The only option to sustain production growth is to increase yields. Within the developing world, average regional grain yields are the highest in North Africa, and the lowest in Sub-Saharan Africa. Yields are highly dependent on the use of additives, particularly fertilizers. The principal factor limiting yield response to fertilizer use is the inadequate supply of water during the growing season. Although water availability varies considerably across regions, it has been a serious problem in many countries. According to World Bank studies, depletion and degradation of water resources have become major problems facing many low-income countries (Crosson and Anderson, 1992; Cleaver and Schreiber, 1994). Within 10 years, if the population grows at projected rates, per capita water availability will decrease by an average 20% in developing countries, and by 34% in African countries. The agricultural sector consumes over half the annual freshwater withdrawals in most developing nations and could face greater competing demands from household and industrial uses in the future.
The sparse rainfall that characterizes much of Sub-Saharan Africa affects the response to and demand for fertilizer (Seckler et al., 1991; Harold et al., 1994). Farmers are reluctant to risk fertilizer use until rain begins to fall, because inadequate moisture will fail to dissolve fertilizer nutrients (especially nitrogen) and crops can "burn." Irrigation can make the use of fertilizer profitable and increase agricultural output. However, in Sub-Saharan Africa, only 4.3% of all arable land is irrigated. This is low, even when compared with other developing regions. In Latin America, 13% of the arable land is irrigated, and 38% is irrigated in Asia (FAO, 2003b). The world average is 19%. A potential exists to expand irrigated areas in Sub-Saharan Africa, but required investments will be costly. Increasing the use of fertilizer raises production costs. In many low-income countries, particularly in Sub-Saharan Africa and Latin America, almost all fertilizer is imported, and the lack of adequate foreign exchange constrains availability.
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