Zinc fractionation in a Cecil soil as influenced by organic acid treatments

Abstract

A greenhouse study was conducted to examine the effect of organic acid additions on Zn distribution within various Zn fractions in a Cecil soil. Four aliphatic acids were used, oxalic, malonic, succinic acids and L-malic, at three different concentration levels, 10−2mol L−1, 10−3mol L−1 and 10−4mol L−1. Organic acid treatments were applied to wheat (Triticum aestivum) grown in a greenhouse during a 10 week period. A sequential Zn extraction technique was performed on the soil for each treatment, with the quantity of Zn in each fraction being determined. Organic acid treatments were found to alter the quantity of Zn in the exchangeable, organic and Mn oxide fractions. An inverse relationship was found between Zn extracted from the exchangeable fraction and organic acid concentration for all acid treatments. Succinic and malonic acids at 10−2 and 10−3 mol L−1 were the only treatments that resulted in significantly higher Zn levels in the organic fraction compared to the control. Zn levels in the manganese oxide fraction were significantly lower than the control treatments. Zn associated with the amorphous and crystalline Fe oxide soil fractions was not affected by organic acid additions. The Zn concentration in wheat tissue showed an inverse relationship between exchangeable Zn and organic acid concentration similar to that in the exchangeable fraction. Differences in Zn wheat tissue concentration were attributed to both organic acid type and concentration. It was postulated that the observed shifts in Zn levels between the various Zn fractions resulted from the dissolution of Mn and Fe oxide fractions by organic acids and the readsorption of organo-Zn complexes onto the exchangeable — organic fraction of the soil.