Field observations that quantify agricultural phosphorus (P) losses are critical for the development of P reduction strategies across the Eastern Corn Belt region of North America. Within this region, surface water bodies including Lake Erie are sensitive to non-point P loadings. It is therefore imperative to quantify the impact of agricultural crop production on surface and subsurface water quality. This study characterized discharge, P concentrations, and P loads in surface runoff and subsurface drainage from 38 edge-of-field research sites in Ohio. Over the four-year study period, 31 ± 16% (mean ± one standard deviation) of annual precipitation became subsurface discharge while 7 ± 8% became surface discharge. Subsurface discharge accounted for 81 ± 23% of annual discharge, 71 ± 26% of annual dissolved reactive phosphorus (DRP) load, and 69 ± 27% of annual total phosphorus (TP) load. A P balance was also developed using management and loading data from the study sites. Under prevailing management practices, P removal (i.e., surface losses, subsurface losses, crop uptake) was greater than P input (i.e., atmospheric deposition, fertilizer application) on 60% of fields. Even so, further reduction of edge-of-field P losses will likely be necessary to meet watershed-scale P load recommendations. Findings suggest that balancing P inputs with crop uptake may not be sufficient to reduce edge-of-field losses due to a combination of legacy P and high-intensity rainfall events. Implementation of management practices targeting P-source will be needed in conjunction with practices at the edge-of-field targeting P-transport in order to meet recommended P loading targets in the Eastern Corn Belt region.
Bibliographical noteFunding Information:
The authors would like to thank the landowners of the study sites who provided access to the fields and management data; Jedediah Stinner, Katie Rumora, Marie Pollock, Phil Levison and Sara Henderson for their help in data collection and site maintenance; and Eric Fischer for analytical expertise. The authors would like to acknowledge the continued support of The Ohio State University in hosting the USDA ARS Soil Drainage Research Unit and providing academic access to faculty resources, libraries, and students. Funding for this project was provided in part by several sources including: The 4R Research Fund ( IPNI-2014-USA-4RN09 ); US EPA ( DW-12-92342501-0 ); Conservation Innovation Grants ( The Ohio State University – 69-3A75-12-231 ; Heidelberg University – 69-3A75-13-216 ); NRCS Mississippi River Basin Initiative; The Nature Conservancy; Ohio Corn and Wheat Growers Association; Ohio Soybean Association; NRCS Cooperative Conservation Partnership Initiative and NRCS Conservation Effects Assessment Project.
- Subsurface drainage
- Water quality