Enumeration, Effectiveness, and pH Resistance of Rhizobium meliloti Populations in Oregon Soils
1980
Barber, Lynn E.
The number of Rhizobium meliloti cells in the soil of alfalfa (Medicago sativa L.) fields and the effectiveness and pH resistance of strains of R. meliloti isolated from the soil were analyzed for their relationships to soil parameters. Soil samples were collected from three alfalfa-growing areas of Oregon and analyzed for pH, exchangeable H, soil bases, P, N, and organic matter content, and cation exchange capacity. The number of infective R. meliloti cells was estimated using the plant-infection assay. The nodulation effectiveness of each isolated R. meliloti strain was ranked using alfalfa growth response in tube culture and in comparison to uninoculated no N and N-amended controls. The ability of each strain to initiate growth in media adjusted to pH values of 4.5, 5.0, 5.5, 6.0, and 6.5 was determined. The number of R. meliloti cells in the soil was greater with increased soil pH and with decreased age of the alfalfa stand. Although the average ability of the strains of rhizobia to initiate growth at low pH increased with age of the alfalfa stand from which they were isolated, the strain effectiveness decreased with stand age. Average effectiveness of the strains increased with inoreased soil percent base saturation and with decreased soil exchangeable H, N, and organic matter contents.
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