Right behind cereals, legumes are the second most important source of human food and animal forage. It is through nitrogen fixation that legumes provide plant tissue that is high in protein. In agricultural practice, legumes are used as an organic way to amend the soil and reduce crop nutrient deficiency. Mankind has known for millenniums of the importance of legumes environmentally.
Legumes are able to provide the benefits of nitrogen fixation thanks to a strain of soil bacteria. Rhizobia bacteria penetrate the legumes' roots, creating pink nodules that bind nitrogen gas found naturally in the atmosphere. This fixation provides a usable source of nitrogen to the legumes in return for carbohydrates needed by the bacteria. This mutual interaction between the two species is known as a symbiotic relationship.
Incorporating legumes into the diet is a healthy, inexpensive way of supplying required nutrients to the body. Naturally low in fat, with no cholesterol, legumes are nutrient dense compared to their calorie ratio. Legumes are great sources of iron, potassium, selenium, magnesium, zinc, B vitamins and fiber. They are also the primary source of protein in vegetarian diets and in a number of traditional cultural diets.
Legumes used as a green crop, or cover crop, provide many benefits to the soil. According to the USDA, legumes improve soil quality by increasing soil organic matter, improving soil porosity and structure, recycling nutrients, decreasing soil pH, diversifying microorganisms and alleviating disease problems. Planting legumes as a cover crop also helps reduce soil erosion.
Planting legumes with other forage crops helps improve nitrogen availability to companion crops. The USDA states that in legume and perennial grass mixtures, legumes not only supply their own nitrogen but also supply approximately 36 percent of the nitrogen needs of the grass crop growing alongside them. Another advantage to using legumes as a cover crop is their function as a non-chemical weed control for crop fields and pastures.
Depending on the use, there are over 16,000 different species of legumes to choose from. To name a few, forage legumes include beans, peas, peanuts, soybeans, clovers, birdsfoot trefoil and alfalfa. For human consumption, garbanzo beans, lima beans, black beans, kidney beans, navy beans, pinto beans, black-eyed peas, split peas and brown, red or green lentils are all nutrient-packed legumes.