Effect of integrated land management, slope position and land-use type on soil physicochemical properties, discharge, species richness and carbon stock in Geda watershed, north Shewa Ethiopia

Watershed based integrated land management is a recent approach to curb land degradation in Ethiopia and introduced in 2012 in Geda watershed, central highlands of Ethiopia. However, the impacts of the interventions on indicators of some ecosystem services were not assessed. The objectives of this study were to explore the effects of the interventions on soil properties, soil moisture content and water discharge, plant species richness, biomass production and carbon stock by comparing treated site with integrated land management measures and the adjacent untreated site. Samples were collected from treated and untreated sites in the upper and lower slope positions, from cropland, grazing land and Tree Lucerne plantation based on standard procedures for each objective. The collected data were analyzed following standard statistical procedures with respect to treatment, slope position, land-use type, and soil depth. The introduced integrated land management significantly (p ≤ 0.001) improved most of the soil physicochemical properties, the soil moisture content, water discharge, plant species richness, biomass production and carbon stocks. Clay, total N, available P and soil organic carbon were significantly higher at p = 0.001 and exchangeable K at p = 0.05 in the treated site compared to the untreated one. This could be due to higher organic matter accumulation and improved vegetation growth as a result of prohibited free grazing, and reduced erosion by the conservation structures. Sand and bulk density were significantly (p = 0.001) higher in the untreated site that could be attributed to erosion due to absence of conservation measures and compaction by livestock trampling during free grazing practice. Generally, the introduced integrated land management measure improved clay content of the soil by 63.51%, OC by 133%, NPK of the soil by 69.84%, 78.49% and 22.73% respectively. The soil moisture content increased by 14.82 19.35% and water discharge increased by 588% over the untreated one, which could be due to reduced runoff and evaporation, improved infiltration and storage processes attributed by the conservation structures and vegetation covers. Besides, total plant richness, regeneration of shrubs and indigenous tree species were increased by 18%(N=27),70.59% (N=12) and 66.67% (N=2) respectively, in the treated site compared to the untreated one. In addition, an average 10.72±0.84 Mg ha-1 additional carbon stock was observed due to the intervention. Prohibited free grazing and land-use change could have contributed to higher species richness, regeneration of indigenous trees and accumulation of higher plant biomass and accumulation of higher carbon stocks. Tree Lucerne plot showed higher biomass production and carbon stock by plant biomass depicting the positive impact of land-use changes. Tree Lucerne plot significantly (p = 0.05) improved the upper soil carbon stock which could be due to its N fixing capacity and fast decomposition of the leaves. However, the lower soil carbon stock was significantly (p = 0.001) higher in the crop land of the treated site which could be ascribed to the conservation structures and tillage operations, that conservation structures trap and accumulate transported organic materials from upper slope; and tillage facilitates aeration and decomposition processes. Planting Tree Lucerne combined with physical structures as a biological measure and on highly degraded part of the landscape resulted higher plant biomass production and carbon stock through plant biomass. Thus, integrating physical, biological, and grazing management is a good land-use practice to be expanded to other degraded landscapes.