Effect of Soil and Foliar Application of Zinc Sulfate Fertilizer on Zn and Protein Content of Grain, and Zn Content of Rice Tissues at Different Growth Stages

Although there are numerous studies on the effect of soil and foliar application of Zn on rice yield, knowledge on Zn distribution in rice tissues through simultaneous soil and foliar application of Zn is limited. Therefore, The current experiment was conducted to explore the effect of soil and foliar application of zinc sulfate fertilizer on Zn and protein content of grain, and Zn content of rice (Oryza Sativa L.) tissues at different growth stages of Hashemi local cultivar. This filed experiment was carried out on two factors (soil application of Zn at three levels and foliar application of Zn at four levels) using complete randomized block design with three replications. The maximum grain yield (4283 kg ha-1) was recorded at simultaneous application of 20 kg Zn ha-1 (basal soil application) with foliar application of Zn solution at ripening stage, giving 32% increase compared to the control (2915 kgha-1). The highest increase in leaves and stems Zn content (2 times) was recorded at the combined treatments (10 kg Zn ha-1 and foliar spray at the maximum tillering stage). Also, the maximum increase in panicle and rice grain Zn (around 2.5 times) was obtained by application of 10 kg Zn ha-1 and foliar spray at the flowering stage. The highest linear correlation coefficient was found between grain and panicle Zn content (0.58**). Meanwhile, the grain protein content positively correlated with grain Zn content (0.68**), panicle Zn content (0.64**) and Zn content of stem (0.64**). Among the aerial parts, the highest linear correlation coefficient was found between Zn content of panicle and leaves at ripening stage (0.69**), Zn content of leaves and stems at flowering stage (0.65**), Zn content of stems at ripening stage and root Zn content at flowering stage (0.45**). The fitted stepwise multiple regression analysis  among protein content of rice grains and Zn content of all rice tissues at different rice growth stages indicated that grain Zn content, Zn content of leaves and stems at ripening stage had positive significant relationship with protein content of grains. According to adjusted coefficient of determination, these characters demonstrated 56% of protein content variations. It can be concluded that soil application of 20 kg Zn ha-1 in combination with Zn foliar application of  0.5% Zn sulfate at flowering stage of rice plant enhance grain yield and quality.