Soil Regeneration for Improved Uplands Revegetation Vic Claassen Land, Air and Water Resources University of California, Davis Plant cover provides excellent erosion protection on upland soils and protects watersheds from sediment movement for thousands of years. Sites that have lost their topsoil horizons through disturbance, however, lack the ability to grow and sustain plant cover. These sites continue to produce sediment to watercourses in the Tahoe Basin. California Department of Transportation studies in granite soils suggest that soil moisture and soil nitrogen are commonly limiting to plant growth in disturbed uplands areas. These areas have been stripped of soil organic matter that retains moisture and that provides a steady supply of plant-available nitrogen. Because large amounts of organic materials are needed to regenerate adequate soil levels, the amendments must be in forms that do not leach nutrients to local watersheds. Incubation chamber experiments suggest that amendments of various types of yard trimmings composts to granite sands (open symbols) release less N than an existing native topsoil collected from the Tahoe Basin (closed symbol) (Figure 1). With additional soil incubation time, however, the rates of N release approach that of the topsoil. Additional work is currently in progress to develop evaluation methods for appropriate mixes of other organic materials, including pine needles mulches, agricultural composts, wood chips from forest thinning, etc. Such mixes would improve water holding capacity of the soils, retain nutrients, and reduce sediment loss through support of a sustainable vegetation and ground cover. Other related projects (California Department of Transportation, Lahontan Regional Water Quality Control Board, California Integrated Waste Management Board) involve development of rapid organic matter characterization methods to facilitate screening of materials specified for field construction projects, the influence of organic matter quality on rainfall infiltration properties and effective field application methods. Fig. 1. Nitrogen yield (mg N per column) during a 586 day aerobic incubation of topsoil from Luther Pass in the Tahoe Basin and decomposed granite sands receiving amendments (500 kg N/ha) of various composts.