Estimation of critical limit for zinc in rice soils

Abstract

Abstract Twenty surface soil samples were collected from Nainital Tarai (foothills of Himalya) where “Khaira”; disease (Zn deficiency of rice) is prevalent. Rice (Oryza sativa L. variety IR‐8) was grown in pots for 8 weeks after transplanting. Experiments were conducted to determine the suitability of five soil Zn extractants: dilute acid (HCl + H2SO4) mixture; DTPA‐(NH4) 2CO3, pH 7.3; dithizone; NH4OAc, pH 4.6; and 2N MgCl2 to predict Zn deficiency. Critical values for soil available Zn were established for rice by the old and new Cate and Nelson procedures1. Zinc extracted from the soils with dithizone; NH4OAc, pH 4.6; 0.2N MgCl2. and DTPA‐(NH4) 2CO3 pH 7.3 was significantly correlated with the uptake of Zn by the rice plants. The correlation between Zn extracted with the dilute acid (HCl + H2SO4) mixture and plant Zn was not statistically significant. The ex‐tractants which extracted greater quantities of Zn gave higher critical values and vice versa. It is concluded that all extracting solutions except the dilute acid (HCl + H2SO4) mixture were found to he suitable for predicting available Zn in rice soils of Tarai.