Spatial variability of soil fertility under different land use Types in Assosa District, Western Ethiopia

Abstract

A study was conducted to evaluate the spatial variability of soil fertility under different land use types, in Assosa District, western Ethiopia. Three different land use types, namely; cultivated, grazing, and forestland considered for this study. Surface soil samples (0-20 cm depth) were collected from three kebeles (Amba 8, Abirhamo, and Amba 12) which are considered representative of the study sites. Total of 54 soil samples in triplicates (27 disturbed and 27 undisturbed) were collected from the three land use types. The obtained results indicated that the moisture contents of soil reduced from 17.89 to 14.58%, pH from 5.72 to 5.3. 1In addition, the same trend was observed for organic carbon that decreased from 3.52% to 1.42%, total nitrogen from 0.35% to 0.16%, available phosphorus from 5.16 to 3.36 mg kg -1 , extractable sulfur from 5.33 to 3.89 mg kg -1 , extractable zinc from 4.7 to 0.84 mg kg -1 , boron from 1.7 to 0.27 mg kg -1 . In contrast, there were increasing in soil bulk density from 1.15 to 1.25 g cm -3 , exchangeable acidity from 0.63 to 2.07 cmol+ kg -1 , exchangeable Al from 0.13 to 1.44 cmol+kg -1 . It was concluded that land use change has a significant effect on soil quality and crop productivity in the Assosa district. The conversion of forest land to cultivated and grazing; increases soil acidity, exchangeable acidity, and exchangeable Al and decreasing the amount and availability of Phosphorus, nitrogen, organic carbon, and deficiency problems of some micronutrient (B and Zn). As a result, soil fertility and crop productivity might decline. Therefore, attention should be given to correct soil nutrient status and site-specific management should be taken on cultivated lands by the concerned bodies and the farmers in the study area.