Implications of land uses and land cover conversion on soil quality in the lower Alwero watershed Gambela region Western Ethiopia

Abstract

Land use and land cover (LULC) changes, driven by policy interventions and shifting socioeconomic activities, have raised increasing environmental concerns and contributed to land degradation in Ethiopia’s lowlands. Over the past three to four decades, these changes have altered landscape structures, including the Lower Alwearo watershed, often resulted unintended ecological consequences, such as declining soil quality. Therefore, the objective of this study was to assess the effect of LULC changes on soil health using a set of scientifically validated soil quality indicators. A total of 131 disturbed and 58 undisturbed soil samples were collected across different LULC types and analyzed for key physicochemical properties. The samples were analyzed for standard attributes in the laboratory, and the results were subjected to Principal Component Analysis (PCA) to identify a Minimum Data Set (MDS) of the most influential soil indicators, which informed the construction of a Soil Quality Index (SQI) using a weighted additive approach. Statistical analysis showed a significant difference in soil quality indicators across LULC types. Among the LULC types, there is a clear trend in the variation of SQI values decreasing from natural forests and grasslands (1.0) to mechanized farmlands (0.86), largely due to intensive tillage and nutrient depletion, whereas smallholder farmlands benefit from minimal disturbance and traditional conservation practices. Woody grasslands showed moderate soil quality (SQI = 0.90), reflecting the effects of biomass extraction and grazing pressure. Seven key soil quality indicators, such as total nitrogen, cation exchange capacity, exchangeable calcium, exchangeable magnesium, available phosphorus, and bulk density were identified as critical metrics for soil quality monitoring in the watershed. Despite widespread land conversion, overall soil quality remains relatively high, partly due to under-utilization of cleared land and continued reliance on indigenous land management practices. The study recommends integrating these indicators into land use monitoring frameworks to guide sustainable land management. It further emphasizes the importance of conservation-based agriculture, regular soil assessment, and the incorporation of indigenous conservation practices into policy design to ensure environmental resilience and agricultural productivity in Ethiopia’s lowland ecosystems and beyond.