Influence of Zinc Sources and Levels on Zinc Fraction Distribution in Calcareous Soil under Groundnut (Arachis hypogaea L.)

Zinc deficiency is a major constraint to crop production in calcareous soils due to high soil pH and calcium carbonate–induced zinc fixation, which reduces zinc availability to plants. The present study was conducted to evaluate the effects of different zinc sources and application levels on zinc fractionation dynamics in calcareous soil under groundnut cultivation. A field experiment was laid out in a factorial randomized block design with two zinc sources and four application levels, replicated three times. Soil samples were collected at flowering, peg formation, and harvest stages and analyzed for different zinc fractions using a sequential extraction procedure. The results showed that water-soluble and exchangeable zinc fractions were significantly higher under Zn-EDTA application, particularly at 10 and 15 mg kg⁻¹, indicating improved zinc availability in calcareous soil. In contrast, ZnSO₄ application resulted in greater accumulation of zinc in specifically sorbed, carbonate-bound, Fe–Mn oxide-bound, organic matter-bound, and residual fractions, reflecting stronger zinc fixation under alkaline conditions. The residual fraction was the dominant pool of total zinc and increased with higher zinc levels and advancing crop growth stages. Total zinc content increased significantly with zinc application rate and was consistently higher under ZnSO₄ compared to Zn-EDTA. This research article explains in detail how Zn-EDTA maintains more labile zinc fractions for immediate plant uptake, while ZnSO₄ promotes long-term zinc stabilization in calcareous soils.