Edge of Field Phosphorus Export via Tile Drainage and Overland Flow from Reduced Tillage Systems in Ontario
Van Esbroeck, Christopher J. G.
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This study examined the role of tile drainage and overland flow in field-scale phosphorus (P) export from reduced tillage systems, as well as the influence of event type and antecedent conditions on P export during major runoff events. Three field-scale sites representing a range of soil, climatic, and management conditions, were monitored intensely for an 18 month period. Annual P export from the sites ranged between 0.267 and 0.419 kg/ha. The non-growing season (NGS) was an important period for P export due to the volume of discharge during the period. Tile drainage contributed the majority of combined annual discharge at all sites (78-83%). Tile drainage was an equal or dominant contributor to annual total P (TP) export. Overland flow was the dominant transport pathway for soluble reactive P (SRP) at two of the three sites. The nature of the discharge events (e.g. rain on soil, rain on snow, and radiation melt) influenced P speciation in runoff. Particulate P + soluble unreactive P (PP+SUP) concentrations were highest during events where rain fell on bare soil. The proportion of TP as SRP in major events appeared to decline over the NGS. Understanding the seasonality of P export, the relative role of tile drainage and overland flow, and the influence of event type will improve our ability to manage non-point source P export.