Seawater intrusion associated with climate change and sea level rise (SLR) has been postulated for the last decade that causes negative impact on worldwide environmental resources. In Thailand, however; the pertaining information to its effect on soil properties in agricultural areas has not been clearly reported yet. Hence, this study aimed to investigate the seawater intrusion effect on soil properties in agricultural areas of Nonthaburi Province, Thailand. Five study locations, which anticipated to be affected by seawater intrusion, were selected based on the different distances from the Chao Phraya River. Soil morphological properties at depth of 0-15 and 15-30 cm were recorded, besides disturbed soil samples at depth of 0-15, 15-30, 30-60, 60-90 and 90-120 cm were collected to determine the soil physical and chemical properties. Additionally, the soil electrical conductivity (ECe) and sodium adsorption ratio (SAR) analyses demonstrating soil salinity and sodicity were monthly conducted from March 2018 to February 2019 and their annual average values were calculated. The results revealed that all soils were deep to very deep, consisted of silty clay, clay textures, and its field soil pH varied from 6.0-8.0. Soil saturated hydraulic conductivity rating exhibited that it was very slow to moderate. ECe and SAR values of these soils ranged from 0.21-4.38 dS m-1 and 8.29-41.89 consecutively, which trended to increase from its annual average during March and April 2019 as well as July and August 2019. These results suggested that seawater intrusion could be presumptively regarded as a co-factor affecting the variability of soil salinity and sodicity occurring at the interval of insufficient freshwater content for forcing seawater. The implementation strategies for freshwater management and planning are required to prevent future potential seawater intrusion.

Soil salinity and sodicity are the major environmental issues that lead to the deterioration of soil properties, nutrient cycling, and soil ecosystems around the globe. Nevertheless, the reciprocal effects of salinity and sodicity levels on depth-wise soil organic matter (SOM) and micronutrients remain elusive, particularly in Thailand. For a better understanding of such an issue, soil samples were collected from 38 sites at depths of 0–20, 30–50, 60–80, and 80–120 cm where they were affected by salts with variable levels of salinity and sodicity, having electrical conductivity (EC_e), and exchangeable sodium percentage (ESP) from 0.20–74.70 dS m^–1, and 2.74%–113.23%, respectively. Soil physicochemical properties, including distribution of sand, silt, and clay, pH, soil organic carbon (SOC), and micronutrients (Fe, Zn, Mn, Cu, and B) were determined. The results exhibited that SOC content, ranging from 3.36–14.74 g kg^–1, was higher in topsoil (0–20 cm) compared to the other three soil depths and it correlated negatively with EC_e (0–20 and 80–120 cm) and ESP (80–120 cm), suggesting the declines in SOC amount due to high salinity and sodicity levels. Topsoil Mn concentration (0.06–182.06 mg kg^–1) also tended to be greater than the other soil depths while Fe concentration in that soil depth (0.02–33.99 mg kg^–1) tended to be smaller. The EC_e correlated negatively with the concentrations of Fe, Cu (all soil depths), and Zn (30–50 and 60–80 cm), and positively with Mn concentration (60–80 and 80–120 cm), suggesting that the availability of Fe Cu and Zn is vulnerable to high salinity and sodicity levels. Overall, our findings highlight that high salinity and sodicity levels brought about a reduction in SOC content and low concentrations of micronutrients in soils, irrespective of Mn concentration.

Information to aid the selection of suitable cultivated areas remains meager for mung bean, despite it being a socio-economically important legume crop in Thailand. Hence, a user-friendly soil assessment tool is required to help properly choose planting areas. We aimed to provide a decision support system for mung bean cultivation in central Thailand. Soil suitability classes were performed using relevant factors and data essential for mung bean cultivation in 22 provinces in central Thailand. A decision support system was developed as soil map and mobile phone application using data based on soil suitability classes. Information of mung bean growth and yield grown in experimental fields with different soil suitability classes was used for preliminary validation. The main areas were very suitable (S1) and moderately suitable (S3) for mung bean plantation, accounting for 1,319,841 and 1,327,804 ha, respectively. The number of pods per plant and yield per plant of mung bean were higher in S1 areas (12.83–16.65 pods per plant and 8.35–12.43 g/plant, respectively) than in S3 areas. The mung bean yield was also greater in S1 areas (1613.8–2158.7 kg/ha) than in S3 areas (735.8–1138.6 kg/ha). The findings suggest the possibility of using developed decision support system.

Monitoring the Effects of Sea Level Rise on some Soil Properties Related to Salt Affected Soils in Agricultural Areas of Lower Central Plain, Thailand