Temporal and Spatial Patterns of Nutrient Cycling in a California Sierra Foothills Watershed.

Oak-woodland-annual grasslands of the Sierra Foothills in California are an important ecoregion for rangeland, wildlife habitat and watershed ecosystem services. It is important to understand the interactions amongst nutrient cycling, soil respiration, terrain attributes and the dynamic soil properties in order to make well-informed land-use decisions. The objective of this study was to determine spatial and temporal relationships amongst nutrient cycling (particularly inorganic nitrogen) with soil respiration, terrain attributes and soil properties, such as moisture and temperature. The study occurred in a 36 ha watershed that has not been grazed in the past 15 years. A total of 100 characterized soil profiles have been instrumented with moisture and temperature sensors at soil horizon boundaries. Twenty-four of those sites were chosen for soil respiration measurements and the use of Plant Root Simulator (PRS) probes (Western Ag Innovations, Inc) to measure nutrient cycling dynamics. Soil respiration measurements were done with the Licor 8100 (LI-COR, Lincoln, NE). The sites were chosen based on four distinct terrain categories that varied in solar radiation exposure and topography. Two of the categories were further split into ‘tree’ and ‘grass’ components to determine any potential influence of vegetation with the aforementioned variables. The soil respiration and PRS measurements were obtained January through May in 2011. Results confirm previous studies which found inorganic nitrogen flushing out of the soil with the initiation of the wet season. Future pursuits include conducting spatial analysis on the aforementioned variables, determining factors influencing soil moisture and temperature, and coupling stream chemistry measurements with the nutrient cycling temporal variations.