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

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Clover residue effectiveness in reducing orthophosphate sorption on ferric-hydroxide coated soil
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Soil Sciences thesis Ph. D
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Thesis (Ph. D.)--University of Florida, 1987.
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Includes bibliographical references (leaves 148-154).
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by George William Easterwood.

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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





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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.




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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






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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:





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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.





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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.





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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



I I i
I I I
I I -- I
to I I I
10 I l I
I.a j I


e +



I I I






I I : I I I I




o4
I IIIII





I0 I'1 I I +





00 14I 1 0 I H I I 1





0 1 I


1ol I I.4I I 1 I I *, l I





I I o o 1I I |iO ,I *o I I 4 I I 0 o4 z1 1




S I I *II




,. I I ,I aJIi to I C 4





I l 9 I q 4 -4 l II NI I 00.I1e c -I I-I l I I II ,. 0






I I m II I + I1 1 w M ,I I O o 1 1 1 w 1 1 1c to 19 +I-+ E- IX CI C ,a *4






29







o, q o
11 1









I 4 SI I + I M o I V
S I 0 01 cc 1 0 I0 01 I I


ol a



w I I







4J 1 M I I,, 0 I 0 1 I > i 1







.,i co I *,i I 0 I





WI I II cc





-,41 t o
I I *




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I 1 I I I




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I e 0 I a


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Al aI om 0I C14 l w *M I rc












































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O
1m)

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-i co



um




















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SrA














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31









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8





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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
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CO c00








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47










































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- .





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CYH


(O)








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C60
- H W 'a cz 0 < 2









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0) C)




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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

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.

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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.

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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.

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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)„

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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.

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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

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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

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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.

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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

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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

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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

PAGE 65

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.

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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.

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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.

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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.

PAGE 120

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

PAGE 139

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

PAGE 142

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

PAGE 145

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

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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

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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.

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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

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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

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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.

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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

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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.

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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.

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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..

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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.

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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.

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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

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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

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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

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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