Determination of tolerable soil loss limit using quantitative biophysical model: a case study in Andit Tid watershed, central highland of Ethiopia

Soil is a crucial resource providing essential ecosystem services and is facing rapid degradation. To ensure its sustainability, conservation measures are essential, and establishing the tolerable soil loss limit (TSLL) is critical for assessing degradation risks, prioritizing actions, and evaluating their effectiveness. This study aimed to determine the TSLL for the Andit Tid watershed using a biophysical model that evaluates soil erosion resistance by integrating key soil parameters. Therefore, to capture the status of soil parameters 40 disturbed and undisturbed soil samples, including soil depth data, were collected, analyzed in a soil laboratory, and subjected to rigorous normality tests and trend analysis for reliability. The normalized data were processed through a unitless score converter matrix to obtain the soil aggregate score followed by the determination of TSLL through the soil aggregate group and soil depth matrix. Accordingly, the study establishes a critical TSLL of 10 t ha⁻1 yr⁻1 for the Andit Tid watershed. Specifically, the watershed experienced five TSLLs 7.50, 8.80, 10, 11.30, and 12.50 t ha⁻¹ yr⁻¹ covering an area of 4.10%, 23.00%, 10.70%, 45.40%, and 16.70% respectively. These findings provide a foundational benchmark for targeted soil conservation and sustainable land management by highlighting the role of targeted, watershed-specific TSLL in enhancing ecosystem resilience.