Soil Fertility Assessment and Mapping of Becheke Sub-Watershed in Haramaya District of East Hararghe Zone of Oromia Region, Ethiopia

Abstract

Lack of area-specific information on soil fertility is presenting unprecedented challenge to bring about increased and sustainable productivity in Ethiopia in general and the study area in particular. In view of this, a study was conducted at Becheke Sub Watershed in Haramaya District of East Hararghe Zone of Oromia Region, Ethiopia, to study selected physicochemical properties of soils under different land units and map fertility status of soils of the study area. Based on land use type, soil color, altitude, slope gradient and soil management practices, the study area was divided into7 land units (LUs). A total of 21 composite surface soil samples were collected for laboratory analysis. The results revealed that the dominant textural classes are sandy loam and sandy clay loam with the sand fraction dominating the soil separates’ proportion. Bulk density of the soils under different LU varied from 1.32 to1.59 gcm^-3, while the total porosity ranged from 40.00 to 50.12%. The lowest bulk density and the highest total porosity were recorded in the virgin land. The pH values varied between slightly acid and neutral with values of 6.04 to 7.17. The soils are generally low in organic matter with values that ranged between 1.02 to 3.92%. Following the low organic matter content, the total N content of the soils was also dominantly low in which values of 0.06 to 0.18 were recorded. The soils were generally better in their available P content (10.67-24.55 mg/kg). The CEC of the soils under the study area ranged from 24.85 to 42.31 and was medium to very high. The soils were also relatively rich in Ca and Mg, whereas K was low in soils of land unit 2. The exchange complex is dominated by Ca²⁺ followed by Mg²⁺. Generally the extractable micro nutrients were found to be medium to high except Cu which was low to medium. The soil fertility map developed for OM, total N, available P, CEC, Ca, Mg, Fe, and Cu clearly indicates areas of the sub-watershed where these attributes optimum and not optimum. In general, the soils under different land units exhibited difference in the measured soil attributes. The physical parameter studied indicate that the soils are good, while chemical fertility parameters such as OM, total N, K, and Cu are limiting in soils of some land units. Therefore the use of integrated soil fertility management strategy with inclusion and combination of manure, compost, crop rotation, biological and physical soil and water conservation and other practices together with chemical fertilizer and improved crop varieties gives the better production and keeps the soil fertility status to a better level. However, soil analysis by itself cannot go further than the identification of soil nutrients status due to intricate nature of soil. Therefore, the nutrient supplying powers of the soil sand demanding levels of the plants need further correlation and calibration works to come up with site-soil-crop specific fertilizer recommendation.

Keywords: Physicochemical Properties; Soil Fertility; Mapping