C-Farm: A Simple Model to Evaluate the Carbon Balance of Soil Profiles

Soil carbon (Cs) cycling is an essential component of agroecosystems models. Simulating Cs cycling has become an issue of societal importance for Cs storage can play a role reducing the rate of increase of atmospheric CO2 concentration. To participate in carbon trading markets, growers have to evaluate their local, sitespecific options to increase Cs or reduce Cs losses. This paper introduces C-Farm, a daily-time step cropping systems model that allows calculating the Cs balance using a one-pool soil organic matter sub-module. In C-Farm the Cs turnover rate depends non-linearly on Cs and on environmental and management controls. Two long-term experiments were selected to evaluate C-Farm: a wheat-summer fallow 70+ years experiment at Pendleton, Oregon, and the continuous wheat experiment at Rothamsted in the United Kingdom. C-Farm simulated well the long-term Cs evolution observed in these experiments. In addition, simulations performed in the dryland US Pacific Northwest show its applicability for assessing Cs storage rates in a region with large variation in precipitation. C-Farm can be easily customized to a large array of local conditions, providing robust estimates of shortand long-term on-farm carbon storage rates. The model is being further developed to provide estimates of nitrous oxide emission.