ent balance in soils of SSA (Henao and Baanante, 2006), underpinned by poverty, affects 95 million hectares of arable land that have reached such a state of degradation that only huge investments in soil restoration can make them productive again (IFDC, 2006). In densely populated SA, soil is often irrigated with polluted or contaminated water because of poor resource management and competition for the resource. The overpumping of groundwater aquifers also has led to the deposit of salt on the land, which destroys soil productivity.
Socioeconomic, political, and cultural factors reinforce conditions that affect soil quality. For example, the main source of fuel for household energy in SA, other than fossil fuel, is wood, crop residues, and cattle manure (Venkataraman et al., 2005). The use of those traditional fuels has set in motion a cycle of natural resource degradation. Rather than being used as soil amendments, crop residues and manure are removed, and this has depleted the soil organic carbon (SOC) pool, created a negative nutrient budget, increased the susceptibility of soils to erosion, and reduced agronomic productivity. Runoff from soil leads to contamination and eutrophication of water resources, and the incomplete combustion of the biomass leads to emission of soot and noxious gases that have adverse effects on human health (Venkataraman et al., 2005). The degradation of the environment as a whole is a self-reinforcing system (Figure 5-1), and there is an urgent need to identify and foster technologies and management practices that can break the cycle of agrarian stagnation, enhance food security, and improve the environment.
Soil provides the physical, chemical (including water), and biological environment for sustaining plant growth. There are strong interdependences among soil characteristics, and maximizing the productivity of the soil requires attention to each of them. Because soils and the climatic and socioeconomic conditions in which they exist differ regionally, approaches to soil management are highly situational. There are many soil types in SSA and SA, from the highly erodible desert Aridisols and the easily compacted Alfisols to the less-permeable Vertisols (clayey soils with low infiltration rate and high susceptibility to erosion), and each has distinct needs and vulnerabilities. Some crops grow better than others in particular soil types, and the nutrient content of soils can vary widely.
Nevertheless, successful soil management systems have several common objectives: to increase carbon content, enhance water infiltration, ensure the availability of water at the plant-root zone, reduce erosion, create a positive nutrient budget, and encourage beneficial organisms.