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Received: 3rd January, 2026; Accepted: 18th March, 2026

Abstract

The Soil Quality Index (SQI) of various nutrient management practices under a rice-rice cropping system was evaluated after 23 years of residual effects in a long-term fertilizer experiment (LTFE) conducted at RARS, Pattambi, Kerala. The LTFE comprised twelve treatments involving different levels of NPK application, imbalanced nutrient combinations, and integrated nutrient management practices. Principal Component Analysis (PCA) was performed using 28 soil indicators encompassing physical, chemical and biological properties. Four principal components with eigenvalues greater than one were retained, together explaining 83.1% of the total variance. The maximum SQI was recorded in treatment T8, which received 100% NPK in combination with farmyard manure (FYM). Overall, SQI values ranged from 1.82 to 3.01. Relative Soil Quality Index (RSQI) values were calculated to classify the nutrient management practices into poor, medium, and high soil quality categories. The results indicated that integrated and balanced fertilizer applications were most effective in sustaining and improving soil quality in laterite soils. Integrated nutrient management treatments (T8, T9, T10, and T11), along with the lime-amended treatment (T4), were categorized under medium soil quality, whereas the remaining treatments fell into the poor soil quality category.