Biowater’s PhD student Mette Carstensen has, together with colleagues, produced a paper on controlled drainage. Their research questions were: Can controlled drainage be applied during the drainage season (September to April) without harming winter crops? How will it affect N and P loss? And will it enhance denitrification in the root zone? To answer these questions they investigated controlled drainage under Danish conditions on a loamy soil. Controlled drainage is a groundwater management technique reducing the drainage intensity by elevating the water table of the field. The three-year study was conducted on a field with four drainage systems of approx. one ha each. They used a before-after-control-impact (BACI) study design to quantify the effect of controlled drainage. The study showed that harvest yield was unaffected by controlled drainage. The considerable reduction of N and P loss via drainage water was mainly driven by the reduction in drain flow and not denitrification. In contrast to other countries, controlled drainage has not been accepted as an official mitigation measure in Denmark.
The study design is shown in the figure below:
Carstensen et al 2019 J Environ Qual
Carstensen M. V., Børgesen, C.D., Ovesen, N.B., Poulsen, J.R., Hvid, S.K., and Kronvang, B. 2019. Controlled Drainage as a Targeted Mitigation Measure for Nitrogen and Phosphorus. J. Environ. Qual. 48:677–685 (2019) doi:10.2134/jeq2018.11.0393.
Featured image photo: Mette V Carstensen.