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Long-Term Changes in Mollisol Organic Carbon and Nitrogen

Univ. of Illinois at Urbana-Champaign, Dep. of Natural Resources and Environmental Sciences, W-503 Turner Hall, 1102 S. Goodwin Ave., Urbana, IL 61801

View larger version (17K): [in this window] [in a new window]   Fig. 1. Comparison of organic C and total N concentrations in archived soil samples from 1901 to 1910 measured at the time of sampling and again in 2002.

View larger version (25K): [in this window] [in a new window]   Fig. 2. Percentage differences in soil organic C and N concentrations between original and recent sampling and between grass or prairie soils and paired cultivated fields by sample groups and soil depth. Triangles indicate individual site differences; lines illustrate the range. For each comparison type and within a depth, mean of site differences significantly different from zero at p < 0.05 shown with *; p < 0.01 shown with **. NS, not significantly different (p > 0.05). Paired t tests used. ANOVA used.

View larger version (11K): [in this window] [in a new window]   Fig. 3. Percentage differences in organic C and total N contents in the soil profile (0–100 cm) between original and recent sampling and between grass or prairie soils and paired cultivated fields by sample groups. Triangles indicate individual site values; lines illustrate the range. NS, mean of site differences not significantly different from zero (p > 0.05) using paired t test for each comparison type. Statistical comparison is available in Table 3.

View larger version (11K): [in this window] [in a new window]   Fig. 4. Mass differences by sample groups for organic C and total N in the soil profile (0–100 cm) between original and recent sampling and between grass or prairie soils and paired cultivated fields. Triangles indicate individual site values; lines illustrate the range.

View larger version (17K): [in this window] [in a new window]   Fig. 5. Mean organic C and total N profile mass by time period, with standard errors. The 1870 are virgin prairies sampled in 2002 (n = 3), 1904 is the mean mass calculated by Hopkins and Pettit (1908) for cultivated black clay loams (flat prairie) and brown silt loams (undulating prairie) sampled between 1901 and 1907 in central Illinois (n = 41), 1957 represents the cultivated fields from USDA (1968) data (n = 6), and 2002 is the mean of each of our cultivated fields (n = 18). The break indicates that the 1870 virgin prairie date is uncertain and represents precultivation conditions. Means followed by the same letter are not significantly different at the 0.05 level.