The idea to grow a crop that improves the land and prepares it for other crops is thousands of years old. But scientists continue to search for new and better ways to use what are called cover crops.

Aref Abdul-Baki is with the Agricultural Research Service of the United States Department of Agriculture. He works at the Sustainable Agricultural Systems Laboratory in Beltsville, Maryland.

Mister Abdul-Baki has found some cover crops that resist worms that attack tomatoes. These crops are sunn hemp, cowpea and velvet bean. They are planted during the months when the main crops are not normally grown. In states with moderate climates like Maryland and Virginia, the winter months are a good time to grow cover crops.

For tomatoes, cover crops can be planted in September. They can be turned over in the soil in May. The same method can be used for other summer crops like peppers, sweet corn, green beans and some melons.

After the cover crop is cut and turned, the result is a layer of organic material. This will provide fertilizer for the new crop. Also, the cover crop provides extra nitrogen to the soil.

Cover crops mixed with soil into mulch prevents the growth of unwanted plants. It also keeps soil from drying out and prevents the loss of soil.

In hot, dry parts of California, cover crops help keep down soil temperatures. They also reduce water loss and erosion.

Mister Abdul-Baki has shown that cover crops can save farmers a lot of money. Tomato farmers, for example, have used methyl bromide to treat their soil before they plant their tomatoes. This chemical kills many kinds of organisms that harm crops. Such treatment can increase the size of the harvest. But the government restricts the use of methyl bromide. And countries have agreed to an international treaty to ban it.

Mister Abdul-Baki has found that farmers who use cover crops with tomatoes save one-thousand-four hundred dollars per hectare. Farmers save on chemicals and also fertilizer. And Mister Abdul-Baki says the farmer produce as many, or more, tomatoes per hectare as compared to no use of cover crops.

Some cover crops provide enough seed for the next growing season. This can reduce costs even more.

This VOA Special English Agriculture Report was written by Mario Ritter. This is Steve Ember.