Will Variable‐Rate Nitrogen Fertilization Using Corn Canopy Reflectance Sensing Deliver Environmental Benefits?

Abstract

Within‐field variability of corn (Zea mays L.) N need calls for development of precision fertilizer application strategies. One approach many are investigating is in‐season canopy reflectance sensing. Justification for this strategy partly rests with the premise it will improve N use and reduce N loss from fields. The objective of this study was to determine the potential environmental benefits using corn canopy reflectance sensing for N fertilization. On 16 field‐scale sites, multiple blocks of randomized N rate plots (0–235 kg N ha−1) traversing fields were side‐dressed between the V7 and V11 growth stages. Sensor measurements were obtained from these and adjacent N‐rich reference strips at side‐dressing. Environmental indicators were examined at the determined optimal nitrogen rate (Noptimal) and the nitrogen rate the producer used (Nproducer). A partial nitrogen mass balance (PNB) on response blocks within fields highlighted how variable Noptimal likely resulted in multiple and different N loss pathways. For many fields, Noptimal was less than Nproducer, and the observed trends were as expected: higher yield efficiency (YE), higher nitrogen fertilizer recovery efficiency (NFRE), lower unaccounted for N, and less postharvest inorganic N. For a measurement examining canopy sensor‐based N applications, N savings of 10 to 50 kg N ha−1 would be expected, but savings varied by reflectance readings, soil type, and fertilizer and grain prices. In some situations sensor‐based N would be greater than Nproducer. Given that sensor information can be processed into an N rate that approximates Noptimal, the results support sensor‐based N applications have potential for environmental benefits.