The Effect of Nitrogen and Zinc Amount on Physiological Properties, Yield and Protein Content of Wheat Grain under Terminal Heat Stress Condition

Heat stress during grain filling period can lead to the reduction of grain yield of wheat. Therefore, in order to evaluate the probable mitigative effect of nitrogen and zinc application of heat stress on physiological properties, grain yield and protein content of wheat (Chamran cultivar), a split-split plot experiment based on RCBD in four replications was carried out in an experimental field of Khuzestan Agriculture and Natural Resources University, Ahvaz, Iran during autumn of 2018-19 growing season. Experimental factors were three planting date (22 November, 11 December and 31 December) as main plot, four nitrogen levels (0 as a control, 75, 150 and 225 kg ha-1 N from urea 46%) as subplot and zinc levels (0 as a control, 10 and 20 kg ha-1 from zinc sulfate) in subplots. The results showed that the delay in planting significantly (P≤0.01) reduced grain protein, leaf chlorophyll index, cell membrane stability index, grain yield, biological yield, and harvest index. Nitrogen application reduced the effects of heat stress on wheat grain yield so that by consuming 75, 150 and 225 kg N ha-1 in cultivation, wheat grain yield was improved by 43%, 59% and 64% for 11 December cultivation date and 50%, 70% and 55% for 31 December cultivation date, respectively, compared to control fertilizer. Zinc application also reduced the effects of heat stress on wheat grain yield, where at late and very late cultivation dates, with the application of 10 and 20 kg ha-1 zinc, wheat grain yield was improved by 5%, 6%, 35% and 40%, respectively. Consumption of zinc also reduced the effects of heat stress on wheat grain yield by increasing grain weight and caused a 24% increase in grain weight. Wheat harvest index decreased by about 18% due to heat stress. Meanwhile, application of nitrogen and zinc at 150 and 10 kg ha-1, respectively, showed the greatest effect in reducing the adverse effects of terminal heat stress on the agronomical and physiological properties of wheat. In general, in case of delayed cultivation, the use of zinc (at least 10 kg ha-1) and nitrogen (at least 150 kg ha-1) can reduce the harmful effects of terminal heat stress in Ahvaz climate and improve physiological (chlorophyll content and cell membrane stability), agronomic and protein content of bread wheat.