Soybeans being cultivated for weed control. Click the image for more information about it.

Grain-Forage Crop Rotations Seen Boosting Soil Quality

By Luis Pons
April 14, 2006

Farmers looking to maintain soil quality may want to get back to planting extended rotations of grain and forage crops. So indicates an Agricultural Research Service (ARS)-led study released today.

The study—headed by soil scientist Douglas Karlen of ARS' National Soil Tilth Laboratory in Ames, Iowa—found that crop rotations covering a minimum of five years, including at least three years of forage crops interspersed with corn and soybean, resulted in higher soil-quality ratings than either continuous corn or a two-year corn-soybean sequence.

The longer-term rotations also had an additional benefit: They were more profitable than continuous corn production.

ARS is the U.S. Department of Agriculture's (USDA's) chief scientific research agency.

Collaborators in the study included scientists with the Soil Quality Team of USDA's Natural Resources Conservation Service and Iowa State University.

According to Karlen, the study shows the need to create new markets and new uses for forage crops so that producers will have financial incentives to diversify their crop rotations.

Larger farm size, specialization, and separation of agricultural crop and animal enterprises—along with pressure to maximize short-term profit throughout the nation's corn and soybean belt—have decreased implementation of long-term crop rotations over the past 50 years. The result, according to Karlen, has been crop rotations that leave land bare for nearly six months each year, spurring organic-matter decomposition and erosion if the soils are tilled.

The researchers collected soil samples from three long-term crop rotation studies and one long-term organic study in Iowa and Wisconsin. They analyzed the samples for several physical, chemical and biological soil-quality indicators that were then used to develop an overall soil-quality index (SQI).

Soil samples from extended rotations that included at least three years of forage crops such as alfalfa or oats scored the highest SQI values. The lowest SQI values were associated with continuous corn.

This study will appear in the May/June 2006 issue of Agronomy Journal. It is scheduled to be posted on the journal's website today at http://agron.scijournals.org/.