Title: Decomposition, function, and maintenance of organic matter in a sandy nursery soil
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00099362/00001
 Material Information
Title: Decomposition, function, and maintenance of organic matter in a sandy nursery soil
Physical Description: ix, 96 leaves : ill. ; 28 cm.
Language: English
Creator: Munson, Kenneth Richard, 1952-
Copyright Date: 1982
Subject: Humus   ( lcsh )
Peat   ( lcsh )
Sandy soils -- Florida   ( lcsh )
Seedlings -- Soils -- Florida   ( lcsh )
Soil Science thesis Ph. D
Dissertations, Academic -- Soil Science -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: by Kenneth Richard Munson.
Thesis: Thesis (Ph. D.)--University of Florida, 1982.
Bibliography: Bibliography: leaves 92-95.
General Note: Typescript.
General Note: Vita.
 Record Information
Bibliographic ID: UF00099362
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000319150
oclc - 09318565
notis - ABU6001


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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.



ACKNOWLEDGEMENTS ........................................ i

LIST OF TABLES ......................................... ...

LIST OF FIGURES ............................................ vii

ABSTRACT .............................................. viii

GENERAL INTRODUCTION ...................................... 1

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


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


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


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


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


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



Kenneth Richard Munson

December 1982

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

nursery soil.

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

once outplanted.

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.



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

Study Area

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










c L

E m
0 3


-2 S




E I;

o c-

o II

C -

w ,

o a

a- U


(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.

Sampling Scheme

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.

Statistical Analysis

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.
variation variation

OM treatment

rep (treatment)


time x treatment

time x rep (treatment)



pH treatment

rep (treatment)


time x treatment

time x rep (treatment)





Seedling treatment
-error a- rep (treatment)


fumigation x treatment

-error b- fumigation x rep (treatment)



data treatment

-error a- rep (treatment)


time x treatment

-error b- time x rep (treatment


Results and Discussion

Peat Decomposition

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



0 -

E >







Ls ^

1o 0 Lo o

Nc Ni -_ -


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
----------------------ppm ---------------------------

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

Months after

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
peat application.

- 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.

N utrient-/
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

months previously.

.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 -------
1980 Crop

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

1981 Crop

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 -----
1980 Crop

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

1981 Crop

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

(Table 1-2).

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
fumigation treatment.

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

SValues in
a = .05).

columns are not significantly different (Duncan's,

(wudd) uo!q.lJu8u3uo3 uIN

I I I \



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ur 0 3r

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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. -

Treatment 1980

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.



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

Study Area

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.










1. m


w f



c.JI I -
0 N0 N^ N" N a
CO 01 i
I. I t" -,

U r
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= N
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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.

Sampling Scheme

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
among treatments.

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

total 503

Seedling and Treatment
soil data treatment 12 components material 3

(error) rep (treatment) 15 rate 2

total 27 material x rate 6
control 1

total 12

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



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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-

in rates.

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.


W .



c E


m 0
u I

0 Z
40- 4-,)

Cm o





- I-



















S I n

\ \\

C,, I\I


cD N( 08 10


\ I N

w w

0. ~ ` \

7 / "I







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 r

.Q V-













0 eq ~ eq eq A eq


I >

9 0.y
s y^

eq .0

X ^-
eq A

o Lt
0 2


*0 3


Z 'S

" i S


0 U0

C1 11



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

fertilizer-Zn retention.

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.


C control




Sawdust 1



4.2 a1

5.0 ab

5.8 bc

6.6 cd

6.4 cd



5.6 bc

6.2 cd

9.0 e

5.0 ab

5.0 ab

6.0 bc


6.0 abc

7.2 cd


5.2 ab

5.6 abc

5.8 abc

5.2 ab

6.6 bcd

10.2 e

5.0 ab

5.8 abc

5.6 abc


0.6 a

1.1 a

0.8 a

18.8 c

15.6 b




1.1 a

0.6 a

1.2 a


3.1 ab

2.4 ab


2.7 ab

7.0 bcd

10.8 d

18.8 e

3.1 ab


2.8 ab


3.8 abc

3.6 abc

SValues in

(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

cm mm






--- gm /seedling---
















0.9 2.4 1.6

1.3 3.3 1.6

1980 Crop






1981 Crop






- 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

1980 Crop

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

1981 Crop

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

exchange complex.

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
1980 1981

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

unamended soil.

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

subsequent years.

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.

General Conclusion

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,

especially calcium.


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.



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------------------

Unamended 2
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.
Not determined.

/ These elements were not determined due to lack of a suitable ashing procedure for
this material.

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.

Chemical Analysis

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.

Statistical Analysis

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

. 41














" o


u '

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.

= C0

1 0 11



o- o

> ,

C, Cu, O


. t


>. -a
5s _z


= ^'oi

Cl, u O cfl

? t

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

7 months.

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

the soil.

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







U ,


u fa



o 'r




I U,


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

gas exchange.

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