Prediction of liquid municipal biosolid and precipitation induced tile flow in a Southern Ontario agricultural field using MACRO

This paper focuses on calibration and validation of a dual-permeability soil water flow model, MACRO, to simulate liquid municipal biosolid (LMB) and precipitation induced vadose zone flow to a monitored tile drain system in a structured silt-loam soil, in southern Ontario Canada. The model was calibrated primarily on the basis of site-measured soil hydraulic parameters (encompassing tillage effects associated with LMB application), and field-monitored soil water content, soil water tension, and tile drain discharge for fall site conditions. LMB application for calibration data sets were carried out using an AerWay SSD system. Overall, daily tile drain discharge, soil water content, and soil water tension were well predicted by the following model calibration of primarily soil hydraulic parameters (specifically soil porosity, saturated hydraulic conductivity and van Genuchten soil desorption curve factors). The calibrated model was then validated using two additional daily data sets for two spring/summer study periods, both employing an LMB application. The modeling results were evaluated in part via statistical measures (i.e. average error and root mean square error); which indicated excellent agreement between daily simulated and measured tile drain discharges, soil water content and soil water tension. Overall, for certain LMB applications the modeling approach that was taken slightly under-predicted the degree of immediate application-induced macropore flow in the top 0.4 m of the soil. Generally, MACRO was found to be less adept at handling what was considered to be true bypass flow as a result of soil cracking during the drier soil conditions.