Legumes are the pods, or fruits, of the flowering plants of the pea family. There are more than 18,000 varieties of legumes. Some well-known legumes include beans, clover, peas, peanuts, and soybeans. Legumes are an important source of food for people and animals because they are high in protein. Where legumes growLegumes can be found all over the world, though most types occur naturally in warm or tropical parts of the world. Most of the legumes that are sold as crops are grown in temperate (mild) climates. Physical featuresLegumes grow in many forms ranging from herbs and vines to shrubs and large, woody trees. Most have soft green stems and flowers with five petals that later grow into pods. Pods are the part of the plant that contains the seeds. The pods exist in a variety of shapes, sizes, and textures. Nitrogen fixationLegumes play a useful environmental role because they participate in a process known as nitrogen fixation. Through this process, nitrogen, which is abundant in the air but in a form that most organisms cannot use, is converted to a form that can be used. Nitrogen is important to all living things. Therefore the process that makes it available is important as well. Most plants get their nitrogen from the soil, but legumes actually take it from the atmosphere with the help of special bacteria in the soil. The bacteria enter the root system of the legume. They take atmospheric nitrogen from the air in the soil and turn it into ammonia, which is a nitrogen compound. Both the bacteria and the legume then convert the ammonia to nutrients that are essential for their growth. In this way, the bacteria and the legume both benefit from their relationship. When legume plants are plowed into the soil after their seeds have been harvested, they release the nitrogen they made into the soil. This makes the nitrogen available to other plants, which then take it up through their roots. The animals that eat the plants benefit as well because they obtain the nitrogen they need from the plants. Types of legumesCertain species of legumes are widely used as food for humans and farm animals. Although there are many types of legumes, however, fewer than 20 are considered important in world agriculture. Some of the most important are soybeans, peanuts, beans, clover, and alfalfa. SoybeansSoybeans are nutritious and easily digestible. They are also one of the richest and cheapest sources of protein. In fact, the protein content of soybeans is twice as high as that of meat. Soybeans are used mainly to feed livestock, while soybean oil is used to make such products as ice cream, salad dressing, soap, and explosives. The United States is the world's largest producer of soybeans today. The other major soybean-producing regions are located in Brazil, Argentina, and China. PeanutsPeanuts are grown in the warm temperate or subtropical areas of Africa, Asia, and Indonesia. Peanuts are high in protein, fatty oils, and calories. In contrast to soybeans, which are used mostly as animal feed, humans eat peanuts directly or in the form of butter, and oil. Beans and peasBeans and peas are the staple diet of many people because of their high nutritional value. They are rich in proteins and vitamins and also easy to cook. Both are best grown in cool, mild areas. CloverRed clover and white clover are two of the most common legumes used to add nitrogen to the soil for other crops. They are first grown on fields and then plowed into the soil as fertilizer. This method is commonly called green manuring. Both these varieties of clover are also used as grazing crops and hay for feeding livestock. AlfalfaAlso called lucerne, alfalfa is the oldest known plant used as livestock feed. It is fed to animals in the form of hay, silage (freshly cut alfalfa plants), and meal. It has been grown as a crop in the Middle East since 1000 BC. Today, it is widely grown all over the Western Hemisphere, Europe, and Australia. Harmful legumesKudzu, a tropical vine legume, was introduced into the southern United States to enrich worn-out land and to protect against erosion. It soon became unpopular, however, because it grows so fast over trees and shrubs that it kills them by cutting off all sunlight. Locoweeds grow in the prairies of the western United States and are poisonous to grazing livestock. |