Screening of Cowpea for Phosphorus Use Efficiency from Rock Phosphate.
Sabiou Mahamane1, W. A. Payne1, Richard H. Loeppert1, J. C. Miller2, and D. W. Reed2. (1) Soil and Crop Sciences, Texas A & M University, College Station, TX 77840, (2) Department of Horticulture, Texas A& M University, College Station, TX 77840
A major factor limiting crop production in Sub-saharan Africa is soil phosphate deficiency. In West Africa, cowpea (Vigna ungiculata) is grown on acid, sandy soils that are very low in most nutrients, mainly phosphorus. Previous investigations addressing the issue have shown that mineral phosphate fertilizer addition improves cowpea yields; however, commercial phosphate fertilizers are seldom used by resource-poor farmers because of their expense and poor availability. Rock phosphate represents an alternative phosphate source. In the present study conducted in a greenhouse, a core collection of six hundred ninety four cowpea accessions was evaluated for phosphate-deficiency stress tolerance and for efficiency of utilization of P from rock phosphate. Plants were grown for 8 weeks in Nacogdoches pine forest soil. This soil is sandy (91% sand), strongly acid (pH 4.7), and low in P (3 ppm Melich III P). Two treatments of P as Tahoua rock phosphate (0 and 300 mg P/kg of soil; 100 to 30 mesh in-1) from Niger were applied. Optimal rates of the other nutrients were provided as Hoagland's solution (minus P) alternately with water. At harvest, plant height, shoot and root dry weights, and shoot P-content were determined, and shoot-to-root ratios were computed. Differences in the genotypic ability to adapt to P-deficiency stress and to acquire P from rock phosphate will be discussed. In the 0 P treatment, adaptive genotypes would be those which make use of the naturally low concentration of Fe-oxide bound P to maintain biomass production. Responsive genotypes would be those which are able to utilize P from rock phosphate. Some cowpea accessions are neither responsive nor adaptive, while others are responsive and adaptive. This data will be potentially useful in the selection of cowpea germplasm for (1) adaptation to West African soils of low to moderate P fertility, and (2) ability to utilize P from poorly soluble rock phosphate.