Soils and Climate Change: Managing C

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Soils and Climate Change Managing C N
John M. Duxbury Dept. Crop and Soil
Sciences Cornell University jmd17_at_cornell.edu
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Anthropogenic Carbon Dioxide History
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Soil C Sequestration

• Requires switch to permanent no-tillage
• Average SOC sequestration rate of 0.35 t/ha/y
  when no-tillage practice is adopted
• SOC sequestration is finite (expect 20-30 yr in
  USA) and reversible

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Soil C Sequestration

• Potential varies with current soil OC level and
  texture

• Difference between minimum and maximum SOC levels
  is manageable OC
• M1 no-tillage
• M2 reduced tillage

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Soil C Sequestration
But.. Switch to no-tillage also causes
changes in emissions of N2O and CH4 due to -
increased N fertilizer inputs - soil conditions
that promote denitrification Example
for rainfed corn in USA
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Estimated Effect of Tillage Practice on Relative
GWP from Rainfed Corn in USA

is CO2-Ce source - is CO2-Ce sink

• for soybean rel. GWP changes from -303 to -138

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Uncertain Long-Term GWP Effect of No-Tillage

• The balance of permanent positive or negative GWP
  components associated with no-till agriculture
  will determine the long-term GWP outcome

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Soil N Management
Goal Improve N efficiency to reduce inputs and
environmental losses

• Utilize N Decision Support Systems
• Soil testing - including real time, e.g.
  pre-sidress nitrate test (PSNT)
• Extension expertise
• Participate in nutrient management planning
  programs
• Computer based decision tools
• - precision agriculture with variable rate
  technology

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Soil N Management

• Follow Recommended Practices
• Strive for balance and synchrony between
  available N supply and crop demand

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Effect of N Timing and Tillage on N2O Emissions
from Continuous Maize
simulated 2 in. rainfall event clay loam soil
Tan et al., in review
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Soil N Management

• Follow Recommended Practices
• Incorporate or inject N into soil to avoid
  volatilization of NH3 and N2O from urea
  fertilizer and animal manures
• Use mixtures of NO3- and NH4- N sources to
  provide rapidly and more slowly assimilated N
  forms, including mixtures of inorganic and
  organic sources
• Capture NO3- that is not used by the main crop by
  using cover crops important with manure and when
  a production problem reduces crop yield and N
  recovery

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Soil N Management

• Follow Recommended Practices
• Dont forget manure management
• - Fully anaerobic CH4
• - Partially anaerobic N2O
• - Aerobic neither

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Summary

• C sequestration in soil requires a change to
  permanent no-tillage, where annual C
  sequestration rates average 350 kg/ha/yr
• Soil C sequestration benefits of no-tillage may
  be largely offset by increased emissions of N2O
  and CH4 needs more research
• The principles of sound field level N management
  are well known these can be promoted within the
  context of reducing greenhouse gas emissions and
  other environmental effects, in addition to
  profitability
• Nitrogen management should also reduce off-site
  losses of NH3 and NO3- from the system as these
  can lead to additional generation of N2O

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Global Carbon Dioxide Budget

• Only 42 of emitted CO2 is
• retained in the atmosphere

• CO2 from land conversion
• is 25 of fossil fuel source

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