ABSTRACT
Nitrogen (N) is an essential macronutrient which strongly influences wheat grain yield and end-use quality. N plays a key role in yield formation, as it is required for canopy production; suboptimum supply affects many physiological processes with typical reductions of total leaf area, leaf area duration, leaf photosynthesis per unit area and so biomass production. If N is limiting, increasing N supply will increase grain yield given no other physiological constraints. However, harvestable dry matter does not increase in direct proportion to N supply, with the result that the efficiency of N use is highly dependent on the level of N supply (Sylvester-Bradley et al., 2009). Yield will ultimately reach a plateau that is then indicative of other limiting factors. N is a critical constituent of grain protein, and concentration and composition are important determinants of wheat end-product quality. High grain protein concentrations (GPC) are generally required for bread making (12-13%) while lower concentrations are adequate for feed wheat. Biofuel or distilling require the lowest GPC, as a negative correlation has been reported between grain N content and alcohol yield (Kindred et al., 2008).
