Characterization of soil of Jijiga plain in the Somali regional state of Ethiopia

Abstract

Low soil fertility and poor soil fertility management practices constrain crop production in Ethiopia. Diagnosing soil fertility problems and characterizing soils are a prerequisite for formulating appropriate soil fertility management practices. However, most soil fertility problems in Ethiopia are not diagnosed, and the soils are not characterized. This invariably leads to lack of documented information for judicious application of soil ameliorative measures to increase crop yields. This study was, therefore, aimed at characterizing soil of Jijiga Plain in the Somali Regional State of Ethiopia on which wheat is commonly grown. The study was conducted during the main cropping season of 2012/2013. The study area was stratified in to three altitude categories 1650 - 1700, 1750 - 1800, 1850 - 1900 meters above sea level prior to sampling. Then, a total of 3 x 2 x 30 x 3 = 540 disturbed soil samples were collected from the surface (0-15 cm) and subsurface (15-30 cm) layers across the altitude categories. The samples were composited treatment-wise to 3 x 6 = 18 sub-samples. The composite soil sub-samples were analyzed for selected soil physico-chemical properties. The data were analyzed using descriptive statistics. The results indicated that both the surface and subsurface soils are clayey in texture. The pH of the soil at the layer of 0 - 30 cm ranged from 8.37 to 8.82 and is rated as strongly alkaline. The exchangeable Ca²⁺ contents of the soil at the surface and subsurface soil layers were 24.52 and 30.52 cmol+/kg, respectively, which is rated as very high in both soil layers; the exchangeable Mg²⁺ content is 7.36 cmol+/kg in the surface soil layer, which is rated as high, but 10.21 cmol+/kg in the sub-surface soil layers, which is rated as very high. The exchangeable Na+ content of the soil ranges from 0.33 to 2.16 cmol+/kg, which is rated as medium to high. The exchangeable K+ contents of the surface and subsurface soil layers are 1.1 and 1.4 cmol+/kg, respectively, which are rated as high and very high in the surface and sub-surface soil layers. The cation exchange capacity of the soil ranges from 37.17 to 40.49 cmol+/kg, which is rated as high to very high. The percent base saturation in the surface soil is 89.63% whereas that in the sub-surface soil is 109.23%, which is rated as very high. The contents of soil organic carbon (1.81%) and total nitrogen (0.13%) in the surface soil layer were found to be medium whereas those of the sub-surface soil layer were found to be low. However, the available phosphorus contents of both the surface (2.4 mg kg^-1 soil) and sub-surface (1.87 mg kg^-1 soil) soil layers were found to be very low. It could, thus, be concluded that, the soil of the study area is characterized by strong alkalinity with high contents soluble calcium carbonate, very low content of plant-available phosphorus, and medium contents of soil organic matter as well as total nitrogen. However, the texture and other chemical properties of the soil do not appear to limit crop production. Therefore, there is a need to take ameliorative measures aimed at lowering the pH and increasing availability of soil phosphorus, soil organic carbon, and total nitrogen to improve wheat and other crop yields in the study area.

Keywords: Available phosphorus; Cation exchange capacity; Soil organic carbon; Soil organic matter; Soil texture; Soil pH