Soil resistivity measurements to evaluate subsoil salinity in rice production systems in the Vietnam Mekong Delta

Abstract

Rice is a staple crop in the Vietnam Mekong Delta (VMD) in which more than half of Vietnam's rice is produced. However, rice production in the VMD is threatened by increasing saltwater intrusion due to land subsidence and climate change induced sea level rise. Saltwater intrusion into lowland areas through the canal system or capillary rise of saline water from near surface saline water tables may result in salt accumulation in the topsoil. Therefore, it is important to disentangle the two effects and their relative importance to implement appropriate strategies for water and salinity management for adapting rice production systems of the VMD to climate change. Here, we report on the possibility of using geoelectrical methods to evaluate the potential threat of subsoil salinity to rice production. To evaluate the level of subsoil salinity, we measured soil electrical resistivity using an ARES II to a depth of 40 m in a case study comprising five locations in the VMD. Electrical resistivity measurements were calibrated to soil types, which were identified through evaluating 1 m core sections obtained by drilling down to 40 m depth. The relationship between drilling data and soil resistivity was determined by applying clustering and principal component analysis. Resistivity values smaller than 3 Ω m were clearly identified as indicative for a saline water table. The results show a direct link between the depth of the saline water table and the proximity to the sea, but not to the rice production system (single, double, or triple cropping). This study proved for the first time the applicability of the electrical resistivity tomography method for identifying groundwater tables and evaluating subsoil salinity on an agricultural field scale in the VMD.

Evaluating topsoil salinity via geophysical methods in rice production systems in the Vietnam Mekong Delta

“…Soil electrical resistivity of the rice paddy fields was measured during the dry season and after rice harvest. The measurement was conducted using ARES II (GF Instruments s.r.o., Czech Republic) and interpreted and visualized as described in Nguyen et al (2023). The ARES II measurements were carried out with different electrode spacings from 1 to 4 m, allowing an effective depth of up to 10, 20, 30 and 40 m of resistivity measurements, respectively.…”

Comparison of Electromagnetic Induction and Electrical Resistivity Tomography in Assessing Soil Salinity: Insights from Four Plots with Distinct Soil Salinity Levels

“…Electromagnetic induction (EMI) and electrical resistivity tomography (ERT) are two near-surface geophysical techniques that allow the electrical conductivity of soil to be measured and therefore for properties that are correlated with it to be monitored to depths that can reach up to several meters. These properties can be soil salinity [1][2][3][4][5][6], soil sodicity [7], soil water content [8][9][10][11][12][13][14][15], particle size distribution [16][17][18][19], soil cation exchange capacity [20][21][22][23], and organic matter [24].…”