Assessing Soil Physical Properties for Soil Quality Evaluation in the Bangsal Sub-Watershed of the Brantas Watershed

Abstract

Soil physical quality plays a fundamental role in sustaining agricultural productivity by regulating root development, water movement, and soil aeration. This study aimed to evaluate soil physical quality in the Bangsal Sub-Watershed of the Brantas Watershed using the Soil Physical Quality Index (SPQI) and to examine its relationship with the Normalized Difference Vegetation Index (NDVI). Soil samples were collected from representative agricultural land units and evaluated using six physical indicators: effective soil depth, soil texture, bulk density, drainage, permeability, and available water capacity. Each indicator was scored and integrated into the SPQI using equal weighting coefficients. A simple linear regression analysis was performed to determine the relationship between NDVI and SPQI. The results showed that SPQI values ranged from 2.505 to 4.676, indicating moderate to very high soil physical quality. Horticultural land units exhibited the highest SPQI values, whereas several dryland and paddy field units showed lower physical quality due to limitations in bulk density, drainage, and available water capacity. Regression analysis revealed a moderately strong positive relationship between NDVI and SPQI (R² = 0.6599), suggesting that vegetation condition reflects soil physical quality. These findings demonstrate that integrating field-based soil assessment with NDVI can support soil quality monitoring and sustainable watershed management. Future studies should incorporate soil chemical and biological indicators to achieve a more comprehensive evaluation of soil quality.

Contribution to Sustainable Development Goals (SDGs):
SDG 2: Zero Hunger
SDG 15: Life on Land