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Title: The importance of intra-management practice variability in sediment and phosphorus loss from agricultural fields

item MILLER, MELISSA - Pennsylvania State University
item Saporito, Louis - Lou
item Buda, Anthony
item GALL, HEATHER - Pennsylvania State University
item Veith, Tameria - Tamie
item WHITE, CHARLES - Pennsylvania State University
item WILLIAMS, CLINTON - Pennsylvania State University
item BRASIER, KATHRYN - Pennsylvania State University
item Kleinman, Peter
item WATSON, JOHN - Pennsylvania State University

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/29/2018
Publication Date: 7/29/2018
Citation: Miller, M.D., Saporito, L.S., Buda, A.R., Gall, H.E., Veith, T.L., White, C.M., Williams, C.F., Brasier, K.J., Kleinman, P.J., Watson, J.E. 2018. The importance of intra-management practice variability in sediment and phosphorus loss from agricultural fields. ASABE Annual International Meeting, July 29-August 1, 2018, Detroit, Michigan. P. 1-17.

Interpretive Summary: Understanding the interactions of hydrological processes with field management is critical to controlling sediment and phosphorus losses from agriculture. In this study, we examined phosphorus and sediment loads as a function of runoff to assess the effects of shallow-disk manure injection versus surface manure broadcasting on runoff water quality. Dissolved and total phosphorus losses were appreciably lower with shallow-disk manure injection, while sediment and particulate phosphorus losses were unaffected by manure application strategy. Findings suggest shallow-disk manure injection is an effective strategy to reduce the washoff of manure phosphorus sources in runoff.

Technical Abstract: Eutrophication and sedimentation are pervasive challenges in the Chesapeake Bay watershed. Shallow-disk manure injection is a promising technology to mitigate phosphorus (P) losses in runoff while maintaining the water quality benefits of no-till, including reducing particulate P and sediment losses. However, its effectiveness as a P mitigation strategy is not fully understood, as hydrologic variability exists across spatial and temporal scales, confounding the results of field studies seeking to quantify the benefits of shallow-disk injection. In this study, we regressed loads of total solids (TS), total P (TP), dissolved P (DP), and particulate P (PP) against flow depths to evaluate the effectiveness of shallow-disk manure injection versus broadcasting for reducing P and sediment losses. Overland and subsurface flow from twelve plots in central Pennsylvania were measured and sampled for TS and P from January 2013 to May 2017. The plots received manure via either surface broadcasting or shallow-disk injection for three years, followed by two years of broadcasting across all plots. Load-discharge (L-Q) relationships were developed to determine how P and TS losses changed with increasing flow. L-Q analyses revealed dilution of all P constituents and near-chemostatic behavior for TS for both application methods. However, shallow-disk injection was more effective in promoting dilution of DP, and to a lesser extent, TP, with no difference between application methods for TS and PP. Intra-practice variability was largely dependent on relative contributions from overland and subsurface flow, due to increased dilution from subsurface flow. Overall, the results suggest that shallow-disk injection appears to be an effective practice to reduce TP and DP losses without negating the benefits of no-till.