TILLAGE AND CROPPING EFFECTS ON PREFERENTIAL FLOW AND SOLUTE TRANSPORT

Recent evidence suggests that crop roots in soil may significantly alt er preferential flow processes and thus impact non-point-source pollut ion from agricultural land. Therefore, the objectives of this study we re to evaluate: (i) the effect of tillage practices on the leaching of surface ap, plied 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 solu te leaching through field soil. On soil cropped to corn and soybean, t wo tracer solutes were applied, Br- by spraying and Cl- under ponded c onditions, on two different dates (during vegetative and reproductive stages) during 2 different years to a total of 22 2 X 2-m(2) plots. Th ree 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 x 1-m(2) 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 p rofile than bromide, even though the latter had been sprayed on the so il before pending the Cl- application. With equal volumes of water inf iltrating at the soil surface, solutes moved significantly deeper into the soil profile for between row (BR) than for in row (LR) positions for each tillage and crop treatment, despite the attempt to equalize i nitial conditions near the soil surface in the BR and IR positions by application of water 3 days before chemical application. This work sho ws that solute transport properties vary as a function of(a) position relative to the crop row, (b) tillage, (c) stage of growth, and (d) cr op species. These factors should be considered when modeling is used t o assess regional scale non-point source pollution and when determinin g best management practices.