DECOMPOSITION, FUNCTION, AND MAINTENANCE OF
ORGANIC MATTER IN A SANDY NURSERY SOIL
KENNETH RICHARD MUNSON
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
I wish to thank Dr. E. L. Stone for his guidance as my com-
mittee chairman, and for sharing with me his scholarship, enthusiasm,
and keen sense for reason. I also wish to thank Dr. W. L. Pritchett,
Dr. E. L. Barnard, Dr. R. F. Fisher, Dr. C. A. Hollis, and Dr.
D. H. Marx for their advice during the course of this investigation.
I appreciate the laboratory support provided by Mary McLeod,
and the statistical advice of John Shelton.
I gratefully acknowledge Container Corporation of America for
allowing me to conduct this research at the company nursery. I
particularly wish to thank Mr. Dale Rye for his conscientious co-
operation and practical perspective.
Finally, I thank the Cooperative Research in Forest Fertilization
program for providing financial support.
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ........................................ i
LIST OF TABLES ......................................... ...
LIST OF FIGURES ............................................ vii
ABSTRACT .............................................. viii
GENERAL INTRODUCTION ...................................... 1
LITERATURE REVIEW .......................................... 4
CHAPTER I. FIELD MACROPLOT STUDY WITH PEAT
Introduction .............................................. 10
Materials and Methods ................................... 11
Study Area ........................................ 11
Experimental Design and Conduct .................... 11
Sampling Scheme ................................... 14
Laboratory and Chemical Analyses .................... 15
Statistical Analysis ................................. 16
Results and Discussion ........................... ......... 18
Peat Decomposition ................................... 18
Effects on Soil Chemical Properties ................... 22
Effects on Seedling Development ...................... 27
Effects on Mycorrhizae and Incidence of
Charcoal Root Rot ...................... ........ 37
CHAPTER II. FIELD MICROPLOT STUDY WITH VARIOUS ORGANIC
Introduction ............................................. 40
Materials and Methods ............................... ... 41
Study Area ............................... ..... . 41
Experimental Design and Conduct ............ ...... .... 41
Sampling Scheme ................................. 44
Analyses .................................. ..... -45
Results and Discussion ................................. .. 47
Decomposition ........................................ 47
Effects on Soil Chemical Properties ........... ........ 54
Effects on Seedling Development ...................... 63
Effects on Mycorrhizae and Incidence of Charcoal
Root Rot ...................................... 70
Utility of the Microplot Method ....................... 72
General Conclusions .................................. 74
CHAPTER III. LABORATORY INCUBATION OF VARIOUS
Introduction ........... ... ............................ 76
Materials and Methods ............. .... .......... .. ...... 77
Experimental Design and Conduct ..................... 77
Chemical Analyses .................................. . 79
Statistical Analyses .............. ................ .. 79
Results and Discussion ................................... 81
CO2 Evolution as Influenced by Amendment ........... 81
CO2 Evolution as Influenced by Amendment Rate ...... 88
Utility of the Method for Predictive Purposes .......... 91
LITERATURE CITED ............................ .......... . 92
BIOGRAPHICAL SKETCH ........ ................... .. .. ...96
LIST OF TABLES
1-1. Analysis of variance designs used for treatment compar-
isons ................................. .... ... ........ 17
1-2. Soil reaction as influenced by peat amendment .......... 23
1-3. Soil nutrient status as influenced by peat application and
time of sampling ........................................ 24
1-4. Soil nutrient status after 21 months as influenced by peat
application averaged across fumigation, and by fumigation
averaged across all peat rates .......................... 26
1-5. Physical parameters of two successive crops of slash pine
seedlings as influenced by peat amendment averaged across
fumigation treatment .................................... 28
1-6. Physical parameters of two successive crops of slash pine
seedlings as influenced by fumigation averaged across all
peat treatments ......................................... 29
1-7 Element concentrations of slash pine seedling shoots grown
in 1981 as influenced by peat amendment averaged across
fumigation treatment .................................... 31
1-8. Elemental contents of slash pine seedling shoots grown in
1981 as influenced by peat amendment averaged across
fumigation treatment .................................... 35
1-9. Elemental contents of slash pine seedling shoots grown in
1981 as influenced by fumigation averaged across all
peat treatments ................... .. .... .......... .... 36
1-10 Ectomycorrhizal infection as influenced by peat addition
and fumigation ......................................... 38
2-1. Chemical characteristics and particle size distribution of
four organic materials used as nursery soil amendments.. 43
2-2. Analysis of variance designs used for comparisons among
treatments ............................................. 46
2-3 Soil nutrient and OM status as influenced by four organic
amendments at 3 and 18 months after application ......... 58
2-4. Double-acid extractable concentrations of Mn and Zn in
soil-amendment mixtures 3 and 18 months after appli-
cation ................................................. 62
2-5. Physical parameters of slash pine seedlings as influenced
by four organic amendments averaged across application
rates in 1980 and 1981 .................................. 64
2-6. Element concentrations (% dry weight) and contents (mg/
seedling) of slash pine seedling shoots as influenced by four
organic amendments averaged across application rates ... 66
2-7. Microelement concentrations (ppm dry weight) of 1981 slash
pine seedling shoots as influenced by four organic amend-
ments averaged across application rates ................. 67
2-8. Approximate percentages of short roots colonized by
ectomycorrhizal fungi as influenced by treatments ....... 71
3-1. Chemical characteristics of organic materials and unamended
soil ................................... ............... 78
3-2. Analysis of variance designs used for comparisons of CO2
evolution among materials and rates ..................... 82
3-3. Monthly (4 week) CO2 evolution from 100 g nursery soil
incubated with 2 g (ash free) organic material from several
sources .................................... .......... 83
3-4. Monthly (4 week) CO2 evolution from 100 g nursery soil
incubated with 1, 2, and 3 g (ash free) peat or pulp mill
waste ................................................... 89
LIST OF FIGURES
1-1. Field plot arrangement showing random locations of treat-
ment, fumigation subplots, and 0.1 m2 sample quadrats .. 13
1-2. Organic matter decomposition in an unfumigated nursery
soil amended with peat at three rates ................... 19
1-3. Nitrogen and Mn concentrations in slash pine seedlings
shoots grown in 1981 as influenced by peat amendment
averaged across fumigation treatment ................... 32
1-4. Elemental concentrations of slash pine seedling shoots
grown in 1981 as influenced by fumigation averaged
across peat treatment ................................... 33
1-5. Nitrogen and P contents of slash pine seedling shoots
grown in 1981 as influenced by peat amendment averaged
across fumigation treatment ............................. 34
2-1. Bucket microplot location, microplot with soil + organic
mixture, and the cross section of nursery bed with micro-
plots in place .................... ...................... 42
2-2. Organic matter decomposition in a nursery soil amended
with four organic materials at three rates ............... 49
2-3. Soil reaction as influenced by four organic amendments
applied at three rates ................................... 56
3-1. Schematic of laboratory incubation apparatus showing
incubation vessel and CO2 trap for 1 of 36 units ........ 80
3-2. Cumulative CO2 evolution from 100 g of nursery soil
amended with 2 g ash-free OM from several sources ..... 86
3-3. Cumulative CO2 evolution from 100 g of nursery soil
amended with three rates of pulp mill waste and peat ... 90
Abstract of Dissertation presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the
Requirement for the Degree of Doctor of Philosophy
DECOMPOSITION, FUNCTION, AND MAINTENANCE OF
ORGANIC MATTER IN A SANDY NURSERY SOIL
Kenneth Richard Munson
Chairman: Earl L. Stone
Major Department: Soil Science
Decomposition of organic soil amendments (OM) and their effects
on soil properties and seedling growth were examined in a Florida
forest nursery. Peat was applied at 22.4, 44.8, and 67.2 mt/ha to
field macroplots, with and without fumigation. Peat, sewage sludge,
shredded pine cones, and old pine sawdust applied at 22.4, 44.8, and
89.6 mt/ha were tested in field microplots. Two slash pine(Pinus elliottii
var. elliottii Engelm.) crops were grown in the macro- and microplots. In
a third study, CO2 evolution was monitored during laboratory incubation
of the foregoing materials, plus pine bark and pulp mill waste, in
About 20% of the peat applied at the higher rates in the macroplots
had decomposed after 21 months. Soil reaction was lowered below the
control by 0.3 pH unit/l% peat.
Seedlings from peat-treated plots were heavier, and had greater
N and P concentrations than control seedlings. Seedlings from fumigated
subplots had greater dry matter, but lower concentrations of most nu-
trients, than those from unfumigated soil.
After 18 months the loss rates of OM in the microplots at, respec-
tively, the 22.4, 44.8, and 89.6 mt/ha additions were as follows: Peat, 62,
51, 51%; sludge, 51, 54, 44%; cones, 51, 68, 68%; sawdust, 73, 53, 50%.
Peat decomposed 2 22 times more rapidly in the microplots than in the
As in the macroplots, peat lowered soil reaction. Cones and sawdust
lowered pH slightly after 12 months. Sludge increased pH from 5.7 to
6.5 initially, then reduced it to 4.8 after 3 months.
Peat decomposed without appreciable changes in N/OM ratios. The
high N concentration (5.6%) in sludge resulted in leaching of NO3 and
Seedlings from peat-amended soil had greater shoot-N contents,
and those from sludge-treated plots had greater concentrations of most
elements than control seedlings. Cones or sawdust did not reduce growth
or N-uptake below the control.
Under laboratory conditions for 7 months, < 5% of the sawdust,
cones, and bark had decomposed. Sludge, mill waste, and peat lost
10, 11, and 1%, respectively, of the added carbon.
Increasing demands for wood products and a decreasing area of
productive forest land emphasize the need for efficient reforestation
procedures. In the United States over 2 million acres were artificially
reforested in 1980, principally by planting seedlings grown in specialized
forest nurseries. Most of this planting stock, 1.4 billion, was grown as
"bare root" seedlings. Thus, reforestation programs begin in the nursery
with production of quality stock that will meet the objective of survival
and growth after outplanting.
Nursery management practices such as cultivation, fumigation and
entire seedling removal place intense demands on the soil resource. With-
out preventative measures the resource can be rapidly depleted, resulting
in a loss of productivity (Thompson and Smith 1947). This loss may be
manifested by seedlings of low quality with a low potential to survive
One such preventative measure is organic matter (OM) maintenance.
Such maintenance, however, is the most common problem associated with
nursery soil management (Abbott and Fitch 1977). Nurseries are normally
established on sites characterized by well-drained, sandy soils. These
properties facilitate seedbed formation, fumigation when necessary, soil
moisture control and seedling lifting. The frequent additions of in-
organic nutrients and water, however, coupled with well-aerated soils
produce conditions conducive to rapid OM decomposition. This process
is accelerated by the climatic conditions of the southeastern United
Organic materials used in OM maintenance programs include
(a) those grown on-site (cover crops) and (b) those brought to
the site. Although the use of cover crops is the conventional method
of OM maintenance, rapid decomposition of green crops after incor-
poration into the soil has led to questioning of their actual value
(Davey and Krause 1980).
Exogenous sources of OM have been used for many years, and
currently are receiving considerable attention. A large variety of
materials have been used, including peat and sawdust. Several
studies have examined the influence of OM additions on seedling growth
and, to a lesser extent, on soil properties (Wilde and Hull 1937,
Davey 1953, Brown and Myland 1979). Relatively little emphasis has
been placed on quantifying the decomposition of any organic materials
applied to nursery soils.
Therefore, a series of three studies were conducted to examine
the influence of several organic materials on OM levels, selected soil
properties and seedling development. Peat was emphasized due to
the occurrence of peat deposits in Florida. The first study consisted
of operational-scale field plots testing addition of peat at three rates
with or without fumigation, over a 21-month period. The second
study consisted of field microplots comparing peat, sawdust, shredded
cones, and sewage sludge at three rates over an 18-month period.
The third study, under laboratory conditions, compared the decomposi-
tion of the foregoing materials plus two others--bark and pulp mill
waste--over a 7-month period.
The overall thrust of the investigation was to provide quanti-
tative information on the decomposition of organic materials, especially
peat, and on their effects on seedling development when applied to
sandy nursery soils in Florida.
The history of the plant and soil sciences reveals that the impor-
tance of organic matter (OM) with regard to plant growth was one of
the major revelations of early investigators. A chronological sequence
of investigators, including Bacon, Van Helmont, Boyle, Glauber, Mayow,
Woodward, de Saussure, Liebig, and Lawes and Gilbert, conducted a
progressive series of trials, errors, and observations which eventually
demonstrated the great influence of OM on plant growth and development
(Russell 1973). The more precise description of the role of OM in plant
functions has come about in the past century largely by virtue of tech-
nological advances which have improved the separation, detection, and
characterization of OM components at the compound and ionic levels.
Subsequent research on the formation, composition, function and
fate of soil OM has been reviewed by several authors (Waksman 1938;
Kononova 1961; Schnitzer and Khan 1972, 1978; Allison 1973).
Ever since OM was shown to have such decided effects on plant
growth, its maintenance has carried a position of prominence in soil
management. Because decomposition is a degenerative process, the
task of maintaining a given level of OM is never accomplished. Several
studies have demonstrated the rapid decomposition rates of agronomic
crop residues and green manures. For example, Parker (1962) showed
a 65% loss of cornstalk residue when buried in the soil for 20 weeks.
Brown and Dickey (1970) reported losses of 50% in 3 months and 93%
in 18 months for wheat straw buried in soil. Sain and Broadbent (1977)
showed a 40% loss of buried wheat straw between November and April.
More substantive reviews of the rapid decomposition of agronomic crop
residues have been provided by Russell (1973) and Allison (1973).
The problems associated with OM maintenance are nowhere more
appreciated than in soil-based nursery systems which produce orna-
mental or forest tree seedlings. The moist but well-aerated soils and
frequent nutrient additions in most nurseries produce ideal conditions
for microbial oxidation of organic residues. The problem is further
accentuated by complete crop removal, as opposed to most agricultural
crops where much of the plant remains in the field after harvest. A
contemporary review of the function and maintenance of OM in forest
nursery soils is presented by Davey and Krause (1980). They sub-
divide OM into two general fractions: (a) stable, and (b) dynamic.
They point out that the stable fraction has an equilibrium level which
varies with geographic location. The cooler temperatures, and often the
presence of finer-textured soils in the more northern nurseries result
in OM equilibrium levels of 3 to 5%. In the lower coastal plain of the
southeastern United States this level is often near 1%. Such geographic
variation in OM equilibrium levels is discussed further by Brady (1974).
Since little can be done to significantly increase the stable OM
fraction, OM maintenance programs must be directed at manipulating
the dynamic fraction. For practical purposes, this fraction consists
of organic materials which have not been re-synthesized into humic
substances. Methods to maintain or increase this dynamic fraction
have included growing materials on-site in the form of cover crops
or bringing materials to the site.
The use of cover crops has been the conventional method of OM
maintenance, being practiced by 92 of 99 nurseries surveyed by Abbott
and Fitch (1977). A study by Sumner and Bouton (1981) in a Georgia
nursery compared several spring and fall sown cover crops. Summer
crops of sorghum and pearl millet yielded 13.2 and 12.1 mt/ha, while
a winter crop of crimson clover + ryegrass yielded 8.3 mt/ha. Soil
organic matter content was initially 1.1% which led them to conclude
that it was not possible to increase the OM content above a level of
1.4 to 1.6%, even if a rotation involving 2 years of cover cropping
were practiced. Such an increase is not an unreasonable expectation,
however, as suggested by Pritchett (1979). An addition of 10 mt/ha
(dry weight) of cover crop is equivalent to an initial increase of
0.5% OM in the surface layer. Much of this will decompose in the
first few months after incorporation. Moreover, some studies have shown
that incorporation of green manures will accelerate the loss of carbon
and nitrogen from the native OM (Broadbent 1948, Lohnis 1926). A
general conclusion of this brief review is that substantial increases in
OM may be achieved only by addition of exogenous materials.
The, historical use of exogenous materials for OM maintenance was
discussed by Allison (1973) and Davey and Krause (1980). The survey
by Abbott and Fitch (1977) showed the most commonly used organic
materials and the numbers of nurseries reporting their use as follows:
sawdust, 35; peat, 14; manure, 7; rotted bark, 5; wood chips, 3;
mushroom compost, 3. Investigations on the use of sawdust have
demonstrated that fresh materials may create nutritional or phytotoxic
problems, but that composting renders them more useful for plant
growth (Turk 1943, Allison and Anderson 1951, Davey 1953, lyer
and Morby 1979). Peat has been used extensively in northern nur-
series with generally good results on plant growth (Burd 1918, Wilde
and Hull 1937, Lunt 1961, Brown and Myland 1979). Manure, rotted
bark and mushroom compost have been used successfully but are only
locally available. Wood chips have been used to some extent but
generally have been too coarse to be of immediate value as OM (Lunt
The recent emphasis on land application of municipal sewage sludge
has resulted in some nurseries using the digested material directly from
the treatment facility, or as a packaged product, such as "Milorganite,"
sold by the city of Milwaukee, Wisconsin. Several studies have examined
the organic matter and nutritive value of various sludges (Gouin 1977,
Sommers 1977, Magdoff and Amadon 1980). The general concern in ap-
plying sludge is the possibility of high contents of heavy metals and
calcium. The latter may result in increasing pH well above that con-
sidered to be optimum for pine seedlings (5.0 to 6.0, Armson and
Sadreika 1979). Additionally, since most sewage sludges have high
nitrogen contents (2 to 7%), even moderate application rates may result
in large leaching losses of nitrates. This can accelerate the leaching
losses of Ca, Mg and K (Raney 1960). Ultimately, application of any
organic amendment should be preceded by adequate knowledge of its in-
fluences on plant growth.
Once a material has been determined to be a suitable amendment
in terms of plant growth, the question of availability at a reasonable
cost arises. Diminishing supplies of waste wood in recent years and
competing demands have reduced availability of low cost chips and saw-
dust. This, coupled with their limitations as amendments, has made
nursery managers search for other materials. The availability of
alternate materials, however, depends on each individual nursery's
An examination of organic materials available to forest nurseries
in Florida reveals that peat has attractive possibilities. Peat has been
used successfully in northern nurseries, as cited earlier, and has been
shown to have low to moderate decomposition rates as well as having ben-
eficial effects on plant growth (Feustel and Byers 1933). An account
of the distribution and utilization of the peat resources in Florida is
provided by Davis (1946). Although the major peat resource is in
south Florida, a significant number of deposits occur in the northeast
and north central portion of the state. Furthermore, the majority of
north Florida peats are acidic in reaction. Since most of the forest
nurseries in Florida are located in the northern portion of the state,
the potential for using peat in these nurseries appears promising. The
ability to exploit such deposits, however, rests on combinations of
ownership, managerial and logistical considerations unique to each nursery.
The benefits derived from OM additions appear to be well docu-
mented. Questions of how much to apply and to what degree seedling
quality will increase, however, remain largely unanswered. Until the
criteria indicative of seedling quality are clearly established, the latter
question cannot be answered. An answer to the first question is
attainable assuming that a given level of OM is set as an objective.
Optimum application rates for various materials are functions of
(a) their effect on seedling growth, and (b) the rate of decomposition.
Although several of the aforementioned studies evaluated the effects of
organic additions on seedling growth and on decomposition under labor-
atory conditions (Feustel and Byers 1933, Allison 1965, Agbim et al.,
1977), there is little quantitative information on decomposition rates
under field conditions. Such information is required for knowledgeable
decisions in formulating OM maintenance programs.
FIELD MACROPLOT STUDY WITH PEAT
Woody materials such as sawdust, chips and bark have been used
as soil amendments during the past several decades, but recently have
become less available at a low cost due to more complete use in manu-
facturing processes, such as fuel, or for other purposes. Nursery
managers are therefore searching for new alternative sources and re-
evaluating the old. One such alternative is peat. Peat has been used
extensively in nurseries in the Lake States, primarily because peat
deposits were fairly abundant and within reasonable trucking distance
to the nursery. Far less emphasis has been placed on peat as an or-
ganic amendment for nurseries in the Southeast. Several nurseries in
Florida are fairly close to peat deposits making use of peat a potential
The overall hypothesis of this investigation is that pine nursery
seedlings can be grown continuously in the same ground without need
for alternate-year cover cropping and regular soil fumigation, provided
that soil organic matter is maintained at or above its current level by
appropriate additions. This study examined the utility of peat for this
purpose, including its rate of decomposition, its effect on selected soil
properties, and its influence--with and without soil fumigation-- on
seedling growth, mycorrhizal status and incidence of charcoal root rot.
Materials and Methods
The study was conducted at the Container Corporation of America
forest tree nursery near Archer, Florida. The soil in the study com-
partment is classified as Millhopper sand (loamy, siliceous, hyperthermic
Grossarenic Paleudult). This series consists of moderately well drained,
moderately permeable soils that formed in thick beds of sandy and loamy
marine sediments. Prior to clearing and grading as a nursery in 1970,
the area had been successively cultivated, abandoned, and planted to
slash pine (Pinus elliottii var. elliottii Engelm.). The first seedling
crop was grown in 1971. Mean July and January monthly temperatures
are 270 and 140 C, respectively. Annual precipitation averages 1240 mm,
most of which occurs in summer and winter.
Experimental Design and Conduct
The shredded peat applied as a soil amendment was obtained from
a commercial peat mine, 45 km distant. It would be classified as a
medisaprist, apparently derived from grasses and sedges. It is acid,
pH 4.5 (in water). Its dry weight composition is ash, 14%; C, 53.7%;
N, 2.85%(3.3% ash-free basis); C/N, 18.8; CEC, 100 to 200 meq/100 g.
Total elemental concentrations (ppm) are as follows: P, 160; K, 90;
Ca, 1250; Mg, 415; Cu, 3; Fe, 950: Mn, 5; Zn, 3.
The experiment was established in a compartment that had been
under a 1: 1 or 1: 2 cover crop : pine rotation for 8 years. The
primary cover crop used had been pearl millet [Pennisetum glaucum
(L.) R. Brown]. The crop immediately preceding the experiment
was slash pine established after fumigation. Following experimental
treatment, two additional crops of slash pine were grown successively
in 1980 and 1981. Contrary to routine procedure, the experimental
beds were not fumigated except as a designed treatment. With ex-
ception of this and the peat application, almost all other cultural
practices--sowing, weed control, fungicide sprays, irrigation and
fertilization--were identical, with routine treatment of operational slash
pine beds in this compartment. The only further exception was that
seedlings in the experimental area were not top-mowed late in the
Four rates of peat (0, 22.4, 44.8, and 67.2 dry mt/ha) with three
replicates were applied to 6 x 18-m plots covering a total area of
18 x 72 m (Fig. 1-1). The intent of the additions (Pl, P2' P3, res-
pectively) was to raise soil organic matter (OM) levels by approximately
1, 2, and 3% above the native level of 1%. The treatments were arranged
in a completely randomized design. Each plot was three standard nur-
sery beds in width, but measurements were confined to a 4 x 16-m area
in each plot. The 1-m wide border around the sample area served as
a buffer against soil mixing during nursery operations. A subplot,
6-m long, in each central bed (per plot) was fumigated with MC-2
(98% methyl bromide, 2% chloropycrin) (Fig. 1-1) after peat application
(1980) or tillage (1981), and 1 week prior to sowing. The fumigated
plots were in the same location in both years.
Peat was applied with a front-end loader in April 1980, spread
uniformly by hand, and incorporated to 20 cm using a mould-board
plow and repeated discing. Seed was sown in May 1980 and 1981 to
achieve a postemergent density of 28 stems/0.1 m2. The fertilizer
regime consisted of pre-plant applications of 672 kg/ha 5-10-20 in 1980
and 0-10-20 in 1981, followed by four maintenance applications of
168 kg/ha 10-10-10 in 1980 and only two in 1981. The postemergence
fertilizers were broadcast as granular and liquid in 1980 and 1981, res-
pectively. All fertilizer materials had a micronutrient mix of Mn (.2%),
Fe (.1%), Zn (.05%), B (.05%), and Mg (.06%). The lower amounts of
fertilizer nutrients supplied in 1981 apparently account for the smaller
total dry matter production in that year.
Soil samples were taken before and after peat application, then
subsequently at 3-month intervals for 21 months. At each sample period,
three composite samples, each consisting of 15 cores, 2.5-cm diameter x
20-cm deep, were taken randomly from each replicate plot. Soil from
the fumigated subplots and the interbed area was not included in the
Seedling samples were taken on three 0.1 m quadrats in each
fumigated and unfumigated subplot (Fig. 1-1) at the end of the 1980
and 1981 growing seasons. Samples were taken by pressing a steel
frame (0.1 m2 x 15-cm deep) into the soil and hand lifting all seed-
lings within the frame. An additional 10 seedlings were randomly
sampled from each fumigated and unfumigated subplot for a quali-
tative evaluation of charcoal root rot infection.
Laboratory and Chemical Analyses
Soil samples were air-dried and sieved to pass a 2-mm mesh.
Organic matter was determined by loss-on-ignition after combustion of
a 25- to 30-gram sample at 5500 C for 8 hours. Ash content of the peat
was determined similarly. Organic C was determined on the peat by
the Walkley-Black wet oxidation technique (Jackson 1958). Soil pH was
measured in a 2 : 1 distilled water-to-soil ratio using a standard glass
electrode. Total soil N was determined by the micro-Kjeldahl method
(Bremner 1965). Soil samples were extracted with a double acid solution
(0.05 N HCL + 0.025 N H2SO4, Page et al., 1965); K, Ca, Mg, Cu,
Mn and Zn in the extract were determined by atomic absorption spec-
trophotometry, and P by a Technicon Autoanalyzer II (Technicon Indus-
trial Systems 1978). Peat and tissue samples were dry ashed and
digested in 6 N HCL; K, Ca, Mg, Cu, Mn, and Zn were determined by
atomic absorption spectrophotometry. Nitrogen and P in these materials
were determined colorimetrically on a Technicon Autoanalyzer II following
block digestion (Technicon Industrial Systems 1978).
Seedlings were measured individually for height and stem diameter,
and collectively (by 0.1 m2 quadrats) for oven dry weights. The
percentage of mycorrhizal short roots on five seedlings was estimated
after a visual scan of the root systems at 7 x magnification.1 A short
root was considered mycorrhizal if it had a hyphal mantle. Incidence
of charcoal root rot was determined by a visual analysis of external
infection symptoms2 on the 10 seedlings sampled for this purpose.
Data analyses were conducted using general linear model pro-
cedures in the Statistical Analysis System (Barr et al., 1979). The
change in soil organic matter over time was characterized by equations
generated from individual plot means. Mean soil pH values within sample
periods and mean values for the seedling physical and chemical variables
were compared using Duncan's multiple range test at a = .05 (Snedecor
and Cochran 1967). The analysis of variance designs used for com-
parisons among treatments are presented in Table 1-1.
1 The technique and sample number were suggested by Dr. D.H. Marx,
Director, Institute for Mycorrhizal Research and Development, USDA
Forest Service, Athens, GA.
2 This procedure was conducted under the guidance of Dr. E.L. Barnard,
Forest Pathologist, Florida Division of Forestry, Gainesville, FL.
Table 1-1. Analysis of variance designs used for treatment
Variable Source of d.f. Variable Source of d.f.
time x treatment
time x rep (treatment)
time x treatment
time x rep (treatment)
-error a- rep (treatment)
fumigation x treatment
-error b- fumigation x rep (treatment)
-error a- rep (treatment)
time x treatment
-error b- time x rep (treatment
Results and Discussion
Statistical analyses showed that the decline in OM over a 21-month
period did not follow a common pattern for the four levels of peat
application treatment, thus requiring each treatment to be evaluated
separately. The data were examined by generating equations that de-
scribed the mean course of decomposition (Fig. 1-2). Analyses showed
that the control and Peat 1 (22.4 mt/ha) data were neither linear nor
quadratic, and are thus best described by horizontal lines. Both the
Peat 2 (44.8 mt/ha) and Peat 3 (67.2 mt/ha) levels showed only linear
OM percentages measured immediately following peat application
were lower than expected from the amounts applied. The expected and
observed percentages were 1.64 and 1.43, 2.29 and 1.95, and 2.94 and
2.48 for Peat 1, 2, and 3, respectively, or about a 15% reduction. Two
possible causes of this discrepancy are (a) the peat application may
have been less than estimated, or (b) the plow-down process placed
some peat below the 20-cm sample zone. In any case, the discrepancy
does not affect the hypothesis or results of the study.
The last consequential organic addition to the study site had
been the cover crop plowed down 14 months previously. Hence, the
indigenous soil organic matter at the beginning of the study was as-
sumed to be relatively stable. It proved remarkably so, with the
1o 0 Lo o
Nc Ni -_ -
I311VV OINVOIO %
control treatment showing no measurable decrease in OM over the
21-month period (Fig. 1-2). Likewise, the higher total OM content
of the Peat 1 treatment appeared constant, presumably because cumu-
lative decomposition of the added peat was too small to be detected
against background variability of both soil and intermixed peat. In
contrast, the Peat 2 and 3 treatments display the expected cumulative
decrease despite high variability (Fig. 1-2). The slopes appear linear,
with the higher rate having the steeper slope. This indicates that
decomposition rate is proportional to application rate. Thus, optimizing
residence time of peat in soil may be best achieved by smaller applications
at frequent intervals rather than by less frequent large additions.
The latter is consistent with the findings of Lund and Doss (1980).
They observed that organic matter content of plots treated with 90,
180 or 270 mt/ha (wet weight) of dairy manure all reached a common
level in approximately 70 months. Such a time requirement obviously
must vary with both the soil environment and composition of the added
organic material. Perhaps by coincidence, however, the projected slopes
of the Peat 2 and 3 treatments would indicate return to the level of the
control in 64 and 74 months, respectively.
The latter extrapolation is highly speculative but emphasizes the
moderate loss rate. In contrast, a hypothetical curve used as an illus-
tration by Davey and Krause (1980) proposed that two-thirds of a
20 mt/ha addition of peat would be lost in the first year. A further
comparison is with the loss rates revealed by subsidence studies in
cultivated peat land in south Florida (Knipling et al., 1970).
Carbon dioxide evolution from each 1% OM (ash free amounted to
1.58 mt/ha yr- Calculated loss rate from the Peat 2 treatment in
the present study is roughly similar, 1.65 mt/ha yr1 for each 1% OM
initially added as peat (i.e., exclusive of native soil OM).
In the present study, as with most field studies, variability
limits precise determination, as is illustrated by the scatter of observed
OM values around the generated lines in Figure 1-2. Spatial variability
was reduced by intensive soil sampling. The influence of other sources
of soil variability, however, including seedling lifting, discing, bed
reestablishment and seasonal differences in decomposition rates can neither
be eliminated nor accounted for.
Although decomposition of the peat used in this study is relatively
slow, its high N content (3.31% on an ash-free basis) and narrow C/N
ratio nevertheless make it a major source of N for plant growth. More-
over, this N becomes available gradually, i.e., it is a "slow release" N,
which accords well with the year long growth period of pine seedlings.
Thus, assuming net N mineralization to have been proportional to de-
composition, i.e., no further reduction in C/N ratio, the Peat 2 and 3
treatments released approximately 179 and 257 kg/ha N, respectively,
over the 21-month period. These amounts compare with 141 kg/ha
inorganic N added by routine fertilization practice to the two seedling
crops grown in this period. Actual rates of N mineralization from added
peat are yet to be determined by specific studies. It is clear, however,
that any comparison of peat with other organic materials must consider
N supply as well as contribution to soil OM.
Effects on Soil Chemical Properties
Soil reaction. The mean pH values at the various sample periods
are presented in Table 1-2. Because rainfall, intermittent fertilizer
additions and irrigation with high Ca water affect soil reaction, the
most meaningful analysis is comparison among treatments at the same
sample date. The immediate effect of peat application on soil pH re-
flects its own low pH, 4.5, and the very low exchange capacity of the
mineral soil. At the time of application, each 1% increase in OM de-
creased pH by .3 unit. Twenty-one months after application, the
buffering effect was even more pronounced, with pH decreasing .6 unit
for each 1% OM.
A range in pH values from 5 to 6 is considered satisfactory for
most coniferous species (Armson and Sadreika 1979). In this study,
pH values in the unamended plots showed relatively high seasonal fluc-
tuations (5.5 6.1) with an overall mean pH near 6. In contrast, the
Peat 1, 2 and 3 treatments showed slightly less fluctuation and main-
tained overall pH values of 5.5, 5.3 and 5.1, respectively. Additional
measurements of soil pH in the study plots will determine the persistence
of the peat treatment effects.
Soil nutrient status. Statistical analyses of chemical data from
samples of unfumigated soil taken initially and at the end of the first
and second growing seasons show significant effects due to treatment
and sample time, with no interaction (Table 1-3). Peat treatments in-
creased N and Mn levels; the N was obviously from the peat itself, and
the Mn increase was probably due to increased Mn solubility at the lower
pH levels after peat additions. The changes in nutrient status over time
Table 1-2. Soil reaction as influenced by peat amendment.
Months after application
Treatment Initial 0 3 6 9 12 15 18 21
Control1/ 5.9 2/ 5.6 a3/ 5.5a 5.7a 5.5a 5.6 a 6.la 5.8a 5.8a
Peat 1 6.0 5.5a 5.3b 5.7a 5.5a 5.4b 5.8ab 5.7a 5.5b
Peat 2 6.0 5.3b 5.2b 5.3b 5.0b 5.3b 5.7b 5.5b 5.3b
Peat 3 6.0 5.2b 4.9c 5.1b 4.9b 5.2c 5.4c 5.4b 5.1c
1 Peat 1, 2, 3 refer to application rates.
2 Two probable causes of the lower pH in the control plots after peat
application are slight contamination with peat from adjacent treated
plots during the incorporation process and the pre-plant fertilizer
application. A slight increase in OM was also observed in the control
plots after peat incorporation.
3/ Values in each column which have the same letter are not significantly
different (Duncan's, a = .05 ).
Table 1-3. Soil nutrient status as influenced by peat application and
time of sampling.
N P K Ca Mg Mn Zn
Control 209 a3/ 48 24 149 8 4.7 a .44
Peat 1 367 ab 43 22 194 11 5.2 ab .43
Peat 2 518bc 44 24 192 10 5.6b .44
Peat 3 695c 40 24 180 11 5.6b .45
0 441 40 a 32 a 192 ab 12 a 5.0 a .36 a
9 480 40 a 20 b 140 a 7b 5.0a .38 a
21 421 51b 18 b 205 b 11 a 5.8b .60 b
/ N = total. Other elements extractable by .025 N H SO + .05 N HCI.
- Averaged over samples taken initially, and 9 and 12 months after
- Values in subcolumns with the same letter or no letter are not signi-
ficantly different (Duncan's, a = .05).
- Averaged over peat treatments in unfumigated soil.
reflect management practices. Accumulations of P, Mn and Zn are from
inorganic fertilizer additions. Losses of K and Ca in the first year may
be due in part to crop uptake, but most likely are due to leaching with
nitrates mineralized from the peat.
A comparison of nutrient status in fumigated and unfumigated
soil 21 months after peat application showed significant effects of both
peat and fumigation without significant interaction (Table 1-4). The
difference in peat treatments follows a similar pattern as discussed previ-
ously (Table 1-3). The unfumigated plots had lower P and Zn values
and higher Mn values than the fumigated plots. The latter may be
explained by greater uptake of Mn by seedlings grown in the fumigated
plots as compared to seedlings grown in the unfumigated plots (Table 1-9).
The differences in P and Zn values cannot be accounted for.
The lowering of pH by peat addition would have some influence
on nutrient availability. Additionally, peat influences soil nutrient
status by its own elemental contribution and by absorption of fertilizer
nutrients. Krause has shown the latter effect to be of little consequence.
Likewise, with the exception of nitrogen, this peat contained low amounts
of most nutrients. These facts are consistent with the small differences
among the peat rates in Tables 1-3 and 1-4. Comparison of seedling
nutrient contents, however, as discussed in a later section, shows
that seedlings from the peat-amended plots contained significantly greater
amounts of most nutrients than those in control plots. The apparent
stability of soil nutrient levels coupled with greater nutrient removal
1 Krause, unpublished data in Davey and Krause (1980).
Table 1-4. Soil nutrient status after 21 months as influenced by peat
application averaged across fumigation, and by fumigation/ averaged
across all peat rates.
Treatment N p K Ca Mg Mn Zn
--------------------------- ppm -----------------------
Control 192 a31 54 a 19 171 9 4.5 a .57
Peat 1 379 ab 49 ab 19 208 14 5.1 ab .67
Peat 2 487 bc 46 b 19 227 11 5.8b .65
Feat 3 656 c 44 b 18 206 12 6.0 b .67
Fumigated 436 51 a 19 202 12 4.9 a .69 a
Unfumigated 420 46 b 18 205 11 5.8b .60b
..Second fumigation with 448 kg/ha MC-2 9
2 N = total. Other elements extractable by
.025N H SO + .05N HC1.
SValues in subcolumns with the same letter or no letter are not signi-
ficantly different (Duncan's, a = .05).
from the peat-amended plots is circumstantial evidence that peat improved
the soil fertility status with respect to meeting crop needs.
These results further demonstrate that additions of OM, in this
case acid peat, in these sandy, poorly-buffered soils can have a signif-
icant effect on conditions for plant growth.
Effects on Seedling Development
Physical parameters. Seedling development was significantly influ-
enced by both peat and fumigation, but without an interaction effect.
Shoot height was the only physical parameter that consistently
increased in response to peat application (Table 1-5). This is of little
practical interest since operational seedlings often must be mowed during
the latter part of the season to avoid excess height. More notable are
the stem diameter and dry matter values, which, in both years tended
to increase with peat application, although the differences were not
statistically significant. The difference in total dry matter between
the crops is due largely to lower amounts of fertilizer applied in the
second year (see Experimental Design and Conduct).
The effects of fumigation were more apparent, with all physical
parameters being greater for seedlings grown in fumigated soil in both
years (Table 1-6). Seeds sown in the fumigated plots germinated
slightly sooner and had more rapid cotyledonary growth than seedlings
in unfumigated soil, possibly due to nutrient release and pathogen
control. Presumably this early advantage in development was carried
throughout the growing season.
Table 1-5. Physical parameters of two successive crops of slash pine
seedlings as influenced by peat amendment averaged across fumigation
Treatment Seedling Height Stem Oven-dry weight Dry Shoot/root
number d la. shoot root matter ratio
nolm cm mm -------- g/m -------
Control 210 23.5 a-1 5.6 910 280 1190 3.3
Peat 1 220 23.9 a 5.4 890 250 1150 3.6
Peat 2 190 25.9b 6.3 1060 300 1360 3.6
Peat 3 200 26.4b 6.0 1070 300 1370 3.6
Control 320 21.1a 4.0 6303/ 180 810 3.5
Peat 1 270 22.7b 4.4 700 180 890 3.9
Peat 2 270 24.0b 4.6 720 190 910 3.8
Peat 3 260 23.3 b 4.6 710 190 900 3.7
letter or no letter
- Values in columns (within crop year) with the same
are not significantly different (Duncan's, a = .05).
Table 1-6. Physical parameters of two successive crops of slash pine
seedlings as influenced by fumigation 1/ averaged across all peat
Treatment Seedling Height Stem Oven-dry weight Dry Shoot/root
number dia. shoot root matter ratio
no Im cm mm --------g -----
Fumigated 200 26.0 a21 6.2a 1070a 310 a 1380 a 3.5
Unfumigated 210 23.8 b 5.4b 890 b 260 b 1150 b 3.5
Fumigated 300 a 24.2 a 4.6 a 770 a 210 a 980 a 3.6
Unfumigated 260 a 21.4b 4.2b 610 b 160 b 770 b 3.8
- Fumigation with 448 kg/ha MC-2.
- Values in subcolumns with the same letter or no letter are not signi-
ficantly different (Duncan's, a = .05).
Chemical parameters. Chemical analyses of the 1981 crop show
that peat treatment had no effect on concentrations of P, K, Ca,
Mg, Cu and Zn (Table 1-7), but that concentrations of N and Mn
were greater in seedlings grown in peat-amended soil (Fig. 1-3). The
increased N levels may be due to greater retention of NH4-N by the
higher CEC, and certainly by additional N mineralized from the peat
during decomposition. The increased Mn levels are associated with
increased Mn solubility at the lower soil reaction in the peat treatments
The effects of fumigation were evident, with N, P, K, Ca, Cu,
and Zn concentrations being greater in seedlings grown in unfumigated
soil (Fig. 1-4). Total elemental contents of N, P (Fig, 1-5), Mg, Mn,
and Zn (Table 1-8), as calculated from concentration and shoot weight/
unit area, were greater in seedlings grown in peat-amended soil. Coupled
with the fact that neither dry matter production nor extractable soil
nutrient concentrations were generally affected by peat treatments, this
indicates that peat enhanced nutrient uptake by the seedlings.
The larger seedlings grown in fumigated soil had significantly higher
total contents of K, Mg, Cu, and Mn (Table 1-9), although concentra-
tions were generally lower than those from the unfumigated treatments
(Fig. 1-4). In contrast, the N content was greater in seedlings grown
in unfumigated soil (Table 1-9), despite the fact that seedlings from the
fumigated soil were heavier (Table 1-6).
Table 1-7. Element concentrations of slash pine seedling shoots
grown in 1981 as influenced by peat amendment averaged across
Treatment Tissue concentration
P K Ca Mg Cu Zn
----- % ----- ---- ppm ---
Control .151/ .76 .51 .10 5.1 38
Peat 1 .16 .76 .48 .11 5.2 45
Peat 2 .17 .77 .50 .10 5.4 43
Peat 3 .17 .72 .49 .10 4.9 41
a = .05).
columns are not significantly different (Duncan's,
(wudd) uo!q.lJu8u3uo3 uIN
I I I \
(%) uo!ijJuaeouoo N
L; .' <
ur 0 3r
0 r V
m ( -
.; C r
I i I I \ .
SI I I I-,-
F^ > ,
- .- L
Table 1-8. Elemental contents of slash
1981 as influenced by peat amendment
pine seedling shoots grown in
averaged across fumigation
Treatment Tissue content
K Ca Mg Cu Mn Zn
-------- gm2 ----- ------mg2 ----
Control 4.75/ 3.17 0.59 a 3.2 140 a 23 a
Peat 1 5.29 3.39 0.78 b 3.6 140 a 31b
Peat 2 5.45 3.55 0.74b 3.8 260b 31b
Peat 3 5.09 3.39 0.72 b 3.5 280 b 28 b
SValues in columns with the same letter or no letter are not signi-
ficantly different (Duncan's, a = .05).
Table 1-9. Elemental contents of slash pine seedling shoots grown in
1981 as influenced by fumigation!1 averaged across all peat treatments.
Treatment Tissue content
N P K Ca Mg Cu Mn Zn
--------- gm ------ --- ----mg/m -----
Fumigated 6.9 a 1.142 5.59 a 3.67 0.79 a 3.8 a 240 a 28
Unfumigated 7.7b 1.11 4.71b 3.08 0.63b 3.3b 170 b 28
- Fumigation with 448 kg/ha MC-2.
- Values in columns with the same letter or no letter are not signifi-
cantly different (Duncan's, a = .05).
Thus, the compensatory value of peat additions, particularly for
N-nutrition, becomes more apparent. A comparison of N contents of
seedlings grown in unfumigated soil with amount of N applied in fer-
tilizer showed that, in both years, more N was taken up by the crop
than was applied as inorganic fertilizer. The difference was made up
by N mineralized from organic matter. Assuming uptake of 80% of the
fertilizer-N, which is liberal, and no appreciable atmospheric inputs,
seedlings grown in soil without peat addition received 28 and 66% of
their tissue-N in 1980 and 1981, respectively, from native OM and a
small fraction of peat pulled into the plots during tillage. In contrast,
seedlings grown in unfumigated soil with peat addition obtained 44 and
71% of the tissue-N in 1980 and 1981, respectively, from the peat and
native OM. As discussed previously, the peat decomposition data in-
dicate that the Peat 2 and 3 treatments released approximately 179 and
257 kg/ha N over the 21-month period. Presumably some N was miner-
alized from the Peat 1 treatment as well. This clearly demonstrates the
N-nutritional advantages provided by peat additions.
Effects on Mycorrhizae and Incidence of Charcoal Root Rot
An additional interest of this study was the effect of peat and fumi-
gation treatments on mycorrhizal infection and incidence of charcoal root
rot (CRR). As shown in Table 1-10, mycorrhizal infection was greater
in the unfumigated soil than in the fumigated soil in both years. My-
corrhizal infection was also greater in peat amended than in unamended soil,
notably so in 1980.
1 Estimates of N concentration in the shoots of the 1980 crop and roots
of both crops made from analyses not cited here.
Table 1-10. Ectomycorrhizal infection
and fumigation. -
as influenced by peat addition
unfumigated fumigated unfumigated fumigated
----------- % short roots infected -------------
Control 34 9 34 14
Peat 1 39 13 39 21
Peat 2 58 9 35 20
Peat 3 60 31 40 15
1/ Fumigated each year with 448 kg/ha MC2.
- Fumigated each year with 448 kg/ha MC-2.
This indicates that natural repopulation of the fumigated soil with
mycorrhizal fungi did not occur rapidly and was facilitated by peat.
The latter point suggests that artificial inoculation of seed beds with
mycorrhizal fungi may be more successful in soils amended with peat.
Inspection of root samples taken from the 1980 and 1981 crop showed
no visual symptoms of CRR in any treatment.
Annual fumigation is used routinely in many lower coastal plain
nurseries to avoid or control root-rot diseases, especially CRR caused
by Macrophomina phaseolina tassi (Goid.) (Seymour and Cordell 1979).
This is a costly and time consuming operation which also temporarily
reduces or eliminates mycorrhizal fungi and organisms responsible for
nitrogen mineralization and nitrification. It may be speculated that
increasing soil OM levels would provide a substrate to support a larger
and more diverse microbial population, which may give beneficial organ-
isms a competitive advantage over pathogenic organisms. The higher OM
levels may also facilitate production of seedlings with improved physio-
logical quality and greater resistance to pathogenic infection. Thus,
continued observations from unfumigated beds in the study area may
provide additional evidence on the influence of organic matter on CRR.
In summary, the use of peat as an organic matter amendment in
southern forest nurseries has decided benefits. These include pH buffer-
ing capacity, improved soil physical conditions, and improved soil fertility
conditions--especially with regard to nitrogen. Decomposition rates are
lower than anticipated, which would reduce annual costs associated with
OM maintenance. In Florida at least, peat deposits occur in proximity
to many nurseries, increasing the feasibility of use.
FIELD MICROPLOT STUDY WITH VARIOUS ORGANIC MATERIALS
Maintenance of organic matter in forest tree nurseries is an old
problem with no new solutions. In an attempt to maintain existing levels,
nursery managers currently use cover crops, exogenous organic materials
or often a combination of both (Davey and Krause 1980).
The declining availability at low costs of conventional amendments
such as sawdust, wood chips and bark prompts a search for alternate
sources of organic materials. Once a grower locates an adequate supply
of a promising material, pragmatic questions arise concerning application
rates, decomposition rate or residence time, and effects on seedling and
soil chemical properties.
Full-scale field tests of various materials consume space and effort,
whereas greenhouse pot trials are subject to regimes of soil, temperature,
leaching and moisture quite different than those of the field. Accordingly,
a method of microplot field trials was designed to study both the value of
such a procedure and the performance of four common organic amend-
ments applied at three rates. The questions of interest were decomposi-
tion rates, effects on selected soil properties, seedling growth, mycorrhizal
development, and incidence of charcoal root rot.
Materials and Methods
This experiment was conducted at the same nursery as the field
study (Ch. 1) and was installed in a 14-m section of a buffer bed in
a control plot of that study (Fig. 2-1).
Experimental Design and Conduct
The materials tested were peat, 20-year-old pine sawdust from a
large pile exposed to normal weathering, municipal sewage sludge, and
shredded pine cones. The peat was obtained from the same source as
in the prior study (Ch. 1). Activated sewage sludge was obtained from
drying beds at the University of Florida waste treatment facility. Saw-
dust and cones were obtained from the St. Regis Paper Company nursery
near Lee, Florida. The cone residue (principally from slash and loblolly
pine) was from a seed extractory located at the nursery. The application
rates tested were 22.4, 44.8, and 89.6 mt/ha (dry weight), which would
approximate 1, 2, and 4% increases over the native OM level. The actual
increases were generally lower than expected due presumably to greater
than recognized variability in moisture and ash contents of the materials,
but also to mixture with greater soil weight than calculated. The chemical
characteristics and particle size distribution of the materials used are
listed in Table 2-1.
The microplots consisted of plastic buckets 3-rm thick, 30-cm dia-
meter, and 35-cm deep (Fig. 2-1). To insure natural soil water flux,
approximately 60% of the surface area of the sides and bottom was per-
forated by 5-cm diameter holes.
I A N
c.JI I -
0 N0 N^ N" N a
CO 01 i
I. I t" -,
U 0 Nfl
L N" 1. N
o N N"
u e n o a o ] v
N N N
3 n 3 i
C0 0 N N
u N N
^^ I in
nr 5 D >n o o .
Cu N N N N
(flt I N
LW N C N
WE U N u
Lm 0o m . .
Cu5 Z N N N
SIn Nu N
i2>- *- -
WL N N" N"- ". L
0 tN N N
_g | l' to I s
ram i I -; ^ 3 "
L- 3 i a
' ,** I *n ^
Several cubic meters of unfumigated topsoil from an area adjacent
to the study were piled and mixed repeatedly with a front-end loader
and tractor. For each treatment, three buckets of soil were mixed in
a portable cement mixer with an appropriate amount of organic material.
Samples for analysis were removed; then two buckets (replicates) were
filled with the mixture, and the remainder discarded. A total of 28
buckets were prepared representing 4 materials x 3 rates x 2 replicates
+ 4 controls. Treatments were arranged in a completely random fashion.
The microplots were buried to the rim in the nursery bed (Fig. 2-1) and
the surrounding soil compacted around them. The buckets were sturdy
enough to withstand removal and replacement for successive crops.
In the first year, 1980, 2-week-old slash pine (Pinus elliottii var.
elliottii Engelm.) seedlings were transplanted immediately after installa-
tion in mid-June. In 1981, the plots were in place when the entire bed
was sown by the normal operating practice on May 1. Subsequently,
seedlings received the normal operational watering, fertilization, fungi-
cide treatments and weed control as described in Chapter 1, excepting
no addition of pre-plant fertilizer. The buckets were lifted at time of
harvest and the soil + organic matter mixtures were stored between late
February and mid-April 1981 in plastic bags in an open nursery shed.
Bulk soil samples were taken before and after the organic matter
additions and composite samples at 3-month intervals, including the time
between crops. Each composite sample consisted of four cores, 2.5 cm
diameter by 30-cm deep, from each bucket.
At harvest, the soil mixture in each microplot was passed through
6-mm hardware cloth to remove all roots. Organic fragments larger than
6 mm were returned to the soil mixture. The galvanized hardware cloth
increased extractable zinc contents as will appear later.
It was assumed that as many roots grew into the plots from external
seedlings as grew out of the plots from internal seedlings, and hence
root weights represented production by the seedlings in the bucket.
This assumption was not valid when the seedling density within the plot
was much lower than outside density as happened with the sludge treat-
ments in 1980.
Soil and plant samples were processed and analyzed as described in
Chapter 1. Organic particles greater than 2 mm were kept with the soil
sample. Mycorrhizal infection and incidence of charcoal root rot were
assessed on five seedlings in each microplot by the procedures described
in Chapter 1.
Likewise, the statistical analyses followed the procedures described
in Chapter 1. The analysis of variance designs used for comparisons
among treatments are presented in Table 2-2.
Table 2-2. Analysis of variance designs used for comparisons
Variable Source of variation d.f. Variable Source of variation d.f.
Organic matter treatment 12 pH treatment 12
(error a) rep (treatment) 15 (error a) rep (treatment) 15
time 5 time 5
time x treatment 60 time x treatment 60
(error b) time x rep (treatment) 75 (error b) time x rep (treatment) 75
subsample error 336 total 167
Seedling and Treatment
soil data treatment 12 components material 3
(error) rep (treatment) 15 rate 2
total 27 material x rate 6
Results and Discussion
The patterns of decomposition for the various materials and rates
are described by linear regression equations (Fig. 2-2). The high
r2 values ( > .90) indicated that the overall course of decomposition
is linear despite seasonal variations in soil temperature and the dis-
turbance incident to seedling harvest and reestablishment.
After 18 months, the peat treatments had lost 62, 51 and 51% of
the amounts applied at the 1, 2, and 4% rates, respectively ("loss" in
this discussion refers only to organic substance) Thus, the decom-
position rate was much more rapid than in the field macroplot study
(Ch. 1) where the 1, 2, and 3% treatments lost 0, 21, and 19% of the
amounts applied. Possible reasons for the difference between the two
studies are discussed later. The respective similarity in loss rate from
the two higher applications within both studies, however, confirms that
decomposition rate is roughly proportional to the amount added when this
exceeds 1%. Linear extrapolation of the regressions in Figure 2-2 indi-
cates that OM levels of the 1, 2, and 4% peat treatments would reach
that of the control (1.3%) in 29, 35, and 35 months, respectively. In
actuality, accumulation of a resistant fraction of OM likely would render
the approach to the control level asymptotic.
At the end of 18 months, the sludge treatments had lost 51, 54,
and 44%, respectively, of the organic content added at the 1, 2, and
4% rates. These values would suggest that the sludge was more resistant
._ .a C
u.. r "
1- I I I
L L (
Q- Q- l/
--0 4 -o0
0 o) Z
i C 0 I I 0
--o W -O LL
In / <
N / ( -" O
SIn q N -t
8311LVIN OINVO80 %
to decomposition than any of the other three materials. A more probable
explanation, however, is that decomposition was reduced by the large
size and low porosity of the sludge particles. Initial air drying of sludge
produced firm aggregates, 78% of which were larger than 2 mm (Table 2-1).
Hence, the area of soil-sludge contact was limited and exchange of
02 and CO2 with soil air restricted. The large fraction of coarse par-
ticles (44% > 6 mm) also produced a clumped distribution of sludge in
the soil-sludge mixture. This is probably the major reason why initial
OM levels were considerably lower than calculated. Apparently, this
affected only the accuracy of the OM levels in the samples taken since
the precision of the samples taken over the 18-month period appears good.
Laboratory incubation and field studies have shown that decom-
position of other sludges is generally more rapid than observed here
(Terry et al., 1979; Varanka et al., 1976; Miller 1974). Thus, sludge
decomposition rates observed in the present study may be underestimates.
Linear extrapolation of the equations (Fig. 2-2) shows that the OM levels
in the 1, 2, and 4% rates would reach that of the control (1.3%) in
35, 33, and 40 months, respectively. Thus, decomposition appears to
be somewhat proportional to application rate.
Decomposition of the shredded cones proceeded rapidly: 51, 68,
and 68% for the 1, 2, and 4% rates, respectively, after 18 months. The
68% loss is the largest of any material applied at 2 or 4%. No explanation
can be offered for the lower loss rate at the 1% addition, a reversal con-
trary to results with the other three materials. Despite the coarse size
(Table 2-1) and outward woodiness of the cone fragments, their internal
structure seems susceptible to microbial attack. Extrapolation of the
regressions (Fig. 2-2) shows return of OM levels to that of the control
in 36, 27, and 27, months, respectively.
Losses after 18 months from the 1, 2, and 4% sawdust treatments
amounted to 73, 53, and 50%, respectively. The 73% loss was the great-
est of those for all materials and rates. Loss from the 2% treatment may
be compared with results from a laboratory incubation study (Allison
and Murphy 1963) in which 2% fresh slash pine sawdust mixed with soil
lost 28% of its carbon in 12 months. This would extrapolate to 42% in
18 months, less than 53% observed in the present study.
Extrapolation of the regressions in Figure 2-2 indicates that OM
levels in the 1, 2, and 4% treatments would return to that of the control
(1.3%) in 25, 34, and 36 months, respectively.
If the sludge is excluded from comparison because of the particle
characteristics discussed earlier, as well as its very different chemical
properties (Table 2-1), then the other three materials rank as follows
in respect to decomposition after 18 months (actual percentages in
Application Ranking Calculated time
rate for 100%
1% sawdust (73) > peat (62) > cones (51) 25-36 months
2% cones (68) > sawdust (53) = peat (51) 27-35 months
4% cones (68) > sawdust (50) : peat (51) 27-35 months
Only the 1% cone treatment deviates from an overall decomposition rank-
ing of 1% > 2% = 4%, within materials, and cones > sawdust > peat, with-
As already mentioned, reasons for the lower decomposition of the
1% cone treatment are lacking. A speculative explanation, however,
is that the generally coarse particle size limited the area of soil-particle
contact and hence opportunity for initial colonization by higher fungi,
which expedite decomposition of lignaceous materials, especially when
nitrogen availability is low. Sawdust and the higher rates of cones
might have provided more numerous opportunities for such colonization.
The somewhat more rapid decomposition of cones, generally, may be
attributed to the previous decomposition history of peat and (old) saw-
dust. The similarity of the latter two is surprising, however, in view
of their very different histories and the great differences between them
in nitrogen contents (3.31 vs. 0.198%, ash-free; Table 2-1). As indicated
later (Table 2-3), the nitrogen contents of total OM increased (C/N de-
creased) as the soil-cone and soil-sawdust mixture decomposed, but never
approached that of the soil-peat treatments.
Although decomposition at 18 months varied somewhat with material
and rate of application, the linear extrapolations for Figure 2-2 suggest
that all treatment effects upon soil OM content would disappear by 36
months. Only the 4% sludge treatment would exceed this time and, as
noted, the potential decomposition rate of this material may have been
underestimated. In general, the results of this study would suggest
that where maximizing residence time of applied organic materials is an
objective, this may best be achieved by frequent applications at the
lowest rate rather than applications of the same total quantity in larger
but less frequent additions. Such conclusions, however, must be modified,
as indicated below.
The question of how well the microplot method predicts relative
decomposition of various materials under actual field conditions cannot
be answered. Direct comparison is possible only for peat, used in both
the field macroplot study (Ch. 1) and the microplots. As noted, de-
composition in the macroplots was about 20% after 18 months for the
2 and 3% additions as compared with about 50% for the 2 and 4% rates
of the present study. Several factors may have contributed to ac-
celerated decomposition in the latter. First among these was the intimate
mixing of soil and peat, which could not be duplicated even by repeated
field tillage. Additionally, harvest of the first crop and screening to
remove roots fragmented the remaining peat particles and thoroughly
remixed the soil. It is possible that the bucket framework (40% of the
surface area), or air gaps and interfaces between the microplot mixtures
and surrounding soil retarded moisture movement and so led to longer
retention after rain or irrigation. Finally, soil samples were taken from
0-30 cm-depth for the microplots versus 0-15 cm for the macroplots.
The 15-30-cm layer obviously is less subject to severe and rapid drying
and may have been more favorable for the higher fungi mentioned earlier.
If decomposition of the other organic materials was similarly ac-
celerated, then the calculated 25- to 36-month residence time indicated
above should be extended 2 to 21 times, to 5 71 years, to represent
field performance. Such duration would allow maintenance of OM levels
2 or 3 times greater than that of the control (1.3%), for example, by
heavy additions (45-90 mt/ha) at intervals of 4 to 6 years.
Effects on Soil Properties
Soil reaction. Soil reactions between pH 5 and 6 are generally
regarded as optimum for pine seedling production (Armson and Sadrieka
1979). The seasonal course of nursery soil pH is affected by nutrient
uptake and leaching, by the effects of applied fertilizers and by the
cumulative additions of bases in irrigation water. In consequence, statis-
tical comparisons were limited to those between materials and rates within
each sampling date.
Reaction of the unamended control soil increased irregularly from
about pH 5.7 to 6.0 at 18 months (Fig, 2-3), presumably reflecting the
excess of calcium in the irrigation water over that lost by leaching of
unutilized fertilizer nitrogen (as NO3) and also CI A total of 141 kg/ha
each of N and K20, as KC1, was applied at intervals to the two success-
ive pine crops grown in the microplots as described earlier in Chapter 1.
Addition of acid peat lowered the pH 0.3 unit for each 1% increase
in OM (Fig. 2-3). This effect persisted throughout both seasons with
reaction more or less paralleling changes in the unamended control, but
at levels reflecting higher CEC.
As expected, the high base content and reaction of the sludge
initially increased pH of the soil-sludge mixture. This response was
abruptly reversed, with the two higher treatments falling from pH 6.6-6.7
to 4.5 at 3 months. Decreases during the first 9 to 12 months can be
ascribed to nitrification and rapid leaching of NO3 from a material with
a narrow C/N ratio (Table 2-1). The subsequent slow increase is
generally similar, although steeper, to that of comparable peat treatments.
S I n
cD N( 08 10
\ I N
0. ~ ` \
7 / "I
CHd) NOIOV3~ lIOS
The marked increase in initial pH following addition of shredded
cones apparently is due to the relatively high potassium content (.34%,
Table 2-1), combined with low CEC of the raw woody material. The
subsequent fall of reaction to that of the unamended control at 6 months
probably reflects increased CEC, hence lower base saturation, as de-
composition progressed (Fig. 2-3), although some leaching may have
occurred. A lesser pulse of increase at 12 months, i.e., early in the
second growth period, is unaccounted for, but again followed by a
Addition of "old" sawdust decreased pH slightly below that of the
controls during the first year, and somewhat more so between 12 and 18
Soil nutrient status. Changes in the soil nutrient status over the
18-month study period are the net results, not only of the composition
of materials (Table 2-1) and decomposition per se (Fig. 2-2), but also
of (a) crop uptake, (b) fertilizer additions, as discussed earlier in
Chapter 1, (c) production of excess NO3 and hence leaching of bases,
(d) cumulative addition of Ca in irrigation water, and (e) leaching from
soil by excess irrigation and rainfall.
Selected chemical properties of soil samples taken at 3 and 18 months
after the organic additions are listed in Table 2-3. The unamended con-
trol soil showed no detectable decrease in OM, but an apparent decrease
in N and K. The latter two are due to leaching and crop uptake. Des-
pite such uptake, extractable P, Ca and Mg increased as a result of
fertilizer additions (it was discovered that coarsely ground limestone
eq eq eq ~ C O d = A CA eq e
0 eq ~ eq eq A eq
" i S
was used as a partial filler in the granular fertilizer used in 1980). Ad-
ditional Ca inputs were received from irrigation water.
The high N content (2.85%) of the peat additions resulted in signi-
ficant increases in total soil N. Although both OM and N levels decreased
over 15 months, the N/OM ratios changed only slightly. Hence, release
of available N was more or less proportional to total OM decomposition.
Extractable P, Mg, and Ca increased, whereas K decreased similarly to
the control, and presumably for the same reasons. Apparently, the greater
CEC of the peat did not lead to greater retention of applied K. Potassium
uptake by seedlings must be considered, however, as discussed later.
As with peat, the high content of N in sludge (5.7%) resulted in
significant increases of total soil N. Organic matter, N, and N/OM ratios
decreased over the 15-month period, with the magnitude of reduction in-
creasing with the application rate. The reduction in N/OM ratios indicates
that N was mineralized and removed from the system at a rate greater than
OM was being oxidized. This effect was more pronounced at the higher ap-
plication rates. Nitrogen losses between 3 and 18 months are roughly
equivalent to 680, 1656 and 2437 kg/ha for the 1, 2, and 4% application
rates (based on 30 cm depth and bulk density of 1.33). Those quan-
tities are far in excess of possible seedling uptake. Such losses occur
largely through leaching of NO3, which in turn removes equivalent
amounts of cations (Raney 1960). Although the sludge initially contained
1. 55% Ca and 0.47% Mg (Table 2-1), no influence of the latter is evident
from analyses at 3 months. Likewise, K contents of the sludge-amended
plots are well below those of the cone treatments, although K concentrations
in the original materials are comparable. Calcium losses must have been
greatest in the first 3 months when pH decreased abruptly (Fig. 2-3),
but continued through to 18 months, despite Ca inputs from fertilizer
materials and irrigation water.
The sludge initially contained 2.39% P, presumably in both organic
and inorganic forms. Extractable quantities present at 3 months are
equivalent to much less than half the additions in sludge, and decreased
by 1/3 to 1/2 in the following 15 months. This decrease is not accounted
for by excess seedling uptake (Table 2-6) and its mechanism is unex-
The addition of shredded cones, a low-N material, greatly reduced
the N/OM ratio of the soil-OM mixture. Only slight losses of N occurred
over the 15-month period, although OM decreased markedly. Thus, N/OM
ratios increased accordingly. At 3 months those ratios were markedly
lower than that of the control, but at 18 months the ratio for the 1%
treatment approached that of the control (Table 2-3). Extractable Ca and
P changed little over the period, while Mg increased as a result of
fertilizer additions. The high content of K in the cones is reflected in
high soil K at 3 months (Table 2-3). At 18 months, K levels in the
cone-soil mixture decreased by roughly 50%, although still higher than
the other materials. The excess K loss was not accounted for by in-
creased crop uptake, and hence must be attributed to leaching. Ad-
ditional amounts of K may also have been lost in the 0-3 month period.
As expected, sawdust had the widest C/N ratio of the four materials
(Table 2-1). Over the 15-month period, OM levels decreased while N
levels remained nearly constant. A marked rise in N/OM ratios reflected
this disproportionate loss of OM with respect to N. Extractable P and
K changed little over the period, while Mg increased as a result of fer-
tilizer additions. Calcium levels increased as a result of both fertilizer
and irrigation water additions.
At 3 months, extractable Mn had increased significantly in all
treatments, except at the 1% rate of peat and the 1 and 2% rates of saw-
dust (Table 2-4). Increases were greatest in the cone and sludge treat-
ments, a result of the higher Mn contents of these materials (Table 2-1).
Between 3 and 18 months, the unamended soil and the cone and sawdust
treatments showed no net change in Mn, while the sludge plots decreased
to the level of the control,and the peat treatment increased. Excluding
the sludge, Mn levels in excess of the control were presumably due to
slightly greater retention of fertilizer Mn in the amended plots.
Initially, levels of extractable Zn were increased only in the sludge
treatments, a result of the high Zn content of that material (Table 2-4).
After 15 months, Zn levels in the sludge treatments had decreased 30-50%,
but were still higher than for the other materials. The slight increases
for some materials and rates over that of the control are a result of
Extractable copper concentrations were unaffected by treatment and
are not presented.
Table 2-4. Double-acid extractable concentrations of Mn and Zn in soil-
amendment mixtures 3 and 18 months after application.
Material Rate Mn Zn
3 mo. 18 mo. 3 mo. 18 mo.
(Duncan's, a = .05).
columns with the same letter are not significantly different
Materials with a narrow C/N ratio, such as peat and sludge, may
be beneficial through supplying available nitrogen for plant growth,
but leaching of excess NO3 after high rates of application can accelerate
loss of cations. This effect is increased by materials which lower pH,
since the cation exchange capacity (CEC) of OM is "pH-dependent."
The reduction in CEC is in the vicinity of .2 to .3 meq/100 g per 1% OM,
per pH unit, for the materials studied by Kalisz and Stone (1980). In
contrast, materials with a wide C/N ratio, e.g., sawdust and cones, pro-
duce little or no NO3, and hence cation losses are small. Decisions
about the application rates of amendments should consider the nutritional
ramifications, including pH effects.
Effects on Seedling Development
Physical parameters. Comparisons were made among the control and
three rates for each organic material within each year. Since individual
seedlings were the units of measure, variability was extremely high. Only
a few effects proved significant, and so mean values were averaged across
rates within materials (Table 2-5).
In 1980, 10 to 15 seedlings were transplanted into the microplots.
The result, after transplanting mortality, was seedling densities well
below the normal of 28 seedlings/0.1 m2. Additional mortality occurred
in the sludge-treated plots. The cause is unknown but presumably was
either pathogenic or chemical. Excess NO3 and Mn or Zn solubility as
the pH dropped are possible agents. In 1981, direct, operational seed-
ing produced seedling densities nearer the normal.
Table 2-5. Physical parameters of slash pine seedlings as influenced by
four organic amendments averaged across application rates in 1980 and
Material Seedlings Height Stem Dry weight Shoot/root
microplot diameter shoot root total ratio
--- gm /seedling---
0.9 2.4 1.6
1.3 3.3 1.6
- Underlined values are significantly different from the control
(Duncan's, a = .05).
Mean weight of seedlings from the peat treatments was greater
than that of the controls, although only shoot weight in 1980 and
root weight in 1981 attained significance. Seedlings from the peat
treatments were also heavier than those from any other material.
Reasons for this superiority are obscure but may include greater
nitrogen availability, improved soil physical properties, or even growth
stimulating substances from the peat (Lee and Bartlett 1976).
Seedlings from the sludge treatments were generally smaller and
lighter than those of the controls or any other amendment. Seedling
height decreased as application rate increased. The lower weight
obviously is not due to lack of available N or P (Table 2-3, 2-6), but
may be associated with the tissue concentrations of Mn and Zn nearly
threefold greater than from any other treatment (Table 2-7). As men-
tioned under Methods, a reliable estimate of root weight was not obtained
in 1980 because of low seedling density in the microplots.
Overall, seedlings from the cone and sawdust treatments differed
little from those of the controls except in having slightly--but non-
significantly--larger root systems in the second year. This lack of
difference is surprising in view of the wide C/N ratios of the amend-
ments, and especially so in the second year when only 34 kg/ha of
fertilizer-N was applied.
Chemical parameters. The effects of treatment on elemental con-
centrations and contents were compared as described for the physical
parameters. Since few effects were significant, values were averaged
across rates, and thus one value per variable is presented
Table 2-6. Element concentrations (% dry weight) and contents
(mg/seedling)l/ of slash pine seedling shoots as influenced by
four organic amendments averaged across application rates.
Material Seedlings N P K Ca Mg
% mglsdln % mg IsdIn % mglsdin % mg Isdln % mglsdin
Control 10 1.5 21.4 .16 2.3 .71 10.4 .50 7.3 .09 1.3
Peat 11 1.3 26.52/ .17 3.4 .67 13.5 .38 7.6 .09 1.8
Sludge 5 2.2 25.2 .20 2.2 .71 3.3 .67 7.8 .14 1.7
Cones 11 1.3 20.6 .17 2.7 .80 12.5 .37 5.8 .09 1.3
Sawdust 10 1.4 20.5 .16 2.4 .74 10.9 .45 6.8 .09 1.3
Control 28 1.2 11.2 .17 1.6 .71 6.6 .52 4.9 .11 1.0
Peat 13 1.3 16.0 .19 2.3 .73 8.5 .48 5.6 .10 1.2
Sludge 18 1.4 10.1 .23 1.6 .65 4.8 .53 4.0 .13 0.9
Cones 21 1.3 9.9 .20 1.5 .83 6.3 .42 3.2 .10 0.8
Sawdust 23 1.3 11.9 .19 1.8 .80 7.2 .43 3.8 .10 0.9
SSeedling contents may differ from those calculated from concentration x weight
(Table 2-5) because of rounding errors.
- Underlined values are significantly different from the control (Duncan's, a = .05).
Table 2-7. Microelement concentrations (ppm dry weight) of 1981 slash
pine seedling shoots as influenced by four organic amendments averaged
across application rates.
Material Seedlings per Cu Mn Zn
Control 28 5.4 95 61
Peat 18 5.2 184! 61
Sludge 18 6.1 486 180
Cones 21 5.6 161 63
Sawdust 23 5.7 193 60
-Underlined values are
(Duncan's, a = .05).
significantly different from the control
for each material per year (Table 2-6). Significant differences among
rates within a material are mentioned in the discussion that follows.
Seedling densities vary between years as described earlier.
The peat treatment had no significant effect on N and P con-
centrations in either year. Greater shoot weights, however, resulted
in greater absolute contents of both elements (Table 2-6). Nitrogen and
P concentrations did not vary with peat rate, which indicates little or
no benefit from the high levels of N that presumably were available
in the higher peat treatments (Table 2-3). Although the control seed-
lings dropped from 1.5% N in 1980 to 1.2% N in 1981, the seedlings
from the peat treatment did not change from 1.3%. The reduction in N
concentration is attributed to the low amount of fertilizer-N applied
(34 kg/ha). Since the seedlings from the peat-amended plots did not
show the drop in N concentration, peat must have been a stabilizing
influence on the N-nutrition of the seedlings. Calcium concentrations
were significantly lower in 1980 than in the control seedlings, which
may have resulted from reduced availability of this element as increased
CEC from the peat additions lowered its percentage saturation on the
The sludge treatments resulted in greater tissue concentrations of
N, P, Ca and Mg in 1980 (Table 2-6), reflecting the high content of
these elements in the sludge. These increases, however, were propor-
tionally less than the large differences between the soil concentrations
of the sludge treatments and the control (Table 2-3). As previously
described, large amounts of N were lost from the sludge-amended soils,
reducing the initially high cation content. Consequently, only P
concentration was significantly greater in the 1981 crop. This em-
phasizes the potential for cation leaching when large quantities of
high-N organic materials are applied.
Nitrogen concentrations of shoots from the cone treatments did
not differ from the controls in either year, despite the wide C/N ratio
of the amended soil. Shoot content of N was lower in 1981 due to lower
weight. Potassium concentrations were higher in both years, although
significantly so only in 1980. This reflects the relatively high K content
of the cones. Although soil K diminished between 3 and 18 months
(Table 2-3), its level was still higher than in the other treatments,
As compared with the controls, the sawdust treatments had little
influence on elemental concentrations or contents in either year (Table
2-6). The only exception to this was Ca concentrations in 1981, which,
as in the cone treatments, were lower than in control seedlings. The
20-year exposure of sawdust to weathering and decomposition processes
doubtless had removed the easily and moderately decomposable fractions
although the C/N ratio was still > 300. The relative inertness to rapid
decomposition, coupled with low contents of N, P, K, Ca, and Mg,
resulted in the sawdust having less chemical influence on the soil and
subsequent plant growth than the other materials tested.
None of the amendments significantly increased shoot Cu concen-
tration (Table 2-7), despite the wide differences in concentration between
the sludge (450 ppm) and other materials (3 ppm). Shoot Mn concen-
trations were roughly 2 times greater for the peat, cone, and sawdust
treatments, and 5 times greater for the sludge, as compared to the
unamended control (Table 2-7). This difference was roughly pro-
portional to the Mn composition of sludge and cones, while not so for
peat and sawdust (Table 2-1). Tissue concentrations of zinc were only
3 times greater in the seedlings from the sludge treatment than from the
controls, while the other treatments had no apparent effect. This is
despite the fact that sludge contained nearly 100 times more Zn than the
cones, which had 3 to 7 times more than peat or sawdust (Table 2-1).
Additional Zn was added to the system from fertilizer materials and from
the galvanized hardware cloth used to screen out roots when the seedlings
were harvested in 1980. The latter contributed zinc to the soil (Table 2-4)
and subsequently to the seedlings in 1981. Seedlings from the peat-
treated microplots had Zn concentrations 20 to 30% greater than seedlings
from the field macroplot study (Ch. 1, Table 1-7). Additionally, soil
samples taken at the end of each study from plots which had received the
lowest rate of peat showed 4 times more Zn in the microplots (2.4 ppm;
Table 2-4) than in the field macroplots (0.67 ppm; Table 1-4).
Effects of Mycorrhizae and Incidence of Charcoal Root Rot
No visible evidence of charcoal root rot infection was found in any
The influence of treatment on percentage of short roots colonized
by ectomycorrhizal fungi is presented in Table 2-8. Peat treatments
markedly increased colonization in both years, as compared to the un-
amended control. In 1980, the lower rates of sludge treatments had no
influence, whereas the higher rate increased colonization, despite the
Table 2-8. Approximate percentage of short roots colonized by
ectomycorrhizal fungi as influenced by treatments.
Material Rate % Short roots colonized
Control 0 37 18
Peat 1 58 44
2 70 46
4 43 57
Sludge 1 35 38
2 35 19
4 62-1 26
Cones 1 39 43
2 37 37
4 27 47
Sawdust 1 31 36
2 27 21
4 21 26
Only 12 seedlings were alive at harvest.
poor seedling survival. Contrastingly, in 1981 colonization in the low
rate treatment was twice as great as for the controls, while the two
higher rates showed only slight increases. Colonization at the highest
rate of cone addition was lower than the controls in 1980, but in 1981
all rates were superior to the controls. Similarly, all rates of sawdust
addition resulted in a smaller percentage of mycorrhizal short roots in
1980, but an increase in 1981. The reduction in colonization by the
wide C/N ratio materials (cones and sawdust) may be due to early effects
on seedling nutrition.
Utility of the Microplot Method
The microplot method developed in this study proved to be a satis-
factory means of comparing decomposition of various materials at several
rates. The significance of such information awaits further comparisons
of decomposition in microplots vs. field plots for cones, sludge and
sawdust, as was done for peat. A comparison of selected features from
the control and peat 2 treatments follows:
Decomposition Correlation 1981 seedling development
dry weight shoot N
Micro Macro Micro Macro Micro Macro Micro Macro
------- %------ ------r -- ----g/m--- ---%-----
Control 0 0 --- --- 364 729 1.2 1.1
Peat 2 51 21 .95 .21 504 941 1.3 1.3
1 Field macroplot data are from unfumigated plots (Ch. 1).
This comparison indicates that decomposition was more rapid and
measured with greater precision in the microplots than in the large-scale
field plots. Reasons for this were discussed earlier. Extrapolating the
residence time of peat in the microplots to performance under actual field
conditions requires multiplying by a factor of 2-21 times.
Dry weight of seedlings from the microplots was roughly half that
of seedlings from the macroplots. The weight ratio of the control and
peat 2 treatment seedlings is roughly proportional in both studies (i.e.,
microplot, .72; macroplot, .77). Shoot N concentrations in both studies
seem to correlate almost directly. Thus, it appears that the microplot
method predicts relative differences in seedlings grown in amended and
Modifications of the methodology that may improve precision are
(a) additional replications, and (b) maintenance of uniform seedling num-
ber in each microplot. The latter may be achieved by sowing a 10 to
20% excess of seeds, then thinning to the desired density several weeks
after germination. Also, pre-plant fertilizer mixtures could be incor-
porated into the soil-OM mixtures to more closely parallel field conditions.
The method was inexpensive in terms of materials and was labor
intensive for only a few 2 to 3-day periods when the plots were installed
and lifted at the beginning and end of the growing season. Because the
microplot containers were made of sturdy plastic they can be used in
With some modifications as described, the microplot method appears
to be a useful means of testing a variety of organic materials, combin-
ations, and application rates with respect to OM decomposition, effects
on soil chemical properties, and seedling responses.
Half or more of the added OM decomposed in the 18-month period of
study, regardless of material or rate. The exception was a 44% loss
from the 4% sewage sludge application, and here decomposition probably
was retarded by coarse particle size and drastic changes in the soil
chemical environment. Losses from shredded cones, the only material not
subjected to prior decomposition, were greater than from the other three
materials, which in turn were roughly comparable. Within each material
and rate, decomposition was a linear function of time. In contrast, OM
content of the control soil (1.3%) did not change perceptibly.
Peat-amended soils maintained a lower reaction throughout the
study period. Cones and sawdust had little influence except in the last
3 to 6 months. Reaction in the sludge-treated plots at first increased to
above pH 6, then lowered below pH 5 as nitrification occurred.
The most notable effects on soil concerned nitrogen transformations.
Peat decomposed without appreciable changes in N/OM ratios, and thus
served as a source of "slow release" N for seedling uptake over the
growing season. The high content of readily mineralized N in sludge
resulted in leaching of excess NO3 and concurrent losses of cations,
In terms of seedling growth, the most notable effects were first
year mortality and high tissue concentrations of Mn and Zn in the
sludge treatments. Surprisingly, cones and sawdust did not reduce
growth or nitrogen uptake below that of the control despite high C/N
ratios in the soil.
The microplot method used to test the materials proved satisfactory
but could be improved with some modifications. Overall, the response of
seedlings, soil chemical properties, and OM residence time varied with
organic material and rate of application. Ideally, the nature of these
responses should be determined prior to the full-scale operational use of
any exogenous organic material.
LABORATORY INCUBATION OF VARIOUS ORGANIC MATERIALS
For many years exogenous sources of organic materials have been
used as supplements to cover crops in attempts to maintain the organic
matter content of forest nursery soils. Many studies have evaluated the
effects of organic matter additions on plant growth and, to a lesser ex-
tent, on soil properties (Brown and Myland 1979, Davey 1953, Wilde and
Hull 1937). In contrast, with the exception of the notable work by
Allison and Murphy (1963), Allison and Klein (1961), Pinck et al. (1950),
and Allison et al. (1949), little attention has been given to characterizing
the decomposition of various types and application rates of organic mater-
ials. Allison and Murphy (1963) concluded that rates of decomposition of
sawdust and bark differ markedly with tree species. Since the variety of
organic materials available for application to nursery soil differs greatly
in physical and chemical properties, field testing of the actual effects on
soil and seedlings is eventually necessary.
Full-scale field testing, even in small plots, however, requires time
and effort, and is subject to variability induced by weather and manage-
ment. Such effort and variability would be reduced if laboratory incu-
bation of organic materials could serve as a screening test for rates of
decomposition. Such a test might also provide more exact information
on the course of decomposition than is possible to obtain under field
conditions. Accordingly, a laboratory incubation study was designed
to examine the same materials used in the field microplots (Ch. 2),
thus allowing a comparison of the methods. Two additional materials,
pulp mill waste and fresh pine bark, were included.
Materials and Methods
Experimental Design and Conduct
The decomposition of peat, old slash pine sawdust, fresh slash pine
bark, shredded cones, sewage sludge, and pulp mill waste was evaluated
by measuring CO2 evolution from mixtures of these materials with a nur-
sery soil incubated at 220 C. The soil used was from bulk samples taken
prior to peat application in the field macroplot study (Ch. 1). The pine
bark and pulp mill waste were obtained from industrial mills, and other
materials were the same as used in the prior studies (Ch. 1,2). The
mill waste consists largely of short cellulose fibers and wood residues not
used in paper manufacturing. All materials were ground to pass a 20 mesh
sieve prior to mixing with soil. Table 3-1 presents the chemical character-
istics of materials and nursery soil.
Erlynmeyer flasks (125 ml) were prepared with 100 g of nursery
soil mixed with the equivalent of 2 g ash-free organic material (equi-
valent to 44.8 mt/ha) and 0.25 g NH4NO3. The mixtures were then wetted
to field capacity. Peat and mill waste were also added at rates of 1 and
3 g of ash-free material/100 g of soil. Controls were prepared identically
but without organic addition. Three replicates of each treatment, includ-
ing controls and blanks (empty flasks) resulted in a total of 36 flasks.
These were arranged in a completely randomized fashion.
Table 3-1. Chemical characteristics of organic materials and un-
amended soil .
Material pH Ash C N C/N P K Ca Mg Cu Mn Zn
----% ------ ------------------ ppm------------------
soil 5.8 99 0.7 3.02 35 44 35 149 9 5 0.4
Peat 4.5 14 53.7 2.85 19 160 90 1250 415 3 5 2
Sludge 6.7 24 42.7 5.69 8 23900 2750 15500 4690 450 84 1249
Cones 6.2 1 56.5 0.30 188 215 3400 225 405 3 28 14
Sawdust 4.5 4 61.6 0.19 324 25 55 325 70 3 9 4
Bark 4.0 1 53.4 0.17 314 100 410 1575 215 2 12 13
Mill waste 3.1 30 39.0 0.19 205 621 -3
/ P, K, Ca, Mg, Cu, Mn, Zn are expressed as extractable (.05N HCI + .025N H250 )
for soil and total for organic amendments.
/ These elements were not determined due to lack of a suitable ashing procedure for
The incubation system followed the basic procedure described by
Stotzky et al. (1958). Each incubation flask was connected by plastic
tubing to two 2.5 cm x 20 cm glass test tubes (Fig. 3-1). The first
tube was a precaution against the possible back-flow. The second con-
tained 20 ml 0.1N NaOH to absorb CO2. Air supplied to the incubation
flasks was scrubbed of CO2 and humidified by passing through flasks
containing 0.3 NNaOH and water, respectively.
The possible influences of moisture and available N and C on limiting
microbial respiration in the flasks were examined near the end of the
study. Each flask received 1.5 ml H20 at week 17, 0.1 g NH4NO3 in
2 ml HO0 at week 19, and 135 mg glucose in 1 ml H Oat week 27.
Carbon dioxide evolution was determined by titration of the NaOH
with 0.1NHC1 at weekly intervals for 30 weeks according to procedures
outlined by Stotzky et al. (1958).
The chemical composition of the organic materials was determined
by methods described in the prior studies (Ch. 1, 2). The methods
used for the bark and mill waste were the same as those used for pre-
viously described sawdust.
Differences in CO2 evolution among the treatments were evaluated
using general linear model procedures (Barr et al., 1979). Comparisons
were made among all materials at the common rate, among the three rates
of peat, and among the three rates of mill waste. Weekly CO2 values were
summed by month. The monthly means were compared using Duncan's
multiple range test (Snedecor and Cochran 1967). The analysis of
variance designs used for comparisons are presented in Table 3-2.
Results and Discussion
CO2 Evolution as Influenced by Amendment
Mean monthly CO2 evolution varied considerably among materials
(Table 3-3). All treatments showed an initial flush of microbial activity
due in part to re-wetting the air-dried soil. After 1 month, sludge and
mill waste had evolved six times, and the other materials two times more
CO2 than the control. Thus, the soil itself was responsible for only
part of the total CO2 output, with the remainder due to the material,
presumably from the most easily decomposed fraction. The mill waste
and sludge evidently had larger fractions of easily oxidized C than the
other materials. Although not measured, the sludge and mill waste must
have increased pH of the mixtures (Table 3-1), and unlike the nursery
environment, there was no leaching of NO3 Hence, the several mixtures
created very different chemical environments. It is probable that the
high pH mixtures favored high bacterial populations.
Differences during the second and third months were more pro-
nounced, with CO2 evolution rates following the order: mill waste >
sludge > bark Z cones z sawdust > peat > control. This pattern
remained fairly stable for the remainder of the incubation time (Table 3-3),
but the magnitude of the differences became smaller. This, coupled
Table 3-2. Analysis of variance designs used for comparisons of CO evol-
ution among materials and rates. One month is the sum of 4 weeks.
Material comparison Rate comparison
Source d.f. Source d.f.
Treatment 6 Rate 2
Rep (treatment) 14 --error a-- Rep (rate) 6
Month 6 Month 6
Month x treatment 36 Month x rate 12
Month x rep (treatment) 84 --error b-- Month x rep (rate) 36
Total 146 Total 62
Table 3-3. Monthly (4 week) CO2 evolution from 100 g of
nursery soil incubated with 2 g (ash free) organic material
from several sources.
Month Control OM source
Feat ludge Cones sawdust Bark Mill waste
1 24.9 d- 41. 7cd 176.7 a 63.6 c 59.6c 58.7c 134.4
2 2.7e 6.2e 64. 3 b 1.5cd 13.4d 22.8c 156.5a
3 2.2 e 4,7e 31.6 b 13.2c 9.6d 13.1c 141.0 a
4 1.3d 7.6cd 20.2b 7.8cd 12.Oc 7.Sed 73.2a
5 ** 3.7b 8.5b 12.6b 10.7b 9.7b 3.2b 31.7a
6 10.4b 15.2 ab 18.4 ab 20.4 ab 19.8 ab 9.3b 37.3a
7 4.3b B.0 ab 16.8 ab 8.6ab 9.9 ab 8.5ab 20.2a
8 47.7 53.4 48.0 39.0 41.0 56.1 45.9
E 1-7 49.5 91.9 341.1 142.8 134.0 123.2 594.3
!I Values in rows with the same letter are not significantly different (Duncan's,
a = .051.
1.5 ml H20 added at week 17.
** 0.1 g NH4NO3 in 2 ml H20 added at week 19.
*** 135 mg glucose in 1 ml H20 added at week 27.
with greater variability among replicates for unknown reasons, resulted
in greater error and hence less precision in identifying differences in
the later months of incubation.
Bark, cones, sawdust and peat reached an approximate steady state
of CO2 evolution in 1 month, the sludge in 21 months, and the mill waste
not until 4 months. At the beginning of the fifth month the series of
additions described in the Methods section were made to determine what
factor was limiting microbial respiration. There was no response to the
water addition at 17 weeks, indicating that moisture was not limiting
respiration. Additional N at week 19 increased CO2 evolution by 18% in
mill waste, and up to 190% in bark (Table 3-3, months 5 and 6). Al-
though the relative increases between the fifth and sixth month were
large, the absolute amounts of CO2 evolved were small with respect to
the initial carbon addition. The immediate, and more or less uniform
increase in CO2 production in all treatments upon addition of glucose
in week 27, demonstrates that available carbon had been a limiting factor
(Table 3-3, month 8).
Examination of cumulative CO2 evolution (Fig. 3-2) shows that after
7 months the percentage of added carbon remaining was as follows:
mill waste, 89.7; sludge, 93.0; sawdust, 98.2; cones, 97.8; bark, 98.2;
peat, 99.1. Although the amount of carbon oxidized appears low, given
the length of the incubation period, the results parallel those of Allison
and Klein (1961) for wood and bark particles of several conifer species.
They found that less than 7% of the added carbon was oxidized during
a 2-month period. They suggested two explanations: (a) salt concen-
tration from nitrates, and (b) acidity resulting from nitrification.
1 0 11
C, Cu, O
Cl, u O cfl
I I ~
(6W) -Zo oa! Ifelnwo ul
The same factors may have reduced CO2 evolution in the current study
given the liberal amount of N supplied as NH4NO3. An additional factor
may have been a reduction in gas exchange due to fine organic particles
accumulating on the soil surface and reducing the pore sizes at the soil-
air interface. For example, the CO2 evolved from the sludge treatment
was roughly half of that measured by Agbim et al. (1977) when incubating
various mixtures of spruce sawdust and sewage sludge in soil. In that
study, sludge alone (22.4 mt/ha) + soil lost 28% of the added carbon in
1 year, whereas in the current study the 44.8 mt/ha rate lost 7% in
The percentages of added carbon lost are equivalent to the percent
OM lost, which for the materials are as follows: mill waste, 10.3; sludge,
7.0; sawdust, 1.8; cones, 2.2; bark, 1.8; peat, 0.9. The considerably
lower decomposition rates in this study as compared with those of Fig-
ure 2-2, indicate that the incubation procedure underestimates the
decomposability of the materials when subjected to field conditions.
Comparison of materials, moreover, shows that sludge decomposed more
rapidly than cones, sawdust, and peat, whereas in the microplot study
(Ch. 2) sludge was more resistant than cones, and roughly equivalent
to sawdust and peat. Considering that the materials in the incubation
study were finely ground, the above results add support to the sug-
gestion that sludge decomposition in the microplot study was reduced by
coarse aggregate size of the sludge particles which limited contact with
Differences between the two studies are presumably due to the very
different environmental conditions under which decomposition occurred.
These conditions include temperature, moisture and chemical regimes,
as well as more variable microbial populations in the field study, in-
cluding rhizosphere populations.
Since the incubated materials were not subject to leaching, mineralized
ions, NO3, and H accumulated. This may have resulted in concentrations
unfavorable for higher fungi.
CO2 Evolution as Influenced by Amendment Rate
Comparisons of CO2 evolution among the three rates of peat or mill
waste show only a few differences which occurred between 2 and 5 months
(Table 3-4). Subsequently, unexplained experimental variability pre-
vented large mean differences among rates from being declared significant
(Table 3-4, months 6 and 7).
Examination of cumulative CO2 evolution (Fig. 3-3) shows the per-
centages of added carbon lost as follows: peat 1, 0.2; peat 2, 0.9;
peat 3, 1.0; mill waste 1, 11.4; mill waste 2. 10.3; mill waste 3, 7.5.
Thus, as application rate increased, peat decomposition rate increased
while that of mill waste decreased. Losses from the corresponding ap-
plication rates in the field microplot study (Ch. 2, 4% rather than 3%)
after 7 months are as follows: peat 1, 24.1; peat 2, 19.8; peat 4, 19.8.
The corresponding application rates in the full-scale field study (Ch. 1)
show decomposition rates after 7 months as follows: peat 1, 0; peat 2,
7.0; peat 3, 6.3. The magnitude of the losses are very different among
Table 3-4. Monthly (4 week) CO evolution from 100 g of nursery soil
incubated with 1, 2, and 3 g (ash free) peat or pulp mill waste.
Month Material Peat Mill waste
Rate 1% 2% 3% 1% 2% 3%
-------------------- mg --------------------
1 36.41! 41.7 48.7 100 134 121
2 4.3b 6.2a 6.5a 68 b 156 a 141 a
3 3.1b 4.7a 4.7a 43 c 141 a 133b
4 l.lb 7.6a 4.9 ab 40b 73 a 87 a
5 0.0 b 8.5 a 8.8a 35 32 63
6 2.3 15.2 22.6 41 37 61
7 4.6 8.0 18.9 27 20 40
8 48.0 53.4 51.5 49 46 54
E 1-7 51.8 91.9 115.1 354 593 646
Within rows and within materials, values with the same letter or no
letter are not significantly different (Duncan's a = .05).
1.5 ml H 0 added at week 17.
0.1 g NH NO3 in 2 ml H20 added at week 19.
***135 mg glucose in I ml H20 added at week 27.
135 mg glucose in 1 mi H0 added at week 27.
(6W) .0 0Ai;felnwflo ul
the studies, and decomposition in the microplot study (Ch. 2) was great-
est at the 1% application rate but conversely in the other two studies.
Nevertheless, the studies agree in showing similar rates of loss from the
two higher rates, respectively.
Utility of the Method for Predictive Purposes
A simple, easily maintained incubation system such as the one used
in this study may be useful for initial characterization of organic materials
being considered as prospective nursery soil amendments. Although an
extrapolation to field conditions is limited, the results nonetheless provide
comparative data on amounts of easily oxidized C and effects of application
rates on decomposition.
The results of this study indicate that unaltered tree components,
such as bark, sawdust and cones, have similar decomposition rates. In
contrast, sludge and mill waste, although subjected to previous chemical
and biological degredation, have considerably greater carbon oxidation
rates. Relative to the other materials, peat oxidizes slowly--which is
consistent with the results of the field microplot study (Ch. 2). The
present study also shows that the residence time of added C varies with
the source and rate of application as demonstrated in Chapter 2.
The laboratory incubation procedures as used in this study did not
provide reliable estimates of the decomposition rates of the same organic
amendments tested under field conditions. A suggested modification of
the procedure would be to reduce the nitrogen applied and to inter-
mittently mix the soil + OM mixtures to increase surface area and facilitate