Integrating canopy sensing and soil nitrogen for improved corn nitrogen management

Active canopy sensing may improve corn (Zea mays L.) nitrogen (N) management, but little has been done to evaluate soil N content to improve the utility of sensors. This study investigated the usefulness of integrating canopy sensing tools and soil N content to estimate grain yield and N requirement at various corn development stages. Six to seven N rates at 35–45 kg urea-N ha^–1 increments were pre-plant applied in 12 sites throughout Minnesota. Canopy-sensing measurements were obtained at the V4, V8, V12, and R1 stages. Soil (0–30 and 0–60 cm) NH₄–N and NO₃–N concentrations were measured at the V4, V8, and V12 stages. Adjusting sensor measurements with soil NO₃–N (0–30 cm) measured at the V4 stage provided the best trade-off between gains in prediction accuracy and practicality for soil sampling. At the V4 stage, predictions of N requirement with soil N alone (RMSE = 41.3 kg N ha^–1) and soil-N–adjusted sensor measurements (RMSE ranging from 39.6 to 42.7 kg N ha^–1) were similar but better than predictions with unadjusted sensor measurements (RMSE ranging from 61.0 to 72.9 kg N ha^–1). Although the utility of canopy sensing without soil-N adjustments improved at later development stages, the most accurate predictions of N requirement were obtained with soil-N–adjusted sensor measurements collected at V8 and V12 (RMSE as low as 32.5 kg N ha^–1). Our study shows that early-season canopy sensing (up to V8) coupled with soil N measurements may be a viable alternative to improve in-season N management.