In‐Season Optimization and Site‐Specific Nitrogen Management for Soft Red Winter Wheat

Site‐specific N management based on an in‐season assessment of crop N status may offer producers increased grain yield, profitability, and spring N fertilizer use efficiency (SNUE). The goal of this study was to determine the distinct contributions of (i) in‐season N rate optimization and (ii) site‐specific N management. Our objective was to compare site‐specific and field‐specific N management with typical growers' practices to determine if site‐specific N management (i) increased soft red winter wheat (Triticum aestivum L.) grain yield, (ii) reduced N inputs, (iii) increased SNUE, and (iv) reduced within‐field grain yield variability. Research was conducted at eight sites in 2000, 2001, and 2002. A randomized complete block design with two or five N management systems was used at two and six sites, respectively. Site‐specific management did not improve grain yield compared with field‐specific management when based on the same in‐season estimation of optimum N rates. At sites where site‐specific or field‐specific systems were compared with typical growers' practices, grain yield benefits of in‐season N optimization (up to 2267 kg ha−1) were apparent. For grain yield, in‐season optimization of N rate was more important than site‐specific management. A large reduction in N inputs (up to 48.6%) was also attributed to in‐season N rate optimization. After incorporating in‐season optimization, a further reduction in N inputs (up to 19.6%) was possible through site‐specific application. Site‐specific N application maximized SNUE compared with either field‐specific or typical growers' practices at all sites and reduced within‐field grain yield variance at four sites.