Addressing agricultural phosphorus loss in artificially drained landscapes with 4R nutrient management practices

Agricultural phosphorus (P) loss has been linked to the eutrophication of surface water bodies throughout the world. As a result, minimizing offsite P transport has become a priority in many rural watersheds. In the US Midwest and other subsurface tile-drained regions, there is a critical need to identify nutrient management practices that decrease P loss in both surface and subsurface discharge. An edge-of-field (EOF) network monitoring 38 agricultural fields was established in northwest Ohio, United States, to quantify the impacts of prevailing and novel crop production and conservation management practices on surface and subsurface P concentrations and loads. In this study, we evaluate nutrient management practices across these fields with varying characteristics in order to identify a suite of management practices within the 4R nutrient management framework (right source, right rate, right time, and right place) that reduce agricultural P loss in artificially drained landscapes. EOF monitoring data indicate that applying organic fertilizers at P-based rates, soil testing and following recommended application rates, avoiding fertilizer application during wet periods of the year (e.g., winter and early spring) and prior to large precipitation events, and placing fertilizer below the surface are all practices that result in decreased P loss. Findings also highlight the importance of field hydrology on surface and subsurface P transport and suggest that water management practices may also be effective at decreasing P loss. While the effectiveness of the nutrient management practices evaluated in this study will likely vary across fields with different characteristics, implementation of these practices should be considered a directionally correct (i.e., will reduce nutrient loss) approach for addressing excess P loss from artificially drained landscapes.