The effect of land management practices on soil physical and chemical properties in Gojeb Sub-river Basin of Dedo District, Southwest Ethiopia

Abstract

This study was undertaken to evaluate the effect of cultivation, fallow and woody land with and without soil bund on soil physical and chemical properties in Gojeb river basin of Dedo district. Landscape of the basin was divided in to three slope positions as upper (25 to 35%), middle (15 to 25%) and lower (5 to 15%). From each slope position, purposely three land use types (cultivated, fallow and woody) lands conserved with and without soil bund were selected. Accordingly, a total of 54 composited soil samples, from 3 slope positions x 3 land use types x 3 replications x 2 conservation system (with and without soil bund) were considered to collect soil sample for soil physical and chemical properties analysis. For both composited and core sampled soil sample collection systematic random sampling techniques were conducted through considering similarity of slope gradient, soil types and land use cover. Analysis of variance (ANOVA) and mean separation was carried out by Turkey test using R-version 3.2.2 (2015). Additionally, Pearson's correlation analysis was done by using Statistical Package for Social Sciences (SPSS version 20).The result showed that soil bulk density and sand fraction decreased from upper to lower slope position. In contrast, total soil porosity, gravimetric soil moisture content, fraction of clay and silt were increased from upper to lower slope position. With respect to land use soil porosity, gravimetric soil moisture content, clay and silt proportion of woody land >fallow land> cultivated land. However soil bulk density and sand fraction highest in the cultivated land than fallow and woody land. Similarly, for all land uses conserved with soil bund has highest gravimetric soil moisture content, soil porosity, clay and silt fraction than similar land uses not conserved with soil bund. Soil chemical parameters [pH, EC, Av.P, OM, OC, TN, CEC,[exchangeable cations (K, Ca and Mg), exchangeable sodium percentage (ESP) and percent base saturation (PBS)] were significantly increased from upper to lower slope position while exchangeable sodium was not significantly increased. All soil chemical parameters, mean value of woody and fallow land were highest than cultivated land. Similarly, land uses conserved with soil bund has highest mean value than land uses without soil bund. The result of Pearson's correlation matrix also confirmed that several soil phyisical and chemical parameters have a positive relationship, particularly soil organic matter/organic carbon was strongly correlated with cation exchangeable capacity and clay content. In conclusion, the result affirmed that soil physicochemical property of the study area was strongly influenced by land use and conservation difference in addition to topographic position variation. Therefore, to conserve soil resources it needs highest attention of policy makers as well as land use planners to concentrate their efforts on land management/conservation strategies based on land use system and slope variation.