Effect of humic acid on yield, yield components and physiological parameters of wheat in deficit irrigation conditions

In order to effect of humic acid on yield, yield components and physiological parameters of wheat in deficit irrigation conditions this research was done as split plot in randomized complete blocks design with three replications. main plots consisted: full irrigation, no irrigation at the beginning of stem elongation, and no irrigation at the pollination stage and sub plots included different levels of humic acid fertilizer (0, 100, 200 and 300 mg/L). Results showed that interaction of irrigation and humic acid on number of seeds per spike and 1000 grain weight at 1% probability level and number of spikes per unit area and harvest index was significant at 5% probability level. Grain yield under the effect low irrigation and humic acid was significant at 1% probability level. The highest leaf area index and crop growth rate were affected in full irrigation and 300 mg.L-1 humic acid and least of them were obtained in low irrigation stress conditions in different periods and no foliar application of humic acid. The highest grain yield was obtained in full irrigation (5035 kg.ha-1) and foliar application with 300 mg.L-1 humic acid (4462 kg.ha-1). The lowest grain yield was obtained in no irrigation at the pollination stage (2355 kg.ha-1) and no-humic acid (2667 kg.ha-1). As a result, foliar application 300 mg.L-1 of humic acid in different periods of low irrigation stress improved the physiological indices and increased yield components compared to control (no foliar application).