MICRORELIEF AND RAINFALL EFFECTS ON WATER AND SOLUTE MOVEMENT IN EARTHWORM BURROWS

Macropores have been implicated in preferential transport of water and solutes in soil, but mechanisms of transport are not fully understood. Our objective was to determine the effect of surface microrelief, microlandscape position, and rainfall intensity on water and solute transport in burrows created by the earthworm Aporrectodea tuberculata. Water, Br-, and dye movements in burrows were determined in buckets packed with Waukegan silt loam (fine-silty over sandy or sandy-skeletal, mixed, mesic Typic Hapludoll) and incubated with earthworms. One centimeter of simulated rainfall was applied at intensities of 2, 4, 7, and 10 cm h-1, and an instantaneous application of water. As rainfall intensity increased, less Br- and dye were displaced from the soil surface, but displaced Br- and dye were distributed more evenly with depth and deeper in the soil. The same percentage of burrows conducted at low and high intensities, indicating that increased volumes of water were transported in conducting burrows as intensity increased. Burrows located at the lowest elevations in surface microdepressions showed deeper staining than other burrows for the instantaneous treatment and for all treatments combined. A small number of burrows were responsible for deep displacement of water and solute for each treatment. Models designed to predict flow in burrows must consider the quantity of water available to a burrow, which is a function of surface position, and flow within a burrow, which is a function of the internal characteristics of a burrow.