Effects of flooding on nodulation and growth of tropical forage legumes

Abstract

Three greenhouse experiments were carried out to study the effects of: a) flooding for 20 day periods on plants of different ages; b) increasing periods of flooding; c) increasing moisture levels during the experimental period. The first experiment was carried out in two hydromorphic soils with the soybean cultivar Santa Maria (Glycine max). Assimilation of mineral N as well as symbiotic N stopped after flooding at any age. While nodules on younger plants were maintained, but did not grow, those on 45 day old plants disappeared almost entirely. The second experiment was carried out in one hydromorphic soil with Stylosanthes guyanensis, Phaselous atropurpureus and Centrosema pubescens. S. guyanensis appeared to be the most tolerant species to longer flooding periods up to 45 days while C. pubescens was the most affected. Rotting of roots and nodules was more pronounced on C. pubescens, and new roots and nodules were regenerated in the water above the soil. None of the plants died during the 45 day flooding period. The third experiment was carried out in vermiculite with the forage soybean Santa Maria (Glycine max). Nodule weight and plant growth increased up to 100% of the water holding capacity of the vermiculite, but decreased at 135%. C. pubescens was less affected by water stress than was soybean but was more affected by excess water. While nodule numbers of soybeans, increased up to 135% water holding capacity, those of C. pubescens decreased above 65%.