MANAGING YIELD AND WATER-USE OF PEARL-MILLET IN THE SAHEL

Drought occurs often in the West African Sahel, but studies have shown that soil water availability is not usually the limiting factor to pe arl millet [Pennisetum glaucum (L.) R. Br.] production, and that field water-use efficiency (WUE)-i.e., the ratio of yield to evapotranspira tion (ET)-is almost always very lo,v. The purpose of this study mas to determine management effects on yield and water use of pearl millet f or a range of climate conditions in the Sahel. Grain and aboveground d ry matter yield, daily vapor pressure deficit, and soil mater data wer e taken during four gears of contrasting rainfall. Within any given ye ar, genotype, plant population, and fertilizer had relatively small to no effect on ET, but large effects on yield. When high plant populati on (greater than or equal to 20 000 hill ha(-1)) was combined with hig h fertilizer application (greater than or equal to 40 kg N ha(-1) and greater than or equal to 18 kg P ha(-1)) during the wettest year, tota l ET was increased by approximate to 50 mm. High fertilizer applicatio n tended to slightly increase ET and thereby deplete soil water reserv es, but this was not associated with yield decline. Yield and water-us e data refute the view that, by maintaining fields at low fertility an d low plant populations, farmers reduce risk of crop failure during dr ought by reducing crop water use. Compared with traditional practices that use plant populations as low as 5000 hill ha(-1) and zero fertili zer input, moderate plant population (10 000 hill ha(-1)) and fertiliz er application (20 kg N ha(-1) and 9 kg P ha(-1)) substantially increa sed yield and approximately tripled WUE even during 1984, the driest y ear on record. In general, grain yield was better predicted from ET wi thin different management categories when corrections were made for me an daily vapor pressure deficit during the growing season ((VPD) over bar). The study provides evidence for the need to moderately increase pearl millet plant population and fertilizer application in the Sahel to efficiently use available water without risk of crop failure throug h depletion of soil water reserves. It also provides a practical, albe it empirical, basis for predicting yield under different management sy stems from seasonal ET and (VPD) over bar data.