TRANSPLANTING COMMON BEANS INOCULATED WITH Rhizobium AS STRATEGY TO INCREASE NITROGEN BIOLOGICAL FIXATION IN RAINFED CONDITIONS

Biological nitrogen fixation is a viable alternative for corn (Zea mays L.) and dry bean (Phaseolus vulgaris L.) crop production through the establisment of an efficient simbiosis Rhizobium-leguminosae; this is not a simple process due to the competition among introduced and native strains in the soil. Biological nitrogen fixation was estimated in dry bean cv. Michoacán 12-A-3, cultivated by direct sowing or by seedling transplant under rainfed conditions. A mixed inoculant of Rhizobium leguminosarum bv. phaseoli conformed by the strains CP Méx 1, CP Méx 2, and CP Méx 22, was used. There were eight treatments including direct seeding and seedling transplanting. The following data were collected when plants were established: number of rhizobia in the soil and in the inoculated seeds; at the flowering stage, it was estimated the behaviour of the introduced strains in the soil, the percentage of nodules produced by the incoming and native strains, and the number and dry weight of effective and ineffective nodules, as well as nitrogenase activity. Results showed that the transplanted seedlings had a significantly higher effective nodule dry weight than the directly sowed seeds. For the remaining traits there were not significant differences.