This week, for the first time, we supplied ferrous sand for use in the bulb growing region. The sand and gravel, which are enveloped in a thin ferrous coating, are used to control phosphorus levels. Thanks to a relatively simple, but well thought-out, system, the amount of phosphorus that ends up in surface water is cut by no less than 90%. Environmentally-friendly and effective.
In the past, large amounts of phosphorus were applied to the flower bulb fields in this region; and nowadays a lot of phosphorus is still ending up in the surface water via the soil water. This is not desirable and results in an exceedance of the standards of the Water Framework Directive. It leads to the eutrophication of the surface water, resulting, among other things, in the growth of blue-green algae.
A constant and relatively shallow groundwater level is of key importance in the cultivation of flower bulbs. This is why practically all of the fields have a drainage system that maintains the groundwater at precisely the right level. Research shows that this drainage system plays a relatively large part in the phosphorus load in surface water. This is not good. But perhaps such drainage systems could themselves actually offer a solution to the problem.
Substantially less phosphorus
Since 2010, Wageningen University & Research (WUR) has been conducting extensive research
into the application of ferrous sand around these drains. The idea is pretty simple: when the systems are installed, drainage sand is usually applied around the drainage pipes to promote the fluid flow of the soil water into the pipes. If, instead of the traditional drainage sand one applies ferrous sand, the phosphorus-rich water flows over the ferrous sand, the phosphorus binds to the iron and thus no longer flows, via the drainage system, into the surface water. The research shows that the method reduces the phosphorus load transported to the surface water – long-term – by over 90%.
The installation of such a system is of course not cost-free. And partly because of a lack of sufficient practical examples, only a few growers have made the transition to ferrous sand. But this will probably change very soon: the Royal General Bulb Growers’ Association (KAVB) and Delphi have received a POP3 subsidy, which is available to five companies in the South-Holland part of the Rijnland District Water Control Board’s area. This initial project constitutes the starting point for a roll-out of an environmentally-friendly and extremely effective means of controlling phosphorus in the flower bulb sector. The drinking water sector thus plays its part with its residuals in bringing about a cleaner environment!
The following are involved in this project: Alterra, Rijnland District Water Control Board,
Waterboard Hollands Noorderkwartier, Deltares, Arcadis and Van der Geest Grond- en Drainagewerk.