UBC Theses and Dissertations
The effects of 2- and 3-year grassland set-asides on plant available nitrogen and greenhouse gas emissions in Delta, British Columbia Fausak, Lewis Karl
Since 1993, the Grassland Set-Aside (GLSA) Stewardship Program has incentivized farmers in the western Fraser River delta, British Columbia, Canada to plant a grass-legume mixture on active cropland and leave it fallow for 1-4 years to improve soil quality and provide wildlife habitat. Benefits to wildlife are well documented, but not well understood for soil quality. Study objectives were to quantify the effects of 2- and 3-year GLSAs on plant available nitrogen (N), crop production, soil quality, and greenhouse gas emissions. A field experiment was established in 2017 on a productive and unproductive field with fertilizer treatments (0 and 80-kg N ha⁻¹) compared across GLSA treatments (i) AC – GLSA biomass removed and (ii) 2G – 2-year-old GLSA biomass was incorporated, and seeded with beans. In 2018, fertilizer treatments (0 and 100-kg N ha⁻¹) were compared across the same GLSA treatments and (iii) 3G –3-year-old GLSA biomass was incorporated, and seeded with potatoes. Active carbon (POXC) and aggregate stability (MWD) were measured 3 times per growing season, plant available nitrogen (PAN) was sampled every 2 weeks from May-September, and carbon dioxide, methane, and nitrous oxide were measured weekly from May-September and every 3 weeks from October-April. MWD increased in 2G and 3G in the year of incorporation relative to AC and POXC increased for 3G relative to AC and 2G. Average seasonal PAN did not differ across treatments but was higher earlier in the season for 2G. Bean yields were greater in 2G compared to AC in the productive field, but otherwise crop yields did not respond to GLSA. N content of bean crops did not differ between treatments, was higher for 3G compared to AC in the unproductive field. 2G increased carbon dioxide emissions in 2018, but 3G only increased emissions in the 2018 production season. Nitrous oxide emissions treatments were higher in 2G treatments across all seasons, but lower in 3G treatments in the 2018 production season. Results suggest 2- and 3-year GLSAs do not increase average PAN to subsequent crops, but increase PAN earlier in the season, and increase crop yield and quality depending on subsequent crops.
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