The frequency of days with poor soil trafficability across the Canadian Prairies was determined from simulated soil moisture at soil polygon level during the growing season (April to September) with the Versatile Soil Moisture Budget (VSMB) model. Each soil polygon had a pre-determined critical soil moisture threshold in the first layer (0–5 cm) to trigger poor trafficability. The assessment of soil trafficability was limited to those polygons with good suitability rating for growing grain crops. For each of May, July and September, the polygon modelled soil moisture values were boot strapped into three percentile categories to reflect the highest risk (25th percentile), average conditions (50th percentile) and better than average conditions (75th percentile) for the entire climate period (1971 to 2000). We found that on average, soils with higher clay content (mostly those from eastern Manitoba, the northern fringes of the agricultural zone coinciding with the boreal forest zone and the Alberta Peace River region) had 5 to 9 days of poor trafficability at seeding time (May). In July, the zone with poor soil trafficability (close to two weeks) expanded northward to the Peace River Region of Alberta, northern Saskatchewan and eastern Manitoba. At harvest time (September), poor soil trafficability (>10days) was concentrated in eastern Manitoba which also had the most days with poor soil trafficability at the start and mid-season months. The wet phase represented by the 75th percentile category showed that 10–14 days of poor trafficability can be expected on soil polygons with heavy textures. There were fewer days (1–4) with poor trafficability during dry years (the 25th percentile binned values). The soil trafficability maps generated from this study are a baseline for comparing trafficability levels under climate change scenarios and for planning agricultural activities.
