Abstract
AbstractSoil surface aggregates and macropores have the potential to greatly influence the transport of surface‐applied agricultural chemicals in soil and to surface and groundwater. We studied the effects of a 1.0‐cm layer of 4.5‐ to 12.5‐mm surface aggregates, a 3‐mm artificial macropore, and their combination on the transport of surface‐applied Br− and Sr2+ tracers (as SrBr2) under simulated rainfall, with the underlying soil initially dry or prewetted to a certain depth (about 7 cm). Air‐dried Kirkland soil (fine, mixed, thermic Udertic Paleustoll), <3.5‐mm size, was packed in duplicate 15‐cm‐diam., 30‐cm‐long, sectionable Plexiglas columns (Cole‐Parmer Instrument Co., Niles, IL) to a bulk density of 1.26 Mg m−3. During the rainfall, surface runoff or macropore flow out of the column bottom was measured and analyzed for Br− and Sr2+. After the rain, the column was sectioned in 1.15‐cm increments to determine soil water, Br−, and Sr2+ content distributions. Without a macropore, the surface aggregates reduced the overall movement of Br− in soil and increased Br− in runoff, the effects being much greater in prewetted columns than in nonprewetted columns. A macropore, by itself, also reduced the movement of the main Br− pulse as it allowed surface solution (runoff) to move down and infiltrate laterally below the main wetting front. Surface aggregates greatly increased Br− content of the macropore flow and of the wetted soil around the macropore below the main wetting front. Aggregates or the initial condition did not change the Sr2+ movement much but increased Sr2+ content of runoff or macropore flow.
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