Influence of Seawater Intrusion on the Properties of Paddy Soils in Lower Central Plain, Thailand

Abstract

The objective of this study was to monitor the changes of some soil properties as influenced by the seawater intrusion in the paddy soils on the Lower Central Plain of Thailand. The paddy soil samples were collected monthly at depths of 0-15, 15-30, 30-60, 60-90 and 90-120 cm from five sites located in Nonthaburi and Pathum Thani provinces. A grab sample method was used to monthly collect the water samples at the Chao Phraya River and the water reservoir nearby the soil sampling sites. Some physical and chemical properties of soil, as well as some chemical properties of water, were analyzed every single month from March 2018 to February 2020. The variability of the chemical properties for soil and water between the year was statistically performed by Student’s t-test. The results demonstrated that soil moisture in the first year (March 2018-February 2019) ranged from 22.99-79.04% and in the second year (March 2019-February 2020) ranged from 9.87-88.98%. The electrical conductivity of soil, sodium adsorption ratio of soil and the electrical conductivity of water in the first year ranged from 0.32-4.42 dS/m, 7.04-37.23 and 0.26-1.6 dS/m, respectively and in the second year ranged from 0.47-5.73 dS/m, 3.63-31.45 and 0.21-6.73 dS/m, respectively. According to the observed electrical conductivity and sodium adsorption ratio of soil, it could be indicated that these soils in the study areas were affected by salts. The variability comparison of the data obtained from the first and second years revealed that the electrical conductivity of soil had increased in the second year while the sodium absorption ratio had decreased (P < 0.05). The electrical conductivity and sodium adsorption ratio of water in the first year and second year revealed a statistically significant difference (P < 0.05). Based on these findings, the severity of soil and water salinity had increased in the second year, which was in line with the highest salinity level of water in the Chao Phraya River with possessing the increase trend in the second year. Thus, the management and planning for freshwater utilization to extrude the potential seawater intrusion in the future are required.