Need for inoculation of common bean (Phaseolus vulgaris L.) in senegal andassessment of nitrogen fixation using N-15 isotope dilution technique

A field experiment was conducted at Eel Air station, in Dakar using N-15 is otope dilution technique and the non nodulating soybean (Glycine max) varie ty m129 as reference plant to estimate nitrogen fixation in common bean (Ph aseolus vulgaris). Dry matter production and nitrogen accumulation were inc reased in plants inoculated with Rhizobium strain ISRA 355 compared to unin oculated plants (+31% and +50%, respectively) and in 20 N-fertilized plants compared to non N fertilized plants (+36% and +39%, respectively). In addi tion %Ndfa was increased in common bean inoculated with strain ISRA 355 (+3 2% higher than non inoculation) or supplied with 20 kg N/ha (+37% higher th an non N fertilization). However, the amount of fixed nitrogen was increase d by the interaction inoculation x 20 N-fertilization only (+155% over the value averaged across all uninoculated plants). From all treatments, estima tes of fixed nitrogen were ranged between 63 to 139 kg N/ha. Beside this es timation, nitrogen fixation was found to be inhibited in common bean suppli ed with 80 kg N/ha. Thus, 20 kg N/ha should be considered as starting rate of nitrogen fixation in common bean cultivated at Eel Air experimental stat ion.