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Examining selected soil properties on the lower Fraser River delta following four-year grassland set-aside Porter, Maria Teresa


Intensive cultivation, combined with poor drainage and heavy precipitation, has led to soil degradation in the lower Fraser River delta region (LFRD) of British Columbia, an important agricultural area of the province. The Delta Farmland & Wildlife Trust (DF&WT), a non-profit organization in the LFRD, partners with farmers to implement conservation practices such as grassland set-asides (GLSA). Farmers seed fields with grasses and clover and leave them to rest for one to four years. GLSA programs have been used worldwide, but program goals, GLSA duration, and the geographical contexts of these programs vary widely. The objectives of this study were to evaluate the effects of three- and four-year GLSAs on selected soil properties in the LFRD. Samples were collected from seven operating farm sites in 2018, and five in 2019. Sites were classified as productive or unproductive, and each comprised of a GLSA seeded in 2015 and an adjacent field under annual crop rotation (ACR). Previously collected data from 2015 and 2016 was included in the analyses. At depth 0–7.5 cm, GLSA had greater aggregate stability than ACR at productive and unproductive sites. GLSA had significantly lower bulk density and higher aeration porosity than ACR at depth 0–7.5 cm after the three years, but not after four years. The improvements to aggregate stability under GLSA were observed in 2015 and 2016 and were maintained thereafter. In 2018 and 2019, at depth 0–7.5 cm, aeration porosity decreased at ACR but not at GLSA. Total carbon and total nitrogen were significantly higher in GLSA than ACR after four years only at depth 30–45 cm. GLSA did not yield significant improvements in soil properties at depths below 7.5 cm, nor did they fully restore compacted soils. Still, GLSA remain a useful management practice for farmers in the LFRD and can improve soil quality in the first year of GLSA while protecting and maintaining soil structure from further degradation in the third and fourth years.

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