INFLUENCE OF LOW-MOLECULAR-WEIGHT ORGANIC-ACIDS ON ZINC DISTRIBUTION WITHIN MICRONUTRIENT POOLS AND ZINC UPTAKE BY WHEAT

A greenhouse study was conducted to examine the effects of four soil solution organic acids on the distribution of Zn within various soil micro nutrient pools and their influence on Zn uptake by wheat. L-malic, malonic, oxalic, and succinic acids at four concentration levels, 0, 10(-2) mol/L, 10(-3) mol/L, and 10(-4) mol/L were applied to pots growing wheat (Triticum aestivum) over a period of 10 weeks. A sequential Zn extraction technique was performed on the soil for each treatment, with the quantity amount of Zn in each fraction being determined using atomic absorption spectroscopy. Soil Zn fractions significantly affected by the organic acid treatments were the exchangeable, organic and Mn oxide fractions. An inverse relationship existed between Zn extracted from the exchangeable fraction and organic acid concentration for all acid treatments. Succinic and malonic acids at higher concentrations were the only treatments to be significantly higher in organic Zn compared to the control. All treatments were significantly less than the control for Zn levels in the manganese oxide fraction, however there were nonsignificant differences between organic acid treatments. Organic acids had no affect on the quantity of Zn associated with the amorphous and crystalline Fe oxide soil fractions. Zinc concentration in wheat tissue showed an inverse relationship between exchangeable Zn and organic acid concentration similar to that in the exchangeable fraction. Differences in amounts of Zn in wheat tissue were attributed to both organic acid type and concentration. It was concluded that organic acids may be important in influencing the distribution of Zn between the various soil fractions and thus affecting its availability to the plant.