NITROGEN AND PHOSPHORUS UPTAKE IN PEARL-MILLET AND ITS RELATION TO NUTRIENT AND TRANSPIRATION EFFICIENCY

Depending on soil and rainfall characteristics, pearl millet [Pennisetum glaucum (L.) R. Br.] production in the Sahel can be limited by inefficient use of nutrients, especially N and P, or by inefficient use of water. This study measured pearl millet N and P uptake and compared the efficiency with which N, P, and water are used for growth under varied soil P and water availability. Millet,vas grown outdoors in semiarid West Texas using rain-sheltered pots of low pH, P-deficient sandy soil. Treatments consisted of four P levels (0-56 g m(-2)) and two water treatments (stressed and not). Plant P concentration decreased strongly with plant age; added P and water stress increased stem and leaf P concentration. Plant N concentration also decreased with age and increased with water stress, but decreased with added P Because of the effects of age, water availability, and P level on organ nutrient concentration, P-use efficiency (PUE) increased with age, decreased with water stress, and decreased with added P Nitrogen-use efficiency (NUE) also increased with age and decreased with water stress, but tended to increase with added P Shoot transpiration efficiency (WUE(T)) increased with water stress and added P, and so varied inversely with PUE throughout the growth cycle. Phosphate root uptake efficiency (PRE) was less sensitive than PUE to age, P availability, and water stress, because of the compensating effect of root growth; PRE was also positively correlated with WUE(T) and yield. For crop improvement programs interested in increasing both P- and water-use efficiency, PRE is probably a better selection index than PUE.