Abstract
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.