ĐÁNH GIÁ SỰ BIẾN ĐỘNG ĐẤT MẶN VÀ ĐẤT PHÈN VÙNG ĐỒNG BẰNG SÔNG CỬU LONG SAU 30 NĂM SỬ DỤNG

Saline soils and acid sulfate soils are the main soil types in the Cuu Long River Delta which play an important role for rice production in the delta as well as in Vietnam. Under the influences of climate changes, land use and others, saline soils and acid sulfate soils in the delta have been changing in both area and quality. Our survey for these soils in Cuu Long River Delta in 2005 showed that total area of the saline soils increased 177,714.5 ha compared to the data of previous survey in 1975; of which the areas of the strongly saline soil and the moderately and slightly saline soil increased 26,744.7 ha and 199,757.1 ha respectively, while the total area of mangrove saline soil decreased 48,787.3 ha. Total area of the acid sulfate soils decreased 261,590.7 ha compared to the data of the survey in 1975; of which the potential acid sulfate soil decreased 594,880.6 ha, while the actual acid sulfate soil increased 333,289.8 ha. By comparing the soil analysis data from the survey in 1975 and from our survey in 2005, we found that the quality of these soils was significant change after 30 years of using. The particle sizes were slightly changed, especially in the top soil layers because of influences of water regime. The pH value of the acid sulfate soils decreased in the most of soil samples. The total nutrient contents such as organic carbon, nitrogen, phosphorus and potassium slightly changed in most saline soil samples, but significantly decreased in acid sulfate soil samples, especially for organic carbon and total nitrogen. The available nutrient such as phosphorus, potassium, calcium, and magnesium slightly decreased in both saline and acid sulfate soils. Keywords: saline soil, acid sulfate sois, Cuu Long River Delta.