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
<ol>
	<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>
	<li>Blair, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Soil+carbon+fractions+based+on+their+degree+of+oxidation,+and+the+development+of+a+carbon+management+index+for+agricultural+systems.">Soil carbon fractions based on their degree of oxidation, and the development of a carbon management index for agricultural systems.</a> Aust. J. Agric. Res. 46, 1459-1466 (1995).</li><li>Schimel, D. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Soil+organic+matter+dynamics+in+paired+rangeland+and+cropland+toposequences+in+North+Dakota.">Soil organic matter dynamics in paired rangeland and cropland toposequences in North Dakota.</a> Geoderma. 36, 201-214 (1985).</li><li>Parton, W. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+factors+controlling+soil+organic+matter+levels+in+great-plains+grasslands.">Analysis of factors controlling soil organic matter levels in great-plains grasslands.</a> Soil Sci. Soc. Am. J. 51, 1173-1179 (1987).</li><li>Wu, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Labile+organic+C+and+N+mineralization+of+soil+aggregate+size+classes+in+semiarid+grasslands+as+affected+by+grazing+management.">Labile organic C and N mineralization of soil aggregate size classes in semiarid grasslands as affected by grazing management.</a> Biol. Fertil. Soils. 48, 305-313 (2011).</li><li>Jones, D. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant+and+mycorrhizal+regulation+of+rhizodeposition.">Plant and mycorrhizal regulation of rhizodeposition.</a> New Phytol. 163, 459-480 (2004).</li><li>Harrison, K. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+changing+land+use+of+soil+radiocarbon.">The effect of changing land use of soil radiocarbon.</a> Science. 262, 725-726 (1993).</li><li>Jinbo, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Land+use+effects+on+the+distribution+of+labile+organic+carbon+fractions+through+soil+profiles.">Land use effects on the distribution of labile organic carbon fractions through soil profiles.</a> Soil Sci Soc. Am. J. 70, 660-667 (2006).</li><li>Whalen, J. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Carbon+and+nitrogen+mineralization+from+light-+and+heavy-fraction+additions+to+soil.">Carbon and nitrogen mineralization from light- and heavy-fraction additions to soil.</a> Soil Biol Biochem. 32, 1345-1352 (2000).</li><li>Gregorich, E. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Towards+a+minimum+data+set+to+assess+soil+organic+matter+quality+in+agricultural+soils.">Towards a minimum data set to assess soil organic matter quality in agricultural soils.</a> Can. J. Soil Sci. 74, 367-385 (1994).</li><li>Hamer, U., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Priming+effects+in+different+soil+types+induced+by+fructose,+alanine,+oxalic+acid+and+catechol+additions.">Priming effects in different soil types induced by fructose, alanine, oxalic acid and catechol additions.</a> Soil Biol. Biochem. 37, 445-454 (2005).</li><li>Feng, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shifting+sources+of+soil+labile+organic+carbon+after+termination+of+plant+carbon+inputs+in+a+subtropical+moist+forest+of+southwest+China.">Shifting sources of soil labile organic carbon after termination of plant carbon inputs in a subtropical moist forest of southwest China.</a> Ecol. Res. 26, 437-444 (2011).</li><li>Tisdall, J. M., Carter, M. R., Stewart, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+of+soil+aggregates+and+accumulation+of+soil+organic+matter.">Formation of soil aggregates and accumulation of soil organic matter.</a> Structure and Organic Matter Storage in Agricultural Soils. , 57-96 (1996).</li><li>Zou, X. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Estimating+soil+labile+organic+carbon+and+potential+turnover+rates+using+a+sequential+fumigation-incubation+procedure.">Estimating soil labile organic carbon and potential turnover rates using a sequential fumigation-incubation procedure.</a> Soil Biol. Biochem. 37, 1923-1928 (2005).</li><li>Cambardella, C. A., Elliott, E. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Particulate+soil+organic+matter+changes+across+a+grassland+cultivation+sequence.">Particulate soil organic matter changes across a grassland cultivation sequence.</a> Soil Sci. Soc. Am. J. 56, 777-783 (1992).</li><li>Strosser, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+for+determination+of+labile+soil+organic+matter:+an+overview.">Methods for determination of labile soil organic matter: an overview.</a> J. Agrobiol. 27, 49-60 (2010).</li><li>Jenkinson, D. A., Powlson, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effects+of+biocidal+treatment+on+metabolism+in+soil+V:+a+method+for+measuring+soil+biomass.">The effects of biocidal treatment on metabolism in soil V: a method for measuring soil biomass.</a> Soil Biol. Biochem. 8, 209-213 (1976).</li><li>Vance, E. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+extraction+method+for+measuring+soil+microbial+biomass+C.">An extraction method for measuring soil microbial biomass C.</a> Soil Biol. Biochem. 19, 703-707 (1987).</li><li>De-Polli, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chloroform+fumigation-extraction+labile+C+pool+(microbial+biomass+C+&amp;#34;plus&amp;#34;)+shows+high+correlation+to+microbial+biomass+C+in+Argentinian+and+Brazilian+soils.">Chloroform fumigation-extraction labile C pool (microbial biomass C &amp;#34;plus&amp;#34;) shows high correlation to microbial biomass C in Argentinian and Brazilian soils.</a> Cienc. Suelo. 25, 15-22 (2007).</li><li>Olson, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Energy+storage+and+the+balance+of+producers+and+decomposers+in+ecological+systems.">Energy storage and the balance of producers and decomposers in ecological systems.</a> Ecology. 44, 322-331 (1963).</li><li>Pennock, D., Carter, M. R., Gregorich, E. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chapter+1,+Unit+1,+Soil+sampling+designs.">Chapter 1, Unit 1, Soil sampling designs.</a> Soil Sampling and Methods of Analysis. , (2008).</li><li>Luizao, R. C. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Seasonal+variation+of+soil+microbial+biomass:+the+effects+of+clearfelling+a+tropical+rainforest+and+establishment+of+pasture+in+the+central+Amazon.">Seasonal variation of soil microbial biomass: the effects of clearfelling a tropical rainforest and establishment of pasture in the central Amazon.</a> Soil Biol. Biochem. 24, 805-813 (1992).</li><li>Horwath, W. R., Paul, E. A., Weaver, R. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microbial+biomass.">Microbial biomass.</a> Methods of soil analysis part 2: microbiological and biochemical properties. , 753-773 (1994).</li><li>Jenkinson, D. S., Ladd, J. N., Paul, E. A., Ladd, J. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microbial+biomass+in+soil:+measurement+and+turnover.">Microbial biomass in soil: measurement and turnover.</a> Soil Biochemistry. , 415-471 (1981).</li><li>Blazier, M. A., Gungor, E. B. O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poultry+litter+fertilization+impacts+on+soil,+plant,+and+water+characteristics+in+loblolly+pine+(Pinus+taeda+L.)+plantations+and+silvopastures+in+the+mid-South+USA.">Poultry litter fertilization impacts on soil, plant, and water characteristics in loblolly pine (Pinus taeda L.) plantations and silvopastures in the mid-South USA.</a> Principles, application, and assessment in soil science. , 43-74 (2011).</li><li>Blazier, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Straw+harvesting,+fertilization,+and+fertilizer+type+alter+soil+biophysical+properties+in+a+loblolly+pine+plantation+in+the+mid-South+USA.">Straw harvesting, fertilization, and fertilizer type alter soil biophysical properties in a loblolly pine plantation in the mid-South USA.</a> Biol. Fertil. Soils. 45, 145-153 (2008).</li><li>Blazier, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Loblolly+pine+age+and+density+affects+switchgrass+growth+and+soil+carbon+in+an+agroforestry+system.">Loblolly pine age and density affects switchgrass growth and soil carbon in an agroforestry system.</a> For. Sci. 58, 485-496 (2012).</li><li>Blazier, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nitrogen+and+carbon+of+switchgrass,+loblolly+pine,+and+cottonwood+biofuel+production+systems+in+the+Southeast+United+States.">Nitrogen and carbon of switchgrass, loblolly pine, and cottonwood biofuel production systems in the Southeast United States.</a> For. Sci. 61, 522-534 (2015).</li><li>Zhang, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Decomposition+differences+of+labile+carbon+from+litter+to+soil+in+a+tropical+rain+forest+and+rubber+plantation+of+Xishuagbanna,+southwest+China.">Decomposition differences of labile carbon from litter to soil in a tropical rain forest and rubber plantation of Xishuagbanna, southwest China.</a> Eur. J. Soil Biol. 55, 55-61 (2013).</li><li>Nelson, D. W., Sommers, L. E., Sparks, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Total+carbon,+organic+carbon,+and+organic+matter.">Total carbon, organic carbon, and organic matter.</a> Methods of soil analysis. Part 3: chemical methods. , 961-1090 (1996).</li><li>Huang, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlation+among+soil+microorganisms,+soil+enzyme+activities,+and+removal+rates+of+pollutants+in+three+constructed+wetlands+purifying+micro-polluted+river+water.">Correlation among soil microorganisms, soil enzyme activities, and removal rates of pollutants in three constructed wetlands purifying micro-polluted river water.</a> Soil Biol. Biochem. 70, 221-228 (2012).</li><li>Kong, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enzyme+and+root+activities+in+surface-flow+constructed+wetlands.">Enzyme and root activities in surface-flow constructed wetlands.</a> Chemosphere. 76, 601-608 (2009).</li><li>Cui, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+nutrient+removal+efficiency+and+microbial+enzyme+activity+in+a+baffled+subsurface-flow+constructed+wetland+system.">Evaluation of nutrient removal efficiency and microbial enzyme activity in a baffled subsurface-flow constructed wetland system.</a> Bioresour. Technol. 146, 656-662 (2013).</li><li>Jenkinson, D. S., Wilson, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+microbial+biomass+carbon+and+nitrogen+in+soil.">Determination of microbial biomass carbon and nitrogen in soil.</a> Advances in nitrogen cycling in agricultural ecosystems. , 368-386 (1988).</li><li>Sparling, G. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interference+from+plant+roots+in+the+estimation+of+soil+microbial+ATP,+C,+N,+and+P.">Interference from plant roots in the estimation of soil microbial ATP, C, N, and P.</a> Soil Biol. Biochem. 17, 275-278 (1985).</li><li>Christie, P., Beatte, J. A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Significance+of+sample+size+in+measurement+of+soil+microbial+biomass+by+the+chloroform+fumigation-incubation+method.">Significance of sample size in measurement of soil microbial biomass by the chloroform fumigation-incubation method.</a> Soil Biol. Biochem. 19, 149-152 (1987).</li><li>McLaughlin, K. K., Hobbie, S. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+labile+soil+organic+matter+fractionation+techniques.">Comparison of labile soil organic matter fractionation techniques.</a> Soil Sci. Soc. Am. J. 68, 1616-1625 (2004).</li><li>Xia, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Variation+of+soil+labile+organic+carbon+pools+along+an+elevational+gradient+in+the+Wuyi+Mountains,+China.">Variation of soil labile organic carbon pools along an elevational gradient in the Wuyi Mountains, China.</a> J. Resour. Ecol. 1, 368-374 (2010).</li></ol>

The authors have nothing to disclose.

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...

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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 ...

The overall goal of this sequential fumigation incubation procedure is to estimate labile carbon and the potential carbon turnover rate in soil. This method can answer key things in the soil microbiology field, such as the amount of substrate that soil microbes use to transform nutrients in the soil. One of the main advantages of this technique is that it's relatively simple to use and inexpensive.Prior to collection, identify differences in soil properties and vegetation within the collection site. Using the appropriate coefficients of variation, determine the number of samples needed and the distance of variability. For heterogeneous soil conditions, designate a grid sample pattern wherein the distance between sample points on each transect is smaller than the distance of variability within an experimental unit.Clear organic matter from the soil surface at the sample points. Using an auger, collect each soil sample. For each transect of the grid, mix the samples in a single container.Place each composite sample in a cooler with ice packs immediately after collection. Once field work is completed, sieve the soil samples. Clean the mesh with water after sieving each sample.For each composite soil sample, place three individual 100 gram samples into beakers. Cover the beakers with laboratory film and pre-incubate the beakers at 25 degrees Celsius for 10 days. Then, for each sample, remove the film and place one gram of soil in a pre-weighed aluminum weigh boat.Record the combined weight of the moist soil and weigh boat. Dry each sample in the weigh boats at 105 degrees Celsius for 48 hours. Check the weight every eight hours for the first 24 hours and then every six hours until no more weight is lost.Using the known weights of the weigh boats, determine the weight of the dry soil. Calculate the dry to moist soil weight ratio. To begin the fumigation, place a damp paper towel at the bottom of each of two glass vacuum desiccators with porcelain plates.Designate one desiccator for fumigation. For each sample, prepare three narrow glass vials, each containing 30 grams of soil. Label each vial in pencil on laboratory tape.For each set, place two vials in the fumigation desiccator and the third vial in the other desiccator. Place the fumigation desiccator in a fume hood. Cover the bottom of a 100 milliliter beaker with boiling stones.In the fume hood, pour 50 milliliters of ethanol-free chloroform into the beaker. Place the beaker in the center of the fumigation desiccator and close the desiccator. Connect the fumigation desiccator to a vacuum pump.Turn on the vacuum pump and allow the chloroform to boil for 30 seconds. Then, turn off and disconnect the pump to allow air into the desiccator. Repeat this step twice more.Boil the chloroform a fourth time for two minutes. Then, close off the desiccator to maintain the vacuum. Turn off and disconnect the vacuum pump.Close and seal the other desiccator. Store both desiccators in a dark area at room temperature for 24 hours. Next, place the fumigation desiccator in a fume hood.Vent the desiccator and remove the paper towel. Place vials with soil into the desiccator, close the desiccator, connect the vacuum pump, and open the vacuum to remove chloroform gas from the soil samples. Run the vacuum for five minutes, and then vent the desiccator.Perform this step four more times, then remove the soil-filled vials from the desiccator to prepare them for incubation procedures. To prepare incubation containers, label wide-mouth polypropylene bottles for the fumigated and non-fumigated subsamples. Label three more bottles as no soil controls for later titration.For each labeled bottle, drill a hole in the center of a size 10 rubber stopper and insert a 15 centimeter length glass rod into the hole. Affix a 40 milliliter glass vial to the glass rod with a rubber band. Then, add one gram of soil from the original pre-incubated soil sample to each of its three subsamples.Place one milliliter of deionized water into one of the bottles labeled for fumigated soil. Place a vial of fumigated soil into the bottle. Pipette one milliliter of two molar sodium hydroxide into the glass vial of the stopper assembly.Carefully stopper the bottle and seal the bottle with laboratory film. Repeat this process for the remaining soil samples. Prepare the no soil containers in the same way but without soil samples.Store the incubation chambers in a dark area at room temperature for 10 days. After incubation, carefully remove the vial of sodium hydroxide from an incubation container. Pipette two milliliters of one molar barium chloride into the vial.Add one drop of phenolphthalein to the vial. Add a magnetic stir bar to the vial, and begin stirring the mixture on a stir plate. With a burette, slowly add 0.1 normal hydrochloric acid until the solution appearance changes from red to colorless.Record the volume of hydrochloric acid added. Repeat the titration for all of the incubation chambers noting the no soil values separately. Using the titration data and the dry-moist soil weight ratio, calculate the carbon dioxide mineralized during incubation of the soil samples.From this, calculate the microbial biomass carbon for each set of samples. Perform seven more rounds of fumigation and incubation on the fumigated samples, calculating the mineralized carbon dioxide after each cycle. Using this data, determine the amount of labile organic carbon and the potential turnover time for each fumigated sample by non-linear regression.The sequential soil fumigation and incubation method identify differences in labile organic carbon, or LOC, and potential carbon turnover rates among different vegetation conditions. Soybean conditions have the highest LOC values, which was associated with biomass deposition during soybean harvests. Loblolly pine plantations had the highest potential carbon turnover rates, which was associated with acidic pine litter being the dominant source of soil organic matter.The loblolly pine and switchgrass alley cropping system had the broadest array of sampling site conditions and the switchgrass pasture had the greatest variation in soil textures among sampling sites. Both of these conditions exhibited wide ranges of both LOC values and potential carbon turnover rates. Once mastered, this technique takes about 30 minutes per sample over the course of an 80 day period that it takes to run each sample.To conduct this procedure accurately, some of the things to remember are to make sure the desiccators are sealed tightly, as well as the incubation chambers, and to not breathe too closely to the vials that contain sodium hydroxide. In tandem with this procedure or following this procedure, there's several different enzyme assays that can be conducted in soil to better understand soil microbial function. After watching this video, you should have a good understanding of how to conduct Labile Carbon Analysis using the sequential fumigation incubation procedure.Don't forget that working with chloroform can be extremely hazardous. You need personal protection equipment and a fume hood to conduct these procedures safely.

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11.3K 조회수.  Louisiana State University Agricultural Center. The overall goal of this sequential fumigation incubation procedure is to estimate labile carbon and the potential carbon turnover rate in soil. This method can answer key things in the soil microbiology field, such as the amount of substrate that soil microbes use to transform nutrients in the soil. One of the main advantages of this technique is that it's relatively simple to use and inexpensive.Prior to collection, identify differences in soil properties and vegetation within the co...