Productivity of dry bean is constrained by the competition with weeds for scarce nutrients and water in eastern Africa. Trials were conducted at Cornell University in 1996 and in central Uganda during the two seasons of 1997 to test the hypothesis that bean crop nutrition can be improved while increasing the relative competitiveness of bean with annual weed species. Soil levels of available N, P, and K were varied in the main plots. Subplots consisted of bean and two weed species in pure stands and bean mixed with each of the weed species. The weed species were black nightshade and smallflower galinsoga at Cornell and smallflower galinsoga and hairy beggarticks in Uganda. Bean yield was the most suppressed by hairy beggarticks with a mean reduction of 48%. Bean nutrient uptake and growth decreased relative to the weed nutrient uptake and growth when N and P were applied, but the relative competitiveness of bean increased with K application. The K effect on bean yield was greater than the P effect in two out of three trials. Alternative practices for the supply of N and P need to be evaluated for increasing bean yields while reducing the relative benefit to weeds.

Nomenclature: Black nightshade, Solanum nigrum L. SOLNI; hairy beggarticks, Bidens pilosa L. BIDPI; smallflower galinsoga, Galinsoga parviflora Cav. GASPA; dry bean or bean, Phaseolus vulgaris L.