Inventories of soil organic carbon (SOC) stocks for 1960, 1990 and 2000 have recently become available for Belgium. From these inventories we selected three agricultural regions (Polders, Loam belt and Condroz) with 60 to 80 % of the agricultural area under cropland in order to analyse the driving forces of the changes in SOC stocks over time. The observed values of SOC stocks of typical soil associations for each agricultural region are compared to simulations with the RothC soil carbon model. After estimating the local parameters by fitting the model to SOC values from a long term experiment in central Belgium, the model was run from 1960 to 2000 for typical soil profiles of soil associations in the three agricultural regions. The main factors inducing changes in SOC stocks are the increase in plough depth as a result of continued mechanisation in the 1960s and the sustained input of organic amendments in the form of farm yard manure and slurry. In contrast to earlier publications on CO2 emissions from agricultural soils, the model did not predict a decrease in SOC stocks for the period 19902000. The decrease in animal manure production observed during the 1990s for those regions with a concentration of intensive livestock breeding in Flanders suggests that SOC stocks in croplands will continue to decrease. This will lead to an emission of 0.41 Mt CO2 per year for the three main cropland areas of Belgium in the near future and hence partly offset the carbon sequestration potential of improved cropland management (0.95 Mt CO2 per year).