| The objectives of this study were to determine and model the effects of earthworms on water and solute movement in soil. Microrelief and rainfall effects on water and solute movement were determined in packed buckets inoculated with earthworms (Aporrectodea tuberculata). A solution of Br{dollar}sp-{dollar} and Rhodamine WT dye was uniformly sprayed across each soil surface and rainfall was applied at one of five intensities. Buckets were excavated in 1 to 3 cm depth increments. Br{dollar}sp-{dollar} and dye decreased exponentially with depth. Less chemical was displaced at higher intensities. Displaced chemical was distributed deeper and more uniformly as intensity increased. The percent of burrows stained with dye was unaffected by intensity, suggesting that increased volumes of water were flowing in conducting burrows. A small number of burrows, generally located at low points in surface microdepressions, were responsible for deep penetration of dye.; Field experiments were conducted to determine earthworm effects on movement of Rhodamine WT dye, infiltration rate, and macroporosity in tilled and nontilled soils with or without residues. Dye was uniformly applied across a small area in each of five tillage-residue treatments. Following rainfall, plots were excavated in eight depth increments. Dye was displaced deeper and distributed more uniformly with depth in nontilled soils with residues. Infiltration rate, determined at 0, 3, and 12 cm tensions with a disk permeameter, did not differ by tillage-residue treatment. However, a 1.62 cm pulse of methylene blue solution infiltrated much faster in nontilled soils with residues, indicating increased macropore continuity. The deep displacement of Rhodamine WT was attributable to this increased continuity.; A model was developed which considers matrix infiltration and storage of ponded water in surface microdepressions prior to flow in burrows. If water continues to accumulate on the surface it eventually intersects a burrow. This burrow conducts all water delivered to the microdepression. If the burrow fills, surface storage accumulates again until the next burrow is intersected. Water flow in individual burrows is modeled with a kinematic wave approximation. The model was most sensitive to matrix infiltration properties and surface storage capacity. |
