Fertilizer and crop management practices to reduce phosphorus transport in snowmelt runoff from surface drained agricultural watersheds in the Prairie Pothole Region

Responsible agricultural land drainage considers the balance between allowing farmers to manage water while limiting environmental impacts. This study evaluates the role of fertilizer and crop management practices to achieve this goal under Canadian Prairie Pothole Region conditions. In September of 2020, a wetland consolidation project was initiated on a Dark Brown Chernozem (Typic Boroll) using surface ditches to drain eight ephemeral wetland watersheds within a single field. Different fertilizer or crop management practices were applied annually for 3 years to each drained watershed and assessed for their influence on crop phosphorus (P) uptake and yield, along with dissolved reactive P (DRP) concentration and total soluble P load in snowmelt runoff. Practices evaluated included (1) variable rate fertilizer application for annual grain crops; (2) post-harvest grain crop residue incorporation through shallow tillage; and (3) annual forage species mixture for hay harvest, and were compared to an annual grain crop control treatment with constant rate fertilizer application and no post-harvest tillage. Variable rate fertilizer application significantly reduced DRP concentration (64%–69% of control) in 2 of 3 years and total soluble P load (50% of control) in 1 year of snowmelt runoff with no significant crop yield reduction. The forage mixture also significantly reduced DRP concentration relative to the control in 2 years. Differences among treatments are attributed mainly to differences in P fertilizer application rates. Therefore, fertilizer or crop management practices that increase utilization of applied and residual soil P can be effective in reducing P transport from drained agricultural watersheds.