The coastal land in the Red River Delta can be described as saline soil in the southeastern coastland and acid sulfate soil in the eastern coastland. For a long time ago, with a social foods demand, the coastal land had been used and upgraded to cultivate rice. Soil salinity and soil characteristics have affected on rice cultivation activity, especially in the dry season when salinity intrusion occurs. Chemical use and cultivation method are improved rapidly in order to attain high productive yields and soil resource optimality. This study aims to clarify the influence of sedimentary characteristic on cultivation activity in the coastal agricultural land by considering the alkaline ion concentration changes. The irrigation system and chemical use in the fields also are considered in the survey. Survey and sampling work carried out at the coastal rice fields represent for saline soils and acid sulfate soils. Sampling places were located by GPS handle equipment. Soil samples were taken using portable boring equipment and investigated in the laboratory. Sampling map, soil map and irrigation system map were made by GIS application. There is a difference in alkaline ion concentrations between saline soil and acid sulfate soil. The sedimentary characteristics of the Red River system and the Thai Binh River system have been mentioned as an explanation for high calcium ion concentration in saline soil and the lack of calcium in acid sulfate soil. Irrigation system has played an important role in reducing soil salinity and ion concentrations in the cultivation soil layer. The effect of “washing method” on soil improvement has been clearly explained when considering soil map, irrigation system and ion concentration changes. The relation between main ion concentrations in the surface soil layer of cultivated land and inhabitants' activities should also be investigated to clarify the complicated relationship between human activities and the changing natural environment. Then, an optimal land use can be found in the coastal land, where the marine agriculture such as shrimp pond has being expanded, replacing the rice field due to the economic demand.