To learn whether soil properties important to production agriculture and environmental quality have changed significantly in the past half-century in California, we analyzed archival samples and samples collected in 2001 from the same locations. Comparisons of organic matter content, pH, electrical conductivity, total nitrogen, total carbon and plant- available phosphorus showed significant changes since the mid-1900s. Across the state we found increases at the 95% confidence level for plant-available phosphorus, total carbon, pH, and percent clay, and increases at the 90% confidence level for percent silt and total nitrogen. We measured significant decreases at the 95% confidence level for electrical conductivity and percent sand. Based on this sample of 125 soils, we believe that California’s soil chemical quality has not decreased significantly over the past 60 years. However, increased clay percen-tages may be interpreted as a sign of accelerated erosion, which is a sign of decreased soil quality.

The UC Sierra Foothill Research and Extension Center (SFREC) is located in the heart of typical California blue oak and live oak woodlands within metavolcanic terrain of the Sierra Nevada foothills. These types of woodlands often exist at the interface between urban, wild and agricultural lands and are used extensively for livestock grazing, wildlife habitat and surface water supply. Soil surveys for this region and within SFREC depict relatively few soil types compared to areas that support more-intensive agricultural land uses. Despite this inferred homogeneity, our study showed that the biogeochemical and physical properties of soils vary sharply over short distances of less than 10 feet and also experience changes by season and as a result of storm events. An understanding of soil variability in this setting is important to assess rangeland productivity, perennial grass and oak restoration potential, carbon sequestration, stream flow generation and stream water chemistry.

Long-term water quality records for assessing natural variability, impact of management, and that guide regulatory processes to safeguard water resources are rare for California oak woodland rangelands. This study presents a 20-yr record (1981-2000) of nitrate-nitrogen (NO3-N) and suspended sediment export from a typical, grazed oak woodland watershed (103 ha) in the northern Sierra Nevada foothills of California. Mean annual precipitation over the 20-yr period was 734 mm yr(-1) (range 366-1205 mm yr(-1)). Mean annual stream flow was 353 mm y(-1) (range 87-848 mm yr(-1)). Average annual stream flow was 48.1 +/- 16% of precipitation. Mean annual NO3-N export was 1.6 kg ha(-1) yr(-1) (range 0.18-3.6 kg ha(-1) yr(-1)). Annual NO3-N export significantly (P < 0.05) increased with increasing annual stream flow and precipitation. Mean daily NO3-N export was 0.004 kg ha(-1) d(-1) (range 10(-5) to 0.55 kg ha(-1) d(-1)). Mean annual suspended sediment export was 198 kg ha(-1) yr(-1) (range 23-479 kg ha(-1) yr(-1)). There was a positive relationship (P < 0.05) between annual suspended sediment export, annual stream How and precipitation. Mean daily suspended sediment export was 0.54 kg ha(-1) d(-1) (range 10(-4) to 155 kg ha(-1) d(-1)). Virtually no sediment was exported during the dry season. The large variation in daily and annual fluxes highlights the necessity of using long-term records to establish quantitative water quality targets for rangelands and demonstrates the difficulty of designing a water quality monitoring program for these ecosystems.