Degradation mapping in Southeast Asia using a partial soil health index based on physicochemical indicators

Abstract

Assessing soil degradation in Southeast Asia (SEA) is challenging because most studies are country-specific and indicator-based, relying on disparate metrics that hinder a regionally integrated view of soil health. To address this gap, a regionally calibrated partial Soil Health Index (pSHI) was developed to integrate widely available physicochemical indicators—soil organic carbon (SOC), bulk density (BD), pH, precipitation, slope, and clay—into a unified framework. A regional dataset assembled via systematic review was modeled using a pedotransfer function (PTF) coupled with Random Forest (RF) to integrate and weight indicators. The final model showed strong validation (R² ∼ 0.773; MAE ∼ 0.015; RMSE∼0.029), with clay (70.4 %) and pH (17.2 %) dominating the signal, followed by SOC (4.6 %), precipitation (4.1 %), and slope (2.3 %); BD (1.4 %) was negligible and excluded. Although limited to physicochemical attributes, the pSHI captures broad shifts in soil health rather than isolated changes in single parameters. Across SEA, pSHI values indicate predominantly poor–moderate soil health, with representative ranges: Cambodia 0.44–0.45 (moderate); Malaysia 0.31–0.34, Myanmar 0.35, and Vietnam 0.29–0.41 (poor); and Indonesia 0.27–0.45, Laos 0.33–0.42, the Philippines 0.30–0.45, and Thailand 0.31–0.45 (poor–moderate). The pSHI provides a scalable tool to diagnose degradation, prioritize restoration, and support regional soil-conservation policy; biological indicators can be incorporated as harmonized datasets emerge.