Utilization of municipal solid waste composts for biological weed control in vegetable crop production systems

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Title:
Utilization of municipal solid waste composts for biological weed control in vegetable crop production systems
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x, 142 leaves : some col. ill. ; 29 cm.
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Ozores-Hampton, Monica, 1957-
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Subjects / Keywords:
Weeds -- Control   ( lcsh )
Crop science   ( lcsh )
Compost -- Environmental aspects   ( lcsh )
Horticultural Science thesis, Ph. D   ( lcsh )
Dissertations, Academic -- Horticultural Science -- UF   ( lcsh )
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bibliography   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1997.
Bibliography:
Includes bibliographical references (leaves 132-141).
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Monica Ozores-Hampton.

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University of Florida
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Table of Contents
    Title Page
        Page i
    Dedication
        Page ii
    Acknowledgement
        Page iii
    Table of Contents
        Page iv
        Page v
    List of Tables
        Page vi
        Page vii
    List of Figures
        Page viii
    Abstract
        Page ix
        Page x
    Chapter 1. Introduction
        Page 1
        Page 2
        Page 3
        Page 4
    Chapter 2. Literature review
        Page 5
        Page 6
        Page 7
        Page 8
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        Page 28
        Page 29
        Page 30
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    Chapter 3. Influence of compost: Water ratio on ivyleaf morningglory germination
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
    Chapter 4. Municipal solid waste compost maturity influence on weed seed germination
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
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    Chapter 5. Immature compost suppresses weed growth under greenhouse conditions
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
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        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
    Chapter 6. Municipal solid waste compost use for biological weed control in vegetable crop production
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
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        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
        Page 95
        Page 96
    Chapter 7. Residual effects of municipal solid waste-biosolids compost on snap bean production
        Page 97
        Page 98
        Page 99
        Page 100
        Page 101
        Page 102
        Page 103
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        Page 106
        Page 107
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        Page 109
        Page 110
        Page 111
        Page 112
    Chapter 8. Conclusions
        Page 113
        Page 114
        Page 115
        Page 116
    Appendix. Analysis of variance tables
        Page 117
        Page 118
        Page 119
        Page 120
        Page 121
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        Page 125
        Page 126
        Page 127
        Page 128
        Page 129
        Page 130
        Page 131
    List of references
        Page 132
        Page 133
        Page 134
        Page 135
        Page 136
        Page 137
        Page 138
        Page 139
        Page 140
        Page 141
    Biographical sketch
        Page 142
        Page 143
        Page 144
        Page 145
Full Text











UTILIZATION OF MUNICIPAL SOLID WASTE COMPOSTS FOR BIOLOGICAL
WEED CONTROL IN VEGETABLE CROP PRODUCTION SYSTEMS

















By

MONICA OZORES-HAMPTON


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

UNIVERSITY OF FLORIDA


1997


















I dedicate this thesis to my husband John and my

parents Carlos and Lucia and all minorities, especially

women pursuing a professional career.






The essence of life

is hidden in you



as the entire tree

with all its branches,

roots, leaves, flowers,

fruit, fragrance and shade



are all hidden in the seed


Kabir













ACKNOWLEDGMENTS


I would like to express my appreciation to the cochair

of my supervisory committee Dr. Thomas Obreza for his

financial support, manuscript review, and for his general

willingness to help, and to my chair Dr. Peter Stoffella for

the moral support, statistical knowledge, manuscript review,

and for the time and patience he took to answer innumerable

questions. I cannot say enough thanks to Dr. Obreza and Dr.

Stoffella for enhancing my professional career during the

last 3 years. My gratitude is also extended to the other

members of my committee, Dr. G. Fizpatrick, Dr. D. Graetz,

and Dr. H. Bryan, for their time, professional contributions

and willingness to help.

I would also like to express my gratitude to the many

other people from the Southwest Research and Education

Center at Immokalee who were involved in this work and have

been willing to share their time, knowledge and friendship,

especially to Vija Reinholde, Bill Sherrod, and Dr. Charles

Vavrina.


iii














TABLE OF CONTENTS



ACKNOWLEDGMENTS .. .. ....... iii

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

LIST OF FIGURES .. ... ............. viii

ABSTRACT . . . . . . . . . . .. ix

CHAPTERS

INTRODUCTION . . . . 1

LITERATURE REVIEW . . . . . . . . .. 5

Municipal Solid Waste ... .. . . . 5
Physical Effects of Organic Mulches . . .. 8
Phytotoxic Effects of Organic Mulches . . . 19
Crop Yield Responses to Compost Application . 26

INFLUENCE OF COMPOST:WATER RATIO ON IVYLEAF MORNINGGLORY
GERMINATION . . . . . . . .. 32

Introduction . .. .... . . . 32
Materials and Methods . . . . . 33
Results and Discussion .......... . 35
Summary . . . . . .... .. .. .36

MUNICIPAL SOLID WASTE COMPOST MATURITY INFLUENCE ON
WEED SEED GERMINATION ..... . . ... 41

Introduction . . . . . . .. . .. 41
Materials and Methods . . . ... 44
Results and Discussions . . . .. . .. 48
Summary . . . . . . . . .. . 53

IMMATURE COMPOST SUPPRESSES WEED GROWTH UNDER GREENHOUSE
CONDITIONS . . . . . . . . . . 59

Introduction . . . . . . . . 59
Materials and Methods . . . . . .. 61
Results and Discussions . . .. . . . 65














Summary . . . . . . . .. .

MUNICIPAL SOLID WASTE COMPOST USE FOR BIOLOGICAL WEED
CONTROL IN VEGETABLE CROP PRODUCTION ....

Introduction . . .. .. ...
Materials and Methods . . . . ..
Results and Discussions . ... . . .
Summary . .* . . .

RESIDUAL EFFECTS OF MUNICIPAL SOLID WASTE-BIOSOLIDS
COMPOST ON SNAP BEAN PRODUCTION .* ...


Introduction . . . . . . .
Materials and Methods . . . ...
Results and Discussions . . .....
Summary . . . . . .. .

CONCLUSIONS . . .. .. ...

APPENDIX ANALYSIS OF VARIANCE TABLES .....

LIST OF REFERENCES ..............

BIOGRAPHICAL SKETCH .. .... . ...


. . 97
* 99
* 103
* 106

* 113

* 117

0 132

. 142


. 70


* 77

* 77
. 79
* 83
* 88


* 97














LIST OF TABLES


Table page


2.1. Effect of burial depth on weed seed germination 29

2.2. Extraction methods for seeds compost maturity test 30

2.3. Compost extraction methods for organic acids . . 31

3.1. Volatile fatty acids concentration of composts 38

3.2. Compost:water extract ratios and compost age influence
on final percent germination and mean hours to
germination (MHG) . . . . . . . .. 39
4.1. Elemental concentration and chemical analysis of
composts maturity . .. .. 55

4.2. Volatile fatty acids concentration of composts 56

4.3. Influence of compost extracts from varying compost
maturities on seed germination and radicle length
. . . . . . . . . . . . 57

4.4. Weed seed germination as affected by immature (8-week-
old) compost . . ... . . . 58

5.1. Chemical and physical characteristics of three
different-aged composts . . . . . .. 72

5.2. Volatile fatty acids concentrations in three
different-aged composts . . . . . .. 73

5.3. Effect of mature and immature compost on emergence
and seedling growth of ivyleaf morningglory . 74

5.4. Immature (8-week-old) compost thickness influence on
percent emergence and mean days to germination (MDG)
of three weed species .. . . . . ... 75

5.5. Compost maturity and thickness influence on percent
emergence and mean day to germination of several weed














species . . . . . . . . . . 76

6.1. Elemental concentration and chemical analysis of
immature compost . . . . . . . .. 91

6.2. Volatile fatty acids concentration of different
compost maturities .............. 92

6.3. Influence of MSW compost (4-week-old) on % weed cover
and weeds dry weight in 1995 and 1996 experiments .
. . . . . . 0. . 93

6.4. Influence of MSW compost (8-week-old) on % weed cover
and weeds dry weight in 1995 and 1996 experiments .
. . . . . . . . . . . 94

6.5. Influence of compost (4 and 8-week-old) on zucchini
yield . . . . . . . . . . 95

7.1. Chemical analysis of immature composts . . 108

7.2. Residual effect of 4 and 8-week-old compost on soil
pH, organic matter and soil nutrient concentration,
1996 experiment . . . . . . . 109

7.3. Residual effect of 4 and 8-week-old compost on soil
pH, organic matter and soil nutrient concentration,
1997 experiment . . . .... ... 110

7.4. Residual effects of composts and fertilizer on snap
bean plant stand and marketable yield, 1996
experiment . . . . . . . . . I

7.5. Residual effects of composts and fertilizer on snap
bean plant stand and marketable yield, 1997
experiment . . . . . . . . . 112














LIST OF FIGURES


Figure page


3.1. Compost:water extract ratios of 20 g:50 ml (A),
20 g:100 ml (B), and 20 g:200 ml (C) and compost age
effects on ivyleaf morningglory germination . 40

6.2. Overview 50 days after treatments of 1995
experiment . . . . . . . . . . 96


6.3. Control plots (top) as compared with 7.5 cm of
municipal solid waste and biosolids compost (bottom)
240 days after treatments, 1995 experiment . . 96














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

UTILIZATION OF MUNICIPAL SOLID WASTE COMPOST FOR BIOLOGICAL
WEED CONTROL IN VEGETABLE CROP PRODUCTION SYSTEMS

By

MONICA OZORES-HAMPTON

AUGUST 1997


Chairperson: Peter J. Stoffella
Co-chairperson: Thomas A. Obreza
Major Department: Horticultural Sciences

Immature municipal solid waste (MSW)-biosolid composts

were evaluated as potential biological weed control agents

in vegetable crop row-alleys. Ivyleaf morningglory (Ipomoea

hederacea L.) was used to determine a compost maturity

bioassay. A 20 g (dry weight) of MSW compost:50 ml water

extract resulted in the widest percent seed germination

range to varying compost maturities.

Ivyleaf morningglory, barnyardgrass (Echinochloa crus-

galli L.), common purslane (Portulaca oleracea L.), and corn

(Zea mays L.) seeds were used in the bioassay to determine

the relative potential of 3-day, 4-week, and 8-week-old

composts (containing 2474, 1790, and 1776 mg'kg-' acetic

acid, respectively) to inhibit germination and reduced

seedling growth. Extract from 8-week-old compost was the








most phytotoxic (delayed and reduced germination) to seeds

of 14 important economic weed species.

Immature and mature composts were applied as mulch in

pot culture to determine the effect on weed seed emergence.

Compost (3-day-old) delayed ivyleaf morningglory emergence

by 4 days and decreased emergence by 50% than no mulch.

Seed emergence of eight weed species covered with 2.5 or 10

cm of either mature or immature (8-week-old) compost

decreased as compared with a control. Reduction and delayed

germination from immature compost were more prominent with

the thinner layer (2.5 cm) than with mature compost.

Compost thicknesses of 3.8 (49 tha-1), 7.5 (99 tha'1),

11.3 (148 tha-1), and 15 cm (198 tha-1) were applied to

vegetable crop row-alleys. Immature compost applied at 7.5

cm or thicker completely inhibited weed growth for 240 days

after treatment under low weed pressure. Complete weed

control by 4-week-old compost only lasted 65 days under

higher weed pressure, especially with yellow nutsedge

(Cyperus esculentus L.). Weed cover was reduced by 50% with

11.3 cm of compost than the control, 240 DAT.

Acetic acid levels in 4-week-old compost were 1221 and

4128 mg'kg' in the two field experiments. Immature compost

provided effective weed control in vegetable crop row-

alleys due to physical and chemical effects (short-chain

fatty acids). Eight months later, compost matured, and was

used as a soil amendment that increased snap bean yields.













CHAPTER 1
INTRODUCTION

An annual 10% loss of potential agricultural

production in the United States has been attributed to weeds

(Dusky et al., 1988). Weeds can cause reduction in crop

quality and yield by competing for light, water, and

nutrients, and can increase harvesting cost. Herbicides are

the most utilized pesticides in any agricultural system.

Their popularity is due to cost savings in farm labor,

selectivity on the weed, their ability to increase yield,

and reduction in production costs (Altieri and Liebman,

1988). The costs, effectiveness of weed control, and labor

to apply herbicides is lower as compared with mechanical

weed control, therefore growers have become dependent on

chemical weed control.

Although application of herbicides contributes to high

yields and lower production costs, long-term herbicide usage

may have a negative impact on the environment. In the last

decade, environmental concerns associated with pesticide

usage in agriculture have increased. In Florida, the

Environmental Protection Agency (EPA) restricted alachlor

and metolachlor herbicides due to ground water contamination

and the negative effect on wildlife and humans (Crnko et









al., 1992). A major pathway for herbicide removal from

croplands is in surface runoff water and sediment carried in

the water (Schneider et al., 1988).

Organic mulches were an important method of weed

control before the development of herbicides in commercial

vegetable production systems. In those systems, to

completely discourage weed growth, a mulch layer of 10-15 cm

is needed (Marshall and Ellis, 1992). In general, weed seed

germination declines as burial depth increases, probably due

to unfavorable conditions such as high or low temperature,

absence of sufficient moisture, 02, light, and high CO2

levels (Baskin and Baskin, 1989). Mulches can often be as

effective as conventional herbicides in controlling weeds

(Aparbal-Singh et al., 1985). Diversification of weed

management options is in demand, since growers have fewer

registered herbicides, certain weed species have become

tolerant to herbicides, and increasing environmental

concerns for their use.

Suppression of weed growth is one of the most important

effects of organic mulches (Grantzau, 1987; FAO, 1987).

Weed reduction under mulch is due to the physical presence

of the material on the surface, and/or the action of

phytotoxic compounds generated by microbes in the composting

process (Niggli et al., 1990). Identification of the

phytotoxins in extracts from immature MSW composts indicated

the presence of acetic, propionic, and butyric acids in high









concentration (DeVleeschauwer et al., 1981). Acetic acid

concentration in immature MSW compost was reported between

6,000 and 28,000 mg-kg-1 (Keeling et al., 1994). The effect

of combining immature MSW compost with nitrogen (N) did not

improve vegetables germination rate, suggesting minimal

involvement of C:N ratio. Low seed germination and growth

inhibition were attributed to phytotoxity (Kelling et al.,

1994).

Mature compost reduced weed growth in row-alleys of

vegetable crops compared to an untreated control (no compost

application), however, herbicide plots provided better weed

control than compost plots (Roe et al., 1993a). Organic

mulches may improve the soil as the organic material

decomposes, reducing erosion, minimizing compaction,

increasing soil water-holding capacity, slowing the release

of nutrients, increasing soil microbial activity, and

controlling soil temperature (Foshee et al., 1996; Marshall

and Ellis, 1992; FAO, 1987).

The objectives of this investigation were as follows:

(a) determine the compost:water ratio for development of a

bioassay procedure that can be used to evaluate compost

suitability for potential biological weed control; (b)

identify the composting maturity stages) that result in

maximum inhibition of weed seed germination and early

seedling growth suppression of economically important weed

species; (c) determine the effect of compost thickness and








4

maturity stage on weed emergence suppression and/or seedling

growth under greenhouse conditions; (d) evaluate various

immature MSW compost thicknesses for biological weed control

in vegetable row-alleys, and subsequent yields of bell

pepper and zucchini squash; and (e) evaluate the residual

effect of soil-incorporated MSW compost applied in the

previous year for row-alley weed control (with and without

inorganic fertilizer) on snap bean production.













CHAPTER 2
LITERATURE REVIEW

Municipal Solid Waste

Composting is a biological decomposition process in

which microorganisms convert organic materials into a

relatively stable humus-like material. During

decomposition, microorganisms assimilate complex organic

substances and release inorganic nutrients (Metting, 1992).

An adequate composting process should kill pathogens and

stabilize organic carbon (C) before the material is land-

applied (Chaney, 1991).

In 1997, 24.3 million metric tons of solid wastes were

produced in Florida (almost 4.3 kg per person per

day)(Goldstein, 1997), which was twice the national average

(Smith, 1995). Therefore, solid waste disposal in Florida

is a serious concern, since population is increasing,

shallow groundwater tables require that landfills be lined

to comply with regulation, and increasing tipping fees that

averaged $46.15 Mg-1 in 1993 (Smith, 1995). In Florida,

materials such as municipal solid waste (MSW), yard

trimmings (YT), and biosolid (B) are high-volume wastes that

could be composted instead of landfilled or incinerated

(Smith, 1994c). The largest portion of solid waste is MSW.

5








6

Nationally, composting may be an attractive waste management

tool, since 30-60% of the waste materials can be composted

in an environmentally safe matter (Smith, 1995). In

Florida, there are 44 operating composting facilities, of

which 29 compost YT (Smith, 1995).

Annually in Florida, 11 million Mg of MSW, 3 million Mg

of YT, and 0.5 million Mg of animal manure could be

composted (Smith, 1994c). In Florida, the majority of

wastes are landfilled or burned, rather than recycled by

composting. A significant (50-65%) reduction in waste

volume would occur during biological decomposition,

therefore if all biodegradable material in Florida was

composted, 8 million tonnes of compost would be produced

annually (Smith, 1995).

The largest potential compost user is the agricultural

industry (Parr and Hornick, 1992). Compost utilization in

agriculture is an effective method of disposal that would

reduce the need to expand landfills or production of new

incinerators. Additionally, compost could provide water

resource conservation, and may reduce the pollution

potential of inorganic fertilizers and pesticides. Amending

Florida's sandy soils with compost may allow the frequency

and rate of irrigation and fertilizer applications to be

reduced (Ozores-Hampton, 1993). New technology and

development of processed solid waste materials have resulted










in products of high quality to be used by the agricultural

community (Bryan and Lance, 1991).

Florida is a major vegetable-producing state, with

149,850 ha under cultivation each year (FASS, 1997). Sandy

soils used for agriculture in Florida have low native

fertility (Brady, 1974). Proper fertilization is necessary

to maximize yield and fruit quality (Hochmuth and Maynard,

1996). To obtain high crop production, fertilizer inputs

are usually high. Minimizing fertilizer leaching or runoff

has become important due to potential negative environmental

impacts.

Soil application of compost provides an alternative to

current methods of waste disposal, and simultaneously may

decrease water and fertilizer usage to crop production

systems (Ozores-Hampton et al., 1994). A farmer's input

costs could potentially be reduced through water and

fertilizer conservation, which would also decrease negative

environmental effects (Ozores-Hampton, 1993). Municipal

solid waste compost can also provide a significant role in

the development and maintenance of soil organic matter

content (Parr and Hornick, 1992).

From a urban viewpoint, compost production represents a

safe disposal method for thousands of tons of waste

materials produced every year, but the current official

recommendations for compost use in Florida agriculture are

very general. Development of alternative production systems










for vegetable crop that are environmentally 'friendly' yet

maintaining optimum yields are need. Composts made from

waste materials may provide a significant role in these

alternative systems.



Physical Effects of Organic Mulches

Suppression of weed growth is one of the most important

effects of organic mulches (Grantzau, 1987; FAO, 1987).

Organic mulches can reduce soil erosion by heavy rain,

minimize soil compaction, increase water holding capacity of

the soil, slow the release of nutrients, increase microbial

activity in the soil, and control soil temperature (Foshee

et al., 1996; Marshall and Ellis, 1992 and FAO, 1987).

Weed growth can often be controlled by organic mulches

at a level comparable to that achieved with herbicides

(Singh et al., 1985). To completely discourage weeds, a

layer of 10-15 cm is required for optimum weed control when

mulch is composed of composted materials (Marshall and

Ellis, 1992). Unmulched cut flower beds had more weed than

those mulched with 3, 5, or 7 cm of bark (Grantzau, 1987).

Applications of wheat (Triticum aestivum L.) straw between

3.4 and 5.1 tha-I or metolachlor increased corn (Zea mays

L.) yields by 15% over unmulched corn (Wicks et al., 1994).

In an Oxic Haplustult soil, different burn treatments

were compared to no-burn mulch practices in sugarcane










(Saccharum spp.). Cane yield of the first ratoon crop was

17 tha'1 higher in the mulched treatment than burn

treatments with the higher yields attributed to increased

soil water retention and reduced weed growth (Ball-Coelho et

al., 1993). Living mulch, close-mowed, chemically

growth-regulated sodgrasses, pre- and postemergence

herbicides, and hay-straw mulch treatments were compared

during a 6-year period in an establishing an apple (Malus

domestic Borkh.) orchard (Merwin and Stiles, 1994). Trunk

cross-sectional area and fruit yield were higher for

hay-straw and pre- and postemergence herbicide treatments as

compared with living mulch, close-mowed and chemically

growth-regulated sodgrasses. Soil K, P, and B, and leaf K

concentrations were higher under the hay-straw mulch, but

serious phytophthora spp. root rot and meadow vole

depredation occurred in hay-straw and living mulch plots

(Merwin and Stiles, 1994).

Sawdust, straw, and bark mulches improved weed control

in kiwi fruit (Actinidia deliciosa) with thicker layer

providing greater weed control, but all mulches were more

effective than the herbicide simazine (Ingle and Bussell,

1988). The use of organic mulch in herb production

(distilled Citronella Java herb at 5 tha-1) controlled weeds

as effective and at lower cost than simazine, diuron, and

oxyfluorfen (Singh et al., 1985). Similar weed control

results were observed by Kolb (1983) in Geranium










macrorrhizum where several mulches (bark, sawdust, and

straw) performed as effective as basamid soil disinfestation

before planting. Cultivation costs were decreased by 40 and

20% when bark mulch and straw, respectively, were compared

with unmulched controls in ornamental shrubs (Kolb et al.,

1985). Municipal solid waste compost at 224 t'ha-1 reduced

weed growth in row-alleys of bell pepper (Capsicum annuum

L.) as compared with an untreated control (no compost

application); however, herbicide plots provided better weed

control than compost plots (Roe et al., 1993a).

Four weed management practices (sawdust mulching,

repeated spring-summer cultivation, hand-hoeing and two

herbicides) were compared in two cropping systems [corn and

asparagus (Asparagus officinalis L.)] (Wardle et al., 1993).

The fumigation-incubation techniques suggested that mulching

had stimulatory effects on soil microbial activity and

biomass (Wardle et al., 1993). Mulches effects on soil

microbial populations may be a result of increased water,

organic matter, or nutrients in the soil. Higher

populations of microbes were found in mulched areas, but

nitrifying and denitrifying organisms were found only in

more concentrated mulch areas between corn rows (Doran,

1980).

Straw mulch can be a temporary storage medium for

herbicides and can provide an important role in decreasing

the movement of chemicals to the subsurface of soil under









conservation tillage (Dao, 1991). Mulching tomatoes

(Lycopersicon esculentum Mill.) with rice (Oryza sativa L.)

straw almost always increases yields since it minimizes

erosion, reduces weed growth, decreases compactation, and

prevents contact between soil and fruit (Foshee et al.,

1996).



Influence of Seed Burial

The soil seed bank is the major source of weed

infestation (Hall et al., 1987). Seeds of certain weed

species can remain viable in soil for 20 years or more

(Conn, 1990). Information on the lifespan of weed seeds in

soil is of great interest due to potential weed problems.

Crop yield losses from weed interference will exist for a

long period as weed seeds remain alive in the soil (Lewis,

1973). The most remarkable seed longevity studies in the

United States were initiated by Beal in 1879 and Duvel in

1902 (Darlington, 1951). After a 80-year burial, seeds of

curly dock (Rumex crispus L.) and mullein (Verbascum

blattaria L.) were still viable. After burial for 39 years,

36 of the original 107 species in Duvel's study still had

viable seeds (Froud-Williams, 1987). In recent a study, 11

weed species in Alaska had more than 6% seed viability 4.7

year after burial (Conn, 1990). In warm and humid areas, 6%

of the original population of 20 weed species remained

viable after 5.5 years of burial (Egley and Chandler, 1983).










Weed seeds that remain viable in the soil for long

periods of time have the potential to form long-lived seed

banks (Baskin and Baskin, 1985). These buried seeds can

germinate at any time during the growing season if the

conditions are favorable for germination. To illustrate

this effect, seeds of Lobelia inflata L. can germinate if

exposed to light, a condition that appears when forests are

disturbed (Baskin and Baskin, 1992). Long time seed-

survival in the soil is influenced by seed dormancy and

resistant to seed deterioration (Fellows and Roeth, 1992).

Acidic conditions, water-logging, and low 02 in the soil

favor the maintenance of dormancy and increases seed

survival. In contrast, cultivation decreases seed

longevity, apparently by increasing soil aeration, exposing

seeds to light, and generally improving the conditions for

germination. High soil temperatures can increase

germination and reduce weed seed survival.


Influence of Burial Depth

Seeds become buried by the action of wind, water and

frost heave (Baskin and Baskin, 1987). The burial effect on

seed viability is probably due to insulation; buried seeds

are protected from environmental fluctuation that normally

occurs at the soil surface (Campbell and Staden, 1994).

Small size seed may facilitate burial because the ease of

movement into cracks in the soil (Lewis, 1973). Depth of










seed burial markedly affects percentage germination and

emergence (Blackshaw, 1992; Baskin and Baskin, 1987; 1989).

In general, non-dormant weed seed germination declines

as burial depth increases. In Erodium cicutarium L. and

Agropyron psammophilum Gillet & Senn., percentage

germination of buried seed, percentage emergence, and

emergence of seedlings were negatively correlated with

burial depth (Blackshaw, 1992; Zhang and Maun, 1990). Weed

species and the depth at which germination was decreased is

shown in Table 2.1. Reisman-Berman et al. (1991) concluded

that seed burial inhibited germination and emergence of

Datura ferox L. and D. stramonium L. and simultaneously

decreased secondary dormancy.

Campbell and Staden (1994) reported a similar

antagonistic effect of burial depth on seeds of Solanum

mauritianum Scop, however, factors others than absence of

light, constant temperature, and high level of CO2 inhibited

germination when seed were buried at 15 cm. Seeds buried at

4 cm the occurrence of secondary dormancy was higher due to

more adverse conditions at the soil surface than at 15 cm

depth. Seeds at 4 cm depth were more resistant to control

by application of herbicides by having a delayed emergence

under favorable conditions. The decline in viability with

shallow rather that deep burial can be attributed to greater

environmental extremes (Miller and Nalewaja, 1990).








14

Inhibition of germination at greater depth is probably

due to the lack of promoting factors such as light,

temperature fluctuation, and moisture content (Baskin and

Baskin, 1989). At greater depths, decrease germination can

be attributed to acetaldehyde, ethanol, acetone, ethylene,

allelophatic compounds, and higher levels of CO2 resulting

from biological activity (Reisman-Berman et al., 1991).

For most weed species, germination decreases

drastically as burial depth increases. However, there are

exception such as Bromus rigidus Roth. where no effect of

burial depth on germination was observed (Gleichsner and

Appleby, 1989). They attributed low seed germination at

the soil surface to lack of contact with moist soil for

sufficient periods of time to allow for germination

(Gleichsner and Appleby, 1989).


Burial Can Induce Seed Dormancy

Weed seeds under buried conditions can remain dormant

for long periods of time (Davis et al., 1993; Baskin and

Baskin, 1992). Dormancy is a delaying mechanism that

prevents germination under conditions unsuitable for

completion of the plant life cycle (Baskin and Baskin,

1987). Seeds that remain viable in the soil, may

germinated when conditions became favorable (Baskin and

Baskin, 1992).

Depth of burial can affect seeds by inducing an

enforced and/or secondary dormancy (Baskin and Baskin,










1985). Enforced dormancy occurs when the seed is deprived

of its requirements for germination, for example, by the

absence of sufficient moisture, 02, light, or a suitable

temperature. If no special physiological mechanisms are

involved then seeds can be considered quiescent. Seeds

deep in the soil are probably prevented from germination by

lack of 02 (Baskin and Baskin, 1987). Depth of burial can

affect the frequency of secondary dormancy (Campbell and

Staden, 1994). Buried imbibed seeds can enter secondary

dormancy under unfavorable conditions such as darkness, high

or low temperature, absence of sufficient moisture, 02, and

high CO2 levels (Baskin and Baskin, 1987).

Although temperature is the major environmental factor

causing seed dormancy, a strong interaction between

temperature and darkness exists in seed under buried

conditions (Baskin and Baskin, 1985). Campbell and Staden

(1994) reported that several species of weed seeds lying on

the soil surface had a very strong tendency to enter

secondary dormancy due to drastic environmental fluctuation.

They concluded that increases in burial depth can result in

a reduction in secondary dormancy. Although germination is

drastically reduced under buried conditions, seeds can

germinate if environmental conditions are favorable

(quiescent seeds).

Problems may result under field conditions because

dormancy characteristics can be changed as a result of










burial (Davis et al., 1993). The accurate light

requirements in a long term burial can be followed by a

period where light is inhibitory (Hall et al., 1987). The

light requirement may permit buried seeds to remain dormant

for extended periods of time (Nolan and Upadhyaya, 1988).

Spotted knapweed (Centaurea maculosa Lam.) is a light-

requiring species where 25% of the seeds remained viable but

dormant in the soil after 8 year (Davis et al., 1993). The

ecological implication is that buried seed cannot germinate

until the site is disturbed and seeds are brought to the

soil surface for light exposure (Baskin and Baskin, 1992).

Changes in seed dormancy can also be related to water

content of the soil. Spergula arvensis L. released ethanol

and acetaldehyde, products of anaerobic metabolism after

four weeks of burial, thereby inhibited germination (Hall et

al., 1987). Although germination will occur under favorable

conditions, there are a number of species that have an

annual cycle of dormant and non-dormant periods (Baskin and

Baskin, 1985; 1987). The existence of these cycles

indicates that the dormant bank of seeds in the soil is in a

state of continual physiological change that ensures their

dormancy status is always appropriate for the prevailing

seasonal conditions. These physiological transitions can be

related to changes in membrane properties (Baskin and

Baskin, 1985). A 2-year study of three populations of

Penstemon palmer indicated that dormancy induction during










winter and dormancy release during summer functioned to

confine germination to periods during autumn or early spring

and permitted persistence of the seed bank (Meyer and

Kitchen, 1992).


Seed Properties Affecting Survival Under Burial
Conditions


Long-term seed survival in the soil is influenced by

seed dormancy and resistance to seed deterioration (Fellows

and Roeth, 1992). Lewis (1973) concluded that the most

persistent weed seeds are those with hard seed coats.

Studies with Rumex, Chenopodium and Matricaria spp.

indicated that the protection by the highly cuticularized

and suberized layers covering the seed is sufficiently able

to reduce deterioration thereby reducing germination.

Fellows and Roeth (1992) reported that shattercane (Sorghum

bicolor L. Moench) with tight glumes survived longer buried

than sorghum with no glumes. The glumes may contain a

germination inhibitor that can assist in retaining dormancy

and provide resistance to decomposition of the seed. Glume

tannin and lignin contents were higher than cultivated

sorghum. Yellow starthistle (Centaures solstitialis L.)

produce dimorphic achenes. Achenes of the plumed type have

visible pappi and those of the plumeless have no pappi.

Seed viability decreased faster for plumeless achenes than

plumed achenes after 6 and 10 years (Callihan et al., 1993).

Plant phenolics can have a significant role as










protectants against fungi and other pathogens. Tannin

content in sorghum seed cultivars correlated negatively with

seed-molding indices. For mold-resistant sorghum seed, the

levels of flavan-4-ols were higher than for mold-susceptible

cultivars (Jambunathan et al., 1986).

Although the soil seed reserve (seed bank) decreases

significantly over time, large quantities of viable seeds

per ha remain, indicating that seed of certain weed species

can last for many years in the soil. Certain weed species

such as spotted knapweed can produce an average of 1000

seeds per individual plant in which only 5% remained viable

after a 7 year period resulted in 400,000 viable seeds per

plant sufficient to cause new infestations and persistence

in the field (Davis et al., 1993).

Long-term seed survival under burial can be influenced

by seed dormancy and resistance to seed decomposition. In

most weed species when burial depth increases, germination

of non-dormant seed decreases. Burial conditions are not

optimal for germination. Depth of burial affects the

frequency of secondary dormancy. Buried imbibed seeds can

enter secondary dormancy under unfavorable conditions such

as darkness, high or low temperature, absence of sufficient

moisture, 02, light, or high CO2 level. More tolerant seed

coat, glumes, and plumed achenes can increase the resistance

to deterioration under burial conditions. Chemical

compounds produced by seeds, such as tannin, can play a










significant role in protecting the seed against

microorganism activity in the soil.

Results of seed survival in the soil can be used to

predict the severity of future weed problems and to

determine the feasibility of eradicating a particular weed

by eliminating seed production.

Conventional weed control practices (herbicides) do not

eliminate buried seed. The lack of germination of dormant

and nondormant seed makes weeds extremely difficult to

control or eradicate. Information on weed seed dormancy,

burial depth, and resistant seed coat can contribute to the

development of integrated pest management systems or aid in

the development of chemicals that stimulate germination of

buried seeds.

Integrated pest management programs that incorporate

chemical, biological control, and plant competition should

be adopted where possible, since some weed species with

persistent seed banks can escape from chemical control.


Phytotoxic Effects of Organic Mulches


Crop injuries produced by crop residues have been

reported (Patrick and Kock, 1958; Lynch, 1976; Lynch, 1977;

Lynch, 1978; Toussoun et al., 1968). Stunted and chlorotic

plants were observed when crops were planted immediately

after crop residue incorporation or by planting the next

crop directly into crop residues (Patrick and Kock, 1958).










Substances capable of inhibiting germination, growth

and respiration of tobacco (Nicotiana tabacum) seedlings

were obtained after residues from timothy (Phleum pratense

L.), corn, rye (Secale cereale L.), or tobacco had been

allowed to decompose under anaerobic conditions. Production

of the toxic products can be influenced by the plant

species, degree of residue maturity, water content, soil pH,

and time of decomposition.

The most favorable conditions for the production of

toxins are poorly-drained and acid soil, but the production

of such compounds is not limited to such soil. The

phytotoxic substances obtained by water extraction inhibited

respiration of tobacco seedlings and also induced darkening

and necrosis of root cells (Patrick and Koch, 1958). Wheat

straw decomposition under anaerobic condition formed

phytotoxic products that inhibited the extension of

coleoptiles and roots of barley seeds.

Chemical analysis of the extracts resulted in the

presence of fatty acids [acetic (most phytotoxic),

propionic, and butyric] under anaerobic condition, but not

in aerobic environments (Lynch, 1976 and 1977). Ferulic

acid extracted from wheat, reduced germination and growth of

two weed species (Liebel and Worsham, 1983). Dead green rye

reduced growth of broadleaf weeds by 41 to 99% than the

control perhaps due to the presence of organic acids

(Worsham, 1984).










Water extract from 3 week-old YT compost decreased

germination of several perennial and annual weeds in petri

dishes upon exposure to temperatures over 60C (thermophilic

stage of composting) (Shiralipour and McConnell, 1991).

Materials identified that produced such injuries to crops

are chicken manure, green manure, and plowed crop residues

(Zucconi et al., 1981a). Raw and treated pig slurries were

highly inhibitory to the germination and root growth of

barley and wheat perhaps due to the presence of phenolic

acids (Maureen et al., 1982). Aeration of the pig slurry

was the most effective system in removing the inhibitory

activity.

In recent years land application of composts made from

waste materials has been associated with damage to crops by

phytotoxic compounds in the compost (Chanyasak et al., 1983;

Hadar et al., 1985). Poor compost quality and immaturity

have been associated with crop injuries (Zucconi, 1981a).

Crop damages was directly related to the relative level of

immaturity or instability of the compost (Jimenez and

Garcia, 1989). Compost maturity can be regarded as the

degree to which a compost product is free of phytotoxic

substances that can cause delayed seed germination, plant

damage, or seed and plant death. In contrast, stability is

associated with a compost that utilizes N and 02 in

significant quantities to support biological activity and

generates heat, CO2 and water vapor (FDACS, 1994).










A bioassay cress (Lepidium sativum L.) test as

suggested by Spohn (1969) can be used to evaluate compost

maturity. Germination percentage of cress seeds increased

as compost aged, but only when the composting stage changed

from thermophilic to the final mesophilic stage (Anid,

1986). Plant damage has often been associated with a high

C:N ratio of the organic material before humification,

and/or production of ammonia in the soil (Zucconi et. al.,

1981b). However, Zucconi et al. (1981b) demonstrated a

lower cress seed germination in the presence of toxins

during organic matter decomposition and in free ammonium

extracts. The presence of these toxic compounds are

temporary in nature, and are associated with microbes

dominant during the early stages of the composting. There

is a rapid decrease of toxins after this stage, but the

compounds do not totally disappear after 8 weeks (Zucconi et

al., 1981b).

Toxicity to plants has been reported to be related to

composting methods. Toxins disappeared faster in static

piles than with the window compost production method

(Zucconi et al., 1981b). The presence of toxins can be

related to unstable compost or poor composting processes.

The nature of these compounds can be directly associated

with lower seed germination rates of sensitive plants used

as a bioassay. If germination index is above 60, olive

(Olea europaea L.) trees were not damaged, but a period of










adaptation was required for normal growth (Zucconi et al.,

1981b). Different methods to evaluate compost toxicity with

bioassay test and chemical testing for organic acids are

listed in the literature (Tables 2.2 and 2.3).

Identification of phytotoxin in extracts from fresh and

5-month-old MSW compost indicate that fresh compost

contained acetic, propionic, isobutyric, butyric, and

isovaleric acid in largest concentration (DeVleeschauwer et

al., 1981). When cress seeds were exposed to different

concentrations of acetic acid, a concentration of 300 mg'kg'

resulted in growth inhibition (DeVleeschauwer et al., 1981).

Keeling (1994) reported that the percentage germination of

seven vegetable crops decreased in immature MSW alone, as

compared with combinations of immature MSW and peat, sand,

or limestone. When water extracts from immature MSW compost

were analyzed, the major compound identified was acetic acid

at concentrations between 6,000 and 28,000 mg'kg-1. The

combination of immature MSW compost and N did not improve

percentage germination, suggesting that the shortage of

available N was not the cause of low germination.

Therefore, reduced seed germination and growth inhibition

was attributed to acetic acid phytotocixity (Kelling et al.,

1994).

Low rates of immature MSW compost produced inhibitory

effects attributed to the presence of short-chain fatty

acids, especially propionic acid and n-butyric acid on the










growth of komatsuna (Brassica rapa L. 'pervidis'),

especially in the early stages of development (Chanyasak et

al., 1983). The accumulation of acetic acid in soil is

governed by the 02 content, although well-aerated soils

produce anaerobic micro-environments to induce anaerobic

fermentation of cellulose. Acetic acid can be catabolized

in normal aerobic respiration to CO2 while under anaerobic

conditions CH4 can be produced (Lynch, 1977). Application

of immature compost to arable soil may inhibit seed

germination or reduce root length of seedlings, by the

presence of phytotoxic substances in the compost (Jimenez

and Garcia, 1989).


Precautions necessary when Using Composted Organic
Mulches


Application of organic mulches for weed control can

have negative effects on crop plants. Merwin et al. (1995)

compared natural mulches (hay, wood chips, and recycled

paper pulp) and herbicides in an apple orchard for 4 years.

Crop market value was higher with hay mulch than with

herbicides, but serious trunk damage by meadow and pine vole

(Microtus spp.) was observed in mulch treatments. Over a 6-

year period, apple trunk diameter and fruit yield were

higher in both hay-straw and herbicide treatments than a

non-herbicided control, but serious Phytophthora spp. root









rot and meadow vole depredation were found in hay-straw

mulch plots (Merwin and Stiles, 1994).

Organic mulch application produced less-perfect weed

control than herbicides. Merwin et al. (1995) reported that

in an apple orchard, managing weeds at the edges of the

mulched strips and weeds around the bases of the tree was

problematic. For commercial fruit production, an additional

spot treatment will be required with herbicides for

acceptable weed control. Niggli (1990) reported that in an

orchard, utilization of fresh oak bark resulted in improved

annual weed control under the trees as compared with mature

bark. Mulches are more expensive to establish and maintain

than herbicide application. Due to organic breakdown,

material must periodically be added to maintain a desired

thickness.

It is important to determine if the provided benefits

of the mulches compensate for the additional application

expense. Higher establishment and maintenance costs of the

organic mulches were offset by their prolonged efficacy over

successive years in the Merwin et al. (1995) experiment.

Economic studies indicate that organic mulches can only be

used for some fruit varieties, when the increased crop value

justifies the greater costs (Merwin et al., 1995).










Crop Yield Responses to Compost Application

Compost application has produced positive results for a

wide variety of crops. Contradictory crop response results

were found when compost was compared with a traditional

fertilizer program (Smith, 1994a). Compost application to

soil can improve physical and chemical properties such as

water-holding capacity, cation exchange capacity, bulk

density, and percentage organic matter, and can increase the

microbial population (Gallardo-Lara and Nogales, 1987;

Fitzpatrick and Verkade, 1991). However, compost can be

associated with negative effects on seed germination and

crop yield when applied to soil in an immature state.

Combining compost and inorganic fertilizer has generally

been more effective in producing a positive plant response

than separate application of either material alone. As

fertilization regulations become stricter, organic materials

will play a more important role in fertilizer efficiency by

increasing nutrient holding capacity of the soil and

decreasing nutrient leaching.

Amending soil with composted materials such as

biosolids, MSW, and YT has been investigated extensively,

and has been reported to increase crop yields of bean

(Phaseolus vulgaris L.), blackeyed pea (Pisum sativum L.),

okra (Abelmoschus esculentus L.) (Bryan and Lance, 1991)

tomato, squash (Cucurbita maxima Duch. Ex Lam.), eggplant

(Solanum melongena L.) and bean (Ozores-Hampton and Bryan,










1993a; Ozores-Hampton and Bryan, 1993b; Ozores-Hampton and

Bryan, 1994; Ozores-Hampton et al., 1994), watermelon

(Citrullus vulgaris Schrad.) and tomato (Obreza and Reeder,

1994; Obreza and Vavrina, 1994), corn (Gallaher and

McSorley, 1994a; Gallaher and McSorley, 1994b), and pepper

(Capsicum annuum L.) (Roe et al., 1993b; Stoffella, 1995).

Annual production of compost made from Florida's solid

waste could be easily assimilated by the Florida vegetable

crop industry. If only 45 t'ha'1 were applied to each of the

170,000 ha of vegetables annually grown in Florida, 7.7

million metric ton of compost could be recycled each year

(Smith, 1994c).

Biosolids. Biosolids are sources of all plant

nutrients and organic C. As an alternative disposal method,

biosolids application to agricultural land can be safe,

feasible, and cost-effective as compared with traditional

disposal methods. In Florida, biosolids application to

soils was reported to increase yields of several vegetable

crops including tomatoes, squash, and beans (Bryan and

Lance, 1991). In calcareous soil, application rates as low

as 3 to 13.5 t'ha-1 resulted in crop yield increases for

tomatoes, squash, and beans (Bryan and Lance, 1991; Ozores-

Hampton et al., 1994).

MSW and YT compost. The effects of MSW and YT compost

on crop growth are only beginning to be investigated due to

recent availability of these materials in large quantities








28

(Smith, 1990; Smith, 1995). Soil incorporation of MSW

compost was reported to increase yields of several vegetable

crops including corn, tomato, squash, bean, okra

(Abelmoschus esculentus L.), cabbage (Brassica oleracea L.),

cucumber (Cucumis sativus L.), blackeye pea, pepper,

eggplant, and watermelon (Smith, 1995). In Florida, MSW

compost application rates of 90 tha'1 resulted in crop yield

increases for bean (Ozores-Hampton and Bryan, 1993b) and

watermelon (Obreza and Reeder, 1994).









Table 2.1. Effect of burial depth on weed seed germination.


Weed species Soil depth with no germination Reference
(cm)


Datura ferox t 10 (Reisman-Berman and Kigel,
1991).
Datura stramonium t 10 (Reisman-Berman and Kigel,
1991).
Agropyron psammophilum 2 8 (Zhang and Maun, 1990)

Erodium cicutarium ? 9 (Blackshaw, 1992)

Cyperus esculentus 2 50 (Lapham and Drennan, 1990)

Setaria faberi t 6 (Mester and Buhler, 1991)

Solanum mauritianum 2 15 (Campbell and Staden, 1994)

Malva pusilla i 8 (Blackshaw, 1990)

False chamomile 2 5 (Mekki and Leroux, 1991)












Table 2.2. Extraction methods for seed compost maturity test.


Species Conditions Compostmwater ratio Data collected Reference




Cress seeds 27C-dark-24 h water content to 60 t germ-GI-root elongation Zucconi et al., 1981a and 1981b
water extracted by
pressure (250 atm)
Lettuce 23C-Dark-5 days 1:10 W/v % germination-root lengh Tamn and Tiquia, 1994
Chinese cabbage 10 ml/dish
Tomato 15-20 seeds
Green beans Blender for 20 min

Barley 10 seeds at 23C for not described % germination-root lengh Maureen et al., 1982
Wheat 48 h-dark

Brassica chinensis 16-8 h it/dark 8 % W/V air dry material % germination-root lengh Wong and Chu, 1985
6 days-25 seed Shaking for 2 h
7 ml extract
Australian pine 27C-16/8 It/dark 20 DW/100 ml water % germination Shiralipour and McConnell, 1991
Brazilian pepper For 2 weeks
Punk tree 20 ml-50 seeds
Ear tree

B. parachinensis 16-8 lt/dark 3,6,9,12,15, and 18 %W/V S germination-root lengh Wong, 1985
for 6 day-25C
7 ml











Table 2.3. Compost extraction methods for organic acids.


Compostswater ratio Type of analysis Organic acids Reference




200 g dry wt/600 ml Gas chromatography Acetic, butyric and propionic Lynch, 1977

20 g FW/100 dist Gas chromatography-MS Acetic and butyric Keeling et al., 1994
Shaken for 1 h
10 g dry wt/50 ml Gas chromatography Acetic DeVleeachauwer et al., 1981














CHAPTER 3
INFLUENCE OF COMPOST:WATER RATIO ON IVYLEAF MORNINGGLORY
GERMINATION


Introduction

Immature compost decreased and delayed germination and

growth of seedlings by accumulating phytotoxic compounds in

the liquid phase (Inbar et al., 1990). Compost with high

C:N ratio can potentially accumulate organic acids such as

acetic, propionic, and butyric acids. Low C:N ratio

composts may accumulate high concentration of ammonia

(Jimenez and Garcia, 1989; Chanyasak et al., 1983; Hadar et

al., 1985). A compost can be considered mature if

phytotoxic substances that can cause delayed and/or reduced

seed germination, plant injury, or death are absent.

Zucconi et al. (1981b) reported lower cress seed

germination in the presence of phytotoxin produced during

composting MSW in compost extracts free of NH4. The most

phytotoxic organic acid was acetic, which can inhibit cress

seed growth at a concentration over 300 mg'kg-'

(DeVleeschauwer et al., 1981). Shiralipour et al. (1997)

demonstrated that inhibitory effects of acetic acids on seed

germination of Cucumis sativus 'Poinset' was a metabolic

phenomenon, and not the effects of high ionic strength or pH










imbalance. To isolate the compost phytotoxic effect,

compost water extract can be prepared and a bioassay can be

utilized to measure plant response to phytotoxic compounds

(Keeling et al., 1994; Tam and Tiquia, 1994; Wong, 1985).

Phytotoxins present in immature compost are water soluble

(Inbar et al., 1990). However, the dilution factor

(compost:water ratio) can influence plant response to the

bioassay (Wong, 1985).

The objectives of this investigation were to determine

the optimum compost:water ratio for development of a

bioassay procedure for subsequent evaluation of composts as

biological weed control.



Materials and Methods

The compost utilized for the experiments was provided

by Bedminster Bioconversion of Tennessee, Inc. Sevierville,

Tennessee. Municipal solid waste and biosolids are

processed though a three-compartment Eweson digester in an

aerobic environment for 3 days and then cured for 8-weeks

with a window composting method. Volatile fatty acids

concentration of 3-day-old and mature co-compost are

presented in Table 3.1.

A bioassay was developed based on rapid germination

rate and uniformity, with ivyleaf morningglory (Ipomoea

hederacea L.) as indicator species. Weed seeds were

obtained from Valley Seed Service, Fresno, Ca. Treatments








34
included immature compost (1, 2, and 3-day-old), and mature

compost (1-year-old). Distilled water was used as the

control.

Compost extracts were prepared with 20 g (dry weight)

compost mixed with 50, 100, or 200 mL of distilled water

(1:2.5, 1:5, and 1:10 ratio, respectively) and allowed to

incubate for 30 min, but agitated manually every 10 min.

Mixture were filtered through Whatman's No.l paper placed in

a funnel and the water extract collected. When necessary,

filtrate volume was increased by manual pressing.

Petri dishes (9 cm diameter) were lined with Whatman's

No.1 filter paper, compost extract (3 mL) added, ivyleaf

morningglory seeds (25) were placed in each dish, then

sealed with parafilm. Each petri dish was considered a

replication, with a total of 6 replications per treatment.

The dishes were placed in a dark incubator at 27C for 84 h

(Zucconi et al., 1981a; 1981b) in a randomized complete

block experimental design. The total number of germinated

seed was counted every 12 h. Seeds were considered to have

germinated when the length of the visible radical equaled

the length of the longest dimension of the seed (Peterson

and Harrison, 1991). Mean hours to germination (MHG)

(Gerson and Honma, 1978) was determined according to the

following formula:

MHG = (NIT1 + N2T2 +.......+ NxTx)/total number of seeds

germinated










N = Number of seeds germinating within consecutive time

interval

T= Time (in hours) from beginning of the test to end of a

particular interval.

Data were subjected an analysis of variance and

treatment means were separated with Duncan's Multiple Range

Test, 5% level.


Results and Discussion

The compost:water ratio x compost age interaction was

significant for percentage germination. Therefore, compost

age effects were analyzed within each of the compost:water

ratios (Fig 3.1). Lower final percentage germination

resulted with 3-day-old compost than the other composts when

50 mL of water was utilized for dilution (Table 3.2).

Extracts from 2-day-old compost resulted in lower final

percentage germination than 1-day-old, mature, and the

control when 100 mL was utilized for dilution. Final

germination percentages were similar among compost ages when

200 mL of water was utilized for dilution. Seed germination

sensitivity to phytotoxins in compost extract was higher in

the more concentrated extracts.

Higher MHG was obtained with 3-day-old compost compared

to 1-day-old, 2-day-old, mature compost, and the control

with 50, 100, or 200 mL of water (Table 3.2). Compost

extract prepared with 50 mL of water had the most MHG








36
differences among composts over a longer period of time (Fig

3.1). The use of 50 mL of water provided a concentrated

extract that could be used to detect differential

germination responses among composts with 1-day difference

in age.

The addition of 100 or 200 mL of water decreased seed

germination of ivyleaf morningglory as compared with the

control. Similar results were observed by Wong (1985) who

evaluated several compost:water ratios. Generally, as the

compost concentration increased, percentage germination and

root length of Brassica parachinensis decreased (Wong,

1985).

Dilution factor can play a significant role when

compost maturity is evaluated by a bioassay. The most

differential effect of compost extract on ivyleaf

morningglory seed germination was obtained when 20 g (dry

weight) compost was mixed with 50 mL of water. Bioassay is

a biological method to measure indirectly the presence of

phytotoxic compounds in compost. This bioassay can be

utilized to evaluate the effect of immature compost on weed

seed germination and seedling growth.

Summary

Dilution factor (compost:water ratio) can influence

seed germination for assessing compost maturity. The

influence of compost:water ratio and compost age on ivyleaf

morningglory seed germination was evaluated. A bioassay was








37

developed by extracting 20 g of compost of different

maturities with 50, 100, or 200 mL of water, then measuring

percent germination over 96 h. A 20 g (dry weight) compost:

50 mL of water extract resulted in the widest percentage

seed germination and MHG variation in response to varying

compost maturity.










Table 3.1. Volatile fatty acids concentration of
composts.



Compost age

Fatty acid 3-day Mature

-------- -------(mg-kg1)----------
Acetic 2474 13
Propionic 311 <10
Isobutyric 24 <10
Butyric 171 <10
Isovaleric 62 <20
Valeric <40 <40










Table 3.2. Compost:water extract ratios and compost age
influence on final percent germination and mean hours to
germination (MHG).


Final germination MHG
Compost:water Compost age (%)

20:50 1-dav-old 94.3Az 9 7_h


2-day-old
3-day-old
mature
control

1-day-old
2-day-old
3-day-old
mature
control

1-day-old
2-day-old
3-day-old
mature
control


97.2a
44. Ob
99.8a
99.8a

99.8a
90.Ob
95.3ab
99.8a
99.8a

99.8
99.8
96.5
99.8
99.8


60.0 Oab
64.8a
38.4c
21.6d

48.Ob
48.Ob
60.Oa
21.6c
14.4d

26.4bc
31.2ab
33.6a
21.6c
21.6c


"Mean separation by Duncan's Multiple
within compost:water extracts.


Range Test (PS0.05)


20:100


20:200







































N

(%)


0 12 24 36 48 60 72 84 96
Time (h)



Fig. 3.1. Compost:water extract ratios of 20 g:50 ml
(A), 20 g:100 ml (B), and 20 g:200 ml (C) and compost age
effects on ivyleaf morningglory germination.














CHAPTER 4
MUNICIPAL SOLID WASTE COMPOST MATURITY INFLUENCE ON WEED
SEED GERMINATION


Introduction

More than 500 million tons of municipal and farm waste

materials are generated in the United States each year

(FDACS, 1994). The Environmental Protection Agency (EPA)

has estimated that approximately 65% of the waste is

biodegradable organic material (Smith and Cisar, 1993). In

recent years, compost produced from diverse wastes has

become available on a commercial scale (Bryan and Lance,

1991; Ozores-Hampton, 1993b; Rosen et al., 1993). The

largest potential user of compost is agriculture (Parr and

Hornick, 1992).

Compost utilization has been reported to increase crop

yield (Bryan and Lance, 1991; Gallardo-Lora and Nogales,

1987; Ozores-Hampton et al., 1994: Roe et al., 1993; Rosen

et al., 1993). However, crop injury associated with soil

incorporation of plant residues has been reported (Lynch,

1976, 1977, and 1978; Patrick and Koch, 1958; Toussoun et

al., 1988). Similarly, crop damage from phytotoxic

compounds has been associated with composts made from waste

materials (Chanyasak et al., 1983; Hadar et al., 1985;








42
Jimenez and Garcia, 1989). Utilization of immature or poor

quality compost has resulted in crop injury (Zucconi et al.,

1981a). Crop damage is directly related to the relative

level of maturity or instability of the compost.

Compost maturity can be regarded as the degree to which

the material is free of phytotoxic substances that can cause

delayed or reduced seed germination, plant injury, or death

(FDACS, 1994). In contrast, stability is associated with

compost that utilizes N and 02 in significant quantities to

support biological activity and generate heat, CO2 and water

vapor (Jimenez and Garcia, 1989). Plant damage has often

been associated with a high C:N ratio (>30) of the organic

material before humification, production of ammonia in the

soil, and low 02 levels in the soil that can result in poor

root growth (Inbar et al., 1990; Jimenez and Garcia, 1989).

Zucconi et al. (1981b) demonstrated reduced cress seed

germination in the presence of toxins produced during

organic matter decomposition. The presence of these toxic

compounds is transitory in nature, and is associated with

microbes dominant during the early stages of composting.

There is a rapid decrease of phytotoxins after the early

stage, but the compounds have varying levels of volatility,

and did not totally disappear after 8 weeks of composting

(Zucconi et al., 1981b).

Plant toxicity associated with immature compost may be

related to composting methods. Phytotoxins disappear faster









in static piles than with the window compost production

method (Zucconi et al., 1981b). A seed germination index of

sensitive plants was used in a bioassay to indicates the

presence of toxins (Zucconi et al., 1981b). If cress

germination index was above 60, olive trees were not

damaged, but a period of adaptation was required for normal

growth (Zucconi et al., 1981b).

Identification of phytotoxin in compost extracts from

immature and 5-month-old compost indicated that immature

compost had higher concentrations of acetic, propionic,

isobutyric, butyric, and isovaleric acids (DeVleeschauwer et

al., 1981). Acetic acid concentration of 300 mg'kg' or

higher resulted in growth inhibition of cress seeds

(DeVleeschauwer et al., 1981). Similar responses were

reported by Keeling et al. (1994) when germination rates of

seven vegetable crops were decreased in immature MSW compost

alone, as compared with combinations of immature MSW

compost, with peat or N (from KNO3). Acetic acid (6,000 to

28,000 mg'kg-') was the major compound identified in water

extracts from immature MSW compost (Keeling et al., 1994).

Immature MSW compost with N did not improve germination rate

of vegetable crops, suggesting no involvement of C:N ratio,

but low seed germination and growth inhibition were

attributed to presence of phytotoxic compounds (Keeling et

al., 1994).

Weed suppression by organic materials may be due to









phytotoxic compounds and/or the physical presence of the

materials on the surface of the soil. To isolate the

chemical effect, compost water extract can be prepared and a

bioassay can be utilized to measure plant response to

phytotoxic compound (Keeling et al., 1994; Tam and Tiquia,

1994; Wong, 1985). The phytotoxins in the immature compost

are water soluble (Inbar et al., 1990). However, the

dilution factor (compost:water) can influence plant response

to the bioassay (Wong, 1985).

The objectives of this investigation were to: identify

the composting stages) where maximum inhibition of seed

germination and early seedling growth occurred in weed

indicator species; and establish a compost-water extract

that would produce the most phytotoxic effects on the

germination of economically important weed species.





Materials and Methods

The compost utilized for the experiments was provided

by Bedminster Bioconversion of Tennessee, Inc., Sevierville,

TN. Municipal solid waste (MSW) and biosolids were co-

processed through a three-compartment Eweson digester in an

aerobic environment for 3 days, and then cured for 8 weeks

using the window composting method.

Compost chemical and physical properties were measured

by the Soil and Water Science Department, University of










Florida, Gainesville (Table 4.1). Moisture concentration

was obtained by oven-drying 10 g (wet weight) compost at

105C for 24 h. Total N and C concentrations were measured

on compost samples that were air-dried for 4 days, ground in

a Spex 8000 Mixer/Mill, and combusted at 1010C in a Carlo-

Erba NA-1500 C/N/S analyzer. Total nutrient and trace

metals were analyzed according to EPA Method 3050 (USEPA,

1990). The compost samples were acid-digested and analyzed

by Inductively Coupled Argon Plasma Spectroscopy (ICAP).

Electrical conductivity (EC) and pH were measured using a

2:1 (by volume) water-to-soil suspension.

Volatile fatty acid (acetic, propionic, butyric,

isobutyric, valeric and isovaleric) concentrations in

composts were determined by Woods End Research Laboratory,

Inc., Mt. Vernon, ME (Table 4.2). Compost extracts were

prepared by extracting 20 g (dry weight) compost with 50 mL

distilled water, and were frozen before they were sent to

the laboratory. Upon arrival, the extracts were diluted

1:10 and 1:1000 with distilled water, then run through HPLC

anion column, eluted with 0.15 mM H2SO4.


Compost extract maturity

Seeds of ivyleaf morningglory (IPOHE1), corn ('rugosa';

ZEAMA), barnyardgrass (Echinochloa crus-galli L. ECHCG), and

common purslane (Portulaca oleracea L. POROL) were used as

1 Abbreviations are Weed Science Society of America approved
computer codes.








46
plant indicator species in a bioassay. Ivyleaf morningglory

and corn represented large-seeded plants and barnyardgrass

and common purslane represented small-seeded plants.

Bioassay species were selected due to their high germination

rate, uniformity, and visible radicle. Weed seeds were

obtained from Valley Seed Service, Fresno CA and corn seeds

from Asgrow Seed Company, Kalamazoo, MI. Treatments were

immature 3-day old, 4-week-old, 8-week-old, and mature 1-

year-old composts. The optimum compost-to-water ratio for

extract preparation was 20 g (dry weight) to 50 mL distilled

water. Mixtures were allowed to stand for 30 min, with

manual agitation every 10 min. The extract was then

gravity-filtered through Whatman No. 1 filter paper. When

necessary, filtrate volume was improved by manual pressure.

The EC of the extracts was measured with a conductivity

meter.

Petri dishes (9 cm diameter) were lined with Whatman

No. 1 filter paper, 3 mL of compost extract was added, 25

seeds were placed in each dish, and the dishes were sealed

with parafilm. Distilled water was used as a control

treatment. Each treatment was replicated six times, where

one petri dish was considered a replication. Petri dishes

were arranged in a randomized complete block experimental

design, and were incubated at 27C in the dark for 96 h.

Seeds were considered to have germinated when the radicle

length equaled the length of the longest dimension of the










seed (Peterson and Harrison, 1991). Germinated seeds were

counted and radicle length was measured after 4 days for

IPOHE, 6 days for ECHCG, 4 days for POROL, and 7 days for

ZEAMA. Germination index (GI), (Zucconi et al., 1981a) was

determined according to the formula GI = (% seed germination

x root length growth in % of control)/100. Mean days to

germination (MDG) (Gerson and Honma, 1978) was determined

according to the following formula:

MDG = (NiT1 + N2T2 +.......+ NXT,)/total number of seeds

geminated, where

N = Number of seeds germinating within consecutive time

intervals, and

T= Time (in days) from beginning of the test to end of a

particular interval.

Weed germination

Weed seeds of 14 species were obtained from Valley Seed

Service, Fresno, CA. An extract made from 20 g (dry weight)

8-week-old compost and 50 mL distilled water was prepared as

previously described. Distilled water was used as a

control. Petri dishes were arranged in a randomized

complete block experimental design, with six replications of

each treatment. Incubation was at 27C in the dark for 96

h. Germinated seed was counted for each species at the end

of the experiment.

Data were subjected to analysis of variance, and

treatment means were separated by t-test or Duncan's








48
multiple range test, 5% level. Percentage germination data

among treatments that were greater than 40%, were subjected

to square-root arcsine transformation prior to analysis of

variance.




Results and Discussions

Compost extract maturity

Compost maturity affected final percentage germination,

root length, GI, and MDG for each of the species evaluated

(Table 4.3). Germination was delayed and decreased by

extracts from 3-day-old, 4-week, and 8-week-old composts

compared with the control and mature compost. Percentage

germination was reduced most by 8-week-old compost for ECHCG

and ZEAMA. These results are not consistent with previous

reports by Zucconi et al (1981b), who reported that 3 to 4-

week-old MSW compost reduced cress germination the most.

These results may be attributed to differences in compost

composition, pile management such as turning frequency, and

moisture content, which may have influenced the biochemical

status of the compost products. Compost extract salt

concentration was ruled out as a factor in reducing

germination, since the highest extract EC (8.3 dS-m-1) was

obtained from mature compost.

Root length was also decreased by 3-day old, 4-week,

and 8-week-old composts compared with the control (Table










4.3). Root length was reduced most by the 8-week-old

compost for three of the four species evaluated (IPOHE,

ECHCG, and ZEAMA). These results are similar to those

reported by Wong (1985), who determined for Brassica

parachinensis that root length decreased as compost extract

phytotoxicity increased. Mature composts produced an

increase in IPOHE root length of 60% after incubating for 4

days (Table 4.3) as compared to the control. Radicles were

3 cm long with 8-week-old compost, compared with 8 cm long

with mature compost. The long radicles developed in IPOHE

with mature compost may have been due to the absence of

phytotoxins (Table 4.2) and higher nutrient concentrations

in the mature compost (Table 4.1) as compared with the

control.

Growth index (GI with reference to the control)

decreased in 3-day old, 4-week, and 8-week-old compost

treatments for each of the weed species (Table 4.3). The

greatest numerical GI decrease was obtained with 8-week old

compost for one of the four species evaluated (ZEAMA). The

GI was higher than the control (>100) with mature compost

for IPOHE, POROL, and ZEAMA. The increase in the GI may

have been due to a higher percentage germination and longer

root length as a result of higher nutrient content (Table

4.1) and lack of phytotoxins (Table 4.2) in the mature

compost. This result is not consistent with those of Wong

and Chu (1985), who reported seed germination suppression










and shorter root length of Brassica chinensis in compost

extracts made from 2 to 4-week-old compost, suggesting a

high phytotoxin concentration earlier than 8 weeks.

Toxicity of compost extracts remained high even after 8

weeks of composting, and was possibly a consequence of

infrequent pile turning between 4 and 8 weeks.

DeVleeschauwer et al. (1981) and Wong (1985) reported that

at least 4 months of composting was required for phytotoxins

to diminish in MSW compost. Additionally, Zucconi et al

(1981b) reported that phytotoxin tended to increase for a

period of time before entering a stage of progressive

decrease.

The highest MDG were obtained with 3-day, 4-week, and

8-week-old compost in the four species when compared with

the control. Immature compost not only decreased

germination and root growth, but delayed the rate of

germination than the control or mature compost. The time

frame when compost is considered phytotoxic to plants can

vary among composts. The phytotoxic stage will depend on

compost substrate, composting methods, and pile management

(Jimenez and Garcia, 1989). Compost utilized in this

experiment remained phytotoxic after 8 weeks of composting

(Table 2), since acetic acid concentrations over 300 mg'kg'1

are considered phytotoxic to plants (DeVleeschauwer et al.,

1981). Other organic acids, such as butyric acid (Table 2),

may be increasing phytotoxicity of the 8-week-old compost









above that of 3-day and 4-week-old compost (DeVleeschauwer

et al., 1981). Only 1-year-old compost had acetic acid

concentration lower than 300 mg'kg'1 (Table 4.2), and had no

effect on percentage germination and MDG for each of weed

species evaluated (Table 4.3).


Weed germination

The greatest decreases in germination, root growth, GI,

and MDG were obtained with 8-week-old compost (Table 4.4),

therefore its extract was used to evaluate germination

response of 14 economically important weed species.

Germination of most weed species was inhibited when exposed

to compost extract (Table 4.4). Cress, wild mustard

[Brassica kaber (DC.) L.C. Wheeler. SINAR], lovegrass

[Eragrostis ciliaris (L.) R. Br. ERACI], or dichondra

(Dichondra repens J.R Forst & G. Forst. DICCA) seeds did not

germinate at all. Compost extract decreased the germination

of large crabgrass [Digitaria sanguinalis (L.) Scop. DIGSA],

pigweed (Amaranthus retroflexus L. AMARE), wild radish

(Raphanus raphanistrum L. RAPRA), curly dock (Rumex crispus

L. RUMCR), Florida beggarweed [Desmodium tortuosum (Sw.) DC.

DEDTO], and ground cherry (Physalis ixocarpa L. PHYIX) by

over 80% as compared with the control. Barnyardgrass,

ivyleaf morningglory, and purslane germination decreased

between 15 and 30%. Yellow nutsedge (Cyperus esculentus L.

CYPES) tuber sprouting was not affected by compost extract.

Reduction of seed germination due to presence of








52

organic acids in compost has been reported for cress, onion

(Allium cepa L.), cabbage, cauliflower (Botrytis cauliflora

L.), lettuce (Lactuca sativa L.), and tomato (Keeling et

al., 1994). Although reduction of weed seed germination of

Florida beggarweed, yellow nutsedge, and ragweed (Ambrosia

artemissifolia L.) was associated with the presence of

organic acids by Shiralipour and McConnell (1991), their

compost extracts were made from 3-week-old immature yard

trimming waste that was exposed to temperatures over 60C,

simulating a compost pile.

Ammonia was associated with the phytotoxic response of

plants to pig spent litter (Tam and Tiquia, 1994) and

biosolids (Hirai et al., 1986). However, phytotoxicity

persisted in sterilized, NH4-free extracts of MSW compost

(Zucconi et al., 1981a). In general, for composts with C:N

ratio like those used in this experiment, plant

phytotoxicity is associated with the presence of organic

acids (Zucconi et al., 1981a and 1981b; Wong and Chu, 1985;

and Hadar et al., 1985). Trace metals such as copper have

also been associated with plant phytotoxicity (Tam and

Tiquia, 1994). However, in our experiment Cd, Cu, Pb, Ni,

and Zn concentrations were higher in mature compost than in

immature composts, suggesting that they had no effect on

seed germination, root growth, GI, and MDG for each of the

weed species evaluated (Table 4.1). In addition, these

metals tend to be associated with organic compounds in










compost, and are not extracted well by water (Eichelberger,

1994). Therefore, extracts from immature compost most

likely delayed and decreased weed seed germination due to

phytotoxic compounds (volatile fatty acids, especially

acetic acid) produced during the composting process.

Implications from this investigation suggests that immature

compost may be a viable alternative weed control method.




Summary

The influence of MSW and biosolids compost maturity on

germination of several weed species seeds was evaluated.

Ivyleaf morningglory, barnyardgrass, common purslane, and

corn were selected as plant indicators to determine compost

maturity stage with maximum germination inhibition.

Immature 8-week-old compost extract decreased percentage

germination, root growth, germination index (a combination

of germination percentage and root growth), and increased

mean days to germination (MDG) of each indicator species.

Immature 8-week-old compost extract effect on germination

percentage of 14 economically important weed species was

evaluated. Extract from 8-week-old compost inhibited

germination of most weed species, except yellow nutsedge

for which tubers were used as propagules. Compost extracts

from immature (3-day, 4-week, and 8-week-old) compost with

respective acetic acid concentrations of 2474, 1790, and








54
1776 mg'kg-1 delayed and reduced germination percentage of

important economic weed species, indicating that such

compost can potentially be utilized as an alternative method

of weed control.










Table 4.1. Elemental concentration and chemical analysis of
composts maturity.


Compost age
Characteristic 3-day 4-weeks 8-weeks Mature


------ (% dry weight)--------
C 37.1 39.1 35.7 34.3
N 1.15 1.23 1.20 1.6
P 0.24 0.29 0.27 0.32
K 0.28 0.30 0.31 0.31
Ca 2.04 2.18 2.37 3.1
Mg 0.20 0.23 0.27 0.32
Fe 0.77 0.92 0.98 1.15
------ (mg'kg'1 dry weight)x----
Cd 4.3 3.75 3.50 5.63
Cu 127 184 178 229
Mn 174 219 220 300
Pb 207 212 264 283
Ni 32.4 42.8 44.0 51.5
Zn 446 561 552 720
------ Additional properties------
Moisture (%) 47.0 35.6 37.5 47.6
C:N 32:1 32:1 30:1 24:1
pH 7.2 6.8 6.3 7.7
E.C. (dS-m-1) 6.6 8.8 9.4 6.7
G.Iz 0 0 0 100

* Germination Index (Zucconi et al., 1981a; 1981b).








56
Table 4.2. Volatile fatty acids concentration of composts.



Compost age

Fatty acid 3-day 4-weeks 8-weeks Mature

-------------(mg-kg')-----)-----------

Acetic 2474 1790 1776 13
Propionic 311 102 262 <10
Isobutyric 24 <10 22 <10
Butyric 171 113 265 <10
Isovaleric 62 <20 <20 <20
Valeric 33 <40 <40 <40














Table 4.3. Influence of compost extracts from varying compost maturities on seed germination and radicle length.





Compost age
Variable 3-days 4-weeks 8-Weeks Mature Control


Ivyleaf morningglory (IPOHE)
Final germ.(%) 81 c, 86 bc 77 c 97 a 95ab
Root length (cm) 4.0 b 5.0 b 3.0 c 8.0 a 5.0 b
GI 83 bc 106 b 59 c 175 a --
MDG 3.0 a 3.0 a 3.0 a 1.0 b 1.0 b
Barnyardgrass (ECHCG)
Final germ. (%) 77.0 a 68.0 a 40.7 b 72.0 a 67.0 a
Root length (cm) 1.9 c 1.2 d 0.7 e 4.1 b 5.3 a
GI 43.0 b 24.0 c 12.0 c 85.0 a --
MDG 3.5 b 3.2 b 5.0 a 2.6 c 2.6 c
Common purslane (POROL)
Final germ. (%) 72.0 73.0 66.0 80.0 78.0
Root length (cm) 1.0 b 1.0 b 1.0 b 3.2 a 3.0 a
GI 13.0 b 19.0 b 14.0 b 108.0 a ---
MDG 2.1 a 2.0 a 2.0 a 1.5 b 1.5 b
Corn (ZEAMA)
Final germ. (%) 59 b 64 b 14 c 99 a 100 a
Root length (cm) 1.0 b 1.0 b 0.2 c 6.0 a 7.0 a
GI 18.0 b 17.0 b 1.0 c 113 a --
MDG 3.0 a 4.0 a 2.8 ab 2.0 b 2.0 b

SMean separation in rows within species by Duncan's Multiple Range Test (PS.05)










Table 4.4. Weed seed germination as affected by immature
(8-week-old) compost.


Weed species Control Compost

--------- % ----------
Cress 100* 0
Wild mustard 95* 0
Large crabgrass 61* 2
Barnyardgrass 69* 51
Pigweed 89* 4
Wild radish 13* 1
Florida beggarweed 56* 11
Curly dock 43* 3
Ground cherry 37* 7
Lovegrass 36* 0
Ivyleaf morningglory 96* 77
Common purslane 78* 66
Dichondra 95* 0
Yellow nutsedge" 32 20


Mean separation within species by
Z Tubers were used as propagules.


t-test (PsO.05).














CHAPTER 5
IMMATURE COMPOST SUPPRESSES WEED GROWTH UNDER GREENHOUSE
CONDITIONS


Introduction

Weed management options for vegetable crop production

requires greater diversification because the number of

registered herbicides is decreasing, development of

resistant weed species to herbicides, and environmental

concerns of herbicide usage. In Florida, the EPA has

restricted several herbicides used by vegetable growers due

to groundwater contamination and harmful effects to wildlife

and humans (Crnko et al., 1992).

Weed growth suppression is an important effect of

organic mulches (FAO 1987; Grantzau 1987). Suppression can

be attributed to their physical presence as a soil surface

cover, and/or by the action of phytotoxic compounds in the

material originating from the composting process (Niggli et

al. 1990). Mulching with organic material was an important

weed control method before synthetic chemicals were

developed for commercial vegetable crop production. In the

mulching system, a 10 to 15-cm thick layer was needed to

completely discourage weed growth (Marshall and Ellis,

1992).










In general, weed seed germination decreases as burial

depth increases (Baskin and Baskin, 1989), so mulches can

often be as effective as herbicides in controlling weed seed

germination (Singh et al. 1985). When straw and bark mulch

were compared with unmulched controls in ornamental shrubs,

weed control cultivation costs decreased by 20 and 40%,

respectively (Kolb et al. 1985). Mature, stable compost

applied to vegetable crop row-alley reduced weed growth as

compared with the control treatment (no compost), but

herbicides provided better weed control than the compost

(Roe et al., 1993a).

Plant injury resulted when poor-quality, immature

composts were used as a soil amendment, and damage was

directly related to the relative level of compost immaturity

or instability (Zucconi et al., 1981a). Compost maturity

can be defined as the degree to which the material is free

of phytotoxic substances that can cause delayed or reduced

seed germination, plant injury, or death (FDACS, 1994).

Zucconi et al. (1981b) reported lower seed germination in

cress due to the presence of phytotoxins produced during

organic matter decomposition and in free ammonium extracts.

Toxin presence is temporary, and is associated with

byproducts of the microbes that dominate during early

composting stages.

Phytotoxins in water extracts of fresh MSW compost had

acetic, propionic, isobutyric, butyric, and isovaleric acid








61
in the largest concentrations (DeVleeschauwer et al., 1981).

Exposure of cress seeds to varying acetic acid

concentrations resulted in growth inhibition at a

concentration of 300 mg'kg"' (DeVleeschauwer et al., 1981).

Phytotoxins in immature compost are water soluble (Inbar et

al., 1990), so water can be used as a carrier of these

compounds in greenhouse (pot) or field conditions (Zucconi

et al., 1981a; Zucconi et al., 1981b; Keeling et al., 1994).

Water extracts of immature (3-day, 4-week, and 8-week-old)

MSW composts resulted in delayed and reduced germination of

important economic weed species (Ozores-Hampton et al.,

1996; Shiralipour et al., 1991).

The objective of this investigation was to determine

the capacity of various mulch thicknesses and maturity

stages of MSW+biosolids compost to suppress weed emergence

and/or seedling growth under greenhouse conditions.




Materials and Methods

Compost Properties

Composts were provided by Bedmininster Bioconversion of

Tennessee, Inc., Sevierville, TN. Municipal solid waste and

biosolids were co-composted through a three-compartment

Eweson digester in an aerobic environment for 3 days, then

cured for 8 weeks using a window composting method.

Samples included 3-day and 8-week-old material, which was










assumed to be immature, and approximately 1-year-old

material that had been stored at the composting facility,

which was assumed to be mature.

Compost chemical and physical properties were measured

by the Soil and Water Science Department, Univ. of Florida,

Gainesville. Compost subsamples were analyzed for pH and

electrical conductivity of a saturated extract, and total C,

N, and metals concentrations on a dry weight basis.

Composts were also subjected to two maturity tests: a

germination index evaluation (GI), also known as a cress

test (Zucconi et al., 1981b), and a chemical test (volatile

fatty acids). Concentration of volatile fatty acids such as

acetic, propionic, butyric, isobutyric, valeric and

isovaleric acids were determined by Woods End Research

Laboratory, Inc., Mt. Vernon, ME. Extracts were prepared

with 20 g compost dry weight and 50 ml of distilled water.

Samples were diluted 1:10-1:1000 with distilled water and

analyzed by HPLC anion column, eluted with 0.15mM H2SO4.


Compost Maturity Evaluation

Ivyleaf morningglory was selected as an indicator

species based on its rapid and uniform germination rate to

determinate the effect of immature compost on weed

emergence. Plastic pots (2.5 L) were filled with 2.5 cm of

gravel and 5 cm of coarse sand (20/30 grade). Ivyleaf

morningglory seeds were sown (10 seed/pot) 1.0 cm deep in










the sand, and treatments were a 7.5 cm mulch layer of

immature 3-day-old compost, commercial media (Metro-mix

220), and a control. Pots were irrigated manually maintain

field capacity. No fertilizer was added to the pots.

Greenhouse temperatures were 30C Max 13.9C Min, and

average relative humidity was 39%. The experimental design

was a randomized complete block with six replications of

each treatment.

Germinated seeds were counted daily until no further

emergence occurred (8 days). Mean days to germination (MDG)

was determined according to the following formula (Gerson

and Honma, 1978):

MDG = (NiTi + N2T2 +.......+ NxTx)/total number of seeds

geminated, where

N = Number of seeds germinating within consecutive time

intervals, and

T= Time (in days) from beginning of the test to end of a

particular interval. Eight days after sowing 10 seedling

were harvested from pots, and roots free of soil or media,

oven dry for 5 days at 700C and weight recorded.

Compost Thickness Evaluation

Ivyleaf morningglory, barnyardgrass, and common

purslane were selected to determine the minimum immature

compost thickness needed to decrease weed emergence.

Plastic pots (2.5 L) were filled with 10, 7.5, 5, and 2.5 cm

of coarse quartz sand (20/30 grade), respectively. Ivyleaf








64

morningglory (10 seed/pot), barnyardgrass (25 seed/pot) and

common purslane (25 seed/pot) were planted in the sand at

1.0, 0.5, and 0.25 cm depths, respectively. Compost (8-

week-old) was layered over seeds at 2.5, 5, 7.5, and 10 cm

thicknesses.

Pots were irrigated manually to maintain field

capacity. No fertilizer was added to the pots. Greenhouse

temperatures were 34.4C maximum and 20.0C minimum, and

average relative humidity was 41%. The experimental design

was a randomized complete block with four replications.

Emerged seedlings were counted daily until no further

emergence occurred [ivyleaf morningglory (10 days),

barnyardgrass (13 days), and common purslane (25 days)].

Final seed emergence and MDG were calculated.


Compost Maturity and Thickness Evaluation

Barnyardgrass, common purslane, ground cherry, large

crabgrass, wild mustard, pigweed, Florida beggarweed,

dichondra and ivyleaf morningglory were used to determine

the minimum compost thickness and the optimum compost

maturity stage to reduce weed emergence. Plastic pots (2.5

L) were filled with either 10 or 2.5 cm of coarse quartz

sand (20/30 grade). Each weed species were sown with 25

seeds/pot at 1.0 cm depth in the sand, except purslane and

pigweed which were sown at 0.5 cm depth. Compost (8-week-

old) were layered over seeds at 2.5 and 10 cm thicknesses.








65

Pots were irrigated manually to maintain field capacity. No

fertilizer was added to the pots. Greenhouse temperatures

in the greenhouse were 37.2C maximum and 26.7C minimum,

and average relative humidity was 52%. The experimental

design was a randomized complete block with four

replications. Emerged seedlings were counted daily until no

further emergence occurred (21 days, except ivyleaf

morningglory, and barnyardgrass only 13 days). Final seed

emergence and MDG were calculated.

Statistical Analysis. Data were subjected to analysis

of variance and main effects partitioned into orthogonal

contrasts. Percentage emergence data differences greater

than 40% were square-root arcsine transformed prior to

analysis. Means were separated by Duncan's multiple range

test.



Results and Discussion

Carbon, N, and metal concentrations in composts were

typical for material made from a combination of domestic

garbage and biosolids feedstocks (Table 5.1). The 32:1 and

30:1 C:N ratio of the 3-day and 8-week-old composted,

respectively suggested that they had not yet stabilized.

The cress test on the two younger composts resulted in a GI

of 0 (Table 5.1), indicating potential presence of

phytotoxic compounds associated with early stage of

composting (Zucconi et al. 1981b). Compost acetic acid










concentrations (Table 5.2) were higher than the 300 mg'kg-'

level indicated as critical for compost maturity

(DeVleeschauwer et al., 1981). These data supported the

assumption that 3-day and 8-week-old composts were immature.



Compost Maturity Evaluation

Immature 3-day-old compost resulted in a 50% decrease

in emergence as compared with the control (Table 5.3).

Percentage emergence was similar between artificial media,

mature compost, and control treatments. Immature compost

delayed emergence by 3.4 days than the control. MDG was

similar between artificial media and mature compost,

although emergence was delayed as compared with the control.

Shoot and root dry weights were lower for plants grown

in 3-day-old compost than mature compost, artificial media

and the control (Table 5.3). Shoot dry weight was higher in

plants grown in the mature compost than the control or

artificial media, perhaps due to nutrients supplied by the

compost (Table 5.1). However, higher root dry weights

occurred in the control as compared with the mature compost.

Compost salt concentration (as measured by EC), heavy

metals concentration, or C:N ratio could have decreased weed

growth in the 3-day-old compost treatment. However,

chemical analyses showed only small differences in compost

extract EC, and lower Cd, Cu, Pb, Ni, and Zn concentrations

in 3-day-old as compared with mature compost (Table 5.1),










suggesting that these factors did not cause plant growth

reduction. In addition, certain heavy metals tend to bind

with compost organic compounds, so they are not extracted

efficiently by water (Eichelberger, 1994). Phytotoxicity,

associated with high C:N ratio compost like those used in

this experiment (Table 5.1), in generally attributed to

organic acids (Zucconi et al., 1981a; Zucconi et al., 1981b;

Wong and Chu 1985; Hadar et al., 1985). The observed

delayed and decreased weed seed emergence and seedling

growth attributed to the 3-day-old compost may have been due

to phytotoxic compounds (volatile fatty acids, especially

acetic acid) produced during the composting process (Table

5.2).


Compost Thickness Evaluation

Percentage emergence for each weed specie was greater

in the control than in any compost thickness treatment.

(Table 5.4). Ivyleaf morningglory and barnyardgrass

emergence decreased quadratically as compost thickness

increased. Common purslane did not emerge in any compost

treatment. Compost caused MDG to increase as compared with

the control. Mean days to germination increased linearly as

compost thickness increased for ivyleaf morningglory and

barnyardgrass. Chanyasak et al. (1983) reported that

immature compost inhibited the growth of Komatsuna (Brassica








68

rapa 'pervidis'), and attributed it to the presence of fatty

acids, especially propionic and n-butyric acid.



Compost Maturity and Thickness Evaluation

Emergence for each weed specie was greater in the

control than where compost was applied as mulch (Table 5.5).

Common purslane, large crabgrass, pigweed, Florida

beggarweed, and dichondra did not germinate under 10 cm of

mature compost or either depth of immature compost. Compost

maturity x thickness interactions or compost maturity had no

significant effect on emergence for barnyardgrass, pigweed,

and dichondra, but emergence was less under immature compost

than mature compost for the other five species.

Compost thickness did not affect pigweed and dichondra

emergence, but barnyardgrass emergence was less with 10 cm

than with 2.5 cm compost thickness. Compost maturity and

thickness interaction for emergence was significant in

common purslane, ground cherry, large crabgrass, Florida

beggarweed, and ivyleaf morningglory. Mature compost, 10 cm

thick, reduced emergence of common purslane, ground cherry,

large crabgrass, Florida beggarweed, and ivyleaf

morningglory, whereas immature compost 2.5 or 10 cm thick

reduced emergence of common purslane, ground cherry, large

crabgrass, Florida beggarweed, and ivyleaf morningglory. No

weeds emerged under the 10 cm thickness of immature compost.








69
MDG was higher for plants grown in mature compost than

the control for common purslane, ground cherry, large

crabgrass, pigweed, and dichondra. Germination of Florida

beggarweed was delayed about 2 days when covered with 2.5 cm

of mature compost than the control, while barnyardgrass

germination was delayed about 2 days when covered with 2.5

cm of immature compost as compared with the same depth of

mature compost.

Increased inhibition of weed seed germination in

immature compost as compared with mature compost may have

been associated with higher acetic acid concentration (1776

versus 13 mg'kg-1). Reduced seed germination and growth

inhibition of onion (Allium cepa L.), cabbage, cauliflower

(Botrytis cauliflora L.), lettuce (Lactuca sativa L.),

cress, perennial ryegrass (Lolium perenne L.), and tomato

seeds exposed to immature MSW compost were attributed to

acetic acid phytotoxicity (Kelling et al. 1994).

Additionally, the physical presence of the compost can

decrease emergence and increase MDG by creating unfavorable

conditions i.e. high temperature and absence of sufficient

moisture, 02, and light (Baskin and Baskin, 1989). Seed

burial studies by Blackshaw (1992) concluded that burial

depth markedly affected seed germination and seedling

emergence.

Immature MSW compost applied as a surface mulch may be

an effective alternative weed control method, whether










applied alone or in combination with chemical herbicides

when placed in a distant proximity from the developing crop,

i. e. row-alleys. In general, immature compost can inhibit

weed growth either due to its content of phytotoxins

produced in the early composting stages (i.e. short chain

fatty acids), or the physical presence of the materials on

the soil surface.



Summary


The influence of immature MSW and biosolids compost on

emergence and MDG of several weed species was evaluated

under greenhouse conditions. Plastic pots were filled with

composts of varying maturity and thickness. An experiment

consisted of a 7.5 cm layer of 3-day-old compost, mature and

stable compost, artificial medium, and a control (sand)

placed on ivyleaf morningglory seeds. Immature 3-day-old

compost decreased percentage emergence, shoot and root dry

weight, and increased MDG of ivyleaf morningglory. A second

experiment consisted of immature (8-week-old) compost at

depths of 2.5, 5, 7.5, 10 cm, and an untreated control

placed on sown seeds of weed species. No emergence was

obtained in common purslane at any of the immature compost

treatments. Mean days to germination increased linearly as

immature compost thickness increased in ivyleaf morningglory

and barnyardgrass.








71

Eight economically important weed species were sown in

pots with either mature and immature (8-week-old) compost at

depth of 2.5 and 10 cm, and a untreated control. Control

pots had higher percentage emergence than compost treatments

in all species evaluated. There was no emergence with

mature compost at 10 cm depth and immature compost at 2.5 or

10 cm depth for common purslane, large crabgrass, pigweed,

Florida beggarweed, and dichondra. Significant compost

maturity x depth interactions occurred for percentage

emergence of common purslane, ground cherry, large

crabgrass, Florida beggarweed, and ivyleaf morningglory. A

thinner compost layer was needed to suppress weed seed

germination using immature 8-week-old compost than mature

and stable compost.

Immature (3-day and 8-week-old) compost with respective

to acetic acid concentrations of 2474 and 1776 mg'kg-1

delayed and reduced germination percentage of economically

important weed species. These studies suggests that immature

compost can be potentially utilized as an alternative method

of weed control.










Table 5.1. Chemical and physical characteristics of
three different-aged composts.

Compost age

Property 3-days 8-weeks Mature


C (%) 37.1 35.7 34.3
N (%) 1.15 1.20 1.6
P (%) 0.24 0.27 0.32
K (%) 0.28 0.31 0.31
Ca (%) 2.04 2.37 3.1
Mg (%) 0.20 0.27 0.32
Fe (%) 0.77 0.98 1.15
Cd (mg'kg-1) 4 4 6
Cu (mg-kg-1) 127 178 229
Mn (mg-kg-1) 174 220 300
Pb (mg'kg-1) 207 264 283
Ni (mg-kg-1) 32 44 52
Zn (mg-kg-1) 446 552 720
Moisture (%) 47.0 37.5 47.6
C:N 32:1 30:1 24:1
pH 7.2 6.3 7.7
E.C. (dS'm-) 6.6 9.4 6.7
G.I.z 0 0 100


Germination
al., 1981b).


Index (Zucconi et al.,


1981a; Zucconi et










Table 5.2. Volatile fatty acids concentrations in three
different-aged composts.

Compost age
Fatty acid' 3-days 8-weeks Mature


---------------- (mg-kg-1) ---------------

Acetic 2474 1776 13
Propionic 311 262 <10
Isobutyric 24 22 <10
Butyric 171 265 <10
Isovaleric 62 <20 <20
Valeric <40 <40 <40

zAnalysis performed by Woods End Research Laboratory,
Vermon, ME.










Table 5.3. Effect of mature and immature compost on
emergence and seedling growth of ivyleaf morningglory.



Emergence Shoot Root
Treatment (%) MDGz (g dry weight/pot)


Commercial media 96.7ay 4.6b 0.24b 0.05b
Mature compost 95.Oa 4.2b 0.30a 0.06b
3-day-old compost 51.7b 6.8a 0.04c 0.02c
Control 95.Oa 3.4c 0.25b 0.12a

zMDG = Mean days to germination.
YMeans followed by the same letter are not significantly
different at PS0.05 according to Duncan's Multiple Range
Test.
x Metro-mix 220.










Table 5.4. Immature compost (8-week-old) compost
thickness influence on percent emergence and mean days to
germination (MDG) of three weed species.

Weed Species
IPOHE ECHCG POROL

Treatment % Emerg. MDG2 % Emerg. MDG % Emerg. MDG


Control (C)
Compost, 2.5 cm
Compost, 5.0 cm
Compost, 7.5 cm
Compost, 10 cm


94.3
87.5
92.3
94.5
20.0


3.7
4.5
4.2
4.9
5.0


67.5
76.3
79.9
41.3
0.0


3.3
3.2
4.2
6.2


4.9
0.0
0.0
0.0
0.0


52.0


Contrasts

C vs. compost. **Y
Compost linear **
Compost quadratic**


~MDG = Mean days to germination


zMDG = Mean days to germination
Y**, *, and NS indicate significance
or not significant, respectively.


at PSO.01, PsO.05,












Table 5.5. Compost maturity and thickness influence on percent emergence and mean day to germination of several weed
species.



ECHCG POROL PHYIX DIGSA AMARE DEDTO DICCA IPOHE

Treatment % E. MDG % E. MDG % E. MDG % E. MDG % E. DG % E. MDG % E. MDG % E. MDG

Control (C) 61 4.0.by 41 2.7 21 7.0 60 6.7 27 6.1 58 3.7* 35 7.7 100 2.7b
Mature (2.5 cm)" 70 5.0 b 18 5.4 27 8.0 12 11.2 20 11.6 25 7.6 9 13.4 79 5.0a
Mature (5.0 cm) 0 0 0 0 0 0 0 98 3.5b
8-week (2.5 cm) 50 6.9 a 0 5 8.6 0 0 0 0 81 3.7b
8-week (5.0 cm) 0 0 0 0 0 0 0 0 -

Contrasts

C vs compost ** ** ** ** ** ** ** **
Mat. vs 8-week NS ** NS ** NS **
2.5 vs 5.0 cm ** ** NS ** NS **
Comp. x thick. NS ** NS ** NS **
interaction

'MDG Mean days to germination; % E= % Emergence.
YMeans followed by the same letter are not significantly different at P<0.05 according to Duncan's Multiple Range Test,
5% level.
SCompost depths.
**, *, and NS indicate significance at P0s.01, PS0.05, or non significant, respectively.














CHAPTER 6
MUNICIPAL SOLID WASTE COMPOST USE FOR BIOLOGICAL WEED
CONTROL IN VEGETABLE CROP PRODUCTION


Introduction


Weed growth suppression is one of the most important

attributes of organic mulches (FAO, 1987; Grantzau, 1987).

These mulches control weeds due to their physical presence

as a surface cover, or by the action of phytotoxic compounds

they may contain (Niggli et al., 1989). Other beneficial

properties of organic mulches include reduced soil erosion,

decreased soil compaction, increased water holding capacity,

slow nutrient release, increased microbial activity, and

soil temperature moderation (FAO, 1987; Foshee et al.,

1996), all of which can increase crop yield.

Weed seed germination was inhibited when seed were

buried in the soil (Baskin and Baskin, 1989), and

germination inhibition increased with burial depth (Reisman-

Berman and Kigel, 1991). Germination inhibition by soil

burial is probably due to the lack of promoting factors such

as light, temperature, or moisture (Baskin and Baskin,

1989). To completely discourage weed growth in the field, a

mulch layer 10 to 15 cm thick was needed, and best results

were obtained with composted materials (Marshall and Ellis,










1992).

Chemical effects of phytotoxic compounds (volatile

fatty acids and/or ammonia) in compost, higher CO2 levels

resulting from biological activity, and high temperature can

decrease weed seed germination below the surface of the soil

(Jimenez and Garcia, 1989; Tam and Tiquia, 1994; Shiralipour

et al., 1991). However, phytotoxicity persisted in

sterilized, NH4-free extracts of MSW compost (Zucconi et

al., 1981a). A mulch of dead green rye that reduced

broadleaf weed growth from 41 to 99% was found to contain

several germination-inhibiting organic acids (Worsham,

1984). A water extract of 3-week-old YT compost decreased

germination of several perennial and annual weeds in petri

dishes upon exposure to high temperature over 60C

(thermophilic stage of composting) (Shiralipour and

McConnell, 1991). Reduced seed germination and growth

inhibition of onion, cabbage, cauliflower, lettuce, cress,

perennial ryegrass, and tomato were attributed to acetic

acid phytotocixity (Kelling et al., 1994). Low rates of

immature MSW compost reduced early growth of komatsuna due

to the presence of short-chain fatty acids, especially

propionic acid and n-butyric acid (Chanyasak et al., 1983).

The objectives of this investigation were to evaluate

several thicknesses of 4 and 8-week-old immature MSW

composts as biological weed control in vegetable row-alleys,

and evaluate compost effects on yield of bell pepper or










zucchini squash.

Materials and Methods


Bedminister Bioconversion of Tennessee, Inc. provided

the 4 and 8-week-old MSW-biosolids composts, which were co-

processed through a three-compartment Eweson digester in an

aerobic environment for 3 days, then cured for 8 weeks using

the window composting method. Compost samples were

evaluated for maturity with biological (cress test) (Zucconi

et al., 1981a and 1981b) and chemical (volatile fatty acids)

methods.

Compost chemical and physical properties were measured

by the Soil and Water Science Department, Univ. of Florida,

Gainesville (Table 6.1). Moisture concentration was

obtained by oven-drying 10 g (wet weight) compost at 1050C

for 24 h. Total N and C concentrations were measured on

compost samples that were air-dried for 4 days, ground in a

Spex 8000 Mixer/Mill, and combusted at 1010C in a Carlo-

Erba NA-1500 C/N/S analyzer. Total nutrient and trace

metals were analyzed according to EPA Method 3050 (USEPA,

1990). The compost samples were acid-digested and analyzed

by Inductively Coupled Argon Plasma Spectroscopy (ICAP).

Electrical conductivity (EC) and pH were measured using a

2:1 (by volume) water-to-soil suspension. Concentrations of

volatile fatty acids such as acetic, propionic, butyric,

isobutyric, valeric and isovaleric acids in compost extracts

were measured by Woods End Research Laboratory, Inc., Mt.










Vernon, ME (Table 6.2). Extracts were prepared from 20 g

compost (dry weight) and 50 mL distilled water. Raw

extracts were diluted 1:10 to 1:1000 with distilled water

and analyzed using an HPLC anion column, eluted with 0.15mM

H2SO4.

Field experiments were conducted in autumn, 1995 and

winter/spring, 1996 at the Univ. of Florida, Southwest

Florida Research and Education Center, Immokalee, FL. The

soil was Immokalee fine sand (sandy, siliceous, hyperthermic

Arenic Haplaquods) with less than 2% organic matter, and pH

(1:2 soil:water) of 6.7. Experimental plots were naturally

infested with high populations of goosegrass (Eleusine

indica (L.) Gaertn.), yellow nutsedge, and common purslane.



1995 Experiments

Two field experiments were conducted simultaneously,

using a randomized complete block design with four

replications of each treatment. The first experiment

included treatments of 3.8, 7.5, 11.3, and 15 cm (49 tha-1,

99 tha-1, 148 tha-', 198 tha-1) thicknesses of 4-week-old

immature compost applied as mulch, paraquat (0.6 kg'ha-1)

applied with a backpack sprayer, and an untreated control

(Fig 6.2). The second experiment included treatments of

3.8, 7.5, and 11.3 cm thicknesses of 8-week-old immature

compost and a control. In both experiments, the compost was

placed in both inter-row spaces between three 0.75 m wide,








81

0.15 m high soil beds covered with plastic mulch. Each plot

was 4.8 m long. Nitrogen, P and K fertilizers were applied

under the plastic mulch at 270, 80, and 300 kg'ha-',

respectively. Bell peppers 'Prisoin' transplants (6-week-

old) were planted in the field in Oct, 1995 with 0.35 m

between plants and 1.8 m between rows. Subsurface

irrigation was used to maintaining a water table about 0.6 m

below the soil surface throughout the growing season.

Insects and diseases were monitored according to Univ. of

Florida guidelines with recommended chemical control applied

as needed (Hochmuth and Maynard, 1996).



1996 Experiments

Two field experiments were conducted simultaneously,

using a randomized complete block design with four

replications of each treatment. The first experiment

included treatments of 2 (26 tha-'), 3.8, 7.5, and 11.3

thicknesses of 4-week-old immature compost, paraquat (0.6

kg'ha-'), and a untreated control. The second experiment

included treatments of 2, 3.8, 7.5, and 11.3 cm thicknesses

of 8-week-old immature compost and a untreated control.

Compost was placed in a row-alley as previously described in

6 m long plots. Nitrogen, P and K fertilizers were applied

under the plastic mulch at 100, 30, and 133 kg-ha-1,

respectively. Zucchini squash ('Consul') were direct-

seeded in a single row with 0.30 m between plants and 1.8 m










between rows on 21 Feb 1996. Zucchini squash were planted

in three-row plots consisting of 0.75 m wide and 0.15 m high

soil beds covered with white-on-black polyethylene mulch.

The plants were irrigated as previously described.


Weed Control Evaluation

Weed control was visually evaluated as percentage weed

cover, identification of the dominate weed species, and

above-ground weed dry weight (g'0.02 m2). Above-ground weed

dry weight biomass was determined by removing the shoots of

weeds present in a 0.02 m2 area within each plots. Weed

samples were dried at 70C for 3 days and then weighed.

Observations were made at 25, 65, 90, 150, and 240 days

after treatments (DAT).

Bell pepper could not be harvested due to Phytophthora

spp. Zucchini was harvested 11 times and yield was measured

from 10 plants as number and weight of medium and small

fruits.

Data were subjected to analysis of variance (ANOVA) and

main effects partitioned into orthogonal contrasts.

Percentage weed ground cover data (if >40% difference within

experiment) were subjected to arcsin-square-root

transformation prior conducting an ANOVA.










Results and Discussion


Compost Maturity Tests

The cress test for compost maturity resulted in a

germination index below 60 (Table 6.1) indicating the

presence of phytotoxic compounds associated with early stage

of composting (Zucconi et al., 1981b). Compost acetic acids

concentrations were higher than 300 mg'kg"1 (Table 6.2),

which has been indicated as a critical level for defining

immature compost (DeVleeschauwer et al., 1981). In

addition, compost C:N ratios were above 20:1, which

indicated an unstable compost that could cause N-

immobilization. Therefore, immature composts were used in

each field experiment. Both the 4 and 8-week-old compost

complied with the U.S. Environmental Protection Agency's

criteria for land application with no restriction on use or

application rate (Kidder and O'Connor, 1993).


1995 Experiments


Control plots were populated primary by goosegrass and

small percentages of common purslane, yellow nutsedge, large

crabgrass, wandering cudweed (Gnaphalium pensylvanicum

Willd.) and eclipta (Eclipta prostrata L.). In the

herbicide plots, weed populations changed from goosegrass to

common purslane, and finally to blue toadflax (Linaria

canadensis L. Dumont) from 1 to 240 days after treatment

(DAT). Weeds grew at the at the edge of the polyethylene










mulch interface in the 3.8-cm compost treatment, with

primary weed species of primrosewillow (Ludwigia

octovalvis), common purslane, Florida pusley (Richardia

scabra L.), large crabgrass, and goosegrass.

Compost (4-week-old) reduced percentage weed cover and

weed dry weight for 240 DAT as compared with the control

(Table 6.3). Compared to the herbicide treatment, 4-week-

old compost reduced % weed cover and weed dry weight for 240

and 90 DAT, respectively. At 240 DAT, the 3.8 cm thickness

decreased weed cover by 87% and 50% as compared with the

control and herbicide treatment, respectively. Similar weed

reduction was obtained with mature MSW compost (224 t'ha-1)

in row-alleys of bell pepper than untreated control.

Herbicide provided improved weed control over mature compost

(Roe et al., 1993a).

There was no difference in % weed cover and weed dry

weight between 4-week-old compost thicknesses for the first

25 DAT. Percent weed cover and weed dry weight decreased

linearly as compost thickness increased. The 7.5, 11.3, and

15 cm thicknesses completely inhibited weed germination and

growth for 240 DAT (Fig 6.3), which is consistent with

previous reports that utilized conifer bark, oak bark and

rape straw to suppress weed in an apple orchard (Niggli et

al., 1990). Weed reduction was attributed not only a

physical, but also a chemical effect.

Compost (8-week-old) reduced percentage weed cover and










weed dry weight as compared with the control from 1 to 240

DAT (Table 6.3). AT 240 DAT, the 3.75 cm thickness reduced

weed cover by 58% than the control. There was no thickness

effect on weed dry weight for the first 25 DAT. Percent

weed cover and weed dry weight decreased linearly as compost

thickness increased. The 7.5, 11.3, and 15 cm thicknesses

of 8-week-old compost completely inhibited weed germination

and growth for 240 DAT. In another study, extract from 8-

week-old compost decreased weed seed germination and growth

of important economic weed species (Ozores-Hampton et al.,

1996).

Heavy rains that occurred 3 weeks after bell pepper was

transplanted resulted in spread of Phytophthora spp. in the

soil, resulting in the death of a majority of the plants.

Therefore, yield data were not measured for experiments in

1995.



1996 Experiment

Weed pressure was higher in winter, 1996 than autumn,

1995, especially due to a high population of yellow

nutsedge. Control plots were populated early in the season

by goosegrass, yellow nutsedge, common ragweed (Ambrosia

artemisiifolia L.), and later by large crabgrass and hairy

indigo (Indigofera hirsuta). In the herbicide treatment,

the primary weeds were goosegrass, common purslane, and

Florida pusley. In compost treatments, weed pressure was








86
high at the compost/polyethylene mulch interface, where the

primary weed species were yellow nutsedge, large crabgrass,

hairy indigo, broadleaf signalgrass (Brachiaria platyphylla

Griseb. Nash), Florida pusley, and goosegrass.

Compost (4-week-old) reduced percentage weed cover and

weed dry weight from 1 to 240 DAT than the control (Table

6.4). Herbicide reduced weed cover and weed dry weight more

effectively than compost from 90 to 240 DAT. Percent cover

and weed dry weight decreased linearly as compost thickness

increased, except for weed dry weight with 4-week-old

compost 25 DAT. The 11.3 cm thickness of 4-week-old compost

decreased weed cover and weed dry weight by 54 and 79%,

respectively, as compared with the control 240 DAT.

Compost (8-week-old) reduced weed cover and dry weight

for 240 and 90 DAT as compared with the control,

respectively (Table 6.4). Percent weed cover and weed dry

weight decreased linearly as compost thickness increased.

The 11.25 cm thickness reduced weed cover and weed dry

weight by 20 and 51%, respectively, than the control, 240

DAT.

Our observations were consistent with Edwards et al.

(1994), where application of newsprint and broiler litter

decreased the number of large crab grass seedlings, henbit

(Lamium amplexicaule L.), cutleaf evening primrose

(Oenothera laciniata Hill), and bitter cress (Cardamine

hirsuta L.) as compared with the control, illustrating the










potential for decreasing herbicides in cotton production.

Zucchini yield or fruit size did not differ among

treatments for either compost age (Table 6.5). There were

no visible signs of plant stunting, chlorosis, or injuries

during the crop cycle associated with immature compost high

in acetic acids (Table 6.2). DeVleeschauwer et al. (1981),

reported that immature compost with a high concentration of

acetic acid can be detrimental to plant growth, but in those

experiments compost was applied in close proximity to the

crop root system. Our experiments suggests that immature

compost applied as a mulch in row-alleys between raised

polyethylene beds can be used for weed control, since the

compost is located at considerable distance from the crop

root zone.

Compost provided insufficient weed control at the

mulch/polyethylene interface at the lower compost rate.

Weed growth there was vigorous due to non-uniform compost

spreading and a sloping bed shoulder. To achieve more

effective weed control, the bed shoulder should have a 90

degree angle with the soil surface to allow an even compost

thickness. Merwin et al. (1995) reported difficulties in

controlling weeds in an orchard at the mulch edges, where

weeds also grew vigorously.

Under low weed pressure, immature 4 or 8-week-old MSW-

biosolids compost provided excellent weed control for 8

months when applied as at 7.5 cm thick mulch. To control










weeds under higher weed pressure, a thicker compost

application would be needed, weed control for shorter-lived

crops (less than 8 months) could be achieved with thinner

compost application.

Immature composts can potentially provide biological

weed control, and could be combined with chemical herbicide

in an integrated program that would provide an

environmentally-safe method of waste product utilization.

The first year, immature compost can be utilized in

vegetable crop row-alleys for weed control. In the

subsequent crop, compost may be used as a soil amendment to

increase vegetable crop production. Diversified weed

management programs that incorporate prevention, cultural,

mechanical, and biological weed control methods should be

adopted where possible, since some weed species with a

persistent seed bank can escape chemical control.


Summary


Composting MSW and biosolids can be an attractive

alternative waste management practice as landfilling cost

increases. Compost maturity is a major issue that the

composting industry is facing as it attempts to provide a

high quality product to the agricultural community. The

potential for using immature compost (mixture of household

garbage and biosolids) for weed control in vegetable crop

row alleys was evaluated.








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Two field experiments were conducted with 4 and 8-week-

old compost in 1995 and repeated in 1996. Treatments were

4-week-old compost at 3.8 (49 tha-1), 7.5 (99 tha-1), 11.3

(148 tha-1), and 15 cm (198 tha-1) thicknesses in the

autumn, and 2.0 (26 tha-1), 3.8, 7.5, and 11.3 cm

thicknesses in the winter applied as a mulch; paraquat at

0.56 kg'ha-'; and an untreated control in row alleys between

raised, polyethylene-covered soil beds. Treatments using 8-

week-old compost consisted of 3.8, 7.5, 11.3, and 15 cm

thicknesses in autumn and 2.0, 3.8, 7.5 and 11.3 cm

thicknesses in the winter applied as a mulch, and an

untreated control. Weed control was evaluated visually as

percentage weed ground cover, dominant weed species, and

total weed dry weight.

In the autumn 1995 experiment, under low weed pressure,

4-week-old compost at 7.5 cm or greater thickness completely

inhibited weed germination and growth for 240 days after

treatment. In the winter 1996 experiment with 4-week-old

compost, complete inhibition of weed growth was obtained for

only 65 DAT with 7.5 cm or greater thickness due to higher

weed pressure, especially yellow nutsedge. In the winter

experiment, a 50% reduction in weed cover was obtained with

11.25 cm of compost than the control, 240 DAT.

In the autumn 1995 experiment, 8-week-old compost at

7.5 cm or greater thickness completely inhibited weed

germination and growth for 240 DAT. In the winter 1996








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experiment, 8-week-old compost at 11.25 cm thickness reduced

percent weed cover as compared with the control, 240 DAT.

In general, weed cover and weed dry weight decreased

linearly as compost thickness increased.

Inhibition of germination or subsequent weed growth may

be attributed to both the physical effect of the mulch and

the presence of phytotoxic compound (fatty acids) in the

immature compost. Acetic acid was present in concentrations

of 1221 mg'kg-' (autumn) and 4128 mg'kg-' (winter) in the 4-

week-old compost, and 1118 mg'kg' (autumn) and 3113 mg'kg-1

(winter) in the 8-week-old compost. As weed growth pressure

increases, thicker compost layers may be more effective for

weed control, except when yellow nutsedge is the dominate

weed species. Immature compost may provide an effective

alternative weed control method for row-alleys in vegetable

crop production systems.