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Original article

Soil CO2  emissions from a cultivated Mollisol: Effects of organicamendments, soil temperature, and moisture

Lu-Jun Li a,*,1, Meng-Yang You a,1, Hong-Ai Shi a,b, Xue-Li Ding a, Yun-Fa Qiao a, Xiao-Zeng Han a,*

a Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin 150081, Chinab Northeast Agricultural University, Harbin 150030, China

a r t i c l e i n f o

 Article history:

Received 22 June 2012

Received in revised form

25 December 2012

Accepted 31 December 2012

Available online 10 January 2013

Handling editor : Yakov Kuzyakov

Keywords:

Mollisols

Soil organic amendment

Soil respiration

Temperature sensitivity

Water-lled pore space

a b s t r a c t

A  eld experiment was conducted to examine the inuences of long-term applications of maize straw

and organic manure on carbon dioxide (CO2) emissions from a cultivated Mollisol in northeast China and

to evaluate the responses of soil CO2  uxes to temperature and moisture. Soil CO2  ux was measured

using closed chamber and gas chromatograph techniques. Our results indicated that the application of 

organic amendments combined with fertilizer nitrogen, phosphorus and potassium (NPK) accelerated

soil CO2   emissions during the maize growing season, whereas NPK fertilization alone did not impact

cumulative CO2 emissions. Cumulative CO2 emissions were higher from soils amended with pig manure

relative to those with maize residue. Cumulative CO2 emissions during the growing season were 988 and

1130 g CO2   m2 under applications of 7500 and 22,500 kg ha1 pig manure combined with NPK,

respectively, which were 42 and 63% higher than the emissions from the control (694 g CO 2  m2). The

applications of 2250 and 4500 kg ha1 maize straw combined with NPK marginally increased soil CO 2emissions by 23 and 28% compared with the control, respectively. A log-transformed multiple regression

model including both soil temperature and moisture explained 50e88% of the seasonal variation in soil

CO2  uxes. Cumulative soil CO2  emissions were affected more by applied treatments than by soil tem-

perature and moisture. Our results suggest that the magnitude of the impact of soil amendments on CO2

emissions from Mollisols primarily depends on the type of organic amendments applied, whereas theapplication rate has limited impacts.

 2013 Elsevier Masson SAS. All rights reserved.

1. Introduction

Increased atmospheric carbon dioxide (CO2) has been consid-

ered a major contributor to global warming as well as climatic

change [1,2]. Although arable soil has been identied as one of the

main CO2   sources in agroecosystems due to inappropriate man-

agement practices, it can also serve as a net sink for atmospheric

CO2 through appropriate agricultural management [3,4].

Organic amendments (e.g., straw and organic manure) havebeen widely used in agroecosystems due to their positive roles in

soil fertility improvement and climate change mitigation via soil

carbon sequestration [3,5,6]. Previous studies have shown various

responses of soil CO2   emissions to applications of organic

amendments [7,8]. The amount of soil CO2 emissions is dependent

on many factors, primarily the type and level of applied organic

amendments [9], as well as the quantity of carbon already in the

soil   [10]. In fact, soil management, plant cover and soil nutrient

status can not only alter soil respiration, but also change the tem-

perature sensitivity of this process [11]. Thus, the overall response

of soil CO2 emissions to organic amendments is a complex process

and remains uncertain.

Soil temperature and moisture have been identied as the mostimportant environmental factors inuencing soil CO2  emissions

[12,13]. The temperature effect is commonly described as an

exponential equation [12], whereas the effects of soil moisture are

not always consistent [14]. The lack of consensusamong trialscould

result from the collective impacts of differences in soil types  [15],

experiment duration and methods of CO2  emission measurement

[16], added to the confounded effects of soil temperature and

moisture   [17,18]. Therefore, the roles of soil temperature and

moisture in soil CO2 emissions are still unclear.

Mollisols in northeast China are characterized by a high car-

bon content and   ne texture. Due to intensive cultivation and

*   Corresponding authors. Northeast Institute of Geography and Agroecology,

Chinese Academy of Sciences, 138 Haping Rd, Harbin 150081, China. Tel.:  þ86 451

8660 2940; fax: þ86 451 8660 3736.

E-mail addresses:   lilujun@neigaehrb.ac.cn   (L.-J. Li),   xzhan@neigaehrb.ac.cn

(X.-Z. Han).1 These authors contributed equally to this work.

Contents lists available at SciVerse ScienceDirect

European Journal of Soil Biology

j o u r n a l h o m e p a g e :   h t t p : / / w w w . e l s e v ie r . c o m / l o c a t e / e j s ob i

1164-5563/$ e   see front matter    2013 Elsevier Masson SAS. All rights reserved.

http://dx.doi.org/10.1016/j.ejsobi.2012.12.009

European Journal of Soil Biology 55 (2013) 83e90

mailto:lilujun@neigaehrb.ac.cnmailto:xzhan@neigaehrb.ac.cnhttp://www.sciencedirect.com/science/journal/11645563http://www.elsevier.com/locate/ejsobihttp://dx.doi.org/10.1016/j.ejsobi.2012.12.009http://dx.doi.org/10.1016/j.ejsobi.2012.12.009http://dx.doi.org/10.1016/j.ejsobi.2012.12.009http://dx.doi.org/10.1016/j.ejsobi.2012.12.009http://dx.doi.org/10.1016/j.ejsobi.2012.12.009http://dx.doi.org/10.1016/j.ejsobi.2012.12.009http://www.elsevier.com/locate/ejsobihttp://www.sciencedirect.com/science/journal/11645563mailto:xzhan@neigaehrb.ac.cnmailto:lilujun@neigaehrb.ac.cn

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low organic material return, a remarkable decline in soil organic

carbon (SOC) in croplands has occurred over the last several

decades in the Mollisols. To improve the  ne texture and increase

the SOC content of these soils, organic amendments (e.g. crop

straw and organic manure) have been widely applied in the re-

gion. However,   eld observations on the responses of soil CO2emissions to long-term organic material incorporations into high

carbon soils are still limited. The objectives of this study were to

examine the inuences of long-term applications of organic

amendments combined with chemical fertilizers on CO2   emis-

sions from Mollisols in China and to clarify the responses of soil

CO2   uxes to soil temperature and moisture. We hypothesized

that soil CO2   emissions might be enhanced by long-term appli-

cations of organic amendments due to the incorporation of 

exogenous carbon.

2. Materials and methods

 2.1. Site description

The experimental site was located at the Hailun National

Experiment Station of Agroecosystems of the Chinese Academy of 

Sciences (47260N, 126380E). The mean annual temperature was1.5   C, and the lowest and highest mean monthly values

were  23   C in January and 21   C in July, respectively. The mean

annual precipitation was 550 mm, more than 80% of which occur-

red from MayeSeptember. The frost-free period is approximately

120 days. The soil is a loamy loess and classied as Typic Hapludoll.

 2.2. Experimental design

The eld site is on a at plain and was a native prairie before the

land wascleared forcropping more than 100 years ago. A long-term

eld experiment was established in a randomized block design in

1990 based on four treatments with three replicates: no fertilizer

(Control), chemical fertilizer made up of nitrogen, phosphorus and

potassium (NPK), NPK fertilizer plus maize straw (NPK þ MS1), andNPK fertilizer plus double the maize straw of NPK   þ   MS1

(NPK  þ   MS2). In 2001, we added two additional treatments with

three replicates: NPK fertilizer plus pig manure (NPK  þ  OM1) and

NPK fertilizer plus triple the pig manure of NPK   þ   OM1

(NPK þ  OM2). Each replicate covered a surface area of 12    5.6 m2

and was separated from other replicates by a 0.7-m buffer strip. A

maizeesoybeanewheat crop rotationwas established, and the crop

was maize in 2011. Maize was sown on May 8 and harvested on

September 26, 2011. To increase soil temperature to stimulate

maize germination in early spring, the   eld was split into ridges

(approximately 10 cm in height) and furrows using a ridge plow.

The distance between adjacent ridges was 70 cm. The depth of 

tillage was approximately 20 cm.

The fertilizer applications were as follows: 1) 120 kg N ha1

,60 kg phosphorus pentoxide (P2O5) ha

1, and 30 kg potassium

oxide (K2O) ha1 for maize; 2) 20.25 kg N ha1, 51.75 kg P2O5 ha

1,

and 30 kg K2O ha1 for soybeans; and 3) 75 kg N ha1,

60kgP2O5 ha1, and30kgK2O ha

1 for wheat. Themaize strawand

organic manure were applied as follows (dry-weight basis):

2250 kg ha1 in NPK   þ   MS1, 4500 kg ha1 in NPK   þ   MS2,

7500 kg ha1 in NPK þ OM1, and 22,500 kg ha1 in NPK þ OM2 for

the 3 year rotation. Urea was split into two applications for the

treatments receiving N fertilizer, the basal and supplementary

fertilizers, with a ratio of 1:2 for maize. The pig manure was com-

posted before application. Straw and organic manure applications

were performed in the previous year after crop harvest. The maize

straw contained 411 mg organic C g1 and 6.7 mg total N (TN) g1;

the pig manure contained 265 mg organic C g

1

and 31 mg TN g

1

.

 2.3. Measurement of CO 2 uxes

Soil CO2  ux was measured using closed chamber and gas chro-

matograph techniques during the maize growing season. Gas sam-

pling was initiated on May 27, 2011 at the time of emergence and

ended on September 30, 2011 with the maize harvest. During the

maize growing season, gas sampling was conducted once per week

between 9:00 and 11:00 am, the optimal sampling time to represent

the average daily CO2 ef ux in this region [19]. The CO2 ux was not

measured on July 30 due to heavy rain. Four gas samples were col-

lected at 0, 10, 20, and 30 min after closure of the chamber from

a septum installed at the top of the closed chamber

(0.7m 0.2m 0.25 m) using a 20 ml gas-tightsyringe.The collected

gas samples were immediately transferred to pre-evacuatedvials and

transported tothe laboratory for analysis. The collected gasesincluded

the CO2 from both rhizosphere respiration and native soil respiration.

Carbon dioxide concentration was determined using a gas

chromatograph (GC-2010, Shimadzu Corp., Japan) equipped with

a ame ionization detector (FID) using an 80/100 mesh Chromosorb

102 column. Carbon dioxide ux was calculated from the change in

CO2  concentration in the chamber vs. closure time using the fol-

lowing formula:

 f   ¼   r  Dc =Dt   V = A  273=ð273 þ T Þ   (1)

where f istheCO2 ux(mgCO2 m2 h1), r istheCO2 density under

standard conditions (mg m3),  Dc /Dt  is the change in CO2  concen-

tration in the chamber (m3 m3 h1), V is the chamber volume (m3),

 A isthe soil surface area (m2), and T is the airtemperature inside the

chamber (C). Cumulative soil CO2  emission (g CO2  m2) was cal-

culated by summing the average production of two neighboring

uxes, multiplied by the collection interval time.

 2.4. Soil sampling and analyses and measurement of micro-climate

 factors

Soil samples (0e

20 cm) were collected within each block inearly October 2011. Eight soil samples were randomly collected and

then mixed thoroughly to form a composite. After the visible roots,

fauna and organic debris were removed by hand, soil samples were

sieved(

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data at the 5% level. A one-way analysis of variance (ANOVA) with

least signicant difference was used to test the differences in maize

yield, biomass, soil property parameters, and cumulative CO2 emis-

sions among the six treatments at  P  ¼  0.05. The relationships be-

tween straw biomass, maize yield, root biomass, and SOC

concentration and cumulative CO2  emissions were examined using

linear regression. Nonlinear regression analyses were used to

determine the relationships between soil temperature, moisture,

and soil temperature combined with moisture and soil CO2  uxes.

The response of soil CO2  uxes to soil temperature was descri-

bed by an exponential function:

 f   ¼   a expðbT Þ;   (2)

where f  is the soil CO2  ux at soil temperature  T  and  a  and  b  are

regression coef cients. The temperature sensitivity (Q 10), dened

as a multiplier of soil CO2  ux for a 10   C increase in soil temper-

ature, was calculated as follows:  Q 10 ¼  exp (10b).

To clarify the effects of soil moisture on soil CO2   ux, we

removed the possible confounding effect of soil temperature on soil

CO2 ux by standardizing soil CO2 ux to a soil temperature of 10 C

using the following equation:

 f   ¼   f 10expðlnQ 10  ðT   T 10Þ=10Þ;   (3)

where f  is the soil CO2  ux measured in the  eld, f 10 is the soil CO2uxat 10 C (T 10), Q 10 is the temperature sensitivity listed in Table 2,

and T  is the soil temperature measured in the  eld at a 5 cm depth.

3. Results

 3.1. Soil properties, crop yield and biomass

The NPK   þ   OM2 fertilization increased SOC content by 12%

compared with the control (P  <  0.05, Table 1). However, the SOC

contents in treatments NPK, NPK   þ   MS1, NPK   þ   MS2, and

NPK þ OM1 were not signicantly different from that in the control(P  >  0.05; Table 1). Total N content signicantly increased by 24%

over the control under the NPK þ OM2 treatment (Table 1). The pH

value under the NPK þ OM2 treatment was higher than that under

NPK þ  MS1 (P  <  0.05; Table 1).

Crop grain, straw, and root biomasses in the control plots were

signicantly lower than in all other treatments (P  <  0.05; Table 1).

Compared with the control, the applications of NPK, NPK  þ  MS1,

NPK þ  MS2, NPK  þ  OM1, and NPK  þ  OM2 signicantly increased

straw biomass by 45, 46, 62, 11, and 20%, respectively and increased

root biomass by 50, 139, 138, 110, and 126%, respectively (all

P  <  0.05; Table 1).

 3.2. Soil temperature and moisture

Soil temperature varied from 4 to 37   C during the maize

growing season, with averages of 21   C and 18   C at 5 and 10 cm

depths, respectively (Fig. 1a, b). Soil temperatures at both 5 and

10 cm depths reached maxima on June 24 (Fig.1a, b) when the soil

WFPS was lower than at most other sampling times (Fig. 1c). Mean

soil temperatures during the growing season were 19.5 and 19.3  C

at a 5 cm depth (Fig. 1a) and 17.4 and 17.5   C at a 10 cm depth for

NPK   þ   OM1 and NPK   þ   OM2, respectively (Fig. 1b), which were

lower values than those in the control treatment (5 cm: 22   C,

10 cm: 19.7   C). Soil moisture ranged from 25 to 51% WFPS during

the maize growing season and was higher on average in the control

than in the other treatments (Fig. 1c). Soil moisture was sig-

nicantly correlated with cumulative precipitation between two

neighboring measurement times (r 2 ¼   0.54e0.63,   n   ¼   18,

P  <  0.001).

 3.3. Seasonal variations in soil CO 2  uxes and cumulative CO 2emissions

Soil CO2   uxes, regardless of organic or chemical fertilizer

application, increased gradually from the experiment’s beginning

in May and reached a maximum on August 6 (Fig. 2a). Soil CO2uxes then declined gradually until the harvest at the end of Sep-

tember. The mean soil CO2 ux during the maize growing season in

the control treatment was 215 mg CO2   m2 h1, which was sig-

nicantly lower than those in the treatments of organic manure

applications (NPK   þ   OM1, 310 mg CO2   m2 h1; NPK   þ   OM2:

355 mg CO2 m2 h1; P  <  0.05).

Based on soil CO2  uxes, cumulative CO2  emissions during the

maize growing season in the control, NPK, NPK þ MS1, NPK þ MS2,

NPK þ OM1, and NPK þ OM2 treatments were estimated to be 694,

678, 853, 889, 988, and 1130 g CO2  m2 (Fig. 2b). Cumulative CO2

emissions in the NPK   þ   OM1 and NPK   þ  OM2 treatments were

signicantly higher than that in the control by 42 and 63%,

respectively (both   P  <   0.05); the NPK   þ   MS1 and NPK   þ   MS2

treatments marginally increased CO2   emissions by 23 and 28%,

respectively (P  <   0.1). In contrast, NPK fertilization alone did not

signicantly impact cumulative CO2 emission (P  >  0.05; Fig. 2b). In

addition, there was no signicant difference in soil CO2  emissionsbetween NPK þ  OM1 and NPK  þ  OM2 or between NPK  þ  MS1 and

NPK þ  MS2 (both P  >  0.05; Fig. 2b).

 3.4. Impacts of micro-climate factors on soil CO 2 uxes

During the maize growing season, an exponential model

explained 26e34% of the seasonal variations in soil CO2  uxes in

only four out of the six treatments at a 10 cm depth (Table 2). Using

only the data from the elongation to the harvest stage, however, we

found improved relationships between soil temperature and CO2uxes (R2 ¼ 0.43e0.91, P  <  0.05; Table 2). The temperature sensi-

tivity (Q 10) of soil CO2   uxes during the growing season ranged

between 1.87 and 3.00 (Table 2). Correlation analysis showed poor

relationships between soil CO2 uxes and WFPS during the growingseason (Table 3). After excluding the masking inuence of soil

temperature, we found greatly improved relationships between

 Table 1

Soil properties, maize yield and biomass under different fertilization treatments. The values are the means ( n ¼  3) with SE.

Treatment SOC (g kg1) TN (g kg1) pH Grain (kg ha1) Straw (kg ha1) Root (kg ha1)

Controla 28.20(0.17)bb 2.06(0.03)b 5.91(0.02)ab 5797(344)d 3922(180)d 517(30)c

NPK 27.66(0.09)b 2.06(0.02)b 5.92(0.05)ab 8384(146)b 6348(341)c 775(42)b

NPK þ  MS1 29.89(0.26)ab 2.21(0.11)b 5.69(0.02)b 8449(103)b 7455(458)b 1238(111)a

NPK þ  MS2 28.75(0.10)ab 2.14(0.05)b 5.76(0.17)ab 9394(312)a 7177(181)bc 1232(98)a

NPK þ  OM1 28.57(0.47)ab 2.18(0.08)b 5.76(0.12)ab 6446(124)c 8173(455)ab 1090(162)a

NPK þ  OM2 31.56(0.74)a 2.55(0.08)a 6.01(0.04)a 6981(120)c 8700(195)a 1166(125)a

a Control: no fertilizer, NPK: chemical fertilizer NPK, NPK  þ   MS1: NPK plus maize straw, NPK  þ  MS2: NPK plus twice as much maize straw, NPK  þ   OM1: NPK plus pig

manure, and NPK þ  OM2: NPK plus three times the pig manure.b

The different letters in each column indicate the signi

cant difference at  P  <  0.05.

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soil CO2   uxes and WFPS in the 5 cm layer (Table 3), whichexplained 30e60% of the seasonal variations in soil CO2  ux. Fur-

thermore, a log-transformed multiple regression model including

both soil temperature and moisture [log( f )   ¼   a   þ   b T   log(W )]

accounted for 50e88% of the seasonal variation in soil CO2  uxes

(Table 4).

Cumulative CO2 emissions were signicantly correlated with the

harvested straw and root biomass (r 2 ¼ 0.62, n  ¼ 18, P  

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related to organic amendment quality, in which the C/N ratio has

been shown to be a good predictor of the decomposition of organic

amendments applied to soils [28]. The pig manure, with a low C/Nratio (w9), could decompose more easily than the maize residue

with a higher C/N ratio (w61). Therefore, pig manure most likely

provided more easily degradable and potentially more soluble

carbon for microbial activity than the maize residue and thus led to

greater soil CO2 emissions. Our results suggest that the magnitude

of the impact of soil amendments on soil CO 2 emissions primarily

depends on the type of organic amendments applied to the test soil,

whereas the rate of application has limited effects on cumulative

soil CO2  emissions as shown by the absence of a remarkable dif-

ference in CO2 emissions under different application rates of a given

organic amendment (Fig. 2b).

Despite the increased soil CO2  emissions, the combined use of 

organic amendments and chemical fertilizers improved or at least

maintained the SOC content of the studied Mollisols (Table 1). This

indicates that the carbon inputs to the soils were larger than or at

least in equilibrium with the carbon losses from soils induced by

the organic amendment applications.

4.2. Effects of soil temperature and moisture on the temporal

variation of soil CO 2 uxes

The temporal variation in soil CO2 uxes is commonly related to

soil temperature, moisture or both  [12,31,32]. In the present study,

however, only 26e34% of the seasonal variations in soil CO2  uxes

could be explained by soil temperature with an exponential

equation under certain treatments (Table 2), which implied that

other factors were affecting the CO2  uxes. In our study, enhanced

CO2  uxes were observed after the applications of both basal and

supplemental fertilizers (Fig. 2a). Moreover, an exponential equa-

tion described the relationship between soil temperature and CO2uxes well under all treatments when we restricted the analysis to

the period from the elongation stage to the harvest time:  R2 valueswere also greatly improved (0.43e0.91) given this time restriction,

accompanied by increases in Q 10 values (1.87e3.00; Table 2). Thus,

we believe that a disturbance, most likely related to plowing or

fertilization, affected soil CO2  emissions at the seedling stage and,

further, partly modied the inuence of soil temperature on CO2uxes, as shown by a previous study [33].

Previous studies have shown that soil moisture status can also

inuence soil respiration   [14,34]. However, the present study

found a poor relationship between soil CO2   uxes and WFPS.

There could be several reasons for this result. The narrow range

of soil WFPS (25e51%,  Fig. 1c) in the studied   eld might have

resulted in the observed weak inuence on soil CO2   uxes [35].

Soil temperature was also an important factor regulating the

effects of moisture on CO2  uxes [36]. Previous researchers havenoted that the effects of soil moisture on CO2   uxes are partly

obscured by soil temperature, because soil moisture and tem-

perature usually change simultaneously   [34,37]. In the present

study, we found improved relationships (R2 ¼   0.30e0.60) be-

tween soil CO2   uxes and WFPS after the masking inuence of 

soil temperature was excluded (Table 3). Furthermore, the log-

transformed multiple regression model including both soil tem-

perature and moisture was much better able to explain the sea-

sonal variations in soil CO2  uxes than the regression model with

moisture alone, with or without excluding the inuence of 

temperature (Tables 3 and 4). Therefore, our results showed that

there was a signicant interdependence between soil tempera-

ture and moisture in their effects on soil CO2  uxes in the studied

Mollisols.

 Table 2

Relationships between soil CO2   ux ( f ) and soil temperature (T ) at 5 and 10 cm

depths during the maize growing season.

Treatment Depth

(cm)

Entire maizegrowing period

(n ¼  18)

(May 27eSeptember 30,

2011)

From elongation to harvest

only (n ¼  13)

(July 1eSeptember 30, 2011)

Equation   R2 Q 10b Equation   R2 Q 10

Controla 5  e

  0  e

  f  ¼  57.703exp(0.0627T )

0.43* 1.87

10   e   0.06   e   f  ¼  54.911

exp(0.0711T )

0.58** 2.04

NPK 5   e   0.17   e   f  ¼  51.821

exp(0.0677T )

0.72*** 1.97

10   f  ¼  93.234

exp(0.0412T )

0.26* 1.51   f  ¼  62.770

exp(0.0684T )

0.81*** 1.98

NPK þ  MS1 5   e   0.14   e   f  ¼  44.806

exp(0.0793T )

0.58** 2.21

10   f  ¼  88.912

exp(0.0530T )

0.33* 1.70   f  ¼  53.671

exp(0.0832T )

0.72*** 2.30

NPK þ  MS2 5   e   0.10   e   f  ¼  34.516

exp(0.1030T )

0.82*** 2.80

10   f  ¼  79.630

exp(0.0571T )

0.27* 1.77   f  ¼  37.764

exp(0.1097T )

0.91*** 3.00

NPK þ  OM1 5   e   0.20   e   f  ¼  65.664

exp(0.0820T )

0.70*** 2.27

10   f  ¼  101.244

exp(0.0566T )

0.34* 1.76   f  ¼  68.940

exp(0.0866T )

0.76*** 2.38

NPK þ  OM2 5   e   0.04   e   f  ¼  65.412

exp(0.0935T )

0.74*** 2.55

10   e   0.13   e   f  ¼  67.284

exp(0.0984T )

0.79*** 2.68

Correlation signicance levels: *P  <  0.05, **P  <  0.01 and ***P  <  0.001.a Control: no fertilizer, NPK: chemical fertilizer NPK, NPK þ MS1: NPK plus maize

straw, NPK þ MS2: NPK plus twice as much maize straw, NPK  þ OM1: NPK plus pig

manure, and NPK  þ  OM2: NPK plus three times the pig manure.b Q 10: temperature sensitivity.

 Table 3

Relationships between soil CO2  ux ( f ) and soil WFPS (W ) in the 5 cm layer during

the maize growing season (n ¼  13).

Treatment Equation   R2 P    Excluding the inuence of soil

temperature

Equation   R2 P 

Controla  f  ¼  10.005W 

 188.059

0.31 0.048   f  ¼  17.777

exp(0.0423W )

0.39 0.023

NPK   f  ¼  6.815W 

 32.567

0.20 0.127   f  ¼  39.393

exp(0.0246W )

0.41 0.019

NPK þ  MS1   f  ¼  16.631W 

 309.019

0.46 0.011   f  ¼  15.485

exp(0.0524W )

0.60 0.002

NPK þ  MS2   f  ¼  12.650W 

 134.627

0.20 0.121   f  ¼  26.696

exp(0.0369W )

0.53 0.005

NPK þ  OM1   f  ¼  12.657W 

 123.650

0.20 0.128   f  ¼  40.125

exp(0.0312W )

0.35 0.033

NPK þ  OM2   f  ¼  16.018W 

 163.948

0.19 0.142   f  ¼  54.677

exp(0.0309W )

0.30 0.054

a Control: no fertilizer, NPK: chemical fertilizer NPK, NPK þ MS1: NPK plus maize

straw, NPK þ MS2: NPK plus twice as much maize straw, NPK  þ OM1: NPK plus pig

manure, and NPK  þ  OM2: NPK plus three times the pig manure.

 Table 4

Relationships between soil CO2 ux ( f ) and soil temperature (T ) at a 5 cm depth and

soil WFPS (W ) in the 5 cm layer during the maize growing season (n ¼  13).

Treatment Equation   R2 P 

Controla log( f ) ¼  1.732 þ  0.018  T  log(W ) 0.50 0.007

NPK log( f ) ¼  1.709 þ  0.019  T  log(W ) 0.79  

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When a separate analysis was conducted for each treatment

individually, the seasonal variations in soil CO2  ux rates could be

positively explained by the seasonal variations in soil temperatureand moisture. For all treatments together, however, we observed

that the treatments with lower mean soil temperatures and

moisture had higher CO2   emissions than others. These results,

combined with the positive relationships between soil tempera-

ture, moisture and CO2  uxes (Table 2), indicated that cumulative

CO2   emissions during the growing season were affected more by

the applied amendments than by soil temperature and moisture in

the cultivated Mollisols.

It is noteworthy that the closed chamber system is known to

underestimate soil CO2   uxes by approximately 10% due to the

effective volume being larger than the volume of the chamber itself 

[38]. Thus, a further study comparing a closed- and an open-

chamber methodology is needed to obtain a calibration factor for

the Mollisols.

5. Conclusion

Applications of organic amendments combined with NPK

accelerated CO2  emissions from soils, whereas NPK fertilization

alone did not signicantly impact cumulative CO2 emissions. More

cumulative CO2 was emitted from soils amended with pig manure

relative to those with maize residue. The log-transformed multiple

regression model log( f ) ¼ a þ b T  log(W ) including soil temperature

and moisture accounted for 50e88% of the season variation in soil

CO2   uxes. Cumulative soil CO2   emissions during the growing

seasonwere affected more by the applied amendments than by soil

temperature and moisture in the cultivated Mollisols in northeast

China. Our results suggest that for the Mollisols, the magnitude of the impact of soil amendments on soil CO2   emissions depends

primarily on the type of organic amendments applied, whereas the

application rate has limited impacts.

 Acknowledgments

Thiswork was funded by the Strategic Priority Research Program-

Climate Change: Carbon Budget and Related Issues of the Chinese

Academy of Sciences (no. XDA05050501), the National Key Basic

Research Program of China (no. 2011CB100506), the Natural Science

Foundation of China (no. 41101283 and 41101282), and the Key

Laboratory of Mollisols Agroecology, Northeast Institute of Geogra-

phy and Agroecology, Chinese Academy of Sciences (no. 2011ZKHT-

01). We thank Gui-Dan Sun for laboratory assistance and Wei-Li Gao

and Xiu-Ling Wen for their participation in the  eld sampling. We

also thank three anonymous reviewers for their helpful comments

and suggestions, which improved the manuscript.

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