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University of Manitoba Faculty of Agricultural and Food Sciences Department of Plant Science

Can Organic Crop Production
be a N2O Mitigation Strategy?

Megan Westphal, Martio Tenuta, Martin Entz

This article is a brief summary of the project. View Megan's poster for more details.

Figure 1. Megan Westphal collects gas chamber samples from the Glenlea Long-Term Rotation Study for her Master's work on N2O emissions.

Introduction

Nitrous oxide (N2O) is now the third most important greenhouse gas (GHG) due to its effect on global climate change. N2O has 300x the global warming effect of CO2. Agriculture is the major contributor of N2O emissions to the atmosphere due to nitrogen (N) additions to the soil, primarily from the use of synthetic N sources applied before the crop can utilize large amounts of N.

Perennial legumes (i.e. alfalfa) are used in organic systems to provide N and other nutrients to the soil for subsequent cash crops. However, the amount of N2O emitted from organic systems is not well understood.

Objectives

  • To determine N2O emissions from perennial alfalfa with emphasis on the plow down phase.
  • To determine N2O emissions from organic wheat following alfalfa in an organic perennial rotation as
    well as conventional wheat and soybean in a grain-only rotation..

Methodology

  • Study site at the University of Manitoba's Glenlea Long-Term Organic Crop Rotation Study near Winnipeg, MB.
  • Vented static chamber method.
  • Soil and agronomic measures were also obtained using WET sensor.
  • Gas chromatography for gas analysis for N2O.
Table 1. Crop type and corresponding nitrogen (N) source.
Crop N Source
Conventional Wheat Urea (46-0-0) (101 kg/ha N, 2014 & 2015)
Conventional Soybean Biological nitrogen fixation
Organic Wheat 2013 &2014 fall plow down alfalfa
Organic Alfalfa Biological nitrogen fixation & composted cattle manure (2014 only)

Results

N2O flux was tracked daily, allowing for emission episodes to be identified. Conventional wheat had larger emission episodes than organic wheat, and emissions were generally low for both conventional soybean and organic alfalfa. See the poster for daily N2O flux data, including emission episodes.

Conventional wheat and soybean had greater cumulative N2O emissions than both organic wheat and organic alfalfa (Figure 2). N2O emissions per unit of yield were also lower for organic wheat than for conventional wheat (Table 2).

Figure 2. Organic & conventional wheat, organic alfalfa & conventional soybean 2014 crop year cumulative N2O emissions. Error bars indicate standard error.

 

Table 2. 2014 average spring wheat yield, protein content (%), and yield scaled emissions for conventional and organic cropping systems.
Management Yield (kg/ha) Protein content (%) Yield-scaled Emissions (g N2O-N / kg grain)
Conventional 3488 14.5 177
Organic 2450 13 66

View the poster for more results and discussion.

Conclusions

  • The use of alfalfa as a N source in organic cropping systems emitted less N2O than the conventional urea fertilizer.
  • Wheat yields in organic cropping system were approximately 30% lower; however yield scale emissions were half that of conventional wheat yield scale emissions.
  • Higher N2O emissions in the fertilized treatments were attributed to higher amounts of available inorganic N early in the growing season in the conventional plots.
  • Higher N2O emissions in the 2015 plough down alfalfa crop compared with the 2014 alfalfa crop were attributed to greater soil moisture content in 2015.
  • The use of alfalfa in organic cropping systems could be used as a N2O mitigation strategy; however, further research is needed to increase yields in organic systems.

Copyright and Liability

This page created September 2016.