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, according to new research from USDA's Agricultural Research Service.
Longer-term rotations also were more profitable than continuous corn production.
According to soil scientist Douglas Karlen, the study shows the need to create new markets and uses for forage crops so producers 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.
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.