Climate, landscape, and management effects on nitrate and soluble phosphorus concentrations in subsurface drainage discharge in the western lake erie basin

Subsurface drainage, while an important and necessary agricultural production practice in the Midwest, contributes nitrate (NO3) and soluble phosphorus (P) to surface waters. The magnitude of NO3 and soluble P losses in subsurface drainage varies greatly by landscape, climate, and field management factors. This study evaluates the combined impact of these factors on observed P and NO3 concentrations in subsurface drainage water in Northwest Ohio. Factors significantly impacting NO3 concentrations included rainfall, N and P fertilizer application rate & timing, Soil Test P, soil texture, season, drain spacing, site relief, tillage, temperature, and crop. These findings provide evidence of NO3 loss via leaching following fertilizer application, and indicate that BMPs specifically targeted at reducing NO3 concentrations and soil matrix flow of NO3 following spring fertilizer application will have the greatest impact on NO3 losses from subsurface discharge. Factors significantly impacting soluble P losses included P fertilizer application rate and timing, rainfall, season, crop, soil texture, site relief, Soil Test P, tillage, and temperature. BMPs specifically targeted at P fertilizer management and prevention of soluble P movement via preferential flow pathways during rainfall events will have the greatest impact on soluble P losses from subsurface drainage systems.