Labile organic carbon (LOC) and the potential carbon turnover rate are sensitive indicators of changes in soil nutrient cycling processes. Details are provided for a method based on fumigating and incubating soil in a series of cycles and using the CO2 accumulated during the incubation periods to estimate these parameters.
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Method Article
Assessment of Labile Organic Carbon in Soil Using Sequential Fumigation Incubation Procedures
In This Article
Summary
Abstract
Management practices and environmental changes can alter soil nutrient and carbon cycling. Soil labile organic carbon, a readily decomposable C pool, is highly sensitive to disturbance. It is also the primary substrate for soil microorganisms, which is fundamental to nutrient cycling. Due to these attributes, labile organic carbon (LOC) has been identified as an indicator parameter for soil health. Quantifying the turnover rate of LOC also aids in understanding changes in soil nutrient cycling processes. A sequential fumigation incubation method has been developed to estimate soil LOC and potential C turnover rate. The method requires fumigating soil samples and quantifying CO2-C respired during a 10 day incubation period over a series of fumigation-incubation cycles. Labile organic C and potential C turnover rate are then extrapolated from accumulated CO2 with a negative exponential model. Procedures for conducting this method are described.
Introduction
Due to its vital roles in carbon (C) and nutrient cycling and its sensitivity to soil change, soil LOC is an important parameter to measure as an indicator of soil organic matter quality. Forests and agroecosystems to a large degree depend on the mineralization of nutrients in soil organic matter as a source of nutrients. Management activities can change the pool size and turnover rate of soil organic C, resulting in changes in nutrient supply1. Soil organic C consists of two primary fractions of recalcitrant C, which has turnover rates of several thousand years, and LOC, which has turnover rates from a few weeks to a few years2,3,4. Soil labile ....
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Protocol
1. Collect Soil to Get Samples Representative of Conditions within the Experimental Area and within Experimental Units20
- Identify any differences in site properties such as slope and soil properties including texture, bulk density, pH, organic horizon depth, and/or nutrient concentrations. Identify any differences in vegetation type within plots. Use known or published estimates of coefficients of variation for site properties to estimate the number of samples required to attain a pre-specified relative error.
- Sample soil using an auger or other collection device in a pattern based on site and experimental unit conditions.
- ....
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Results
The SFI method has been used as described in this paper in a series of experiments conducted in the southeastern United States24,25,26,27. Together, these experiments encompassed a variety of vegetation types, including loblolly pine (Pinus taeda L.), switchgrass (Panicum virgatum L.), cottonwood (Populus deltoides Bartram ex Marsh.), and soybean (Glycine max L. Merr.). The method was sensitive at determining differences in LOC and/or potenti.......
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Discussion
The SFI method is an effective protocol for detecting differences in soil LOC and potential C turnover rates over a range of management practices (such as fertilization, tillage, vegetation control, and harvest practices) and soil conditions. Soil LOC content and C turnover rate can be used to understand alterations of nutrient cycles. The SFI method also provides measurement of microbial biomass C from the first fumigation-incubation event. The ability to measure soil LOC, C turnover, and microbial biomass C concurrentl.......
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Disclosures
The authors have nothing to disclose.
Acknowledgements
The authors gratefully acknowledge Michelle Gonzales, Kenny Kidd, Brad Osbon, and all other personnel that conducted the laboratory procedures for these data. The authors are thankful for assistance from Andrew Scott in developing software coding to conduct model-fitting procedures. The authors also appreciate the funding from the U.S. Department of Agriculture National Institute of Food and Agriculture, Sustainable Agriculture and Research & Education, Sun Grant South Central region, and the National Council of Air and Stream Improvement that made possible the studies from which representative results provided in this paper were drawn.
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Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| Soil auger sampling kit | JMC | PN039 | Several other manufacturers of punch augers are available |
| Parafilm | Curwood | PM999 | |
| Aluminum weighing boats | Fisherbrand | 08-732-103 | |
| General purpose drying oven | Fisher Scientific | 15-103-0511 | Many other manufacturers of general purpose laboratory ovens are available |
| 10.5 L vacuum desiccator | Corning | 3121-250 | |
| Glass scintillation vial | Wheaton | 968560 | |
| Glass threaded vials, 41 ml | Fisherbrand | 03-339-21N | |
| Chloroform, stabilized with amylenes | Sigma-Aldrich | 67-66-3 | |
| Boiling chips | Fisher Scientific | S25201 | |
| Glass rod | Fisherbrand | S63449 | |
| Size 10 rubber stopper | Fisherbrand | 14-130P | Rubber stoppers can be purchased as solid and drilled in center to install glass rod or bought with a hole to insert glass rod |
| Wide-mouth PPCO bottle, 0.5 L | ThermoScientific | 3121050016 | |
| Sodium hydroxide, reagent grade | Sigma-Aldrich | S5881 | |
| Barium chloride | Sigma-Aldrich | 202738 | |
| Phenolphthalein indicator | Fisher Scientific | S25466 | |
| Hydrochloric acid solution, 0.1 N | Fisher Scientific | SA54-4 |
References
- Blair, G., et al. Soil carbon fractions based on their degree of oxidation, and the development of a carbon management index for agricultural systems. Aust. J. Agric. Res. 46, 1459-1466 (1995).
- Schimel, D. S., et al.
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