Thirty-year Changes in Mineral Soil C in a Cumberland Plateau Forest as Influenced by Soil N Forms and Topography

Increases in atmospheric C have resulted in concerns about global warming and interest in finding means to sequester atmospheric C through land management strategies. The purpose of this study was to (i) compare changes in mineral soil C after a 30-year interval and (ii) examine the role of inorganic-N, soil texture, and topography in these changes. Soil samples were collected at permanently identified points on the Camp Branch Watershed, a second growth oak forest on the Cumberland Plateau in central Tennessee, in July of 1976 and archived. These points were re-sampled in July of 2006 and both archived and new samples of the 0 to 10 cm increment of the mineral soil were analyzed for C and N using the same procedures. Paired comparisons revealed changes in C and N were distinct to each of the 8 soil series. Comparison of 2006 samples to 1976 samples indicated changes in C concentration ranged from -13.1% to +12.0%. Changes in C mass ranged from -11.3% to +8.3%. Increases in C were most closely associated with increases in the C/total-N ratio. C was positively correlated to exchangeable inorganic-N in 1976 (r 2 = 0.387) and 2006 (r 2 = 0.107). Regression analysis revealed C increased with increasing azimuth and decreasing elevation in 1976 (r 2 = 0.140). C was predicted only by clay content in 2006 (r 2 = 0.079) and exhibited a negative relationship. Since topography was no longer a predictor of mineral soil C in 2006, we speculate that changes in forest cover also influenced changes in mineral soil C.