Assessment of zinc availability to rice in Mollisols of North India

The objectives of this study were to (1) characterize zinc (Zn) fractions a nd their relation to Zn extracted with mixed-bed ion exchange resin capsule s and (2) assess the relationships between the latter and Zn uptake by rice in 12 Mollisols from North India. The Resin Absorption Quantity (RAQ) of Z n was measured after 1 and 14 days of anaerobic incubation. Six organic and inorganic Zn fractions were determined on anaerobic soil. Zinc uptake by r ice was studied in a greenhouse experiment. Soil Zn fractions under reduced conditions followed the order residual Zn (80%)>carbonates and amorphous o xides bound Zn (12%)>weakly organically bound Zn. (3%)>crystalline oxides b ound Zn (2%)>strongly organically bound Zn (2%)>water soluble + exchangeabl e Zn (1%). RAQ-Zn was best correlated with Zn bound to carbonates and amorp hous oxides. Due to negative interactions between bicarbonate and Zn uptake , correlations between relative dry matter yield or total Zn uptake and the different Zn fractions, DTPA-Zn measured on dry soil, or RAQ Zn were not s ignificant. Adjusting soil test values according to soil pH improved the pr ediction of relative dry matter yield, but further studies are required to determine whether the resin capsule can be used as a soil test for Zn in ca lcareous soils.