Relating Phosphorus Loss in Snowmelt Runoff to Soil Phosphorus Concentrations from Cattle Winter Bale-Grazing Sites.

The feeding of bales of dry hay or straw over the winter to beef cattle spatially dispersed over annual cropland or pastures (i.e. bale-grazing) has become common practice on the Canadian Prairies, replacing confined winter feeding in drylot pens.  In addition to saving producers the cost of spreading manure, it is assumed that the direct deposit of urine and feces will enhance soil fertility significantly. However, this practice also increases the risk of nutrient loss during spring snowmelt runoff while soils are still frozen, which is the main source of runoff on the Prairies. A four-year study was conducted in Swift Current Saskatchewan to determine the effects of in-field winter bale grazing on soil fertility and on snowmelt runoff, using 350 m² microwatersheds established in Russian wild rye (RWR) and crested wheat grass (CWG) pastures.  These pastures were bale-grazed in alternate years, each for two years total, and were compared to controls with no bale-grazing or with fall-spread, unincorporated manure.  Soil samples (0-10 and 10-20 cm) were collected in fall 2008 – 2012, and were analyzed for Olsen P, Mehlich P, total soil P, total soil organic P and CaCl₂-P. Runoff samples were collected during each annual snowmelt event (spring 2009-2013), and were analyzed for total dissolved P, total particulate P, soluble phosphate (SRP) and P forms with ³¹P-NMR spectroscopy. This presentation will link changes observed in pasture soil P concentrations to P forms and concentrations observed in snowmelt runoff in years with and without bale-grazing, and to manure spreading in each year. Not surprisingly, there are potential problems with contaminants from animal wastes in surface runoff.