Nitrogen efficiency components of winter cereals

A model to describe the importance of different physiological processes to explain grain yield differences (Delta G(w)) between cropping systems (Huggins and Pan, 1993) was modified to evaluate the nitrogen use efficiency of different cereals. The method uses measurements of grain yield (G(W)), grain N (N-g), above-ground plant biomass (B), above-ground plant N (N-t), applied fertilizer N (N-f), and post-harvest inorganic soil N in control plots without fertilizer (N-h) The components are N supply (N-s), N uptake efficiency (N-t/N-s), assimilation efficiency (B/N-t), harvest index (G(w)/B) and N harvest index (N-g/N-t). For a first verification of the model different winter cereal species, i.e., one genotype of winter wheat, one of winter rye and one of spelt wheat, were compared in a 2-year field experiments at two sites with different soil fertility and climate. The modified nitrogen efficiency component analysis provided a good understanding of yield differences at different levels of applied N and soil fertility. The method could be useful for selection of genotypes with a high N use efficiency in breeding programmes.