Browsing by Subject "Electrical conductivity"

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Evaluating topsoil salinity via geophysical methods in rice production systems in the Vietnam Mekong Delta
(2023) Nguyen, Van Hong; Germer, Jörn; Asch, Folkard
The Vietnam Mekong Delta (VMD) is threatened by increasing saltwater intrusion due to diminishing freshwater availability, land subsidence, and climate change induced sea level rise. Through irrigation, saltwater can accumulate in the rice fields and decrease rice production. The study aims at evaluating topsoil salinity and examining a potential link between topsoil salinity and rice production systems in a case study in the Tra Vinh province of the VMD. For this, we applied two geophysical methods, namely, 3D electrical resistivity tomography (ARES II) and electromagnetic induction (EM38‐MK2). 3D ARES II measurements with different electrode spacings were compared with EM38‐MK2 topsoil measurements to evaluate their respective potential for monitoring topsoil salinity on an agricultural scale and the relationship between land‐use types and topsoil salinity. Results show that EM38‐MK2 is a rapid and powerful tool for obtaining high‐resolution topsoil salinity maps for rice fields. With ARES II data, 3D maps up to 40 m depth can be created, but compared with EM38‐MK2 topsoil maps, topsoil salinity was underestimated due to limitations in resolution. Salt contamination of above 300 mS m−1 was found in some double‐cropped rice fields, whereas in triple‐cropped rice fields salinity was below 200 mS m−1. Results clearly show a relation between topsoil salinity and proximity to the saline water sources; however, a clear link between rice production and topsoil salinity could not be established. The study proved that geophysical methods are useful tools for assessing and monitoring topsoil salinity at agricultural fields scale in the VMD.
Mapping saline groundwater under rice‐paddy fields in Vietnam's Mekong Delta
(2025) Nguyen, Van Hong; Germer, Jörn; Pham, Tien Duy; Asch, Folkard; Nguyen, Van Hong; Institute of Agricultural Sciences in the Tropics (Hans‐Ruthenberg Institute), University of Hohenheim, Stuttgart, Germany; Germer, Jörn; Institute of Agricultural Sciences in the Tropics (Hans‐Ruthenberg Institute), University of Hohenheim, Stuttgart, Germany; Pham, Tien Duy; Vietnam National University, An Giang University, Faculty of Agriculture and Natural Resources, Long Xuyen, Vietnam; Asch, Folkard; Institute of Agricultural Sciences in the Tropics (Hans‐Ruthenberg Institute), University of Hohenheim, Stuttgart, Germany
Climate change, decreased river flow and land subsidence lead to saltwater intrusion posing a significant threat to rice production in Vietnam's Mekong Delta (VMD), one of the world's largest rice exporting regions. Soil salinity in the VMD can be caused by saltwater intrusion into lowland areas through the canal system, or by capillary rise of water from the near surface saline water table, both resulting in salt accumulation in the top soil. Developing appropriate management strategies for adapting rice production systems of the VMD to climate change, both in terms of water and salinity management, requires characterizing and subsequently monitoring of the spatial distribution and temporal dynamics of salinity in the near‐surface aquifers underneath the rice producing area. The distribution of subsurface salinity was investigated using electrical resistivity tomography in the VMD's province, Tra Vinh, as a case study area. Soil salinity was measured for profiles of approximately 300 m length at 44 locations along geological transects in a case study area. Results show that saline water appears at a shallow depth, particularly along the coast and the lower reaches of rivers. Double‐cropped rice fields seem to be more susceptible to salinization via the near‐surface aquifer than other rice cropping systems. The study suggests that temporal fluctuations of the near‐surface aquifer and the dynamics of the exchange between the river and the shallow aquifer need to be investigated in future research.