Outdoor hog-rearing operations are of interest for both producers and consumers due to high product quality, animal welfare status, and low input and potential environmental risks. However, hog manure is rich in phosphorus (P), an environmentally sensitive nutrient, and distribution of different P fractions down the soil profile in these production systems is not well understood. The objective of this study was to determine the spatial variability of soil P in different soil depth intervals following 1-year outdoor farrowing sows in a 0.5-ha paddock in cold-temperate climate of Eastern Canada. Soil samples were collected with 0-15, 15-30, and > 30 cm depth intervals (up to 60 cm or the depth that sampling was possible) in grazing/rooting, feeding, wallow, and farrowing hut areas. Soil samples were analyzed for Olsen P (Pol), organic P (PO), and total P (PT). Areas with more frequent presence of hogs showed 45-80% greater Pol concentrations, and movement of soluble PO down the soil profile was higher in these areas compared with the grazing/rooting area. The PO formed 80% of PT throughout the paddock, and the spatial distribution of PO was similar to PT in all soil depth intervals but different from Pol. Results also showed that PO concentrations in the paddock decreased at > 30 cm depth except for the feeding area. Findings of this study reveal that farrowing sow cycle in an outdoor hog-rearing farm setting can result in hot spots of P, which enhance the risk of environmental pollution.
Keywords: Excretion; Hot spot; Outdoor hog; Phosphorous fractions; Soil depth; Spatial variability.