LEACHABILITY AND DISTRIBUTION OF ZINC APPLIED TO AN ACID SOIL AS CONTROLLED-RELEASE ZINC CHELATES

Fertilizers that contain zinc (Zn)-EDTA and Zn-lignosulfonate (Zn-LS), which can also be coated with rosin, were placed at the top of column s of an acid Calcic Palexeralf soil which were periodically irrigated. The liberated Zn remained mostly on the top of the column when the so urce of Zn was Zn-LS but Zn migrated through the column when Zn-EDTA w as applied. The use of a coating on the Zn-EDTA fertilizer diminished the loss of Zn by leaching from 52% to 20% at the end of the experimen t at the highest coating percentage (36%). The distribution of the Zn in the soils was studied by fractionation and showed that added Zn rem ained in the soils in more favorable forms for uptake by plants in com parison with the control soil. The labile fraction (F1) and especially that organically complexed increased, and the percentage correspondin g to the residual fraction that was 89% in the native soil diminished in all cases being in the most favorable case by 25%. Correlations bet ween the extracted fractions (r=0.57-0.99, P<0.01%) showed that, in ge neral, a dynamic equilibrium existed between them. The DTPA-extractabl e Zn also correlated positively with the most labile Zn fractions, alt hough the significance level depended on the depth.