Effects of land uses and slope gradients on soil physicochemical properties in Woynwha watershed, Northwest Ethiopia

Abstract

Soil quality degradation has become a major problem that results in low agricultural productivity and increasing food insecurity in sub-Saharan Africa. Improving our understanding of how different land uses and slope positions affect soil properties is critical for developing best land management practices. The objective of this study was to examine effects of land uses and slope gradients on physicochemical properties of the soil in the Woynwha watershed, Northwest Ethiopia. Composite soil samples were collected from 0- to 20-cm depth in three major land uses (natural forest, cultivated, and grazing lands) and three slope positions (upper, middle, and lower) with three replications using an auger. In addition, undisturbed soil samples were collected using a core sampler for bulk density analysis. The collected soil samples were analyzed following standard procedures. The variation in soil properties among land uses and slope positions on soil properties was determined using analysis of variance. Means comparison was performed using the least significant difference test at a 5% significance level. The results revealed that land use types and slope gradients showed statistically significant (p < 0.01) differences in sand, silt, clay, bulk density, pH, available phosphorus (Av P), total nitrogen (TN), organic carbon (OC), cation exchange capacity (CEC), and exchangeable bases of the studied soil. The highest mean values of bulk density (1.64 g cm⁻³) and lowest total porosity (37.67%) were measured under grazing lands at steeper slopes. On the other hand, the highest total porosity (64.30%), clay (59.33%), silt (21.33%), soil pH (6.62), OC (3.58%), TN (0.32%), CEC (51.20 cmol_c kg⁻¹), Ca²⁺ (11.27), Mg²⁺ (2.50), K⁺ (1.63), and Na⁺ (0.43 cmol_c kg⁻¹) were observed in the lower slopes of natural forest. The highest (6.0 mg kg⁻¹) and lowest (2.33 mg kg⁻¹) contents of Av P were recorded in croplands of lower slopes and grazing lands of upper slopes, respectively. Hence, we conclude that integrated nutrient management and sound land use planning should be implemented for improving soil fertility and crop productivity in the study area and others having similar environment. However, soil properties variability under different depths and agroecologies needs to be examined through further research.