Dynamics of Zinc Fractions in Soil as Affected by Zinc Fertilization in a Maize-maize Cropping Sequence in Upper Brahmaputra Valley Zone of Assam, India

Zinc is considered as an important micronutrient for maize which is a promising emerging cash crop for the state of Assam, India. A field experiment was conducted at the experimental farm of Krishi Vigyan Kendra, Jorhat, Assam Agricultural University during 2018-19 and 2019-20 to study the dynamics of zinc fractions in soil in a maize-maize cropping sequence as affected by zinc fertilization. The experiment was laid down in a randomized block design (RBD) with twelve treatments combinations of basal and foliar application of zinc through zinc sulphate and zinc oxide nanoparticles (ZnO NPs). The results revealed that zinc fertilization significantlyinfluenced the studied zinc fractions in soil during both the years under investigation. The distribution of different zinc fractions in soils at harvest was found in the following order: water soluble plus exchangeable-Zn < complexed-Zn < crystalline sesquioxide bound-Zn < amorphous sesquioxide bound-Zn < residual-Zn. Among the zinc treatment combinations, soil application of Zn @ 3.75 kg ha-1 in combination with foliar application of 500 ppm ZnO NPs exhibited the highest concentration of water soluble plus exchangeable-Zn content (1.10 ppm) in soil. The highest concentration of complexed-Zn (2.95 ppm), amorphous sesquioxide-bound-Zn (4.11 mg kg-1), crystalline sesquioxide-bound-Zn (3.76 ppm), residual-Zn (125.65 ppm) and total-Zn (137.33 ppm) were recorded in the treatment receiving soil application of Zn @ 7.5 kg ha-1. Among the zinc fractions studied, the concentration and percent contribution of water soluble plus exchangeable-Zn to total-Zn was the lowest while residual-Zn fraction contributed the highest to the total soil zinc pool. Furthermore, path coefficient analysis revealed that the water soluble plus exchangeable-Zn had the highest contribution towards the plant available DTPA extractable-Zn in soil. Moreover, all the fractions of zinc were found to be significantly and positively correlated with each other indicating existence of dynamic equilibrium of zinc in soil