The legumes or bean family (Fabaceae or Leguminosae) contains over 16,000 plants. Each plant bears its seeds within a structure known as a pod. All legume species have compound leaves that sport several leaflets per stem. The legume family has the unique ability to form a symbiotic relationship with bacteria, enabling the two to fix nitrogen within the soil, which renders the surrounding area nutrient-rich. This aids in the growth of the legumes and also surrounding plant life.
Legumes have a long history that dates as far back as 5,000 years ago, when farmers in ancient China cultivated the soybean, which they considered to be one of five sacred grains. Ancient Rome and Greece used alfalfa to feed their horses. In the United States, Thomas Jefferson introduced the idea of using red clover to replenish crop fields exhausted by overplanting of tobacco and cotton.
Rich in protein and with valuable amino acid compositions, legumes are a valuable livestock forage. Only grass forage holds more importance in human and animal consumption, according to the University of Minnesota. A common practice is to mix a field with perennial grasses and legumes to offer an ideal livestock forage. In the central United States, legumes are widely fed as a forage to cattle and sheep.
Legumes help enrich and build soil by providing nutrients. The plants also aid in water filtration within the soil. They add valuable organic compost to the surrounding area. Earthworms thrive in areas planted with legumes, due to the abundant organic compost. The added population of earthworms within the soil helps to aerate the entire area while enriching the soil with worm droppings.
Legume varieties grow as annuals, biennials and perennials. Most perennial legumes, such as alfalfa, grow abundantly for three or more years without needing to be replanted. During their life cycle, they set seed each season, which helps replenishes the field with ongoing new plants. Biennial legumes place all their energy into growing the first year; the second year they set seed before dying. Annual legumes grow, flower, set seed and die within a single season.
A symbiotic relationship exists between legumes and the Rhizobia bacteria. A legume's root system gives the bacteria all the nutrients that they requires for life, and in exchange the bacteria supplies a continuous supply of nitrogen to the surrounding soil. The bacteria live within most soil and quickly attach to the plant's root system. Innoculated legume seeds can be purchased and are beneficial in areas deficient in Rhizobia bacteria.