Geostatistical Assessment of the Spatial Variability of Acid Soils Properties in the Southeastern Highlands, Arsi Zone, Ethiopia

Abstract

This research was conducted with the objective of generating quantified information on the spatial variability of soil properties and apply them to improve the planning and management of acid soils in the highlands of Arsi zone, Ethiopia. In this research, the spatial variability of soil pH-H2O, pH-K, percent organic carbon (% OC), cation exchange capacity (CEC), exchangeable acidity, and exchangeable aluminum is studied. Four kriging and 3 deterministic interpolation methods were evaluated for their prediction accuracy. Hence, Ordinary Kriging (OK) and Empirical Bayesian Kriging (EBK) were found to be superior for prediction of pH-H2O and pH-K; while Universal Kriging (UK) for CEC and % OC; and UK and Local Polynomial Interpolation (LPI) for exchangeable acidity and exchangeable aluminum. Finally, OK was applied for analysis and interpretation of pH-H2O and pH-K; UK for CEC, % OC, exchangeable acidity and exchangeable aluminium. Soils in the range of pH-H2O:4.49-5.3 cover about 82% of the total area. About 56% have pH-H2O less than 5.1 and CEC values between 2.96 and 20.01 meq/100 g. Generally, the CEC varied from 2.96 in the very strongly acidic to 37.1 meq/100 g soil. The % OC content is generally good, and varied with altitudinal gradations. Exchangeable acidity varied from 0.1–4.28 meq/100 g. Kriging interpolation based on the data range of 0.1 - 2.4 meq/100 g showed that 68% of the total area has exchangeable acidity greater than 0.5 meq/100 g. These results are found to be very useful for improving research and development planning, management, and evaluation of the effectiveness of measures to be taken to address productivity problems on the studied area.