Cover Cropping

Cover Crop Benefits

Many annual cash crops in temperate regions are planted in the spring and harvested in the fall, leaving the soil bare, and thus open to the erosional forces of wind and water for several months each year. Quick-growing cover crops, particularly cereals such as barley, oats, rye, and winter wheat, as well as mustards, can take advantage of fall weather and put on substantial biomass to minimize soil loss caused by wind and rain. These crops can also take up—or immobilize—nutrients, such as nitrate, that are susceptible to loss down through the soil. This maintains the nutrients in the rooting zone so they are accessible to the following cash crop and reduces the input of nutrients to groundwater or surface water, the latter of which can lead to toxic algal blooms or anoxic zones. Reduced leaching by such cover crops, also known as “catch crops,” has helped improve water quality in locations such as Chesapeake Bay. Cover crops can also protect against soil and nutrient loss in perennial agroecosystems, such as orchards and vineyards, where they are planted between the rows.

In addition to maintaining soil nutrients, cover crops can add nitrogen to the soil. Legume cover crops, such as clovers, cowpeas, fava beans, field peas, and vetches, host bacteria that convert atmospheric nitrogen into forms used by the plant. When the crop is mowed, rolled, or undercut and incorporated, soil microbes mineralize the organic nitrogen, making it available for the following cash crop. These nitrogen-fixing legumes, also known as “green manures,” are particularly important to organic or other low-input agroecosystems, in which fertilizer derived from the Haber-Bosch process is not or only minimally used. Legume [Page 109]cover crops are also recommended by some researchers as a strategy for developing agricultural sufficiencies in sub-Saharan Africa and other food-insecure regions.

A relatively new use of cover crops is “biodrilling,” particularly in systems with reduced tillage. Fall-planted cover crops form root channels in soft, wet soil. Without cultivation, these root channels, some as small as 1 millimeter in diameter, remain and allow the cash crop to penetrate compacted zones and reach deep soil moisture that would otherwise be inaccessible. This can help reduce water stress in the summer.

Cover crops can also provide pest control in agroecosystems, depending on both the pest species and cover crop species present. Cover crops may compete with weeds for resources or suppress their growth through allelopathic chemicals. They may also provide a “biofumigation” function, reducing populations of plant parasitic nematodes or the incidences of diseases (e.g., club root or Verticillium wilt) or pathogens (e.g., pea root rot). Cover crops may also indirectly control pest species, such as by providing favorable habitat that maintains or increases populations of beneficial nematodes or beneficial insect predators and parasitoids.

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