Ecological Modelling 153 (2002) 291 – 295 Short communication Initialisation of the soil organic matter pools of the Daisy model Sander Bruun *, Lars S. Jensen Institute of Agricultural Sciences, The Royal Veterinary and Agricultural Uniersity, Thoraldsensej 40, DK-1871 Frederiksberg C, Denmark Received 11 July 2001; received in revised form 19 December 2001; accepted 4 January 2002 Abstract Like most other contemporary models of long-term soil organic matter (SOM) dynamics, Daisy partitions the refractory component of the SOM into two or more pools. In long-term simulations, the initial distribution of SOM between these two pools influences the simulations. However, as these pools do not correspond to any measurable entities the distribution of SOM cannot be initialised by a simple measurement. Daisy has usually been initialised by using a standard distribution, which almost corresponds to equilibrium. In applications of other models, the initial distribution between the different pools of organic matter has been chosen by assuming equilibrium at the beginning of the simulation, by using standard values or by calibrating the initial distribution to optimise simulation performance. However, as we show here the initial distribution of SOM between the different pools influences simulations notably, and the appropriate distribution is dependent on changes in management and climate at the site before the onset of a simulated experiment. This is done by simulating a scenario and initialising the Daisy model in to different ways: (1) by assuming equilibrium at the beginning of the simulation; and (2) by simulating the preexperimental management history of the site. This shows that it can be important to use plausible assumptions to initialise SOM models, and that often the only way to initialise the model is to simulate the preexperimental period of the site. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Model initialisation; Soil organic matter models; Daisy www.elsevier.com/locate/ecolmodel Soil organic matter (SOM) models used to model the long-term evolution of SOM have been reviewed several times (McGill, 1996; Molina and Smith, 1998). Most contemporary models of SOM partitions the non-living, refractory SOM into two pools (Parton et al., 1987; Hansen et al., 1991; Coleman and Jenkinson, 1996; Franko, 1996). However, as these pools do not correspond to any measurable entities the division introduces an initialisation problem (Falloon and Smith, 2000). The fact that the initial distribution of C between the different pools and not only the initial amount of C in the soil is dependent on the history of the simulated site is obvious, but has not been given much emphasis in applications of SOM models. * Corresponding author. Tel.: +45-352-83481; fax: +45- 352-83468. E-mail address: sab@kvl.dk (S. Bruun). 0304-3800/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0304-3800(02)00017-0