RESUMO
To reduce atmospheric CO(2) concentrations and provide food for a growing world population, sustainable management practices must be adopted. An important consideration in the development of sustainable practices is the maintenance of soil organic carbon (SOC). Critical assumptions, with unknown errors, are used to calculate SOC maintenance requirements. This study investigated the impact of three approaches for estimating belowground nonharvested carbon (NHC) on SOC maintenance requirements, SOC and nonharvested C mineralization rate constants, and the capacity of the soil to sequester carbon. Common protocols were used to develop databases from eight historical carbon studies. The SOC to CO(2) (k(SOC)) and NHC to SOC (k(NHC)) rate constants were calculated using the model NHC(a)/SOC(i) = k(SOC)/k(NHC) + dSOC/dt(1/k(NHC)SOC(i)), where NHC(a) is the amount of applied NHC, SOC(e) is SOC at the equilibrium point, t = time, and SOC(i) is the initial SOC value. Analysis showed that (i) despite the difficulty in measuring belowground biomass, it is needed to calculate the SOC and NHC mineralization rate constants when using nonisotopic approaches; (ii) decreasing NHC by reducing the relative contribution of roots to NHC reduced the calculated SOC maintenance requirements and the amount of corn stover that could be sustainably harvested; iii) changes in the belowground NHC calculation approach do not result in a consistent impact on calculated rate constants; iv) changes in the belowground NHC calculation approach had a minimal impact on the calculated carbon sequestration potential (k(NHC)NHC)/k(SOC); (v) SOC at the beginning of the experiments was negatively correlated with temperature, while k(SOC) was positively correlated with tillage intensity; and (vi) the k(SOC) and k(NHC) rate constants can be used to directly assess the impact of different management scenarios on carbon turnover.