Drainage Water Recycling in Tile‐Drained Agricultural Landscapes: An Integrated Review of Hydrologic and Water Quality Performance, Co‐Benefits, Trade‐Offs and Research Gaps

ABSTRACT

Drainage water recycling (DWR) is an emerging practice in tile‐drained agricultural landscapes that stores tile drainage in reservoirs and reapplies it as supplemental irrigation, jointly targeting agronomic and environmental objectives. A systematic search identified 27 peer‐reviewed records examining DWR, including 11 field‐based studies (two of which were field‐modelling hybrid analyses), eight modelling studies, seven review/synthesis papers and one dataset paper. Reported outcomes include reductions in nitrate–nitrogen losses of up to 37% and reactive phosphorus of up to 39%, together with yield increases of up to 61% for maize and 31% for soybean in dry years. These concurrent benefits, reduced pollutant loads, more reliable on‐farm irrigation supplies and improved crop yield distinguish DWR from most other edge‐of‐field practices. DWR systems may also provide aquatic and wetland habitats, attenuate runoff and generate aesthetic and recreational co‐benefits, especially when integrated with constructed wetlands or other best management practices. However, land requirements, potential salinity build‐up and microbial contamination in reservoirs, and uncertain net greenhouse gas balances highlight the need for careful design, adaptive operation and monitoring. A pronounced lack of independent long‐term field data on water quality, phosphorus dynamics, surface runoff, habitat services and greenhouse gas emissions remains a critical research bottleneck.