2006 Volume 79 Issue 12 Pages 725-737
This study aims to clarify the main ion concentrations in paddy field surface soil from 0 to 100cm in depth along the coast of the Red River Delta, Northern Vi etnam, represented by Nam Dinh Province. There is a relation between total dissolved solid (TDS) and Na+concentration. Na+and Cl- concentrations in paddy fields increase gradually and the abundance of Cl- concentration in soil proclaims the influence of seawater intrusion. Washing is reported to reduce the high salinity in the cultivation-layer soil of paddy fields. Furthermore, the impact of seawater intrusion on soil salinity of coastal paddy fields has been considered. The top soil layer of coastal salt-affected paddy fields has the highest sodium absorption ratio (SAR) values, and shows the strongest salinity influence in both the flood season and the dry season. Soil samples near the Day River mouth have high SAR values with considerable Na+ concentrations in the dry season. The exchange selectivity between Ca2+, Mg2+and Na+ has also been studied by considering changes in the SAR under different conditions of soil composition and land cover. In coastal agricultural land, the SAR in the surface soil layer can be used to evaluate the influence of salinity. The SAR in cultivated soil is used to assess the influence of salinity problems on the paddy field.
