Data evaluation of LUCAS soil survey laboratory data : survey 2009, 2012 and 2015

In 2015 topsoil samples were collected in all 28 Member States of the European Union under the Soil module of the LUCAS survey. Previous surveys were performed in 2009 and 2012, but with restricted coverage. All soil samples were analysed by a central laboratory using standard methods. The results of the laboratory analysis were evaluated for their practicality to characterise the status and changes of European topsoil physical and chemical conditions. The evaluation covers aspects of data compliance to specifications, conformity to data structures and value ranges, consistency between parameters and surveys. The parameters evaluated were: coarse fragments, clay silt and sand content, pH in CaCl 2 and H 2 O, organic carbon, calcium carbonate, total nitrogen, soluble phosphor, extractable potassium and cation exchange capacity. Despite general common characteristics the reported laboratory results from the various soil surveys also display some notable differences. For laboratory methods and delivery of results from the 2009 and 2015 survey detailed specifications were available. No such specifications were available for the methods and delivery of the 2012 laboratory results. The data largely comply to the specifications for file format and content. Low adherence to the specifications was noted for parameter position in the file. This is potentially problematic when parameters with a similar range of values are interchanged, as for silt and sand or pH(CaCl 2 ) and pH(H 2 O). For the 2012 survey the values for total nitrogen were reported in the wrong unit, which in the absence of specifications for the data may not be obvious. The checks of conformity found incompatible data types and duplicates for the key field containing the sample identifier. This reduces the number of samples that can be unambiguously assigned to LUCAS points for a geographic location by up to 10% (2009). The codes indicating measurements below the limit of detection and the values used differed between documents and years. In data for the 2012 and 2015 results numeric entries were used, which is a potential source of error when analysing the data. The evaluation of consistency between parameters of a survey showed few cases outside the expected range. However, the temporal consistency of a parameter with repeated samples shows a degree of variability that is several times higher than for the repeated laboratory analysis of a sample and viable unfeasible for 15% of the samples from soils high in organic material. This indicates a sizable variability in soil conditions between repeated samples. Uncertainties in the data were identified for CaCO 3 and soluble phosphor at low concentrations. The values for cation exchange capacity would appear to be highly variable and to be used with particular caution, if at all. The evaluation found that the results from the laboratory analysis of the LUCAS Soil survey are valuable to characterise European topsoil conditions. A change in data delivery format would ease some of the format issues found. Including the analysis of texture parameters in revisited sample locations would help in the identification of problems in the stability of repeated samples.