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Interlaboratory Tests by Section III – Fertiliser Analysis

Section III – Fertiliser Analysis – regularly conducts interlaboratory tests for the purpose of quality assurance and for validating and reviewing analytical methods.
Over the past 25 years, this group has carried out internal interlaboratory tests to validate and assure the quality of assay methods for macronutrients and micronutrients, pollutants, nitrification inhibitors and other compounds. Tests performed in recent years include:

  • Interlaboratory test to validate the assay methods for “organic compounds” and “organic carbon” in organic and organic-mineral fertilisers,
  • Chromium VI in ashes,
  • Selenium, arsenic and mercury in mineral fertilisers,
  • ICP-OES for macro-elements and trace elements in different types of fertilisers,
  • Fluorine in sewage sludge and lime (Ziegeleikalk)
  • Carbonates in lime and fertilisers containing lime,
  • Total nitrogen and available nitrogen and
  • Total phosphorus and potassium concentration in agricultural fertilisers

Since 2009, section III has offered an “VDLUFA EU Fertiliser Ring-Test” every year for EU accredited fertiliser testing laboratories in all countries. By participating in these test, laboratories can verify and document the quality of their analysis procedures. Between 28 and 48 laboratories from 21 member states and Turkey have participated over the past five years. To date, 9 interlaboratory tests have been performed on the following fertilisers:

  • 2009: NPK fertiliser containing sulphur,
  • 2010: Carbonic magnesium lime,
  • 2011: NPK fertiliser containing isobutylene urea and micronutrients,
  • 2012: Kornkali fertiliser,
  • 2013: NPK fertiliser,
  • 2014: NP fertiliser,
  • 2015: Liquid micronutrient fertiliser,
  • 2016: Magnesium calcium carbonate (dolomitic limestone),
  • 2017: Calcium ammonium nitrate (CAN 27) and Urea 46.

The range of analytes includes macro- and micronutrients (different forms of nitrogen, diffent solubilities for other macronutrients; anorganic pollutants according to EU-regulation (VO(EG) 2003/2003), VDLUFA methods and EN- respectively ISO-norms.

The participants receive a certificate specifying their ranking in the different analyses. Accreditation bodies in Germany require that test laboratories provide certificates indicating their successful participation in qualified fertiliser tests.


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