Variability of Nitrogen and Carbon in Surface Soils of Six Forest Types in the Oregon Cascades

Soil samples were collected from sites typical of six forest habitat types in the western Oregon Cascades to determine the variability in total N, C, and mineralizable N. Within each type, 20 samples of surface soil (0‐15 cm deep) were removed from around the outside perimeter of a 0.25‐ha plot. Averages of 23, 28, and 70 samples were needed to estimate the population mean of total N, C, and mineralizable N, respectively, with an accuracy of ±10% at a 95% probability. Variability was not reduced by reporting data on the basis of mass per area rather than concentration, but the method of reporting data affected the relative ranking of sites. Within‐site variability was not generally related to microsite differences in slope or coarse fragment content.