Name: assessment of labile organic carbon in soil using sequential fumigation incubation procedures
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Description: Watch this Scientific Journal Video about Assessment of Labile Organic Carbon in Soil Using Sequential Fumigation Incubation Procedures at JoVE.com

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 &amp; 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.

1. Collect Soil to Get Samples Representative of Conditions within the Experimental Area and within Experimental Units20
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	<li>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 rel...

<ol>
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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...

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 C consists of readily decomposable substrates such as microbial biomass C, low-molecular-weight compounds (amino acids, simple carbohydrates) from plant rhizodeposition, and decomposition byproducts and leachates from plant litter1,4,5. Because soil labile C is readily decomposable, it is highly sensitive to management practices and natural phenomena that disturb or alter soil6. Soil labile C serves as the primary energy source for soil microorganisms in the decomposition of organic matter7. As such, LOC impacts nutrient cycling to a greater degree than does stable forms of soil organic C8. Soil microorganisms are also responsible for the majority of heterotrophic respiration that occurs during decomposition of recalcitrant soil organic matter facilitated by the priming effect of LOC9,10,11. This respiration plays a substantial role in global C cycles because soil organic C is approximately double that of atmospheric C11.
As a result of its importance in terrestrial ecosystems, several methods have been developed to estimate soil LOC. These methods can be delineated into three general classifications: physical, chemical, and biochemical. Densitometric separation methods are physical methods that consist of separating soil organic C into heavy or light fractions or into coarse and fine particulate organic C12,13,14,15. Separation methods are relatively easy to perform, but they do not often produce consistent results because these fractions vary with soil type mineral composition, plant material size and density, and soil aggregate consistency13,15. Separation methods also produce only quantitative information about LOC15.
Several chemical methods are available for LOC estimation. Aqueous extraction of organic carbon is relatively easy to perform, and the methods often provide easily reproducible results. However, these extractions do not involve the whole spectrum of available substrates for microorganisms15. Several oxidation methods for chemical fractionation of soil organic C have been developed. Oxidation methods have the advantage of characterizing the quantity and quality of labile organic C, although some methods require work with hazardous chemicals and there is variability among the methods in reproducibility of results15. The acid hydrolysis extraction method is another type of chemical fractionation procedure that can measure the quantity and quality of LOC, but results of this method do not facilitate interpretation of its biological properties13,15.
Biochemical methods for interpretation of soil LOC have been developed. Labile organic C can be measured as CO2 released by microorganisms in respiration assays. These assays provide estimates of true mineralizable organic matter, but typically only the most labile compounds are mineralized during the assays15. Soil microbial biomass C measured by fumigation-incubation16 and fumigation-extraction17 has been used to develop inferences about LOC. However, these procedures provide estimates of C in microbial biomass rather than LOC. Both fumigation procedures include subtraction of values from non-fumigated soil to determine microbial biomass C, but it has been suggested that values obtained without subtraction of non-fumigated soil provide a measure of labile organic fractions of C in addition to microbial biomass18.
The sequential fumigation-incubation (SFI) procedure13 for measuring LOC is a biochemical method adapted from the fumigation-incubation procedure16 for soil microbial biomass C measurement. The SFI method has some advantages relative to other methods of estimating LOC. A conceptual basis for the method is that LOC is the microbially degradable C that governs microbial growth and that LOC is physically accessible and chemically degradable by soil microorganisms. Under field conditions, microbial growth is typically limited by carbon availability, nutrient availability, available pore space, and/or predation. These factors are nearly eliminated by fumigation, creating unimpeded conditions for microbial growth. No nutrients are removed during the incubation period of the method. Over the course of multiple fumigation and incubation cycles, microbial growth becomes limited by C quantity and quality (lability)13. The accumulated CO2 respired during the incubation cycles is used to extrapolate LOC with a simple negative exponential model11,13,19. The potential C turnover rate can also be derived from the slope of the exponential model, so the SFI method has the advantage over most other LOC methods of simultaneously estimating the concentrations and potential turnover rate of LOC11. For other methods, information on the potential turnover rates of LOC can only be ascertained if tracers such as 14C are used13. The SFI method is thus a relatively simple and inexpensive technique for obtaining measurements of both LOC and its potential turnover rates.

<table border="0" cellpadding="0" cellspacing="0" width="674">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Soil auger sampling kit</td>
			<td style="width:131px;">JMC</td>
			<td style="width:119px;">PN039</td>
			<td style="width:167px;">Several other manufacturers of punch augers are available</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Parafilm</td>
			<td style="width:131px;">Curwood</td>
			<td style="width:119px;">PM999</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Aluminum weighing boats</td>
			<td style="width:131px;">Fisherbrand</td>
			<td style="width:119px;">08-732-103</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">General purpose drying oven</td>
			<td style="width:131px;">Fisher Scientific</td>
			<td style="width:119px;">15-103-0511</td>
			<td>Many other manufacturers of general purpose laboratory ovens are available</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">10.5 L vacuum desiccator</td>
			<td style="width:131px;">Corning</td>
			<td style="width:119px;">3121-250</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Glass scintillation vial</td>
			<td style="width:131px;">Wheaton</td>
			<td align="right" style="width:119px;">968560</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Glass threaded vials, 41 mL&#160;</td>
			<td style="width:131px;">Fisherbrand</td>
			<td style="width:119px;">03-339-21N</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Chloroform, stabilized with amylenes</td>
			<td style="width:131px;">Sigma-Aldrich</td>
			<td style="width:119px;">67-66-3</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Boiling chips</td>
			<td style="width:131px;">Fisher Scientific</td>
			<td style="width:119px;">S25201</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Glass rod</td>
			<td style="width:131px;">Fisherbrand</td>
			<td style="width:119px;">S63449</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Size 10 rubber stopper</td>
			<td style="width:131px;">Fisherbrand</td>
			<td style="width:119px;">14-130P</td>
			<td>Rubber stoppers can be purchased as solid and drilled in center to install glass rod or bought with a hole to insert glass rod</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Wide-mouth PPCO bottle, 0.5 L</td>
			<td style="width:131px;">ThermoScientific</td>
			<td align="right" style="width:119px;">3121050016</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Sodium hydroxide, reagent grade</td>
			<td style="width:131px;">Sigma-Aldrich</td>
			<td style="width:119px;">S5881</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Barium chloride</td>
			<td style="width:131px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">202738</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Phenolphthalein indicator</td>
			<td style="width:131px;">Fisher Scientific</td>
			<td style="width:119px;">S25466</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Hydrochloric acid solution, 0.1 N</td>
			<td style="width:131px;">Fisher Scientific</td>
			<td style="width:119px;">SA54-4</td>
			<td></td>
		</tr>
	</tbody>
</table>

assessment of labile organic carbon in soil using sequential fumigation incubation procedures

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.

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...

Watch this Scientific Journal Video about Assessment of Labile Organic Carbon in Soil Using Sequential Fumigation Incubation Procedures at JoVE.com

Assessment of Labile Organic Carbon in Soil Using Sequential Fumigation Incubation Procedures

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.

Management practices and environmental changes can alter soil nutrient and carbon cycling. Soil labile organic carbon, a readily decomposable C pool, is ...

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