Evaluating Cover Crop Mixtures as Precision Nitrogen Management Tools

Nitrogen fertilization is often necessary to reach the full productivity potential of cereal crops, but surplus N fertilizer can lead to environmental harm and economic losses. In crop fields that vary in topography and soil type, uniform N fertilizer applications often result in zones of N deficiency and surplus. Meeting crop demands for N while minimizing losses within heterogeneous fields will require improved synchrony of N supply and crop demand over space and time. Complementing ongoing efforts to apply variable rate technologies to meet this need, this proposal will evaluate an agroecological approach – grass/legume cover crop mixtures – to advance precision N management by reducing variation in N fertilizer needs while improving soil health. Our objectives are to: 1) determine how grass/legume cover crop mixtures interact with topographic position and weather to impact crop yield and N fertilizer needs, and 2) determine the effects of cover crop mixture use on soil organic matter (SOM) in heterogeneous crop fields. Using an existing field experiment with three landscape positions, three winter covers, and four N fertilizer rates, we will measure and model the impact of a grass/legume cover crop on spatial and temporal variation in soil N supply, crop yield, and the optimum N fertilizer rate. We will also test the effects of cover crop composition and initial SOM level on the formation of new SOM using 13C tracing. Our project will substantially increase cropping system productivity, profitability, resilience, and soil health, aligning with goals of the USDA A1102 program area.