Plants that belong to the legume family (Leguminosae) have pods in which beans grow. Legumes absorb nitrogen from the air. Many crops that are unable to do this are dependent on the nitrogen that is present in the soil. Most soils in tropical areas do not contain sufficient nitrogen, an important nutrient. For this reason growing legumes (in addition to other staple crops such as potatoes, maize and rice) is a good way for farmers in tropical areas to enrich the soil. The legume crops also provide extra food for the daily diet of both humans and animals. Legumes must never be eaten raw. Nevertheless, they have so many advantages that it is worthwhile growing and processing them. Soya beans are a legume that is very rich in nutrients and there are a number of products that can only be made from soya. Soya beans and soya products can also be sold and can therefore be a source of extra income.