Stabilization of carbon in composts and biochars in relation to carbon sequestration and soil fertility

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<ul><li><p>io</p><p>RAusnmrald Te</p><p>Received 18 January 2012Received in revised form 20 February 2012Accepted 26 February 2012Available online 22 March 2012</p><p>Keywords:Organic amendments</p><p>1. Introduction Applying organic residues, such as those resulting from compost-</p><p>Science of the Total Environment 424 (2012) 264270</p><p>Contents lists available at SciVerse ScienceDirect</p><p>Science of the Tot</p><p>j ourna l homepage: www.e lseCarbon (C) sequestration in soil has been recognized by the Inter-governmental Panel on Climate Change (IPCC) as one of the possiblemeasures through which greenhouse gas emissions can be mitigated(Follett, 2001). Strategies for increasing its sequestration in soils havebeen investigated including conservation tillage, soil amendmentswith biosolids and organic wastes, and improved crop rotation (Lal,2004; Sissoko and Kpomblekou-A, 2010). However, capitalizing onthis potential climate-change mitigation measure is not a simpletask and the issue is complicated by the fact that intensive farmingtechniques generally lead to the depletion of C from soil, thus reduc-</p><p>ing, to agricultural land could increase the amount of C stored inthese soils and contribute signicantly to the reduction of greenhousegas emissions (Bustamante et al., 2010). Thus composting can con-tribute in a positive way to the twin objectives of restoring soil qualityand sequestering C in soils. Applications of organic residues can leadeither to a build-up of soil C over time, or a reduction in the rate atwhich organic matter is depleted from soils. Therefore the applicationof organic residues is likely to reverse the decline in soil C storage thathas occurred in recent decades, thereby contributing to the build-upin the stable C fraction in soils (De Neve et al., 2003).</p><p>One of the problems with the use of organic residues such as com-</p><p>ing its capacity to act as a C sink (Lal, 2009;2010).</p><p> Corresponding author at: Centre for Environmentalation (CERAR), University of South Australia, SA 50956218; fax: +61 8 8302 3124.</p><p>E-mail address: Nanthi.Bolan@unisa.edu.au (N.S. Bo</p><p>0048-9697/$ see front matter 2012 Elsevier B.V. Alldoi:10.1016/j.scitotenv.2012.02.061Heavy metalsImmobilizationDecompositionMineralizable nitrogenMicrobial biomass carbonThere have been increasing interests in the conversion of organic residues into biochars in order to reduce therate of decomposition, thereby enhancing carbon (C) sequestration in soils. However energy is required toinitiate the pyrolysis process during biochar production which can also lead to the release of greenhouse gas-ses. Alternative methods can be used to stabilize C in composts and other organic residues without impactingtheir quality. The objectives of this study include: (i) to compare the rate of decomposition among variousorganic amendments and (ii) to examine the effect of clay materials on the stabilization of C in organicamendments. The decomposition of a number of organic amendments (composts and biochars) was exam-ined by monitoring the release of carbon-dioxide using respiration experiments. The results indicated thatthe rate of decomposition as measured by half life (t1/2) varied between the organic amendments and washigher in sandy soil than in clay soil. The half life value ranged from 139 days in the sandy soil and187 days in the clay soil for poultry manure compost to 9989 days for green waste biochar. Addition ofclay materials to compost decreased the rate of decomposition, thereby increasing the stabilization of C.The half life value for poultry manure compost increased from 139 days to 620, 806 and 474 days with theaddition of goethite, gibbsite and allophane, respectively. The increase in the stabilization of C with the addi-tion of clay materials may be attributed to the immobilization of C, thereby preventing it from microbial de-composition. Stabilization of C in compost using clay materials did not impact negatively the value ofcomposts in improving soil quality as measured by potentially mineralizable nitrogen and microbial biomasscarbon in soil.</p><p> 2012 Elsevier B.V. All rights reserved.Article history:a b s t r a c ta r t i c l e i n f oStabilization of carbon in composts and band soil fertility</p><p>N.S. Bolan a,b,, A. Kunhikrishnan c, G.K. Choppala a,b,a Centre for Environmental Risk Assessment and Remediation (CERAR), University of Southb Cooperative Research Centre for Contaminants Assessment and Remediation of the Enviroc Chemical Safety Division, Department of Agro-Food Safety, National Academy of Agricultud Department of Environmental Engineering, Gyeongnam National University of Science anSanderman and Baldock,</p><p>Risk Assessment and Remedi-, Australia. Tel.: +61 8 8302</p><p>lan).</p><p>rights reserved.chars in relation to carbon sequestration</p><p>. Thangarajan a,b, J.W. Chung d</p><p>tralia, SA 5095, Australiaent (CRC CARE), University of South Australia, SA 5095, AustraliaScience, Suwon-si, Gyeonggi-do 441-707, Republic of Koreachnology, Dongjin-ro 33, Jinju, Gyeongnam, 660-758, Republic of Korea</p><p>al Environment</p><p>v ie r .com/ locate /sc i totenvposts and manures as a means of terrestrial C sequestration is theirrelatively fast rate of degradation, leading to the release of carbon-dioxide, thereby becoming a source (rather than a sink) for green-house gas emission (Godbout et al., 2010). Therefore there havebeen increasing interests in the conversion of organic residues intobiochars in order to reduce the rate of decomposition, thereby en-hancing C sequestration in soils (Kookana et al., 2011). However en-ergy is required to initiate the pyrolysis process during biochar</p></li><li><p>production which can also lead to the release of greenhouse gassessuch as carbon-monoxide and methane (Gaunt and Lehmann,2008). Alternative methods can be used to stabilize C in compostsand other organic residues without impacting their quality in relationto improving the physical, chemical and biological fertility of soils.The objectives of this study include: (i) to compare the rate of decom-position among various organic amendments and (ii) to examine theeffect of clay materials on the stabilization of C in organic amend-ments. The fertilization value of C-stabilized composts was examinedby monitoring potentially mineralizable N (PMN) and microbial bio-mass C in soil.</p><p>2. Materials and methods</p><p>using poultry manure compost and poultry manure biochar. The ef-</p><p>2.3. Decomposition experiments</p><p>The decomposition of organic amendments was measured by mon-itoring the release of carbon-dioxide (CO2) using respiration asks. Thesoil samples were mixed with unamended or amended composts andbiochars at a rate of 50 g C kg1 soil, corresponding to approximately25 Mg organic carbon per ha to a depth of 5 cm. The soil sampleswere placed in 3-dm3 jars containing a CO2 trap (30 mL of 1 MNaOH), and a beaker containingwater tomaintain awater-saturated at-mosphere. Additional jars containing only the CO2 traps and waterserved as blanks. The jars were then incubated in the dark at 24 C.Three jars per treatment were removed at various intervals over a peri-od of 360 days for the analysis of CO2 in theNaOH trap and total C in soilsamples. After precipitation of the trapped CO2 as BaCO3 using BaCl2, theamount of evolved CO2 was determined by back-titration of unreacted</p><p>Table 1Characteristics of soils and organic amendments used in this study.</p><p>265N.S. Bolan et al. / Science of the Total Environment 424 (2012) 264270Soil/amendments Sand(g kg1)</p><p>Silt(g kg1)</p><p>Claya</p><p>(g kg1)</p><p>Arable soil 218 384 398Vegetable soil 246 257 497Vineyard soil 228 138 634Turf soil 324 197 479Copper mine soil 387 235 378Shooting range soil 487 123 390Poultry manure compost Cow manure compost Poultry manure biochar Green waste biochar </p><p>afect of stabilizing agents on the decomposition of poultry manureand poultry manure compost was examined using the vegetablesoil. The effect of unamended and amended poultry manure on mi-crobial biomass carbon and potential mineralizable nitrogen was ex-amined using the arable soil.</p><p>2.2. Stabilization of carbon</p><p>The stabilization of C in both composts and biochars was exam-ined by co-composting these samples in the presence of various claymaterials that include goethite, gibbsite and allophane. Around 1 kgof poultry manure compost or poultry manure biochar were mixedwith these amendments at the rate of 50 g kg1 and incubated inan aerobic digester supplied with air at 1.44 L min1 at a moisturecontent of 30% (w/w) in a temperature controlled room (37 C) for3 months. A control sample was also incubated in the absence ofthese amendments. We used chemical fractionation of C in compostsand biochars to monitor C stabilization (Bhupinderpal-Singh et al.,2004).2.1. Soil and organic amendments</p><p>Four surface (015 cm depth) soil samples one each from differ-ent land-use practices (vineyard, vegetable cultivation, arable crop-ping and sports turf) were used in this study. To examine the effectof metal contamination on decomposition of organic amendments, acopper mine soil and a shooting range soil were also used. The or-ganic amendments used in this study include two composts (poultrymanure and cow manure composts) and two biochars (poultry ma-nure biochar and green waste biochar) (Table 1). Synthetic claysamples of goethite [(FeO(OH))], gibbsite [Al(OH)3] and allophane[(Al2O3)(SiO2)1.32.5(H2O)] were used to examine their effect onthe stabilization of C in composts and biochars.</p><p>The effect of soil type on carbon decomposition was examinedMajor clay minerals include kaolinite, chlorite, illite and feldspar.NaOH using 0.3 M HCl. The amount of C released was calculated usingthe following equation (Bloem et al., 2006):</p><p>R MWC VbVs M 0:5=DW 1</p><p>where R is the amount of C released (g C kg1 soil), MWC is themolec-ularweight of C (12 g mol1), Vb is the volume ofHCl for blank titration(L), Vs is the volume of HCl for sample titration (L), M is the concentra-tion of HCl (0.3 M), DW is the dry weight of the soil (kg), and 0.5 is thefactor to account for the fact that 2 mol of OH is consumed by 1 mol ofCO2.</p><p>2.4. Fractionation of soil carbon</p><p>Fractionation of C in both unamended and amended poultry ma-nure compost and biochar was measured to examine the effect of Cstabilization using various clay materials on the redistribution of C.The procedure used to fractionate soil C sequentially is similar tothat of Bhupinderpal-Singh et al. (2004) for soil sulfur and C. This se-quential fractionation technique was found suitable for fractionatingsulfur and phosphorus into various pools in soils (Hedley et al.,1982). The initial design of the fractionation was to determine rstthe exchangeable ionic forms of C in the organic amendmentsextracted on to ion exchange resins (resin-C). Solid-phase non-exchangeable forms of C were extracted in alkali extractions of twostrengths. Hence, conceptually labile organic C fraction would beextracted by 0.1 M NaOH and less labile fractions extracted by 1 MNaOH (Hedley et al., 1982). The C fractions not extracted with eitherresin or the 0.1 M NaOH extractant were termed as the recalcitrant orchemically stable fraction. Stabilization of C in organic amendmentsusing this fractionation technique was also compared with the rela-tionship between pyrophosphate extractable C and Fe and Al(Matus et al., 2008).</p><p>pH Total C(g kg1)</p><p>Total N(g kg1)</p><p>Total Cu(mg kg1)</p><p>Total Pb(mg kg1)</p><p>6.14 7.21 0.812 21.53 4.356.78 10.5 1.12 17.82 2.127.28 6.12 0.721 175.2 3.237.34 11.2 0.634 10.31 1.675.67 3.21 0.123 450.2 586.66.12 4.56 0.134 157.4 346.78.12 301 23.5 10.42 3.017.87 367 17.8 7.32 1.568.17 456 2.25 3.45 2.348.67 576 1.56 2.27 0.57</p></li><li><p>forms of C in organic amendments and soils (Marschner et al.,2008). Both physical and chemical fractionation studies involving or-ganic residues have demonstrated that labile C fractions decomposefaster than non-labile C fractions (Bernal et al., 1998). The physicaland chemical structures including surface area, condensation grade</p><p>0 100 200 300 400Incubation period (days)</p><p>0</p><p>20</p><p>40</p><p>60</p><p>Carb</p><p>on re</p><p>mai</p><p>ning</p><p> (g/kg</p><p> soil)</p><p>y=60e-7e-05xR2=0.864</p><p>y=60e-2E-04xR2=0.922</p><p>y=60e-0.005xR2=0.741</p><p>y=60e-0.009xR2=0.795</p><p>Perc</p><p>enta</p><p>ge o</p><p>f tot</p><p>al c</p><p>arbo</p><p>n</p><p>0%</p><p>20%</p><p>40%</p><p>60%</p><p>80%</p><p>100%</p><p>120%</p><p>Resin0.1 M NaOH1 M NaOHResidual</p><p>PM CM BPM BGW</p><p>aa</p><p>b b</p><p>a a</p><p>b</p><p>ab</p><p>ba a</p><p>Fig. 2. Carbon fractions in poultry manure compost (PM), cow manure compost (CM),poultry manure biochar (BPM) and green waste biochar (BGW). Within various frac-</p><p>266 N.S. Bolan et al. / Science of the Total Environment 424 (2012) 2642702.5. Microbial biomass carbon</p><p>Microbial biomass C and PMN in the arable soil treated withamended and unamended poultry manure compost were measuredto examine the effect of C stabilization using various amendmentson the fertilization value of composts. Microbial biomass was mea-sured using the chloroform-fumigation extraction method (Vance etal., 1987). The arable cropping soil was incubated with unamendedor amended poultry manure composts at eld capacity for 14 days.To measure microbial biomass C, 10 g of incubated soil sampleswere fumigated with ethanol-free CHCl3 in a desiccator. The fumigat-ed and non-fumigated samples were extracted using 0.5 M K2SO4 andthe extract was ltered and analyzed for dissolved organic carbon(DOC) using a TOC analyzer. Microbial biomass C was calculatedusing the following equation:</p><p>Microbial biomass C mg=kg EC=KC 2</p><p>where EC=(organic C extracted from fumigated soils (mg/kg)organic C extracted from non-fumigated soils (mg/kg)) andKC=0.45, value which represents the efciency of organic C extrac-tion (Jenkinson and Ladd, 1981).</p><p>2.6. Potentially mineralizable nitrogen</p><p>Potentially mineralizable N as determined by anaerobic incuba-tion is often considered to reect the organic matter pools being min-eralized (Keeney and Bremner, 1996). Anaerobic mineralizable N isdetermined as the difference between the ammonium (NH4+) ionsmeasured in two sets of 2 M KCl extracts. One is extracted immediate-ly (1:10 soil: extractant, 1 h shaking) and the other in the same man-ner after a seven-day incubation at 40 C with the soil covered bywater. The concentration of NH4+ ions in the 2 M KCl extracts wasmeasured following the method proposed by Mulvaney (1996).</p><p>2.7. Analysis of data</p><p>The rst-order decay rate equation was used to calculate the de-composition rate of C:</p><p>N N0exp kt 3</p><p>where N0 is the initial amount of C recovered at day 0 (g C/kg soil), Nis the concentration of residual C in the soil at that instant in time(g C/kg soil), t is time (day) and k is the rst-order decay rate con-stant. The C half-life (t1/2=time (day) taken to reduce C concentra-tion to half of the initial value) was calculated from the rateconstant (k).</p><p>All experiments were conducted with three replicates. The datacollected were analyzed statistically using SPSS 17 software. Duncan'smultiple range test was used to compare the means of the treatments,variability in the data was expressed as the standard deviation, and aPb0.05 was considered to be statistically signicant.</p><p>3. Results and discussion</p><p>3.1. Decomposition of organic amendme...</p></li></ul>

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