Tillage and cropping effects on preferential flow and solute transport

Recent evidence suggests that crop roots in soil may significantly alter preferential flow processes and thus impact non-point source pollution from agricultural land. Therefore, the objectives of this study were to evaluate: (i) the effect of tillage practices on the leaching of surface applied chemicals, (ii) the spatial and temporal variations in preferential flow pathways under corn and soybean cropping during the growing season, and (iii) the effect of application method on solute leaching through field soil. On soil cropped to corn and soybean, two tracer solutes were applied, Br by spraying and Cl under ponded conditions, on two different dates (during vegetative and reproductive stages) during 2 different years to a total of 22 2 × 2-m plots. Three days before chemical application, plants and surface residues were removed from each plot, a 2-cm simulated rainfall was applied, and the plot surface was covered. Sprayer application of Br was followed by ponded applications of chloride and tracer-free water. Four days after chemical application, within the central 1 × 1-m area of each plot, at least 10 core samples (7.6- or 11.5-cm diameter) were collected in 10-cm depth increments to a maximum depth of 1.5 m. Chloride, applied under ponded surface conditions, consistently moved deeper into the profile than bromide, even though the latter had been sprayed on the soil before ponding the Cl application. With equal volumes of water infiltrating at the soil surface, solutes moved significantly deeper into the soil profile for between row (BR) than for in row (IR) positions for each tillage and crop treatment, despite the attempt to equalize initial conditions near the soil surface in the BR and IR positions by application of water 3 days before chemical application. This work shows that solute transport properties vary as a function of (a) position relative to the crop row, (b) tillage, (c) stage of growth, and (d) crop species. These factors should be considered when modeling is used to assess regional scale non-point source pollution and when determining best management practices.