| Popis: |
The effects of soil acidity on growth of legumes are influenced by plant species, the rhizobia and the symbiotic system. Two pot experiments were conducted for 6 weeks to examine the effects of soil acidity on non-symbiotic growth, nodulation and N2 fixation of winged bean. In the non-symbiotic growth study, 7 soil treatments (unamended control (pH 4.6), addition of CaCO3 (pH 4.9, 6.1), addition of Al2(SO4)3 alone or in combination with CaSO4 at two pH levels (pH 4.1, 4.4)) were imposed on a sandy soil (Cambic Arenosol) while in the nodulation experiment three pH levels (pH 4.4, 4.6 and 5.2) were applied. Results from the non-symbiotic growth study showed that the application of Al2(SO4)3 (pH 4.1) depressed growth of roots and plant tops and reduced P concentration in the latter to 0.16%, below the critical level of 0.20%. It is suggested that an Al-induced P deficiency was the overriding factor limiting growth of winged bean at pH 4.1. All three cultivars were tolerant of soil pH 4.4. In the nodulation study, the low pH (4.4) treatment reduced nodulation, total nitrogenase activity and symbiotic growth of the plant. These results suggest that nodulation and N2 fixation in the winged bean-Bradyrhizobium symbiosis are limited by low pH; these limitations are greater than that on growth of the host plant. |
