Nitrous Oxide Emissions in Switchgrass Areas

Introduction

Abstract:

Our goal is to understand how switchgrass yield and nitrous oxide emissions change over changing nitrogen rates.

Objective: To determine the impact of nitrogen rate on nitrous oxide emissions from soils planted in switchgrass and to monitor the controlling environmental factors of nitrous oxide production.

Switchgrass has large potential as a bioenergy crop for the Great Plains:

  • High yields
  • Non-invasive
  • Protects soil, water, and air quality
  • Sequesters atmospheric carbon
  • Creates wildlife habitat
  • Returns marginal farmland to production
  • Low agricultural inputs: equipment readily available, low herbicide requirements
  • However this crop needs nitrogen fertilizer to attain maximum yield. When soil moisture is high (after a rainstorm for instance) pore spaces within soil aggregates are saturated creating anaerobic sites for denitrification to occur. Through denitrification soil microbes convert excess nitrogen (N) from the fertilizer to nitrous oxide (N2O), a potent greenhouse gas.

    Nitrous Oxide

  • 300 times the global warming effect of CO2
  • Remains in atmosphere for 100-120 years
  • Destroys ozone
  • Microbial soil release 75% of US N2O emissions
  • To improve nitrogen efficiency nitrous oxide concentrations and yield rates need to be analyzed to help switchgrass crop management, protect water resources, and minimize greenhouse gases.

    Experimental Method

    The nitrogen fertilizer distribution on plot divisions

    Method:

  • Gas samples were extracted using static chambers
  • The gas samples were run through a gas chromatograph to determine the nitrous oxide concentration
  • Soil samples were taken using a soil probe to 15cm depth
  • KCl extraction was performed to determine the inorganic nitrogen remaining in the soil
  • Volumetric soil moisture was measured at time of sampling using soil moisture probe

  • Static Chamber


    Soil Probe


    Gas Chromatograph


    KCl Extraction

    Results and Discussion

    Fig. 1 Daily N2O-N flux in switchgrass throughout the 2014 growing season. Vertical bars across the top represent the amount of precipitation. Black arrow represents urea fertilizer application.


    Fig. 2 Soil nitrogen measured from 0-5cm depth for each Nrate, with standard error.



    Fig. 3 Average soil moisture on the experimental site


    Fig. 4 Cumulative N-N2O flux in switchgrass during 2014 growing season. Bars represent standard error.



    Fig. 5 The mean cumulative fluxes per treatment rate, with standard error.





    Fig. 6 Mean emission factors per treatment.

    Conclusions

  • The N2O flux increased substantially as the Nrate increased until 100kgN/ha, after which the change in flux was statistically insignificant.
  • The largest N2O fluxes occurred when the soil moisture and soil nitrogen were high.
  • There was significant loss of N at high Nrates; the largest being 4.54% which occurred at 150kgN/ha.

  • About Me

      Meaghan Dustin

    • McGill University
    • Bioresource Engineering U3
    • Hometown: Ottawa, Ontario, Canada
    • Hobbies: McGill Woodsmen Team, Skiing, Skating, Anything Outdoors!

    REU Experience

    Manhattan, KS

    Tuttle Creek, Pillsbury Crossing, Konza Prairie



    Hutchinson, KS

    Wheat Farm

    Underground Salt Mine & Cosmosphere



    Kansas City, MO

    World War Memorial



    Wyoming, OK

    Fourth of July!



    Cawker City, KS

    World's Largest Ball of Twine



    Denver, CO

    Red Rock State Park

    Golden

    Denver Zoo

    Acknowledgements

    • This material is based upon work supported by National Science Foundation Grant: REU Site: Summer Academy in Sustainable Bioenergy; NSF Award No.: SMA-1359082, awarded to Kansas State University.
    • Dr. Charles W. Rice, Kansas State University
    • Andrew McGowan, NSF IGERT, Kansas State University

    References

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