Soil moisture retention enhancement for drought mitigation using NDMI-guided forest site selection and biochar amendment

This study examines the effectiveness of biochar amendment in enhancing soil moisture retention and mitigating drought throughout the dry season, using multispectral satellite imagery, Normalized Difference Moisture Index (NDMI) analysis, and field experimentation. The study area is a 450-hectare dry dipterocarp forest in northern Thailand. Three experimental scenarios were established: undisturbed topsoil (S1), excavated and backfilled pits without compaction (S2), and excavated pits amended with 10% v/v biochar without compaction (S3). Soil moisture content was measured daily at depths of 10, 20, and 30 cm for 151 consecutive rain-free days. Biochar-amended pits (S3) improved soil moisture retention across all measured depths. Compared to S1 and S2, S3 exhibited higher seasonal mean volumetric water content (%VWC), greater cumulative moisture availability, and delayed time to 50% depletion (t₅₀). In contrast, S2 accelerated near-surface drying with limited benefit for deeper storage relative to S1. These findings demonstrate that combining NDMI with biochar amendment can extend the residence time of plant-available water, potentially mitigating short-term water stress and contributing to hydrological conditions that could influence surface fuel moisture dynamics.