Indexing Soil Quality Over 45 Years of Long‐Term Fertilization in an Acid <i>Alfisol</i> of North Western Himalayas

ABSTRACT Sustaining long‐term crop productivity and soil quality are essential for the stability of agricultural ecosystems. However, prolonged use of unbalanced chemical fertilizers under intensive cropping systems consistently degrades soil quality and threatens sustained productivity. Hence, a comprehensive evaluation of long‐term fertilizer experiments and their effect on soil quality is essential to determine the best practices that support soil functionality and sustains crop yields. The present study evaluates the effects of 45 years of fertilization on soil quality in wheat under maize–wheat cropping system experiment in an acid Alfisol . Physical, chemical and biological soil quality indicators were analysed at two soil layers viz. (0–15 and 15–30 cm) under 11 treatments comprising different fertilizer and amendment regimes, that is, 50% NPK, 100% NPK, 150% NPK, 100% NPK + hand weeding, 100% NPK + Zn, 100% NP, 100% N, 100% NPK + farmyard manure (FYM), 100% NPK (‐S), 100% NPK + lime and control, arranged in a randomized complete block design. Results from the present study indicated that, balanced dose of NPK application in combination with FYM or lime significantly enhanced wheat grain yield by ~53.9% and ~41.2%, respectively, over sole 100% NPK fertilizers. FYM and lime amended treatments notably reduced soil bulk density, enhanced nutrient availability, and microbial indicators relative to control, 100% NPK and imbalanced fertilizer treatments. Furthermore, principal component analysis (PCA) was computed to identify key soil quality indicators in both soil layers. In the surface soil layer, the highest value of soil quality index (SQI) was observed under 100% NPK + FYM (0.99), followed by 100% NPK + lime (0.97), whereas omission of N, P, K or S led to substantial reduction in SQI. Contrarily, the value of SQI decreased in the sub‐surface layer. Among the selected soil quality indicators, highest contribution towards SQI at surface soil layer was of soil microbial biomass nitrogen (SMBN; 85%), followed by pH (10%) and water holding capacity (4%), whereas in sub‐surface soil, bulk density (70%), pH (26%) and available sulphur (4%) were primary contributors. Additionally, except bulk and particle density all other soil quality indicators correlated positively with wheat grain yield. Hence, these findings emphasize the critical role of continuous soil quality monitoring and the integrated use of balanced fertilizers, organic amendments, and lime to maintain soil health and optimize crop yields in acid Alfisols .