Fieldcase Zedelgem by Ghent University and InagroGhent University and Inagro test filter systems for drain water in arable fields. Both organisations cooperate to develop solutions to reduce phosphorus (P) losses originating from drained agricultural fields.
The basic concept to reduce these P losses is installing a filterbox containing a P sorbing material (PSM) at the end of the drainage tubes. This forces the water through the filter material and allows the removal of P from it before entering the ditch (Figure 1).
Image: Schematic overview of the installation of P filters in the field
In the previous year trials with homemade P filters filled with mostly iron-coated sand (ICS) and with Diapure in one particular case as PSM (Figure 2), showed variable results. While most filters processed volumes of 4000 to 13000 liters of water per day (as desired) some others showed issues with clogging. Further, P removal rates varied widely from 59 to 92 %.
Image: homemade filters were tested in the field
Based on these results, it was decided to re-evaluate the two filter materials (ICS and Diapure) and test one custom-made prototype of a P filter in the field in winter of 2018/2019 (Figure 3). Moreover, a test was performed to evaluate whether a difference in the P concentrations and P removal rates was observed when water samples are taken weekly or daily.
Image: Schematic of the custom-made filter prototype and picture of the filter installed in the field
As the drainage season is still ongoing and water samples are still being analysed in the lab. A clear view of this years’results will only be available by the first half of May 2019.