Edge of Field Runoff and Phosphorus Losses from Regions with Cold Temperate Climates: Importance of the Non-Growing Season.

In agricultural systems, the magnitude and speciation of phosphorus (P) loss, and the partitioning of P losses between surface and subsurface pathways can vary with soil texture and slope, climatic region and land use/management practices employed on fields. However, P losses can also vary in time in response to season, event-based climatic drivers, antecedent moisture conditions and management practices. At present, there is a paucity of field data collected under winter conditions. An improved understanding of the magnitude, speciation and flow paths of P loss occurring throughout the non-growing season, and, the climatic drivers of such processes, is needed to apply and evaluate appropriate Best Management Practices (BMPs) and improve modelling efforts. In Southern Ontario, Canada, we examined year-round, high-frequency dissolved and particulate P losses over four years from six fields under corn-soybean-winter wheat rotation, where multiple BMPs are used (nutrient management, subsurface P placement, rotational conservation tillage and the periodic use of cover crops).  Spatial and temporal patterns in edge of field P losses will be discussed, emphasizing processes occurring throughout the non-growing season and highlighting the importance of individual and combined BMPs in mitigating P losses.