Modelling C and N dynamics in forest soils with a modified version of the CENTURY model

The CENTURY model of soil organic matter turn-over developed by Parton and co-workers has been used successfully for grasslands to predict dynamics of C, N and other nutrients. It was tested here for decomposition of a range of forest litters and for N mineralisation in forest soils. Modifications to the CENTURY model were necessary to match model output to empirical findings. These modifications included: (1) incorporation of additional woody litter pools (i.e. fine-wood and coarse-wood) (2) allowing the N content of soil organic matter (SOM) pools to vary (3) constraining N mineralisation and immobilisation to the active SOM pool (4) incorporation of a small flux of mineral N to the resistant SOM pool (5) allowance of mycorrhizal uptake of N, and (6) re-formulation of temperature and moisture effects on decomposition. Other possible changes, such as giving greater flexibility to the critical N concentration for mineralisation, were tested but found not to improve model performance. dified model largely accounted for the effects of initial lignin and N concentration on subsequent litter decomposition rate, litter N concentrations and critical N concentrations for the commencement of mineralisation. Consequently, the model could successfully simulate realistic time courses of N immobilisation and subsequent mineralisation for a range of litter types. The present model also successfully predicted the critical N concentration for N mineralisation across a wide range of litter samples from forests and other vegetation sources. Net N mineralisation was successfully simulated in forest soils, which were either untreated, irrigated or fertilised.