Nitrogen utilization efficiency in wheat: A global perspective

Understanding factors underpinning the variability in nitrogen (N) utilization efficiency (NUtE) [i.e. grain yield per unit of N uptake at maturity (Nup(MAT))] is critical to direct future improvements in breeding and agronomic management. To our knowledge, no study has summarized changes in wheat NUtE across a wide range of experimental conditions. We performed a synthesis-analysis using published data to provide a global perspective of NUtE trends in wheat by (i) benchmarking against yield limited by Nup(MAT), and (ii) assessing factors contributing to the variation in NUtE. The final database encompassed 55 studies (n = 529). A nonlinear model explained yield as a function of Nup(MAT). The gap between actual yield and Nup(MAT)-limited yield was negligible at the lowest range of Nup(MAT) and increased to similar to 2000 kg ha(-1) as Nup(MAT) levels increased. Hence, opportunities to enhance yield through improving NUtE would be more likely at greater-than-average yield and Nup(MAT) levels. The negative correlation between grain protein concentration and the residuals between NUtE and Nup(MAT) indicated a challenge to increase yield without penalizing grain protein. Further, there are greater opportunities to increase NUtE in fall-than winter-sown wheat. Identifying the determinants of NUtE will enable to narrow the gap between actual and Nup(MAT)-limited yields.