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DCA Publikationer Validity and analytical robustness of the Olsen soil p test and other agronomic soil p tests used in the northern Europe DCA rapport, nr. 71, 2015 Af Gitte Holton Rubæk (Editor)  Analyses of soil P status with soil P tests have for many years formed the cornerstone for recommendations on how to fertilise agricultural soils. The increasing awareness of the role of soil P as a contributor to surface water eutrophication together with the renewed focus on phosphate rock as a valuable non-renewable resource has put emphasis on the way we utilise P in soils, fertilisers, manure and waste products. To ensure this, a valid,precise and reliable soil P test method is crucial. Olsen P (in Denmark known as “Ptallet” or “fosfortallet”) is the official soil P test method, but it has long been recognised that Olsen P results vary too much and apparently systematically between labs and over time. Moreover an increasing body of evidence indicates that the Olsen-P method too frequently does not reflect the P availability to plants in soil. It is therefore clear that initiatives leading to better soil P tests in Denmark with high laboratory precision and valid information on soil P status for farmers, researchers and authorities are highly needed. This report gives recommendations on how to improve soil P testing in Denmark and a draft for an updated protocol for the Olsen P analysis is presented. |