Nitrogen fixation and plant growth of common bean (Phaseolus vulgaris L.) at different levels of phosphorus availability

The efficacy of the alumina system for differentiating between bean (Phaseolus vulgaris L.) genotypes for growth at different levels of phosphorus availability was determinated. In addition to response to P levels, comparisons were made between plants receiving N either from fertilizer or nitrogen fixation. When the cv. Carioca was provided with either 100 ppm of N or inoculated withRhizobium leguminosarum biovarphaseoli, differences in shoot dry weight and nodule number were related to P level. There was a greater proportion of green, ineffectivevs. red, active nodules at the low P concentration than at the higher P concentration. In a second experiment, two cvs., Puebla 152 and Carioca and the breeding line UW 24-21, either were inoculated with rhizobia or provided with 150ppm of N. Each genotype-nitrogen combination was grown at 8 levels of P. There was a positive effect of P level on shoot dry weight, nodule number and nodule mass. Root mass was affected less than nodule or shoot mass by the P level of the growth medium. Nodule mass, but not P concentration in the nodules, was affected by P level, whereas in the other plant tissues, P concentrations were lower at lower P levels in the media.