Effect of plant population density on dry matter partitioning and yield in a short-duration cultivar of cowpea (Vigna unguiculata) grown in the tropics

Abstract

SUMMARYAn erect, 60-day cultivar of cowpea, IT84S–2246, was grown with adequate soil moisture at two locations in Nigeria in 1990/91, Ibadan (7° N) and Kano (12° N), contrasting in total incident radiation (Q) and at plant population densities of 1·9–7·7 and 5·4–16·3 plants/m2, respectively. Leaf area, radiation interception and dry matter (DM) accumulation and partitioning were measured. Total shoot and seed dry weights were greater at Kano (mean 4·10 and 1·61 t/ha, respectively) than at Ibadan (mean 1·89 and 0·68 t/ha, respectively), and greater athigher plant densities. Relationships between the reciprocal of total shoot (Wt) and seed dry weight (Ws) per plant and plant population density (Np) determined at Kano and Ibadan were linear and parallel; intercepts, however, were significantly different (P < 0·005). The theoretical maximum potential Wt and Ws per unit area (i.e. 1/b) was therefore the same at Kano and at Ibadan, 448 and 170 g/m2, respectively. However, the optimum Np at Kano and Ibadan was markedly different, c. 10 and 40 plants/m2, respectively. These differences in the relations between DM yields and Np at Kano and Ibadan are examined in terms of leaf area, radiation interception and the partitioning coefficient, and the implications for the design of other agronomic investigations in cowpea are discussed.