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Title: INORGANIC CARBON ANALYSIS BY MODIFIED PRESSURE-CALCIMETER METHOD

Author
item Sherrod, Lucretia
item Dunn, Gale
item PERTERSON, G - COLORADO STATE UNIV
item Kolberg, Robert

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2001
Publication Date: 1/1/2002
Citation: Sherrod, L.A., Dunn, G.H., Perterson, G.A., Kolberg, R.L. 2002. Inorganic carbon analysis by modified pressure-calcimeter method. Soil Science Society of America Journal. (2002) 66: 299-305.

Interpretive Summary: Soil organic carbon analyses using high temperature induction furnace combustion methods have become increasingly popular because of advances in instrumentation. Combustion methods, however, also include carbon from CaCO3 and CaMg(CO3)2 found in calcareous soils. Separate analysis of the inorganic carbon must be done to correct soil carbon data from combustion methods. The analysis of CO2 by pressure calcimeter method described by Loeppert and Suarez (1996) is a direct, accurate and inexpensive method, but the complexity of the pressure calcimeter apparatus makes large sample runs impractical. The objective therefore of this research was to develop a fast, efficient and precise inorganic carbon method by modification of the pressure calcimeter method that covers the complete analytical range.

Technical Abstract: Soil organic carbon (SOC) analyses using high temperature induction furnace combustion methods have become increasing popular because of advances in instrumentation. Combustion methods, however, also include C from CaCO3 and CaMg(CO3)2 found in calcareous soils. Separate analysis of the inorganic C (IC) must be done to correct C data from combustion methods. Our objective was to develop a fast, efficient and precise IC method by modification of the pressure calcimeter method. We modified the pressure calcimeter by using Wheaton serum bottles (20-mL and 100-mL volumes) sealed with butyl rubber stoppers and aluminum tear-off seals as the reaction vessel and a pressure transducer monitored by a digital V meter. Our gravimetric IC determination of six soils, representing a wide range of IC, from the North American Proficiency Testing program (NAPT) showed a strong correlation when regressed against IC from the modified pressure calcimeter method ( slope of 0.99, r2 = 0.998). The method detection limit (MDL) was 0.17 g IC kg -1 for the 20-mL serum bottles and the limit of quantification (LOQ) was 0.30 g IC kg -1. The 100- mL serum bottle had a MDL of 0.42 with a LOQ of 2.4 g IC kg-1. When using a 100-mL Wheaton serum bottle as the reaction vessel with a 0.50-g sample size, soils containing up to 120 g IC kg-1, which represent a 100 % CaCO3 equivalent, can be analyzed within the V output range of the pressure transducer. The time allowed for the acid to neutralize IC in the NAPT soils was significant at the 0.05 alpha level for five out of the six evaluated at 1, 2, 4, 6, 14, 18, and 24 h. The minimum time required to neutralize the maximum IC content for most soils was 6 h. Soil organic carbon determined by subtraction of IC from total C from combustion analysis correlated well with SOC determined by the Walkley-Black method for both NAPT soils and 72 soils from eastern CO, with slopes of 0.99, 0.96 and r2=0.99 and 0.99, respectively.