Professional Development Program






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Unit 2: Applying Ecological Principles

Cover Crops

Cover crops are a key practice in many agricultural ecosystems. Farmers and ranchers across the U.S. use them in a variety of settings: vegetable and field crop farms, orchards, vineyards, and pasture-based livestock operations. They can boost profits the first year they are planted, and can improve the bottom line even more over the years as their soil-improving effects accumulate. Some of the ecological and economic benefits for cover crops are listed below. Click on each item to learn more.
Cover crop benefits:

Cut fertilizer costs.

Cover crops reduce fertilizer costs by contributing nitrogen to cash crops and by scavenging and mining soil nutrients. Red clover companion-seeded with oats and hairy vetch, for example, had an estimated fertilizer replacement value of 65 to 103 lb. nitrogen per acre in a four-year study in Wisconsin. In another study in the Pacific Northwest, Austrian winter peas, hairy vetch and NITRO alfalfa provided 80 to 100 percent of a subsequent potato crop’s nitrogen requirement.

Reduce the need for herbicides and other pesticides.

Cover crops can suppress weeds and reduce damage by diseases and insects through a variety of mechanisms. Depending on the species, cover crops have been shown to:

  • outcompete weeds for water, nutrients, and space.
  • block light and alter the frequency of light waves that affect soil temperature.
  • produce compounds that provide natural herbicidal effects.
  • create an inhospitable environment for many soilborne diseases.
  • encourage beneficial insect predators and parasitoids.
  • produce compounds that reduce nematode pest populations.

Improve yields by enhancing soil health.

Cover crops can enhance soil quality by improving infiltration of excess water, relieving compaction, improving the structure of overtilled soil, adding organic matter that encourages beneficial soil microbial life and enhancing nutrient cycling.

Prevent soil erosion.

Cover crops hold soil in place, reduce crusting and protect against erosion due to wind and rain. The aboveground portion of cover crops also helps protect soil from the impact of raindrops.

Conserve soil moisture.

Residue from mown or killed cover crops increases water infiltration and reduces evaporation. Lightly incorporated cover crops serve dual roles: they trap surface water and add organic matter to increase infiltration to the root zone. Proper timing of cutting and/or tilling the cover crop can reduce possible negative impacts of the residue holding too much moisture for planting in wet years, or living cover crop plants drawing too much soil moisture in dry years.

Protect water quality.

By slowing erosion and runoff, cover crops reduce nonpoint source pollution caused by sediments, nutrients and agricultural chemicals. By taking up excess soil nitrogen, cover crops can prevent N leaching to groundwater.

There is a cover crop to fit just about every farming situation. Go to the next page to learn about some of the principles for selecting cover crops and to see some examples of how cover crops are being used.
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