Does Conversion to Perennial Systems Affect Net Greenhouse Gas Emissions and Soil Health?
Siobhan Stewart, Aaron Glenn, Mario Tenuta, Brian Amiro, Department of Soil Science, University of Manitoba, Winnipeg, MB R3T 2N2
3 Site Description and Design:
1 Objective:
2 Background:
• There are observed greenhouse gas (GHG) increases in the
atmosphere, with agriculture responsible for 10% of
Canada’s emissions - mainly nitrous oxide (N2O) and
methane (CH4) gas
• N2O has a GHG potential that is 300 times more powerful
than carbon dioxide (CO2), and is predominantly lost from
manure and fertilizer application to agricultural fields
• Agricultural soils have the potential to be net carbon sinks,
through C sequestration, when producers adopt perennials
in their crop rotations
• Prairie producers have converted to annual cropping
systems from perennial crops due to changing market
economies, alternative crop demand, and use of biofuels as
an alternate energy source
• TGAS MAN is the only site in Western Canada that
measures surface GHG continuously throughout the year
• Short-term benefits of alfalfa in annual crop rotations on net
GHG emissions and soil health is not understood
• This project will help determine the short-term inclusion
impact of perennials (alfalfa) in an annual cereal/oilseed
cropping system
To investigate the short-term impacts of a perennial forage (alfalfa)
in an annual cereal/oilseed crop rotation on C and N cycling in
agricultural soils and influence on net GHG emissions (CO2 and
N2O) and soil health.
CO2
• TGAS MAN is located 20 km south of Winnipeg at the University of
Manitoba’s National Centre for Livestock and the Environment (NCLE)
• The study site consists of four 4-hectare plots on Red River and Osborne clay
with two crop treatments imposed: cereal/oilseed and alfalfa (Figure 1)
• After decades in annual rotation, Plots 1 and 4 were sown to alfalfa in May
2008, while Plots 2 and 3 were planted to a spring wheat crop for the 2008
growing season
• High Erucic Acid Rapeseed will be sown onto Plots 2 and 3 in Spring 2009
Harvest
Alfalfa
Wheat
establishment
maturation
Photosynthesis
and growth of
wheat
4 Methodology:
• Micrometeorological instrumentation at the site measures
surface GHG emission fluxes continuously throughout the
year from four experimental plots
• A highly sensitive tunable diode laser (TGA100A Campbell
Scientific Inc., Photo 1) measures CO2 and N2O
concentrations of the gases emitted from the soil (Photo 2)
• Fluxes of each gas are determined from the gas concentration
difference between two heights (Photo 3) and the turbulent
transfer of gases by wind
• A weather station (Photo 4) provides supporting
environmental measurements, such as soil temperature, soil
moisture content, precipitation and solar radiation inputs, that
influence GHG emissions
• Soil samples are taken monthly during the growing season to
distinguish inorganic nitrogen as a driver of N2O emissions
and indicator of soil health
Figure 1. Diagram of site layout and instrumentation location (A) and cropping treatments
(B) at the TGAS MAN site
N2O
Fertilizer application
5 Findings:
N2O
• The beginning of the 2008 growing season (Figure 2) shows a loss of soil
carbon from the alfalfa plots, due to the slow establishment of alfalfa in
the first year and low N2O emissions due to the absence of N fertilizer
addition with alfalfa at seeding
• In contrast, the spring wheat took up C, drawing in CO2 with plant
growth, and shows a burst of N2O emissions in early June following
fertilizer application
Post-harvest
Spring
Thaw
• As the summer progressed, soil became a C sink as alfalfa established,
and with wheat maturation and harvest, it became a C source
May 1
Nov 21
Figure 2. Nitrous oxide (N2O) and carbon dioxide (CO2) fluxes from both treatments
throughout the 2008 growing season (100 g ac-1 N2O-N is equivalent to 1/10 lbs Nac-1)
TGA
• The project continues to determine the short-term effects of perennials in
cropping rotations and the benefits alfalfa offers for carbon sequestration,
soil health improvement, and the reduction of N2O emissions
GI
SAT
Photo 1. Trace Gas Analyzer (TGA) with
datalogger and reference gas cylinders
Photo 2. Wheat plot with gas monitoring station
and sonic anemometer-thermometer (SAT)
Photo 3. Alfalfa plot with gas monitoring
station and gradient intakes (GI)
Acknowledgements: Thank you to Jenna Rapai and Brad Sparling for site upkeep and technical support and to Robert Janzen for summer site maintenance.
Photo 4. Weather station
For more information about this project, please contact
Siobhan at [email protected]