We employed the Daily CENTURY (DayCent) soil organic matter model in a number of sensitivity simulations, in an attempt to quantify the effects of various factors on soil carbon (SC) levels. The site chosen for the simulations was Ames, Iowa, USA (42.03 deg N, 93.63 deg W), between 1894 and 2005. A control simulation was carried out using realistic assumptions of farming practices (tillage type, rotation pattern, fertilization, cultivar choice) and actual observed weather data (temperature and precipitation). The observed increase in atmospheric CO2 concentration during this time period was accounted for in the simulations. The sensitivity simulations varied one aspect of the simulation for the entire period. When compared against [...]