Improving nitrogen use efficiency in cereal grain production with optical sensing and variable rate application

losses due to surface runoff range between 1 and 13%In 2001, N fertilizer prices nearly doubled as a result of increased (Blevins et al., 1996; Chichester and Richardson, 1992).natural gas prices. This was further troubling when considering that the world N use efficiency (NUE) in cereal grain production averages Urea fertilizers applied to the surface without incorpo-only 33%. Methods to improve NUE in winter wheat (Triticum aesti- ration can result in NH3 volatilization losses in excess vum L.) have not included high spatial-resolution management based of 40 % (Fowler and Brydon, 1989; Hargrove et al., on sensed plant growth properties nor on midseason prediction of 1977). In cooler temperate climates, NO3 losses through grain yield. Our objective was to determine the validity of using in- tile drainage have approached 26 kg N ha1 yr1, or season estimates of grain yield (INSEY) and a response index (RI) 23 % of the total N applied (Drury et al., 1996). In to modulate N at 1-m2 spatial resolution. Four winter wheat field general, loss of N only occurs when mineral N (NH4experiments were conducted that evaluated prescribed midseason and NO3) are present in excess of plant needs (JohnsonN applications compared with uniform rates that simulated farmer and Raun, 1995).practices. Our methods recognize that each 1-m2 area in wheat fields needs to be sensed and managed independently and that the need for fertilizer N is temporally dependent. Averaged over locations, Spatial Scale of Nitrogen Availability NUE was improved by 15 % when N fertilization was based o