Biochar suppression of N 2 O emissions from an agricultural soil: effects and potential mechanisms Sean Case Dr Jeanette Whitaker, Centre for Ecology and Hydrology Dr Niall McNamara, Centre for Ecology and Hydrology Dr David Reay, University of Edinburgh

Overview 1.Introduction – soil N 2 O emissions and biochar 2.Observed effect of biochar addition on soil N 2 O emissions 3.Investigating the mechanisms N stable isotope experiment 5.Conclusions 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar Dynamotive Energy Systems, (2009)

Soil N 2 O production Use NH 4 + and O 2 Activity peaks at mid range (50 – 60 %) of water filled pore space NH 4 + (Ammonium) NO 2 - NO 3 - (Nitrate) NO N2ON2O N2N2 Nitrifying bacteria Denitrifying bacteria Use NO 3 - and C Anaerobic conditions Activity increases as soil approaches saturation N2ON2O 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

Biochar addition and soil N 2 O emissions – a (very) brief history Yanai et al., (2007), Soil Sci. and Plant Nut., 53, Biochar addition observed to suppress soil N 2 O emissions in laboratory Very few published papers showing consistent N 2 O suppression following biochar application to field N 2 O suppression put down to several different mechanisms Soil aeration pH change Substances on biochar (e.g. ethylene, α-pinene) N immobilisation 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

Field experiment: Biochar – Hardwood biochar (400°C), 50 tonnes ha -1 Crop – Miscanthus Giganteus X (Elephant grass) Soil – Sandy loam, low inorganic-N Seasonal greenhouse gas measurements Significant suppression in first measurement Sporadic measurements? Not timed with rain events? n = 5 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

Laboratory experiment Soil cores wetted to high gravimetric water content Cumulative N 2 O emission reduction of at least 49 % within 48 hours Adapted from Case et al. (2012), Soil biology and Biochemistry, in press Wetting event n = 4 Miscanthus crop soil Wetting event n = 5 Arable soil – recently N fertilised 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

1. Increased soil aeration ? All treatments wetted to same % of WHC/WFPS Still suppression with increasing biochar content Increased soil aeration is not the key mechanism Biochar has a higher water holding capacity (WHC) than soil May increase soil aeration, inhibiting denitrification 97 % suppression Wetting event n = 4 Adapted from Case et al. (2012), Soil biology and Biochemistry, in press 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar Miscanthus crop soil

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 N 2 O to N 2 during denitrification ? Soil pH increases with biochar content in field and lab pH shift not strongly correlated with N 2 O production Suspect not the ‘key’ mechanism n = 15 Soil incubated with biochar in the field one year after application 3. Ethylene Our biochar not found to produce ethylene 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

4. Nitrogen immobilisation ? Lower N 2 O evolution - sorption of ammonium or nitrate to the surface of biochar? (Spokas et al., 2011) Especially in biochar created at low temperatures with high concentrations of surface oxygen groups Miscanthus crop soil (initially low-N) Arable crop soil (initially high-N) n = 4 n = 5 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

4. Nitrogen immobilisation ? Lower N 2 O evolution - sorption of ammonium or nitrate to the surface of biochar? (Spokas et al., 2011) Especially in biochar created at low temperatures with high concentrations of surface oxygen groups What is the effect of biochar addition on the soil N cycle? 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

Arable soil – rapeseed/winter wheat rotation 2 % Biochar added to half of cores Water added to reach 70% Water Filled Pore Space Ammonium nitrate fertiliser added (0.1 mg g -1 N), 10% 15 N enrichment Measurements for 6 days NH 4 14 NO 3 Soil + biochar NH 4 15 NO 3 Soil 15 N stable isotope experiment ‘Mirrored’ 15 N addition treatments Label: Ammonium Nitrate Analysed with Monte Carlo (Müller et al., 2007) or FLUAZ methods (Mary et al., 1998) 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

Humus Plant residue (+ biochar) Ammonium (NH 4 + ) Nitrate (NO 3 - ) Microbial biomass Ammonia (NH 3 ) N2ON2N2ON2 Gross mineralisation Volatilisation Nitrification Immobilisation Remineralisation Denitrification Additional analyses: pH, total CN, qPCR genetic analyses Direct microbial assimilation of plant residue N Adapted from Mary et al., (1998) The N cycle 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

Humus Plant residue (+ biochar) Ammonium (NH 4 + ) Nitrate (NO 3 - ) Microbial biomass Ammonia (NH 3 ) N2ON2N2ON2 Gross mineralisation Volatilisation Nitrification Immobilisation Remineralisation Denitrification Directly measured Calculated Additional analyses: pH, total CN, qPCR genetic analyses Direct microbial assimilation of plant residue N Adapted from Mary et al., (1998) Organic-N The N cycle 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

Preliminary results N 2 O emissions suppressed with biochar CO 2 emissions increased with biochar n = 8 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

Conclusions 1.Addition of this biochar suppresses N 2 O emissions in the lab following wetting events – limited evidence in the field 2.Increased soil aeration, pH change or ethylene production are not the key mechanisms to explain N 2 O suppression in this case 3.Biochar addition may immobilise soil inorganic-N due to physical/chemical nature of biochar surfaces, could this explain N 2 O suppression in this case? 4.Stable isotope studies are needed to investigate this 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

Acknowledgements: Jeanette Whitaker, Niall McNamara, David Reay, Emily Bottoms, Mike Whitfield, Simon Oakley, Andy Robertson Thank you 1. Soil N 2 O 3. Effect 4. Mechanisms5. 15N Exp. 6. Conclusions 2. Biochar

References 1.Case S. D. C., McNamara N. P., Reay D. S., Whitaker J., 2012, The effect of biochar addition on N 2 O and CO 2 emissions from a sandy loam soil - The role of soil aeration. Soil biology and Biochemistry, in press 2.Mary B., Recous S. and Robin D., A model for calculating nitrogen fluxes in soil using 15 N tracing. Soil Biology and Biochemistry 30, Müller, C., Rütting, T., Kattge, J., Laughlin, R.J., Stevens, R.J., Estimation of parameters in complex 15N tracing models by Monte Carlo sampling. Soil Biology and Biochemistry 39, 715– Spokas K. A., Novak J. M., Venterea R. T., Biochar’s role as an alternative N- fertilizer: ammonia capture. Plant and Soil 350, Yanai Y., Toyota K., Okazaki M., Effects of charcoal addition on N 2 O emissions from soil resulting from rewetting air-dried soil in short-term laboratory experiments. Soil Science and Plant Nutrition 53, 181.

Future work 1.Inducing high N 2 O emissions in the field via water addition 2.Ongoing biological work (qPCR looking at NirK and AmO enzymes) N stable isotope experiment – finish analyses and develop further hypotheses