Benchmarking nitrogen utilisation efficiency in wheat for Mediterranean and non-Mediterranean European regions

Water and temperature stress during critical periods of grain yield formation are distinctive of wheat crops in Mediterranean environments. However, nitrogen (N) availability may also constrain grain yields in these environments. Benchmarks of yield response to N uptake in Mediterranean conditions are lacking, and extrapolation from non-Mediterranean environments is not warranted. We hypothesised that under Mediterranean environments (1) maximum N uptake would be lower, thus the range of N uptake would be narrower, and (2) N utilisation efficiency (NUtE, yield per unit N uptake) would be reduced along the whole range of N uptake than under non-Mediterranean conditions. To test these hypotheses, we compiled published data of yield and N uptake from Mediterranean (n = 340) and non-Mediterranean environments (n = 563) of Europe. Wheat in Mediterranean environments had lower average grain yield (4.1 vs 7.1 Mg ha(-1)), lower average N uptake (131 vs 166 kg N ha(-1)), lower average NUtE (33 vs 47 kg grain kg N-1), and higher average grain N concentration (2.4 vs 1.8%) than crops in non-Mediterranean environments. Boundary functions relating yield and nitrogen uptake captured the lower yield of wheat along the whole range of N uptake as hypothesised; these functions could be used for benchmarking wheat crops in Mediterranean regions of Europe, and possibly other Mediterranean environments.