GreenLab Course
Production - Expansion
Principles
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The GreenLab model refines classic process-based models
Functioning in GreenLab vs PBM
Computing biomass production
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GreenLab is based on the classic production model
dW = LUE . PAR . (1 - e-k LAI)
applying it to successive growth cycles.
The well-known formulation describes production for a unit area (1 m2). In the GreenLab model, the unit area is defined as the "plant Area", leading to a unique equation linking production from plant to crop scale.
Computing the LAI.
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In PbMs, LAI estimation is not obvious. In GreenLab LAI computation is
replaced by a total leaf area / plant area ratio.
At high densities it has been shown that this ratio tends towards the LAI.
The total leaf area results from organogenesis that defines the number of new leaves for each cycle, and their respective areas computed from biomass partitioning
Organ compartments
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In classic PbMs, biomass is spread among the different organ compartments, defined by organ types.
In GreenLab, each organ compartment is in fact split into several compartments related to their ages:
- their physiological age, as defined in botanical architecture
- their ontogenetic age (in other words the date they appear)
Under these conditions, each GreenLab organ compartment, called cohorts (see next page), contains organs with the same physiological properties, the same age and constrained by the same environmental conditions.
Organ expansion dynamics
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Organ expansion dynamics are often assumed to be stable (for instance expressed as a ratio between existing organs)
In this model, the function defining the ability to store biomass is considered as a non-constant, hidden function, showing a generic shape, related to genetics and fitted from the model applications on real measurements.
Model expression
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The GreenLab model can be fully expressed by a set of mathematical expressions allowing:
- theoretical model studies; in particular equilibrium production conditions can be analysed (see study case in Applications)
- parameter identification
- reversing parameters and variables for instance, finding the density from the measurements on plants already modelled.