I'm Steve Ember with the VOA Special English Agriculture Report.

Many different kinds of plants are part of the leguminosae group. They are called legumes. These plants can produce their own nitrogen. Beans are legumes. Peanuts are legumes. Alfalfa is a legume. There are also many different kinds of trees that are legumes.

As a food, beans are high in protein. Most beans also contain a lot of nutrients such as calcium, iron, phosphorus and niacin. Some beans contain amino acids and lysine.

The leaves of bean plants and other legumes also are high in nutrients. They are often fed to farm animals. Some farmers grow legumes especially for their animals. Cows, goats and other animals are permitted to eat the leaves on the plants in the fields.

Many farmers around the world know the value of growing legumes along with their main crops, or between harvests. The legumes replace nitrogen used by crops. They also provide a cover for the soil to help protect it from heavy rains and strong winds.

The roots of the legume plants hold the soil in place. This keeps the soil from being blown away by the wind or washed away by rain. The roots also loosen the soil. This lets the rain reach deep into the ground.

Legumes produce nitrogen through a process involving bacteria in the soil and nitrogen in the air. The bacteria form small growths on the plant roots. These growths are called nodules. They capture the atmospheric nitrogen that has entered the soil.

The nodules change the nitrogen into ammonia, a form of nitrogen that plants can use. The process is called nitrogen fixation. The bacteria needed for the process, rhizobia or frankia, are found in most soils. But if they are not present in the soil in a field, they can be "painted" on the legume seeds before the seeds are put in the ground. A local agriculture agent can show how to do this.

When planted next to fields, legume trees will add nitrogen to the soil. They provide shade and protect young crop plants from the heat of the sun. They provide firewood. And their wood can be used as building material. Some legume trees also provide medicines and chemicals for coloring cloth.

This VOA Special English Agriculture Report was written by Bob Bowen. Read and listen to our reports at voaspecialenglish.com. I'm Steve Ember.