Martina Aigner
Since the year 1995 the FAO/IAEA Soil Science Unit has been organizing annual Proficiency Tests (PT) on the analysis of plant materials for (enriched) 15N and since the year 2004 also for 13C isotope abundance as well as for the element concentrations of nitrogen and carbon.
Due to the re-organization of the tasks implemented by the FAO/IAEA in the year 2008 the Soil Science Unit has established a new collaboration with the University of Wageningen, The Netherlands, already organizing regu-lar PTs on 15N and 13C in plant materials at the natural abundance level since several years (see the International Plant-analytical Exchange Programme IPE on their homepage,
http://www.wepal.nl/website/about_wepal/Scope.htm).
The Wageningen Evaluating Programs for Analytical Laboratories (WEPAL) is accredited for the organization of Interlaboratory Studies by the Dutch Accreditation Council RvA since April 26, 2000 (registration number R002). The accreditation is based on the ILAC-requirements (Guidelines for the ILAC-requirements for the competence of providers of proficiency testing schemes, ILAC-G13:2000). The accreditation covers the quality
system of the organisation as well as all the parameters mentioned in the scope.
It was agreed between the Soil Science Unit and the PT-organizer to include one 15N-enriched plant material (range: 0.1 – 2.5 % 15N atom excess) per year into the IPE test sample set. A bulk amount of uniformly 15 N-enriched plant material was produced by the FAO/IAEA Soil Science Unit and sent to WEPAL for milling, ho-mogenization and bottling through the routine test sample production process for PTs. This 15N-enriched material was sent out together with 3 other not enriched plant ma-terials.
In February 2008 all participants in PTs previously or-ganized by the Soil Science Unit were invited to partici-pate in the WEPAL IPE programme. Participants were invited to perform analysis of any determinand offered in the WEPAL IPE scheme including 15N (enriched and/or natural abundance level), total N (N-elementary), Kjeldahl-N, 13C and total C (C-elementary). The partici-pation fee for one round of PT in 2008 (round IPE2008.2) was covered by the IAEA (Figure 1).
Twenty-four participants that were registered in the "SSU PT scheme" in previous years were provided with the WEPAL test sample set IPE 2008.2 consisting of the four test samples of 20 g plant material each. Eleven
laborato-one IAEA-participant reported only Kjeldahl-N-data. The Soil Science Unit also participated in this round of PT.
Evaluation criteria for IAEA-participants Calculation of Z-score
For all analytical data a Z-score is calculated according to the formula:
sd X z =(X − mean)
in which:
X = the reported value
Xmean = the mean of all values after outlier elimination sd = standard deviation of all values after outlier elimina-tion
All participants received the quarterly evaluation report 2008.2 (April-June 2008) from WEPAL providing a de-scription of the test sample preparation, statistical evalua-tion criteria, outlier calculaevalua-tion and results of all reported
analytical results performed on all determinants. Partici-pant's performance in 15N- and 13C atom abundance analysis was acceptable, if the z-scores of the 15N-enriched test sample were within the accepted control limits:
-2 ≤ z ≤+2 acceptable results
-3 ≤ z ≤+3 warning (doubtful results)
-3 > z >+3 not acceptable (out of control limits)
Data could also be compared to the data reported to WEPAL by the IAEA-SSU.
A certificate for "successful participation" is provided to stable isotope laboratories supported by the IAEA that showed proficiency in both the isotope- and elementary analysis of Nitrogen (i.e. 15N isotope abundance and total N analysis, i.e. N-elementary or Kjeldahl-N) and / or Carbon (i.e. 13C isotope abundance and C elementary) of the 15N enriched test sample.
(a) (b)
acceptable 7 (100%)
(c) (d)
Figure 1. Performance of IAEA participants. a: 15N abundance determination; c: total N determination (N-elementary and N-Kjeldahl); c: 13C abundance determination; d: total C determination.
acceptable 8 (67%) warning
1 (8%) not acceptable
3 (25%)
acceptable 8 (73%) not acceptable
3 (27%)
acceptable 7 (87%) not acceptable
1 (13%)
Figure 2. Geographical distribution of IAEA participants.
Conclusions
The first Joint Proficiency Test for stable isotopes in plant materials by WEPAL and IAEA was successful and will be continued in this form (Figure 2). The new PT round IPE2009.2 has already been started and test samples were sent out in February 2009.
The big advantage of comparing analytical data to those of a large and increasing number of analytical
laborato-ries worldwide will provide high confidence in the laboratory's analytical performance and is an invaluable tool for external quality control. It is hoped that in the future more stable isotope laboratories will make use of this opportunity to assess their analytical performance and provide evidence of the sustainable high quality of their analytical data.
Publications
Dercon, G., Poesen, J., Deckers, J., Govers, G., Tacuri, E., Villavicencio, A., Iglesias, C., Loaiza, G. (2009). Non-linear behaviour of soil translocation in response to slope gradient by mechanized tillage in steepland agriculture:
The role of tillage speed and soil surface roughness. Catena (in press).
Cobo, J.G., Dercon, G., Monje, C., Mahembe, P., Gotosa, T., Nyamangara, J., Delve, R., Cadisch, G., 2009. Crop-ping strategies, soil fertility investments and land management practices by smallholder farmers in communal and resettlement areas in Zimbabwe. Land degradation and Development (in press).
Cayci, G., Heng, L.K., Öztüurk, H.S., Sürek, D., Kütük, C, Sağlam, M. (2009). Crop yield and water use efficiency in semi-arid region of Turkey. Soil & Tillage Research 103, 65-72.
Heng, L.K., Hsiao, T., Evett, S., Howell, T., Steduto, P. (2009). Validating the FAO AquaCrop model for irrigated and water deficient field maize. Agron J 101,488-498.
Hsiao, T.C., Heng, L., Steduto, P., Rojas-Lara, B., Raes, D., Fereres, E. (2009). AquaCrop—The FAO Crop Model to Simulate Yield Response to Water: III. Parameterization and Testing for Maize. Agron J 101,448-459.
Mabit, L., Benmansour, M., Walling D.E. (2008). Comparative advantages and limitations of Fallout radionuclides (137Cs, 210Pb and 7Be) to assess soil erosion and sedimentation. Journal of Environmental Radioactivity, 99(12), 1799–1807.
Mabit, L., Bernard, C. (2009). Spatial distribution and content of soil organic matter in an agricultural field in Eastern Canada, as estimated from geostatistical tools. Earth Surface Processes and Landforms (In press).
Mabit, L., Klik, A., Benmansour, M., Toloza, A., Geisler A., Gerstmann, U.C. (2009). Assessment of erosion and deposition rates within an Austrian agricultural watershed by combining 137Cs, 210Pbex and conventional measure-ments. Geoderma, 150(3-4), 231–239.
Mabit, L., Klik, A., Toloza, A., Benmansour, M., Geisler A., Gerstmann, U.C. (2009). Measurements of the
effec-Geographical distribution of participants in WEPAL IPE2008.2 Number of labs (percentage)
Asia 3 (25%)
Europe 3 (25%) Latin America
5 (42%)
Africa 1 (8%)
physical Research Abstracts (USB), Volume 11, European Geosciences Union-General Assembly 2009. Abstract EGU2009-4507. pdf, 2 pages.
Shakhashiro, A., Mabit, L. (2009). Results of an IAEA inter-comparison exercise to assess 137Cs and total 210Pb ana-lytical performance in soil. Applied Radiation and Isotopes, 67(1), 139–146.
Zapata, F., Nguyen, M. L., (In Press). Chapter 7. Soil erosion and sedimentation studies using environmental ra-dionuclides. In: Environmental Radionuclides-Tracers and Timers of Terrestrial Processes. Editor: Klaus Froeh-lich. Elsevier.
Websites
Soil and Water Management and Crop Nutrition Section:
http://www-naweb.iaea.org/nafa/swmn/index.html
Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture:
http://www-naweb.iaea.org/nafa/index.html
FAO website: http://www.fao.org/waicent/FAOINFO/AGRICULT/Default.htm FAO/AGL (Land and Water Development Division):
http://www.fao.org/ag/agl/default.stm
The Soils Newsletter is prepared twice per year by the Soil and Water Management & Crop Nutrition Section, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture and FAO/IAEA Agriculture and Biotechnology Laboratory, Seibersdorf.
International Atomic Energy Agency
Wagramer Strasse 5, P.O. Box 100, Printed by the IAEA in Austria,