Engil Pereira, Emma Suddick , Johan Six University of California, Davis

1. On-farm field experiment to investigate biochar effects on soil structure and N2O emissions Engil Pereira, Emma Suddick, Johan Six University of California, Davis 2012 US Biochar Conference – Sonoma State University, Rohnert Park, CA. July 29 – August 1, 2012

2. Outline • Biochar production and study site: Dixon Ridge Farm • Soil structure – Potential for additional C sequestration • N2O emissions - Link with N2O consumers • Concluding remarks

3. Dixon Ridge Farm • Winters, CA • Organic walnut farm and processing facility • BioMax 50: Waste management and energy production • Savings: $45,000 / year • Closing the loop: Biochar! Russ Lester, co-owner of Dixon Ridge Farms

4. Walnut biochar

5. Study site • Established in June 2010 at Dixon Ridge Farm • Area: 12 acres • 4 treatments with 3 replicates each • Compost and cover crop Tree Row Tractor Row Sampling Locations:

6. Experimental Approach GHG emissions (CO2 and N2O) Soil moisture content Biochar + Soil Soil mineral N Soil structure (aggregation) Soil microorganisms Soil pH

7. Soil structure: Aggregation Key properties Aggregates -> Protected fractions: C sequestration Maintenance of soil moisture and aeration Soil microorganisms Silt and Clay (< 53 μm) Microaggregates (53 - 250 μm) Small Macroaggregates (250 - 2000 μm) Large Macroaggregates (> 2000 μm)

8. Biochar and soil aggregates • Due to surface charge, biochar may promote soil aggregation • This mechanism may increase C sequestration

9. Large Macroaggregates (> 2000 μm) Small Macroaggregates (250 - 2000 μm)

10. Microaggregates (53 - 250 μm) Silt and Clay (< 53 μm) - Unaggregated

11. Biochar and soil aggregates • Biochar did increase soil aggregation when combined to compost during the first year of study; • During the second year of observations, macroaggregates were disrupted, freeing microaggregates and silt and clay particles. • In conclusion, in this study biochar did not sustain an increase in soil aggregation and therefore additional C sequestration.

12. Potential to reduce N2O emissions 60% By increasing soil CEC,biochar will lead to NH4+ adsorption and prevention of nitrification. N2O N2O N2 NO3- NH4+ Nitrification Biochar Denitrification Leaching

13. N2O sampling • Samplings happen once a week • Or, for 7 days after an event (Irrigation, fertilization, precipitation). Tree Row Tractor Row

14. N2O emissions – 1st year Tree Row Control Biochar Tractor Row

15. N2O emissions – 2nd year

16. Link with N2O consumers • Pot trial study using walnut shell biochar • Extraction of microbial DNA • qPCR: Quantification of functional genes • N2O reduction to N2 amoA nirS nosZ NO N2O N2 NH4+ NO3- NO2- nirK N2O producers N2O consumers

17. Concluding Remarks • Decreases in N2O emissions, when observed, happen after wet events (irrigation or precipitation) and in the tree row • Such decreases may be associated to an increase in the bacterial abundance that performs the reduction of N2O to N2 • Biochar closes the loop at Dixon Ridge Farm with economic and environmental benefits.

18. Acknowledgements • California Energy Commission • CNPq - Brazil • Six lab members, in special to Rafaela Conz, Garret Heinz and NeeleHolzenkaempfer