Spatial and Temporal Assessment of Soil Structure Variability and the Influence of Structure On Hydraulic Behavior in a Tile Drained Silt Loam.

This talk will highlight results from a series of field experiments conducted on a seemingly uniform, macroporous, tile drained silt loam soil with a plowpan layer present, in southwestern Ontario. The primary objectives of the work were to evaluate: the spatial variability of macroporosity with respect to topographic location and tile drain location, the influence of soil drying on soil structure and pore size distribution, and the hydraulic response of the tile drains under antecedent moisture conditions ranging from relatively dry to extremely wet. Results from the work show that the tile drains did not significantly (p ≤ 0.1) influence the spatial distribution of visible macroporosity or the unsaturated soil hydraulic properties, however, between different locations within the same field there were significant differences in these same properties. Field saturated hydraulic conductivity (Kfs) was significantly different between different locations within the field, and also between different positions relative to tile drain location. Both Kfs and the unsaturated soil hydraulic properties were significantly influenced by soil drying. During infiltration events the hydraulic response of the tile drain was found to be strongly influenced by antecedent moisture content, event intensity, and the plowpan layer, with the plowpan layer acting to restrict downward water movement until a saturation threshold at the base of the A horizon was reached, upon which time macropore flow into the B horizon was initiated. Overall, this work places into context how spatial and temporal variability along with soil structural elements can influence the hydrologic characteristics of a macroporous, tile drained, agricultural field.