effects of amendment of different biochars on soil carbon mineralisation and sequestration

Effects of amendment of different biochars on soil carbonmineralisation and sequestration

Lei OuyangA Liuqian YuA and Renduo ZhangAB

AGuangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation TechnologySchool of Environmental Science and Engineering Sun Yat-Sen University Guangzhou 510275 China

BCorresponding author Email zhangrdmailsysueducn

Abstract The aim of this study was to determine the impact of addition of different biochars on soil carbonmineralisation and sequestration Different biochars were produced from two types of feedstock fresh dairy manureand pine tree woodchip each of which was pyrolysed at 300 500 and 7008C Each biochar was mixed at 5 (ww) with aforest loamy soil and the mixture was incubated at 258C for 180 days during which soil physicochemical properties andsoil carbon mineralisation were measured Results showed that the biochar addition increased soil carbon mineralisationat the early stage (within the first 15 days) because biochar brought available organic carbon to the soil and changedassociated soil properties such increasing soil pH and microbial activity The largest increase in soil carbon mineralisationat the beginning of incubation was induced by the dairy manure biochar pyrolysed at 3008C Soil carbon mineralisation wasenhanced more significantly by the dairy manure biochars than by the woodchip biochars and the enhancement effectdecreased with increasing pyrolysis temperature Although the biochar addition induced increased soil carbonmineralisation at the beginning of the incubation soil carbon mineralisation rates decreased sharply within a shorttime (within 15 days) and then remained very low afterwards Carbon mineralisation kinetic modelling indicated thatthe stable organic matter in biochars could be sequestrated in soil for a long time and resulted in high levels of carbonsequestration especially for the woodchip biochars pyrolysed from higher temperatures

Additional keywords biochar carbon sequestration feedstock pyrolysis temperature soil carbon mineralisation soilphysicochemical properties

Received 25 June 2013 accepted 2 September 2013 published online 17 January 2014

Introduction

Soil plays a key role in the global carbon (C) cycle Soil is themost important terrestrial C sink that releases carbon dioxide(CO2) into the atmosphere There is much interest in biocharapplications to soils as a means of improving soil quality andsequestering C in soils (Lehmann et al 2006 Lehmann 2007Laird 2008) Biochar is the product of biomass throughpyrolysis Several studies have shown the potential role ofbiochar in climate change mitigation by offsetting C emissionassociated with the burning of fossil fuels (Lehmann 2007 Laird2008)

Soil C mineralisation is the CO2 efflux produced from soilmetabolic processes which are influenced by many soilproperties The amount and availability of soil organic C hasa large impact on the atmospheric CO2 concentration becausesoil organic C can be decomposed and eventually returned to theatmosphere (Lal et al 2007) The decomposition rate of soilorganic C is determined by various soil physicochemical factorsFor instance Blagodatskaya and Kuzyakov (2008) reported thatthe amount of primed CO2 emission increased with increasingsoil pH Warnock et al (2007) proposed that alteration of soilproperties including surface area pH and CN ratio was partlyresponsible for changes of soil microbial biomass and activityand could consequently influence soil carbon mineralisation

Biochar addition has been shown to have important effectson soil physicochemical properties including improvement ofsoil structure increase in soil pH and enhancement of soilaeration and water retention capacity (Wardle et al 2008Downie et al 2009 Laird et al 2010) Nonetheless resultsabout C mineralisation in soils following biochar addition arenot consistent in the literature Novak et al (2010) reportedthat biochar addition did not significantly change soil Cmineralisation possibly attributable to the highly condensedaromatic structure that was physically resistant to degradationZimmerman et al (2011) observed that biochar produced at lowtemperatures stimulated C mineralisation due to decompositionof labile components of biochar over a short term whereasbiochar produced at high temperatures suppressed Cmineralisation Luo et al (2011) found that biocharsproduced with different pyrolysis temperatures consistentlypromoted soil C mineralisation Besides the differences insoils and biochars used in these studies the diverse resultsshould also be related to the accompanying changes in soilphysicochemical properties following biochar applications(Sohi et al 2010)

The importance of biochar as a C sequestration agent requiresfull understanding of its properties and the mechanismscontrolling its activity in soils (Abdullah et al 2010 Spokas

Journal compilation CSIRO 2014 wwwpublishcsiroaujournalssr

CSIRO PUBLISHING

Soil Research 2014 52 46ndash54httpdxdoiorg101071SR13186

2010) For example the volatile matter content in biochar shouldbe a simple indicator to evaluate the stability of biochar in soils(Zimmerman 2010) The CN ratio in biochar can change theratio of fungi to bacteria in soils and hence affect the turnover ofsoil organic matter (Helfrich et al 2008) All of these biocharproperties are largely dependent on the feedstock and pyrolysiscondition for biochar production As shown in the literaturebiochars made from wood have higher CN values than thosemade from grass (Krull et al 2009) Higher pyrolysistemperatures result in lower volatile matter content andhigher CN ratio in biochar (Braadbaart et al 2004 Downieet al 2009 Krull et al 2009)

To better understand the change in soil C mineralisationand sequestration following biochar additions it is necessary toquantify the characteristics of different biochars and the effectsof biochars on soil physicochemical properties associated withsoil C cycling The objectives of this study were to investigatethe characteristics of biochars made with different feedstocksand pyrolysis temperatures and to study effects of the differentbiochars on soil physicochemical properties (eg soil pH soilorganic C soil dissolved C) related to soil C mineralisationand sequestration It was hypothesised that treatments withbiochars made with different feedstocks and pyrolysistemperatures affected soil physicochemical properties as wellas soil C mineralisation and sequestration differently

Materials and methods

Production of biochar

Two different types of biomass feedstock (fresh dairy manureand pine tree woodchip) were used for biochar productionfollowing the procedure of Yu et al (2013) Briefly after air-drying and crushing each of the feedstocks was filled intocrucibles sealed with lids to prevent oxygen from enteringand then pyrolysed in a muffle furnace heating at a rate of108Cminndash1 and holding for 1 h at 300 500 or 7008C Biocharsproduced from dairy manure at the low (3008C) medium(5008C) and high (7008C) temperatures were denoted DLDM and DH respectively whereas biochars produced fromwoodchip were denoted WL WM and WH respectivelyAfter cooling each biochar was passed through a 2-mmsieve Biochar characteristics were examined as followsStructural characteristics of biochars (eg distributions ofpores and particles) were observed from scanning electronmicroscopy (SEM) (Peng et al 2011) Surface organicfunctional groups presented on the biochars were determinedby Fourier transform infrared spectroscopy (FTIR) (NicoletiS10 Thermo Fisher Scientific Inc Waltham MA USA)(Luo et al 2011) Biochar ash content (ww in ) wasdetermined by dry combustion at 7608C in air for 6 h using alaboratory muffle furnace (Novak et al 2009) Volatile matterwas estimated from weight loss of biochar after combustion at9008C for 6min in a ceramic crucible (Zimmerman et al 2011)Specific surface area (SSA) of biochar was evaluated using theBrunauer Emmett and Teller (BET) nitrogen (N) adsorptiontechnique (Brunauer et al 1938) Concentrations of elementalC hydrogen (H) and N were determined with an elementalanalyser (Vario EL Elementar Analysensysteme GmbH HanauGermany) (Baneschi et al 2013) from which CN ratios were

estimated Biochar pH was measured using a pH probe with a1 25 (ww) suspension of biochar in deionised water (Luo et al2011)Water-extractable concentrations of NO3

ndashwere measuredwith an ion chromatograph (DX-600 Dionex Corp SunnyvaleCA USA) following Yu et al (2013) The initial dissolvedorganic C (DOC) of biochars was determined with the methodof Bruun et al (2012) Briefly 5 g of biochar was suspendedin 25mL 001 M CaCl2 which was shaken on a low speedreciprocal shaker for 1 h The supernatant was filteredthrough a micro-filter (045mm) The extract was analysedfor DOC on a total organic C (TOC) analyser (TOC-V CSHShimadzu Corp Kyoto Japan)

Soil collection and experimental design

Soil samples (0ndash10 cm depth) were collected in the DinghushanNature Reserve (2380902100ndash2381103000N 11283003900ndash1128330

4100E) Guangdong Province in southern China After air-drying the soil samples were sieved with a 2-mm sieve andthoroughly homogenised The soil was a forest loamy soil with40 sand 35 silt and 25 clay and with a bulk density of122 g cmndash3 Total C H and N and initial DOC of the soil weremeasured using the methods mentioned above

An incubation experiment was conducted at 258C for180 days as follows Each of the six types of biochar wasmixed into 120 g of the air-dried soil sample based on a rate of5 (w w on an air-dried weight basis) and soil without biocharaddition was used as the control The seven treatments weredenoted with S (for soil) followed by the biochar treatmentacronym and CK (the control) The initial C contents for CKSDL SDM SDH SWL SWM and SWHwere 107 303 202247 363 323 and 263mg C gndash1 soil respectively The bulkdensity of the mixture of soil and biochar was calculated asfollows (Adams 1973)

rb frac14 100=frac12ethx=r1THORN thorn eth100 xTHORN=r2 eth1THORNwhere rb is the bulk density of the mixture of soil and biochar(g cmndash3) x is the percentage by weight of biochar r1 is the bulkdensity of biochar (g cmndash3) and r2 is the bulk density of soil(g cmndash3) A glass cylinder was filled with biochar particles Thefilled volume and mass of biochar in the cylinder were used tocalculate the biochar bulk density (Pastor-Villegas et al 2006)Bulk densities were 122 060 060 059 029 041 and038 g cmndash3 for the soil and biochars DL DM DH WLWM and WH respectively Based on Eqn 1 the initial bulkdensities of the soilndashbiochar mixtures were 116 116 116105 111 and 110 g cmndash3 for SDL SDM SDH SWL SWMand SWH respectively Each of the mixtures of soil and biocharor the soil alone was packed into a 500-mL pot based on the bulkdensities above The pot was covered with a piece of plasticsheet to prevent moisture loss A few small holes were prickedon the plastic sheet to keep atmosphere pressure inside the bottleFor each pot deionised water was added to retain a volumetricwater content of 80 of field water capacity (the water content atsuction of 330 cm) determined based on the soil-water retentioncurve (Ouyang and Zhang 2013) During the incubation periodthe soil water content was adjusted weekly based on weight lossTwenty-four replicates (pots) were prepared for each treatment

Effect of biochar on soil C mineralisation and sequestration Soil Research 47

Chemical analyses

Soil organic C (SOC) DOC microbial biomass C (MBC) pHand CN ratio were measured on days 0 5 15 30 50 80 120and 180 of the incubation experiment These measurements wereconducted using three destructive samples from the replicates oneach sampling date The SOC of the mixtures was measuredby oxidation with potassium dichromate (Peng et al 2011)DOCwas measured using the method of Bruun et al (2012) andMBC was determined using the fumigationndashextraction methodin which soil K2SO4 extract was analysed using the TOCanalyser (Brookes et al 1985) Sample pH and CN ratiowere measured using the methods mentioned above

Soil C mineralisation measurements were conducted everyday from days 0 to 15 every 3 days from days 16 to 60 andevery 10 days from day 61 to the end of incubation usingthe method of Tang et al (2011) At each measurement day theinitial concentration of CO2 within the headspace of eachincubation pot was measured with an infrared ray gasanalyzer (IRGA) Then the pot was airproofed After 2 hoursthe concentration of CO2 within the headspace of the pot wasmeasured with IRGA The CO2 emission rate was calculatedusing the following relationship

FCO2 frac14 frac12ethDC=DtTHORNethVMC=224THORNethT1=T2THORNethP2=P1THORN=ms eth2THORN

where FCO2is the CO2 emission rate (mgC sndash1 gndash1 soil) DCDt is

the CO2 concentration gradient calculated with the twomeasurements at each measurement day (mg gndash1 soil sndash1) V isthe headspace volume (L) MC is the C molecule weight(gmolndash1) T1 is the temperature in the normal state (273K)T1 is the air temperature in the headspace (K) P1 is the airpressure in the normal state (1013 105 Pa) P2 is the airpressure in the headspace (Pa) and ms is the dry mass oftotal incubated soil in the pot (g) Carbon mineralisationkinetics was fitted with a two-pool model as follows (Cayuelaet al 2010)

Cr frac14 f expethk1tTHORN thorn eth100 f THORN expethk2tTHORN eth3THORN

where Cr is the C fraction remained in the soil () f is the Cfraction of the active or fast turnover pool () k1 is thedecomposition rate constant for the active pool (dayndash1) k2 is

the rate constant for the slow turnover pool (dayndash1) and t is theincubation time (days) The humification coefficient (h) isdefined as the fraction of organic matter remaining in the soilafter 1 year and is calculated with Eqn 3 by setting t= 365 days(Bradbury et al 1993) The humification coefficient gives anestimation of the stable organic matter remaining in the soil andit is used as an indicator of C sequestration potential (Cayuelaet al 2010)

Statistical analyses

All data were analysed using the SPSS software package(SPSS Inc 2003) Significant differences among differenttreatments and sampling dates were tested by the one-wayanalysis of variance (ANOVA) in which the post-hoc test ofleast significant difference (lsd) was used The two-wayANOVA was used to identify the primary factors (feedstockand pyrolysis temperature) on C mineralisation Differencesbetween the values were considered to be statisticallysignificant at P = 005 The coefficient of determination (R2)was used to determine the accuracy of regressions

Results

Biochar properties

The measured physicochemical properties of the biochars andsoil are listed in Table 1 The pH values of biochars weresignificantly higher than that of the soil (P lt 005) Thewoodchip biochars had higher CN ratio and specific surfacearea than the dairy manure biochars The volatile component ofthe biochars decreased with increasing pyrolysis temperatureand the dairy manure biochars contained a higher volatilecomponent than the woodchip biochars Under the samepyrolysis temperature the concentrations of available N weresignificantly higher in the dairy manure biochars than in thewoodchip biochars (P lt 005) Most of the initial DOC valueswere significantly higher in the biochars especially in the dairybiochars produced at lower temperatures than in the soil(Plt 005) Higher pyrolysis temperatures resulted in greatersurface areas higher pH values and ash contents and loweravailable N contents (Table 1) Scanning electron microscopy ofthe biochars showed that biochar particles became smaller as thepyrolysis temperatures increased (Ouyang and Zhang 2013)

Table 1 Selected physicochemical characteristics of biochars and soilDL DM and DH Biochars produced with dairy manure at the low (3008C) medium (5008C) and high (7008C) temperatures respectivelyWLWM andWHbiochars produced with woodchip at the low medium and high temperatures SSA specific surface area of biochar DOC dissolved organic carbon Results forpH ash content volatile matter NO3

ndash-N and DOCwere calculated based on three replicates and are presented as mean standard deviation values of C H Nand SSA were obtained from one measurement ndash Data not determined

Property Soil DL DM DH WL WM WH

pH (1 5 wv) 425 plusmn 003 746 plusmn 001 928 plusmn 009 970 plusmn 003 716 plusmn 004 796 plusmn 004 101 plusmn 012C () 107 393 190 279 512 432 311H () 067 379 113 097 447 203 101N () 008 268 116 109 097 111 061CN ratio 134 146 164 257 529 389 514Ash content () 503 plusmn 162 637 plusmn 233 687 plusmn 078 401 plusmn 212 556 plusmn 154 592 plusmn 243Volatile matter () 386 plusmn 201 137 plusmn 060 121 plusmn 113 301 plusmn 128 650 plusmn 047 131 plusmn 032SSA (m2 gndash1) 115 143 441 834 2404 673 124NO3

ndash-N (mg kgndash1) ndash 131 plusmn 070 105 plusmn 075 993 plusmn 101 125 plusmn 051 876 plusmn 065 839 plusmn 053DOC (mg kgndash1) 691 plusmn 82 339plusmn 14 172 plusmn 83 978 plusmn 10 110 plusmn 89 634 plusmn 41 589 plusmn 66

48 Soil Research L Ouyang et al

Graphs of FTIR are presented for the dairy manure biochars(Fig 1a) and the woodchip biochars (Fig 1b) produced undertemperatures from 300 to 7008C The spectrums includedseveral adsorption bands The band around 800ndash1600 cmndash1

was associated with aromatic C-H C=C C=O stretching2900 cmndash1 with aliphatic C-H stretching and 3400 cmndash1 withO-H stretching respectively As the charring temperatureincreased adsorption intensities of biochar at the bands3400 cmndash1 and 2900 cmndash1 decreased indicating a reduction ofO-H and aliphatic C-H bonds whereas the adsorption at the band1400 cmndash1 was intensified indicating an increase of aromatic Cespecially for the woodchip biochars (Peng et al 2011)

Carbon mineralisation

Throughout the incubation maximum mineralisation rates wereobserved for all seven treatments on day 1 with the SDLtreatment showing the highest mineralisation rate (Fig 2)For the same feedstock the biochar-induced increases insoil mineralisation at the early incubation stage wereSDL gt SDMgt SDH (increase by 541 269 and 192 timesover CK respectively) and SWLgt SWM gt SWH (increase by258 178 and 161 times over CK respectively) At the laterincubation stage (after about day 15) except for SDL thedifferences of soil C mineralisation rates among the sixtreatments were not significant (P gt 005) Soil cumulativeCO2 emissions were significantly different among the seventreatments ranging from 4131 to 2244mg CO2-C kgndash1

soil dayndash1 at the end of the incubation (Plt 005) (Fig 3)Soil cumulative CO2 emissions were significantly differentbetween treatments with the dairy manure biochars and thewoodchip biochars produced with the same pyrolysistemperature (P lt 005) In all biochar treatments thecumulative C losses in the soil were positively correlatedwith the volatile matter contents in the biochars (R2 = 075)The two-way ANOVA analysis showed that partial h2 valuesfor feedstock v C mineralisation and pyrolysis temperature v Cmineralisation were 0985 and 0993 respectively indicatingthat the pyrolysis temperature and the feedstock were equallyimportant in affecting C mineralisation The temporaldistributions of C mineralisation rates in all treatments weresimilar (Figs 2 and 3)

The C decay patterns in soil after the application of differentbiochars were fitted with the two-pool model As shown inTable 2 values of the C fraction of the active or fast turnoverpool (f) for the seven treatments ranged from 018 to 061whereas values of the humification coefficient (h) were gt99Values of the decomposition rate constant for the active pool (k1)

C-O

Aromatic C-C

Aromatic C=OC=C

Aliphatic C-HO-H

300

500

700

(a) (b)

Aromatic C-C

Aromatic C=OC=CC-O

Aliphatic C-H

700

500

300

O-H

500

Abs

orba

nce

1000 1500 2000 2500 3000 3500 4000

Wave number (cmndash1)

500 1000 1500 2000 2500 3000 3500 4000

Fig 1 Fourier transform infrared spectroscopy (FTIR) of (a) dairy manure biochars and (b) woodchip biochars produced undertemperatures from 300 to 7008C

2

4

6

830

35

40

45 CKSDLSDMSDH

2

0 40 80 120 160 200

4

14

16

18

20

C m

iner

alis

atio

n ra

te (

mg

CO

2-C

kgndash1

soi

l day

ndash1)

Time (day)

CKSWLSWMSWH

(a)

(b)

Fig 2 Soil carbon (C) mineralisation rates (mean standard deviation) of(a) the control (CK soil only) and treatments with dairy manure biochars(SDL SDM SDH soil + dairy manure pyrolysed at 300 500 and 7008Crespectively) and (b) CK and treatments with woodchip biochars (SWLSWM SWH soil +woodchip pyrolysed at 300 500 and 7008C) (n= 3)


in all treatments were ~01 dayndash1 whereas values of the rateconstant for the slow turnover pool (k2) were as low as25 106 to 84 106 dayndash1 The values of f and k2 in allbiochar-treated soils except SDL and SDM were lower than

those of CK After the 180-day incubation all biochar treatmentsled to gt99 of C sequestrated in the mixtures and the h valuesand the remaining C amount were higher in the treatments withthe woodchip biochars than with dairy manure biochars(Table 2) Based on the two-pool model simulation results(Table 3) the amounts of sequestrated C in biochar-treatedsoils will increase by 188ndash328 times compared with the solesoil in 10 years

Soil organic C and dissolved organic C

The biochar application systematically increased SOC althoughthe increases varied with the different biochars (Table 4)Biochars produced under the lower pyrolysis temperature(3008C) increased the SOC more markedly than biocharsproduced at the higher pyrolysis temperatures (500 and7008C) The SOC values of the treatments with the woodchipbiochars were significantly higher than those with the dairymanure biochars produced with the same pyrolysis temperature(Plt 005)

As shown in Fig 4 the DOC values were significantly higher(Plt 005) in most of biochar-treated soils than in the controlThe DOC values in the biochar treatments decreased as pyrolysistemperatures increased With the same pyrolysis temperaturethe dairy manure biochars led to a larger increase in soil DOCthan the woodchip biochars The temporal changes of DOCwhich decreased with time within the whole incubation weresimilar for all treatments

For the different sampling dates the C mineralisation rates ofthe seven treatments were positively correlated with thecorresponding DOC values with R2 values ranging from 0707to 0953 The slopes of the linear relationships decreased from0089 on day 0 to 00024 on day 180 For the samplings on days 05 and 30 the C mineralisation rates and the MBC values ofthe seven treatments also showed a positive relationship with R2

values of 0936 0726 and 0775 respectively However R2

values of the linear regressions between the C mineralisationrates and the MBC values for days 80 120 and 180 were 04280107 and 0034 respectively

Soil pH and CN

Soil pH values significantly increased with the addition ofbiochar (Fig 5) On average the different biochar treatments

50

100

150

200

250

300

50

100

150

200

250

300

CKSDLSDMSDH

CKSWLSWMSWH

Cum

ulat

ive

C m

iner

alis

atio

n (m

g C

O2-

C k

gndash1 s

oil d

ayndash1

)

(a)

(b)

0 40 80 120 160 200

Time (day)

Fig 3 Soil cumulative carbon (C) emissions (mean standard deviation)of (a) the control (CK soil only) and treatments with dairy manure biochars(SDL SDM SDH soil + dairy manure pyrolysed at 300 500 and 7008Crespectively) and (b) CK and treatments with woodchip biochars (SWLSWM SWH soil +woodchip pyrolysed at 300 500 and 7008C) (n= 3)

Table 2 Parameters obtained by fitting the two-pool model tomeasured data

CK Soil only SDL SDM SDH soil amended with biochars producedwith dairy manure at the low (3008C) medium (5008C) and high (7008C)temperatures respectively SWL SWM SWH soil amended with biocharsproduced with woodchip at the low medium and high temperatures f thefraction of organic matter in the active pool k1 the rate constant of the activepool k2 the rate constant of the slow pool h the humification coefficient

Treatment f () k1 (dayndash1) k2 (day

ndash1) R2 h ()

CK 031 0111 46 106 0996 994SDL 061 0107 84 106 0990 991SDM 045 0087 58 106 0996 993SDH 026 0087 34 106 0996 996SWL 023 0112 37 106 0989 996SWM 018 0105 25 106 0994 997SWH 020 0095 30 106 0996 997

Table 3 Remaining fraction of total C (mg C gndash1 soil) in soil over timecalculated with the two-pool model

CK Soil only SDL SDM SDH soil amended with biochars producedwith dairy manure at the low (3008C) medium (5008C) and high (7008C)temperatures respectively SWL SWM SWH soil amended with biochars

produced with woodchip at the low medium and high temperatures

Treatment Day 0 Day 5 Day 180 1 year 5 years 10 years



resulted in an increase of 079ndash221 pH units On the samplingdates SDM and SWH resulted in the largest increases in pHamong the dairy manure biochars and the woodchip biocharsrespectively The dairy manure biochars had greater effect inincreasing soil pH than the woodchip biochars After 120 days ofincubation pH values decreased significantly with time in alltreatments relative to the start of the experiment

Most of the biochar treatments increased the CN ratio of themixtures with the extent of increase related to the feedstock andthe pyrolysis temperature for biochars (Table 5) The CN ratioswere significantly higher in the woodchip biochar treatments

Table 4 Values of soil organic carbon (mg gndash1 soil) with different treatmentsCK Soil only SDL SDM SDH soil amended with biochars produced with dairy manure at the low (3008C) medium (5008C) and high (7008C) temperaturesrespectively SWL SWM SWH soil amended with biochars produced with woodchip at the low medium and high temperatures Values presented in columnsare mean standard deviation (n= 3) Within columns means followed by the same lower case letter are not significantly different (Pgt 005) Within rows

means followed by the same upper case letter are not significantly different (Pgt 005)

Treatment Day 5 Day 15 Day 30 Day 50 Day 80 Day 120 Day 180

CK 843 plusmn 029aDc 879 plusmn 010aD 900 plusmn 034aD 675 plusmn 015aC 656 plusmn 053aBC 606 plusmn 010aB 478 plusmn 026aASDL 284 plusmn 005eC 291 plusmn 079cC 270 plusmn 074eC 258 plusmn 082cB 203 plusmn 070eB 203 plusmn 061dB 201 plusmn 155dASDM 257 plusmn 082cdC 267 plusmn 016cC 258 plusmn 070deC 221 plusmn 065bcB 203 plusmn 080cdAB 192 plusmn 121bcA 187 plusmn 064cdASDH 253 plusmn 155cD 227 plusmn 081bCD 235 plusmn 105cD 204 plusmn 081bBC 195 plusmn 067bcB 176 plusmn 068cB 158 plusmn 067bAASWL 354 plusmn 088fC 325 plusmn 050dB 270 plusmn 067eA 263 plusmn 146dA 262 plusmn 084fA 258 plusmn 123eA 247 plusmn 037eASWM 281 plusmn 041deD 267 plusmn 126cCD 246 plusmn 101cdC 221 plusmn 105bcB 210 plusmn 042dB 204 plusmn 008cAB 184 plusmn 132cASWH 213 plusmn 014bCD 220 plusmn 008bD 197 plusmn 096bBC 207 plusmn 017bBC 189 plusmn 039bABC 179 plusmn 143bAB 173 plusmn 103bcA

80

160

240

320

400

bD

cD

dD

aD cA

dAB

eA

aA

dA

eABC

fA

aB

dA

eA

fA

aB

dB

eBCD

fAB

aAB

cC

dCD

eA

aB

dC

eD

fBC

aC

cD

bD

dC

CKSDLSDMSDH

aD

40

80

120

160

200

aD

abD

bD

aD

aAaA

bAbB

abB

cB

bB

abAB

cBC

abB

cCD

cB

bBC

aC

aCaBC

bD

cC

bD

aD

aAaBaBaABaB

aC

aD

Dis

slov

ed o

rgan

ic c

arbo

n (m

g kg

ndash1 s

oil)

CKSWLSWMSWH

0 40 80 120 160 200

Time (day)

(a)

(b)

Fig 4 Soil dissolved organic carbon values (mean standard deviation)of (a) the control (CK soil only) and treatments with dairy manure biochars(SDL SDM SDH soil + dairy manure pyrolysed at 300 500 and 7008Crespectively) and (b) CK and treatments with woodchip biochars (SWLSWM SWH soil +woodchip pyrolysed at 300 500 and 7008C) (n= 3)

0

2

4

6

8

10

eC

aD

dAdA

aB

dAdeABeAdA

aA

gCfCfCgD

eCdB

eBdB

pH

CKSDLSDMSDH

aC aE

0

2

4

6

8

10

cC

bAbAbB

aBaA

aEaDaC

cC

cAcA cAcB

dCdCcBcB bBbB

180120805

Time (day)

CKSWLSWMSWH

30

(a)

(b)

Fig 5 Soil pH values (mean standard deviation) of (a) the control(CK soil only) and treatments with dairy manure biochars (SDL SDMSDH soil + dairy manure pyrolysed at 300 500 and 7008C respectively)and (b) CK and treatments with woodchip biochars (SWL SWM SWHsoil +woodchip pyrolysed at 300 500 and 7008C) Among the seventreatments for a single day the same lower case letter indicates nosignificant difference (Pgt 005) Among the six sampling days (days 530 80 120 and 180) for a single treatment the same upper case letterindicates no significant difference (Pgt 005) (n= 3)


than in the dairy manure biochar treatments (Plt 005) The CNvalues in the dairy manure biochar treatments increased withthe pyrolysis temperature whereas in the woodchip biochartreatments CN ratio in SWL (3008C) was the highest at theearly incubation stage

Discussion

Similar to other studies (Hamer et al 2004 Hilscher et al2009) all of the biochars examined here stimulated soil Cmineralisation especially at the early incubation stage Theincrease in soil C mineralisation was a result of stimulationof microbial activity through the addition of labile C andnutrients within biochars (Hamer et al 2004) The volatilematter and available nutrients in the biochars (Table 1) couldbe a good source for microorganisms resulting in an increasein SOC and DOC in all biochar-treated soils and consequentlyenhancing the microbial biomass In this study biocharapplication increased the SOC content possibly becausebiochar contained high C content and could protect organic Cfrom utilisation (Glaser et al 2002 Cayuela et al 2010) Inaddition the woodchip biochars were mostly composed ofhighly condensed aromatic structures that were physicallyresistant to degradation Although the application ofwoodchip biochars resulted in higher SOC values the dairymanure biochar treatments contained higher DOC contentwhich could provide a more labile source of energy andnutrients for soil microorganisms (Bowen 2006) The linearrelationships between the C mineralisation rates and DOCvalues of the seven treatments indicated that the enhanced Cmineralisation was partly attributed to increased DOC valuesfollowing biochar additions This may explain the higher Cmineralisation rates in the soil treated with the dairy manurebiochars The different contents of labile C in the seventreatments were also reflected from their distinct microbialresponses As reported by Ouyang and Zhang (2013) theMBC was significantly higher in the biochar treatments thanin the control which showed the stimulating effects of biocharson soil microbial activities Similar results have been reportedin the literature mainly related to the availability of an easilydecomposable non-aromatic fraction of biochar (Steiner et al

2008 Kolb et al 2009 Kuzyakov et al 2009 Novak et al2010) The biochars pyrolysed at lower temperatures induceda greater increase in C mineralisation than the biocharspyrolysed at higher temperatures primarily because thebiochars produced at lower temperatures contained more ofthe incompletely pyrolysed fraction of the feedstock material(Bruun et al 2011) For instance biochars pyrolysed athigher temperatures have less impact on soil MBC and DOCduring the incubation Further the different chemicalproperties and physical structures of biochars which werelargely determined by feedstock and pyrolysis temperaturessignificantly influenced short-term biochar-C loss As shownin Fig 1 more aromatic C-C bonds in biochars pyrolysed athigher temperatures indicated greater chemical recalcitranceand stability of the biochars whereas more aliphatic C-Hbonds in biochars pyrolysed at lower temperatures indicatedmore useable substrate in the biochars (Bruun et al 2008 Yuanet al 2011) The dairy manure biochars decayed faster than thewoodchip biochars which might be due to the lower CN ratiosand higher available-N contents in the dairy manure biochars(Helfrich et al 2008)

The increase in soil pH with biochar application also affectedC mineralisation Increases in soil pH can stimulate CO2

emission and the effect is more pronounced in low pH soils(Blagodatskaya and Kuzyakov 2008 Luo et al 2011) Withrelatively low pH in our soil (425) the significantly increasedpH values in the mixtures after applying biochar shouldpartially contribute to the increased CO2 emission Anotherfactor contributing to the increased CO2 emission in thebiochar-amended soil might be that the biochar enhancedmineralisation of native organic matter in the soil (Wardleet al 2008) Soil CN ratio and pH can change the microbialpopulation and activity (Helfrich et al 2008) The short-termmicrobial responses might also be related to the increasedsolubility of organic matter with the increase in soil pH(Curtin et al 1998) The increased pH values in the originallow pH soil could also enhance the availability of nutrients andconsequently increase soil microbial biomass (Atkinson et al2010 Warnock et al 2010) At the early stage of incubationthe increase in soil pH after biochar addition might benefitr-strategists which are more dominant in higher pH soils(Baringaringth and Anderson 2003) and can rapidly utilise liablecomponents (Fig 5) At the later stage of incubation rates ofsoil C mineralisation were not significantly different among thetreatments A possible reason for the result is that the labilecomposition of biochars was almost mineralised and the soilorganic matter might be adsorbed to biochars either withinbiochar pores or onto external biochar surfaces (Zimmermanet al 2011) Sobek et al (2009) showed that biochars couldadsorb organic matter and protect it from being utilised In thisstudy the lower soil mineralisation rates in the treatmentswith biochars produced at higher temperatures than at lowertemperatures might be partly attributable to their higher surfaceareas with greater adsorption affinity for natural organic matter(Kasozi et al 2010)

Although biochar addition induced significant short-termCO2 emission from the soil rates of soil C mineralisationdecreased sharply within a short period and then remained atstably low values with time Most of the C (gt99) from the

Table 5 Values of the CN ratio in different treatmentsCK Soil only SDL SDM SDH soil amended with biochars producedwith dairy manure at the low (3008C) medium (5008C) and high (7008C)temperatures respectively SWL SWM SWH soil amended with biocharsproduced with woodchip at the low medium and high temperatures Valuespresented are mean standard deviation (n= 3) Within columns meansfollowed by the same lower case letter are not significantly different(Pgt 005) Within rows means followed by the same upper case letter

are not significantly different (Pgt 005)

Treatment Day 5 Day 80 Day180

CK 1372 plusmn 1257aBc 1383 plusmn 0492aB 1083 plusmn 0351aASDL 1350 plusmn 0377aA 1327 plusmn 0061aA 1315 plusmn 0073bASDM 1447 plusmn 0318aA 1473 plusmn 0160aA 1365 plusmn 0914bASDH 1888 plusmn 1182bA 1848 plusmn 0083bA 1721 plusmn 0981cASWL 3068 plusmn 1617eB 2908 plusmn 0988dB 2122 plusmn 0963dASWM 2574 plusmn 0079cA 2551 plusmn 0024cA 2735 plusmn 0202fBSWH 2801 plusmn 0604dA 2699 plusmn 1369cA 2528 plusmn 0958eA


biochar addition remained in the soil for a long time indicatingthat biochar has high C-sequestration potential The lowdegradability of C from biochar has been reported in theliterature (Kuzyakov et al 2009 Major et al 2010) and isstrongly promoted for C-sequestration aims (Lehmann 2007Laird et al 2009) The small rate constant values for the slowturnover pool (in the order of 106 dayndash1) indicate that theincreased C resulting from biochar application will stay in thesoil for long time The higher refractory C in biochar shouldalso account for the C-sequestration potential of biocharAs suggested by Cayuela et al (2010) biochar with morerefractory C and higher CN ratio had higher C sequestrationpotential Compared with the dairy manure biochar treatmentsthe woodchip biochar treatments resulted in lower rates of Cmineralisation and higher values of SOC CN ratio andhumification coefficient suggesting that the woodchipbiochars should have higher C-sequestration potentialAlthough the increase of pyrolysis temperature resulted in adecrease in C content in biochar the treatments with biocharsproduced at higher temperatures showed higher C-sequestrationability as indicated by the lower rate constant for the slowturnover pool and higher humification coefficient

Conclusions

This study investigated the effects of biochars produced fromdairy manure and woodchip under different temperatures on soilC turnover The biochar application induced a rapid increase insoil C mineralisation during the early incubation period (withinthe first 15 days) primarily because of the labile C fraction inthe biochars However rates of soil C mineralisation decreasedsharply after a short period and then remained at stably lowvalues with time Soil physicochemical changes with the biocharaddition including increases in SOC DOC MBC and pHvalues also affected soil C mineralisation and sequestrationThe feedstock and pyrolysis temperature largely determinedthe physicochemical properties of biochars and hence had asignificant impact on effects of the biochars on soil C turnoverand associated soil properties The dairy manure biocharsproduced at lower temperature which contained more labilefraction and relatively easily degradable structure resulted inthe largest increase in soil C mineralisation and the highestmicrobial biomass Although significant C losses from soilstreated with biochars were observed the incorporation ofbiochar increased total SOC and compensated for the Closses in the soil The high humification coefficients and lowrate constants for the slow turnover pool in the biochar-treatedsoils indicated the biocharrsquos C-sequestration potentialMeanwhile gt99 of biochar-induced C remained as stableorganic C in the soil after 180 days further demonstratingthe ability of biochar in sequestering C Biochar producedfrom woodchip and at higher pyrolysis temperature showedhigher C sequestration potential The information from thisstudy should be valuable for the utilisation of biochar for soilC sequestration

Acknowledgements

This study was partly supported by grants from the Chinese National NaturalScience Foundation (Nos 51039007 and 51179212) and Doctoral Fund ofMinistry of Education of China (No 20120171110040)

References

Abdullah H Mediaswanti AK Wu H (2010) Biochar as a fuel 2 Significantdifferences in fuel quality and ash properties of biochars from variousbiomass components of Mallee trees Energy amp Fuels 24 1972ndash1979doi101021ef901435f

AdamsWA (1973) The effect of organic matter on the bulk and true densitiesof some uncultivated podzoilc soils Journal of Soil Science 24 10ndash17doi101111j1365-23891973tb00737x

Atkinson CJ Fitzgerald JD Hipps NA (2010) Potential mechanisms forachieving agricultural benefits from biochar application to temperatesoils a review Plant and Soil 337 1ndash18 doi101007s11104-010-0464-5

Baringaringth E Anderson T-H (2003) Comparison of soil fungalbacterial ratios ina pH gradient using physiological and PLFA-based techniques SoilBiology amp Biochemistry 35 955ndash963 doi101016S0038-0717(03)00154-8

Baneschi I Dallai L Giazzi G Guidi M Krotz L (2013) A method for thedefinition of the carbon oxidation number in the gases dissolved inwaters and the redox variations using an elemental analyser (FlashEA1112) Preliminary data from a stratified lake Journal of GeochemicalExploration 124 14ndash21 doi101016jgexplo201207005

Blagodatskaya E Kuzyakov Y (2008) Mechanisms of real and apparentpriming effects and their dependence on soil microbial biomass andcommunity structure critical review Biology and Fertility of Soils 45115ndash131 doi101007s00374-008-0334-y

Bowen S (2006) Biologically-relevant characteristics of dissolved organiccarbon (DOC) from soil PhD Thesis School of Biological andEnvironmental Sciences University of Stirling Stirling UK

Braadbaart F Boon JJ Veld H David P Van Bergen PF (2004) Laboratorysimulations of the transformation of the peas as a result of heattreatment Changes of the physical and chemical properties Journalof Archaeological Science 31 821ndash833 doi101016jjas200312001

Bradbury NJ Whitmore AP Hart PBS Jenkinson DS (1993) Modelling thefate of nitrogen in crop and soil in the years following application of15N-labeled fertilizer to winter wheat The Journal of AgriculturalScience 121 363ndash379 doi101017S0021859600085567

Brookes PC Landman A Pruden G Jenkinson DS (1985) Chloroformfumigation and the release of soil nitrogen a rapid direct extractionmethod to measure microbial biomass nitrogen in soil Soil Biology ampBiochemistry 17 837ndash842 doi1010160038-0717(85)90144-0

Brunauer S Emmett PH Teller J (1938) Adsorption of gases in multimolecular layers Journal of the American Chemical Society 60309ndash319 doi101021ja01269a023

Bruun S Jensen E Jensen L (2008) Microbial mineralization andassimilation of black carbon dependency on degree of thermalalteration Organic Geochemistry 39 839ndash845 doi101016jorggeochem200804020

Bruun EW Hauggaard-Nielsen H Norazana I Egsgaard H Ambus PJensen PA Dam-Johansen K (2011) Influence of fast pyrolysistemperature on biochar labile fraction and short-term carbon loss in aloamy soil Biomass and Bioenergy 35 1182ndash1189 doi101016jbiombioe201012008

Bruun EW Ambus P Egsgaard H Hauggaard-Nielsen H (2012) Effects ofslow and fast pyrolysis biochar on soil C and N turnover dynamics SoilBiology amp Biochemistry 46 73ndash79 doi101016jsoilbio201111019

Cayuela ML Oenema O Kuikmanw PJ Bakkerz RR van Groenigen JW(2010) Bioenergy by-products as soil amendments Implications forcarbon sequestration and greenhouse gas emissions Global ChangeBiology Bioenergy 2 201ndash213

Curtin D Campbell CA Jalil A (1998) Effects of acidity on mineralizationpH-dependence of organic matter mineralization in weakly acidic soilsSoil Biology amp Biochemistry 30 57ndash64 doi101016S0038-0717(97)00094-1


Downie A Crosky A Munroe P (2009) Physical properties of biocharIn lsquoBiochar for environmental management Science and technologyrsquo(Eds J Lehmann S Joseph) pp 13ndash29 (Earthscan London)

Glaser B Lehmann J Zech W (2002) Ameliorating physical and chemicalproperties of highly weathered soils in the tropics with charcoalmdashareview Biology and Fertility of Soils 35 219ndash230 doi101007s00374-002-0466-4

Hamer U Marschner B Brodowski S Amelung W (2004) Interactivepriming of black carbon and glucose mineralization OrganicGeochemistry 35 823ndash830 doi101016jorggeochem200403003

Helfrich M Ludwig B Potthoff M Flessa H (2008) Effect of litter qualityand soil fungi on macroaggregate dynamics and associated partitioningof litter carbon and nitrogen Soil Biology amp Biochemistry 401823ndash1835 doi101016jsoilbio200803006

Hilscher A Heister K Siewert C Knicker H (2009) Mineralization andstructural changes during the initial phase of microbial degradation ofpyrogenic plant residues in soil Organic Geochemistry 40 332ndash342doi101016jorggeochem200812004

Kasozi GN Zimmerman AR Nkedi-Kizza P Gao B (2010) Catechol andhumic acid sorption onto a range of laboratory-produced black carbons(biochars) Environmental Science amp Technology 44 6189ndash6195doi101021es1014423

Kolb S Fermanich K Dornbush M (2009) Effect of charcoal quantity onmicrobial biomass and activity in temperate soils Soil Science Societyof America Journal 73 1173ndash1181 doi102136sssaj20080232

Krull ES Baldock JA Skjemstad JO Smernik RJ (2009) Characteristics ofbiochar organo-chemical properties In lsquoBiochar for environmentalmanagement Science and technologyrsquo (Eds J Lehmann S Joseph)pp 53ndash65 (Earthscan London)

Kuzyakov Y Subbotina I Chen H Bogomolova I Xu X (2009) Blackcarbon decomposition and incorporation into soil microbial biomassestimated by 14C labeling Soil Biology amp Biochemistry 41 210ndash219doi101016jsoilbio200810016

Laird DA (2008) The charcoal vision a win-win-win scenario forsimultaneously producing bioenergy permanently sequesteringcarbon while improving soil and water quality Agronomy Journal100 178ndash181 doi102134agrojnl20070161

Laird DA Brown RC Amonette JE Lehmann J (2009) Review of thepyrolysis platform for coproducing bio-oil and biochar BiofuelsBioproducts and Biorefining 3 547ndash562 doi101002bbb169

Laird DA Fleming P Davis DD Horton R Wang B Karlen DL (2010)Impact of biochar amendments on the quality of a typical Midwesternagricultural soil Geoderma 158 443ndash449 doi101016jgeoderma201005013

Lal R Follett R Stewart B Kimble J (2007) Soil carbon sequestration tomitigate climate change and advance food security Soil Science 172943ndash956 doi101097ss0b013e31815cc498

Lehmann J (2007) Bioenergy in the black carbon Frontiers in Ecologyand the Environment 5 381ndash387 doi1018901540-9295(2007)5[381BITB]20CO2

Lehmann J Gaunt J Rondon M (2006) Bio-char sequestration in terrestrialecosystemsmdasha reviewMitigation and Adaptation Strategies for GlobalChange 11 395ndash419 doi101007s11027-005-9006-5

Luo Y Durenkamp M Nobili MD Lin Q Brookes PC (2011) Short termsoil priming effects and the mineralization of biochar following itsincorporation to soils of different pH Soil Biology amp Biochemistry43 2304ndash2314 doi101016jsoilbio201107020

Major J Lehmann J Rondon M Goodale C (2010) Fate of soil appliedblack carbon downward migration leaching and soil respirationGlobal Change Biology 16 1366ndash1379 doi101111j1365-2486200902044x

Novak JM BusscherWJ Laird DL AhmednaMWatts DW NiandouMAS(2009) Impact of biochar amendment on fertility of a southeasterncoastal plain soil Soil Science 174 105ndash112 doi101097SS0b013e3181981d9a

Novak JM Busscher WJ Watts DW Laird DA Ahmedna MA NiandouMAS (2010) Short-term CO2 mineralization after additions of biocharand switch grass to a Typic Kandiudult Geoderma 154 281ndash288doi101016jgeoderma200910014

Ouyang L Zhang R (2013) Effects of biochars derived from differentfeedstocks and pyrolysis temperatures on soil physical and hydraulicproperties Journal of Soils and Sediments doi101007s11368-013-0738-7

Pastor-Villegas J Pastor-Valle JF Meneses-Rodriguez JM Garcia M (2006)Study of commercial wood charcoals for the preparation of carbonabsorbents Journal of Analytical and Applied Pyrolysis 76 103ndash108doi101016jjaap200508002

Peng X Ye L Wang C Zhou H Sun B (2011) Temperature- and duration-dependent rice straw-derived biochar Characteristics and its effects onsoil properties of an Ultisol in southern China Soil amp Tillage Research112 159ndash166 doi101016jstill201101002

Sobek A Stamm N Bucheli TD (2009) Sorption of phenyl urea herbicidesto black carbon Environmental Science amp Technology 43 8147ndash8152doi101021es901737f

Sohi SP Krull E Lopez-Capel E Bol R (2010) A review of biochar andits use and function in soil Advances in Agronomy 105 47ndash82doi101016S0065-2113(10)05002-9

Spokas KA (2010) Review of the stability of biochar in soils predictabilityof O C molar ratios Carbon Management 1 289ndash303 doi104155cmt1032

Steiner C Das K Garcia M Forster B Zech W (2008) Charcoal and smokeextract stimulate the soil microbial community in a highly weatheredxanthic Ferralsol Pedobiologia 51 359ndash366 doi101016jpedobi200708002

Tang J Mo Y Zhang J Zhang R (2011) Influence of biological aggregatingagents associated with microbial population on soil aggregate stabilityApplied Soil Ecology 47 153ndash159 doi101016japsoil201101001

Wardle DA Nilsson MC Zackrisson O (2008) Fire-derived charcoal causesloss of forest humus Science 320 629 doi101126science1154960

Warnock DD Lehmann J Kuyper TW Rillig MC (2007) Mycorrhizalresponses to biochar in soilmdashconcepts and mechanisms Plant and Soil300 9ndash20 doi101007s11104-007-9391-5

Warnock DD Mummey DL McBride B Major J Lehmann J Rillig MC(2010) Influences of non-herbaceous biochar on arbuscular mycorrhizalfungal abundances in roots and soils results from growth-chamber andfield experiments Applied Soil Ecology 46 450ndash456 doi101016japsoil201009002

Yu L Tang J Zhang RWuQ GongM (2013) Effects of biochar applicationon soil methane emission at different soil moisture levels Biology andFertility of Soils 49 119ndash128 doi101007s00374-012-0703-4

Yuan J Xu R Zhang H (2011) The forms of alkalis in the biochar producedfrom crop residues at different temperatures Bioresource Technology102 3488ndash3497 doi101016jbiortech201011018

Zimmerman AR (2010) Abiotic and microbial oxidation of laboratory-produced black carbon (biochar) Environmental Science ampTechnology 44 1295ndash1301 doi101021es903140c

Zimmerman AR Gao B Ahn MY (2011) Positive and negative carbonmineralization priming effects among a variety of biochar-amended soilSoil Biology amp Biochemistry 43 1169ndash1179 doi101016jsoilbio201102005


wwwpublishcsiroaujournalssr

2010) For example the volatile matter content in biochar shouldbe a simple indicator to evaluate the stability of biochar in soils(Zimmerman 2010) The CN ratio in biochar can change theratio of fungi to bacteria in soils and hence affect the turnover ofsoil organic matter (Helfrich et al 2008) All of these biocharproperties are largely dependent on the feedstock and pyrolysiscondition for biochar production As shown in the literaturebiochars made from wood have higher CN values than thosemade from grass (Krull et al 2009) Higher pyrolysistemperatures result in lower volatile matter content andhigher CN ratio in biochar (Braadbaart et al 2004 Downieet al 2009 Krull et al 2009)

To better understand the change in soil C mineralisationand sequestration following biochar additions it is necessary toquantify the characteristics of different biochars and the effectsof biochars on soil physicochemical properties associated withsoil C cycling The objectives of this study were to investigatethe characteristics of biochars made with different feedstocksand pyrolysis temperatures and to study effects of the differentbiochars on soil physicochemical properties (eg soil pH soilorganic C soil dissolved C) related to soil C mineralisationand sequestration It was hypothesised that treatments withbiochars made with different feedstocks and pyrolysistemperatures affected soil physicochemical properties as wellas soil C mineralisation and sequestration differently

Materials and methods

Production of biochar

Two different types of biomass feedstock (fresh dairy manureand pine tree woodchip) were used for biochar productionfollowing the procedure of Yu et al (2013) Briefly after air-drying and crushing each of the feedstocks was filled intocrucibles sealed with lids to prevent oxygen from enteringand then pyrolysed in a muffle furnace heating at a rate of108Cminndash1 and holding for 1 h at 300 500 or 7008C Biocharsproduced from dairy manure at the low (3008C) medium(5008C) and high (7008C) temperatures were denoted DLDM and DH respectively whereas biochars produced fromwoodchip were denoted WL WM and WH respectivelyAfter cooling each biochar was passed through a 2-mmsieve Biochar characteristics were examined as followsStructural characteristics of biochars (eg distributions ofpores and particles) were observed from scanning electronmicroscopy (SEM) (Peng et al 2011) Surface organicfunctional groups presented on the biochars were determinedby Fourier transform infrared spectroscopy (FTIR) (NicoletiS10 Thermo Fisher Scientific Inc Waltham MA USA)(Luo et al 2011) Biochar ash content (ww in ) wasdetermined by dry combustion at 7608C in air for 6 h using alaboratory muffle furnace (Novak et al 2009) Volatile matterwas estimated from weight loss of biochar after combustion at9008C for 6min in a ceramic crucible (Zimmerman et al 2011)Specific surface area (SSA) of biochar was evaluated using theBrunauer Emmett and Teller (BET) nitrogen (N) adsorptiontechnique (Brunauer et al 1938) Concentrations of elementalC hydrogen (H) and N were determined with an elementalanalyser (Vario EL Elementar Analysensysteme GmbH HanauGermany) (Baneschi et al 2013) from which CN ratios were

estimated Biochar pH was measured using a pH probe with a1 25 (ww) suspension of biochar in deionised water (Luo et al2011)Water-extractable concentrations of NO3

ndashwere measuredwith an ion chromatograph (DX-600 Dionex Corp SunnyvaleCA USA) following Yu et al (2013) The initial dissolvedorganic C (DOC) of biochars was determined with the methodof Bruun et al (2012) Briefly 5 g of biochar was suspendedin 25mL 001 M CaCl2 which was shaken on a low speedreciprocal shaker for 1 h The supernatant was filteredthrough a micro-filter (045mm) The extract was analysedfor DOC on a total organic C (TOC) analyser (TOC-V CSHShimadzu Corp Kyoto Japan)

Soil collection and experimental design

Soil samples (0ndash10 cm depth) were collected in the DinghushanNature Reserve (2380902100ndash2381103000N 11283003900ndash1128330

4100E) Guangdong Province in southern China After air-drying the soil samples were sieved with a 2-mm sieve andthoroughly homogenised The soil was a forest loamy soil with40 sand 35 silt and 25 clay and with a bulk density of122 g cmndash3 Total C H and N and initial DOC of the soil weremeasured using the methods mentioned above

An incubation experiment was conducted at 258C for180 days as follows Each of the six types of biochar wasmixed into 120 g of the air-dried soil sample based on a rate of5 (w w on an air-dried weight basis) and soil without biocharaddition was used as the control The seven treatments weredenoted with S (for soil) followed by the biochar treatmentacronym and CK (the control) The initial C contents for CKSDL SDM SDH SWL SWM and SWHwere 107 303 202247 363 323 and 263mg C gndash1 soil respectively The bulkdensity of the mixture of soil and biochar was calculated asfollows (Adams 1973)

rb frac14 100=frac12ethx=r1THORN thorn eth100 xTHORN=r2 eth1THORNwhere rb is the bulk density of the mixture of soil and biochar(g cmndash3) x is the percentage by weight of biochar r1 is the bulkdensity of biochar (g cmndash3) and r2 is the bulk density of soil(g cmndash3) A glass cylinder was filled with biochar particles Thefilled volume and mass of biochar in the cylinder were used tocalculate the biochar bulk density (Pastor-Villegas et al 2006)Bulk densities were 122 060 060 059 029 041 and038 g cmndash3 for the soil and biochars DL DM DH WLWM and WH respectively Based on Eqn 1 the initial bulkdensities of the soilndashbiochar mixtures were 116 116 116105 111 and 110 g cmndash3 for SDL SDM SDH SWL SWMand SWH respectively Each of the mixtures of soil and biocharor the soil alone was packed into a 500-mL pot based on the bulkdensities above The pot was covered with a piece of plasticsheet to prevent moisture loss A few small holes were prickedon the plastic sheet to keep atmosphere pressure inside the bottleFor each pot deionised water was added to retain a volumetricwater content of 80 of field water capacity (the water content atsuction of 330 cm) determined based on the soil-water retentioncurve (Ouyang and Zhang 2013) During the incubation periodthe soil water content was adjusted weekly based on weight lossTwenty-four replicates (pots) were prepared for each treatment


Chemical analyses











Results

Biochar properties














C-O

Aromatic C-C

Aromatic C=OC=C

Aliphatic C-HO-H

300

500

700

(a) (b)

Aromatic C-C

Aromatic C=OC=CC-O

Aliphatic C-H

700

500

300

O-H

500

Abs

orba

nce

1000 1500 2000 2500 3000 3500 4000


500 1000 1500 2000 2500 3000 3500 4000


2

4

6

830

35

40

45 CKSDLSDMSDH

2

0 40 80 120 160 200

4

14

16

18

20

C m

iner

alis

atio

n ra

te (

mg

CO

2-C

kgndash1

soi

l day

ndash1)

Time (day)

CKSWLSWMSWH

(a)

(b)











Soil pH and CN


50

100

150

200

250

300

50

100

150

200

250

300

CKSDLSDMSDH

CKSWLSWMSWH

Cum

ulat

ive

C m

iner

alis

atio

n (m

g C

O2-

C k

gndash1 s

oil d

ayndash1

)

(a)

(b)

0 40 80 120 160 200

Time (day)





ndash1) R2 h ()














80

160

240

320

400

bD

cD

dD

aD cA

dAB

eA

aA

dA

eABC

fA

aB

dA

eA

fA

aB

dB

eBCD

fAB

aAB

cC

dCD

eA

aB

dC

eD

fBC

aC

cD

bD

dC

CKSDLSDMSDH

aD

40

80

120

160

200

aD

abD

bD

aD

aAaA

bAbB

abB

cB

bB

abAB

cBC

abB

cCD

cB

bBC

aC

aCaBC

bD

cC

bD

aD

aAaBaBaABaB

aC

aD

Dis

slov

ed o

rgan

ic c

arbo

n (m

g kg

ndash1 s

oil)

CKSWLSWMSWH

0 40 80 120 160 200

Time (day)

(a)

(b)


0

2

4

6

8

10

eC

aD

dAdA

aB

dAdeABeAdA

aA

gCfCfCgD

eCdB

eBdB

pH

CKSDLSDMSDH

aC aE

0

2

4

6

8

10

cC

bAbAbB

aBaA

aEaDaC

cC

cAcA cAcB

dCdCcBcB bBbB

180120805

Time (day)

CKSWLSWMSWH

30

(a)

(b)




Discussion












Conclusions


Acknowledgements


References






















































Chemical analyses











Results

Biochar properties














C-O

Aromatic C-C

Aromatic C=OC=C

Aliphatic C-HO-H

300

500

700

(a) (b)

Aromatic C-C

Aromatic C=OC=CC-O

Aliphatic C-H

700

500

300

O-H

500

Abs

orba

nce

1000 1500 2000 2500 3000 3500 4000


500 1000 1500 2000 2500 3000 3500 4000


2

4

6

830

35

40

45 CKSDLSDMSDH

2

0 40 80 120 160 200

4

14

16

18

20

C m

iner

alis

atio

n ra

te (

mg

CO

2-C

kgndash1

soi

l day

ndash1)

Time (day)

CKSWLSWMSWH

(a)

(b)











Soil pH and CN


50

100

150

200

250

300

50

100

150

200

250

300

CKSDLSDMSDH

CKSWLSWMSWH

Cum

ulat

ive

C m

iner

alis

atio

n (m

g C

O2-

C k

gndash1 s

oil d

ayndash1

)

(a)

(b)

0 40 80 120 160 200

Time (day)





ndash1) R2 h ()














80

160

240

320

400

bD

cD

dD

aD cA

dAB

eA

aA

dA

eABC

fA

aB

dA

eA

fA

aB

dB

eBCD

fAB

aAB

cC

dCD

eA

aB

dC

eD

fBC

aC

cD

bD

dC

CKSDLSDMSDH

aD

40

80

120

160

200

aD

abD

bD

aD

aAaA

bAbB

abB

cB

bB

abAB

cBC

abB

cCD

cB

bBC

aC

aCaBC

bD

cC

bD

aD

aAaBaBaABaB

aC

aD

Dis

slov

ed o

rgan

ic c

arbo

n (m

g kg

ndash1 s

oil)

CKSWLSWMSWH

0 40 80 120 160 200

Time (day)

(a)

(b)


0

2

4

6

8

10

eC

aD

dAdA

aB

dAdeABeAdA

aA

gCfCfCgD

eCdB

eBdB

pH

CKSDLSDMSDH

aC aE

0

2

4

6

8

10

cC

bAbAbB

aBaA

aEaDaC

cC

cAcA cAcB

dCdCcBcB bBbB

180120805

Time (day)

CKSWLSWMSWH

30

(a)

(b)




Discussion












Conclusions


Acknowledgements


References




























































C-O

Aromatic C-C

Aromatic C=OC=C

Aliphatic C-HO-H

300

500

700

(a) (b)

Aromatic C-C

Aromatic C=OC=CC-O

Aliphatic C-H

700

500

300

O-H

500

Abs

orba

nce

1000 1500 2000 2500 3000 3500 4000


500 1000 1500 2000 2500 3000 3500 4000


2

4

6

830

35

40

45 CKSDLSDMSDH

2

0 40 80 120 160 200

4

14

16

18

20

C m

iner

alis

atio

n ra

te (

mg

CO

2-C

kgndash1

soi

l day

ndash1)

Time (day)

CKSWLSWMSWH

(a)

(b)











Soil pH and CN


50

100

150

200

250

300

50

100

150

200

250

300

CKSDLSDMSDH

CKSWLSWMSWH

Cum

ulat

ive

C m

iner

alis

atio

n (m

g C

O2-

C k

gndash1 s

oil d

ayndash1

)

(a)

(b)

0 40 80 120 160 200

Time (day)





ndash1) R2 h ()














80

160

240

320

400

bD

cD

dD

aD cA

dAB

eA

aA

dA

eABC

fA

aB

dA

eA

fA

aB

dB

eBCD

fAB

aAB

cC

dCD

eA

aB

dC

eD

fBC

aC

cD

bD

dC

CKSDLSDMSDH

aD

40

80

120

160

200

aD

abD

bD

aD

aAaA

bAbB

abB

cB

bB

abAB

cBC

abB

cCD

cB

bBC

aC

aCaBC

bD

cC

bD

aD

aAaBaBaABaB

aC

aD

Dis

slov

ed o

rgan

ic c

arbo

n (m

g kg

ndash1 s

oil)

CKSWLSWMSWH

0 40 80 120 160 200

Time (day)

(a)

(b)


0

2

4

6

8

10

eC

aD

dAdA

aB

dAdeABeAdA

aA

gCfCfCgD

eCdB

eBdB

pH

CKSDLSDMSDH

aC aE

0

2

4

6

8

10

cC

bAbAbB

aBaA

aEaDaC

cC

cAcA cAcB

dCdCcBcB bBbB

180120805

Time (day)

CKSWLSWMSWH

30

(a)

(b)




Discussion












Conclusions


Acknowledgements


References






























































Soil pH and CN


50

100

150

200

250

300

50

100

150

200

250

300

CKSDLSDMSDH

CKSWLSWMSWH

Cum

ulat

ive

C m

iner

alis

atio

n (m

g C

O2-

C k

gndash1 s

oil d

ayndash1

)

(a)

(b)

0 40 80 120 160 200

Time (day)





ndash1) R2 h ()














80

160

240

320

400

bD

cD

dD

aD cA

dAB

eA

aA

dA

eABC

fA

aB

dA

eA

fA

aB

dB

eBCD

fAB

aAB

cC

dCD

eA

aB

dC

eD

fBC

aC

cD

bD

dC

CKSDLSDMSDH

aD

40

80

120

160

200

aD

abD

bD

aD

aAaA

bAbB

abB

cB

bB

abAB

cBC

abB

cCD

cB

bBC

aC

aCaBC

bD

cC

bD

aD

aAaBaBaABaB

aC

aD

Dis

slov

ed o

rgan

ic c

arbo

n (m

g kg

ndash1 s

oil)

CKSWLSWMSWH

0 40 80 120 160 200

Time (day)

(a)

(b)


0

2

4

6

8

10

eC

aD

dAdA

aB

dAdeABeAdA

aA

gCfCfCgD

eCdB

eBdB

pH

CKSDLSDMSDH

aC aE

0

2

4

6

8

10

cC

bAbAbB

aBaA

aEaDaC

cC

cAcA cAcB

dCdCcBcB bBbB

180120805

Time (day)

CKSWLSWMSWH

30

(a)

(b)




Discussion












Conclusions


Acknowledgements


References




























































80

160

240

320

400

bD

cD

dD

aD cA

dAB

eA

aA

dA

eABC

fA

aB

dA

eA

fA

aB

dB

eBCD

fAB

aAB

cC

dCD

eA

aB

dC

eD

fBC

aC

cD

bD

dC

CKSDLSDMSDH

aD

40

80

120

160

200

aD

abD

bD

aD

aAaA

bAbB

abB

cB

bB

abAB

cBC

abB

cCD

cB

bBC

aC

aCaBC

bD

cC

bD

aD

aAaBaBaABaB

aC

aD

Dis

slov

ed o

rgan

ic c

arbo

n (m

g kg

ndash1 s

oil)

CKSWLSWMSWH

0 40 80 120 160 200

Time (day)

(a)

(b)


0

2

4

6

8

10

eC

aD

dAdA

aB

dAdeABeAdA

aA

gCfCfCgD

eCdB

eBdB

pH

CKSDLSDMSDH

aC aE

0

2

4

6

8

10

cC

bAbAbB

aBaA

aEaDaC

cC

cAcA cAcB

dCdCcBcB bBbB

180120805

Time (day)

CKSWLSWMSWH

30

(a)

(b)




Discussion












Conclusions


Acknowledgements


References























































Discussion












Conclusions


Acknowledgements


References























































Conclusions


Acknowledgements


References






















































effects of amendment of different biochars on soil carbon mineralisation and sequestration

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