Soil quality assessment for conservation planning: Insights from PCA-based SQI

Soil quality assessment is essential for the sustainable management of fragile hill ecosystems in Northeast India. This study evaluated soil quality under natural fallow, cultivated fallow, and degraded land uses at two depths (0–15 cm and 15–30 cm) in Mokokchung District, Nagaland. A comprehensive set of soil physico-chemical and textural properties was analyzed and reduced to a Minimum Data Set (MDS) using Principal Component Analysis, retaining silt, nitrogen (N), zinc (Zn), and phosphorus (P) as key indicators. The Soil Quality Index (SQI) was computed using linear and nonlinear scoring functions with additive and weighted aggregation methods. Results showed that natural fallow topsoil (0-15cm) exhibited the highest soil quality, whereas degraded subsoil (15-30cm) recorded the lowest. Nonlinear methods demonstrated greater sensitivity to site variability (CV up to 46.36%) compared to linear methods, while weighted indices produced more conservative estimates by emphasizing critical variables. Overall, the study demonstrates the value of PCA-based SQI as a comparative assessment tool for identifying soil quality gradients in shifting cultivation landscapes and provides baseline information for site-specific conservation and land management planning.