Tuning of the proficiency testing methodology for soil fertility analysis. Preliminary results


Nutrients, analysis laboratories.


This work includes the methodology for carrying out a proficiency testing program between Spanish laboratories that offer soil fertility analysis. Aliquots of each of the two large volume samples were prepared, taken from two surface horizons of soils with marked differences between them. Once the homogeneity of aliquots was tested, one sample of each soil was sent to each of the twenty-one participating laboratories, together with the instructions and a format for the submission of results. Throughout the process, special care was taken to ensure the confidentiality of the results of each individual participant. Once the responses were received, the results were analyzed, consensus values were assigned and each result was evaluated using the “z-score” indicator. The exercise was very well received by the participating laboratories, and has been very effective in characterizing the quality of the results issued. It has been shown that there are parameters with very homogeneous results (pH) compared to others with differences incompatible with the reliable agronomic use of analyses (granulometry, assimilable phosphorus, etc.). The urgent need to maintain this type of intercomparison exercise periodically, as an external quality control that increases the reliability of laboratories, is evident.



Abadía JS, Vázquez R, Rellán-Álvarez H, El-Jendoubi A, Abadía A, Álvarez-Fernández A, López-Millán F. 2011. Towards a knowledge-based correction of iron chlorosis. Plant Physiology and Biochemistry 49(5):471-482.

BIPEA. 2018. International Proficiency test provider. Disponible en: https://extranet.bipea.org/documents/plannings/GB/Proficiency-testing-scheme-15.pdf extraído el 9/10/2019.

Laso J, Peris A. 2009a. Evaluación de resultados de ensayos de aptitud. En: Comunicaciones del V Iberolab; Madrid; p. 1-5.

Laso J, Peris A. 2009b. Tratamientos estadísticos de aptitud: aplicación de la mediana para detección de resultados anómalos. En: Comunicaciones del V Iberolab; Madrid; p. 6-11,

Nogueira JM, Nieto de Castro F. 2001. EPTIS: The new European database of proficiency testing schemes for analytical labs. Trends in Analytical Chemistry 20(9):457-461.

Olivares IRB, Souza GB, Nogueira ARA, Toledo GTK, Marcki DC. 2018. Trends in developments of certified reference materials. Trends in Analytical Chemistry 100:53-64.

Porta J, López-Acevedo M, Rodríguez R. 1986. Técnicas y experimentos en edafología. Colegi Oficial d´Enginyers Agronoms de Catalunya. 282 p.

Robijns K, Boone NW, Jansen RTP, Kuypers AWHM, Neef C, Touw DJ. 2019. Commutability of proficiency testing material containing amitriptyline and nortriptyline: A study within the framework of the Dutch Calibration 2.000 project. Clinica Chimica Acta 498:6-10.

Romanyukha A, Grypp MD, Fairchild GR, Williams AS. 2016. Performance comparison of OSLD (Al2O3:C) and TLD (LiF: Mg, Cu, P) in accreditation proficiency testing. Radiation Measurements 93:7-12.

Soil Survey Staff. 2014. Keys to Soil Taxonomy. 12th ed. Washington, D. C.: USDA-Natural Resources Conservation Service.

WEPAL. 2018. International Soil- Analytical Exchange. Quarterly Report. University of Wageningen. Disponible en: http://www.wepal.nl/ extraído el 9/10/2019.

Wojciechowski KL, Melilli C, Barbano DM. 2016. A proficiency test system to improve performance of milk analysis methods and produce reference values for component calibration samples for infrared milk analysis. Journal of Dairy Science 99(8):6808-6827.