Edge of Field Phosphorus Export via Tile Drainage and Overland Flow from Reduced Tillage Systems in Ontario

Abstract

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.