Long-term agricultural field experiments in Northern Europe: analysis of the influence of management on soil carbon stocks using the ICBM model. [Erratum: July 1999, v. 75 (1/2), p. 145-146.]

Land use in general and particularly agricultural practices can significantly influence soil carbon (C) storage. Changes in topsoil C mass measured in long-term agricultural field trials in Sweden and other Northern European countries were compiled and aggregated into seven treatment classes, including manured, fertilized and straw exported. The impact of crop rotations and management practices on C stocks to the topsoil was analyzed using both a static model and a dynamic soil carbon model (introductory C Balance Model; ICBM). ICBM consists of two state variables and four fluxes (governed by four rate-determining parameters), and one parameter, r(e), combining most external factors affecting C mineralization (temperature, precipitation, drainage, etc.). Simple 'front-end models' were used to estimate values for two of the parameters, i (annual C input) and h (humification coefficient) initially based on incomplete records from the field trials, official agricultural statistics and other literature. The r(e) parameter was then optimized for each class of treatments, using an algorithm for non-linear least squares. Initial soil C mass, present C inputs and abiotic conditions, such as soil temperature and moisture, were the deciding factors in whether C stocks declined or increased. Steady-state values calculated using the static and dynamic model were similar for both models, but differed greatly between treatment classes. For cereal-dominated cropping systems where the straw was removed, manure application increased steady-state values about three times (from 3 to 9 kg C m-2), compared with corresponding treatments. Incorporation of straw resulted in intermediate steady-state values (5-6 kg C m-2). C mineralization rates were highest in bare fallow treatments. For one class of soils, C retention in the soil was found to increase significantly with increasing clay content. The hypothesis that the climatic gradients in Northern Europe affect decomposition and primary production rates similarly, leading to the same soil C stocks, could not be rejected.