Cover crops between corn and soybeans in the Midwest could significantly cut nitrate load runoff through subsurface drains. This article from the U.S. Department of Agriculture (USDA) says this reduction would support national efforts to reduce nitrate loads and protect water quality in the Gulf of Mexico.
Excess water laden with nitrates in many Midwestern crop fields drains into subsurface perforated pipes and then flows into surface streams and rivers. The nutrient-rich field drainage reaches the Gulf of Mexico and supports algal blooms that lower water oxygen levels and contribute to developing a devastating “dead zone.”
Agricultural Research Service (ARS) scientists Rob Malone, Tom Kaspar, and Dan Jaynes are using the Root Zone Water Quality Model to assess how using winter rye cover crops in corn–soybean rotations could mitigate nitrate loads in the field-drainage water. The researchers are with the ARS National Laboratory for Agriculture and the Environment in Ames, Iowa. The ARS field-scale computer model was developed to simulate plant growth and the movement of water, nutrients and chemicals within and around the root zones of agricultural crops. ARS is USDA’s chief intramural scientific research agency, and this research supports the USDA goal of promoting agricultural sustainability.
The researchers ran the model simulation for several different planting scenarios at 41 sites across the Midwest from 1961 to 2005. Their results indicated that winter rye crops seeded in no-till corn–soybean systems when the cash crops were mature have the potential to reduce annual nitrate loss in field drainage by about 43 percent, or by 18 pounds per acre.
Larger, regional simulations from the Mississippi River Watershed indicated that producers could introduce winter rye cover cropping on around 30 to 80 percent of the land used for corn and soybean production, and that the cover crop systems could potentially reduce nitrate loadings in the Mississippi River by approximately 20 percent.