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Agricultural Research Service

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New Alfalfa May be Ideal for Poor Soils

By Don Comis
January 25, 2002

Agricultural Research Service scientists in St. Paul, Minn., have added a gene to alfalfa that not only gives it tolerance to acid soil and aluminum, but also lets it naturally produce more nitrogen to stimulate plant growth.

Aluminum makes up about 7 percent of the earth's crust, but it only causes a problem for plants if they are growing in soil that’s also acidic. When crop roots in acid soils take in aluminum, the aluminum inhibits the roots’ growth, reducing their ability to take up water and nutrients needed by the plant. This reduces the plant’s yields.

The gene added by the ARS scientists causes the alfalfa's roots to produce more organic acids that render the aluminum nontoxic.

About 40 percent of the world’s arable land has acid soil. Some soils are naturally acidic, while others become acid for a variety of reasons, including overuse of certain fertilizers. In the southeastern United States, millions of acres of pasture have acid subsoils that limit the productivity of forages. Lime applications on acid soils are often impractical, and the lime may not reach the acid subsoils where roots grow.

In experiments, the genetically transformed alfalfa grew longer roots in acid soils that contained aluminum, indicating the roots were more aluminum-tolerant. But the transformed alfalfa did not grow as well as standard alfalfa in non-acid soil.

The ARS researchers aim to boost production of alfalfa on the American landscape and provide farmers with a profitable and environmentally friendly crop for rotation that improves the soil and breaks pest and pathogen cycles.

The scientists also found that the added gene increases the plant’s ability to naturally produce nitrogen--process known as “fixing” nitrogen, in which the plant is able to transform atmospheric nitrogen into a form that the plant can use to stimulate growth.

The study was funded by a U.S. Department of Agriculture grant and was a joint effort of ARS and the Minnesota Agricultural Experiment Station. ARS is the U.S. Department of Agriculture’s chief scientific research agency.

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