properties of Orangeburg soil samples treated
with FeCOH)^ with applications of P, clover, and P and
clover, from the glasshouse study.
Orangeburg + Fe(OH)^
Zero points of titration occur at pH values of 5.2
to 5.A (Fig. 4-28) to FeiOH)^ treated Orangeburg top
soil. Since this treatment had been used in the
glasshouse experiment, reversion of soil pH from 6.3 to
5.A had occurred. A ZPC value was obtained at pH A.O.
Kaolinite, the major clay mineral in the Orangeburg
soil, possesses ZPC values near this pH. Surface
charge of 1.0 cmol(+)/kg soil is probably produced by

112
pH
Surface Properties of Orangeburg Topsoil
+ Fe(OH) as Determined by Potentiometric
Titration
Fig. 4-28

113
Fe(OH)g addition which increases net positive charge.
However, the integrity of the kaolinite surface should
not have been totally lost after addition of 5.6 g
Fe/kg as Fe(OH)3<
Orangeburg + FeCOH)^ + P
Orthophosphate binds covalently to FeCOH)^ mineral
surfaces releasing OH^0 and OH ligands and produces a
surface with greater net negative charge (Hingston et
al., 1974). This reaction lowers the pH of the ZPC
(Schwertmann and Taylor, 1977). From the results shown
in Fig. 4-29, a decrease in ZPC pH from 4.0 to 3.5 had
occurred suggesting covalent bonding of P to the iron
mineral surface. Increase in positive charge (2
cmol(+)/kg soil) indicates that H+ adsorption possibly
occurs on a more negatively charged surface produced by
orthophosphate specific adsorption with lowering of
kaolinite ZPC.
Orangeburg + Fe(0H)3 + Clover
Humic and fulvic acids from clover are decomposi-
tional products that possess mainly carboxyl functional
groups (Kononava, 1961). Disassociation constants for
humic acid are near pH 5.0 (Greenland, 1971) which is
close to the acetic acid (H^C20) disassociation
constant (4.75) (Weast, 1973). Titration of Orangeburg
soil + FeiOH)^ with clover addition produced a ZPC at
pH 4.70 with 0.01 and 0.1 M NaCl additions. Binding of
soluble Al and Fe by carboxyl groups may have occurred.

114
pH
Fig. 4-29 Surface Properties of Orangeburg Topsoil
+ FeCOH)^ amended with 100 mg P/kg as
Determined by Potentiometric Titration.

115
The 1.0 M NaCl plot did not intersect with other plots
possibly due to mass action of Na replacing A1 or Fe
from the carboxyl group and producing acidity upon
hydration, requiring less H+ from the titration. The
ZPC values from previous plots were not at pH 4.70
indicating surface properties produced from clover
application (Fig. 4-30). A second ZPC was produced at
pH 3.8. Since organic functional groups bind
covalently to iron minerals, partial reduction of
kaolinite ZPC at pH 4.0 may have been produced by
organic ligands binding to FeCOH)^ on the kaolinite
surface. Increased negative charge for H+ adsorption
and reducing pH at the ZPC would result. With clover
addition, positive charge was increased to 2.5 cmol
(+)/kg compared to 1.0 and 2.0 cmol (+)/kg for Orange
burg + Fe(0H)g and plus P addition, respectively.
Orangeburg + Fe(OH)^ With P and Clover Addition
Addition of P and clover produced surface proper
ties similar to clover addition alone. A ZPC value was
obtained at pH 4.75 (Fig. 4-31) which is similar to
carboxyl disassociation constants. If A1 or Fe had
been released into solution with increasing H+
additions, acidity from A1 or Fe hydration could lower
the ZPC of 1 M NaCl to pH 4.50. However, this pH may
be an artifact of the titration from precipitation of

116
PH
Fig. 4-30 Surface Properties of Orangeburg Topsoil
+ FeCOH)^ with 3.15 g/kg Applications as
Determined by Potentiometric Titration.

117
pH
Fig. 4-31 Surface Properties of Orangeburg Topsoil +
FeCOH)^ With 100 mg/kg P and 3.15 g/kg
Clover Applications as Determined by
Potentiometric Titration.

118
insoluble phosphates. A second ZPC of 3.5 with or
thophosphate addition was not found. However a ZPC at
pH 3.9 suggested presence of adsorption of P or organic
components to Fe(OH)g surfaces.
Implications are that functional groups of clover
bonded with A1 and Fe ions in addition to adsorbing on
Fe mineral surfaces. If this is the accurate mecha
nism, P would possess greater plant availability with
clover addition. Results by yield, P uptake, and soil
test methods such as Truog and Bray 2 extractable P
indicate greater P availability with clover applica
tion. Surface properties confirm differences were
produced by clover applications.
SEM Study
Orangeburg +Fe(0H)2 + 100 mg P/kg soil with and
without clover additions (3.15 g/kg) were placed on C
coated A1 stubs at varying clay concentrations. Sam
ples containing 1600, 800, 533 and 320 mg clay/L were
oo concentrated to notice any difference between
treatments. When samples were diluted to 160 mg clay/L
in deionized water, differences in aggregation were
observed. Greater clay dispersion (Fig. 4-32) without
clover pretreatment was observed compared to increased
aggregation with clover pretreatment (Fig. 4-33).

119
Fig. 4-32 Scanning Electron Micrograph (450X) of
Orangeburg + FeCOH)^ Clay Fraction (160 mg
clay/L) From the First Cropping Period.

Fig. 4-33 Scanning Electron Micrograph (450X) of
Orangeburg + FeCOH)^ Clay Fraction (160mg
clay/L Amended With 3.15 g Clover/kg
From the First Cropping Period.

121
Whether this relationship was produced from segregating
clay fractions or existed previously in the soil is
unknown. Much care was taken to isolate clay fractions
with minimal reagent addition. A close up view of an
aggregate magnified 10.000X, from a clover pretreatment
sample is shown in Fig. 4-34. High molecular weight
humic acids contain numerous functional groups (Inoue
and Wada, 1968) which can bind to Fe(OH)g surfaces,
thereby reducing soil surface area. (Schwertmann and
Fisher, 1973). Clay fraction surface area could be
reduced if aggregation of clay particles had occurred.
Conclusions
Incubation studies indicated that P fixation is
reduced with clover pretreatment on soils containing
sesquioxide minerals. Orangeburg topsoil +Fe(OH)^ and
Orangeburg subsoil, coated with goethite, had lowered P
fixation capabilities after receiving clover applica
tion. Increased P fixation capacity was observed on
Orangeburg topsoil without FeCOH)^ application with
increasing clover rates. At 60 d of incubation, P
fixation capacity was reduced on all treatments after
possible P mineralization of clover, and increase in pH
reducing net positive charge on soil mineral surfaces.
After 90 d, P fixation capacity had returned to near
initial levels as pH decreased. Phosphorus fixation

122
Fig. 4-34 Scanning Electron Micrograph (10.000X)
of an Aggregate From Orangeburg + Fe(OH)
Clay Fraction Amended With 3.15 g Clover/kg
From the First Cropping Period.

123
capacity of the Orangeburg soil without FeCOH)^
addition was probably produced by cation bridging of
orthophosphate to organic functional groups. However,
P fixation on FeCOH)^ treated soil and goethite in
Orangeburg subsoil was reduced by organic anion
specific adsorption. Crop production benefited from
clover application. During the first two croppings of
the glasshouse experiment, clover applications
increased greater plant yield, P uptake, and ex
tractable P levels. Without FeCOH)^ addition, cation
bridging of P to organic components would have greater
plant availability than a precipitation product of an
insoluble Fe or A1 phosphate as the soil pH decreased
over time. With FeiOH)^ applications, complexation of
soluble Fe and A1 and/or organic ligand adsorption to
FeCOH)^ surfaces may have increased yield, P uptake and
extractable P levels. After refertilization of the
third crop, P uptake for soil amended with clover was
not significant according to treatment. However yield
and extractable P levels increased with clover applica
tions. Clover effectiveness in reducing P fixation
persisted long after the time span for nutrient miner
alization. Mechanisms of cation bridging and organic
ligand adsorption appear to exist, confirmed data
obtained from the surface charge and SEM study. Sur
face charge studies indicate a negative shift in ZPC
values from P and clover applications, indicative of

124
ligand exchange reactions. Soil treatments with clover
addition had ZPC values of 4.7, near pK values for car
boxyl groups. The main functional group in humic acids
from clover decomposition is carboxyl groups which can
complex acid forming ions in the soil solution. Scan
ning electron microscopy appeared to show greater ag
gregation of the clay fraction with clover amendment,
possibly indicating ligand exchange.

CHAPTER V
FERTILIZER COATING AND PLACEMENT EXPERIMENT
Introduction
After application of water-soluble P fertilizer, P
moves very slowly from the point of placement such that
the orthophosphate is generally immobile in acid soils
(Tisdale and Nelson, 1975). Distribution of fertilizer
P, due to its immobility, is generally less than 1% of
the total soil volume (Lindsay, 1959). Immobility of
fertilizer P is due to rapid reaction with soil
components and metastable precipitation products of
diammonium phosphate (DAP), whose dissolution pH is
7.98, are dicalcium phosphate dihydrate (DCPD) and
struvite (NH^MgPO^'H^O) (Lindsay, 1959). Orthophos
phate ions from the dissolution of fertilizer or solu
bilization of reaction products may form stable sec
ondary products such as varisite, strengite, hydroxyap
atite, or fluorapatite (Lindsay, 1979) or be specifi
cally adsorbed on hydrous oxide mineral surfaces
(Hingston et al., 197A).
Organic matter addition to soils which contain Fe
and A1 oxides has reduced net positive surface charge
and orthophosphate adsorption in acidic environments
(Moshi et al., 197A) Organic addition may also reduce
solution A1 (Bloom and McBride, 1979) or Fe activity
125

126
(Deb and Datta, 1967). Other observations produced
evidence that organic functional groups bonded cova
lently to Fe mineral surfaces or ionically complexed Fe
or A1 solution species (Greenland, 1971).
Clover decompositional products contain high
percentages of organic functional groups (Kononava,
1961) capable of reaction with sesquioxide minerals or
dissolution products above pH 5 (Greenland, 1971).
Studies of freshly humified clover adsorption to allo-
phane (Inoue and Wanda, 1968) exhibited the effective
ness of organic adsorption to mineral surfaces.
The objective of the fertilizer coating experiment
was to assess the effectiveness of coating granules of
DAP with dried and ground clover as measured by dry
matter production, P uptake, and extractable P levels.
Materials and Methods
Soil
An Orangeburg series topsoil + 5.6 g Fe as FetOH)^
and subsoil corresponding to the Bt horizon as charac
terized in Tables 3-1 and 3-2 of Chapter 3 were used in
the fertilizer coating experiment. Ferric hydroxide
was prepared and applied by the same methodology
described in Chapter 3. The soil was limed to pH 6.3
utilizing the liming curve developed in preliminary
experimentation and incubated for 2 wk.

127
Fertilizer Addition
Pots contained 2 kg of soil on a dry weight basis.
The source of phosphate fertilizer applied was DAP with
an application rate of 75 mg P/kg soil to all treat
ments. Variation in method of applications was the
experimental treatment. Fertilizer was either com
pletely mixed with the soil or applied by point place
ment. Point placement methodology consisted of placing
one-half of the fertilizer rate (37.5 mg P/kg) at two
positions spaced 4 cm from pot boundary along the diam
eter fo the pot at a space of 6 cm.. Depth of place
ment was 6 cm.
Clover-coated fertilizer granules were prepared by
mixing small increments of Elmer's glue with dried and
ground clover material until all material was bound
together. Dried and ground clover was placed in a
spherical paraffin mold with 37.5 mg P/kg as DAP placed
in the center of the granule. Fertilizer granules were
coated with 0.25, 0.50, 0.75 and 1.0 g of dried and
ground clover with granule diameters ranging from 9 to
13 mm. Clover-coated granule placement in the soil was
the same methodology as that of the point placement.
Uniform fertilizer addition included 150 mg N/kg
soil as NH^NO^, 150 mg K/kg soil as KC1, and a sec
ondary and micronutrient solution containing 19.8 mg Mg

128
as MgSO^VH^O, 11.A mg Zn as ZnSO^^H^O, 5.09 mg Cu as
CUSO^5H^O and 1.2 mg B as Na2B20y'1OH^O. Fertilizer
application was adjusted to a constant rate by treat
ment assuming 50% mineralization of clover nutrients.
Experimental Design
Eight fertilizer treatments applied to two soils
and replicated three times were set in a randomized
complete block (RCB) design. Fertilizer treatments
were applied to Orangeburg subsoil and Orangeburg
topsoil + 5.6 g Fe/kg as Fe(0H)g. Each soil received P
fertilizer at a rate of 75 mg P/kg soil as DAP.
Treatments were 1) Completely mixed soil without
clover, 2) Completely mixed soil with 1.58 g clover/kg,
3) Completely mixed soil with 3.16 g clover/kg, 4) 2
granules coated with 0.25 g clover, 5) 2 granules
coated with 0.50 g clover, 6) 2 granules coated with
0.75 g of clover, 7) 2 granules coated with 1.00 g
clover, and 8) 2 point placements (uncoated DAP with
same placement as granules.
Statistical analysis of the factorial experiment
in RCB design data was performed utilizing the Statis
tical Analysis System. Mean separation was made using
the single degree of freedom orthogonal contrast tech
nique.
Methods
Two crops of maize were grown for 50 d to assess
the initial and residual effectiveness of the

129
fertilizer treatments. Only top growth above the soil
surface was analyzed during the first cropping period.
The soil was not disturbed other than replanting the
second crop. Soil and plant samples were analyzed
after the second cropping period.
Plant samples were analyzed by previously de
scribed methods.
Soils were sampled after the second cropping
period. Completely mixed soil samples were obtained as
well as samples around the granules or point placement.
Fertilizer residue was discarded but soil samples were
taken up to 2 cm distance from point or granule place
ment. Bulk samples from granule or point placement
treated soil, after soil near granules had been
removed, were compared to completely mixed samples as
well as soil 2 cm from granules.
Soil samples were analyzed for Truog and Bray 2
extractable P and pH.
Results and Discussion
Crop 1
Orangeburg subsoil contained 0.84% Fe as goethite
coating clay mineral surfaces. Orangeburg topsoil was
sandy containing Fe concretions with a citrate-
dithionite-bicarbonate extraction concentration of
0.31% of the soil. Addition of amorphous FeCOH)^ (5.6
g/kg) to the topsoil increased the Fe content to a

130
total of 0.87%. Extractable Fe contents of both soils
were equivalent, but as different mineral solid phases.
Phosphorus uptake by corn was affected by soil
type and placement of fertilizer (Table 5-1). Greater
P uptake was obtained with Orangeburg subsoil than
topsoil + FeiOH)^ for the granule and point placement
applications. This observation appears contradictory
since from characterization data, the subsoil fixed 800
mg P/kg while the FeCOH)^ treated topsoil fixed only
640 mg P/kg. Goethite has less surface per unit weight
than FeiOH)^ (Parfitt et al., 1975). Within the point
placement and clover coated granule microsite, greater
adsorptive surface would be available for P fixation on
the Fe(0H)g treated soil since the fertilizer reacts
with approximately 1% of total soil volume (Lindsay,
1959) resulting in greater P fixation by FeiOH)^
treated soil. Results are inconclusive for the com
pletely mixed treatments. Unlike previous experimenta
tion, time for decomposition of clover prior to
fertilizer addition. Clover and fertilizers were
applied on the same day. Lack of response to clover
addition may be due to lack of time for decomposition
before fertilizer addition. Fertilizer placement as a

131
Table 5-1. Soil and Treatment Effects on P Uptake From
the First Cropping Period.
Treatment
Clov er
Applied
Orangeburg
Fe(OH)
P
m£
+ Orangeburg
Subs oil
Uptake
P/pot
Completely Mixed
(CM) g/kg
0
9.63
11.97
1.58
10.77
8.27
3.15
11.87
10.97
Granule (G)
g/granule
1) 0.25
27.07
29.60
2) 0.50
29.50
31.43
3) 0.75
29.80
30.13
4) 1.00
27.40
29.57
Point Placement
(PP) 0
24.03
33.07
Contrasts p > F
Orangeburg + Fe(OH)_ vs
Orangeburg Subsoil
0.01
CM vs PP
0.01
0.01
G vs PP
0.01
NS
G(3) vs G(1,2,4)
NS
NS

132
granule or point placement exhibited greater superior
ity of P uptake and yield than complete mixing. Com
plete mixing of fertilizer to soil exposed a greater
volume of soil to the fertilizer. Reduction in plant
available fertilizer due to reaction with a greater
volume of soil components reduced fertilizer effective
ness. Apparently, reduction in P uptake by corn due to
complete mixing of the DAP was from reaction of fertil
izer P with larger soil volumes.
No differences in P uptake effectiveness by indi
vidual granule treatments on either soil were observed,
however, clover coated granules were superior in
increasing P uptake to fertilizer point placement on
the Orangeburg + Fe(OH)g treated soil. Theoretically,
clover decompositional products should reduce positive
charge near the granule microsite before dissolution of
DAP, making the orthophosphate fraction more readily
available for plant uptake. Also, dissolution pH of
DAP (7.98) would depress Fe and A1 activity as well as
reduce pH-dependent positive charge near microsites.
Amorphous ferric hydroxide treated soil or
goethite in the Orangeburg subsoil had no effect on the
dry weight yield of the first corn crop. Treatment
effects due to placement of 75 mg P/kg affected dry
matter yield production. As shown in Table 5-2, gran
ules and point placement were superior in dry weight
yield production compared to complete mixing of

133
fertilizer with incremental clover additions.
Treatment effects may be explained by enhanced P uptake
due to placement of P fertilizer material. Lack of
differences in yield on the two soils possibly
indicates that the P rate of 75 mg/kg may have been too
high. Since P uptake was different due to soils, it
should follow that yield would be different by soil as
it was by treatment. However, since P was not a
limiting factor, optimal plant uptake of P across soils
was obtained.
Calcium, Mg, and K uptake by corn followed closely
to P treatment yield. Increased dry matter yield
resulted in increased Ca, Mg, and K uptake but these
elements in plant tissue were not interpreted as being
deficient. Aluminum and Fe concentrations did not
approach toxic levels in the plant during the first
cropping period.
Crop 2
Soil pH values for both soils dropped from the
limed pH values of 6.3 to the indigenous values of A.7
and 5.2 (Table 5-3) for Orangeburg + FeCOH)^ and
Orangeburg subsoil, respectively, over the two cropping
periods. Although A1 and Fe were never at toxic concen
trations within the tissue, the percentage of P within
tissue was lower (< 0.1%) in Crop 2 than the first crop.

134
Table 5-2 Effect of Treatment on Maize Dry Matter
Yield From the First Cropping Period.
Treatment Clover Applied Yield g/pot
Completely Mixed(CM)
0
12.07
1.58
12.05
3.15
13.05
Granule (G) g/granule
1)
0.25
21.97
2)
0.50
22.82
3)
0.75
22.77
4)
1.00
21.50
Point Placement (PP)
0
21.42
Contrasts p >F
CM vs PP 0.01
G vs PP NS
G (2) vs GU.3.4) NS

135
Decrease in pH increased sesquioxide ionic activity and
reduced P availability. There was no apparent differ
ence between pH of completely mixed soil and soil near
granules or spot placement.
Truog extractable P levels of granule treatments
were different with respect to soil. Greater concen
trations of extractable P were found in the soil around
granule placement with Orangeburg subsoil resulting in
increased dry mater yield and P uptake than with
Orangeburg topsoil + Fe(OH)3 (Table 5-4). This obser
vation confirmed the hypothesis that greater adsorptive
surfaces would be available for P adsorption on the
FeCOH)^ treated soil instead of goethite for granule
and point placement.
Truog extractable P levels from soil near fertil
izer granules were also affected by treatment (Table 5-
5). There was no difference between extractable P
levels from granule fertilizers or point placement
resulting in lack of response in plant yield and P
uptake for the two plant growth periods. The highest
Truog extractable P results within granule treatments
came from DAP granules coated with 0.50 g clover.
However, yield was not increased comparatively to other
granules or point placement treatments during either

136
Table 5-3 Effect of Soil and Fertilizer Placement on
Soil pH.After the Second Cropping Period.
Treatment£H Contrast p >F
Completely Mixed
Orangeburg
Orangeburg
+ F e(OH)3
Subsoil
4.67
Topsoil vs
5.24
Subsoil
0.01
Granule
Orangeburg
Orangeburg
+ F e(OH)3
Subsoil
4.68
Topsoil vs
5.23
Sub soil
0.01
Table 5-4. Truog Extractable P Levels on Granule
Samples as Affected by Soil After the
Second Cropping Period.
Treatment Truog P levels Contrast
p >F
mg/kg
Orangeburg
+ F e(OH)3 7.05
Topsoil vs Subsoil
0.05
Orangeburg
subsoil 17.22

137
cropping period. Phosphorus uptake from granule
treatments was superior to point placement on
Orangeburg + Fe soil during the first cropping. Soil
around the granule or point placement possessed greater
concentrations of Truog extractable P than soil from
the completely mixed treatments. Completely mixing
fertilizer with soil increases the volume of soil
capable of reducing fertilizer availability. This
trend was observed throughout the duration of the
experiment. Truog extractable P levels by soil and
treatment were indicative of plant yield and P uptake
measurements since Truog levels denoted highly
available P to plants.
Bray P 2 extractable P levels were affected by
treatment and followed the same trends as the Truog
extractable P results (Table 5-6). Completely mixed
treatments were less effective than granule or point
placement of fertilizer. There was no difference
between granule or point placement methodologies.
Granules coated with 0.5 g clover appeared more
effective in supplying P than other granules
manuf actured.
Reduced P availability reduced plant yield by one-
half if one compares the first to the second crop.

138
Table 5-5. Effect of Treatment on Granule Truog
Extractable P Levels After the Second
Cropping Period.
Treatment
Clover Applied
Truog P
Completely Mixed
(CM)
¡Jlz
mg P/kg
0
6.10
1.58
5.98
3.15
6.10
Granule (G)
g/granule
1)
0.25
10.28
2)
0.50
25.60
3)
0.75
19.63
A)
1.00
18.08
Point Placement(PP)
0
24.85
Contrast
p>F
CM vs PP
0.01
Gran vs PP
NS
Gran (2) vs
Gran (1
.3,4)
0.05

139
Table 5-6 Effect of Granule Treatments on Bray 2
Extractable P Levels After the Second
Cropping Period.
Treatment
Clover Applied
Bray
Completely Mixed
(CM)
g/kg
mg P/kg
0
20.58
1.58
22.08
3.15
19.50
Granule (G)
g/Gran
1)
0.25
38.37
2)
0.25
63.48
3)
0.75
52.63
4)
1.00
47.65
Point Placement
(PP)
0
60.60
Contrast
p > F
CM vs PP
Gran vs PP
Gran (2) vs Gran (1,3,4)
0.01
NS
0.05

140
Reduced P availability also induced a soil and treat
ment interaction in which the P in Orangeburg subsoil
was more available to plants as determined by plant P
uptake (Table 5-7) than P from Orangeburg topsoil +
Fe(0H)g. Differences in P uptake produced a soil and
treatment interaction in which yield was greater on
Orangeburg subsoil than Orangeburg + FeCOH)^ treated
soil (Table 5-8). Similar trends observed during the
first cropping period occurred for the second cropping
period. Point placement and granules were superior in
producing yield and increasing P uptake to completely
mixed placement methodologies. Loss of effectiveness
of the 0.5 g clover coated granule in increasing P
uptake on Orangeburg topsoil + FeiOH)^ was noted only
during the second plant growth period.
Conclusions
Point placement of fertilizer and clover coated
granules were superior to completely mixing fertilizer
and clover to the soil, as measured by corn yield, P
uptake, Truog extractable P and Bray P 2 extractable
levels of soil P. There was no difference in experi
mentation variables between point or granule placement
of fertilizers except increased P uptake on Orangeburg
topsoil + Fe(0H)g during the first cropping period.
Lack of differences in yield between granule and point

141
Table 5-7 Soil and Treatment Effect on P uptake From
the Second Cropping Period
Treatment
Clov er
Applied
Orangeburg
Fe(0H)3
P uptak
+ Orangeburg
Subsoil
e mg/pot
Completely Mixed
(CM) g/kg
0
2.17
2.88
1.58
2.69
3.29
3.15
2.40
3.20
Granule(G)
g/granule
1) 0.25
3.66
9.44
2) 0.50
4.39
9.38
3) 0.75
4.16
7.98
4) 1.00
5.12
8.11
Point PIacement(PP) 0
4.71
9.01
Contrasts
p > f
Orangeburg + FeCOH)^ vs Orangeburg subsoil 0.01
CM vs PP 0.01
G vs PP NS
G (2) vs G (1.3,4) NS
G (1) vs G(2,3,4)
0.01
NS
NS

142
Table 5-8. Soil and Treatment Effects on Yield from
the Second Cropping Period.
Treatment
Clov er
Applied
Orangeburg
Fe(OH)3
+
Yield
g/Pot
Orangeburg
Subsoil
Completely
Mixed(CM)
£/k£
0
2.67
3.60
1.58
3.07
4.50
3.15
3.27
4.27
Granule(G)
g/gr anule
1)
0.25
5.06
10.33
2)
0.50
6.67
9.40
3)
0.75
5.07
9.13
4)
1.00
6.
50
11.43
Point Placement(PP)
0
7 .
07
9.93
Contrasts
p > F
Orangeburg + FeCOH)^ vs
Orangeburg Subsoil
CM vs PP 0.01
G vs PP NS
G(2) vs G(l,3,4) NS
G(4) vs G (1.2.3)
0.01
NS
NS
0.01

143
placements during this period may have been produced by
the fertilizer rate of 75 mg P/kg soil as a
concentrated point on the Orangeburg soil + Fe(OH)^
resulting in sufficient P for plant growth.
Of the granules manufactured and applied, the 0.50
g clover coating rate produced the best results only on
Orangeburg + FeCOH)^ treated soil, as measured by Truog
and Bray P 2 extractable P levels. Possibly coating
thickness was related to time of P release during
microbial degradation which induced increased response
to applied P. No difference between granule and point
placement was observed on Orangeburg subsoil.
Differences between soils included pH, Truog
extractable P levels, P uptake, and yield from the
second cropping period. The pH of 4.7 of the Orange
burg topsoil + FeCOH)^ which would increase A1 and Fe
solution activity and increase net positive charge on
Fe mineral surface reducing P availability. Reduction
in P uptake and yield from the second cropping period
are indicative of these types of changes. Changes over
time were not as dramatic on Orangeburg subsoil. After
liming and fertilizer P application, no differences in
yield with respect to soils was observed during the
first cropping period. However, as the two soils
reverted to their natural status, a difference in yield
with respect to soils was observed from a soil by
treatment interactions during the second cropping

144
period. Truog P measured after the second cropping
period was substantially lower in Orangeburg topsoil +
FeCOH)^ than in the subsoil. Phosphorus deficiency in
maize plants was also observed on the Orangeburg
topsoil during the second cropping period.
Applications of P fertilizers to high-P fixing
soils should be by band or point placement of fertil
izer. If the sequioxide mineral in the soil possesses
a high surface area, consideration to coating the P
source material with an organic material may be favor
able for increasing P uptake by a crop.

CHAPTER VI
SUMMARY AND CONCLUSIONS
Incubation study results indicate that P fixation
is reduced with clover pretreatment on soils containing
sesquioxide minerals. Orangeburg topsoil + FeCOH)^ and
Orangeburg subsoil coated with goethite, had reduced P
fixation capacities with increasing clover application
rates. Increased amounts of P were fixed in Orangeburg
topsoil without FeCOH)^ applications with increasing
clover rates. At 60 d of incubation, P fixation
capacity was reduced for all treatments. Possibly P
mineralization from clover and pH increase reduced net
positive charge on soil mineral surfaces. After 90 d,
P fixation capacity had returned to near initial levels
as soil pH decreased. Phosphorus fixation capacity by
the Orangeburg soil without FeCOH)^ addition probably
was produced by cation bridging of orthophosphate by
organic functional groups. However, P fixation on
FeCOH)^ treated soil and soil with goethite was reduced
by organic adsorption mechanisms. Throughout the dura
tion of the first glasshouse experiment, pretreatment
with clover induced greater plant yield, increased P
uptake except during the third cropping period, and
extractable P levels. Dry weight yields averaged 350%
higher with clover application than without clover
145

146
addition on Fe(OH)g treated soil. Soil FeCOH)^ re
mained in an amorphous state throughout the 180 d of
cropping. Without FeCOH)^ addition, cation bridging of
P to organic functional groups would have resulted in
greater plant P availability than a precipitation prod
uct of an insoluble Fe or A1 phosphate. With Fe(OH)^
application, complexation of solution Fe and A1 and/or
organic ligand coordination to Fe(OH)^ surfaces may
have effectively increased plant yield, P uptake, and
extractable P levels. After P refertilization of the
third crop, P uptake across clover levels was not sig
nificant according to treatment, but yield and
extractable P levels increased with clover rate of
application. Clover effectiveness in reducing P fixa
tion remained long after clover nutrients were mineral
ized. Mechanisms of ionic complexations by organic
functional groups and organic ligand adsorption appear
to exist from data obtained from the surface charge.
Surface charge studies indicate a negative shift in ZPC
values with P and clover application, indicative of
ligand exchange reactions. Carboxyl groups can complex
acid forming ions from soil solutions. Scanning elec
tron microscopy appears to reveal a greater aggregation
of the clay fractions with clover amendment.
A second glasshouse experiment was conducted to
determine effectiveness of coating DAP with clover. If
complete mixing of clover with the soil induced a

147
positive response in lowering P fixation, clover
amendments should reduce P fixation around P fertilizer
microsites. Point placement of fertilizer and clover-
coated granules were superior to completely mixing fer
tilizer and clover ino the soil, as measured by dry
matter yield, P uptake, and extractable P levels.
Clover granules were somewhat superior to point place
ment in increasing P uptake on Orangeburg + FeCOH)^
during initial cropping. Of the granules manufactured,
the 0.5 g-cl over coating produced the best results of
extractable P levels on Orangeburg + FeCOH)^ treated
soil.
When management is considering practices for crop
production on highly-weathered acidic soils possessing
Fe mineral coatings, management practices using an
organic material such as a legume residue to be incor
porated into the soil should be considered because
increases in crop production with minimal input and
less fertilizer costs may be obtained. In the near
future, organic coatings of P fertilizer material may
increase yields on highly weathered soils. Research
reported herein tried to bridge the gap between labora
tory results and plant growth studies. It appeared
that theories developed from laboratory results would
explain effectiveness of fertilizer for plant growth
with clover application.

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BIOGRAPHICAL SKETCH
George William Easterwood was born on April 8,
1955, in Sheffield, Alabama. He was reared in a rural
area whose economy was based largely on agriculture.
He attended and graduated from Cherokee Vocational High
School in Cherokee, Alabama, in 1973. He then attended
the University of North Alabama where he obtained a
B.S. degree in zoology with a minor in chemistry in
1977. After graduation, he was employed at the
International Fertilizer Development Center (IFDC) in
Muscle Shoals, Alabama, for 3 years. During this
period, he developed an interest in agricultural
research and entered the University of Florida in 1980
under the directorship of Dr. J. J. Street. After
graduation with a master's degree in 1982, he returned
to IFDC for a year. In 1984, he returned to the
University of Florida to pursue a Ph.D. degree in soil
science under the directorship of Dr. J. B. Sartain.
155

I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
Chairman
Professor of Soil Science
I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
1
/
>
//
u-.c'
J. G. A. Fiskell
Professor of Soil Science
I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
QO ',^'
J ./ p ilS t r e e t
A ss b ciate Professor of Soil
Science
I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
E. A. Hanlon
Assistant Professor of Soil
Science

I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
W. G. Harris
Assistant Professor of Soil
Science
I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
S. H. West
Professor of Agronomy
This dissertation was submitted to the Graduate Faculty
of the College of Agriculture and to the Graduate
School and was accepted as partial fulfillment of the
requirements for the degree of Doctor of Philosophy.
August, 1987
Dean, Graduate School



BIOGRAPHICAL SKETCH
George William Easterwood was born on April 8,
1955, in Sheffield, Alabama. He was reared in a rural
area whose economy was based largely on agriculture.
He attended and graduated from Cherokee Vocational High
School in Cherokee, Alabama, in 1973. He then attended
the University of North Alabama where he obtained a
B.S. degree in zoology with a minor in chemistry in
1977. After graduation, he was employed at the
International Fertilizer Development Center (IFDC) in
Muscle Shoals, Alabama, for 3 years. During this
period, he developed an interest in agricultural
research and entered the University of Florida in 1980
under the directorship of Dr. J. J. Street. After
graduation with a master's degree in 1982, he returned
to IFDC for a year. In 1984, he returned to the
University of Florida to pursue a Ph.D. degree in soil
science under the directorship of Dr. J. B. Sartain.
155


74
o
o.
oo
E
(0

co
tm S3
Fe Applied g/pot
Fig. 4-8 Phosphorus Uptake by Maize as Affected by
Fe(OH), and P Application at the 1.58 g/kg
Clover Kate During the First Cropping
Period.


151
Kamprath, E. J. 1967. Residual effects of large
applications of phosphorus on high fixing soils.
Agron. J. 59:25-27.
Kittrick, J. A. 1977. Mineral equilibria and the soil
system. p 1-24. ^n Minerals in Soil
Environments. Soil Sci Soc Am., Inc. Madison, WI.
Kononova, M. M. 1966. Soil Organic Matter. 2nd Edition
Pergamon Press, Oxford.
Kunze, E. W. 1965. Pretreatment for Mineralogical
Analysis, p 574-576. In Methods of Soil Analysis,
Part 1. American Society of Agronomy, Inc.,
Madison, WI.
Laverdiere, M. R., and R. M. Weaver. 1977. Charge
characteristics of spodic horizons. Soil Sci.
Soc. Am. J. 41:505-510.
Lehr, J. R., and G. H. McClellan. 1972. A laboratory
scale for evaluating phosphate rocks for direct
applications. TVA Bull. Y-43.
Levashkevich, G. A. 1966. Interactions of humic acid
with iron and aluminum hydroxides. Soviet Soil
Sci. 4:422-427.
Lindsay, W. L. 1959. Behavior of water soluble
phosphate, ^n Proc. Tenth Annual Fertilzier
Conference in the Pacific Northwest. Tacoma, WA.
Lindsay, W. L. 1979. Chemical Equilibria in Soils.
John Wiley and Sons, New York.
Lindsay, W. L., and E. C. Moreno. 1960. Phosphate
phase equilibria in soils. Soil. Sci. Soc. Am.
Proc. 24:177-182.
Lockett, J. L. 1938. Nitrogen and phosphorus changes
in the decomposition of rye and clover at
different stages of growth. Soil Sci. 45:13-24.
Manojlevic, S. 1965. Study of the role of humic acid
in the fixation of soluble phosphorus in soil.
Soil Fert. 29:37-41.
Martell, A. E., and M. Calvin. 1952. Chemistry of the
Metal Chelate Compounds. Prentice-Hall, Englewood
Cliffs, NJ..


5
Surface Charge of Iron Oxides
Surface charge of Fe oxides is pH dependent as
shown in the following model (Parks and deBruyn, 1962):
Charge (+) Charge (0) Charge (-)
Adsorption or desorption of H+ creates either a
positive, neutral or negative charge on the oxide
surface. As a pH-dependent charge is developed, an
anion or cation (A or C+ ion model) is attracted to
and satisfies the electrostatic charge according to the
law of electroneutrality in the outer diffuse electric
double layer. This type of adsorption is termed non
specific adsorption or ionic bonding (Schwertmann and
Taylor, 1977).
A stronger adsorption bond is produced when ions
penetrate the coordination shell of the Fe atom on the
oxide surface and exchange their OH and OH^0 ligands.
A covalent bond is produced between the anion and oxide
and is termed specific adsorption (Stevensen, 1982).
Phosphate Fixation by Iron Oxides
Soils rich in Fe oxides, such as some Utisols and
Oxisols of the tropics, are known for their low avail
ability of phosphate (Kamprath, 1967; Fox and Kamprath,


Maximum clover residue adsorption occurred at pH
6.3 with F e (0 H) ^ addition. Without F e (0 H) g applica
tion, adsorption was dependent on solution ionic
strength.
Clover applications decreased P adsorption within
each sampling time (30, 60, 90 d) for Orangeburg soil
with synthetic FeCOH)^ and Orangeburg subsoil contain
ing goethite but increased P fixation without FeiOH)^
application.
A glasshouse experiment was conducted to measure
maize yield, P uptake and extractable P levels. Two
crops of maize were grown 50 d each prior to P refer
tilization for the third crop. An increase of 350% in
maize yield with increases in P uptake and extractable
P levels was observed with clover and P applications
compared to P fertilization only, on FeCOH)^ treated
soils within cropping periods. A second experiment was
conducted to determine effectiveness of coating
diammonium phosphate (DAP) with clover to reduce P fix
ation around fertilizer microsites. Point placement of
fertilizer and granules was superior to mixing fertil
izer and clover to soil as measured by yield, P uptake,
and extractable P levels. Granules were superior to
point placement in increasing P uptake and extractable
P levels on Orangeburg + Fe(OH)^ soil.
viii


44
covalent bonding. Organic adsorption was not affected
by ionic strength as seen in Fig. 3-8 and 39 but was
greatly affected by changes in soil pH (Fig. 3-4 and 3-
5). Ionic strength ranged from 0.016 to 0.022 units
whereas pH changes within small ranges of ionic
strength greatly affected adsorption measurements. As
pH increases above pH 5.0, organic anions are formed.
However, FeCOH)^ possessed a variable charged surface
so that increases in pH could reduce net positive
charge and adsorption sites on mineral surface thereby
resulting in reduced adsorption. Maximal organic
adsorption occurred at pH 6.3 with residue amendment.
It is also important to observe the effectiveness of
organic adsorption of the FeCOH)^ treated soil compared
to untreated soil. Several orders of magnitude of
adsorption exist in the binding capacity, making the
Fe(OH)^-treated soil an excellent sorbant system for
organic anions.
Crystallization of Fe(OH)^
Changes in crystallization of FeiOH)^ affects sur
face area and reactive sites for organic anion and P
adsorption. Mineralogy of solid phase FeiOH)^ and
FeiOH)^ treated Orangeburg soil were observed over a 6
m period. Solid FeiOH)^ endured wetting and drying
cycles whereas FeiOH)^ treated soil with and without
clover amendment was under a cropping system. At no
time during the 6 m period did the solid FeiOH)^


119
Fig. 4-32 Scanning Electron Micrograph (450X) of
Orangeburg + FeCOH)^ Clay Fraction (160 mg
clay/L) From the First Cropping Period.


9
1965). Phosphate adsorption may occur on organic mate
rial by cation bridging to Fe and A1. Bloom (1981)
determined that P is strongly adsorbed by Al-saturated
peat within the pH range of 3.2 to 6.0. He postulated
that the mechanism of fixation was an adsorption of
orthophosphate to trivalent complexed A1 followed by
the precipitation of amorphous Al-hydroxy-phosphate
such as A1(OH)^*H^PO^. The strength of phosphate
adsorption by this mechanism was less than that for an
Al-permanent charge resin but greater than that on a
weight basis of organic matter obtained from an Andept
soil.
Present Management Practices for Reduction of P
Fixation
There are at present two management alternatives
for favorable P fertility on acidic soils (Sanchez and
Uehara, 1980). One is a high input strategy utilizing
P as an amendment and the other is a more economical
low input strategy. Each method will be discussed.
Phosphorus as an Amendment
Fox and Kamprath (1970) determined that 95% of the
maximum yield could be obtained when the fertilizer
rate was adjusted such that 0.2 ug P/ml existed in the
soil solution as determined by adsorption isotherms on
acidic soils. To obtain that concentration. 700 kg
P/ha were added. Ten y after the initial experiment,
the residual efficiency which is fertilizer P
effectiveness in crop production over time, ranged from


78
Fig. 4-10 Truog Extractable P Levels as Affected by
Clover and Fe(OH) Applications at the 0
mg/kg P Rate During the First Cropping
Period.
Truog Extractable P mg/kg


96
Table 4-13 Response Surface Equations of P and FeCOH)^
Across Clover Application Rates in Relation
to Dry Weight Yield After the Third
Cropping.
Corelation
Response Surface Equation Coefficient
Yield
= .33
Cl over
+ .09 P
Applied (0 g/kg)
+ .12 Fe .01 P*Fe
r2 = .76
Yield
= .88
Clov er
+ .06 P
Applied (1.58 g/kg)
+ .04 Fe .01 P*Fe
r2 = .52
Yield
= 2.28
Clov er
+ .05 P
Applied (3.15 g/kg)
- .23 Fe .002 P*Fe
r2 = .53


Table 4-5 Truog Extractable P Levels Determined After the First Cropping Period
Response Surface Equation
Correlation
Coefficient
P Applied (0 mg/kg)
Truog P = 3.05 0.43 Fe + 0.30 clover 0.05 Fe clover
P Applied (50 mg/kg)
Troug P = 5.43 1.00 Fe + 0.46 clover -0.05 Fe clover
P Applied (100 mg/kg)
Troug P = 7.02 0.99 Fe + 1.07 clover -0.21 Fe clover
r2 =0.40
r2 =0.95
r2 =0.78


34
acidic (pH 4.9), a liming curve after FeCOH)^ applica
tion was essential to determine pH for maximal organic
adsorption. Also the pH of the soil must be greater
than the dissociation constant of the organic acid (pH
> 5.0) to activate organic anions (Greenland, 1971).
Clover rates were similar to residue rates added to the
soil for cover crop production.
Results from the incubation study with respect to
treatment are given in Fig. 3-2 to 3-9. Organic ad
sorption relationships produced by changes in pH are
given in Fig. 3-2 to 3-5 and adsorption relationships
with change in ionic strength are given in Fig. 3-6 -
3-9. Numbers in parenthesis in these figures are soil
pH values. Ionic strength was calculated to be the
total ionic strength of solution minus the ionic
strength of the 0.01 M NaCl solution. Total ionic
strength was calculated by the following equation:
u = 0.013 EC
where 0.013 is a constant and EC is electrical conduc-
_ £
tivity expressed in millimhos cm (Griffin and
Jurinak, 1973).
Stevenson (1982) stated that organic adsorption to
clay surfaces was sensitive to changes in ionic
strength. The mechanism of adsorption is by ionic


114
pH
Fig. 4-29 Surface Properties of Orangeburg Topsoil
+ FeCOH)^ amended with 100 mg P/kg as
Determined by Potentiometric Titration.


TABLE OF CONTENTS
ACKNOWLEDGMENTS iii
ABSTRACT vii
CHAPTERS
I INTRODUCTION 1
II LITERATURE REVIEW 4
Effect of Iron Oxides on Soil Chemical
Properties 4
Present Management Practices for Reduction
of P Fixation 9
Decompositional Products of Organic
Material s 13
Organic Anion and Iron Mineral Interac
tions 17
Organo-Mineral Reactions Affecting P
Fixation 20
III ORGANIC ADSORPTION EXPERIMENT 25
Introduction 25
Materials and Methods 26
Results and Discussion 33
Conclusions 45
IV PHOSPHATE AND ORGANIC AMENDMENT EXPERIMENT...50
Introduction 50
Materials ....51
Methods.... 52
Incubation Study 52
Glasshouse Study 52
Surface Charge 55
SEM Study 56
Results and Discussion 56
Incubation Study 56
Glasshouse Study 65
Surface Charge Ill
SEM Study 118
Conclusions 121
v


8
a first order relationship after 48 hours of reaction
time (Ryden et al., 1977) such as:
[A] = K[A]
when A, t, and K represent phosphate concentrations,
time, and a constant, respectively (Bohn et al., 1985)
Differences in reaction rates were attributed to min
eral and solution Fe and Al (Hsu, 1965). He also
stated that in principle, there was no difference
between precipitation and adsorption reactions. He
noted that whether a Fe^(OH)^^(HjPO^)6 or
Fe^^(OH)^^^(H2PO^)jg compound is formed is irrelevant
since the chemical reaction is the same.
Desorption is also an extremely complex phe
nomenon. If the enthalpies of the mononuclear and bin
uclear Fe phosphate complexes are similar, the binu-
clear adsorption would exhibit greater stability
(Hingston et al., 1974) due to an increase in entropy
(Martell and Calvin, 1952). Slow release of phosphate
from Fe oxides has been attributed to a ring-forming,
binuclear phosphate adsorption (Atkinson et al., 1972)
Phosphorus Fixation by Organic Components
During the decomposition of organic materials in
acidic soils, organic functional groups can form a
stable complex with Fe or Al in solution (Deb and
Datta, 1967). Humic acids extracted from acid soils
usually have a high Al and Fe content (Greenland


140
Reduced P availability also induced a soil and treat
ment interaction in which the P in Orangeburg subsoil
was more available to plants as determined by plant P
uptake (Table 5-7) than P from Orangeburg topsoil +
Fe(0H)g. Differences in P uptake produced a soil and
treatment interaction in which yield was greater on
Orangeburg subsoil than Orangeburg + FeCOH)^ treated
soil (Table 5-8). Similar trends observed during the
first cropping period occurred for the second cropping
period. Point placement and granules were superior in
producing yield and increasing P uptake to completely
mixed placement methodologies. Loss of effectiveness
of the 0.5 g clover coated granule in increasing P
uptake on Orangeburg topsoil + FeiOH)^ was noted only
during the second plant growth period.
Conclusions
Point placement of fertilizer and clover coated
granules were superior to completely mixing fertilizer
and clover to the soil, as measured by corn yield, P
uptake, Truog extractable P and Bray P 2 extractable
levels of soil P. There was no difference in experi
mentation variables between point or granule placement
of fertilizers except increased P uptake on Orangeburg
topsoil + Fe(0H)g during the first cropping period.
Lack of differences in yield between granule and point


102
release into the soil solution or as sites for P reten
tion.
Truog Extractable P
Truog extractable P levels were affected by an
interaction of FeCOH)^ with clover (Table 4-16). With
out FeCOH)^ addition, Truog extractable P levels in
creased with increasing P rates and clover additions.
(Fig. 4-22, 4-23 and 4-24). With FeiOH)^ addition,
Truog P levels were increased with clover application
compared to without clover application. The Fe(0H)g
addition reduced Truog P levels at each P and clover
rate. Variability in Truog P levels on Fe(OH)g treated
soils may result from differences in P taken up by
plants causing reduction extractable P levels.
Bray 2 Extractable P
Bray 2 extractable P levels were affected by P
rates, FeiOH)^ addition, and clover application rates
as a triple-order interaction (Table 4-17). Increases
in extractable P were linear with increasing clover ap
plications (Fig. 4-25, 4-26, and 4-27) and also with
increasing P rates. The FeiOH)^ applications reduced
extractable P levels significantly. Although increases
in extractable P were obtained with clover application
on FeiOH)^ treated soil, increases were not as great


82
Table 4-6 Main Effects of P, Fe(OH) and Clover
Affecting Bray 2 Extractable P Levels From
the First Cropping Period.
P Aapplied
Bray 2
Contrast
p > F
(mg/kg)
Extractable P
0
9.86
0
vs others
0.01
50
20.01
50
vs 100
0.01
100
27.84
Fe Applied
(fc/kg)
0
26.06
0
vs 5.6
0.05
5.6
12.41
Clover Applied (g/kg)
0
14.56
0 vs others
0.01
1.58
18.13
1.58 vs 3.15
0.01
3 .15
25.02


Fig. 3-11 Differential Scanning Calorimetry Plot of
Orangeburg Topsoil with FeCOH)^ and Clover
Addition.


88
with increasing clover rates (Table 4-12 and Fig. 4-16,
4-17, and 4-18). Increases of Bray 2 extractable P
from Fe(OH)^ untreated soil compared to that for Crop 1
may have been produced by precipitation of Fe or A1
phosphates with decreasing soil pH. Reversion of a
calcium phosphate to a Fe or A1 phosphate possessing
greater stability would increase Bray 2 levels. Change
in Bray 2 extractable P may be due to blockage of P
fixation sites by organic ligands reducing the
irreversible binuclear P adsorption.
Crop 3
A third crop was grown for 50 d to determine
clover effectiveness over time in increasing dry weight
yield, P uptake, and Truog and Bray 2 extractable P.
Each treatment was again limed to pH 6.3 utilizing the
liming curve described in Chapter 3. Constant fertil
izer amounts were applied. Rates of 0, 50, and 100 mg
P/kg as DAP were applied to appropriate treatments.
Yield
Dry matter yield was influenced by interaction of
P with FeCOH)^ applications. (Table 4-13). Increasing
rates of P increased dry weight yield (Fig. 4-19, 4-20
and 4-21). Observations of increases in yield on
Fe(0H)g treated soil with increasing clover applica
tions suggested that organic functional groups were
bonded to Fe mineral surfaces, thereby reducing P


Absorbance (445 nm) of Humic Acid in Solution
42
Ionic Strength
Fig. 3-8 Effect of Organic Release From Orangeburg
Topsoil + Fe(OH)_ as Influenced by
Solution Ionic Strength.


27
Chapman 1965). Organic carbon was determined by
dichromate-oxidation techniques (Walkley and Black,
1934). Soil pH was determined in a 1:1 ratio of soil to
water (McLean, 1982). Phosphorus fixation was deter
mined by methodology of Fassbender and Igue (1967) in
which 5 g of soil were placed into a centrifuge bottle
with 100 mL of 100 mg P/L solution. The bottle was
shaken for 6 hours at 180 excursions/min. Separation
between solution and solid phase was accomplished
through millipore filtering (.2 u). Extracts were ana
lyzed for P using methodology described by Murphy and
Riley (1962). Results are given in Tables 3-1 and 3-2.
Fe(OH)^ Synthesis
Amorphous ferric hydroxide was prepared by poten-
tiometrically titrating 2 M Fe(N03)3 with 6 M KOH to pH
8.1 (ZPC). Equivalent concentrations of both reagents
were used in precipitating the Fe(0H)3 (Fig 3-1). To
remove the soluble KN03 formed, approximately 2 L of
deionized water was filtered through 250 g of precipi
tate resulting in negligible concentrations of K+ and
N03 A suspension of Fe(0H)3 in H30 was prepared with
a concentration of approximately 1 M as Fe(0H)3# Rates
of 0 and 5.6 g Fe as Fe(0H)3 were applied to Orangeburg
surface soil by complete mixing.


121
Whether this relationship was produced from segregating
clay fractions or existed previously in the soil is
unknown. Much care was taken to isolate clay fractions
with minimal reagent addition. A close up view of an
aggregate magnified 10.000X, from a clover pretreatment
sample is shown in Fig. 4-34. High molecular weight
humic acids contain numerous functional groups (Inoue
and Wada, 1968) which can bind to Fe(OH)g surfaces,
thereby reducing soil surface area. (Schwertmann and
Fisher, 1973). Clay fraction surface area could be
reduced if aggregation of clay particles had occurred.
Conclusions
Incubation studies indicated that P fixation is
reduced with clover pretreatment on soils containing
sesquioxide minerals. Orangeburg topsoil +Fe(OH)^ and
Orangeburg subsoil, coated with goethite, had lowered P
fixation capabilities after receiving clover applica
tion. Increased P fixation capacity was observed on
Orangeburg topsoil without FeCOH)^ application with
increasing clover rates. At 60 d of incubation, P
fixation capacity was reduced on all treatments after
possible P mineralization of clover, and increase in pH
reducing net positive charge on soil mineral surfaces.
After 90 d, P fixation capacity had returned to near
initial levels as pH decreased. Phosphorus fixation


62
Clover Applied g/kg
Phosphate Fixation Capacity
Amended With Various Clover
Days of Incubation.
Fig. 4-3
of soils
Rat es After 90


24
components reduced the positive charge on the soil sur
face. They found a linear correlation (p>.01) between
increasing percentage of organics and reduction of pos
itive charge. Phosphate adsorption at pH 5.0 was
reduced by the presence of organic matter. They also
observed a linear correlation (p>.01) between a
decrease of phosphate adsorption and increasing C%.
Hinga (1973), also obtained similar results on Kenya
soils.


Table 4-15 Main Effect
Period.
of Fe(0H)g Relating to Soil pH
Changes During
the Third Cropping
Fe Applied (g/kg)
pH
Contrast
p > F
0
6.20
0 vs 5.6
0.01
5.6
5.28
Table 4-16 Response Surface Equations of Fe(0H)g and Clover Acrosss
in Relation to Truog Extractable P Levels After the Third
P Application Rates
Cropping Period.
Response Surface Equation
Correlation
Coeffiecient
P Applied (0 mg/kg)
Truog P =
3.48 .12 Fe + .20 clover -.03 Fe clover
r2 = .59
P Applied (50 mg/kg)
2
Truog P = 7.75 -.28 Fe + .57 clover .10 Fe clover r =.36
P Applied (100 mg/kg)
2
Truog P = 14.54 -1.87 Fe + ,77clover .10 Fe clover r = .98
o
oo


emulation, anchored by a spirit of love, aided me more
than they will ever know.
During the third year of my pursuit of a doctor
ate, I endured a bitter disappointment that almost dev
astated me. Miss Betty Jean (B.J.) Cross, my former
fiancee, passed from this life. She endured the rigors
of graduate school with me and was always supportive.
This beautiful lady, both physically and spiritually,
shall always be in my memory. It is to her, that this
work is dedicated.
IV


57
Table 4-1. Effect of Experimental Parameters on
P Retention Capacity
Source
df
Mean Square
p > F
Time
2
279999
0.0001
REP
1
2759
0.39
Error a
2
1245
Soil
2
550367
0.0001
Clov er
2
3058
0.44
Soil X Time
4
11426
0.03
Clover X Time
4
13726
0.02
Soil X Clover
4
11474
0.03
Soil X Clover
X Time
8
13491
0.01
Error b
24
3611


113
Fe(OH)g addition which increases net positive charge.
However, the integrity of the kaolinite surface should
not have been totally lost after addition of 5.6 g
Fe/kg as Fe(OH)3<
Orangeburg + FeCOH)^ + P
Orthophosphate binds covalently to FeCOH)^ mineral
surfaces releasing OH^0 and OH ligands and produces a
surface with greater net negative charge (Hingston et
al., 1974). This reaction lowers the pH of the ZPC
(Schwertmann and Taylor, 1977). From the results shown
in Fig. 4-29, a decrease in ZPC pH from 4.0 to 3.5 had
occurred suggesting covalent bonding of P to the iron
mineral surface. Increase in positive charge (2
cmol(+)/kg soil) indicates that H+ adsorption possibly
occurs on a more negatively charged surface produced by
orthophosphate specific adsorption with lowering of
kaolinite ZPC.
Orangeburg + Fe(0H)3 + Clover
Humic and fulvic acids from clover are decomposi-
tional products that possess mainly carboxyl functional
groups (Kononava, 1961). Disassociation constants for
humic acid are near pH 5.0 (Greenland, 1971) which is
close to the acetic acid (H^C20) disassociation
constant (4.75) (Weast, 1973). Titration of Orangeburg
soil + FeiOH)^ with clover addition produced a ZPC at
pH 4.70 with 0.01 and 0.1 M NaCl additions. Binding of
soluble Al and Fe by carboxyl groups may have occurred.


Table 3-1 Characterization Data of Orangeburg Surface Soil
Mineralogy
Particle
Size
pH (H20) 0C
CDB +
P Fixation
sand silt
cl ay
1 : 1
%
Fe A1
%
-Fe(OH) +Fe(OH)-
mg/kg
Kaolinite
Quartz
Gibbsit e
14 ^ intergrade
85 1.2
13.8
4.9 1.36
0.31 0.08
190 640
Extractable Bases++
Ca Mg Na K Extractable Acidity+++
cmol (+)/kg
0.77 0.32 0.04 0.04 5.70
+ Citrate-dithionite-bicarbonate
++ NH.OAc (1M) extraction (pH 7.0)
+ + + BaC^-TEA extraction (pH 8.2)
K>
00


Abstract of Dissertation Presented to the Graduate
School of the University of Florida in Partial
Fulfillment of the Requirements for the Degree of
Doctor of Philosophy
CLOVER RESIDUE EFFECTIVENESS IN REDUCING
ORTHOPHOSPHATE SORPTION ON FERRIC-HYDROXIDE
COATED SOIL
By
GEORGE WILLIAM EASTERWOOD
August, 1987
Chairman: Dr. J. B. Sartain
Major Department: Soil Science Department
Laboratory research suggests that organic acids
bind to iron-mineral surfaces, reducing P fixation.
Experiments were conducted to determine 1) maximal
clover residue adsorption, 2) P fixation capacity of
Fe(OH)g treated topsoil and goethite coated subsoil
amended with clover, 3) clover residue effectiveness in
relation to maize yield and extractable P levels, and
4) surface charge with P, clover, and P and clover
applications to Fe(OH)3 treated soils.
Amorphous iron-hydroxide (FeCOH)^) precipitate was
applied to Orangeburg soil (fine, loamy, siliceous,
thermic Typic Paleudult) at rates of 0 and 5.6 g Fe as
FeiOH)^. White clover (Tr i^l^o ium tepens) was grown
hydroponically in Hoagland's solution.
Vll


149
Carroll, D. 1958. Role of clay minerals in the
transportation of iron. Geochemica et
Cosmochimica Acta, 14:1-28.
Chapman, H. D. 1965. Total exchangeable bases, p 902-
904. ^5: Methods of Soil Analysis, Part 1. Am.
Soc. Ag., Inc., Madison, WI.
Chen, Y., N. Senesi, and M. Schnitzer. 1977.
Information provided on humic substances by E4/E6
ratios. Soil Sci. Soc. Am. J. 41:352-358.
Chu, C. R., W. W. Moschler, and G. W. Thomas. 1962.
Rock phosphate transformations in acid soils.
Soil Sci. Soc. Am. J 26:476-478.
Datta, N. P., and N. N. Goswami. 1962. Transformations
of organic matter in relation to the availability
of nutrients to plants, p 223-238. ^n Isotopes
and Radiation in Soil Organic Matter Studies.
Proc. Symp. IAEA/FAO, Vienna.
Datta, N. P., and B. R. Nagar. 1968. Studies on the
decomposition of organic matter in soil in
relation to its maintenance and the availability
of nutrients to plants, and on the origin and
structure of humic acids, p 287-296. ^n Isotopes
and Radiation in Soil Organic-Matter Studies.
Proc. Symp. IAEA/FAO, Vienna.
Day, P. R. 1965. Particle fractionation and particle
size analysis. P 532-543 Iji Methods of Soil
Analysis. Part 1. Am. Soc. Ag., Inc., Madison,
WI.
Deb, D. L., and N. P. Datta. 1967. Effect of
associating anions on phosphorus retention in
soil: II. Under variable anion concentration.
Plant Soil 26(3):432-444.
Dixon, J. B. 1977. Kaolinite and serpentine minerals,
p 357-398. ^n Minerals in Soil Environments.
SSSA. Madison, WI.
Easterwood, G. W. 1982. Liming effect of cabonate
apatites. Master's thesis. University of Florida.
Evans, L. T., and E. W. Russell. 1959. The adsorption
of humic and fulvic acids by clays. J. Soil Sci.
10(1):119-132.


107
Table 4-17 Regression Equations of FeCOH)^ and
Clover Application in relation to of Bray 2
Extractable P Levels After the Third
Clover added
(fc/kg)
Regression Equations
Correlation
Coef ficient
P Applied (0 mg/kg)
0
Bray
P = 8.92 .84 Fe
r2
=
.95
1.58
Bray
P = 13.42 .90
Fe
2
r
=
.41
3.15
Bray
P = 20.52 2.21
Fe
r2
=
.95
P Applied (50 mg/kg)
0
Bray
P = 32.92 3.76
Fe
2
r
=
.97
1.58
Bray
P = 39.60 4.73
Fe
2
r
=
.98
3.15
Bray
P = 42.53 3.73
Fe
2
r
=
.96
P Applied (100 mg/kg)
0
Bray
P = 59.8 6.07
Fe
2
r
=
.96
1.5 8
Bray
P = 66.91 6.29
Fe
2
r
=
.99
3.15
Bray
P = 69.87 5.89
Fe
2
r
=
.98


clover/kg soil could not have been produced solely by P
release at the rate of 7.0 mg P/kg) .
Applications of 100 mg P/kg increased dry weight
yield compared to the 50 mg P/kg rate (Table 4-3 and
Fig. 4-6). Ferric hydroxide treatments decreased maize
yield but an incremental increase in yield was observed
with increasing clover applications. Yield was more
than tripled when clover was applied at 3.15 g
clover/kg soil. Phosphorus availability appeared to be
greater due to clover pretreatment. Results agree with
the previous incubation study relating to P availabil
ity with Fe(OH)^ treatment in acidic (pH 5.2) ranges.
Greater yield was obtained without clover application
if Fe(OH)^ was not introduced into the soil system.
Cation bridging of P to organic functional groups may
have produced this result.
P uptake
Phosphorus uptake by maize plants was affected by
amount of P or FetOH)^ applied. Increasing P rates
increased P in plants while addition of FetOH)^ reduced
P uptake. With increasing rates of clover applied
(Table 4-4 and Fig. 4-7, 4-8 and 4-9), enhanced P
uptake was obtained. Mechanisms relating to clover
amendment effectiveness were not determined. Yield
data appears to relate well to P uptake observations.
Binding of Fe or A1 by organic functional groups or


Tab]L e !3- 2 Characterization Data of_Oraneburg_Subsoil
Mineralogy
Particle Size pH (H^O)
OC
CDB +
P Fixation
sand silt clay 1:1
%
Fe A1
%
mg/kg
Kaolinite
Quartz
Gibbsit e
14 intergrade
Goethite
Ca Mg Na K Extractable Acidity+++
Cmol (+)/kg
57.6
8.6
33.8
5.1
0.40 0.84 0.11
800
Extractable Bases++
0.70 0.86 0.03 0.04
6.21
+ Citrate-dithionite-bicarbonate
++ NH.OAc (1M) extraction (pH 7.0)
+++ BaCl^-TEA extraction (pH 8.2)


150
Fassbender. H. W., and Y. K. Igue. 1967. Comparacin
de methodos radiometricos y col orimetricos en
estudios sobre retencin y transofrmacion de
fosfatos ensuelo. Turialba 17:284-287.
Follett, E. A. C. 1965. The retention of amorphous
colloidal ferric hydroxide by kaolinites. J. Soil
Sci. 16:334-341.
Fox, R. L., and E. J. Kamprath. 1970. Phosphate
sorption isotherms for evaluating the phosphate
requirements of soils. Soil Sci. Soc. Am. Proc.
34:902-907.
Greenland, D. J. 1965. Interactions between clays and
organic compounds in soils. Part II. Adsorption
of soil organic compounds and its effect on soil
properties. Soils Fert. 28:521-531.
Greenland, D. J. 1971. Interactions between humic and
fulvic acids and clays. Soil Sci. 111(1):34-41.
Hammond, L. L. 1978. Agronomic measurements of
phosphate rock effectiveness. p 147-173. Iji
International Fertilizer Development Center,
Seminar on Phosphate Rock for Direct Application,
Muscle Shoals, Ala.
Hashimoto, Y., and H. Takayama. 1971. Inhibiting
effect of nitrohumates and on phosphorus fixation
in soil. VII. Inhibiting effect using synthesized
iron compounds as the fixation materials. J. Sci.
Soil 42(1):37-43.
Hinga, G. 1973. Phosphate sorption capacity in
relation to properties of several types of Kenya
soil. East Afr. Agri. For. J. 38:400-404.
Hingston, F. J., A. M. Posner, and J. P. Quirk. 1974.
Anion adsorption by goethite and gibbsite. II.
Desorptions of anions from hydrous oxide surfaces.
J. Soil Sci. 25(1):16-26.
Hoagland, D. R. and D. I. Arnon. 1938. Growing plants
without soil by the water-culture method. Univ.
of Cal. Ag. Exp. Ssta. Berkeley, CA. Circular 347.
Hsu, P. H. 1965. Fixation of phosphate by aluminum and
iron in acidic soils. Soil Sci. 99(6):398-402.
Inoue, T., and K. Wada. 1968. Adsorption of humified
clover extracts by various clays. Trans. 9th Int.
Congr. Soil Sci., Adelaide, 3:289-298.


72
Plant Dry Weight Yield Affected by Fe(OH)
and Clover Applications at the 100 mg/kg
Rate During the First Cropping Period.
Fig. 4-6
Dry Weight Yield g/pot


117
pH
Fig. 4-31 Surface Properties of Orangeburg Topsoil +
FeCOH)^ With 100 mg/kg P and 3.15 g/kg
Clover Applications as Determined by
Potentiometric Titration.


104
1.58
Clover Applied g/kg
3.15
Fig. 4-22 Truog Extractable P Levels as Affected by
Clover and FeCOH)^ Applications at the
0 mg/kg P Rate During the Third Cropping
Period.
Truog Extractable P mg/kg


135
Decrease in pH increased sesquioxide ionic activity and
reduced P availability. There was no apparent differ
ence between pH of completely mixed soil and soil near
granules or spot placement.
Truog extractable P levels of granule treatments
were different with respect to soil. Greater concen
trations of extractable P were found in the soil around
granule placement with Orangeburg subsoil resulting in
increased dry mater yield and P uptake than with
Orangeburg topsoil + Fe(OH)3 (Table 5-4). This obser
vation confirmed the hypothesis that greater adsorptive
surfaces would be available for P adsorption on the
FeCOH)^ treated soil instead of goethite for granule
and point placement.
Truog extractable P levels from soil near fertil
izer granules were also affected by treatment (Table 5-
5). There was no difference between extractable P
levels from granule fertilizers or point placement
resulting in lack of response in plant yield and P
uptake for the two plant growth periods. The highest
Truog extractable P results within granule treatments
came from DAP granules coated with 0.50 g clover.
However, yield was not increased comparatively to other
granules or point placement treatments during either


7
OH
2
-2
-1
Fe
OP0
O
/
)
\
Fe
/
O
O
O
o
p
+ OH
OH
O
O
Fe
Fe
\
OH2
Reversibly adsorbed P
Irreversibly adsorbed P
Wann and Uehara (1978) determined that phosphate
addition to Fe-oxide-rich Oxisols lowered the ZPC and
increased surface charge density at any pH above the
ZPC. They suggested phosphate as an amendment to in
crease cation exchange capacity. Parfitt et al. (1975)
confirmed the binuclear coordination of phosphate
adsorption in goethite using infrared spectroscopic
analysis. Increasing surface area of major soil Fe
oxides was observed in which amorphous ferric hydroxide
> 1epidocrocite > goethite > hematite. Phosphorus
adsorption also increased with increasing mineral sur
face area.
Kinetics
Hsu (1965) studied phosphate fixation with soils
possessing Fe and Al oxides. He observed a two-stage
reaction rate in which P was fixed rapidly within a few
minutes or hours and a slower rate with increasing
time. Adsorption of P to Fe oxides is postulated to be


54
with 3 M HNO^, evaporated to dryness on a hotplate,
with removal of excess HNO^ by placing each beaker into
the muffle furnace at 450C for 10 m. After cooling,
25 mL of 5 M HC1 were added to the beaker, placed on a
hotplate and evaporated to dryness to completely
oxidize plant material. After cooling, 1 mL of 5 M HC1
was placed in the beaker with water and diluted to a
final volume of 50 mL. Ionic concentrations of Ca, Mg,
K, Al, and Fe were determined by Inductively Coupled
Argon Plasma spectrophotometry. Plant P concentrations
were determined by methodology described by Murphy and
Riley (1962).
Soils were sampled after each maize crop. Soil pH
was determined in 1:1 soil to water ratio (McLean,
1982). Organic C levels were determined by methodology
described by Walkley and Black (1934).
Since reaction products of DAP are CaHPO^^H^O,
CaHPO^, and colloidal ferric phosphate with Orangeburg
soil, proper extractants needed to be chosen for
extraction of these phases. Ballard (1974) compared
various extractant effectiveness on a variety of phos
phate reaction products as independent solid phases and
those phases mixed with soil. In his research Truog
reagent (0.001 M H2S04 + 3 g (NH4)2S04) extracted 100%
of P applied as dicalcium phosphate (DCP) as a solid
phase and 98% DCP mixed with Leon fine sand. Only 2%
of P applied as colloidal ferric phosphate (CFP) as a


45
exhibit crystallinity as observed by XRD or DSC method
ologies. The same result was obtained for the FeCOH)^
treated soil. Differential Scanning Calorimetric plots
of Orangeberg soil + FeCOH)^ clay fractions without
clover amendment and with clover amendment are given in
Fig 3-10 and 3-11, respectively. No Fe mineral en-
dotherm was observed. However, endotherms for both
gibbsite and kaolinite, were observed.
Conclusions
Adsorption study observations in conjunction with
previous research suggested that FeCOH)^ treated soil
exhibited covalent bonding of organic anions whereas
treatments without FeCOH)^ exhibited ionic bonding via
cation bridging. Maximum adsorption of organic con
stituents occurred at pH 6.3 on the FeCOH)^ treated
soil with clover amendment compared to pH 6.2 for
Fe(0H)g untreated soil. After 6 m of investigation,
solid FeCOH)^ and soil FeCOH)^ remained in an amorphous
state.


18
acid participate in the adsorption and their distribu
tion was throughout the organic molecules. Greater
surface area of the humic acid, at or above the pK
value, allows stronger adsorption to the oxide.
Reduction of available functional groups may occur
as cations are complexed from the soil solution (Zunino
and Martin, 1977). Complexation is very effective in
reducing Fe or A1 in solution due to the stability of
the complex (Deb and Datta, 1967). They found that the
stability of the complex is so great that functional
groups are rendered inactive with respect to further
interactions with hydrous oxides. Bloom and McBride
(1979) did research on the complexing ability of metal
ions with humic acids. They observed that humic acids
bind with most divalent metal ions, with the exception
2 +
of Cu as hydrated species. Also, they observed that
humic acids exhibit a strong affinity for trivalent
3 +
ions. The A1 ion is likely bound to three carboxyl
groups, but the case of the mono- and divalent species
adsorption from solution cannot be ruled out (Bloom and
McBride, 1979). Bloom (1979) observed the titration
behavior of Al-saturated organic matter. He observed
that, as the pH of the material is increased, the OH
would most likely form A1(0H) on the organic-matter
exchange sites. As the pH is increased until the
activity of (A1 )(OH ) is exceeded, precipitation of
amorphous AliOH)^ would be induced. Acid addition
on


76
bonding of organic ligands to Fe(OH)^ surfaces would
explain the results obtained.
Truog Extractable P
A reaction product of DAP is dicalcium phosphate
(Lindsay, 1959). Truog reagent is a good extractant
for this phase (Ballard, 1974). Preliminary extraction
with Truog reagent produced an Fe-clover interaction.
Addition of Fe(OH)3 reduced Truog extractable P levels
drastically (Fig. 4-10, 4-11 and 4-12). Without clover
application, P addition of 100 mg/kg slightly increased
Truog P levels which would apply to the dicalcium phos
phate fraction. Inconclusive results were obtained
with Fe(0H)g treated soils regardless of rate of P ap
plication. Without Fe(0H)g application, increases in
Truog extractable P resulted from clover application at
increasing P rates (Table 4-5). Previous mechanisms,
discussed above appeared to have produced these
effects.
Bray 2 Extractable P
Orthophosphate adsorption to iron mineral surfaces
reduces plant available P. Bray 2 extraction is a good
method for determining slightly soluble or desorbable P
reaction products. Bray 2 extractable P was affected
by main effects of P rate, Fe(0H)3 amendment, and


100
adsorption sites. At the 100 mg P/kg rate, addition of
3.15 g clover/kg increased yield 600% compared to
treatments without clover addition. This effect was
produced after an initial clover application and two
previous cropping periods on the same soil. Stability
exists in the effect produced by clover application on
Fe(0H)3 treated soil, whatever the mechanism. Without
FeCOH)^ application, mixed results were obtained with P
and clover application. At 50 mg P/kg, yield was
increased with increasing clover addition but at 100 mg
P/kg, yield was decreased with increasing clover rate
of application.
P Uptake
A second application of fertilizer P masked the
clover effect with respect to P uptake. As seen in
Table 4-14, P uptake was affected by main effects of P
and FeCOH)^ application. Increased rates of P applica
tion increased P uptake whereas addition of FeCOH)^
decreased P uptake.
Soil pH
Since the soil was limed before the third cropping
period, reversion of soil pH to its natural state had
not fully occurred. Differences in soil pH had devel
oped with respect to Fe(0H)3 addition (Table 4-15), but
pH had not decreased to a state that would promote
further extensive P fixation from A1 or Fe


94
Fig. 4-17 Bray 2 Extractable P Levels as Affected by
P and Fe(OH)_ Applications at the 1.58 g/kg
Clover Rate During the Second
Cropping Period.
Bray 2 Extractable P mg/kg


Potentiometric Titration of 450
Mil1iequival ents Fe as F e(NO)^ With KOH.
Fig. 3-1


CHAPTER IV
PHOSPHATE AND ORGANIC AMENDMENT STUDY
Introduction
Reduction of plant available phosphorus in acidic
soils causing an agronomic yield reduction has plagued
man for many years. The problem is produced by reac
tions of phosphates with Fe and A1 hydroxides, alumi
nosilicates and/or the ions released from dissolution
of these minerals (Chu et al., 1962; Lindsay, 1979;
Fox, 1974; Hingston et al., 1974).
A possible management alternative for reducing P
sorption could be addition of organic amendments.
Moshi et al., (1974) measured phosphate adsorption from
two profiles (one cultivated and one under forest envi
ronment) of Kikuyu red clay from Kenya. They reported
that surface-adsorbed organic components reduced the
positive charge on mineral surfaces. There was a high
statistical linear correlation between increasing per
centage organic carbon and reducing positive charge.
Since positive charge was reduced, phosphate adsorption
at pH 5.0 was reduced by the presence of organic
matter. Hinga (1973) obtained similar results on Kenya
soils. Yuan (1980) found that pretreatment with
organic material resulted in partial reduction of P
fixation on a Paleudult.
50


I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
Chairman
Professor of Soil Science
I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
1
/
>
//
u-.c'
J. G. A. Fiskell
Professor of Soil Science
I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
QO ',^'
J ./ p ilS t r e e t
A ss b ciate Professor of Soil
Science
I certify that I have read this study and that in
my opinion it conforms to acceptable standards of
scholarly presentation and is fully adequate, in scope
and quality, as a dissertation for the degree of Doctor
of Philosophy.
E. A. Hanlon
Assistant Professor of Soil
Science


115
The 1.0 M NaCl plot did not intersect with other plots
possibly due to mass action of Na replacing A1 or Fe
from the carboxyl group and producing acidity upon
hydration, requiring less H+ from the titration. The
ZPC values from previous plots were not at pH 4.70
indicating surface properties produced from clover
application (Fig. 4-30). A second ZPC was produced at
pH 3.8. Since organic functional groups bind
covalently to iron minerals, partial reduction of
kaolinite ZPC at pH 4.0 may have been produced by
organic ligands binding to FeCOH)^ on the kaolinite
surface. Increased negative charge for H+ adsorption
and reducing pH at the ZPC would result. With clover
addition, positive charge was increased to 2.5 cmol
(+)/kg compared to 1.0 and 2.0 cmol (+)/kg for Orange
burg + Fe(0H)g and plus P addition, respectively.
Orangeburg + Fe(OH)^ With P and Clover Addition
Addition of P and clover produced surface proper
ties similar to clover addition alone. A ZPC value was
obtained at pH 4.75 (Fig. 4-31) which is similar to
carboxyl disassociation constants. If A1 or Fe had
been released into solution with increasing H+
additions, acidity from A1 or Fe hydration could lower
the ZPC of 1 M NaCl to pH 4.50. However, this pH may
be an artifact of the titration from precipitation of


109
Clover Applied g/kg
Fig. 4-26 Bray 2 Extractable P Levels as Affected by
Clover and Fe(OH) Applications at the
50 mg/kg P Rate During the Third Cropping
Period.
Bray 2 Extractable P mg/kg


85
Table 4-8 Main Effect of Fe(OH) Addition on A1 and
Fe Concentrations in Plant Tissue After the
Second Cropping Period,
A1 Fe Contrast p>F
mg/kg
Plus Fe(OH) 131 133
Plus vs Minus 0.01
Minus Fe(OH)3 83 83
Table 4-9 Main Effect of Fe(OH)^ Treatment on Plant P
Uptake During the Second Cropping Period.
Fe (g/kg) P uptake mean Contrast p>F
mg P/Pot
0
5.6
2.15
0.57
0vs5.6 0.01
Table 4-10 Main Effect of FeCOH)^ Treatment on Soil
pH After Two Cropping Periods.
Fe (g/kg) pH mean Contrast
p > F
0
5.12
5.6
4.95
0 vs 5.6
0.01


90
Clover Applied g/kg
Fig. 4-13 Truog Extractable P Levels as Affected by
Clover and FeCOH)^ Applications at the
0 mg/kg P Rate During the Second Cropping
4
Truog Extractable P mg/kg


2
Phosphorus (P) fixation, which is reduction of
soil solution phosphate by Fe minerals, may occur by
adsorption to the solid phase or precipitation
reactions from the solubility products (Chu et al.,
1962). Adsorption may occur as a mono- or binuclear
covalent bonding to the Fe mineral (Hingston et al.,
1974). Binuclear adsorption is irreversible in that
desorption is negligible. Iron ionic species may
reduce P availability below pH 5.5 through
precipitation reactions. If the solution species of Fe
and H^PO^ reach saturation with respect to the
solubility product of strengite (FePO^*2H2O),
precipitation can result (Lindsay, 1979).
Present management practices for reduction of P
fixation include either P as an amendment, or use of a
low input strategy which includes proper placement,
less costly P sources, and soil amendments such as lime
or silicates (Sanchez and Uehara, 1980). Another man
agement practice that could possibly reduce P fixation
would be to apply an organic amendment to the soil.
Humic and fulvic acids covalently bind to Fe mineral
surfaces (Parfitt et al., 1977) and reduce net positive
charge (Moshi et al., 1974). Complexation of solution
Fe or Al may occur by bonding ionically to the organic
functional groups (Deb and Datta, 1967).
Less costly management practices of applying crop
residue possibly could substantially increase agronomic


112
pH
Surface Properties of Orangeburg Topsoil
+ Fe(OH) as Determined by Potentiometric
Titration
Fig. 4-28


Absorbance (445 nm) of Humic Acid in Solution
36
0.6
0.5
0.4
0.3
0.2
5.0
6.0
6.8
pH
Fig. 3-3
Clover Decompositional Product Adsorption
to Orangeburg Topsoil as Influenced by
Soil pH.


39
bonding. Similar results were obtained from the treat
ments of Orangeburg soil without Fe hydroxide addition.
Increasing lime rates increased soil pH from 4.9 to 6.7
(Figs 3-2 and 3-3) but also increased solution ionic
strength due to increased Ca activity (Figs 3-6 and
3-7). Calcium does not form a strong complex between
negatively charged clay and humic acid, but is effec
tive as a bridge between ions (Stevenson, 1982).
Greenland (1971) observed that organic matter bound to
2 +
clay through Ca cation bridging was easily displaced
by monovalent ions such as NH^ + or Na+. Increases in
pH increase negative charges on mineral surfaces
(Kaolinite) and therefore cation exchange capacity.
Near pH 6.2, less organic anions were extracted by
+ 2 +
NaCl. Possibly Na and Ca ions increased exchange-
3 + 3 +
able A1 or Fe levels. Aluminum and Fe at low con
centrations could reduce organic anions by flocculation
(Stevenson, 1982). Results are inconclusive above pH
6.2.
Stevenson (1982) also stated that organic adsorp
tion to hydrous oxides occurred by ligand exchange or
covalent bonding. Only anions that bind strongly to
oxide surfaces could replace organic anions. This mech
anism is insensitive to solution ionic strength but
highly sensitive to pH. Salt solution extraction did
not affect organic adsorption. Results in Fig. 3-4, 3-
5, 3-8, and 3-9 support this mechanisms organic


75
o
a.
\
oo
E
cu
co
U
Q.
"O O'
Fe Applied g/kg
Fig. 4-9 Phosphorus Uptake by Maize as Affected by
FeCOH)^ and P application at the 3.15 g/kg
Clover Rate During the First Cropping
Period.


17
releasing H+ as the pK value is reached. On a percent
age basis of dry ash-free material, plant residue con
tains 9% carboxylic, 8% alcoholic-OH, 6% phenolic-OH,
and 3% methoxy functional groups producing the high
reactivity of humified organic material.
Inorganic P Released From Clover Decomposition
During the decomposition of clover, inorganic
phosphate may be mineralized. Lockett (1938) postu
lated that P was mineralized and assimilated into
microbial lipids and nucleoproteins. Later P became
available upon disintergration of microbial cells. He
determined that, after decomposition, 59% of the total
P was in organic form and 41% in inorganic form. He
obtained similar results as those observed by Kononava
(1961).
Organic Anion and Iron Mineral Interactions
Unlike cation bridging of organic anions to clays
(Evans and Russell, 1959), the mechanism of humic and
fulvic-acid anion bonding to Fe minerals is by specific
adsorption or ligand exchange (Parfitt et al., 1977).
The process is not sensitive to electrolyte concentra
tions, although it is sensitive to pH since the adsorp
tion maximum inflection point occurs near the pH corre
sponding to the pK of the acid species, which is usu
ally carboxylic and near pH 5.0 (Greenland, 1971). He
reported a very strong bond between oxide and humic
molecules since most functional groups of the organic


Absorbance (445 nm) of Humic Acid in Solution
37
pH
Fig. 3-4 Effect of Soil pH on Organic Release From
Orangeburg Topsoil + FeCOH)^.