Greenhouse Gas Emissions from Soils
as Affected by Addition of Biochar
Natalia Rogovska1, Pierce Fleming2,
David Laird2 and Richard Cruse1
1Dept.
Of Agronomy, Iowa State University
2National Soil Tilth Laboratory, USDA, ARS
Ames IA, 50011
Agriculture may help reduce greenhouse
gas (GHG) emissions through
cropping systems that enhance soil carbon
sequestration
practices that reduce energy consumption
land use changes
Much attention has been given to production of
“carbon neutral” biofuels
Pyrolysis
Thermal decomposition of organic material in the
absence of oxygen
Bio-oil: is used as an
alternative to fossil fuel.
Biochar: used as a CO2 neutral fuel or
soil amendment.
Syngas: can be used as a
natural gas replacement.
What was done
Soil column study was initiated to study the effect
of biochar and manure addition on soil respiration
and N2O emission
Soil used: Clarion fine-loamy, mixed, superactive, mesic
typic Hapludolls
Biochar: 0, 5, 10, and 20 g biochar kg-1 of soil (biochar was
<0.5 mm from slow pyrolysis of mixed hardwood)
Well mixed and packed into the soil columns made of PVC
tubes. Total of 48 columns
Initial soil bulk density ~ 1.1 g cm-3
Manure: 0 and 5 g manure kg-1 of soil added at week 12
0.005 M CaCl2
What was done
Columns incubated at 22oC and 80% relative humidity
for 71 weeks
Leached weekly with 200 ml of 0.005 M CaCl2
Soil bulk density and CO2
emissions monitored through
out incubation period
N2O emissions, soil total C
and N measured at the end
of the study
0-3 cm
3-6 cm
SOIL
6-bottom
SAND
LECHATE
Biochar addition had significant impact on soil bulk density
1.5
C0M
C5
C5M
C10
C10M
C20
C20M
Bulk density (g cm
-3
)
1.4
C0
1.3
aabbcbcc
cc c
Manure
added
aabbbbbc
ccc
aacbcccc
b c
aabbbbcc
c cc
aabbcbcd
bccdcd
dd d
aacbcccd
bdcddd
22
34
43
1.2
1.1
1
8
12
Weeks
69
A
A
Organic C in Soil (whole column)
40
35
Manure
30
Organic C (g)
D
Control
C
B
25
A
D
Recovery of organic C after
71 weeks (end of the study)
C
B
Biochar added
A
20
g kg-1
15
0
5
10
20
10
5
0
0
5
20
10
Biochar C recovery
%
102
109
98
Organic C in Soil (0 - 3 cm)
8
Control
7
F
D
O rganic C (g)
6
5
G
Manure
A
A
Biochar added
E
g kg-1
B C
0
5
10
20
4
3
2
1
0
0
5
10
Charcoal treatment (g-char / kg-soil)
20
Manure C recovery
%
9
17
20
12
Impact of biochar on soil respiration
45
40
Manure effect,
biochar effect,
and time are all
significant
30
C10
C20
COM
C5M
C10M
C20M
14
Manure
added
25
C5
Average CO2 µg cm-2 s-1
-2
CO2 µ g cm s
-1
35
C0
20
F
12
Control
Manure
10
B
D
D
B
E
8
C
6
A
4
2
0
0
15
5
10
20
Biochar, g kg-1 soil
10
5
0
8
9
10
11
12
13
14
Week
15
16
18
22
28
52
Impact of biochar on soil respiration
Respiration increased possibly due to
Increase in aeration and O2 consumption by
aerobic microorganisms
Biochar addition may have lead to
acceleration of decomposition rates of humus
Wardle et al. (2008) observed that mass loss of mixture containing
charcoal and humus was much greater than was predicted if two
components were considered separately
Wardle et al. (2008) Science, vol. 30
Impact of biochar on N2O emissions
N2O flux, µg N2O -N m-2 hr-1
20
Control
Manure
18
16
14
12
A
AB
10
8
6
BC
BC
4
BC
BC
2
C
BC
0
0
5
10
20
Biochar g kg-1
N2O is 296 times more potent than CO2
Relationship between soil bulk
density and N2O flux
N2O flux, µg N2O -N m-2 hr-1
20
15
Control
10
Manure
5
0
-5
1.24
1.26
1.28
1.30
1.32
Soil Bulk density, g cm-3
1.34
1.36
Soil pH (depth = 0-3 cm )
7.50
Control
Manure
7.00
pH
6.50
6.00
5.50
c
c
d
d
c
ab
a
b
5.00
0
5
10
20
Biochar
effect on
soil pH
Biochar added (g /kg-soil)
Ash content of
biochar = 7.5%
Soil pH (depth = 3-6 cm )
7.50
Control
Manure
7.00
pH
6.50
6.00
5.50
c
bc
ab
d
d
e
d
a
CCE = 12.5
5.00
0
5
10
20
Biochar added (g /kg-soil)
Soil pH (depth = 6 cm - bottom )
7.50
Control
Manure
7.00
pH
6.50
6.00
Assuming the ash is
CaO then:
c
d
cd
b
ab
ab
a
a
5.50
5.00
0
5
10
Biochar added (g /kg-soil)
20
Conclusions
Biochar addition to soils significantly :
decreased soil bulk density
increased microbial respiration and CO2 emissions
decreased N2O emissions
increased soil pH
increased levels of soil organic C
Within our ability to measure, no biochar carbon was
mineralized during incubation period
Impact of soil biochar additions
on GHG emissions
Increased CO2 emissions from soil due
to enhanced microbial respiration
+
0
_
Increase C input
to soil due to
enhanced plant
growth
Reduce CO2
emissions due
to decreased
use of lime and
fertilizer
Reduce N2O
emissions from
soils
Increase C
sequestration in
soils (Biochar C
is very stable)
Other unknowns:
Impact of biochar on humus formation?
Impact of biochar on land use?
????
Acknowledgements
National Soil Tilth Lab., USDA, ARS:
Dr. Tim Parkin
Otis Smith
David Meek