Standard Operating Procedure for Soil Total Carbon

Standard operating procedure for soil total carbon

Dumas dry combustion method Global Soil Laboratory Network GLOSOLAN-SOP-03 GLOSOLAN

SOIL TOTAL CARBON Version number : 1 Page 1 of 10 Dumas dry combustion method Effective date : October 28, 2019

SOIL TOTAL CARBON Dumas dry combustion method

VERSION HISTORY

N° Date Description of the modification Type of modification

01 30 July 2019 Finalization of the draft version Compilation of all inputs received by RESOLANs

02 28 October 2019 Final review of the SOP at the 3rd Revision of SOP steps, final GLOSOLAN meeting discussion and agreement

03 04 Etc.

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Contents 1. Brief introduction to total carbon...... 3 2. Scope and field of application ...... 3 3. Principle ...... 3 4. Apparatus ...... 4 5. Materials ...... 4 6. Health and safety ...... 4 7. Sample preparation ...... 4 8. Procedure ...... 5 8.1. Calibration of the apparatus ...... 5 8.2. Determination of the total carbon (TC) content ...... 5 9. Calculation ...... 5 10. Quality assurance/Quality control ...... 5 10.1. Precision test ...... 5 10.2. Trueness test ...... 6 10.3. Control chart ...... 7 11. Reference documents ...... 7 12. Appendix I.—Acknowledgments ...... 8 13. Appendix II.—List of authors ...... 8 14. Appendix III.—Contributing laboratories ...... 8

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1. Brief introduction to total carbon

Analysis and quantification of total soil carbon (TC) is necessary to estimate soil organic matter content, which is a useful parameter when evaluating the productivity of a natural system. Quantification of TC can be used to monitor soil carbon (C) stocks and to evaluate the role and effectiveness of C sequestration to mitigate climate change.

Several methods are used to quantify soil C. The Dumas dry combustion method determines total carbon, representing all chemical forms of C in the soil. Other methods may be used to quantify the various forms of carbon. For example, the Walkley & Black method measures oxidizable organic carbon.

For analysis of TC by dry combustion, an automatic chemical analyser, commonly known as an autoanalyzer, is used. Advantages of using an autoanalyzer are increased accuracy and versatility. An autoanalyzer can be used to quantify carbon, nitrogen, and sulfur. Disadvantages of using an autoanalyzer are equipment initial cost, operating and maintenance costs, and the lower number of labs using an autoanalyzer worldwide.

Additional care must be taken during sample preparation if quantifying TC by the Dumas dry combustion method. A very small sample is used, which requires the samples to be well homogenized. 2. Scope and field of application

This standard operating procedure (SOP) describes, in general terms, quantification of TC content in soil samples by an autoanalyzer. The procedure measures both organic C and inorganic C together. To quantify the organic C fraction only, the inorganic C fraction must be removed or quantified prior to autoanalyzer analysis. Alternatively, the inorganic C can be quantified separately and then subtracted from the TC. 3. Principle

This method is based on the Dumas dry combustion principle. The sample is burned at high temperature (between 900 and 1000 °C or 1400 and 1600 °C) in an atmosphere of pure oxygen. Under these conditions, all C-containing compounds are completely decomposed and converted into carbon oxides (mainly carbon dioxide). The autoanalyzer measures and reports the TC value based on the concentration of carbon oxides present using various procedures (for example, a C gas detector and thermal differences between gas columns).

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4. Apparatus

1. Autoanalyzer for C, with all specific accessories and consumables, including appropriate detection system.

The equipment might also analyse N and S, depending on the manufacturer and model.

2. Analytical balance, ±0.0001 g, to weigh samples and reference materials. 3. Milling system that meets the requirements of the autoanalyzer manufacturer. 4. Crucible set (if needed), depending on the sample size used by the autoanalyzer.

5. Materials

1. Certified Reference Material (CRM) with known C content to calibrate the autoanalyzer. The CRM may vary depending on autoanalyzer manufacturer. Aspartic acid, EDTA, acetanilide, or soil samples with certified total C content may be used. 2. Oxygen gas (O2), along with reference or carrier gases (He, for example), of very high purity (greater than 99.99%). 3. Consumables specific to the autoanalyzer.

6. Health and safety

This SOP does not imply the direct use of dangerous chemical reagents, but appropriate safety precautions are necessary. Catalyser residues are toxic and must be disposed of properly. Gloves, lab coats, and eye protection must be worn when handling reagents and samples. When a special reagent is used (for example, a reference material for equipment control), consult the material safety data sheet (MSDS) and conduct a risk assessment. Take necessary precautions when handling compressed gasses and high-temperature equipment. Follow the manufacturer’s safety guidelines when operating the autoanalyzer.

7. Sample preparation

Follow the sample preparation instructions provided by the manufacturer for use of the autoanalyzer. Probably, a representative portion of the soil sample that was previously treated (dried and sieved to 2 mm) must be porfirised (grind fine and homogeneously) until the entire fraction passes through a sieve of inferior size. Typically, a representative subsample is taken from the bulk sample and milled to a sufficiently fine mesh size. Ensure that milling equipment and sieves do not introduce contamination to the samples.

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8. Procedure

8.1. Calibration of the apparatus

Calibrate the equipment as described in the autoanalyzer instruction manual. Use a CRM provided or recommended by the manufacturer (soil, acetanilide, calcium carbonate, EDTA, glucose anhydrous, etc). The CRM should cover the range of TC typically found in test samples. Store all CRM as indicated by the manufacturer label.

Replicated blanks must also be analysed to determine the baseline according the specific equipment procedure.

8.2. Determination of the total carbon (TC) content

Because the analysis procedure varies between manufacturer’s, analyse samples according to the manufacturer’s guidelines for soil analysis.

The mass of sample weighed is dependent on the TC of the sample and the linear range of the autoanalyzer.

To check autoanalyzer performance, CRM, control samples, and blanks should be incorporated at regular intervals in each test batch. The number and frequency of control and check samples depends on the method used and the calibration stability of the autoanalyzer.

9. Calculation

Report TC using the International Units System as: grams of C (g) per kilogram (kg) of soil, g/kg. Results must be reported on an ovendry soil basis.

The number of decimals reported must conform to the conventional rules of maintaining 3 numbers:  values greater than 100, no decimal reported;  values between 10 and 100, 1 decimal (0.1) reported; and  values less than 10, 2 decimals (0.01) reported.

10. Quality assurance/Quality control

10.1. Precision test

- 5 percent of the samples in a test batch must be replicates to guarantee at least one duplicate sample if the batch is small.

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- Calculate the percent relative standard deviation (% RSD) to determine precision.

Where: s = standard deviation of the replicate result x̄ = mean

- Compare the result with the previously specified precision.

The acceptance requirements for precision testing must be defined by the equipment used, environmental conditions, and other testing factors and by the specifications or requirements for the information use and agronomic criteria.

If the precision test fails, the cause of the failure must be identified and corrective or preventive actions must be developed.

10.2. Trueness test

10.2.1. Recovery test

- Perform triplicate analysis of Certified Reference Material of the analysed matrix (soil) (CRMs) or an Internal Reference Material (IRM), in accordance with the present SOP.

Note: To assess instrument performance, this procedure should be replicated with different levels of TC. Different levels can be selected by using CRM with different concentrations of TC or by simply weighing different masses of the same CRM.

- Calculate the percent recovery based on the equation below.

- Compare the result with the recovery target (%), which is predefined for the usual range of work.

The recovery target must be defined for the usual range of work. The definition should consider the working conditions (for example the characteristics of the equipment used and the environmental conditions). It should also consider the specifications or requirements for the given use of the information and for any agronomic criteria. The recovery can also be considered acceptable if it is within the 95% confidence interval reported for the target value of the CRMs.

If the recovery test fails, the cause of the failure must be identified and corrective or preventive actions must be developed.

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10.2.2. Interlaboratory comparison

The laboratory must participate, at least once a year, in interlaboratory proficiency tests.

If the obtained result is questionable or unsatisfactory, it is necessary to carry out an evaluation, identify the root cause of the problem, and develop corrective and preventive actions.

10.3. Control chart

- Perform the replicate analysis of a control sample or an IRM in a test batch of samples. - Plot the result in a control chart. - Monitor the results.

If results are out of specified limits (or tend to be so), an evaluation must be made. The cause of the noncompliance must be identified, and corrective and preventive actions must be developed.

11. Reference documents

Eurachem. 2014. The fitness for purpose of analytical methods. A laboratory guide to method validation and related topics. Second Edition

Karla, Y.P. 1998. Handbook of reference methods for plant analysis. CRC Press.

Leco Corporation. 2004. Leco Truspec CN Determinator instruction manual

Nelson, D.W. & Sommers, L.E. 1996. Total carbon, organic carbon and organic matter. In D.L. Sparks (Ed.), Soil Science Society of America, book series 5. Methods of soil analysis, Part 3, Chemical methods. Madison, Wisconsin: Soil Science Society of America, Inc.

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12. Appendix I.—Acknowledgments

GLOSOLAN thanks the Latin American Soil Laboratory Network (LATSOLAN); Ms. Floria Bertsch, LATSOLAN Chair; and Ms. Miriam Ostinelli for preparing the first draft of this SOP. GLOSOLAN also thanks the participants in the 3rd GLOSOLAN meeting (28-30 October 2019) for reviewing this SOP.

13. Appendix II.—List of authors

Main authors (in alphabetical order):

 Mr. Rob De Hayr, Department of Environment and Science, Science Division, Chemistry Centre, Australia  Mr. Chris Lee, Kellogg Soil Survey Laboratory, United States of America  Ms. Floria Bertsch, CIA-UCR, Costa Rica  Ms. Miriam Ostinelli, Laboratorio de Suelos CIRN-CNIA-INTA, Argentina  Ms. Nopmanee Suvannang, GLOSOLAN Chair, Thailand

14. Appendix III.—Contributing laboratories

GLOSOLAN thanks the following laboratories for completing the GLOSOLAN form on the method and providing information on their standard operating procedure for the Dumas dry combustion method. This information was used as a baseline for the global harmonization.

From the Asian region:

 Bureau of Soils and Water Management Laboratory Services Division, Philippines  Charles Renard Analytical Laboratory, India  DA Regional Field Office 3-ILD-Regional Soils Laboratory, Philippines  DOA, Malaysia  Fauji Fertilizer Company’s Soil Testing Labs, Pakistan  Horticultural Crops Research and Development Institute, Department of Agriculture, Sri Lanka  ICAR-IISS, Bhopal, India  NIAES, NARO, Japan  Office of Science for Land Development, Land Development Department, Thailand  Soil and Plant Analysis Laboratory, Myanmar  Soil Lab, ISRI, Indonesia  SRDI, Bangladesh

From the Pacific region:

 Office of Environment and Heritage, Soil Health & Archive, Australia  The University of the South Pacific, Alafua Campus, Samoa

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From the Near East and North African region:

 None

From the African region:

 Department of Agricultural Research, Lesotho  Farming & Engineering Services (FES), Malawi  IRD, Senegal  Laboratoire d’Analyse des Sols et des Végétaux – LSV, Togo  Laboratoire des Radioisotopes, Madagascar  Laboratorio regional de analise de solos e plantas, Mozambique  LASEVE, Niger  LASPEE of IRAD, Cameroon  National laboratory for diagnosis and quality control of agricultural products and inputs, Cameroon  Soil Research Institute Analytical Services Laboratory, Ghana  TARI Mlingano LAB, Tanzania  Zimbabwe Sugar Association Experiment Station, Zimbabwe

From the European region:

 Aarhus University, AGRO University laboratory, Denmark  AGES - Institute for Sustainable Plant Production, Department for Soil Health and Plant Nutrition, Austria  Agricultural Institute of Slovenia, Slovenia  Andrija Stampar Teaching Institute of Public Health, Croatia  BRGM, France  Chemisch Biologisch Laboratorium Bodem, Netherlands  Environmental Research Laboratory, United Kingdom  Federal agency for water management (BAW), Institute for land and water management research (IKT), Austria  Institute of Soil Research, Austria  Instituto Politécnico de Castelo Branco/Escola Superior Agrária, Portugal  Instituto Superior de Agronomia (ISA_PT), Portugal  IRD, France  Laboratory of Biogeochemistry and Environmental Protection, University of Warsaw, Biological and Chemical Research Centre, Poland  LSFRI Silava, Latvia  Rothamsted Research, United Kingdom  UKZUZ, Czech Republic  Universidade de Évora, Portugal

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 University of Zagreb Faculty of Agriculture, Croatia  University of Zagreb, Faculty of Agriculture, Department of General Agronomy, Croatia  VITO, Belgium

From the Eurasian region:

 Institute of Biology of Komi Scientific Center of the Ural Branch, Russian Federation  Soil Science Faculty, Lomonosov Moscow State University, Russian Federation

From Latin America:

 Colegio de Postgraduados, Mexico  ECOSUR, Mexico  Embrapa, Brazil  INTA - Inst. de Suelos. Laboratory – LabIS, Argentina  Laboratorio de Suelos UCTB Camagüey, Cuba  Laboratorio de Suelos y Aguas de la Dirección General de Recursos Naturales - Ministerio de Ganadería Agricultura y Pesca (DGRN-MGAP), Uruguay  Soil Health, Plant Tissue and Water Laboratory, Jamaica  Universidad de Concepción Facultad de Agronomía departamento de Suelos, Laboratorio Químico de Suelos y Plantas, Chile

From North America:

 KSSL, United States

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