Please see my June 2012 presentation for updated results and if you are already familiar with biochar! 2nd year (at the time) PhD student Sean Case presents work from the first 18 months of his research project investigating the effect of biochar on greenhouse gas emissions from agriculture, particularly nitrous oxide emissions.

1. Biochar suppression of nitrous
oxide emissions from an
agricultural soil
Sean Case
Dr Jeanette Whitaker, Centre for Ecology and Hydrology
Dr Niall McNamara, Centre for Ecology and Hydrology
Dr David Reay, University of Edinburgh

2. Overview
• Sources of nitrous oxide (N2O) in soil
• Biochar and its uses
• The effect of biochar on N2O emissions
from soil
• Potential mechanisms
• Our research to investigate mechanisms
• Future work
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

3. Soil N2O production
Nitrifying bacteria
N2 O NO
N2 O N2
NH4+
(Ammonium) NO2- Denitrifying
NO3- bacteria
• Use NH4+ and O2 (Nitrate)
• Use NO3- and C
• Activity peaks at mid • Anaerobic conditions
range (50 – 60 %) of
• Activity increases as soil
water filled pore space
approaches saturation
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

4. What is biochar?
Low oxygen environment
~ 350°C > 800°C
Oxygen:Carbon
Biomass Charcoal
Char Soot
Graphite
0.6 0.2
Biochar – if
Adapted from Spokas, (2010) applied to soil
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

5. Biochar for climate change mitigation
• Biochar: C-rich, slow degradation
• C sequestration worldwide?
• Much uncertainty - effect on soil
Dynamotive Energy Systems, (2009)
• Biochar observed to suppress N2O
emissions in laboratory
• No published results showing N2O
suppression following biochar
Yanai et al., (2007), Soil Sci. and Plant Nut., 53, 181-188
application to field
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

6. Does biochar suppress nitrous oxide
emissions in agricultural soil?
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

7. Field experiment:
• Biochar – Hardwood biochar (oak, cherry,
ash trees) 50 tonnes ha-1
• Crop – Miscanthus Giganteus X
• Soil – Clay, low inorganic N
• Seasonal greenhouse gas measurements
n=5
• Significant suppression in
first measurement
• Not seen since
• Sporadic measurements?
Not timed with rain events? June Sept Jan May
2010 2011
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

8. Laboratory experiment
• Biochar – Hardwood biochar (oak, cherry, ash
trees), 22 tonnes ha-1
• Soil cores wetted to high gravimetric water
content
• Greenhouse gas fluxes sampled several times
within 72 hours following water addition
• Suppression of N2O n=4
emissions with
biochar addition
(p < 0.001)
• Cumulative N2O
emission reduction
Wetting event
of at least 60 %
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

9. Why?
1. Increased water holding capacity
2. pH change
3. Inhibitory substances in or on biochar
4. Nitrogen immobilisation
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

10. 1. Water holding capacity
• Biochar has a high water holding capacity
• May take up water from soil, inhibiting
denitrification
n=4 • All treatments
wetted to same
% of water
holding capacity
97 % suppression
(WHC)
• Increased WHC
not responsible
Wetting event
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

11. 2. pH change
• Biochar is a high pH material (8.8)
• Soil pH increase - decreases activity of soil
nitrifying/denitrifying bacteria ?
• Or increases reduction of N2O to N2 during
denitrification ? n = 15
• Soil pH increases with biochar
content in field and lab
• pH shift somewhat correlated
with N2O production in lab
• Relative importance of this
mechanism unknown
• Suspect not the ‘key’ mechanism
n=4
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

12. 3. Inhibitory substances
• Biochar may contain heavy metals or other pollutants (PAHs)
• Fresh biochar, emits gases abiotically and contains surface tars
• Our biochar - no metal or PAHs
n=4 above limits
Abiotic?
• Biochar emits carbon monoxide,
carbon dioxide, ethane
• Unknown composition of surface
tars
• But, CO2 flux (microbial activity)
suppressed with biochar
addition following wetting?
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

13. 4. Nitrogen immobilisation
n = 58 n=8
• Biochar may immobilise inorganic N from soil on
or within its structure
• Addition of high C:N ratio biochar to soil may
increase microbial immobilisation of N
However, N2O
emission suppression
with biochar addition
in both low and high
inorganic-N soils:
• Strong immobilisation
effect or
• Another mechanism at
work
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

14. Conclusions
• Biochar suppresses N2O emissions in the lab
following wetting events – limited evidence in
the field
• Increased water holding capacity of biochar
cannot explain N2O suppression
• Further work needed to investigate other
• pH change
potential mechanisms :
• Presence of inhibitory
compounds
• N immobilisation
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

15. Future work
• Effect: In-situ wetting event in the field – try to
replicate laboratory findings
• Water holding capacity: controlled water holding
capacity with biochar in high inorganic-N soil
• Inhibitory substances: qPCR work - expression of
N2O producing enzymes in soil with biochar
• Nitrogen immobilisation: Leaching column
experiment
1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future

16. Thank you for your attention
Acknowledgements:
Jeanette Whitaker, Niall McNamara, David Reay,
Emily Bottoms, Mike Whitfield, Simon Oakley,
Andy Robertson
«Chaque fois que la science avance d'un pas, c'est qu'un imbécile la pousse, sans le faire exprès.»
‘Every time that science advances a step, it’s because a fool pushes it accidentally’
( Emile Zola - La joie de vivre)