NonlinearAnalysis:RealWorldApplications6(2005)773–795 www.elsevier.com/locate/na Individual-basedmodellingofmicrobialactivityto studymineralizationofCandNandnitrification processinsoil MartaGinovart a , ∗ ,DanielLópez b ,AnnaGras c a Department of Applied Mathematics III, College of Agriculture of Barcelona, Technical University of Catalonia, Urgell 187, 08036 Barcelona, Spain b Department of Physics and Nuclear Engineering, College of Agriculture of Barcelona, Technical University of Catalonia, Urgell 187, 08036 Barcelona, Spain c Department of Agri-Food and Biotechnology, College of Agriculture of Barcelona, Technical University of Catalonia, Urgell 187, 08036 Barcelona, Spain Abstract This work models the dynamics and evolution of carbon (C) and nitrogen (N) related to organic matterinsoilsbyusingindividual-basedsimulations.ThesimulatorINDISIM-SOMcontrolsagroup ofmicrobialcellsateachtimestep,usingasetoftime-dependentvariablesforeachmicroorganism. Thespaceisdividedintosquarecells.Ineachspatialcell,theamountsofdifferenttypesoforganic compoundsarecontrolled.TheseareidentifiedaspolymerizedorganicCandN,labileorganicCand N,mineralcompoundslikeN NH 4 ,N NO 3 ,CO 2 andO 2 .Themodeltakesintoaccounttheactivityoftwo prototypesofmicrobialcells:ammonifiermicroorganismsandnitrifierbacteria.Differentmetabolic pathways and sources of C and N they can use are identified. Some state variables and parameters related to soil organic matter and microbial activity: growth and decay of microbial biomass, and temporalevolutionsofmineralizedintermediateN,mineralNinammoniumandnitrate,CO 2 andO 2 arestudied.Thecalibrationofthesimulationmodelhasmadeuseofdatafromlaboratoryincubation experiments performed on two different types of Mediterranean soils. Both, conceptual validation during the development of the model and agreement of the simulation results with experimental ∗ Correspondingauthor.Tel.:+34934137536;fax:+34934137501. E-mail address: marta.ginovart@upc.es (M.Ginovart). 1468-1218/$-seefrontmatter  2005ElsevierLtd.Allrightsreserved. doi:10.1016/j.nonrwa.2004.12.005