PHYSICAL AND CHEMICAL SOIL PROPERTIES OF MANGROVE FORESTS IN VIETNAM

Recently the area of mangrove (evergreen) forests growing along the coast of Vietnam has been significantly increased by artificial afforestation under the recognition of their ecological role and economic importance. Protection mangrove forests are the largest among all mangrove forests in Vietnam. They act as a belt to prevent coastal roads from erosion and damage due to tides, storms, and tsunamis. However, their role in coastal soil formation is still poorly studied. Soil formation in mangrove forests is influenced by many factors including the following: woody vegetation, tidal saltwater, precipitation, and mountain runoff. The ability of soil to retain water, nutrients, ions, and some other physical and chemical properties is closely related to the soil texture. Long-term monitoring of the soil texture and the content of nutrients in the soil of mangrove forests in the Dam Bay area of the NM Trang Bay allowed us to distinguish 2 groups of soil phases: typical laterite soil in natural mangrove forests and in rhizophore plantings of 2004 and poorly developed laterite soil in cultural cenoses of 2007 and 2013 and in the littoral zone. These two groups have differences in the soil texture depending on the time of stand formation. The total amount of gravel, aleurite, and silt in the first group of soils is higher than that in the second group. The concentrations of nutrients (phosphorus and nitrogen content) in the soil of mangrove forests is quite high, though it gradually decreases from the soil of natural mangrove forests to the littoral zone. In order to effectively prevent erosion of soils and improve their physical and chemical properties, artificial mangrove forests should continuously be grown along the coast lines of the Nha Trang Bay in the Khanh Hoa province, Vietnam.