Land Use Impact on Soil Physical Quality and Soil Structure in Three Highland Watersheds of Ethiopia

Abstract

Continuous monitoring of soil physical quality is essential in determining sustainability of land use in natural and managed ecosystems particularly; mountainous systems such as the Ethiopian highlands, where soil deterioration and degradation can become major threats to ecosystem and productivity. This study focused on assessment of soil physical quality (SPQ) by comparing values of soil indicator properties to their corresponding ‘ideal ranges’ established in literature and determining soil structural stability and aggregate associated carbon as influenced by land use types. It further employs factor analysis to identify appropriate SPQ indicators and soil structural indices that are dominantly influenced by each land use type in the three watersheds (namely; Jeldu, Diga and Fogera) of the Ethiopian highlands. Surface soil samples were collected from four adjacent agricultural land use types (namely; Grass fallow, Tree fallow, Homestead and Continuous field cropping) within each of the three watersheds for study of Dexter “S” index, aggregate associated carbon and aggregate stability and other SPQ indicators. Results revealed that soils were only adequate in Relative Field Capacity and Plant Available Water Capacity in all watersheds. The soils of the watersheds still maintained good physical quality but there are strong indications of low soil structural resilience and tendency to degrade. Factor analysis grouped SPQ indicators and structural indices into three factors: (Factor 1) structural stability (with soil organic carbon, aggregate associated organic carbon and aggregate size being the most dominant soil quality indicators); no dominant attribute for Factor 2 and Factor 3 is mainly soil texture (with clay being the most dominant). Soil improvement programme in the watersheds lies in management practices that will promote proper management of organic carbon as it is the principal SPQ indicator that influenced variation in other soil attributes.