Manure application under winter conditions: Nutrient runoff and leaching losses

Winter application of manure is commonly practiced and potential nutrient losses are difficult to predict. This study was conducted in order to determine nutrient losses via surface runoff and subsurface leachate from winter-applied manure based on its relative placement with respect to snow. A laboratory soil thermal cycling system containing four 15-cm diameter, PVC lysimeters encased in sand and a commercially-available heating cable was used to replicate freeze-thaw field conditions. Dairy manure was applied before, midway through, or upon completion of an artificial snowfall. Runoff and leachate were collected throughout a 4-day snowmelt event and subsequent rainfall simulation. During the snowmelt event, inorganic-nitrogen losses of 76.4, 113.8, and 205.3 μg/cm² were observed for the manure-on-top-of-snow, manure-in-between-snow, and manure-under-snow treatments, respectively, while dissolved reactive phosphorus (DRP) losses of 2.4, 1.5, and 0.7 μg/cm ² were seen. Inorganic-nitrogen losses during the rainfall simulation were significantly less than the snowmelt; however, the losses followed a similar trend. Unlike the snowmelt, DRP losses in surface runoff from the rainfall simulation were 1.1, 1.2, and 2.8 μg/cm² for the manure-on-top-of-snow, manure-in-between-snow, and manure-under-snow treatments, respectively. This research shows that the relative placement of manure with respect to snow plays a significant role in the fate of N and P from winter-applied manure.