Chemical Fractions of Zinc and Their Contribution toward Its Availability under Long-Term Integrated Nutrient Management in Rice–Wheat Sequence in an Acidic Alfisol

Abstract

This study was carried out in an ongoing field experiment initiated during the 1991 kharif season (May–October) on an acidic soil in the Western Himalayas of India to evaluate the effect of integrated nutrient supply on transformation of zinc (Zn) into various chemical pools. The continuous use of chemical fertilizers alone for 20 years brought about marked depletion in different pools of Zn compared to buffer plots, while integrated use of organic and chemical fertilizers recorded greater content than chemically treated plots. Nonspecifically adsorbed exchangeable Zn (Zn I) was the most important fraction of Zn contributing to diethylene triamine penta-acetic acid (DTPA)–extractable Zn. Content of DTPA-extractable Zn also increased in soil with integrated application of chemical fertilizers and organics over the years. Residual Zn was the most dominant form of Zn, contributing about 55% to total Zn, whereas nonspecifically adsorbed exchangeable Zn was the most important fraction of Zn contributing to DTPA Zn.