Static development
Plant properties can optionally be given as driving variables in a separate PG-file (refer to Crop data at the end of this section). In this case, only one series of values for a particular plant property can be read by the model in each simulation, and consequently this option puts limitations to the “multiple plants” approach. If a plant property, such as plant height, is specified more than once in the driving variable file (e.g. if data for different plants are included in the same file), the parameter Plant, Index in PG-file. determines which of the time series will be used.
Albedo can also be given as one constant value for the whole growing season (switch AlbedoVeg, option “static”). The parameter value, aveg, is specified by the parameter AlbedoLeaf.
The last option for static development is to specify values in a parameter table. These parameters are given differently to the model depending on whether multiple plants are simulated or not. If the single big leaf models are used, then the appropriate properties are found in the tables Above ground characteristics with time and Root development with time. In these tables arrays for the different variables can be specified at different day numbers and interpolations are made using a common temporal function defined as:
when t is in an interval between t at tday(i-1) and tday(i). The parameter cform is defined in a table as an array. See viewing functions Leaf Area Index generated from parameters, single canopy and Root Depth generated from parameters, single canopy.
where x(i) is the parameter defined at day number tday(i) in an array from 1 to n. Up to 5 day numbers can be defined, with values > 0 and ≥ 365. If tday(i) is set to 0, only indices lower than i will be considered.
Figure 3.1. Graphical representation of the interpolation procedure used for some plant related properties.
The starting day can optionally be static or a function of air temperature (see switch PlantDevelopment). If the starting day is static, this date is not modified by any environmental property. The starting day, tday(1), can also be put to the day number in the spring when the accumulated sum of air temperatures, tsumplant, above the critical temperature, tcrit, reaches the value of the temperature sum starting value, tstart. The accumulation of temperatures starts when the day length exceeds 10 hours. Five consecutive days in the autumn with day lengths shorter than 10 hours and with temperatures below a critical temperature, tcrit, terminates the growing season. The winter period starts by setting the leaf area index, Al, roughness length, z0, canopy height, Hp, displacement height, d, and surface resistance to the values that correspond to the first index in their vectors. Note that this option concerns single leaf simulations only.
If the multiple big leaves model is used the appropriate properties are found in the tables Albedo vegetation - multiple canopies, Canopy height - multiple canopies, Leaf Area Index - multiple canopies, Root lengths - multiple canopies and Root depths - multiple canopies. For multiple plants a different procedure is used to construct the temporal dynamics during the year than for single plants. Temporal functions are defined in intervals of day numbers from start to optimum and from optimum to end. The interpolations are made using the basic eq. (3.1) but with a different definition of the shape factor compared to eq. (3.2). Now the shape factor is instead defined as:
The same intervals for interpolation are used for: LAI, Al, canopy height, Hp, albedo, aveg, root depth, zroot, root length, Lr. See viewing functions Plant Albedo generated from parameters, multiple canopies, Leaf Area Index - multiple canopies, Canopy Height generated from parameters, multiple canopies, Root Depth generated for parameters, multiple canopies and Root Length generated from parameters, multiple canopies.