Aquaculture impoundment reduces salt leaching efficiency of subsurface drainage systems in neighboring farms

Subsurface drainage is widely used in the management of agricultural soil salinization, with groundwater table control effectively reducing soil salinity. However, surface water bodies can alter regional groundwater flow, potentially impacting the efficiency of subsurface drainage for salt leaching. In this study, we installed subsurface drainage pipes at a coastal farm comprising both actively cropped rice ( Oryza sativa L.) fields and adjacent bare soil patches. After 1 year of subsurface drainage, the soil's apparent electrical conductivity decreased by 49.5%. The groundwater table was influenced by a nearby aquaculture pond. When the pond was full, the groundwater table could no longer be controlled, leading to a reduction in salt leaching efficiency. We found a shift in the dominant drivers of soil salinity dynamics: before impoundment, groundwater table control dominated salt leaching, whereas after impoundment, rainfall became the primary factor regulating salinity. Our findings suggest that coastal farmland salinity management should carefully consider the impact of nearby surface water bodies, such as land‐based aquaculture ponds.