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Biochar: Impacts on Soil Microbes and the Nitrogen Cycle
Kurt Spokas
USDA-ARS, Soil and Water Management Unit, St. Paul, MNAdjunct Professor University of Minnesota – Department of Soil, Water and Climate
Biochar: Production, Properties, & Agricultural UseIllinois Sustainable Technology Center – Champaign, IL
September 1, 2010
USDA-ARS Biochar and Pyrolysis Initiative
GRACEnet Project (30 locations): Greenhouse Gas Reduction and Carbon Enhancement Network
REAP Project (24 locations): Renewable Energy Assessment Project
Biochar and Pyrolysis Initiative (15 locations)
Ongoing field plot trial (6 locations)
Multi-location USDA-ARS research efforts:
Biochar: New purpose not a new material
Pyrolysis, carbonization, and coalification are well establish
conversion processes with long research histories
Except:
Prior emphasis:
Conversion of biomass to liquids (bio-oils) or
gaseous fuels and/or fuel intermediates
Solid byproduct (biochar) has long been
considered a “undesirable side product” (Titirici et al., 2007)
Used as fuel
(3000-4000 BC)
Cave Drawings
(>10,000 to 30,000 BC)
Water filtration
(2000 BC)
Charcoal production
(15th century)
Pyrolysis, carbonization, and coalification are well establish
conversion processes with long research histories
Except:
Prior emphasis:
Conversion of biomass to liquids (bio-oils) or
gaseous fuels and/or fuel intermediates
Solid byproduct (biochar) has long been
considered an “undesirable side product” (Titirici et al., 2007)
What is new
The use (or purpose) for the creation of charred biomass
Atmospheric C sequestration
Dates to 1980’s and early 2000’s(Goldberg 1985; Kuhlbusch and Crutzen, 1995; Lehmann, 2006)
Used as fuel
(3000-4000 BC)
Cave Drawings
(>10,000 to 30,000 BC)
Water filtration
(2000 BC)
Climate Change Mitigation
(1980’s)
Charcoal production
(15th century)
Biochar: New purpose not a new material
Carbon Sequestration RatesEcosystem Range of Natural CO2
Sequestration Rates
(tons C acre-1 yr-1)
Cropland 0.2 to 1
Forest 0.1 to 4
Grassland / Prairie 0.1 to 1
Swamp / Floodplain / Wetland 2 to 4
Biochar Goal is to increase rates of C sequestration
Biochar: Black Carbon Continuum
Thermo-chemical conversion products
Graphite
0 0.25 0.5 0.75 1.0
Oxygen to carbon (O:C) molar ratio
Soot
Charcoal
Char
Combustion residuesCombustion condensates Combustion residues
Biomass
Complete new structure Retains relic forms of parent material
0.2 0.6
Problem Lack of nomenclature uniformity (Jones et al., 1997)
Adapted from Hedges et al., 2000; Elmquist et al., 2006
Biochar: Black Carbon Continuum
Thermo-chemical conversion products
Graphite
0 0.25 0.5 0.75 1.0
Oxygen to carbon (O:C) molar ratio
Soot
Charcoal
Char
Combustion residuesCombustion condensates Combustion residues
Biomass
Complete new structure Retains relic forms of parent material
0.2 0.6
Biochar – Spans across multiple divisions in the Black C Continuum
However, biochar is NOT a new division…
Adapted from Hedges et al., 2000; Elmquist et al., 2006
Biochar
Comparisons of Natural vs. Synthetic
Synthetic (Pyrolysis) Biochar
-Pure homogeneous feedstock
-“Constant” temperature- Industrial Process
-Typically cooled under anaerobic
conditions (no water)- No weather exposure
Natural Biochar
-Heterogeneous feedstock- Impurities
- Soil and oxygen
- Minerals (metals) alter yields(e.g. Robertson, 1969; Bonijolya et al., 1982; Baker, 1989)
- Multiple feedstock sources
- Species and types
-Variable temperature- 80 to 1000 oC
-Air cooled/Precipitation/Solar (UV)- Exposed to environmental conditions
Biochar: Soil Stability
Over a 100 year history of research
Potter (1908) – Initial observation of fungi/microbial degradation of lignite (low grade coal/charcoal)
Biochar Degradation Study Residence Time (yr)
Steinbeiss et al. (2009) <30
Hamer et al. (2004) 40 to 100
Bird et al. (1999) 50-100
Lehmann et al. (2006) 100’s
Baldock and Smernik (2002) 100-500
Hammes et al. (2008) 200-600
Cheng et al. (2008) 1000
Harden et al. (2000) 1000-2000
Middelburg et al. (1999) 10,000 to 20,000
Swift (2001) 1,000-10,000
Zimmerman (2010) 100’s to >10,000
Forbes et al. (2006) Millennia based on C-dating
Liang et al. (2008) 100’s to millennia
Possible Stability Explanation O:C Ratio
Summary of existing literature studies (n=35) on half-life estimation of biochar [Figure from Spokas (2010)]
Biochar
Degradation
Study
Residence
Time (yr)
Baldock and
Smernik (2002)
100-500
Bird et al.
(1999)
50-100
Cheng et al.
(2008)
1000
Forbes et al.
(2006)
Millennia
based on C-
dating
Hamer et al.
(2004)
40 (charred
straw residue)
80 (charred
wood)
Hammes et al.
(2008)
200-600
Harden et al.
(2000)
1000-2000
Liang et al.
(2008)
several
centuries to
millennia
Lehmann et al.
(2006)
100’s
Middelburg et
al. (1999)
10,000 to
20,000
Steinbeiss et
al. (2009)
<30
Swift (2001) 1,000-10,000
Zimmerman
(2010)
100-10,000 O:C molar ratio
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Pre
dic
ted H
alf-life (
years
)
100
101
102
103
104
105
106
107
108
t1/2>1000 yrs 100 yrs < t1/2 < 1000 yrs t1/2 < 100 yrs
Proposed Biochar Mechanisms
1. Alteration of soil physical-chemical properties
pH, CEC, decreased bulk density, increased water holding capacity
2. Biochar provides improved microbial habitat
3. Sorption/desorption of soil GHG and nutrients
4. Indirect effects on mycorrhizae fungi through effects on other soil microbes
Mycorrhization helper bacteria produce furan/flavoids beneficial to germination of fungal spores
Warnock et al. (2007)
Soil Microbe Impacts: Laboratory Incubations
• We know when we are sick….
Fever, aches, pains..…
• How about for soil microbes:
• Look at their “products” – e.g. CO2, CH4, N2O
• Implications on the rates of reaction and
amount of gases produced
•Provide clues into the mechanisms
Biochar impacts on Soil Microbes & N Cycling
44 different biochars evaluated
11 different biomass parent materials
Hardwood, softwood, corn stover, corn cob,
macadamia nut, peanut shell, sawdust, algae,
coconut shell, turkey manure, distillers grain
Represents a cross-sectional sampling of available “biochars”
C content 1 to 84 %
N content 0.1 to 2.7 %
Production Temperatures 350 to 850 oC
Variety of pyrolysis processes
Fast, slow, hydrothermal, gasification
Laboratory Biochar Incubations
Soil incubations:
Serum bottle (soil + biochar)
5 g soil mixed with 0.5 g biochar
(10% w/w) [GHG production]
Field capacity and saturated
Mason Jar (biochar mixed & isolated)
Looking at impact of biochar
without mixing with soil
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
CO
2 P
rod
uction
(mg C
O2
/gsoil/
da
y)
-0.8
-0.6
-0.4
-0.2
0.0
0.2
Biochar Amount (g)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
N2
O P
rodu
ction
(ng
N2
O/g
soil/
da
y)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
CH
4 P
rod
uctio
n
(ng
CH
4/g
so
il/d
ay)
-7
-6
-5
-4
-3
-2
-1
0
Influence of biochar addition on GHG Production
Spokas et al., 2009
Biochar isolated or mixed with soil
CH4 Oxidation
Soil Control Soil + BC (mixed) Soil + Beaker BC
CH
4 O
xid
atio
n r
ate
(g C
H4 g
soil-1
d-1
)
0
2
4
6
8
N2O Production
Soil Control Soil + BC (mixed) Soil + Beaker BC
N2O
Pro
du
ctio
n r
ate
(n
g N
2O
gsoil-1
d-1
)
0
5
10
15
20
25
EthyleneProduction
Rates
So
il
Activa
ted
Ch
arc
oa
l
BC
-1
BC
-2
BC
-3
BC
-4
BC
-5
BC
-6
BC
-7
BC
-8
BC
-9
BC
-10
BC
-11
BC
-12
Eth
yle
ne
Pro
du
ctio
n (
ng
C2
H4
0.5
gchar-1
d-1
)
0
10
20
30
40
Dry
Wet
So
il
Activa
ted
Ch
arc
oa
l
BC
-1
BC
-2
BC
-3
BC
-4
BC
-5
BC
-6
BC
-7
BC
-8
BC
-9
BC
-10
BC
-11
BC
-12
Eth
yle
ne
Pro
du
ctio
n (
ng
C2
H4
gsoil-1
d-1
)
0
5
10
15
20
25
30
Field Capacity
Saturated
Biochar Alone
Biochar + Soil
10% w/w
Wood
Mac n
ut
Wood
DD
GS
DD
GS
Co
b
Co
b
Wo
od
Wood
Pelle
ts
Wood
Peanut
Spokas et al. (2010)
Ethylene Impacts
Soil Microbial Impacts
Induces fungal spore germination
Inhibits/reduces rates of nitrification/denitrification
Inhibits CH4 oxidation (methanotrophs)
Involved in the flooded soil feedback
Both microbial and plant (adventitious root growth)
Ethylene Headspace Concentration ( L L-1
)
0 (control) 1 5 25 50 275
Am
moniu
m C
oncentr
ation (
g N
H4 g
so
il-1)
0
10
20
30
40
50
0 (control) 1 5 25 50 275
N2O
Pro
du
ctio
n (
ng
N2O
gsoil
-1 d
-1)
0
20
40
60
80
100
postN2O
Plot 1 Lower control line
Ethylene Headspace Concentration (0 to 275 ppmv) Ethylene Headspace Concentration (0 to 275 ppmv)
N2O Production NH4+ Production
Closer look at N-
cycling(hardwood sawdust biochar)
0 1 2 3
Nitra
te (
pp
m)
0
20
40
60
80
100
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Nitrite
(p
pm
)
0.0
0.1
0.2
0.3
0.4
0.5
Biochar Amount (g)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
NH
4 (
pp
m)
0
1
2
3
4
5
0 1 2 3
0.0
0.5
1.0
0 1 2 3
0.0
0.5
1.0Biochar Alone
Biochar Alone
Brief Overview of N-cycle
Ammonium (NH4+)
Nitrite (NO2-)
Nitrogen Uptake (plants/microbes)
Nitric Oxide (NO)
Nitrogen Gas (N2)
Nitrous Oxide (N2O)
Nitrification
N2
Mineralization
Organic N
Nitrogen fixation
Em
itte
d to a
tmosphere
Nitrate (NO3-)
Denitrification
Putting the pieces together: Not quite a full picture yet…
Ammonium (NH4+)
Nitrite (NO2-)
Nitrogen Uptake (plants/microbes)
Nitric Oxide (NO)
Nitrogen Gas (N2)
Nitrous Oxide (N2O)
Nitrification
N2
Mineralization
Organic N
Nitrogen fixation
Em
itte
d to a
tmosphere
Nitrate (NO3-)
Denitrification
Increased amounts
Decreased amount
Ethylene Production
•Ethylene could provide a mechanism behind reduced
nitrification/denitrification activity
•Clough et al. (2010) also hypothesized that -pinene
could be involved as a nitrification inhibitor
-pinene observed as volatile from vegetation
involved in insects’ chemical communication
system
•Despite the different chemicals – Same mechanism:
Chemical inhibitors behind the suppression of
N2O production
, 24-Apr-2010 + 00:48:10NRC104
1.01 6.01 11.01 16.01 21.01 26.01 31.01Time5
100
%
5
100
%
5
100
%
5
100
%
5
100
%
5
100
%
RXI5_032210_001_126 Scan EI+ 45-2501.27e7
RXI5_032210_001_099 Scan EI+ TIC
1.27e75.19
5.96 29.198.62 12.9411.739.87 18.2913.65
16.44 22.9518.99
21.7623.78
RXI5_032210_001_092 Scan EI+ TIC
1.27e79.29
8.37
9.8918.3012.15 16.4713.6814.82
20.56 27.4129.00
RXI5_032210_001_091 Scan EI+ TIC
1.27e77.006.005.24
10.9113.68
15.08
18.6721.75
23.81 27.1025.1027.76 29.25
RXI5_032210_001_087 Scan EI+ TIC
1.27e78.64
7.005.68
11.76
11.5413.69
12.4116.21
18.84
17.2520.02
21.81
24.16 29.7126.2027.12
RXI5_032210_001_088 Scan EI+ TIC
1.27e712.0010.419.51
5.69 7.2229.9725.8523.9423.07
21.0420.0113.09 14.41
28.9527.08
To
luene
Be
nze
ne
(13.6
5)
xyle
nes
meth
anol
Naphth
ale
ne
1,2
-dic
hlo
robenzene
eth
ylb
enzene
Acetic A
cid
Wood Ash
Activated Charcoal
Wood pellet
BC
Macadamia
Shell BC
Hardwood
Sawdust
Oak
Hardwood
Bituminous
coal
nonanal
Aceto
ne
2-m
eth
ylb
uta
ne eth
anol
Biochar has a variety of sorbed volatiles = range of potential microbial inhibitors
Headspace Thermal Desorption GC/MS scans of biochars
Fu
rfura
l
(10.9
)
Impact of Biochar Volatiles in Soils
• Volatile organic compounds can interfere with microbial processes
• Terpenoids – interfere with nitrification [Amaral et al., 1998; White 1994]
• Furfural + derivatives – inhibits microbial fermentation & nitrification (Couallier et al.,
2006; Datta et al. 2001)
• Benzene, Esters – Also inhibit microbial reactions
• Still ongoing and developing research area in the plant/microbe research area
• Alterations in VOC content could be sensitive indicators of soil conditions (Leff and Fierer, 2008).
• Sorbed BC volatiles could interfere with microbial signaling (communication): Releasing or sorb signaling compounds
Conclusions
• Another piece to the puzzle: Ethylene + sorbed VOC’s
– Sorbed volatiles and degradation products (ethylene) should be included in the potential biochar mechanisms
– Microbial inhibitors – Could also explain plant effects
Reduction in N2O production : Consequence of sorbed volatiles impacting the
nitrification process Accumulation of NH+
4 and decreased NO-3 production
Length of impact ?
No absolute “Biochar” consistent trends: Highly variable and different responses
to biochar as a function of soil ecosystem (microbial linkage) & position on black
carbon continuum:Typically:
Reduced basal CO2 respiration
Reduced CH4 oxidation activity
Reduced N2O production activity
Reduced NO3 production (availability)
Increased extractable NH4 concentrations
Exceptions DO exist
AcknowledgementsI would like to acknowledge the cooperation:
Dynamotive Energy Systems
Fast pyrloysis char (CQuest™) through non-funded CRADA agreement
Best Energies
Slow pyrolysis char through a non-funded CRADA agreement
Northern Tilth
Minnesota Biomass Exchange
NC Farm Center for Innovation and Sustainability
National Council for Air and Stream Improvement (NCASI)
Illinois Sustainable Technology Center (ISTC) [Univ. of Illinois]
Biochar Brokers
Chip Energy
AECOM
Laboratorio di Scienze Ambientali R.Sartori - C.I.R.S.A. (University of Bologna, Italy)
USDA-ARS Biochar and Pyrolysis Initiative
Technical Support : Martin duSaire, Tia Phan, Lindsey Watson, Lianne Endo,
Kia Yang and Amanda Bidwell
“The Nation that destroys its soil destroys itself”
Franklin D. Roosevelt
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