Estimation of carbon losses by cultivation from soils of the Argentine Pampa using the Century Model

The Century model was used for estimating soil carbon levels under grassland at the regional scale in the Pampean Region of Argentina. Predicted values were compared with observed soil carbon contents obtained from soil surveys and the differences considered to be the results of cropping on soil organic matter. The Pampean Region was divided into five major sub-regions and carbon in the top 20 cm of each estimated by Century using aggregated soil and climatic data. In four of the sub-regions small differences between predicted and observed carbon contents were obtained which suggested little land use effect on soils. In the Rolling Pampa, a northern portion of the Pampean Region, observed carbon content was about half of Century prediction. In this sub-region, the main agricultural area of the country, cropping intensity, rainfall and temperature are higher than in the rest of the Pampas. A degradation index constructed by a multiplicative approach, taking into account percentage of surface cropped, rainfall and temperature was 2-5 times higher in the Rolling Pampa than in the other pampean sub-region. The difference between predicted C and observed C in the Rolling Pampa was attributed to carbon losses by cropping in a warm and wet climate.