Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Abstract Only
Publication Acceptance Date: 7/21/1999
Publication Date: N/A
Technical Abstract: While preferential flow has been identified as a major mechanism of transport for phosphorus and pesticides in many soils, little is known of the temporal dynamics of the process. We conducted a sequential tracer leaching study to investigate the temporal behavior of chemical leaching to a field drain during an irrigation and the subsequent rainfall events over a 14-d period. The herbicides atrazine and alachlor, along with the conservative tracer Br, were applied to a 1-m wide strip immediately before an irrigation. Three additional benzoic tracers, PF, TF, and PF were applied to the strip during the irrigation at 2-hr intervals. Breakthrough of the conservative tracer Br occurred within the first 2-hr of irrigation, indicating that a fraction of the solute transport was through preferential flow paths. The herbicides applied with Br also arrived at the drain within the first 2-hr of the irrigation, indicating preferential transport. .Retardation and attenuation of the sorbing herbicides indicated that there was interaction between the chemicals and the soil along the preferential pathways. The conservative tracers applied during the later stages of irrigation arrived at the subsurface drain faster than tracers applied either immediately before or during early stages of the irrigation. The last tracer (PF), applied 6 hr after the start of irrigation, took only 15 min and 1 mm of irrigation water to travel the 1.2-m distance between the soil surface and the subsurface drain. This study demonstrated that solute transport along preferential flow pathways in this soil is not constant during a leaching event. Instead, transport velocities along preferential pathways increase as the leaching event continues.