Plant cover crops in fall to protect, improve soil

Will Hehemann School of Agriculture, Fisheries and Human Sciences

winter-wheat-photo

Cover crops such as winter wheat add organic matter to a garden’s soil. (University of Arkansas Division of Agriculture photo by Mary Hightower)

As farmers finish harvesting their summer crops, they should consider planting cover crops to revitalize their soil’s nutrient content, Shaun Francis, Extension horticulture specialist for the University of Arkansas at Pine Bluff, said. When seeded in the fall and grown throughout the winter, crops such as grains, grasses or legumes can help ensure healthy, productive soil for the next growing season.

“Cover crops are not grown for harvest, but rather to protect and improve soils,” he said. “They are commonly referred to as ‘green manure’ because at the end of their growing cycle, cover crops should be terminated and tilled back into the soil, where nutrients are released as the plants decay.”

A fall cover crop helps protect against water and wind erosion over the winter, Francis said. During periods of rainfall, the broad leaves of some cover crops intercept raindrops, lessening their impact on soil particles and reducing nutrient runoff. Additionally, the root systems of cover crops help stabilize surface soil during heavy winds.

Cover crops tend to scavenge or trap any nutrients left in the soil that could otherwise be leached out into drainage water. Not only does this ensure nutrient availability for crops, but it also protects local water quality by preventing nutrients from entering the groundwater.

“When tilled into the garden soil and left to decompose, cover crops produce compounds that cement soil components together into aggregates, clumps of soil particles held together by organic matter,” he said. “This results in improved soil structure and the ability for the soil to eventually produce crops.”

Francis said cover crops also contribute to soil fertility and potential for crop production by building up nitrogen in the soil. Legumes, when used as cover crops, acquire and fix atmospheric nitrogen for their own growth. Once the plants die, the legume residue breaks down and releases much of the nitrogen into the soil for later use by spring crops.

“Planting cover crops is also a good form of weed control,” he said. “Cover crops rapidly establish themselves when planted and smother existing weeds. When terminated in the spring, cover crops leave behind residue that acts as a physical barrier that helps suppress weed seed germination. Some cover crops also prevent weeds by competing with them for light, moisture, nutrients and space.”

Cover crops can be planted as a single species or in mixtures. However, before farmers choose which cover crops to plant, they should first consider their overall goal.

“Different cover crops serve different purposes and producers should consider their main objective,” Francis said. “Some crops can be planted to add nitrogen or organic matter to the soil, while others are better at reducing erosion. While all cover crops provide many benefits, some species or mixtures of species are better suited depending on the objective.”

To prevent soil erosion, plant cereal or winter rye, oats or cowpeas. Cereal rye and winter wheat are good cover crops for adding organic matter to the soil. Legumes such as Austrian winter peas, crimson clover and hairy vetch are good providers of nitrogen.

Because of their ability to cover the soil quickly, buckwheat, oats and cereal rye are good cover crops to use for suppressing weeds. Brassica plants such as mustard are known for their pest control properties, as they release chemical compounds that may be toxic to soil-borne pathogens and pests such as nematodes and fungi.

Francis said the most common cover crop mixtures of cover crops include a legume plus a grass or cereal grain, which will provide physical support for the climbing legume.

Farmers can plant cover crops immediately after harvesting the primary crops from their garden, he said. Planting should be done early enough to allow four weeks of growth before the cold weather sets in. Tilling the garden before planting cover crops can help ensure the preparation of a seedbed and aid in weed and insect control.

Plant large seeded cover crops such as peas, hairy vetch, wheat and oats at a depth of 1 to 1.5 inches in closely spaced furrows, Francis said. Small seeded cover crops such as rye grass and buckwheat can be broadcast and covered with a light raking, placing the seeds at a depth of about 0.25 inches. Dry soil should be irrigated often enough to provide the moisture needed for germination to occur.

Cover crops need to be terminated in order for spring and summer crops to reap the benefits of the healthy soil they leave behind, he said. Some cover crops such as oats and oilseed radish are terminated naturally by cold weather. Other varieties should be killed through tillage, mowing or herbicide applications. For guidelines on herbicide applications, farmers should contact their county Extension agent.

“When managed correctly, cover crops can help protect Arkansas gardens from the elements during the winter and replenish the soil’s nutrients for a productive spring,” Francis said.

For more information on planting cover crops, contact Shaun Francis at (870) 575-7224 or franciss@uapb.edu.

The Arkansas Cooperative Extension Program offers its programs to all eligible persons regardless of race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.

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