SEASONAL VARIATION OF Rhizobium trifolii IN CLOVER PASTURES AND CULTIVATED FIELDS IN NORTH CAROLINA

Little is known about native populations of rhizobia in soils of the southeastern United States. In this study, we observed the influence of season on variations of native Rhizobium trifolii populations in different types of field environments in four physiographic regions of North Carolina, using a plant infection and most-probable-number technique. Clover pastures had a higher population of R. trifolii than cultivated fields. Seasonal variation was evident in North Carolina pastures, populations being greatest in January 1979 and lower numbers being observed in the midsummer months. Seasonal distribution differences were not detected in cultivated fields. Physiography in North Carolina did not affect the influence of season on R. trifolii. Rhizobium trifolii constituted from 0.2 to 8.5 percent of the total population of aerobic bacteria in clover pastures and <0.001 to 0.124 percent of the population in cultivated fields.