Effects of Controlled Drainage with Subirrigation on Nutrient Concentrations in an Agricultural Field in the Netherlands

The rising likelihood of extreme weather events like droughts and floods poses a growing threat to reliable crop production for farmers. Soils may become too dry to support crop growth or too wet and flood, resulting in a partial or total loss of yield. Controlled drainage with subirrigation (CD-SI) offers a potential solution to retain and discharge water in agricultural fields by connecting subsoil drainage pipes to a control pit. This setup allows farmers to manage the water levels independently in the control pit, rather than relying on weir levels which are typically controlled by water authorities. Subirrigation can supply water to the control pit during dry conditions, increasing water pressure in the pipes and causing water to infiltrate the soil, thereby recharging water in the agricultural field. However, as the CD-SI system alters the hydrological functioning of the agricultural water system, it can impact (ground)water nutrient dynamics.

While few studies have examined the effects of CD-SI on nutrient concentrations in agricultural water systems, their findings and interpretations have varied widely. Therefore, this study aims to investigate the impact of a CD-SI system installed in an agricultural field in the Netherlands on nutrient concentrations, compared to a reference field without a drainage system. Continuous field measurements of hydraulic head, soil water potential, and soil moisture content were combined with water quality analyses at nine locations, including five groundwater and two surface water sites. Nutrient concentrations and distributions were compared between the experimental and reference fields over six sampling rounds spanning eight months. Additionally, the input (i.e., groundwater) and output water of the CD-SI system were analysed to assess the nutrient flux through the drainage system.

Our results indicate that following manure application, the experimental field exhibited a greater increase in nutrient concentrations in both shallow and deep groundwater compared to the reference field. During subirrigation, nutrient concentrations in the experimental field followed the trends of the nutrient concentrations of the input water of the system. Surface water nutrient concentrations were not influenced by the CD-SI system’s output. Additionally, there appears to be a spatial relation between the nutrient concentrations and distance to the subirrigation pipes.

These findings provide insights into how CD-SI systems influence nutrient concentrations, and distributions under different operational modes (e.g., subirrigation on/off, free/controlled drainage). The results of this study could help policymakers and farmers determine whether CD-SI systems are a suitable solution for improving the hydrological and nutrient situation in their particular hydrogeological and chemical circumstances.