Enriched area closures and bunds significantly improve soil chemical properties in an erosion-prone watershed, Northwestern Ethiopian Highlands

Abstract Despite many years of implementing soil and water conservation (SWC) practices, soil erosion continues to be a serious risk to agricultural productivity and food security in the Ethiopian highlands. Although many studies have shown the overall benefits of SWC measures, their effects vary by location and type, and how different structures and their ages perform under actual field conditions is not well quantified. This study evaluates how different selected SWC practices impact key soil chemical properties in the Ziba watershed, northwestern Ethiopia. Soil samples were taken from nine distinct treatments. These includes 2- and 3-year-old soil bunds, 3-year-old stone bunds (loss and deposition zones), an enriched area closure, along with non-conserved cultivated land and shrub-bush as a control. Soil pH, electrical conductivity (EC), exchangeable bases (Ca²⁺, Mg²⁺, K⁺, Na⁺), available phosphorus (Av. P), soil organic carbon (SOC), and total nitrogen (TN) were analyzed from the sampled soil. One-way analysis of variance (ANOVA) with Least Significant Difference (LSD) for mean separation at p < 0.05, and Pearson correlation analysis was carried out. The results showed that soil and water conservation measures significantly enhanced most soil fertility indicators. The Deposition zones showed higher nutrient levels compared to the soil erosion zones and the control treatments. The mean value of exchangeable bases, SOC, TN, and Av. P, in the soil deposition zones across all bunds, were found significantly higher by 16.8%, 33.5%, 45.3%, and 76.6%, respectively, compared to the soil loss zones. Soil pH remained moderately acidic for all the treatments. Regardless of the treatment types, the EC levels were low and within non-saline limits. Strong positive correlations between SOC and TN emphasized the importance of increased soil organic matter (OM) in restoring soil fertility. The findings showed that SWC practices created localized soil fertility hotspots in the soil loss and deposition zone, with the extent depending on the nature of the conservation type, its age, and landscape positions. These results offer site-specific evidence to support the advancement and expansion of integrated physical and biological SWC methods in erosion-prone highland watersheds of Ethiopia.