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UBC Theses and Dissertations

Field and modeling evaluation of varying durations of short-term grassland set-asides in Delta, British Columbia Hanuszak, Patricia


The Delta Farmland and Wildlife Trust (DF&WT), established in 1993, collaborates with farmers in Delta, British Columbia to enhance degraded agricultural soils. This is achieved by providing funding and support to transition land out of annual crop production and into a short-term (1-4 year) grassland set-aside program (GLSA). Several studies have been conducted to assess select soil properties across various GLSA durations to determine the effectiveness of the DF&WT GLSA program in improving degraded soils. Despite the research conducted thus far, there are still gaps in our understanding of the impacts of 4-year GLSA duration relative to 2- and 3-year durations on soil properties and crop yield due to a lack of consistent sampling parameters and conditions across these studies. The objective of my research was to evaluate the effects of varying durations of GLSAs on soil nutrients and crop yields once the GLSA fields are returned to production. I first conducted an observational study in 2019 to examine soil nutrients and crop yields in the first growing season for former 4-year GLSA fields and paired annual crop rotation fields (ACR). The results from this study, along with associated GLSA research data, were then used to calibrate the Denitrification-Decomposition model (DNDC) for a concurrent simulation of 2-, 3-, and 4-year GLSAs. The observed differences between former 4-year GLSAs and ACR fields were minimal, with no significant effect on crop yield despite variability in soil nutrients between the two field types. However, the calibrated DNDC model 2-, 3-, and 4-year GLSA simulation suggests that GLSAs of increasing duration have the potential to contribute more nutrients to the soil. Further improvement of model performance and replication across a wider range of field baseline characteristics is necessary before definitive conclusions can be drawn regarding GLSA contributions to soil nutrients and crop yields. The results of my field and modeling studies confirm findings of other studies that incorporating GLSA into a crop rotation could enable farmers to reduce nutrient applications for subsequent crops.

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