Legumes such as peanuts, beans and lentils serve as a food source, adding protein to the human diet in times when meat is unavailable or not eaten. Aside from human diet enhancement, legumes offer advantages to animals, birds and insects as well as the environment. In agriculture, legumes used as cover crops enable farmers to improve soil quality, reduce chemical usage and protect water availability.
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Soil Quality Improvement
Farmers have discovered that by growing legumes as cover crops during winter months, they can increase the amount of nitrogen in the soil. Certain legumes planted each winter can “fix 100 to 200 pounds of nitrogen per acre,” according to the University of California Cooperative Extension article, “Selecting the Right Cover Crop Gives Multiple Benefits.” Using legumes aids soil quality, since most non-legume crops such as grass can deplete the soil of its nitrogen. Even summer crop legumes such as cowpeas add nitrogen to the soil. Though legumes take up nitrogen, they also return nitrogen when they decompose.
Chemical Usage Reduction
As cover crops, legumes compete with weeds and bring in beneficial insects, which reduces the need to use herbicides and pesticides on crops. For example, strawberry clover, vetches and cowpeas can suppress weeds. Some legumes attract specific pests. Pea and blue alfalfa aphids appear in crimson clover, but when crimson clover serves as ground cover for pecan orchards, those pests do not harm the pecan crop. In fact, crimson clover pests “serve as alternative food sources for beneficial predators such as lady beetles, green lacewings, soldier beetles, predaceous stink bugs, damsel bugs, and hover flies,” writes Lenny Wells, University of Georgia Cooperative Extension specialist, in the article “Benefits & Use of Legumes in Pecan Orchards.” Then, once the clover dies or stops thriving, the beneficial insects feed on pecan tree pests.
Cover crop legumes need water just as cash crops do to thrive, but some legumes use less water and actually serve as mulch. This living mulch prevents the evaporated loss of water and water runoff by providing structure in the soil. Legumes like cowpeas and hyacinth beans can tolerate drought conditions more readily, meaning farmers do not have to irrigate them as often. Also, using legumes as buffers around water sources helps prevent pollution from agriculture and other runoff into these sources.