Thinking from the Dark Earth in a

Buried Ancient Paddy Soil

Weixiang Wu, Min Yang, Yuxue Liu

College of Environment and Resource Science

Academy of Water Science and Environmental Engineering

Zhejiang University

E-mail: weixiang@zju.edu.cn

Oct, 2010

International Symposium on Environmental Behavior and Effects of

Biomass-Derived Charcoal

Global warming & GHGs

Background

IPCC AR4 FAQ

China becomes the highest CO2 emissioncountry in the earth

Big challenges for the Chinese government

to realize the carbon reduction target

To 2020, CO2 emissions per unit of GDP

will be reduced by 40-45% in China on

the basis of 2005.

GDP↑ CO2↓

Carbon reduction technologies

1）Carbon Capture and Sequestration

(CCS) technology

• Forestry measures

• Ocean sequestration

• …

2）Carbon reduction

• Agricultural Sources

• Industrial Sources

• Domestic Sources

• …

Contribution of agriculture/paddy soil on the

global GHGs emission

(Khalil, et al. 2006)

Chemical fertilizer

The chemical fertilizer was increased from 8×106 t in 1978 to

4.3×107 t in 2003, and increased by 4 times.

1) Massive production results in serious energy input (carbon

emission) and environmental pollution.

2) Low utilization rate of chemical fertilizer lead to nutrient losses

from agriculture land, and become a main contributor to water

eutrophication.

Large amount of fertilizer

Serious nutrient run-offEnergy input

Air pollution

Current situation of soil quality in China

low yield

high yield

middle yield

42.76

31.09

26.15

Fig. Arable land of different yield in China (1996)

Low organic matter content: average 1% in China

Large area of middle and low yield arable land

Lack of nutrients

(Xu Minggang, 2008)

How to achieve the target for

carbon reduction in agriculture !

On the basis of decreasing GHGs emission, maintaining high

yield of food, declining amount of chemical fertilizer use,

improving soil quality……

Terra Preta soil has high

content of

charcoal/biochar ， the

carbon content is up to

15%，compared with 2-

3% in adjacent soils

Radiocarbon dating

revealed charcoal ages

of up to 7000 years (Neves

et al., 2001)

Background soil

Terra Preta

Terra Preta-Amazonian Dark Earth

Characteristics

• High content of C

• Great porosity

• Large surface area

• High charge density

• Great negative surface charge

Biochar:

Biochar: High stability

(Glaser, 2007)

High aromaticity makes it lack of

(bio)chemical reactivity and strongly

resist decomposition

Present for several hundred to thousand years.

(Lehnman, 2006)

What about the stability of

biochar in paddy soil?

Can straw charcoal be

sequestrated in soil?

…

Recent discovery of a Chinese Ancient

Paddy Soil

Archaeological site

The collected soil sample

Micrographs of charcoal in ancient paddy soil

Fig. Micrographs of biochar in the ancient paddy soil

Large amount of straw charcoal in the black layer of

ancient paddy soil can be obviously identified.

Quantification of TOC and BC contents

1

2

3

4

5

6

7

8

9

10

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60

C(g/kg)

depth(cm)

TOC BC

TOC of current paddy soils in China is 10-20 g/kg.

Fig. TOC and BC contents in different layers

Moieties

Location(ppm)

carbonyls aromatics alkyls

210-165 165-90 45-0

charcoal 14.57 83.3 2.13

Table Quantitative NMR spectral analysis of charcoal from ancient paddy soil

NMR spectra of charcoal in ancient paddy soil

FTIR spectra of charcoal

C-H

O-H

FTIR spectra of char in ancient

paddy soil is similar to straw char

Compared with 500℃ 3h, aliphatic

C-H stretching was declined in the

others

Greater aromatic C=C (double bond)

stretching vibrations (1600cm-1) in

char from ancient paddy

C-O-C stretching (1100cm-1) was

the smallest amount in char from

the ancient paddy soil.Fig. FTIR spectra of charcoal

500℃3h: fresh produced rice straw char

SC: rice straw char collected after burying into field 1 year

(002)

XRD spectra of charcoal

All samples have analogous

diffractogram patterns.

Sharp peaks indicate miscellaneous

inorganic components, and is

consistent with the high percentage

of ash. Compare to PDF card, most

of them are SiO2, CaCO3, KCl.

The broad (002) peaks indicate the

structural differences between chars

and graphite.

Fig. XRD spectra of charcoal

SEM-EDX analysis of the straw charcoal

Fig. SEM-EDX spectra of charcoal from ancient paddy soil

The ancient straw charcoal has great porosity.

O/C was higher in the exterior than that of interior.

CO2CO2

pyrolysis

biochar

CO2 CO2

25%

25%

pyrolysis

Burying biochar into soil could be a

possible way for CCS

Straw yield in China was approximately 700 Mt/yr

Potential CO2 reduction: ~73 Mt/yr

In terms of 20% of straw converted to biochar, 30% rate of

production, 50% carbon content, and 5% mineralized

Potential CO2 reduction from straw-char in

China

Effect of biochar amendment on GHGs

emission from paddy soil

Results from upland studies

(Yanai et al. 2007)

charcoal: made from municipal biowaste

(Spokas et al. 2009)

In greenhouse experiments, NOx emissions were reduced by 80% and

CH4 emissions were completely suppressed with biochar additions of

20 g kg-1 to a forage grass stand. (Rondon et al. 2005)

Effect of biochar amendment on CH4 emission from paddy

soil

CH

4 (

mg

kg

-1 d

ry s

oil

)

0

2

4

6

8

10

12

14

16CK

BC1

BC2

BC3

SC1

SC2

SC3

Time (d)

0 7 14 21 28 35 42 49

0

50

100

150

200

250

300

350CKC

BCC1

BCC2

BCC3

SCC1

SCC2

SCC3

Amendment of both kinds of

biochar could significantly

reduce CH4 emission from paddy

soil.

CH4 emission from the paddy

soil amended with 2.5% BC and

SC reduced by 51.1% and

91.2%, respectively as

compared with non-amendment

control soil.

CH4 reduction with biochar

amendment could also be

observed with straw addition

Our research

Effect of biochar amendment on CO2 emission from

paddy soil

Lower amount of CO2 emission

from the waterlogged paddy soil

with the addition of biochar was

observed during the incubation.

But there were no significant

differences among CK, BC and

SC.

Addition of rice straw could

significantly increase CO2

emission from paddy soil. But only

high biochar amendment rate

would result in significantly CO2

emission reduction on day 49.

CO

2(m

g k

g-1

dry

so

il)

0

50

100

150

200

250

300

350

CK

BC1

BC2

BC3

SC1

SC2

SC3

Time (d)

0 7 14 21 28 35 42 49

0

200

400

600

800

1000

1200

1400

1600

1800

CKC

BCC1

BCC2

BCC3

SCC1

SCC2

SCC3

Meth

an

og

en

ic a

cti

vit

y (m

ol

CH

4 h

-1 g

-1 d

ry s

oil

)

0.00

.02

.04

.06

.08

.10

.12

.14

.16

.18

CKBC1BC2BC3SC1SC2SC3

Time (d)

1 4 7 14 28 490.0

.2

.4

.6

.8

1.0

CKCBCC1BCC2BCC3SCC1SCC2SCC3

ab

aa

ab

ba

bb

aa

ab a

cb

cc

aa

cb

dc

dd

ab

cb

bc

dc

de

ab

bb

cd

bc

d aa

ba

bc

cd

cd

bc

dd

ab a

bd

ca

cd

d e

aa

aa

aa

a

ab

aa

aa

bab b

aa

a ab

b bb

ca

bc

bc

bc

a

bc

ba

ab

ab ab

bb

Effect of biochar amendment on methanogenic activity in

paddy soil

Addition of both kinds of

biochar resulted in the

significant decrease of

methanogenic activity in soil

over the whole incubation

period.

In corresponding to the

pattern of CH4 emission,

inhibition was more significant

in soil with SC amendment as

compared with BC amendment.

Under straw addition,

inhibition of CH4 emission was

only observed on day 7 and 14.

Effect of biochar amendment on methanogenic diversity in

paddy soil

DGGE profiles of

methanogen were quite

similar to each other, with

no apparently visible

differences between the

patterns for all

treatments. It indicated

that compositions of the

methanogenic bacteria

have no significant

changes after the

addition of biochar in 49

days.

Effect of biochar amendment on the rice

production

0

1

2

3

4

5

6

7

8

9

10

CK BC SC CKU BCU SCU

TreatmentY

ield

(t

ha

-1)

C C

AB B ABA

SRUSCUBCUCKUSCCK BC

Influence on rice height and yield

CK: control

BC: bamboo char

SC: rice straw char

CKU: urea

BCU: bamboo char + urea

SCU: rice straw char + urea

SRU: slow released fertilizer

Reducing chemical fertilizer application rate

general

amount of fertilizer

rice straw charcoal +

less amount of

fertilizer

Charcoal coated slow released fertilizer

SRF1: charcoal coated slow released fertilizer1

SRF2: charcoal coated slow released fertilizer2

SRF1 SRF2

Influence on concentration of NH4+-N, NO3

--N in surface

water

0.0

0.5

1.0

1.5

2.0

2.5

3.0

CK BC SC SCL RS SRF1 SRF2

TreatmentN

O3

- -N (

mg

/L)

2010.7.27 2010.9.5

CK: general amount of fertilizer

BC: bamboo char + CK

SC: straw char + CK

SCL: straw char +less CK

RS: rice straw + CK

SRF1: charcoal coated slow released fertilizer1

SRF2: charcoal coated slow released fertilizer2

0.0

3.0

6.0

9.0

12.0

15.0

CK BC SC SCL RS SRF1 SRF2

Treatment

NH

4+-N

(m

g/L

)

2010.7.27 2010.9.5

N, P N, P

CO2

CH4

N, P

K

CO2

N, P

K

CO2 CO2 CO2

50%

50%

N, P

CO2

N, P

K

N, P

CO2CO2

N, P

K

CH4

pyrolysis

biochar

CO2 CO2

25%

25%>10%

5%pyrolysis

☺put straw biochar into field

☺put straw into field???

θ C sequestration

θ decline GHGs emission

θ increase crop yield

θ decrease amount of

chemical fertilizer use

θ reduce nutrient run-off

θ improve soil quality

Perspectives

Acknowledgements：• National Natural Science Foundation of

China (NSFC)

• Natural Science Foundation for Outstanding

Young Scholars of Zhejiang Province

• Blue Moon Fund, US

Thanks!