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How has soil quality changed in California over the past 60 years? Using the known locations of archived samples collected by the soil survey staff in the 1940s and 1950s, we resampled 125 locations in California from the Imperial Valley in the south to Tehama county in the north and analyzed samples for properties important to plant production. We collected three samples from the 0- to 25-cm depth at each location and air-dried them for analysis. For each 1945 and 2001 sample pH, electrical conductivity, total nitrogen, total carbon, plant available phosphorus, texture and color was measured. We compared the data across the entire state as well as by current land-use, and geographic region. Across the state, plant-available phosphorus, total carbon, pH, and percent clay increased significantly (95% confidence level) as did percent silt and total nitrogen (90% confidence). In contrast, electrical conductivity, and percent sand decreased significantly (95% confidence). Chroma also decreased significantly statewide (90% confidence level). The degree of change varied according to land-use and geographic region. Based on this sample, California's soil quality has not significantly decreased over the past 60 years. These results also suggest that defining and evaluating soil quality is difficult due to conflicting trends and interpretations of soil quality indices. |
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