Fertilizer placement and application timing as strategies to reduce phosphorus loading to Lake Erie

To reduce the intensity and frequency of harmful algal blooms in western Lake Erie, it has been recommended to reduce the phosphorus load, contributed by the Maumee River watershed (MRW) in northwest Ohio. As the largest contributor of phosphorus to Lake Erie, the dominantly agricultural MRW in northwest Ohio has been recommended to reduce phosphorus loads by 40%. To achieve such reductions, three agricultural nutrient management practices, (1) fertilizer placement within the soil, (2) adjusted seasonal timing of fertilizer application, and (3) adjusted date of fertilizer application to drier days have been recommended. To determine the potential phosphorus load reduction from implementing these three management practices, a SWAT model of the MRW was developed to evaluate the effectiveness of each practice for reducing SRP and total phosphorus (TP) load to the lake. Management scenarios were modeled with variations of the three practices from 2007 to 2012, and compared to historical data. Overall, maximum fertilizer placement had the greatest potential to influence SRP and TP loads; reducing spring SRP and TP loading by 42% and 27%, respectively compared to baseline levels. Seasonal fertilizer application timing also impacted spring SRP and TP loads, but to a lesser degree. Changing the date of application from wetter days to drier days across the watershed did not significantly affect SRP or TP loads, but this result is likely due to limitations of the SWAT simulation. These results indicate that maximizing fertilizer placement has a great potential to reduce TP and SRP runoff from the MRW.