Sensitivity of the Century Model to Scale‐Related Soil Texture Variability

Sequestering C in agricultural soils presents an immediate viable option to reduce atmospheric CO 2 to help mitigate global warming. Agricultural land managers who adopt practices that sequester C might market the sequestered (i.e., stored) C as a C credit to industrial CO 2 emitters who wish to reduce their net CO 2 emissions. Land managers or landowners will need to verify changes in soil organic carbon (SOC) related to a change in management practice to facilitate C credit trading. The objective of this study was to assess the accuracy of Century model predictions of SOC change due to the adoption of no‐tillage using site‐specific data and data from existing soil databases. We hypothesized that (i) using site‐specific soil data would result in the most accurate Century estimates and (ii) Century estimates are sensitive to soil clay percentage. Five paired tillage/no‐tillage farm sites in north‐central Montana were used to test model predictions. Sites were chosen such that soil, landscape, climatic conditions, and historical cropping systems were similar within each tillage/no‐tillage pair. The Century model overestimated SOC content using site‐specific soils data by an average of 10%. Century was sensitive to the effects of clay content when predicting the total amount of SOC in a particular field. There was insufficient evidence to suggest that a linear association exists between clay content and Century‐estimated C change due to no‐tillage. Results suggest that (i) the effect of clay percentage on the rate of C change is not well understood and (ii) the Century model is an acceptable predictor of soil C for C trading. Further examination of the relationship between soil clay content and the rate of C storage in agricultural systems is needed to determine if adjustments to the Century model are required.