Effects of Phosphorus and Water Supply on Yield, Transpirational Water‐Use Efficiency, and Carbon Isotope Discrimination of Pearl Millet

Abstract

Several studies have identified low soil P and water availability as major constraints to pearl millet [ Pennisetum glaucum (L.) R. Br.] production in semi‐arid West Africa. To evaluate the effects of phosphate and water supply on yield, transpirational water‐use efficiency (WUE T ), and carbon‐isotope discrimination (Δ), two varieties of pearl millet were cultivated in pots in a glasshouse at the ICRISAT Sahelian Centre, near Niamey, Niger. Phosphate and water supply had significant effects on yield, WUE T , and Δ. Compared with the control plants, which had adequate water and P availability, yield was reduced 34% by low water supply and 48% by low P supply. Under high P‐supply, water stress increased WUE T by approximately 37%. Under low P‐supply, no effect of water supply on WUE T was observed. Water stress increased Δ by approximately 0.6‰ for low P plants, and 0.9‰ for high P plants. Added P increased Δ by 0.3 to 0.4‰. WUE T and Δ did not differ significantly between varieties. Differences in Δ between green and necrotic leaves were found within both P treatments under low water supply. We attribute changes in Δ to changes in the ratio of external to internal concentration of CO 2 , ( p i / p a ), leakage rates of CO 2 out of bundle‐sheath cells, respiration rates, or chemical composition of the plant material.