EFFECT OF PLANT-POPULATION DENSITY ON DRY-MATTER PARTITIONING AND YIELD IN A SHORT-DURATION CULTIVAR OF COWPEA (VIGNA-UNGUICULATA) GROWN INTHE TROPICS

An erect, 60-day cultivar of cowpea, IT84S-2246, was grown with adequa te soil moisture at two locations in Nigeria in 1990/91, Ibadan (7 deg rees N) and Kano (12 degrees N), contrasting in total incident radiati on (Q) and at plant population densities of 1.9-7.7 and 5.4-16.3 plant s/m(2), respectively. Leaf area, radiation interception and dry matter (DM) accumulation and partitioning were measured. Total shoot and see d dry weights were greater at Kano (mean 4.10 and 1.61 t/ha, respectiv ely) than at Ibadan (mean 1.89 and 0.68 t/ha, respectively), and great er at higher plant densities. Relationships between the reciprocal of total shoot (W-t) and seed dry weight (W-s) per plant and plant popula tion density (N-p) determined at Kano and Ibadan were linear and paral lel; intercepts, however, were significantly different (P < 0.005). Th e theoretical maximum potential W-t and W-s per unit area (i.e. 1/b) w as therefore the same at Kano and at Ibadan, 448 and 170 g/m(2), respe ctively. However, the optimum N-p at Kano and Ibadan was markedly diff erent, c. 10 and 40 plants/m(2), respectively. These differences in th e relations between DM yields and N-p at Kano and Ibadan are examined in terms of leaf area, radiation interception and the partitioning coe fficient, and the implications for the design of other agronomic inves tigations in cowpea are discussed.