UBC Theses and Dissertations
Nitrogen dynamics following incorporation of 3-year old grassland set-asides in Delta, British Columbia Walji, Khalil
The Grassland Set-aside (GLSA) Stewardship Program has been utilized by farmers in the lower Fraser River delta, British Columbia (BC), Canada since 1993. Farmers seed fields in a grass-legume mixture and leave them fallow for up to four years providing feeding habitat for raptors while subsequently improving soil quality. While the wildlife benefits have been well documented, soil quality improvement and benefits to succeeding crops are not well understood. The objective of this research is to quantify the nitrogen benefits to crop production after incorporation of 3-year-old GLSA. A regional experiment was conducted over two years, utilizing production fields transitioning from GLSA, paired with continuously cropped fields (Control) with matching management. A controlled field experiment was also conducted on a single 3-year-old GLSA, comparing fertilizer types, rates and timing of incorporation. In each experiment, soils were sampled every 10-14 days for ammonium (NH4) and nitrate (NO3) while ion probes, installed near the rooting zone tracked plant available nitrogen (PAN) throughout the season. The results from the regional experiment were confounding, in 2015 showing GLSA supplied an additional 18 kg PAN ha-1 compared to Control but showing no PAN benefits in 2016. While the PAN supplied by the GSLA remained consistent each year, the amount supplied by Control in 2016 was relatively higher. In both years, PAN following GLSA peaked later in the season than the Control, likely due to immobilization of nitrogen facilitated by incorporation of biomass with a high carbon to nitrogen (C:N) ratio. Immobilization also delayed NH4 release in the controlled experiment for up to 21 days and NO3 56 days. The controlled experiment also highlighted the importance of fertilizer type to subsequent PAN, showing synthetic treatments consistently supplied more PAN than Organic. Results from this study suggest that 3-year-old GLSAs can potentially improve PAN to subsequent crops; however, benefits provided by GLSA in Delta are dependent on a number of factors which include the C:N ratios of biomass, timing between incorporation and crop planting, precipitation and temperatures, and fertilizer type, all of which impact the timing and quantity of PAN and thus its utility to subsequent crops.
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