MAPPING SPATIAL VARIABILITY OF SOIL FERTILITY STATUS OF DIFFERENT LAND USE AT MUGER SUBWATERSHED, NORTHERN OROMIA, ETHIOPIA

Soil fertility is the ability of a soil to nourish essential nutrients to the plant. In order to implement appropriate soil fertility management in the area where spatial variability of soil prevails, soil fertility status assessment is vital. Hence, this study was conducted in Muger sub-watershed in Ethiopia’s Northern Oromia to assess and map the spatial variability of soil fertility status. A total of 25 composite soil samples were collected from cultivated, grazing and forestland of upper, middle and lower slope positions at a depth of 0-20cm for determination of selected soil physical and chemical properties, and their spatial variability was mapped using ordinary kriging techniques of GIS 10 software. The study indicated that there was significant (p<0.05) differences in the values of sand, silt, soil organic carbon (OC),total nitrogen (TN), zinc (Zn), manganese (Mn) and available sulfur (Av.S) among the different land uses of the area. The study also revealed that soils of the area are predominantly sandy clay loam in texture with moderately acidic (5.565.93) in reaction. Soil organic carbon (OC) was significantly (p<0.05) different across different land uses. The recorded mean values of OC and total nitrogen (TN) were low on cultivated lands but high on grazing and forest lands. Zinc (Zn) content was low on cultivated and grazing lands but high on forest land, indicating that Zn, TN and OC could be the limiting factors for crop growth in the study area. On the contrary, cation exchange capacity (CEC), exchangeable calcium (Ca), Exchangeable potassium (K), and extractable iron (Fe) were high in all land uses. However, copper (Cu), percent base saturation (PBS), extractable manganese (Mn), available phosphorous (Av.P) and available sulfur (Av.S) contents were at medium rate for all land uses. The occurrence of exchangeable bases followed Ca>Mg>K>Na trend in their order of dominance. Soil micronutrients ranged from 57.94-78.42, 6.97-12.37, 2.56-4.45and 0.22-1.31mg kg-1 for Fe, Mn, Zn and Cu, respectively. From the findings of this study, it can be concluded that the soils of the cultivated lands were generally low in OC, TN and Zn and medium in Mn and Av. S. Therefore, there is a need for management of soil organic matter and regular application of nitrogen, zinc, phosphorus and sulfur containing mineral fertilizers to the soil in order to replenish the nutrients. Keywords: Land uses; Macronutrients; Micronutrients; Muger sub-watershed; Ordinary Kriging, Soil, Fertility Assessment