Strategic Nitrogen Supply Alters Canopy Development and Improves Nitrogen Use Efficiency in Dryland Wheat

Abstract

Core Ideas Strategic application of N fertilizer produced a thinner and more open crop canopy. The smaller canopy delayed demand for soil moisture. The smaller canopy reduced shoot mortality and increased harvest index. Higher N uptake from sowing N application did not result in more harvest N. Strategic N application can improve yield in wheat (Triticum aestivum L.) but the reliability of the response in dryland conditions is often low, leading to poor predictability of N responses. The objective of this study was to provide an understanding of how nitrogen use efficiency (NUE) could be improved by strategic N application. Experiments with seven N application timings and two N rates were conducted at two sites over two seasons to evaluate the effects of strategic N supply on N uptake, canopy development, and yield components. Delaying the application of N fertilizer initially produced a thinner, more open crop canopy, compared with application of N at sowing, as indicated by significantly lower light interception (LI) (68 vs. 80%), which was associated with reduced shoot mortality (r = –0.71) and increased harvest index (HI) (r = 0.71–0.96). Nitrogen applied only at sowing had higher preanthesis N uptake (96.6 kg N ha−1 vs. 78.1 kg N ha−1), but did not result in more grain N at harvest. A smaller canopy, resulting from lower initial N supply, was able to respond to late N application, potentially through retaining more soil water at anthesis (80 mm vs. 69 mm at 0–60‐cm depth). The results provide evidence that in rainfed wheat production systems, early season N application is an inefficient strategy to convert biomass and N into grain. Manipulating canopy development through N management can alter canopy size and water use patterns, to improve NUE and reduce risk in dry seasons.