| Abstract: | Research on erosion plots and small watersheds with upland loessal soils containing hydraulically-controlling subsurface horizons showed that as scale increases so does the amount ofarmual runoff Theamount of runoff from 2 to 3 ha watersheds was twice that from 0.008 ha plots. However, the ratio ofrunoff from watersheds to plots was 3.0 from Dec through March, and only 1 .7 during the rest of the year.Georeferenced penetrometer resistance measurements documented the presence of restrictive layers within1 m of the soil surface. Observation wells showed the presence of spatially varying perched water tables.We propose that the runoff difference between plot and watershed scales was re1ated to the increasingimportance of hydraulically restrictive subsurface horizons, especially during the winter months. Waterinfiltrated into linear backslope areas that the plots represent may converge in concave toe slopes areas,creating wetter antecedent conditions and return flow contributions to surface runoff No-tillmanagement reduced sediment production by about 90% on plots and by at least 95% on watersheds; notill reduced runoff about 10% from both plots and watersheds in this study. Conservation managementaffected hydraulic resistance at the soil surface rather than the permeability of deep restrictive layers. |
