Click on image to view larger version.
Fig. 4. Average (with 95% confidence intervals) (a) 
15N values and (b) C/N ratios from muffle furnace experiment for the interaction of muffle burn temperature and duration. The error term for the test of the interaction was the mean expected squared error from the factorial component of the ANOVA, which used sites and soil layers as replicates. Eight preplanned contrasts were performed to compare interaction means while respecting the overall experiment-wide alpha error rate of 0.05: 20 vs. 100, 200, and 400°C at each of 1, 5, 15, and 60 min (four separate contrasts, one per duration); and 200 vs. 400°C at each of 1, 5, 15, and 60 min (four separate contrasts, one per duration). Different letters under the lower confidence interval apply only to preplanned contrasts and indicate that means are different among temperatures whereas different numbers adjacent to letters (e.g., "a1" vs. "a2") indicate different means among duration between 200 vs. 400°C.
