Effect of P and Fe applications to cowpea in three soil types

Cowpea, (Vigna unguiculata L.) was grown using 3 soil types (designated Black, Red and Calcareous) at 4 rates of P (0, 40, 80 and 160 kg/ha) and 4 rates of Fe (0, 2, 4, and 8 kg/ha). Sampling was done fortnightly (starting at 4 weeks after planting) for measurements of leaf area, plant height, leaf dry weight and leaf concentrations of P and Fe. Cowpea plants on P treatment were stunted, irrespective of soil type. The P requirement for good growth on the Black soil was only a quarter that on the other two soils. Different P-Fe ratios (24:1, 17:1 and 12:1) were required for best cowpea growth on the Black Red and Calcareous soils respectively. Significant (P=0.05) increases in growth were obtained with the addition of P while addition of Fe did not lead to any such significant increases in growth on any of the 3 soils. Highest leaf P was obtained in plants grown on the Black soil while the lowest was in plants on the Calcareous soil. © 1986 Martinus Nijhoff Publishers.