The effects of urea fertilisation and genotype on yield, nitrogen use efficiency, δ15N and δ13C in wheat

Abstract

AbstractNew methodologies to assess nitrogen use efficiency (NUE) in field crops could help in the characterisation of large numbers of genotypes and growing conditions. The effects of chemical nitrogen fertilisation on yield: nitrogen taken up by the crop, NUE and its components utilisation efficiency (UTE) and uptake efficiency (UPE) and the stable carbon (δ13C) and nitrogen (δ15N) composition of mature grains and straw were evaluated. A set of 24 wheat genotypes generated over the past four decades by International Maize and Wheat Improvement Center and the Mexican Institute of Forestry, Agriculture and Livestock Research were studied under well‐irrigated field conditions. Five concentrations of urea were applied as a source of N fertilisation. Fertilisation significantly decreased δ15N and increased δ13C, but δ15N was the isotopic trait most strongly correlated with absolute changes in yield and crop nitrogen (N) accumulation caused by different levels of N fertilisation. Both grain δ15N and grain δ13C correlated positively with NUE and UTE. Differences across genotypes in δ13C correlated positively with UTE and negatively with grain N content within each of the N levels assayed. Genotypic differences in δ15N correlated negatively with total grain N accumulated but only at the intermediate levels of N fertilisation. We conclude that under our experimental conditions, natural abundances of 15N and 13C may provide complementary information on how nitrogen fertiliser is used by the plant. However, whereas grain yield and biomass, as well as total N accumulated and NUE, increased in the most recent genotypes, only a tendency for higher δ15N was observed and there was no clear trend for δ13C. Changes in NUE were paralleled by changes in UPE rather than UTE.