Winter Cover Crops Impact on the Distribution of Soil Inorganic Nitrogen and Subsequent Crop Uptake and Yield Following Fall Applied Anhydrous Ammonium.

The coupling of cover crops with spring application of nitrogen (N) has shown improved nitrogen use efficiency, while maintaining crop yields. However, studies have shown that only 50% of central and northern Illinois producers employ spring nitrogen applications. Therefore, the objectives of this research were to determine the efficacy of winter cover crops to impact the distribution of soil inorganic N following fall applied anhydrous ammonium, and evaluate the influence of cover crop integration and fall nitrogen application rates on crop nutrient uptake and yield. The experimental site was located at the Illinois State University Research farm in Lexington, IL. The treatments consisted of a control and two cover crop treatments, daikon radish and cereal rye. Each treatment was further divided into three nitrogen rates 200, 145 and 90 kg N ha^-1 that were applied in the form of anhydrous ammonia. Over a four year period, winter cover crops reduced nitrate leaching and stabilized a greater concentration of soil NO₃-N in the agronomic depths of soil, relative to the control. Within the environmental depth of 20-80cm, fall applying N into a living cover crop stand resulted in 35% (Cereal Rye) and 22% (Daikon Radish) less soil NO₃-N when compared to the control. The 2014 corn yield ranged from 12,489.9-13,712.4 kg ha^-1. The results demonstrate that both the cereal rye and daikon radish treatments yielded significantly higher than the control despite the application rate (90 kg ha^-1 vs. 200 kg ha^-1). Thus, the results of this study suggest that cover crop inclusion into a fall applied system has the potential to advance nitrogen use efficiency, yield and profitability.