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Please see my June 2012 presentation for updated results and if you are already familiar with biochar! …

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.

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  • Say PhD is BASED AT CEH
  • Mention that biochar is important for academics AND with policy makers
  • Say that you will continue these measurements for another year
  • Say that I cannot prove this

Transcript

  • 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 work1. Soil N2O 2. Biochar 3. Effect 4. Mechanisms 5. Investigation 6. Future
  • 3. Soil N2O productionNitrifying 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 saturation1. 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 – ifAdapted from Spokas, (2010) applied to soil1. 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 biocharYanai 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 20111. 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 immobilisation1. 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 event1. 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=41. 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 work1. 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 immobilisation1. 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 experiment1. 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 dun pas, cest quun 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)