Problem Soils of the Paddy Fields in the Eastern Coastal Plain of the Red River Delta, Vietnam

Although the Red River Delta is one of the grain cradles in the rice-producing areas of Vietnam, this area contains salt-affected area. In this study, we aim to clarify the distribution and characteristics of problem soils which have led to the land use condition as follows. The salt-affected land in the eastern region of the Red River Delta can be divided into two groups: one is the land affected by saline soils and the other is by acid sulfate soils. The acid sulfate soils in Hai Phong exhibit high ion concentrations adsorbed on the soil particle surface; their organic matter content assists in the high ion adsorption capability. The contribution of Na+ concentration to the Electric Conductivity(EC) value is considered to be influenced by seawater and there is a linear relationship between the Na+ concentration and Electric Conductivity in Nam Dinh. The increase in the total salt particles represented by the Eelctric Conductivity value indicates the contribution of Na+ as opposed to Ca2+ and Mg2+. The contribution of Ca2+ and Mg2+ is more than that of Na+. The influence of seawater on the paddy fields in Nam Dinh and in Hai Phong has resulted in a difference in the balance between Na+ and [Ca2+ and Mg2+] concentrations on the surface soil. The acid sulfate soil in Hai Phong exhibits high ion concentrations adsorbed on the soil particle surface. The Sodium Adsorption Ratio and Electric Conductivity values of the coastal agricultural soils can be evaluated with regard to the balance of the adsorbed cations on the soil surface.