Performance of controlled drainage in tile-drained agricultural fields: An exploratory scenario analysis with the soil-plant model SWAP

Regular drainage (RD) systems ensure optimal crop growth by preventing oxygen stress and lead to a significant loss of fresh water, a valuable resource that could be used to sustain crops during summer months. Controlled drainage (CD) systems can raise the water table above the subsurface drains using a control pit. However, it remains unclear to which extent CD contributes to better crop yield and more groundwater recharge. While manual controlled drainage (MCD) is managed by hand, climate-adaptive drainage (CAD) offers the possibility to continually adjust the water table based on weather forecast and crop needs. In this work, we conducted an in silico experiment using the SWAP model to investigate the interactions between drainage types (RD and MCD) over a 30-year timeframe, 3 soil textures and different drainage management practices in maize cultivation. MCD leads to an increase in groundwater recharge (between 28 % and 45 %) and it reduces the drainage flux (between 25 % and 17 %) compared to RD. MCD increases maize transpiration mostly in loamy sand soils (+ 0.5 % median). In other soils, transpiration is reduced due to oxygen stress. CAD for the 30-year data did not result in large improvements in crop transpiration and resulted in less groundwater recharge and more drainage than MCD. Although both MCD and CAD offer only minimal improvement of crop transpiration and is highly dependent on soil type, weather conditions and drainage management, they do result in enhanced groundwater recharge, which is crucial for maintaining water availability and supporting ecological systems.