EVALUATION OF SELECTED SOIL PHYSICOCHEMICAL PROPERTIES ACROSS LAND USE TYPES AND SOIL DEPTH IN SUMBE SUB-WATERSHED OF WEST SHOWA ZONE, CENTRAL ETHIOPIA

Abstract

Soil quality is very much affected by land use and also soil depth. A study was conducted at Sumbe sub-watershed, located in the Toke Kutaye District of West Showa Zone of Oromia region, with the objective of evaluation of selected soil physicochemical properties under different land uses and soil depth. The results revealed the existence of spatial variation in soil properties among land use types and with soil depth in a given land use. Relatively higher silt content (47.50%) was recorded in the cultivated land soils, while clay was high (45.00%) in the forest and grazing land soils followed by the cultivated land (32.25%). Higher bulk density value (1.69 gcm-3) was recorded in the cultivated land soils followed by the 40-60 cm layer of the forest (1.26 gcm-3) and grazing (1.25 gcm-3) soils. Relatively higher total porosity value (62.3%) was recorded in the surface layer of the forest land soil followed by the cultivated (57.7%) and grazing lands (54.7%). Soil pH ranged from 4.94 in the surface layer of the cultivated land soil to 6.74 in the 40-60 cm layer of the forest land soils. The OM content ranged from 1.28% at the bottom layer of the cultivated land to 8.49% at the surface layer of the forest land soils, whilst the total nitrogen varied between 0.06% at the extreme bottom layer of the cultivated land to 0.42% at the surface layer of the forest land. Available phosphorus ranged from 2.00 mk kg-1 at the 40-60 cm layers of the cultivated and forest land soils to 6.40 mg kg-1 in the surface layer of the grazing land. Relatively higher (8.35 Cmol(+)kg-1) exchangeable Ca was recorded in soils of the forest land followed by the grazing and cultivated land soils, whereas exchangeable Mg ranged from 2.21 Cmol(+)kg-1 at the surface layer of the grazing land soil to 4.78 Cmol(+)kg-1 at the 40-60 cm layer of the forest land soil. Similarly, exchangeable K ranged from 0.46 Cmol(+)kg-1 at the 20-40 cm layer of grazing land to 1.10 Cmol(+)kg-1 at the extreme bottom (40-60 cm) layer of the forest land, while Na varied from 0.37 Cmol(+)kg-1 in the forest land soils to 0.57 Cmol(+)kg-1 at the 40-60 cm layer of the grazing land soil. PBS increased with xiv soil depth in all the land uses and varied between 33.8% at the surface layer of the grazing land to 69.6% at the 40-60 cm layer of the forest land soils. Cu ranged from 0.11 mg kg-1 at the extreme bottom layer of the grazing land to 0.46 mg kg-1 at the surface layer of the forest land soil. Iron varied from 10.68 mg kg-1 at the extreme bottom layer of forest land soil to 30.63 mg kg-1 at the surface layer of the grazing land. Fe varied from 10.68 mg kg-1 at the extreme bottom layer of forest land soil to 30.63 mg kg-1 at the surface layer of the grazing land. Mn ranged between 51.55 mg kg-1 at the bottom layer of the grazing land soil to 80.63 mg kg-1 at the surface layer soils in the same land use. Zn also ranged from 2.74 mg kg-1 at the 40-60 cm layer of the cultivated land to 11.78 mg kg-1 at the surface layer soils of the same land use. The soil attributes under the cultivated land showed an overall change towards the direction of loss of its fertility compared to the adjacent forest land soils. Generally, the values show that the overall soil condition in the cultivated and grazing lands is deteriorating.