Science Into Practice - Reducing phosphate discharges

Large quantities of phosphate fertiliser are added to watercress to produce high-quality commercially acceptable crops.

However, these applications can result in high concentrations of phosphate being discharged into watercourses.

In response to the Water Framework Directive, regulators have proposed targets for total reactive phosphate discharges into watercourses. One way to reduce phosphate in watercourses is to remove it from the producer's discharge waters. This technology is called phosphate stripping.

In an extension of project FV 338, two soluble phosphate stripping technologies (Phoslock and Virofilter) were investigated. The results showed that substantial reductions in phosphate in watercress bed discharges were technically possible, although at present not economically feasible.

The work also found that the area of bed fertilised at any one time had a large influence on peak concentrations measured in the discharge and that one method for reducing these peaks was to stagger fertiliser applications as much as possible.

Growers are advised to keep a watching brief on phosphate stripping technologies to identify techniques or materials likely to offer effective removal combined with limited residence time that could offer cost-effective capital investment and running costs.

The full grower summary for FV 338a is available on the HDC website.

Date for your diary

HDC/NIAB Onion Sets Open Day (Produce), Cambridge, 29 September.

Call Bruce Napier at the NIAB on 07885 586098 or email

Horticultural Development Company

For details on all HDC activity, visit

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