Growth and yield of common bean cultivars at two soil phosphorus levels under biological nitrogen fixation

The genotypic differences on growth and yield of common bean (Phaseolus vul garis L.) in response to P supply were evaluated in a field experiment unde r biological N-2 fixation. Eight cultivars were grown at two levels of appl ied P (12 and 50 kg ha(-1) of P - P-1 and P-2 respectively), in randomized block design in factorial arrangement. Vegetative biomass was sampled at th ree ontogenetic stages. The effects of genotype and phosphorus were signifi cant for most traits, but not the genotype x phosphorus interaction. The cu ltivars presented different patterns of biomass production and nutrient acc umulation, particularly on root system. At P-1, P accumulation persisted af ter the beginning of pod filling, and P translocation from roots to shoots was lower. The nodule senescence observed after flowering might have reduce d N-2 fixation during pod filling. The responses of vegetative growth to th e higher P supply did not reflect with the same magnitude on yield, which i ncreased only 6% at P-2; hence the harvest index was lower at P-2. The cult ivars with highest yields also presented lower grain P concentrations. A su b-optimal supply of N could have limited the expression of the yield potent ial of cultivars, reducing the genotypic variability of responses to P leve ls.