US agricultural GHG emissions: challenges and opportunities for mitigating plot scale vs. whole farm (and larger) emissions. Delgrosso
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US agricultural GHG emissions: challenges and opportunities for mitigating plot scale vs. whole farm (and larger) emissions. Delgrosso

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Presentation from the WCCA 2011 conference in Brisbane, Australia.

Presentation from the WCCA 2011 conference in Brisbane, Australia.

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  • 1. US Agricultural GHG Emissions: challenges and opportunities formitigating plot scale vs. whole farm (and larger) emissions Steve Del Grosso, et al.
  • 2. OUTLINE• US Agricultural GHG Sources and Sinks• GHG intensity and Nitrogen Use Efficiency• Scaling paradox• Farm system emissions: conventional vs. organic• To what extent does Jevon’s paradox apply?
  • 3. US Agricultural GHG Emissions 300 200Tg CO2 eq. 100 0 -100 Soil CO2 energy use Soil N2O enteric CH4 manure CO2 CH4+N2O
  • 4. x F lu etUS Cropped Land Δ Soil C N ils So ic an rg O d te ga ri RP Ir C & o ps Cr er th O s1 in ra ay lG H al Sm p s& ro n C tio ow ta R Ro i n re stu / Pa ay H 40 30 20 10 0 -10 -20 -30 -40 Tg CO2 eq. yr-1
  • 5. IPCC METHODOLOGY FOR N2O Direct Emissions Indirect EmissionsSynthetic N Organic N Residue N NH3 & NOx Volatilization (10% Synthetic N, 20% Manure N) NO3- Leaching/Runoff (30%) Mineral Soils Organic 0.75% Soils 1% Temperate: 8 kg N2O-N/ha1.0% (applied N) Subtopics: 2.0% (PRP N) 12 kg N2O-N/ha Atmospheric N2O
  • 6. Uncertainty Framework InputUncertainty PDF Input PDF Simulation Scaling ResultsUncertainty Model Uncertainty PDF 95% Confidence Input Interval PDFUncertainty Structural Uncertainty
  • 7. CO N2O gN ha-1 d-1 dr CO yla nd 0 5 10 15 20 25 30 35 40 dr w yla he nd at NE cr op dr pi yl ng an d wh ea M NE t Ic or gr IPCC n/ as so s y/ measured al DAYCENT fa lfa CO TNCO co irr irr ig rn ig at ed at ed co co rn rn /b ar le CO y gr O as nt ar s io co Site Level Mean N2O Emissions rn PA cr op perform better than simple models PA gr as s At plot level, process based models usually av er ag e
  • 8. As scale increases, simple models become more reliable US major Crops N2O 0.6 0.4 Tg N 0.2 0.0 DAYCENT Lower bound DAYCENT Upper bound IPCC Global Anthropogenic N2O 8 6 Tg N 4 2 0 Top Down lower bound Top down upper bound IPCC Del Grosso et al. 2008
  • 9. as scale decreases, CIs get wider 1200% 1000% 800% CI Width 600% 400% 200% 0%20 25 0 5 10 15 20ion Regional N2O Emisisons (gG N) Most of this uncertainty is due to model structure Del Grosso et al. 2010
  • 10. US Corn, Wheat, Cotton, Sorghum Yields and N Fertlizer Applied N fert Tg45 grain yield Tg * 1040353025201510 5 0 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 0919 19 19 19 19 19 19 19 19 19 20 20 20 20 20 20 20 20 20 20 NUE is increasing
  • 11. GHG Intensity for N2O from US Corn and Soy 0.22 g CO2 eq./ g grain 0.29 gCO2/ g grain GHG intensity is decreasing
  • 12. 0.12 Theoretical GHG IntensityN2O CO2-C eq./grain-C 0.1 0.08 0.06 0.04 0.02 0 0 5 10 15 20 25 30 35 N inputs g N m-2
  • 13. 0.12 DayCent GHG Intensity N2O CO2-C eq./grain-C 0.1 0.08 0.06 0.04 0.02 0 0 5 10 15 20 25 30 35 N inputs g N m-2 Irrigated Corn CO - N2O GHG Intensity 0.06 0.05CO2-C eq/grain-C 0.04 0.03 0.02 0.01 0 0 N NT no- corn 0-N, corn NT 0 N 0-N, corn Hi-N, no- High Hi-N, High N NT corn N CT till conventional- till conventional- till till
  • 14. Global Warming Potential CO2 eqvt (kg CO2eqvt ha-1 y-1)System Soil C N2O Energy GHGnetNo-Till 0b 303 b 807 1110 bChisel Till 1080 a 406 ab 862 2348 aOrganic -1953 c 737 a 344 -872 c Cavigelli et al. 2009
  • 15. Greenhouse Gas Intensity GHGnet Crop Yield GHGISystem (kg CO2eqvt ha-1 y-1) (Mg ha-1 y-1) (kg CO2eqvt Mg grain-1)No-Till 1110 b 7.25 a 153 aChisel Till 2348 a 7.14 a 330 aOrganic -872 c 5.12 b -169 b Cavigelli et al. 2009
  • 16. California Annual Grassland Compost Addition Study Change in System Carbon due to Enhanced Production 1800 1600 Compost carbon 1400 Change in system carbon 1200g C m-2 1000 800 600 400 200 0 2008 2012 2016 2020 2024 2028 The change in system carbon is the total system carbon from the compost simulation minus the compost carbon. This represents the carbon sequestration due to enhanced plant production. Updated 13 July 2011
  • 17. California Annual Grassland Compost Addition Study
  • 18. Current US Farming Practices and Mitigation Outlook50% employ conservation tillage or no tillSmall minority use improved fertilizersMost farmers do not greatly exceed recommended ratesSlow release fertilizers and nitrification inhibitors aremore effective in the drier western USPractices that reduce direct N2O are also likely to reduceindirect N2OUrease inhibitors may increase direct N2OModel results suggest that rates could be reduced withstabilized N sources, but need observations to verify
  • 19. Jevon’s Paradox• Many assume that increases in efficiency will solve our problems• Is increasing yield but keeping emissions constant (or decreasing) the same as deceasing emissions but keeping yield constant (or increasing)?• Probably not – as efficiency increases people tend to consume more• So absolute emissions will continue to increase
  • 20. Summary and Issues• Currently available technologies can reduce emissions (in at least some regions) but incentives are needed• at small scales, fluxes can be measured precisely and accurately, but models usually do better at large scales.• Benefits of stabilized N likely scale up to the farm system level and include improved water and air quality• However, entity level observations are not feasible and model uncertainty at the farm scale is huge• If GHG intensity is minimized then yields would plummet• If increasing NUE is the goal then BAU is sufficient• If the goal is to increase yields and decrease absolute emissions then things get challenging• Need to define life cycle analysis boundaries carefully