Optimizing Soil Health and Productivity in Intensive Rice-Wheat Systems Using Conjoint Application of Sewage Sludge

This study assessed the long-term sustainability of integrating sewage sludge (SSL) with recommended (100%) or reduced (75%) doses of chemical fertilizers to enhance soil health, crop productivity, and reduce dependency on synthetic fertilizer inputs in the intensive rice-wheat cropping system (RWCS). A field experiment, established in 2010 and evaluated from 2017 to 2020 in Uttar Pradesh, India, employed nine nutrient management treatments in a randomized complete block design with three replications. Treatments included sole application of 100% recommended dose of fertilizers (RDF: N:P: K::120:60:60) and combinations of sewage sludge (20 or 30 t ha^-1) with either 100% or 75% RDF. Soil (0-15 cm) physicochemical and biological properties were analyzed to identify key soil health indicators (SHIs) and compute a soil health index (SHI). Integrated treatments significantly outperformed sole RDF, with T₃ (100% RDF + 30 t ha^-1 SSL), T₂ (100% RDF + 20 t ha^-1 SSL), and T₉ (75% RDF + 30 t ha^-1 SSL) yielding highest productivity and SHI (0.85-1.0). Alkaline phosphatase, available K, and microbial biomass N were most sensitive SHIs. T₃ notably boosted soil organic carbon, water-holding capacity, and nutrients while lowering bulk density, without exceeding the heavy metal thresholds promoting resilient RWCS aligned with UN Sustainable Development Goals.