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Nitrates in the environment and leaching losses to groundwater are influenced by many factors, including cropping patterns, rate of applied nitrogen, tillage and irrigation practices. To reduce the potential for nitrate pollution, certain areas of the Midwest are basing nitrogen recommendations for corn on residual soil nitrate (RSN) testing.
The most popular cropping pattern is a corn and soybean rotation, but soybean residue, even under no-till conditions, decomposes rapidly resulting in the potential for significant soil loss under heavy winter and early spring rainfall conditions.
As a result, there’s interest in seeding a winter cover crop of rye into the soybean residue to increase surface residues and reduce the potential for erosion losses. This can also be a source of mineralized nitrogen for the next year’s corn crop.
University of Nebraska researchers conducted a 4-year irrigated study with the objective of comparing residual soil nitrate (RSN) accumulation in a continuous corn vs. corn and soybean rotation. This was done with and without tillage, and with and without a winter rye cover crop after soybeans. Even though the rye cover crop tied up a significant portion of the nitrate nitrogen as determined by the RSN samples, much of this nitrogen was later available to the corn crop through mineralization.
The researchers recommended that some nitrogen credit be given to the rye cover crop, reducing the recommended nitrogen fertilizer rate for the subsequent corn crop and reducing the potential for nitrate leaching under…