Ecology–Soil Relations — Abstract of Paper


Factors Influencing Soil Surface Bulk Density on Oak Savanna Rangeland in the Southern Sierra Nevada Foothills
Dennis M. Dudley,¹ Kenneth W. Tate,² Neil K. McDougald,³ and Melvin R. George²


The objectives of this study were to compare soil surface bulk density between rangeland pastures not grazed since 1935, 1975, and 1995 to grazed areas with a 15-year record of light (>1,000 lbs ac^-1 RDM), moderate (600-800 lbs ac^-1 RDM), and heavy (<400 lbs ac^-1 RDM) grazing by beef cattle; and to determine the influence of oak canopy, topographic position, and livestock concentration activities on bulk density. The study was conducted on sandy-loam soils on oak savanna at the San Joaquin Experimental Range in Madera County, CA. A total of 1047 bulk density samples were collected. Soil surface bulk density was 19 percent lower under oak canopy than in adjacent open grasslands. Livestock grazing at all levels increased bulk density above areas excluded from grazing for 5, 25, and 65 years, while there were no significant differences among exclosures. Areas with light grazing had lower bulk density than moderately and heavily grazed sites, which were not different from each other. RDM recommendations at, or above, 800 lbs ac^-1 will likely lead to reduced soil surface bulk density on these soil series. Livestock concentration areas were the most compacted sites in the study.