Spectral assessment of soil salinity and waterlogging using field spectrophotometric observations in an irrigated semi-arid command area of southern India
Description
Soil salinity and waterlogging are major land degradation processes in irrigated command areas of semi-arid regions, significantly affecting soil productivity and land sustainability. This study evaluates the spectral behaviour of salt-affected and waterlogged soils in an irrigated command area of southern India using field-based spectrophotometric observations integrated with laboratory soil analysis. A total of 120 surface soil samples (0-30 cm) were collected during the summer season of 2024 across varying salinity severity levels. Electrical conductivity of the saturation extract (ECe) was determined and related to spectral reflectance recorded in blue, green, red and near-infrared bands using a portable spectrophotosensor. Several vegetation-based and soil-based spectral indices were derived and statistically analysed. Results showed a consistent increase in spectral reflectance with increasing soil salinity across visible and near-infrared wavelengths. Soil-based spectral indices exhibited stronger relationships with ECe compared to vegetation-based indices. Among all indices, the Soil Brightness Index demonstrated the highest correlation with soil salinity, explaining a major proportion of ECe variability. Multiple regression models integrating spectral bands and indices further improved salinity prediction accuracy. The findings confirm that field spectrophotometric observations combined with soil-based spectral indices provide a reliable and cost-effective approach for assessing soil salinity and waterlogging in irrigated semi-arid landscapes.