Pearl Millet Growth as Affected by Phosphorus and Water

The interaction of soiil water and P supply is of paramount importance to pearl millet [Penniseturn gluucum (L.) R. Br.] growth in Sahelian Africa due to unreliable rainfall and low soil P availability. This study was conducted to quantify the growth response of pe:ul millet to water supply and P under conditions analogous to the Saliel in terms of climatle and soil. Millet was grown for 84 d in pots containing 85 kg of Betis: sand (sandy, silicious, thermic Psammentic Paleustalf) at a semiarid1 location near Lubbock, TX, and harvesled at regular intervals. Pots were treated with four levels of applied P (0.00, 1.15, 3.38, rmd 7.77 g P m-z) and two water levels (water stressed and non-water stressed). Whole plant biomass at final h:uvest increased within the non-water stressed treatment from 145 g per pot in the 0.00 g P m-2 level to 626 g per pot in the 7.77 g P m-2 level, and from 64 to 220 g per pot within the water stressed treatments. Analysis of variance showed highly significant statir tical interaction between water and P level during most of the expsriment. Maximum whole plant production rates for non-wai:er stressed plants occurred between 42 and 58 days after emergence (DAE), increasing from 5.0 g d-I in the 0.00 g P m-2 level to 183 g d-a in the 7.77 g P m-2 level, and between 28 and 42 DAE for water stressed plants, increasing from 1.3 g d-I to 8.5 g d-I. Growth rates of plant organs also increased with P level irrespective of water let el. Our study quantifies the strong influence and interaction of P and water supply on pearl millet growth and development in Sahel-li ke environments, and demonstrates that water supply under such conditions cannot be effectively managed for pearl millet production without addressing soil fertility constraints. OIL WATER AND NUTRIENT SUPPLY and their inS teraction are of particular importance in the African Sahel because the staple cereal, pearl millet, is grown under diyland conditions characterized by low and erratic rainfall (Sivakumar, 1989), high potent: a1 evapotranspiration (CochemC and Franquin, 196'7), and impoverished soils (Jones and Wild, 1975) of low water holding capacity (Payne et al., 1990, 199 la). The sandy soils upon which pearl millet is typically ciiltivated have been shown to be so deficient in available soil P (Jones and Wild, 1975; Scott-Wendt et al., 1988; Davis-Carter, 1989) that N-response are often not abtained without some basal P additions (Vidal, 1903; Bationo et al., 198.5; Timofeyev et al., 1988). Growth analysis is a standard method of estimating net photosynthetic production of plants, and serves as a link between merely recording plant production and analyzing it by means of physiological methods (K?et et al. 197 1). There itre very few growth analysis studies of pearl millet (Gregory and Squire, 1979) despite its importance as a major cereal in droughtand famineprone areas of the world. Studies have been conducted (i) under optimal conditions for forage production in W.A. Payne, ICRISAT Sahelian Center, B.P. 12404, Niamey, Niger, West Africa; L.R. Hossner, Dep. of Soil and Crop Sciences, Tetas A&M University, College Station, TX 77843; and R.J. Lascaio, C.W. Wendt, and ,4.B. Onken, Texas Agricultural Experiment Station, Rte 3, Box 219, Lubbock, TX. Received 6 Dec. 1990. *Corresponding author. Published in Agron. J. :83:942-948 (1991). Katherine, Australia (Begg, 1963), (ii) under imgated and unirrigated conditions during the post-mon soon season at Hyderabad, India (Gregory and Scluire, 1979), (iii) as a function of row spacing, using only profile-stored water in a sandy soil at Niamey, Niger (ham-Ali et gl., 1984), (iv) under rain-fed and irrigated conditions at Niono, Mali (Jansen and Gosseye, 1986), and (v) using a 150 d variety of pearl millet during a relatively dry (448 mm) year at Bambey, Senegal (Vidal, 1963). The last author demonstrated that grain yields in excess of 2000 kg ha-' were obtaiiinable by applying relatively high rates of fertilizer. Ikcal subsistence farmers generally obtain much lower yields on this amount of rainfall (Dancette, 1983). Because the response of pearl millet growth l o soil water and P supply has not been systematically investigated, a growth analysis experiment was made in an environment resembling the Sahel in tenns of plant, climate, and soil. Our objective was to measure and analyze the growth response of an African variety of pearl millet to P and water supply in a sandy, acid, and P deficient soil under semiarid conditions. MATERIALS AND METHODS The study was made at the Texas Agricultural Experiment Station near Lubbock, which has a semiarid climate. The pearl millet cultivar ICTP 8203, developed from African landraces by ICRISAT scientists (Rai et al., 1990), was grown in large pots containing an acid, P deficient, Betics sand (sandy, silicious, thermic Psammentic Paleustalf), ard harvested at regular intervals. The experiment consisted of a completely random design with fixed effects (P and water level) and five replications. The Betis soil had a pH in water of 5.5, an available P (Bray 1) of 3 mg kg-I, an organic C content of 2 g k g I , and a CEC of 5.0 cmol kg-'. Physically, it had a bulk density of 1.64 Mg m-3, a sand content of 920 g kg-I, and a clay content of 60 g kg-I. Chemically, physically, and mineralogically, the Betis soil is similar to soils typically sown to millet in 'Niger, Mali, and Senegal (e&, Charreau and Nicou, 1971).