Partitioned Flow Domains of Three Wisconsin Soils

Preferential flow mechanisms have been the subject of increasing research interest because these phenomena contribute to solute transport. Commonly, preferential flow paths are associated with macropores or highly structured soils. Sandy soils are typically weakly structured or structureless. However, they exhibit rapid drainage, which may mimic the hydrology and solute transport effects of macropores. We tested whether a flow domain partitioning scheme could be applied on two sandy soils, by collecting drainage data with time domain reflectometry across small time increments and implementing analytical models using a nonlinear iterative fitting procedure. The analysis was applied to both observed and Leaching Estimation and Chemistry Water Model (LEACHW) drainage of Sparta (mesic, uncoated, Typic Quartzipsamments) and Plainfield sand (mixed, mesic, Typic Udipsamment), as well as strongly structured Dubuque silt loam (fine-silty, mixed, mesic, Typic Hapludalf), where water content was measured with a neutron meter. We found significant differences (P < 0.05) between soils and profile depths relating macropore and matrix flow domains of observed data. Maximum hydrologically effective macropore volumes ranged from 0.018 (1.8%) in Dubuque silt loam to 0.294 (29.4%) in Sparta sand. Mixed results were obtained with flow domain partitioning of drainage simulated with LEACHW. In 5 of 15 cases, macropore and micropore parameter estimates failed to converge. Best agreement of micropore and macropore parameter estimates between observed and modeled drainage was observed in Dubuque soil and poorest concordance in Sparta sand. This analytical scheme may be applied to a wide range of soils if appropriate data describing the hydrological character were available. Research supported by USDA-ARS Management System Evaluation Area and Univ. of Wisconsin-Madison College of Agriculture and Life Sciences.