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Title: Phosphorus transport in agricultural subsurface drainage: A review

item King, Kevin
item Williams, Mark
item MACRAE, MERRIN - University Of Waterloo
item Fausey, Norman
item Smith, Douglas
item FRANKENBERGER, J - Purdue University
item Kleinman, Peter
item BROWN, LARRY - The Ohio State University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2014
Publication Date: 8/13/2014
Citation: King, K.W., Williams, M.R., Macrae, M.L., Fausey, N.R., Smith, D.R., Frankenberger, J., Kleinman, P.J., Brown, L.C. 2014. Phosphorus transport in agricultural subsurface drainage: A review. Journal of Environmental Quality. 44(2):467-85. doi:10.2134/jeq2014.04.0163.

Interpretive Summary: Tile drainage is a common and necessary practice for agricultural production in the poorly drained humid regions of the world. Attention has recently focused on tile drainage as a pathway for phosphorus to enter streams and waterways causing eutrophic conditions in downstream lakes and reservoirs. However, a collective assessment of the extent and understanding of the transport factors and management practices that affect phosphorus movement through subsurface tile drainage is non-existent. We conducted a comprehensive literature review on phosphorus movement through tile drainage and found that phosphorus transport through subsurface tile drainage is a function of soil properties, subsurface drainage design, and agricultural production practices. We also identified several structural and management approaches that could be implemented to reduce phosphorus transport in subsurface drainage. In addition, we also identified three major gaps that need to be addressed. These include: understanding the hydrology of tile drained landscapes, developing and including phosphorus transport routines in simulation technologies, and holistic evaluations of both prevailing and best management practices aimed at reducing subsurface phosphorus transport. This compilation of research on subsurface phosphorus movement will be beneficial to the research community, watershed managers, and policy makers for identifying and guiding research and implementation of practices and programs to address phosphorus transport in tile drained landscapes.

Technical Abstract: Phosphorus (P) loss from agricultural fields and watersheds has been an important water quality issue for decades because of the critical role P plays in eutrophication. Historically, most research focused on P losses by surface runoff and erosion because subsurface P losses were often deemed to be negligible. Perceptions of subsurface P transport, however, have evolved and considerable work has been conducted to better understand the magnitude and importance of subsurface P transport and identify practices and treatments that decrease subsurface P loads to surface waters. The objective of this paper was to critically review research on P transport in subsurface drainage to determine factors that control P losses and identify gaps in the current scientific understanding of the role of subsurface drainage in P transport. Factors that affect subsurface P transport including soil characteristics (e.g., preferential flow, P sorption capacity, and redox conditions), drainage design (e.g., tile spacing, tile depth, and the installation of surface inlets), prevailing conditions and management (e.g., soil-test P levels, tillage, cropping system, and the source, rate, and placement of P application), and hydrologic and climatic variables (e.g., baseflow, event flow, and seasonal differences) are discussed within the framework of intensively drained agricultural settings. Structural, treatment, and management approaches to mitigate subsurface P transport, such as practices that disconnect flow pathways between surface soils and tile drains, drainage water management, in-stream or end-of-tile treatments, and ditch design and management are also discussed. The review concludes by identifying gaps in the current understanding of P transport in subsurface drains and suggesting areas where future research is needed.