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

Depending on soil and rainfall characteristics, pearl millet [Penniset um glaucum (L.) R. Br.] production in the Sahel can be limited by inef ficient use of nutrients, especially N and P, or by inefficient use of water. This study measured pearl millet N and P uptake and compared t he efficiency with which N, P, and water are used for growth under var ied soil P and water availability. Millet,vas grown outdoors in semiar id West Texas using rain-sheltered pots of low pH, P-deficient sandy s oil. Treatments consisted of four P levels (0-56 g m(-2)) and two wate r treatments (stressed and not). Plant P concentration decreased stron gly with plant age; added P and water stress increased stem and leaf P concentration. Plant N concentration also decreased with age and incr eased with water stress, but decreased with added P Because of the eff ects of age, water availability, and P level on organ nutrient concent ration, P-use efficiency (PUE) increased with age, decreased with wate r stress, and decreased with added P Nitrogen-use efficiency (NUE) als o increased with age and decreased with water stress, but tended to in crease with added P Shoot transpiration efficiency (WUE(T)) increased with water stress and added P, and so varied inversely with PUE throug hout 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 cor related with WUE(T) and yield. For crop improvement programs intereste d in increasing both P- and water-use efficiency, PRE is probably a be tter selection index than PUE.