Black plastic tarps as overwinter soil cover influence soil nitrogen and soil water content on farms in British Columbia

Shifting precipitation patterns in British Columbia (BC), Canada, are increasing the challenge of effective overwinter cover cropping in organic vegetable production and driving the need for alternative soil cover options. As an alternative soil cover, farmers are using plastic silage tarps. There is, however, limited understanding about the impact of overwintered tarps on soil conditions or subsequent cash crops. This study compared the impacts of overwinter plastic tarping with cover cropping or no-tarp conditions on plant available nitrogen (PAN), electrical conductivity (EC), volumetric water content (VWC), and crop yield on organic practicing vegetable farms. Between 2019 and 2021, our study spanned three agricultural regions of BC, with replicated field experiments on two farms and unreplicated plots on 12 additional farms. Plant available nitrogen, EC, and VWC were measured in the spring after tarp removal at all farms. Additional measurements were taken at the experimental farms, including PAN throughout the growing season and crop yield. Spring PAN was 1.8 to 7.8 times greater, and EC was 2.6 times greater under the tarps. Spring VWC varied and was likely related to tarp removal timing. Crop yield was not significantly impacted by overwinter treatment. Data indicate that tarps created lower VWC conditions over the winter until early spring after which time VWC under tarped conditions was higher than soil under cover crops. Our findings indicate that overwintered tarps are an effective soil cover strategy for small-scale organic farmers to conserve soil PAN and influence early spring soil water content under changing precipitation regimes.