Simulating Controlled Drainage with Subirrigation at an Experimental Agricultural Field in the Netherlands to Investigate Irrigation Water Effectiveness

Climatic extremes, such as prolonged periods of summer droughts, alternated with wet winters pose a significant challenge for farmers. Uncertainty in water availability over the growing season forces farmers to make management decisions that are not always favorable for optimized crop yield. Under the EU project FARMWISE, a large variety of management strategies are evaluated that could help farmers mitigate future climatic extremes.

This research focuses on a novel system, consisting of controlled drainage with subirrigation (CD-SI), that allows farmers more control on water drainage and irrigation from their field. The system relies on subterranean drainage lines installed under the agricultural fields. These drainage lines are connected to a control pit, allowing the system to be dual used, for both drainage and irrigation using an external water source. The system is under evaluation at a field site in America in the Netherlands, where soil moisture and groundwater heads are monitored at a field equipped with an CD-SI system and at an adjoining reference field. Previous studies at the field site have shown a positive effect on water availability for crops under irrigation conditions. However, it is uncertain what the overall effectiveness is of the supplied irrigation water. The main aim of this study is to determine the division of supplied irrigation water within the CD-SI system to all parts of the water balance, including root water uptake, evapotranspiration and percolation to deep groundwater, and quantify potential losses.

A physics-based 3D integrated surface-subsurface hydrological is developed and calibrated to simulate the functioning of the CD-SI system using HydroGeoSphere. Preliminary model results show simulated the groundwater dynamics that agree with the observations both at the field with the CD-SI system as well as the reference field, confirming the difference in groundwater dynamics that are observed between the observation and reference field. Research into the overall effectiveness of the supplied irrigation water and division between the various elements of the water balance is ongoing.