Location: Soil Dynamics ResearchTitle: A simple, gravimetric method to quantify inorganic carbon in calcareous soils Author
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2016
Publication Date: 8/19/2016
Publication URL: http://handle.nal.usda.gov/10113/5661737
Citation: Rodriguez, J.B., Self, J.R., Arriaga, F.J. 2016. A simple, gravimetric method to quantify inorganic carbon in calcareous soils. Soil Science Society of America Journal. 80:1107-1113. doi:10.2136/sssaj2015.09.0355 Interpretive Summary: A technique termed a “Carbonate-Meter” (CM) was developed to measure inorganic carbon (IC) in calcareous soils. The CM method can be easily assembled, and most laboratories should have the necessary equipment to prepare it making the method easy to use. The CM gravimetric technique was tested against four standards, two calcareous soil with low and high IC content and two pure carbonate minerals, calcite and dolomite; and a series of representative soils from across the US. The detection limit (DL) and the lower limit of quantitation (LLOQ), for dolomite standard were 0.42 and 1.4 g IC kg-1, respectively. Our CM gravimetric method, produced similar results as the NRCS manometric procedure over a wide range of calcareous soils from the USA. Results indicate that the Carbonate-Meter would be an improved methodology for IC analysis of calcareous soils.
Technical Abstract: Total carbon (TC) in calcareous soils has two components: inorganic carbon (IC) as calcite and or dolomite and organic carbon (OC) in the soil organic matter. The IC must be measured and subtracted from TC to obtain OC. Our objective was to develop a simple gravimetric technique to quantify IC. The method can be conducted in all soil testing laboratories with a 6-ml glass vial, a number-1 rubber stopper with one hole, a 6.5 cm glass tube with a 0.5 cm and 0.3 cm outside and inside diameter, respectively and a 50-ml Erlenmeyer flask. The precision and recovery of our gravimetric method was tested with four standards: two calcareous soils and two carbonate pure minerals, using 0.2000 + 0.0200 g. of fine samples and 4.0 ml of 4M HCl-3% FeCl2.4H2O solution. Results after 22-24 h showed 100.55%, 99.73%, 100.45% and 99.58% recovery, for two calcareous soils and pure calcite and dolomite, respectively. The detection limit (DL) and the lower limit of quantitation (LLOQ) for calcite were 0.31 and 1.0 g IC kg-1, respectively. The DL and the LLOQ for dolomite were 0.42 and 1.4 g IC kg-1, respectively. The recovery for IC of the commonly used Modified Pressure Calcimeter (MCP), in the higher pure standards was only of 56%, while the recovery for the Carbonate-Meter gravimetric procedure was 101%. The MPC loses accuracy in samples containing more than 6.0% of IC. The CM does not require to pre-analyze the sample as is the case of the MPC method. The described gravimetric method is simple, non-tedious, cheap and has good precision and accuracy.