Quality of Soil Analyses Can Be Improved

27 February 2012

What is the actual nutrient status in a particular field? Will I need to apply more fertiliser? Or shall I desist because the soil at the moment actually has a surplus of nutrients? To get a clear answer to these questions, the farmer sends in soil samples for analyses.

In recent years there have been problems with the quality of the soil analyses performed at laboratories and questions have been raised about the suitability of the methods of analysis used. A committee under the Danish Plant Directorate and the Environmental Protection Agency has therefore looked into the matter. The results of their work have just been published in a report from Aarhus University.

The committee has focused on soil analyses for soil texture, plant-available phosphorus, and mineral nitrogen which is used for preparing the annual nitrogen prognosis for Denmark.

Soil analysis is an important part of the decision support in farming. Soil maps based on soil analyses are moreover part of the decision support for environmental regulations of the agricultural production. It is therefore important that the methods make use of the latest technology and that the methods used are the most appropriate for that particular circumstance, says the report.

The committee points out that there has been a significant drop in the number of authorised laboratories. There are now only 2-3 laboratories in Denmark that carry out soil analyses and there are no longer any requirements for authorisation, inspections, methods used or quality control. Inter-laboratory comparisons (ring analyses) have shown that there can be large inter-laboratory variations in the results.

Analysis results used for far-reaching decisions

The soil analyses results are increasingly used by the authorities for a range of regulations where they were previously mainly used by the farmer for decisions to be made on the farm.

As soil analyses are increasingly used to determine the potential loss of nutrients from soil, the methods officially recommended should always be the most relevant for the actual situation and should also have a well-documented reproducibility and robustness, according to the report.

The committee recommends the following:

Quality control of the analyses to be improved.
Analyses to be carried out according to well-documented procedures.
Methodology to be routinely updated on the basis of new knowledge.

About the committee on soil analyses:

The committee was appointed in spring 2010 at the request of the Danish Plant Directorate and the Environmental Protection Agency.
The purpose of the committee was to compile an overview of the use, the suitability and the accuracy of soil analyses in Denmark.
The committee also investigated the possibility of improving the analyses of, in particular, mineral nitrogen and plant-available phosphorus in agricultural soil.
The committee is made up of scientists from Aarhus University, University of Copenhagen and the Geological Survey of Denmark and Greenland.

February 2012

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