Soil Quality and Rice-Wheat Productivity Under Four and Half Decades of Differential Nutrient Management in Mollisols of Himalayan tarai

A long-term soil fertility experiment, established in 1971 at Pantnagar, Uttarakhand, India to evaluate the impacts of uninterrupted and integrated nutrient management (INM) on soil quality and productivity in the rice-wheat cropping system (RWCS) under Mollisols of the Himalayan region of tarai. The study comprised nine treatments combination of different levels of nitrogen (N), phosphorus (P) and Potassium (K) fertilizers, farmyard manure (FYM), and zinc (Zn)in a randomized block-design with four replications. Soil physical, chemical, and biological properties and the yield of rice and wheat were assessed to evaluate long-term nutrient effects. The integrated treatment (NPK + FYM + Zn), with NPK at 100% recommended dose (120 kg N ha^-1, 26 kg P ha^-1, and 37 kg K ha^-1), FYM at 15 t ha^-1, and Zn (basal+foliar) at 75-125 mg kg^-1, significantly increased grain yield of both crops and improved key soil physical, chemical, and biological properties, including organic carbon, soil microbial-biomass-carbon (SMBC), enzymatic activities, water-holding capacity, mean weight diameter (MWD), and hydraulic conductivity. Cationic micronutrients [Zn, manganese (Mn), copper (Cu), and iron (Fe)] and microbial populations (bacteria, fungi, and actinomycetes) also increased. Principal component analysis identified available P, K, Zn, Mn, dehydrogenase activity, potentially mineralizable N, SMBC, and MWD as major contributors to soil quality indexed (SQI) and highest (3.864) was recorded under this treatment, outperforming others. Long-term balanced fertilization with N, P, and K along with FYM and Zn is essential for sustaining soil health and crop productivity, supporting INM for sustainable RWCS in the Indo-Gangetic Plains.