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