Zinc Nutrition of Rice as Influenced by Rates of Gypsum and Zn Fertilization of Alkali Soils1

Abstract

AbstractThree field experiments were conducted on Zn deficient alkali soils, two on Natraquic calciorthids, and one on Aquic Camborthids, to determine the effect of gypsum and Zn fertilization alone and in combination on the Zn nutrition of rice IR 8 (Oryza sativa L.). Three rates of gypsum (0, 25, and 50% gypsum requirement of soil) and three rates of Zn (0, 11.2, and 22.4 kg Zn/ha, as ZnSO4‐7H2O) and their possible combinations were tried. At all the three locations, the growth of the rice crop was very poor and exhibited Zn deficiency symptoms in control plots. The yield and Zn uptake was higher in alkali soil high in CaCO3 and low in pH than in soils low in CaCO3 and high in pH. Gypsum application markedly decreased the soil pH, and significantly increased the yield and Zn uptake by rice. This resulted from a marked significant increase in soil and plant Zn concentration, though it remained within marginal levels. Zinc application decreased the pH, but not so appreciably as did gypsum; and markedly increased the available Zn from deficient to adequate levels. This in turn significantly increased Zn concentration and its uptake and resulted in a significant increase in rice grain and straw yield both over control and gypsum treatments. Optimum response of rice to Zn was observed at 11.2 kg Zn/ha except in one of the Natraquic calciorthids where it was 22.4 kg Zn/ha. Gypsum in conjunction with Zn application did not increase either the available Zn or the rice yield. The beneficial effect of Zn application to rice grown on the alkali soils under investigation was far more than that of gypsum.