Enhancing Soil Health in Rice Cultivation: Optimized Zn Application and Crop Residue Management in Calcareous Soils

Crop residue, a readily available biomass, is the largest source of organic matter in soil, and zinc (Zn) significantly influences microbial activity. Understanding the optimal Zn rates for enhanced biological activity in crop residue-amended soils is crucial. A study at RPCAU, Pusa, examined the combined effects of Zn applications and long-term crop residue amendments on soil biological properties in a rice–wheat cropping system. Conducted on Zn-deficient calcareous soil, the experiment used a split-plot design with four crop residue levels (0, 25, 50, and 100%) and four Zn rates (0, 2.5, 5, and 10 kg ha−1). Crop residues were incorporated each season, while Zn was applied initially in 1994 and again in 2018. The results showed significant improvements in soil organic carbon, organic C-stock, and reductions in soil bulk density. A linear–plateau regression model revealed that Zn application at 10 kg ha−1 increased soil active carbon and soil respiration by 35% and 53%, respectively, with the required crop residue levels at 73.73% and 90.28%. ACE protein increased by 9.6% with Zn application at 5 kg ha−1, with a required crop residue level of 91.06%. The highest values of soil available nutrients and grain yield of rice were observed with 100% residue incorporation and 10 kg ha−1 Zn application. Thus, applying 10 kg ha−1 Zn along with 100% crop residue incorporation significantly improves soil biological properties and soil organic carbon levels in calcareous soil under a rice–wheat cropping system.