Long-term agricultural field experiments in Northern Europe: analysis of the influence of management on soil carbon stocks using the ICBM model (vol 72, pg 165, 1999)

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 e xternal factors affecting C mineralization (temperature, precipitation, dra inage, etc.). Simple 'front-end models' were used to estimate values for tw o of the parameters, i (annual C input) and h (humification coefficient) in itially based on incomplete records from the field trials, official agricul tural statistics and other literature. The r(e) parameter was then optimize d for each class of treatments, using an algorithm for non-linear least squ ares. Initial soil C mass, present C inputs and abiotic conditions, such as soil temperature and moisture. were the deciding factors in whether C stoc ks declined or increased. Steady-state values calculated using the static a nd dynamic model were similar for both models, but differed greatly between treatment classes. For cereal-dominated cropping systems where the straw w as removed, manure application increased steady-state values about three ti mes (from 3 to 9 kg C m(-2)) compared with corresponding treatments. Incorp oration 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 i n Northern