Modelling organic matter dynamics in New Zealand soils

To ensure the sustainability of land systems in terms of nutrient cycling a nd maintenance of soil physical conditions, there is a need to understand s oil organic matter (SOM) and its dynamics. lt has been suggested that soil- carbon (C) models developed internationally do not perform well under New Z ealand's unique climatic and soil mineralogical conditions. To test this hy pothesis, we conducted C-14-labelled ryegrass decomposition studies and ass essed the influence of abiotic factors on decomposition rates. These factor s were characterized by estimating system mean residence times (MRTs) from estimates of first-order rate coefficients in a simple, three-compartment m odel. A range of MRTs obtained for decomposition was related to climatic co nditions and soil properties. We summarise this work and extend this study to apply the Rothamsted soil-C turnover model, a five-compartment model, to our data with the view of testing both the model projections and the decom posability factors assumed in the model. (C) 2001 Elsevier Science Ltd. All rights reserved.