Geochemical Interaction and Bioavailability of Zinc in Soil Under Long-Term Integrated Nutrient Management in Pearl Millet–Wheat System

The degree and severity of zinc (Zn) deficiency in soil reduced the agricultural yield and quality, thus encouraging malnutrition in humans worldwide. The study was hypothesized to increase the bioavailability and release of Zn in soil and Zn biofortification in wheat grains under integrated nutrient management (INM). The long-term (54 years) experiment laid out in a split-plot design comprising single (W) and dual (PW) applications of farmyard manure (FYM) (0, 5, 10, and 15 Mg ha⁻¹) and nitrogen (0, 60, and 120 kg ha⁻¹) was studied to understand the distribution of different Zn fractions in soil and their relationship to wheat grain yield and Zn uptake. A laboratory incubation study was performed on surface soils to evaluate the release kinetics of native Zn at field capacity. The different fractions of Zn in soil increased with increasing frequency and levels of FYM application. Residual Zn constituted the maximum proportion (89.03%) of total soil Zn. A high positive correlation (p < 0.01) of diethylenetriaminepentaacetic acid (DTPA)-extractable Zn and total grain Zn content were observed with different Zn fractions. The release kinetics of native soil Zn increased up to 10 days and became almost constant, indicating the establishment of chemical equilibria between the soil solid and solution phase. Thus, long-term INM ensured higher wheat production (6.08 Mg ha⁻¹) and Zn biofortification (38.95 mg kg⁻¹) to combat Zn malnutrition and achieve the United Nations’ sustainable development goals on “zero hunger” and “good health and well-being.”