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Abstract
Dry matter production and dinitrogen fixation characteristics in kudzu (Pueraria lobata Ohwi) and some tropical pasture legumes, centro (Centrosema pubescens) and siratro (Macroptilium atropurpureurn cv siratro) were studied under full sunlight and shaded conditions. Nodulating (T202) and nonnodulating (T201) soybean (Glycine max L. Merr.) isolines, were used as reference crops.
The results obtained showed that:
| 1. | Under full sunlight conditions, the whole plant weight at final harvest was in the following order: siratro > T202 ≧ kudzu > centro ≫ T201. However the root to shoot ratio was significantly higher in kudzu than in the other species, particularly at the later growth stages (105 d after planting). | ||||
| 2. | Total plant N content and carbohydrate accumulation in the legumes followed the same order as that of the whole plant weight. Higher nitrogen (N) and starch accumulation were observed in kudzu roots at the later growth stages, with a simultaneous reduction in the shoot N amount, suggesting that shoot N was retranslocated to the roots. | ||||
| 3. | Under full sunlight conditions, the dinitrogen fixing activity estimated by the 15N dilution method was highest in siratro and lowest in kudzu, while, under shaded conditions, the dinitrogen fixation estimated by the total N difference method decreased significantly in siratro but only slightly in kudzu. | ||||
| 4. | Except for kudzu under mild shading conditions (55% shading) where an increase in the whole plant weight and a fairly constant N amount were observed, shading reduced the total plant weight and N amount in all the legumes. | ||||
| 5. | Shading reduced the root weight, N and carbohydrate amounts in kudzu, while its effect on the shoot weight and dinitrogen fixation activity was negligible. | ||||
Based on these results, it is suggested that kudzu was the most shade-tolerant legume among the species in this study. This is mainly due to the higher activities of dinitrogen fixation and shoot growth at the expense of root growth.