FEATURES OF ALFALFA PRODUCTIVITY IN SYMBIOSIS WITH A NEW STRAIN OF ROOT-NODULE BACTERIA

The rates of photosynthesis, respiration, and nitrogen fixation were investigated in alfalfa plants, cultivar Zaikevich, inoculated with Rhizobium meliloti, strains 425a and M4. The plants were grown in sand-filled pots at different nitrogen levels (0.2, 0.25, 0.5, and 1 Hellriegel N rate). The two strains of root nodule bacteria were shown to differ in their response to nitrogen fertilizer. Nitrogen fixation activity in the plants inoculated with strain M4 was enhanced by exogenous (mineral) nitrogen (0.25 to 1N), whereas that in the plants inoculated with strain 425a was depressed by nitrogen fertilizer. At 0.5N, the plants inoculated with strain M4 were superior to the plants inoculated with strain 425a with respect to the rates of photosynthesis, respiration, and nitrogen fixation and with an increment in fresh biomass production of 46%. Strain M4 obtained by genetical and breeding methods is recommended for alfalfa cultivation in the soils rich in available nitrogen.