Citation: Scharf, P.C., Shannon, D.K., Palm, H.L., Sudduth, K.A., Drummond, S.T., Kitchen, N.R., Mueller, L.J., Hubbard, V.C., Oliveira, L.F. 2011. Sensor-based nitrogen applications out-performed producer-chosen rates for corn in on-farm demonstrations. Agronomy Journal. 103(6):1683-1691. Interpretive Summary: With increasing costs for crop inputs, farmers are interested in better methods to help them apply the amount of nitrogen (N) fertilizer that will maximize profit. This is especially true for fertilizer applications in corn, since more N is applied per acre and to more acres with corn than most other crops. Crop reflectance sensors offer the potential to diagnose crop N need, and when integrated with variable-rate N fertilizer application equipment, can control N application rates for relatively small areas of each field. The purpose of this investigation was to evaluate on farmers’ fields the performance of sensor-based variable-rate N application relative to the constant N rate normally used by the farmer. In 55 replicated on-farm demonstrations conducted from 2004 to 2008 we found that crop reflectance sensors increased profit by $17/acre relative to the producer’s N rate. This additional profit was generated by the sensor-based N application giving slightly higher average corn yield and utilizing about 14 lbs/acre less N fertilizer. This represents a 27% reduction in the amount of N applied beyond what was removed in the grain, thus reducing unused N that can move to water or air. The real-world scale of these demonstrations, and the wide range of production environments encountered suggest that these are reasonable estimates of the outcomes corn producers can expect when adopting sensor-based N sidedressing. Our results confirm that sensors can choose N rates for corn that perform better than rates chosen by producers. Thus, adoption of sensors can improve farmers’ profits and reduce N loss potential from crop fields.
Technical Abstract: Optimal nitrogen (N) fertilizer rate for corn (Zea mays L.) and other crops can vary substantially within and among fields. Current N management practices do not address this variability. Crop reflectance sensors offer the potential to diagnose crop N need and control N application rates at a fine spatial scale. Our objective was to evaluate the performance of sensor-based variable-rate N applications relative to a constant N rate chosen by the producer. Fifty-five replicated on-farm demonstrations were conducted from 2004 to 2008. Sensors were installed on the producer’s N application equipment and used to direct variable-rate sidedress N applications to corn at growth stages ranging from V6 to V16. A fixed N rate chosen by the cooperating producer was also applied. Relative to the producer’s N rate, sensors increased partial profit by $42/ha (P = 0.0007) and yield by 110 kg/ha (P = 0.18) while reducing N use by 16 kg N/ha (P = 0.015). This represents a 27% reduction in the amount of N applied beyond what was removed in the grain, thus reducing unused N that can move to water or air. Our results confirm that sensors can choose N rates for corn that perform better than rates chosen by producers.