Assessing the Effects of Management Practices on Phosphorus Loss from Saskatchewan Cropland and Pasture during Spring Snowmelt Runoff.

Runoff can be a key contributor to the loss of phosphorus (P) from agricultural lands to water bodies.  Beneficial management practices (BMPs) have been developed to minimize P loss.  However, to maximize the benefit of BMPs it is important to understand the physical and chemical forms and concentrations of P in runoff, because physical and chemical P forms differ in their transfer mechanisms and their reactivity in the environment.  The Canadian prairie region is unique in that its hydrology is characterized by long periods of winter, with half the annual precipitation occurring as snowfall.  During spring snowmelt, there is a rapid release of water from snow packs when the mineral soil is frozen, resulting in high surface runoff, and accounting for the majority of nutrient loss in runoff in this region.  From 2009-2016, research was conducted in SE Saskatchewan to study BMPs for the key agricultural practices in this region (annual crop and beef production).  For annual cropland, BMPs included fertilizer reduction and conversion to pasture. For pasture, tested management practices included summer grazing only, fall spread manure and in-field winter bale grazing. We will present flow-weighted concentrations of total dissolved P, total particulate P and total molybdate reactive P throughout each snowmelt runoff event from 2010-2015. We will also present results of analysis on dissolved and particulate samples from the start and end of the main runoff events in 2011 and 2013 by ³¹P-NMR spectroscopy for each BMP. These results will further our ability to develop appropriate BMPs to manage P loss from agricultural soils in this region.