Development of soil quality index for coastal saline soils of Bangladesh

Soil physicochemical properties are key determinants of agricultural productivity, particularly in salinity-affected coastal regions. This study assessed the physicochemical characteristics and soil quality of surface soils collected from Patharghata Upazila, Barguna district, in the south-central coastal region of Bangladesh. Surface soil samples were collected from 0 to 15 cm depth and analyzed for texture, moisture content, bulk density, particle density, porosity, pH, electrical conductivity (EC), organic carbon (OC), organic matter (OM), total nitrogen (TN), available phosphorus, available sulfur, chloride, sodium chloride, and exchangeable potassium. Principal component analysis (PCA) was used to select minimum data set indicators, and a weighted additive model was applied to calculate the Soil Quality Index (SQI). The soils were predominantly silty, with moderate variation in sand, silt, and clay fractions. The mean soil pH (6.15) indicated slightly acidic conditions, while salinity-related parameters showed clear spatial variation, with higher salinity in seafront locations. Organic carbon (0.62-2.22%) and organic matter (1.08-3.83%) contents were generally within acceptable ranges, whereas total nitrogen (0.07-0.2%) remained below the optimum level for crop production. Available phosphorus (3.88-49.68 ppm) and exchangeable potassium (0.12-0.39 meq 100 g^- 1) also varied among sampling sites, reflecting differences in salinity and soil management. PCA identified organic carbon, electrical conductivity, clay content, available phosphorus, and porosity as key soil quality indicators. The SQI revealed considerable spatial variability, with higher values associated with better nutrient status and improved soil structure, and lower values linked to salinity stress and reduced fertility. These findings provide a scientific basis for site-specific soil management, salinity mitigation, and sustainable agricultural planning in coastal Bangladesh.