MODELLING CO2 EXCHANGES OF GREENHOUSE CROPS: A MATTER OF SCALES AND BOUNDARIES
(1). The criteria for choosing a time scale are (Leuduc & Holt, 1987):
- the need for short or long term predictions (for greenhouse crops, this relates with the grower's decisions about daily climate setpoints, or with whole-season growing strategies);
- the frequency of available input data ;
- the time constant of the modelled processes ;
- the variations in forcing variables (light, temperature, CO2). When one forcing variable shows a high variability and the plant response to this factor in non-linear, averaging over a long period would lead to errors in the resulting model.
Under a greenhouse, the modelled system is generally the canopy, but the space scale has to be smaller because of its heterogeneity (important mostly for light interception) and its finiteness. The greenhouse itself introduces some horizontal variability in incident light, and possibly in temperature and CO2.