Core Ideas: Soil test phosphorus remains an important factor in studying dissolved reactive P loss. Identifying higher risk fields with STP could inform future management practices to reduce DRP loss. STP was linearly related to DRP concentration loads in tile‐drained fields. Monitoring STP in addition to implementing other BMPs should be considered to decrease DRP loss. Harmful and nuisance algal blooms resulting from excess phosphorus (P) have placed agriculture in the spotlight of the water quality debate. Sixty‐eight site years of P loading data (combined surface runoff and tile flow) from 36 fields in Ohio were used to see if a soil test P (STP) concentration could be identified that allowed P application while still meeting recommended loss thresholds. Regression analysis revealed that P application to soils with STP concentration in the “critical level” range would result in P losses above the recommended Annex 4 thresholds. In addition, fertilizer application increased the risk of dissolved reactive P (DRP) loss as compared to years in which fertilizer was not applied. We determined that STP was a good screening method to identify fields that are at risk for greater P loss, but STP alone was not a good predictor of DRP loss, suggesting that a more holistic approach that includes upland management, edge‐of‐field practices, and in‐stream approaches will be required to decrease DRP loading.

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.

The US Midwest is expected to experience higher intensity rainfall events along with an increased chance of drought during the mid- and late 21st century under projected future climate scenarios. Development of strategies to mitigate the impact of these projected changes on agricultural production and environmental quality is important for ensuring agricultural resiliency to future climate. This study used the DRAINMOD hydrologic model to simulate subsurface drainage discharge at a field site in the headwaters of the Western Lake Erie Basin using future climate patterns projected by 20 general circulation models. Despite projected increases in rainfall, by the late twenty-first century, subsurface discharge was projected to decrease 7% and 11% under representative concentration pathway (RCP) 4.5 and RCP 8.5, respectively. Reductions in subsurface discharge were attributed to increased temperature and evapotranspiration. The performance of controlled drainage was not projected to change on an annual basis throughout the next century. The benefits of controlled drainage systems as an agricultural best management practice were still evident under the projected climate change of the next century. The role of controlled drainage as a means to potentially retain more crop available water in the soil profile could become critically important under future climate conditions.