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 thats 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 plants 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 worlds 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 plants
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 Agricultures chief scientific