PARTITIONED FLOW DOMAINS OF 3 WISCONSIN SOILS

Preferential flow mechanisms have been the subject of increasing resea rch interest because these phenomena contribute to solute transport. C ommonly, preferential flow paths are associated with macropores or hig hly structured soils. Sandy soils are typically weakly structured or s tructureless. However, they exhibit rapid drainage, which may mimic th e hydrology and solute transport effects of macropores. We tested whet her a flow domain partitioning scheme could be applied on two sandy so ils, by collecting drainage data with time domain reflectometry across small time increments and implementing analytical models using a nonl inear iterative fitting procedure. The analysis was applied to both ob served and Leaching Estimation and Chemistry Water Model (LEACHW) drai nage of Sparta (mesic, uncoated, Typic Quartzipsamments) and Plainfiel d sand (mixed, mesic, Typic Udipsamment), as well as strongly structur ed Dubuque silt loam (fine-silty, mixed, mesic, Typic Hapludalf), wher e water content was measured with a neutron meter. We found significan t differences (P < 0.05) between soils and profile depths relating mac ropore and matrix flow domains of observed data. Maximum hydrologicall y 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 wit h flow domain partitioning of drainage simulated with LEACHW. In 5 of 15 cases, macropore and micropore parameter estimates failed to conver ge. Best agreement of micropore and macropore parameter estimates betw een observed and modeled drainage was observed in Dubuque soil and poo rest concordance in Sparta sand. This analytical scheme may be applied to a wide range of soils if appropriate data describing the hydrologi cal character were available.