mulching and cover crops for soil protection, weed suppression and nutrient management

KC Permaculture Extension Bulletin # M110 March 2016 Author: Steve Mann

Mulching and cover crops for soil protection, weed suppression and nutrient management.

Each spring gardeners get the itch to get out and till the garden. The heady odor of fresh tilled

soil brings a special satisfaction to many. But maybe it not the best practice if we are seeking a

sustainable agricultural system.

By tilling the soil either by means of a moldboard plow, rototilling or heavy disking we are

increasing the soil erosion rates and speeding up soil organic matter decomposition. Soil

aggregates are broken down and the biotic glues that give soil its structure are oxidized leaving

the soil prone to erosion from wind, water and leaching of nutrients.

The level of organic matter present in the soil is a direct function of how much organic material

is being produced or added to the soil versus the rate of decomposition. For a sustainable

growing system we want to balance the production of organic matter with the decomposition rate

of the plant material on the soil surface. In this way we can provide highly usable plant nutrients

as they are needed without the possible environmental effects of using nitrates. Plowing and

tilling leaves the soil surface bare which makes them susceptible to the erosive forces of wind

and water. Conservation tillage practices reduce erosion by protecting the soil surface and


allowing water to infiltrate instead of running off. Tillage also upsets the soil food web which is

a key component of a sustainable production system.

No-Till /Minimal –Till Gardening:

• Protects the soil surface

• Builds soil organic matter

• Protects soil microorganisms

• Reduces work

• Conserves water

• Minimize soil disruption

• Avoid soil compaction

• Reduces Carbon Emissions

Not till gardening can be accomplished using either applied materials or grown in place as a

living mulch. We will look at applied mulches first.

Mulch

Mulch is a material such as straw, leave, woodchips or compost that covers the soil protecting it

from drying out, suppressing weeds and supplying slow release plant nutrients. Landscape

fabric, paper, and plastic film are also widely used for vegetable production.

Many home gardeners are using either newspaper sheets or ground up newspaper as mulch.

Bleached paper is not recommended because of the possibility of dioxin leaching. When using


newspapers some type of organic mulch material is placed on top of the paper usually 3 or more

inches thick.

Type of Mulch Characteristics

• Peat Moss Weed free, poor nutrients hard to rewet if it dries out

• Pine Needles Weed Free long lasting moderate weed suppression.

• Sawdust Weed Free long lasting, good weed stopper good at conserving moisture Don't use from painted or treated wood

• Wood Chips Weed free moderately long lasting, good weed stopper

• Straw Weed free long lasting, good weed stopper and holding moisture

• Stone Weed free long lasting, good weed smothering, no nutrition, mostly for paths and edges

• Compost Weed Free if properly made, excellent plant food

• Bark/Chips Weed free long lasting, good weed suppression

• Hay Good weed suppression but has weed seeds

• Grass Clippings Usually weed free, don't make thicker than 1 1/2 "- 2" may get too hot, possible chemical contamination.

• Hulls and Shells Rich in nutrients, best at smothering weeds, high nutritional content Cotton burr, rice, peanut hulls.

• Leaves Weed free good at smothering weeds, may blow around, breakdown slowly,


Sheetmulching

Before you start any reduced tillage system it is advisable to have your soil tested. If the soil pH

needs adjusting it is best to do one more tilling to incorporate the recommendations of the testing

laboratory. Once the pH has been adjusted then the growing area can be prepared. Flatten or

mow any existing vegetation then spread 6 cups of 5% nitrogen fertilizer per 100 sq ft.

The easiest way to sheetmulch a garden bed it to use overlapping newspaper making sure there is

a continuous covering of between 4 and 8 pages. Make sure that the newspaper is thoroughly

wetted and then cover with a minimum of 3 inches of mulch materials. The paper mulch must

not be allowed to dry out or its breakdown will stop and its benefits for nutrient management will

be negligible. It’s best to sheetmulch lawn in the fall so earthworms and microorganisms can

slowly breakdown the moist newspaper and dead turf, If you sheetmulch in the spring or summer

you will need to apply thicker mulch and some fertile growing medium for planting small seeds.

You can also cut through the paper and plant transplants in the soil below.

Figure 2. Wet newspaper sheetmulching being laid as a weed and light barrier.


Cover crops

Cover crops are living groundcovers that are planted either into or after harvest of the main crop

usually in the fall. Living mulches are cover crops that can be planted before or with the main

crop. They must be managed to control competition for water and nutrients with the main crop.

Cover crops, also known as green manures, are one of the cornerstones of ecologically sensible

agriculture.

Cover crops provide outstanding benefits for the soil, crop and grower including:

• Increasing organic matter content

• Increasing earthworm and beneficial microorganism activity

• Increasing the soil's plant-available Nitrogen

• Stabilizing the soil to prevent erosion

• Bringing minerals to the surface for other crops

• Providing habitat, nectar & pollen for beneficial insects

• Improving water, root and air penetration in the soil

• Increasing the soil's moisture-holding capacity

• Choking out weeds

• Breaking up subsoil

• Reducing populations of pest organisms

• Providing aesthetic value and color

Cover crops can be integrated into your gardening system to protect the soil and provide these

benefits. Cover crops can be part of a conservation biological control system by providing


habitat and nectar for beneficial organisms such as pollinators, predatory insects and spiders. Use

of cover crops, organic soil management practices and reduced soil disturbance by tillage can

lead to lower pest population densities.

Living mulches

There are a number of growing systems suitable to garden scale vegetable production using

cover crops as living mulches. One that is highly suited for home gardens is innerseeding, the

planting of vegetables in beds of living mulches.

Some innerseeding methods:

• relay cropping, the planting of the vegetable crop after the living mulch is growing.

• Overseeding, planting living mulch into growing main crop before or after harvest.

Figure 3. Subterranean clover, Trifolium subterranean used as a living mulch relay cropped with tomatoes and peppers.


Subterranean clover is a great living mulch for transplants like tomatoes, peppers and eggplants.

It has seed germination suppressing allellopathic properties so keep it away from direct seeded

crops.

common name scientific name

cover crop

living mulch characterisitc

N fixing

White clover Trifolium repens L x x It is shade tolerant, withstands traffic, grows fairly low, and survives repeated mowing

x

Vetch Vicia sp. x nitrogen fixer, organic matter for mulch

x

Subterranean clover

Trifolium subterranean x cool season annual legume with allelopathic properties dies back in summer

x

Forage radish Raphanus sativus x breaks up claypan, provides organic matter, fall crop

Cereal rye Secale cereale L. x cool season grass, provides organic matter, mulch material

Crimson clover Trifolium incarnatum x x cool season nitrogen fixer, x

Figure 4. Some cover crops for home gardeners

Figure 5 Forage (daikon) radish with winter wheat as a cover crop.


With the continuing loss of topsoil and environmental issues associated with fertilizer usage

cover corps, living mulches and various mulching methods can help protect our precious natural

resources making gardening less work and more rewarding.

Some further reading:

Abdul-Baki, A. A., J. R.easdale, R. Korcak D. J. Chitwood, and R.N. Huettel 1996. Fresh-

market tomato production in a low-input alternative system using cover-crop mulch.

HortScience, 31(1): 65-69.

Altieri, M. A. (1999) The ecological role of biodiversity in agroecosystems. Agriculture,

Ecosystems and Environment 74:19–31

Anderson, D. F., Garisto, M. A., Bourrut, J. C., Schonbeck, M. W., Jaye, R., Wurzberger, A., &

DeGregorio, R. 199). Evaluation of a paper mulch made from recycled materials as an

alternative to plastic film mulch for vegetables. Journal of Sustainable Agriculture, 7(1), 39-61.

Hartwig, N. L. and H. U. Ammon 2002. Cover crops and living mulches. Weed Science 50:

688-699

Munn, D. A. 1992. Comparisons of shredded newspaper and wheat straw as crop mulches.

HortTechnology, 2(3):361-366.

Sullivan, P. 2004. SUSTAINABLE SOIL MANAGEMENT. ATTRA National Sustainable

Agriculture Information Service. Available online at

http://www.clemson.edu/sustainableag/IP027_soilmgmt.pdf ; last accessed March 10,2014

http://www.clemson.edu/sustainableag/IP027_soilmgmt.pdf�

mulching and cover crops for soil protection, weed suppression and nutrient management

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