Soil Fertility In Ethiopia

Introduction

Soil as a fundamental natural resource performs key environmental, economic and social functions. It is non renewable within human time scales. Soil quality has been defined as the capacity of the soil to function within ecosystem and land use boundaries, to sustain biological productivity, maintain environmental quality and promote plant, animal and human health (Doran et al., 1996). High quality soil not only produces better food and fiber but also help to establish natural ecosystems and enhance air and water quality (Griffiths et al., 2010). Soil fertility changes and the nutrient balances are taken as key indicators of soil quality (Jansen et. al., 1995. Soil fertility is commonly defined as the inherent capacity of a soil

Similar studies also indicated a slower decline in fertility of the soil occurring in many parts of Ethiopia. For instance studies of soil quality after land use change in the highlands of Ethiopia (Bewket and Stroosnijeder 2003: Limeneh et al., 2004: Negassa and Gebrekidan 2004) reported that forest and shrub lands have high fertility compared to grass and cultivated areas. A study conducted in the central parts of Ethiopia by Mulugeta (2004) indicated that organic matter and Total nitrogen (N) content of the soil declined due to deforestation and continuous cultivation. In western Ethiopia Nega and Heluf,(2009) conclude that conversion of natural forest land in to grazing land and cultivated lands caused loses of cation exchange capacity(CEC) in the magnitude of 38 and 50% respectively in the surface(0-20cm)

Similarly Jing et al.,(2011) indicated that the quality and spatial variability of a soil is affected by the nature of the parent material, topography and land use and soil management practices. Topography (elevation) plays a great role in changing the climatic condition of a given area which in turn affects the quality of the soil. For instance the study conducted in the northern part of Ethiopia by Wolde et al.,(2007) indicted that the fertility status of the soil shows variation due to variation in topography(slope) of the area.. In the same way the study conducted by Alemayehu (2007) was found that upslope areas had lower nutrient concentrations than lower areas as a result of erosion of top soil and subsequent deposition in the lower slope position. On the other hand Gregorich et al. (1998) indicated progressive organic carbon losses in upslope shoulder slope position, while lower slope positions and level depressions undergo organic carbon accumulations. Thus variation in soil property due to topography can cause the variation in the presence important nutrients in the