Variations of groundnut and soybean rhizobium populations at different soil depths in a field newly grown to soybean
1988
Banyong Toomsan | Nimitr Vorasoot | Rut Akkasaeng (Khon Kaen Univ., Khon Kaen (Thailand). Faculty of Agriculture. Dept. of Plant Science)
Populations of both groundnut and soybean Rhizobium decreased significantly with depth. Samples taken from the depth of 0-15 cm had the highest numbers of both types of Rhizobium. Samples taken from the row (on the plant) at the depth of 0-15 cm had higher number of Rhizobium than those taken between the rows at the same depth. No significant difference was observed between samples taken from the row (on the plant) and between the rows at the other depths. Nodules of soybean concentrated mainly at the depth of 0-15 cm. Soil samples were taken just a day before soybean harvest. The plants were dead and dry. No nodule was found on the roots despite of large numbers were found at 60 days after planting. This indicated that ploughing must have occurred and Rhizobium must have been released, resulting in higher number of Rhizobium at the depth of 0-15 cm than at the lower depths in the soil profile and in the samples taken from the row (on the plant) than in the samples taken between the rows at this depth. Significant positive correlations were observed between the number (log10 MPN) of both types of Rhizobium with percentages of organic matter, pH, and the amount of extractable calcium, and significant negative correlations were observed between the number (log10 MPN) of both Rhizobium with the electrical conductivity values and percentages of soil moisture content. These soil parameters might play some roles in determining the number of Rhizobium found in this study.
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