Controlled drainage with subirrigation: automatic control to manage freshwater use

Climate change, weather extremes, economic growth, urbanization and increased food production, among other things, are making it more complex to guarantee sufficient freshwater in agricultural and economic sectors. Historically, the Dutch agricultural water management focused on water discharge, which makes it now more vulnerable to droughts. A change is needed to anticipate both wet and dry extremes. Current pipe drainage systems (existing in 34 % of the agricultural fields), installed to discharge water, could be modified to systems to retain and recharge water too. Doing so, so called controlled drainage with subirrigation (CD-SI) systems could be a viable measure to i) discharge water only when needed and ii) retain and iii) recharge water when possible. We show data (years 2017-2022) and process-based model output of four experimental sites at the Dutch Pleistocene uplands where CD-SI is applied. Results show that CD-SI could significantly raise the groundwater level at field scale and increase soil moisture availability to plant roots, leading to higher crop yields. Effects of subirrigation are strongly dependent to i) the geohydrological site characteristics, like a resistance layer to limit excessive downward seepage, ii) sufficiently high ditch levels to prevent fast drainage, and iii) the consideration of how much water is supplied relative to acceptance of drought stress (and thus crop yield). Field experiments show that the water supply for CD-SI could be very large. We show how to limit the required water supply, using automated and online control of CD-SI systems. We use actual field measurements on groundwater levels and soil moisture conditions, weather forecasts and field scale hydrological modeling (using the Soil-Water-Atmosphere-Plant model SWAP) to automatically control CD-SI systems. Doing so, required water supply and drainage level are managed daily, based on the actual and future hydrological conditions, and plant water and oxygen demand, including the acceptance of a percentage of crop’s drought stress.  Results show that significant reductions in water demand for CD-SI systems could be obtained, if only relatively minor reductions in crop yield are accepted.