Winter Rye Cover Crop with Liquid Manure Injection Reduces Spring Soil Nitrate but Not Maize Yield

In maize-based cropping systems, leaching of nitrate-nitrogen (NO3-N) to drainage tile and groundwater is a significant problem. The purpose of this study was to assess whether a winter rye cover crop planted after silage maize or soybean harvest and injected with liquid manure could decrease soil NO3-N without reducing the yield of the following maize crop. An experiment was conducted at 19 sites with predominant occurrence of Mollisols (15 out of 19 sites) in the upper Midwest USA immediately after soybean or maize silage harvest to compare a drilled rye cover crop and a non-cover crop control. Later in the fall, liquid swine or dairy manure was injected into the cover crop and control plots. Rye was terminated the following spring using herbicide, usually before reaching 20 to 25 cm in height, and incorporated with tillage at most sites, after which maize was planted and harvested as silage or grain. Across sites, soil NO3-N at rye termination was reduced by 36% (range = 4% to 67%) with rye compared to no rye. Nitrogen in aboveground rye biomass at termination ranged from 5 to 114 kg N ha−1 (mean = 51 kg N ha−1). Across sites, there was no significant difference in yield of maize silage or grain between treatments. These results demonstrate in a Mollisol-dominated region the potential of a winter rye cover crop planted before manure application to effectively reduce soil NO3-N without impacting yield of the following maize crop, thereby reducing risk of negative environmental impacts.