ZINC FRACTIONS IN SOILS IN RELATION TO ZINC NUTRITION OF LOWLAND RICE

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Abstract
Soil zinc fractionation studies revealed that more than 90% of the total zinc occurred in the relatively inactive clay lattice bound form and that a small fraction, viz., 0.26, 0.74, 1.58 and 0.71% of the total occurred as water-soluble and exchangeable, organic complexed, amorphous sesquioxide, and crystalline sesquioxidebound forms. The applied zinc was transformed to the latter four forms following their relative order of preponderance in native soils and constituted on an average 3.68, 12.17, 19.85, and 5.33%, respectively, of the applied amount. Waterlogging caused an increase in the organic complexed and amorphous sesquioxide-bound forms of native soil zinc with a concomitant decrease in the content of the other forms, suggesting the occurrence of a dynamic equilibrium of these forms in soil. Simple correlation and multiple regression analyses showed that the zinc fractionation data obtained from the soils after incubation were more relevant than the same obtained from the cropped soil in predicting zinc concentration of lowland rice plants. The path coefficient analyses revealed that organic complexed zinc played the most important role in zinc nutrition of lowland rice and lent support to the validity of the zinc fractionation scheme suggested by Murthy (1982) and modified by us in this regard.
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