Evaluation of Soil Acidity in Agricultural Soils of Smallholder Farmers in South Western Ethiopia

Abstract

The purpose of this study was to investigate the status of soil acidity in agricultural soils in West Wollega, East Wollega and West Showa zones of South Western Ethiopia. A total of 478 soil samples were collected in 2006, 2011 and 2012 G.C from 0-20cm depth. Thirteen representative districts from West Wollega, East Wollega and West Showa zones were selected purposively. Samples were collected from farmers’ crop fields and analyzed at Nekemte Soil Research Center Laboratory for pH and exchangeable cations. Acid saturation percentages were derived by dividing exchangeable aluminum to sum of bases multiplied by 100. Data were analyzed by SAS software. Mean soil pH of different districts in West Wollega, East Wollega and West Showa zones ranged from 4.91-5.29, 4.87-5.30, and 5.25-5.50, respectively. Mean exchangeable acidity in different districts in West Wollega, East Wollega and West Showa zones ranged from 1.89-3.84, 1.61-4.76, and 0.18-0.57cmol(+)/kg, respectively. Mean exchangeable aluminum of different districts in West Wollega, East Wollega and West Showa zones ranged from 1.63-3.53, 1.62-4.71, and 0.05-0.32cmol(+)/kg, respectively. Exchangeable acid saturation in different districts in West Wollega, East Wollega and West Showa zones ranged from 50-76, 16-43, and 1-6%, respectively. Mean soil pH of study zones are rated as very strongly to strongly acidic and degree of acidity varies across districts. Moving from West Wollega zone to West Showa zone the extent of soil acidity and exchangeable acidity decreases. The soils of West Wollega and East Wollega zones have very high exchangeable aluminum and acid saturation percentages. Under such extreme acidity, major crops such as maize and sorghum in West Wollega and East Wollega zone may grow under suboptimal soil conditions. Thus, soil fertility research should geared towards ameliorating acidic soils with liming materials and developing crop varieties tolerant to soil acidity and Al toxicity.