15 May 1998

Caution on Stests

BE wary of laboratory reports on sulphur testing until more uniform analysis methods can be agreed. That is the underlying message from a £12,800 HGCA-funded study of the performance and analytical reliability of 10 UK labs.

Variations of up to 100% in results from the same samples were found, says organiser Steve McGrath of IACR Rothamsted.

The ring test exercise obtained reports on a range of identical crop materials, including wheat flour of an internationally certified standard, grass, oilseed rape foliage and wheat grain as well as two soils known to differ in sulphur content.

Only half the labs performed adequately, says Prof McGrath. However, methods for analysing total S are relatively new and not yet standardised. Likewise, there are no internationally certified standard soil samples for ring tests, he notes.

"The analytical problems are worse when sulphur concentrations are low, as is increasingly the case for soil samples. Some of the techniques are not sensitive enough."

All the labs, which Prof McGrath says were aware that the research was taking place, have been informed of the findings. Recommendations as to how they might improve performance have also been made.

"It is up to them to digest the report and decide what to do about it and whether they can change." Investment in new equipment may be required in some cases, he suggests.

"We are obviously concerned because people could be getting the wrong messages," says Frank Oldfield, chairman of the HGCAs oilseeds R & D advisory committee. "We are trying to establish some commonality across the range of labs doing the work and to give advice wherever possible. We hope they will take it on board."

The aim is to undertake a similar exercise in six months time to determine whether there has been any improvement, he explains.