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

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2018 ASABE Annual International Meeting  1801434.(doi:10.13031/aim.201801434)
Authors:   Melissa D. Miller, Lou S. Saporito, Anthony R. Buda, Heather E. Gall, Tamie L. Veith, Charles M. White, Clinton F. Williams, Kathryn J. Brasier, Peter J. A. Kleinman, John E. Watson
Keywords:   Agriculture, dairy manure, erosion, load-discharge, phosphorus, shallow-disk injection, water quality.

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. Shallow-disk injection was more effective in promoting dilution of DP, and to a lesser extent, TP. Though, broadcast plots showed stronger dilution patterns than injection plots for PP, and there was no difference between application methods for TS. Intra-practice variability was largely dependent on relative contributions from overland and subsurface flow, due to increased dilution from subsurface flow. Overall, shallow-disk injection appears to be an effective practice to reduce TP and DP losses without negating the erosion-reducing benefits of no-till.

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