Semidwarf and standard-height cowpea responses to row spacing in differentenvironments

Yield potential of several grain crops has been increased by breeding semid warf cultivars with greater harvest index and growing them at high plant de nsities. We evaluated effects of the semidwarf trait on yield-potential of cowpea [Vigna unguiculata (L.) Walp.] in contrasting, but productive, envir onments. Three semidwarf and three standard-height cowpea lines with simila r indeterminate habits and phenology were evaluated at row spacings of 51, 76, and 102 cm in four field environments where the extent of early vegetat ive vigor varied. Main stems of semidwarf lines were 33% shorter, and they produced 13% less vegetative shoot biomass than standard lines. Average gra in yield of semidwarf lines was 10% greater than that of standard lines and was associated with 11% higher harvest index and 19% greater pod set. Semi dwarf Lines produced relatively greater yield than standard lines at narrow er row spacings (15, 11, and 4% greater than standard lines at 51, 76, and 102 cm row spacing, respectively). Average yield of standard lines did not respond to row spacing. In a: stressful,soil environment that caused extrem e dwarfing of both plant types, there was no difference in grain yield betw een semidwarf and standard lines. Semidwarf lines produced greater yield th an standard lines at narrow row spacing in soil conditions that promoted mo derate to vigorous early plant growth due to impaired reproduction of stand ard, but not semidwarf, lines when competition for light was strong.