Evaluation of a Winter Cereal Rye Cover Crop at Ten Sites Across the US Cornbelt.

A winter cereal rye (Secale cereale L.) cover crop was grown over a 5-yr period on corn-soybean plots at 10 sites across the US Cornbelt, as part of the Corn Systems and Climate Coordinated Agricultural Project.  Cover crop biomass measured in the spring prior to termination varied from 100 to 3000 kg ha^-1, depending on location and year.  Total N in the above-ground biomass prior to termination varied between about 2 to 80 kg ha^-1, reflecting the vastly different amounts of biomass.  Soil nitrate in the spring prior to cover crop termination was consistently lower in the cover crop plots than in the no-cover controls due to uptake of N by the cereal rye biomass.  Soil nitrate in the fall was sometimes lower in the cover crop plots, even though most sites were sampled before cover crop seeding or appreciable growth, suggesting some residual effect of the cover crop even six months after termination.  Soybean yields were unaffected by cover crop growth, regardless of the lag time between termination and planting, suggesting that soybeans may be safely planted immediately after termination or at longer times after termination, as desired.  Corn yields had several site-years with lower yields in the cover crop plots than in the no-cover controls, but overall yields were similar.  Yields were affected more when the temperatures were colder and when there was a shorter time lag between termination and corn planting, consistent with concepts of alleleopathy.  Recommendations for management strategies are discussed.