Study on the distribution of Derris trifoliata Lour. in Giao lac Commune, Giao thuy District, Nam dinh Province

Derris trifoliata is a species which participate in mangrove ecosystem. Species’s distribution depends on many factors, the most important of which is soil structure. Derris trifoliata grows well on clay loam soil or sandy loam soil. Firm ground is less favorable for true mangrove species, so the abundance found along sea-dykes, coastal areas and aquaculture lagoons is much higher than in mangrove core zone. On sandy soil or light sandy loam soil, when sand percentage is high, plants grow poorly with very low density. Study results show that Derris trifoliata can grow on many different types of substrates, but mostly on soil with sand percentage from 39 to 50%, clay from 39 to 45% and limon about 10%. Derris trifoliata grows near sea dykes and aquaculture lagoons, the nearer it is towards sea, the lower abundance and density is. Other ecological factors such as humus content, total nitrogen, C:N ratio, and salinity also affect the distribution of Derris trifoliata but to a lesser extent. In places with high density of Derris trifoliata, although the amount of humus in the soil is not much, the average nitrogen content is high because Derris trifoliata belongs to Fabaceae family, nodules lumps formed on their roots by Rhizobium can fix nitrogen from atmospheric nitrogen.