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Increases in atmospheric C have resulted in concerns about global warming and interest in finding the means to sequester atmospheric C through land management strategies. The purposes of this study were to: (i) compare changes in mineral soil C after a 30‐yr interval, and (ii) examine the potential roles of soil N, soil texture, and topography in these changes. The Camp Branch watershed is a second‐growth, oak‐dominated, mixed hardwood forest on the Cumberland Plateau in central Tennessee. In July 1976, soil samples were collected at permanently identified points and archived. These points were resampled in July 2006 and both the archived and new samples of the 0‐ to 10‐cm increment of the mineral soil were analyzed for C and N. Comparisons revealed that the changes in C and N were distinct to each of the eight soil series occurring on the site. Comparison of 2006 samples to 1976 samples indicated that 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. The change in C was positively correlated with the change in exchangeable inorganic N (r2 = 0.31, P < 0.0001). An overstory inventory indicated a decline in oak domination and site‐specific changes in basal area, density, and stand age. Since regression analysis revealed that the change in C was not predicted by topographic factors or soil texture, we speculate that changes in forest cover influenced the changes in mineral soil C.

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Use of mechanistic models is an increasingly accepted way to evaluate complex processes. The Barber-Cushman model provides a means to simulate nutrient uptake once information on root system characteristics, nutrient uptake, and soil nutrient supply are developed. Objectives of this study were to determine during a growing season: (i) root growth for 1-yr-old black cherry (Prunus serotina Ehrh.), northern red oak (Quercus rubra L.), and red maple (Acer rubrum L.) seedlings; (ii) net plant increase in N, P, K, Ca, and Mg; (iii) soil solution and solid phase nutrient concentrations; and (iv) the influence of root growth and soil nutrient supply changes on nutrient uptake using the Barber-Cushman model. Seedlings were grown in pots containing A horizon soil from two forest sites. Measurements were made on five occasions during the growing season. Root growth averaged 41.5 cm d-1 for red maple compared with 28.0 and 16.7 cm d-1 for cherry and oak, respectively. Seventy-five percent of root growth occurred at the end of the growing season. Total plant N showed the greatest change (25-58%) due to soil source. Model simulations underestimated observed uptake by 31 to 99%. A clear relationship between soil solution nutrient concentration and plant uptake, an important assumption of the model, was not observed. Results indicate care will need to be exercised in the development and use of root growth and nutrient supply values in mechanistic models.