Soil Science Society of America Journal 66:1878-1881 (2002)
© 2002 Soil Science Society of America
DIVISION S-5—PEDOLOGY
Equations for Predicting Soil Organic Carbon Using Loss-on-Ignition for North Central U.S. Soils
Michael E. Konen*,a,
Peter M. Jacobsb,
C. Lee Burrasc,
Brandi J. Talagaa and
Joseph A. Masond
a Dep. of Geography, Northern Illinois Univ., DeKalb, IL 60115
b Dep. of Geography and Geology, Univ. of Wisconsin, Whitewater, WI 53190
c Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
d Conservation and Survey Div. and Dep. of Geosciences, Univ. of Nebraska, Lincoln, NE 68588
* Corresponding author (konen{at}geog.niu.edu)
 |
ABSTRACT
|
|---|
Samples of 255 noncalcareous A, Ap, and AB horizons from selected major land resource areas (MLRA) in the north central USA were used to develop equations for predicting organic C content, as determined with a Leco C analyzer, from weight loss-on-ignition (LOI). Organic C concentrations of the samples ranged from 1.09 to 114.6 g kg-1. Within each MLRA, strong linear relationships were observed between LOI and organic C measured by the Leco instrument, with r2 ranging from 0.94 to 0.98. Predictive equations developed by least-squares regression were significantly different for individual MLRA's. Loss-on-ignition is a rapid, inexpensive, and accurate method for estimating organic C concentration in soils of the north central USA. We recommend that unique predictive equations be developed for individual soil-geographic regions.
Abbreviations: LOI, loss-on-ignition • MLRA, major land resource area • SOC, soil organic C • SOM, soil organic matter
|
INTRODUCTION
|
|---|
SOIL ORGANIC C (SOC) represents a significant component of the global C pool and soil processes are important regulators of CO2 in the atmosphere (Amundson, 2001; Lal et al., 1998). Current interest in C cycling and soil C sequestration require standard techniques to measure SOC concentrations (Kimble et al., 2001). The concentration of SOC is also commonly used as a soil quality index (Sikora and Stott, 1996).
Laboratory measurements of SOC and soil organic matter (SOM) can be time-consuming and costly. Wet chemical oxidation methods require the use of hazardous materials. Automated dry combustion equipment is expensive and can require time-consuming maintenance. In contrast, measurements of LOI require only a muffle furnace, drying oven, and balance, all readily available in most laboratories and relatively inexpensive to purchase, operate, and maintain.
Our purpose in this paper is to develop relationships between LOI and SOC determined by dry combustion and to facilitate use of LOI as a rapid and inexpensive SOC analysis for teaching and research purposes. We investigated LOI-SOC relationships for several MLRA's in the north central USA (Fig. 1)
.
|
Literature Review
|
|---|
Traditional methods of measuring SOC concentration include dry combustion, wet chemical oxidation, and LOI (Nelson and Sommers, 1982; Combs and Nathan, 1998; Kimble et al., 2001). Dry combustion, measuring CO2 evolved from organic matter oxidized in a high temperature furnace, is considered the most precise and accurate procedure today, but the high cost of dry combustion instruments is a limitation to many laboratories. Additionally, the high temperature oxidation liberates C from carbonate minerals, so calcareous samples require acid pretreatments or corrections for carbonate content.
Wet chemical oxidation (Walkley and Black, 1934), the Walkley-Black Procedure, was long the standard of measuring SOM concentration in soils. The procedure has significant uncertainties regarding oxidation of constituents other than SOM and the proportion of total SOM that is oxidized. Today the most significant concern is environmental; the technique generates waste containing strong acid and Cr.
Loss-on-ignition is an inexpensive and reliable technique that has been used for decades by soil scientists, geologists, geographers, and limnologists. Published LOI methods follow the same principle: SOM is oxidized at a moderate to high temperature, with the weight loss being proportional to the amount of SOM in the sample. Schulte and Hopkins (1996) demonstrated that LOI is an accurate and cost and labor-efficient technique for determination of SOC and SOM. Their method has been adopted by the north central region of the Cooperative Extension Service (Combs and Nathan, 1998) and is presently used by several university soil testing laboratories.
Schulte et al. (1991) determined that sample size for mineral soils or number of samples in a furnace did not affect LOI results. They did, however, emphasize that combustion time and temperature are critical factors that vary between reported methods and can compromise the comparability of results. A standard combustion time and temperature is critical to reproducible LOI values. In addition to oxidation of SOM, increasingly higher temperatures can drive off structural water from clays and other inorganic constituents, decompose carbonates and hydrated salts, and oxidize Fe2+ (Schulte and Hopkins, 1996), although carbonates remain stable at temperatures <500°C (Davies, 1974; Dean, 1974; Schulte and Hopkins, 1996). Combs and Nathan (1998) recommended that relationships between LOI and SOC be developed for soils differing in mineralogy and use.
An important factor limiting the comparability of results is that some investigators converted their LOI measurements to SOC concentration while others estimated SOM (Ball, 1964; Davies, 1974; Storer, 1984; Goldin, 1987; David, 1988; Ben-Dor and Banin, 1989; Donkin, 1991; Schulte et al., 1991; Schulte and Hopkins 1996; and Cambardella et al., 2001). Schulte et al. (1991) and Schulte and Hopkins (1996) summarized the range of predictive equations for SOM or SOC reported in the literature. Nelson and Sommers (1982) noted the problems associated with the wide range of factors used to convert SOC to SOM. With the increased interest in C sequestration and the quantification of soil C we believe it is critical to use LOI predictive equations for SOC, not SOM.
|
MATERIALS AND METHODS
|
|---|
Two-hundred fifty-five noncalcareous A, Ap, and AB soil horizons from five different MLRAs in the north central USA were sampled and analyzed using LOI and Leco techniques. Samples were collected from the following MLRAs: MLRA 65 (Nebraska Sand Hills); MLRA 75 (Central Loess Plains); MLRA 95B (southern Wisconsin and northern Illinois Drift Plain); MLRA 103 (central Iowa and Minnesota Till Prairies); and MLRA 108 (Illinois and Iowa Deep Loess and Drift) (Fig. 1). Samples were from Psamments in MLRA 65, Ustolls in MLRA 75, Udolls and Aquolls in MLRA 103, and Udolls, Aquolls, Udalfs, and Aqualfs in MLRA's 95B and 108. The soils sampled for this study formed in glacigenic diamicton, glaciolacustrine sediment, alluvium, eolian sand, loess, and locally derived hillslope sediment. Clay content of the entire sample set ranged from 2 to 45% and sand content from 2 to 96%, although some MLRA subsets had a much narrower textural range (e.g., the samples from MLRA 65 were all sands and loamy sands). The samples are representative of geographically significant soils in the north central region and are also representative of the variety of farming systems and uncultivated native vegetation remnants found in the region.
Organic C concentrations of all samples were measured with an automated dry combustion instrument (Model CHN 600, Leco, St. Joseph, MI), at Iowa State University using the methodology described by Soil Survey Staff (1996). Less than 2-mm soil samples were ground to pass a 60-mesh sieve. Total C was presumed to equal organic C as no calcareous samples were analyzed in this study.
All LOI analyses were run at Northern Illinois University using a muffle furnace (Model 550 Isotemp Series, Fisher Scientific, Pittsburgh, PA). Seventy-two samples could be analyzed concurrently using this particular furnace. The procedure follows the method described by Schulte and Hopkins (1996). Equivalent volumes (approximately 8 g) of <2-mm air-dry soil were placed into 15-mL crucibles. Samples were oven-dried at 105°C overnight, cooled in a desiccator, and weighed. The samples were then combusted at 360°C for 2 h in a muffle furnace. Samples were transferred after the 2-h combustion period to an oven at 105°C for several hours. Samples were then cooled in a desiccator and weighed. Loss-on-ignition was calculated using the following equation:
 |
An internal laboratory standard was included in every analysis run at both labs. Predictive equations for SOC were developed for each MLRA using least squares regression. The Tukey Test as described by Zar (1999) was used to test whether the slopes and intercepts of these equations were significantly different.
|
RESULTS AND DISCUSSION
|
|---|
Measurements on laboratory standards were used to evaluate the precision of the LOI method used in this study (Table 1). The LOI analysis is less precise than Leco SOC determination but is still highly reproducible (coefficient of variation <5%).
View this table:
[in this window]
[in a new window]
|
Table 1. Internal laboratory reference standard results from labs used in this study at Iowa State University (Leco) and Northern Illinois University (loss on ignition, LOI). Different reference standards, with different soil organic C (SOC) concentrations, are used in each lab.
|
|
Strong linear relationships between LOI and SOC were observed for all five MLRA sample sets (Fig. 2)
. The coefficient of determination (r2) for equations developed to predict SOC from LOI for individual MLRAs ranged from 0.94 to 0.98 (Table 2). Tukey's Test indicated that the slopes of the equations for all of the MLRAs except 103 and 108 were significantly different from one another (Table 2). The intercepts for MLRA 103 and 108 were significantly different. Thus, a unique predictive equation exists for soils of each MLRA. The reasons why each MLRA has a different predictive equation were not investigated here, but we speculate that varying SOM composition, clay content, and clay mineralogy are responsible. We note that the equation developed for MLRA 65 (Nebraska Sand Hills) has a much steeper slope than the equation for nearby MLRA 75 (Central Loess Plains), possibly because the MLRA 65 samples have much lower clay and silt content.
View larger version (23K):
[in this window]
[in a new window]
|
Fig. 2. Loss-on-ignition–Leco relationships for soils in five major land resource areas (MLRAs) in the north central USA.
|
|
View this table:
[in this window]
[in a new window]
|
Table 2. Soil organic C (SOC) predictive equations for individual major land resource areas (MLRAs). Slopes and intercepts correspond to Fig. 2.
|
|
In conclusion, LOI is an inexpensive, rapid, and precise method that can be used to accurately predict SOC concentrations in the north central region. Advantages of the method include the large sample numbers that can be run simultaneously and the low cost of equipment. Sample combustion temperature and time are critical components to consider when developing predictive equations, and researchers should standardize these variables. Evidence from this and other studies demonstrate that unique relationships exist for different soil-geographic areas; a universal equation predicting SOC from LOI does not exist.
|
ACKNOWLEDGMENTS
|
|---|
We would like to thank Julie McLaughlin of the Iowa State University Pedometrics Laboratory for her help with sample analysis. This paper is based in part on research supported by the National Science Foundation, Geography and Regional Science and Geology and Paleontology Programs, grants BCS-0079252 and BCS-0079320A and by funding from The Nature Conservancy.
Received for publication January 14, 2002.
|
REFERENCES
|
|---|
- Amundson, R. 2001. The carbon budget in soils. Ann. Rev. Earth Planet. Sci. 29:535–562.[ISI]
- Ball, D.F. 1964. Loss-on-ignition as an estimate of organic matter and organic carbon in non-calcareous soils. J. Soil Sci. 15:84–91.
- Ben-Dor, E., and A. Banin. 1989. Determination of organic matter content in arid-zone soils using a simple "loss-on-ignition" method. Commun. Soil Sci. Plant Anal. 20:1675–1695.
- Cambardella, C.A., A.M. Gajda, J.W. Doran, B.J. Wienhold, and T.A. Kettler. 2001. Estimation of particulate and total organic matter by weight loss-on-ignition. p. 349–359. In R. Lal et al. (ed.) Assessment methods for soil carbon. Advances in Soil Science. CRC Press, Boca Raton, FL.
- Combs, S.M., and M.V. Nathan. 1998. Soil organic matter. p. 53–58. In Recommended chemical soil test procedures for the north central region. North Central Regional Res. Publ. No. 221 (revised). Missouri Agric. Exp. Sta. SB 1001, Columbia, MO.
- David, M.B. 1988. Use of loss-on-ignition to assess soil organic carbon in forest soils. Commun. Soil Sci. Plant Anal. 19:1593–1599.
- Davies, B.E. 1974. Loss-on-ignition as an estimate of soil organic matter. Soil Sci. Soc. Am. J. 38:150–151.[Abstract/Free Full Text]
- Dean, W.E. Jr., 1974. Determination of carbonate and organic matter in calcareous sediments and sedimentary rocks by loss on ignition: Comparison with other methods. J. Sediment. Petrol. 44:242–248.[Abstract/Free Full Text]
- Donkin, M.J. 1991. Loss-on-ignition as an estimator of soil organic carbon in A-horizons of forestry soils. Commun. Soil Sci. Plant Anal. 22:233–241.
- Goldin, A. 1987. Reassessing the use of loss-on-ignition for estimating organic matter content in noncalcerous soils. Commun. Soil Sci. Plant Anal. 18:1111–1116.
- Kimble, J.M., R. Lal, and R.F. Follett. 2001. Methods for assessing soil C pools. p. 3–12. In R. Lal et al. (ed.) Assessment methods for soil carbon. Advances in Soil Science. CRC Press, Boca Raton, FL.
- Lal, R., J.M. Kimble, and R.F. Follett. 1998. Pedospheric processes and the carbon cycle. p. 1–8. In R. Lal et al. (ed.) Soil processes and the carbon cycle. Advances in Soil Science. CRC Press, Boca Raton, FL.
- Nelson, D.W., and L.E. Sommers. 1982. Total carbon, organic carbon, and organic matter. p. 539–580. In A.L. Page et al. (ed.) Methods of soil Analysis. Part 2. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI.
- Schulte, E.E., and B.G. Hopkins. 1996. Estimation of organic matter by weight loss-on-ignition. p. 21–31. In F.R. Magdoff et al. (ed.) Soil organic matter: Analysis and interpretation. SSSA Spec. Publ. 46. SSSA, Madison, WI.
- Schulte, E.E., C. Kaufmann, and J.B. Peter. 1991. The influence of sample size and heating time on soil weight loss-on-ignition. Commun. Soil Sci. Plant Anal. 22:159–168.
- Sikora, L.J., and D.E. Stott. 1996. Soil organic carbon and nitrogen. p. 157–168. In J.W. Doran and A.J. Jones (ed.) Methods for assessing soil quality. SSSA Spec. Publ. 49. SSSA, Madison, WI.
- Soil Survey Staff. 1996. Total carbon, dry combustion, method 6A2. Soil Survey Laboratory methods manual. Soil Survey Investigations Report No. 42, version 3.0. U.S. Gov. Print. Office, Washington, DC.
- Storer, D.A. 1984. A simple high volume ashing procedure for determination of soil organic matter. Commun. Soil Sci. Plant Anal. 15:759–772.
- Walkley, A., and I.A. Black. 1934. An examination of the Degtjareff method for determining soil organic matter, and a proposed modification of the chromic acid titration method. Soil Sci. 37:29–38.
- Zar, J.H. 1999. Biostatistical analysis. 4th ed. Prentice Hall, Upper Saddle River, NJ.
This article has been cited by other articles:
|
|
|
|
 
S. A. Wills, C. L. Burras, and J. A. Sandor
Prediction of Soil Organic Carbon Content Using Field and Laboratory Measurements of Soil Color
Soil Sci. Soc. Am. J.,
March 12, 2007;
71(2):
380 - 388.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
P. M. Jacobs and J. A. Mason
Late Quaternary climate change, loess sedimentation, and soil profile development in the central Great Plains: A pedosedimentary model
GSA Bulletin,
March 1, 2007;
119(3-4):
462 - 475.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
