Improving Nitrogen Use Efficiency in Cereal Grain Production with Optical Sensing and Variable Rate Application

In 2001, N fertilizer prices nearly doubled as a result of increased natural gas prices. This was further troubling when considering that the world N use efficiency (NUE) in cereal grain production averages only 33%. Methods to improve NUE in winter wheat ( Triticum aestivum L.) have not included high spatial‐resolution management based on sensed plant growth properties nor on midseason prediction of grain yield. Our objective was to determine the validity of using in‐season estimates of grain yield (INSEY) and a response index (RI) to modulate N at 1‐m 2 spatial resolution. Four winter wheat field experiments were conducted that evaluated prescribed midseason N applications compared with uniform rates that simulated farmer practices. Our methods recognize that each 1‐m 2 area in wheat fields needs to be sensed and managed independently and that the need for fertilizer N is temporally dependent. Averaged over locations, NUE was improved by >15% when N fertilization was based on optically sensed INSEY, determined for each 1‐m 2 area, and a RI compared with traditional practices at uniform N rates.