Phosphorus export from artificially drained fields across the Eastern corn belt

Authors: Pease, Lindsay; King, Kevin; Williams, Mark; LABARGE, GREGORY - The Ohio State University; Duncan, Emily; Fausey, Norman

Submitted to: Journal of Great Lakes Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2017
Publication Date: 12/12/2017
Publication URL: https://handle.nal.usda.gov/10113/6471019
Citation: Pease, L.A., King, K.W., Williams, M.R., Labarge, G.A., Duncan, E.W., Fausey, N.R. 2017. Phosphorus export from artificially drained fields across the Eastern corn belt. Journal of Great Lakes Research. doi.org/10.1016/j.jglr.2017.11.009.

Interpretive Summary: Freshwater ecosystems are sensitive to excess amounts of phosphorus present in waterways. In agricultural regions, such as the Eastern Corn Belt (Ohio, Indiana, SE Michigan), agriculture represents a potential source of phosphorus loss to waterways. It is therefore critical to quantify the amount of phosphorus leaving typical agricultural fields in surface runoff and via the artificial subsurface drainage that underlies most agricultural land in the Eastern Corn Belt. Results of this study reveal that 80% of agricultural water that enters waterways comes from subsurface drainage systems, and this water carries with it about 70% of the agricultural phosphorus entering waterways. Although subsurface discharge is the primary source of water and phosphorus loss from agricultural fields, surface runoff has significantly greater phosphorus concentrations than water leaving subsurface drains. During high-intensity rainfall events, losses from surface runoff can be greater than losses from subsurface drains. Phosphorus losses represent a small fraction (<5%) of the overall phosphorus budget in an agricultural system. Because of this, it is difficult to reduce phosphorus losses to levels that will promote ecosystem health. This work provides evidence of additional challenges that must be overcome including the historical over-application of phosphorus in the watershed, and the increasing frequency of high-intensity rainfall events. Strategies to reduce phosphorus in the soil must be employed along with strategies to treat, capture, or reduce phosphorus leaving agricultural fields with water to improve the quality of freshwater lakes and streams in the Eastern Corn Belt.

Technical Abstract: 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 discharge (surface and subsurface) water quality. The objective of this study was to characterize discharge, P concentrations, and P loads in surface runoff and subsurface drainage from 38 edge-of-field research sites in Ohio. A regional P budget was also developed using management and loading data from the monitored fields. Over the five-year study period, 31±16% of annual precipitation was expressed as subsurface discharge and 7±8% as 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. 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 the watershed-scale loading targets established by the Great Lakes Water Quality Agreement. 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.