Living Mulch Lit Review m Zum Winkle

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Living Mulch Literature Review

By Mark Zumwinkle

Conventional clean cultivation agriculture is highly

productive when viewed within the time frame of a single

growing season. But the high yields obtained with clean

cultivation often come at the expense of the deterioration of

the soil resource base. Erosion, loss of organic matter and

deterioration of soil structure are all accelerated by

extensive periods clean cultivation. Attempts to develop

reduced tillage methods in the 1950's coincided with the

development of herbicides to make possible planting of row

crops into a killed sod. The water and soil conservative

benefits of the dead sod were dramatic (Beale et al. 1955) but

lasted only until the sod decomposed. In an attempt to

extend the mulch benefit over time, crops were grown in living

sods. But live sods proved to be excessively competitive for

water and nutrients (Kurtz et al., 1952). Refinement of

herbicide technology in the 1960's resulted in a renewed

interest in live mulches suppressed with non-lethal rates of

herbicide.

Living mulch technology has been shown to benefit bothshort and long term productivity by improving soil physical

properties, reducing runoff and erosion, suppressing weeds

and, if the mulch is a legume, transferring symbiotically

fixed nitrogen to the cash crop. These benefits can be offset


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by the potential for the living mulch to compete with the cash

crop for limiting resources, particularly water and nitrogen.

Improvement of Soil Physical Properties

Long-term productivity of agricultural soils is

generally associated with maintenance of adequate levels of

organic matter in order to provide a loose, well drained

physical condition. Living mulches have the potential to

positively alter soil organic matter content by increasing the

total biomass produced by a cropping system. Several studies

have shown that extensive living mulch biomass can be produced

without a significant cash crop yield reduction when the mulch

is temporarily suppressed by mowing, selective cultivation,

herbicides or a combination of these techniques (Vrabel et

al., ____; Harper et al., 1980; Mayer and Hartwig, 1986;

Grubinger and Minotti, 1990; Mangan et al., ____; Beste and

Teasdale, ____). The residue is usually not harvested but

left to decompose in place. When managed in this manner, the

living mulch is a green manure.

Extensive research in the first half of this century on

the long-term effects of regular green manuring showed that,

although soil organic matter losses were lessened by the

addition of plant residues, rarely was there an absolute

increase. Joffee (1955) postulated that there are two

equilibrium levels of organic matter for a given soil: a

relatively high equilibrium under native vegetation and a


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lower equilibrium under continuous cultivation. The

dramatically increased microbial activity due to cultivation

overrrides the ability of green manures to increase organic

matter except when the system approaches the lower

equilibrium.

Living mulch technology is a form of reduced tillage.

Organic matter conservation under living mulch may result from

a combination of increased residue inputs and reduced

stimulation of decomposition from tillage. Microbial

decomposition decreases as the soil temperature decreases

within the range normally found under field conditions.

Living mulches, like sods in general, lower mean growing

season soil temperatures (Bennet et al., 1976; Newhouse and

Dana, 1989).

Living mulch studies that have measured soil organic

matter changes generally confirm earlier green manure

research. Organic matter losses may be minimized and, in

rare cases where initial levels are very low, there may be an

increase. Welker and Glenn (1988) found that organic

matter levels were maintained but not increased after three

years under a mowed tall fescue living mulch in peach orchards

in West Virginia. Bare soil treatments, whether achieved by

cultivation or herbicides, dropped from 2.4% to 2.1%.

Akobundu (1984) found that a living legume mulch of

Psophocarpus palustris Desv. dramatically reduced organic

matter losses after two years of corn production in Nigeria.

Initial levels were reduced 32% and 8% under conventional


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tillage and living mulch, respectively. Lanini et al. (1989)

measured organic matter changes under subterranean clover

living mulch in sweet corn and lettuce at Riverside,

California. Initial levels of 0.78% rose marginally to 0.86%

under subclover and dropped significantly to 0.66% under clean

cultivation.

The soil physical properties most likely to be improved

by additions of organic residues are: bulk density, aggregate

size and stability and water movement. The benefits of

organic matter in mineral soils can be attributed either to

its long-term presence as a stable component (i.e. humus

fraction) of the soil matrix or to the rapid process of

decomposition of relatively accessible microbial substrate

(i.e. proteins, carbohydrates, fats and waxes).

The bulk density of a mineral soil is lowered immediately

by the addition of organic residues due to

simple dilution of a dense material with a less dense

material. But, because the volume of material added by green

manures is small compared to the soil volume, dilution can

explain only small changes in bulk density. A number of

studies have shown strong negative correlations between

organic matter content and bulk density (De Kimpe et al.,

1982, Millette et al., 1980, Coote and Ramsey, 1983). Too

large to be attributed to dilution, such dramatic reductions

in bulk density are more likely a result of the contribution

of organic matter to larger, more stable soil aggregates.

Increased aggregate stability results primarily from


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the cementing action of microbial gums and other intermediate

products of the decomposition of recently added residues.

Secondarily, aggregate stability is enhanced by

increasing total soil organic matter. Chester et al.

(1957) found only a marginally significant correlation

between aggregate stability and total organic matter. The

correlation with soil gums was highly significant. Because

these cementing agents are subject to rapid further

decomposition, continual additions of residue are required

to maintain aggregate stability. Welker and Glenn (1988)

found a large increase in aggregate stability and lower bulk

density under a grass living mulch compared to clean

cultivation in orchard production. Water infiltration was

also increased under the mulch.

Soil Conservation in Living Mulches

Living mulches may prove to be an even more effective

tool for reducing runoff and erosion than presently popular

reduced-tillage systems. Hall et al. (1984) measured water

runoff volume in corn planted on a 14% slope and grown

conventionally, no-till or in a crownvetch living mulch. The

extensive runoff in conventional corn was reduced by 90% and

98% in no-till and living mulch, respectively. Due to the

ability of living mulches to compete with the cash crop for

water, their adoption for the purpose of erosion control will

be limited to humid climates and acreage under irrigation.

Hartwig (____) sugested that because living mulches can be


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more soil conservative than no-till, they may substitute for

expensive terraces, contour strips and sod rotations.

Living mulches can reduce wind erosion by increasing

residue coverage of the soil, by anchoring both soil and plant

material with the living mulch roots, by increasing soil

aggregate size and stability, and by providing a windbreak.

Newhouse and Dana (1989) measured the combined damage from

wind and windblown soil particles in strawberries. A mulch of

perennial ryegrass (Lolium perenne L.) significantly increased

strawberry yield and quality after a spring windstorm. The

mulch also protected strawberry crowns from winter winds and

cold temperatures.

Nitrogen Transfer Between the Mulch and the Cash Crop.

Living mulches may contribute to or compete for the

nitrogen pool available to the cash crop. Generally,

unsuppressed mulches, whether they be legumes or grasses, will

compete for nitrogen. Kurtz et al. (1946, 1952) found that

corn yields in legume and grass sods were reduced 50% compared

to conventional tillage. Adequate nitrogen raised

intercropped corn yields to 15% less than conventional.

Stivers (1956) obtained similar results for corn in

unsuppressed ladino clover.

Suppressed legume mulches have the potential to release

symbiotically fixed nitrogen and reduce fertilizer nitrogen

requirements. Grasses are a net nitrogen sink, even when

suppressed. Scott et al. (1987) compared legume and grass


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living mulches plowed under and replanted annually with

conventional tillage. Over 4 years, grain yields and ear leaf

nitrogen were higher with legumes and lower with grasses when

compared to an unfertilized conventionally cultivated control.

The highest corn yields in the legume mulch were similar to

conventional plots fertilized with 17 kg N/ha. Because the

mulches were plowed under annually and not replanted until

after corn establishment, turnover of legume N was maximized

and competition with the cash crop was minimized. This study,

then, was a highly favorable scenario for nitrogen transfer to

the cash crop.

Suppressed legume mulches will enhance the nitrogen

status of the cash crop in proportion to the extent of the

suppression. This is evidence that a significant portion of

the legume nitrogen comes from dessication and decomposition

of legume plant parts. The extent of mulch suppression caused

by different suppressive techniques can be ranked generally as

follows: none


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sweet corn. The fresh weight of marketable ears and total

nitrogen uptake by sweet corn were higher for plowed down

mulch, chemically suppressed mulch and mechanically mowed

mulch than for unsuppressed mulch and conventionally grown

corn . This was the case across four fertilizer nitrogen

rates from 0 to 150 kg/ha. Grubinger and Minotti (1990) found

partial rototilling (see mulch suppression by partial

rototilling) of a sweet clover mulch to be highly effective at

increasing sweet corn nitrogen status. One month after

rototilling, ear leaf %N was 2.5, 2.1, 1.9 and 1.9 for mulch

rototilled, mowed 5 times, mowed 2 times and unsuppressed,

respectively. The Grubinger study favored nitrogen transfer

by rototilling over mowing because the nitrogen rich mowed

clover residue was bagged and removed. In contrast, Peters

allowed the residue to fall and decompose in place. The

success of mowing as a nitrogen transfer technique may depend

on proper handling of the residue.

Although the ammount of nitrogen supplied by long-

standing legume mulches may be a significant portion of the

total needs of the cash crop, nitrogen does not usually build

up in sufficient quantity to maximize cash crop yields. Scott

et al. (1987) found corn in several legume mulch species to

yield as if the mulch were contributing nitrogen in the range

of 17 kg/ha two years into the study. But the aparent

nitrogen contribution did not rise over the following three

years. There is commonly a positive cash crop response to

additions of fertilizer nitrogen even after several years in


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legume mulch. Cash crop fertilizer nitrogen response curves

in long-standing legume mulches show a "rotation effect" or

absolute yield increase when compared to conventional

cultivation. Mayer and Hartwig (1986) measured the corn grain

yield response to fertilizer nitrogen in an eight year old

crownvetch living mulch. The mulched corn showed a positive

yield response up to 140 kgN/ha. The mulched corn yielded

similar to conventional corn fertilized with 30-55 kg more

N/ha. There may be two components to this response. First,

the mulch has simply not provided enough nitrogen. Second,

there has been an increase in the yield potential of the cash

crop due to the presence of the mulch (improved soil physical

properties, increased available water, slow release of legume-

derived fertility). The value of the nitrogen savings may be

overshadowed by the increase in yield potential, particularly

if the value of the cash crop is high relative to the cost of

nitrogen fertilizer. The magnitude of yield potential

increases reported is highly variable. Bennet et al. (1976)

found that a two year old bromegrass living mulch increased

corn silage yields 137% over conventional corn when all

treatments received 225 kgN/ha. Akobundu (1982) measured an

86% corn grain yield increase in a Psophocarpus palustris

Desv. legume mulch compared to conventional corn when all

treatments recieved 120 kgN/ha. This was in the fourth year

of the study. First year yields were highest in conventional

corn. But the productive potential in subsequent years dropped

in conventional tillage and remained constant in the living


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mulch. The Akobundu study shows that what appears to be an

increase in yield potential in a given year may be the same as

the stemming of the loss of productive potential over a longer

period of time. The study was conducted in the humid tropics

where the detrimental effects of continuous cultivation are

accelerated. Similar trends may occur in temperate climates

over a longer time span. Mayer and Hartwig (1986) found a 15%

increase in corn grain yield in an eight year old crownvetch

mulch compared to conventional practices when 170 kgN/ha was

applied to all treatments. Peters (1986) obtained similar

results for sweet corn in white clover. None of the above

four studies systematically applied water as a treatment

variable. All of the studies extensively suppressed the mulch

during cash crop establishment and growth. It is likely that

the suppressed mulch acted similar to a dead mulch to improve

water infiltration, reduce evaporation, and hence increase

available water.

Competition Between the Mulch and Cash Crop for Water

Living mulches generally compete with the cash crop for

water. Numerous studies have found that both grass and legume

mulches reduce corn yields in a dry year (Kurtz, 1952; Lewis

and Martin, 1967; Carreker et al., 1972). Although

unsuppressed mulches increase soil water recharge by slowing

runoff, increasing infiltration and reducing evaporation from

the soil surface (Bennet et al., 1976; Hall et al., 1984),

this increase is not as great as the loss dure to mulch


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transpitation. Chemically suppressed mulches may either

increase or decrease the water available to the cash crop.

Total seasonal water use will usually be high in suppressed

mulches because they are allowed to grow and transpire

extensively in the spring and fall. But during the period of

extensive suppression, the mulch may temporarily improve

water retention. Humid climates receive ample annual rainfall

but crops often suffer from short duration droughts between

periods of heavy rain. Water may be conserved by a suppressed

mulch under such conditions. Bennet et al. (1976) measured an

increase in corn grain yields and an increase in available

soil moisture in suppressed grass mulches compared to

conventionally cultivated corn in West Virginia. Rainfall was

ample but poorly distributed. Semi-arid climates depend on

fall and spring rains to recharge subsoil moisture. Living

mulches have a detrimental effect on this resource. In

Nebraska, Echtencamp and Moomaw (1989) found living mulches to

be competitive with corn for water except in a wet year.

Mechanical mowing is less effective than chemical suppression

at reducing mulch transpiration. Grahm and Crabtree (____)

applied increasing ammounts of irrigation water to cabbage in

a perennial ryegrass mulch suppressed chemically, mechanically

or not at all. Mowed grass was as competitive for water as

unsuppressed grass. Chemically suppressed grass competed for

water but competition was eliminated at the highest level of

irrigation. For all mulch treatments, the cabbage was showing

a positive yield response to increasing levels of irrigation,


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even at the highest level applied.

Although living mulches have been shown to compete

extensively for both nitrogen and water, suppressed mulch

studies were not found that systematically altered both

resources simultaneously. The ability of a plant species to

compete for water or nitrogen is dependent on the soil volume

explored by the root system. No studies were found that

describe the spacial distribution of the root systems of

either the cash crop or the living mulch over time.

Mulch Suppression

Early attempts to produce corn in living sods were

abandoned in the 1950's because of the ability of the living

mulch to compete excessively with the cash crop for nitrogen

and water. The driving force behind the renewed interest in

living mulches since the 1970's is the search for a wide

variety of mulch supression techniques. The three primary

methods of suppression are: non-lethal rates of herbicide,

mechanical mowing, and maintainance of a clean soil strip,

whether by cultivation or banded herbicide. Less common

methods that show promise include: manipulation of plant

populations (both in the cash crop and the living mulch),

delayed planting of the mulch, and partial cultivation.

Herbicide Suppression of the Mulch

The use of low levels of herbicide for mulch suppression

has had mixed results. A number of studies have shown that


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some mulch species can be suppressed enough to dramatically

reduce competition and still allow the mulch to recover

(Bennet et al., 1976; Elkins et al. 1983; Hartwig, 1985;

Lindgren and Ashley, 1986; Grahm and Crabtree, ____). A

majority of these studies have used grasses. Success with

suppressing legumes chemically has been associated with mulch

species that recover by stoloniferous regrowth. If the

herbicide proves lethal to portions of the mulch stand, the

remaining plants can fill in. Examples of this are Dutch

white clover (Trifolium repens L.) and crownvetch (Coronilla

varia L.). Crownvetch has been successfully maintained as a

chemically suppressed living mulch in corn for over ten years

by Hartwig at Pennsylvania State University.

A major problem with chemical suppression of the living

mulch is that it often allows weeds to become established

inside the mulch (Hughes and Sweet, ____, Graham and Crabtree,

____, Katz and Ilnicki, ____). The same competitive abilities

exhibited by the living mulch are likely causing both the

suppression of the cash crop and the weeds. Most often, the

weed entry window opened by the herbicide is exploited by

annual broadleaf species because they establish quickly.

Perennial weeds must compete through periods of uninterrupted

mulch growth after removal of the cash crop. Hartwig (1977

and 1989) found that crownvetch reduced invasion of the

perennials, dandelion (Taraxacum officinale ___) and yellow

nutsedge (Cyperus esculentus L.) in corn by 74% and 80%,

respectively. Fall regrowth of the crownvetch after corn


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harvest smothered the newly established weeds. In contrast,

the annual weeds, redroot pigweed (Amaranthus retroflexus L.)

and fall panicum (_____) were not controlled at all by the

mulch.

Mechanical Mowing as a Method of Mulch Suppression

Mechanical mowing has been shown to be a viable means by

which competition can be reduced (Vrabel et al., ____; Enache

et al., 1988). There are several advantages to this

technique. Unlike the use of herbicides, mowing has the

potential to maintain mulch vigor, maintain or increase mulch

biomass production, and reduce weed invasion. Also, the

largely as yet undeveloped technology of non-lethal rates of

herbicide is unnecessary with mowing. The primary

disadvantage to mowing is that, because the mulch recovers

rapidly, there may be too small of a window for cash crop

establishment and development.

Mowing the mulch in a late stage of vegetative growth

immediately reduces both the plant canopy and live root mass.

But, unlike herbicide suppression, mulch vigor may be

maintained or increased as a new period of vegetative growth

is initiated. Rather than opening an opportunity for weed

invasion, timely mowing can cut existing weeds and reestablish

the mulch as the dominant species.

Wiles et al. (1989), found that mowing a perennial

ryegrass living mulch reduced competition with chinese cabbage

(Brassica rapa L., Chinensis Group) equivalent to herbicide

suppression. But mowing increased living mulch shoot biomass


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compared to an unsuppressed control. Herbicide suppression

dramatically reduced mulch biomass production.

Lindgren and Ashley (1986) found mowing twice to be as

effective as herbicide suppression at reducing competition by

a white clover mulch in snap beans. But the mulch remained

more vigorous when mowed than when chemically suppressed.

Only total kill of the mulch with herbicides increased bean

yields over mowing. Because the suppression from mowing is

short-lived, more than one mowing may be necessary. Vrabel et

al. (_____) found a single mowing of legume mulches at the

time of sweet corn establishment to be less effective than

herbicide suppression. Costello and Altieri (1994) obtained

broccoli yields equivalent to clean cultivation by

mechanically mowing clover twice. Unless the mulch was mowed

early, competition for light ensued. They suggested that

improved machinery needs to be developed for large-scale

adoption.

Strip Tillage to Reduce Mulch Competition

Mulch suppression by mowing or herbicides alone does not

generally reduce competition enough to produce cash crop

yields equal to conventional clean cultivation. These

practices are usually combined with the creation of a clean

soil strip in which the cash crop is seeded. Living mulches

are usually perennials. The cost of the establishment of the

mulch is significant. The use of perennial mulches allows the

cost of establishment to be ammortized over more than one


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growing season. In the second season of production in a mulch

stand, the newly seeded cash crop must compete with an

established perennial. Creation of a clean soil strip at

planting dramatically reduces competition during the critical

early stage of cash crop establishment by physically

separating the two species a known distance. Vrabel et al.

(____), found that 0.45 m clean soil strips reduced

competition from four legume mulches in sweet corn when the

mulches were established five weeks prior to corn planting.

The soil strips were created by banding the legume seed. The

effect of strips was much less pronounced when legumes were

seeded simultaneously with or five weeks after the corn.

Elkins et al. (1979) found a similar benefit to using banded

herbicide strips in grass mulches for corn production. A 20

cm banded herbicide strip increased corn yields dramatically

compared to corn planted into an undisturbed mulch. Waters

and Ilnicki (1990) compared subclover mulch full stands with

0.55 m planting strips for production of summer squash.

Strips, whether killed with herbicide or cultivation,

significantly outyielded full mulch stands.

The cost of reducing competition with strips may be a

relatively small reduction in mulch biomass productivity

depending on the mulch species. Vrabel et al. (____) found

that strips occupying 50% of the total soil surface did not

significantly reduce white or red clover mulch dry matter.

Alfalfa and ladino clover were reduced by 50%.

The width of the strip needed will vary with the cash


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crop. Loy et al. (1987) found strip widths of 0.5 m to be

insufficient and 1.5 m to be sufficient at eliminating

competition from grass and legume sods in peppers and bush

winter squash.

Manipulation of Plant Populations to Reduce Competition

The relative competitive abilities of the cash crop and

the living mulch determine to what extent plant populations

can be altered to reduce interference by the mulch. Wiles et

al. (1989) found pak choi to be weakly competitive with a

ryegrass mulch. The ryegrass was unaffected by a doubling of

pak choi density. Lowering ryegrass density reduced its

resource use but the effect was variable across growing

seasons. The authors concluded that lowering mulch density

was an undependable control of mulch interference. These

findings are obviously species specific. There may be cash

crops that are highly competitive with mulches. In this case,

increasing cash crop populations may prove to be an important

tool. The use of lower mulch density, however, runs the risk

of allowing weed invasion. Rather than lowering mulch seeding

rates, the grower can control the overall mulch population by

widening the cultivated clean soil strip while maintaining a

local mulch density competitive with weeds.

The use of double cash crop rows with double wide mulch

strips may maintain or increase yields (Loy et al., 1987;

Grubinger and Minotti, 1990). This reduces the complexity of

the field and simplifies field operations in general.


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Specifically, it provides access to the mulch for maintenance.

Delayed Planting of Mulch to Reduce Competition

Competition from the mulch can easily be reduced by

delaying the mulch planting date (Vrabel et al., ____; Regnier

and Stoller, ____). But the cost of waiting will likely be

reduced weed control, lower mulch biomass productivity and

exposure to erosion. The strategy is limited to annual

mulches and perennials in the establishment year. If annual

mulches are shown to improve watershed quality significantly,

the cost of establishment may be partially borne by the

surrounding community. Jurchak (1984) reported strong

commercial grower participation in a government seed cost

share program for planting annual ryegrass into established

tomatoes. Coolman and Hoyt (1993) conceptualalized a system

of relay intercropping summer annual legumes into a nearly

mature crop of broccoli. While this approach reduces

competition with the cash crop, it minimizes the potential

benefits of weed suppression and nitrogen fixation by the

mulch. In addition, use of an annual living mulch increases

the cost of establishment when compared to a perennial mulch.

Another way to get around the cost of establishing an

annual is to allow it to seed itself. The use of subterranean

clover (Trifolium subterraneum L.) or "subclover" is a

dramatic example of this. Subclover is a mediteranean winter

annual that germinates and grows in late summer, goes dormant

through winter, and resumes growth to set seed in spring. The


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seeds lay dormant through mid-summer, leaving a window of

minimal interference for cash crop production. The seeds are

deposited in the surface soil by a downward extending peduncle

(Ilnicki and Vitolo, 1986). Because of this efficient

deposition of seed, subclover has the potential to persist

beyond the establishment year. Extensive weed free stands do

persist in southern and western Australia under grazing

pressure (Lanini et al., 1989).

Several studies have shown subclover to be a weed

suppressive living mulch (Enache et al., 1988; Beste and

Teasdale, 1991; Lanini et al., 1989; Waters and Ilnicki,

____). But, because the cash crop is planted into a vigorous

mulch stand in the spring, a combination of planting strips

and mowing or herbicides is needed to suppress the mulch.

Partial Cultivation as a Mulch Suppressant

Partial or "trashy" cultivation for supression of a white

clover living mulch in sweet corn was investigated by

Grubinger and Minotti (1990). The entire mulch strip was

rototilled, allowing a narrow strip of undisturbed clover

roots to pass between the tiller tines. Mulch stoloniferous

regrowth was extensive but recovery two months after

rototilling was still significantly less vigorous than mowed

or unsuppressed clover. Rototilled clover recovered

completely by the following spring.

A major advantage to partial cultivation appears to be an

appreciable transfer of nitrigen from the clover to the cash


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crop. Grubinger measured 56 kg N/ha incorporated into the

soil in clover residue from the combination of creation of a

planting strip and later partial cultivation. Because most of

the clover was dessicated by cultivation, roots and nodules

probably provided a significant release of nitrogen. Partial

cultivation not only released a large portion of the clover

nitrogen, but the extensive suppression of the living mulch

reduced its ability to compete for nitrogen.

Literature Cited

Akobundu, I.O. 1980. Live mulch: a new approach to weed controland crop production in the tropics. Proceedings 1980 British CropProtection Conference pp. 377-382.

Akobundu, I.O. 1982. Live mulch crop production in the tropics.World Crops 34:125-126 and 144-145.

Akobundu, I.O. 1984. Advances in live mulch crop production inthe tropics. Proc. West. Soc. Weed Sci. pp. 51-57.

Alteiri, M., D.L. Glaser, and L.C. Schmidt. 1990.Diversification of agroecosystems for insect pest regulation:experiments with collards. In S.R. Gliessman (ed.) Agroecology.74-76. Springer-Verlag, N.Y.

Allison, L. E. 1960. Wet-combustion apparatus and procedure fororganic and inorganic carbon in soil. Soil Sci. Soc. Am. Proc.24:36-40.

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Berkowitz, A.R., H.C. Wein and B.F. Chabot. 1986. Competitionfor water between beans and interplanted perennial grass cover


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Beste, C.E., and J.R. Teasdale. 1991. Subterranean clover andvetch mulches for zucchini squash and sweet corn. Proc. NortheastWeed Sci. Soc. 45:110.

Box, J.E., S.R. Wilkinson, R.N. Dawson, and J. Kozachyn. 1990.Soil water effects on no-till corn production in strip andcompletely killed mulches. Agron. J. 72:797-802.

Butler, J.D. 1986. Grass interplanting in horticulture croppingsystems. HortScience 21:394-397.

Clark B. 1994. Organic advantage: researchers are finding thatcover crop mulches have even more cultural advantages overplastic. Am. Veg. Grower. 42:14-19.

Coolman, R.M. and G.D. Hoyt. 1993. Increasing sustainability byintercropping. HortTechnology 3:309-312.

Costello, M.J. and M.A. Altieri. 1994. Living mulches suppressaphids in broccoli. Calif. Agric. 48(4):24-28.

De Haan, R.L., et.al. 1994. Simulation of spring-seeded smotherplants for weed control in corn. Weed Science. 42:35-43.

DeGregorio, R.E. and R.A. Ashley. 1986. Screening livingmulches/cover crops for no-till snap beans. Proc. Northeast WeedSci. Soc. 40:87-91.

Echtenkamp, G.W. and R.S. Moomaw. 1989. No-till corn productionin a living mulch system. Weed Tech. 3:261-266.

Elkins, D.M., J.W. Vandeventer, G. Kapusta, and M.R. Anderson.1979. No-tillage maise production in chemically suppressed grasssod. Agron. J. 71:101-105.

Elkins, D.M., D. Frederking, R. Marashi, and B. McVay. 1983.Living mulch for no-till corn and soybeans. J. Soil and WaterCons.38(5):431-433.

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