Grain nitrogen percentage in wheat and barley grown under a wide range of yielding conditions and in response to post flowering degraining

ALZUETA I; SERRAGO R; ABELEDO LG; MIRALLES DJ; SAVIN R; SLAFER GA

Bento Gonçalvez

Congreso; 6th International Crop Science Congress; 2012

International Crop Science Association

Wheat and barley are the main small-grain crops. Due to industry requirements, grain nitrogen percentage (GNP) must be kept within certain limits (>1.7% in bread wheat and 1.6-1.9% in malting barley). GNP is the end result of the dynamics of carbon (C) and nitrogen (N) accumulation. Not only are these dynamics different but also C accumulation seems mostly sink-limited whilst N accumulation seems mostly source-limited (depending largely on remobilization of vegetative N, absorbed before flowering). However, there is debate in the literature on the appropriateness of generalizations of these limitations. We evaluated how changes in the source:sink ratio during the grain filling period affect GNP in wheat and barley through three experiments, one in Argentina (Buenos Aires) and two in Spain (Agramunt and Gimenells); all in all combining (i) different genotypes, (ii) low and high input levels, and (iii) different source:sink ratios during post flowering (control and hand-trimming the spikes removing 50% of the spikelets 7 days after flowering). The range of yield explored across the environmental conditions was 3.1to 9.9 Mg ha-1. Across this range, wheat showed higher GNP and N content (mgN grain-1) than barley. Trimming the spikes determined higher increases in N than in dry weight of the grains (c. 20 vs. 5 %, respectively). Thus, overall conditions, there was a much greater N than C source-limitation. Response to trimming was also generally sharper in wheat than in barley, though. The magnitude of the response showed interaction between genotypes, level of inputs and sites. Differences in the absolute N content in the grains between species were explained by the proportion of vegetative N remobilized to the grains, which was higher in wheat than in barley. There was a negative relationship between the grain N percentage and the proportion of biomass and N partitioned to the grains (HI:NHI ratio) and the physiological nitrogen use efficiency (NUE). Barley showed higher values of both variables and consequently lower GNP than wheat. In conclusion, we observed a generalized higher N than C source-limitation during grain filling across rather different growing conditions, and that constitutive differences between species in final GNP seemed explained by their differences in HI:NHI ratio and NUE.