Long-term agricultural field experiments in Northern Europe: analysis of the influence of management on soil carbon stocks using the ICBM model

Land use in general and particularly agricultural practices can significant ly 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, includ ing manured, fertilized and straw exported. The impact of crop rotations an d management practices on C stocks in 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, dr ainage, etc.). Simple 'front-end models' were used to estimate values for t wo of the parameters, i (annual C input) and h (humification coefficient) i nitially based on incomplete records from the field trials, official agricu ltural statistics and other literature. The r(e) parameter was then optimiz ed for each class of treatments, using an algorithm for non-linear least sq uares. Initial soil C mass, present C inputs and abiotic conditions, such a s soil temperature and moisture, were the deciding factors in whether C sto cks declined or increased. Steady-state values calculated using the static and dynamic model were similar for both models, but differed greatly betwee n treatment classes. For cereal-dominated cropping systems where the straw was removed, manure application increased steady-state values about three t imes (from 3 to 9 g C m(-2)), compared with corresponding treatments. Incor poration of straw resulted in intermediate steady-state values (5-6 g 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 significantl y with increasing clay content. The hypothesis that the climatic gradients in Northern Europe affect decomposition and primary production rates simila rly, leading to the same soil C stocks, could not be rejected. (C) 1999 Els evier Science B.V. All rights reserved.