The interaction of crop genetics with the environment is also critical in reducing vulnerability to drought. In the Sahel, experts have concluded that nutrient deficiencies are an even greater constraint than low rainfall (Bationo et al. 1998; Breman 1992). Breman (1992) notes that natural vegetation in the 450 mm annual rainfall zone of the Sahel utilizes only 15% of the incident precipitation. The remainder is either lost to evaporation, as runoff or remains in the root zone unutilized. When soil fertility is improved, water use by vegetation can increase to 50% and productivity can increase fivefold, greatly lifting the carrying capacity of the land.
Phosphorus deficiency in the Sahel, for example, renders millet more susceptible to drought; research by ICRISAT and IFDC has found that the application of phosphorus increases plant vigor noticeably, resulting in higher yields and greater drought tolerance, as well as drought avoidance (by causing the plants to mature 1-2 weeks earlier).
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