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

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Abstract
Little is known about native populations of rhizobia in soils of the southeastern USA. The influence of season on variations of native R. trifolii populations was studied in different types of field environments in 4 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 Jan. 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. R. trifolii constituted from 0.2-8.5% of the total population of aerobic bacteria in clover pastures and < 0.001-0.124% of the population in cultivated fields.