• Korean Journal of Soil Science and Fertilizer
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• v.20 no.4
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• pp.369-374
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• 1987

This study was conducted to evaluate the degree of acid tolerance of indigenous Rhizobium in natural soils, and to select the superior Rhizobia for legume forage on hilly land. 153 Rhizobial strains isolated from two host genera, Medicago and Trifolium in the pastures of Yeongnam area were screened on acidic agar plates. The results obtained are summarized as follows: 1. The degrees of acid tolerance of R. meliloti and R. trifolii were ranged from 4.3 to pH 5.5 and from 4.0 to pH 5.5 respectively. 2. Among acid tolerant Rhizobia isolates, two strains of R. meliloti at pH 4.3 and three strains of R. trifolii at pH 4.0 were shown to have the activities of nodulation and nitrogenase. 3. R. trifolii strains were shown to survive about 80 to 99% at the pH range 4.8 to 5.0, while R. meliloti were about 35 to 47% at that pH range. Therefore, more acid tolerant R. meliloti should be developed for legume forage in Korean hilly land.

• Korean Journal of Soil Science and Fertilizer
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• v.22 no.2
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• pp.138-145
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• 1989

Little information is available on the effects of low pH on nodulation and growth of subterranean clover cultivars. Plants of 11 cultivars were inoculated with an acid-tolerant strain of Rhizobium trifolii and grown for 28 days in continuously flowing nitrogen-free nutrient solutions maintained at six constant pH values from 4.0 to 6.5. At pH 4.0, 4 cultivars failed to nodulate and the remainder formed only a few nodules; nodulation was delayed by 2 to 3 days in this treatment. All cultivars nodulated at pH 4.5 but, with the exception of cv. Dwalganup, nodule numbers were significantly less than at $pH{\geq}5.0$. Only in cvv. Clare and Woogenellup were nodule numbers significantly greater at pH 6.5 than at 5.0. Whole plant dry matter yields were strongly depressed at pH 4.0(21 to 33% of maximum). At pH 4.5, relative yields of all cultivars except Dwalganup were significantly depressed without significant reductions in nodule dry weights, suggesting that nodule function was inhibited by acidity. These results are consistent with the view that nodulation and growth of plants dependent on symbiotic nitrogen fixation are much more sensitive to low pH per se than is host plant growth in the presence of adequate mineral nitrogen.