GreenLab Course
Overview
Biomass production.
Plant production
Plant production (biomass) modelling sets out to predict, plant crops quantitatively, and to optimize crop management sequences.
- climatic parameters (light, water, temperature)
- leaf indexes (such as leaf area per m2)
- yield indexes (the ratio of biomass related to the crop compared to the total biomass)
- etc.
Plant production modelling: a macro-scale approach
Plant crop models were introduced by the Dutch researcher de Witt in 1970.
Plant crop models involve various climatic and vegetation parameters, indexes and data:
In those models, also called crop models, biomass production is considered for a unit area (m2) level, not on an individual plant level.
Field experiments have shown relations (laws) explaining macroscopic functional behaviour in plants, without considering the deeply complex physiological processes of photosynthesis or respiration, or considering aspects at cell level.
Agronomic laws
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Thermal time
One noteworthy empirical law at plant level is the notion of thermal time.
Thermal time corresponds to the sum of average daily temperatures received by the plant.
Experiments have proved that plant organ development (both for organogenesis and expansion)
appears unstable depending on the calendar time, but becomes linear with thermal time.
In other words, the occurrence of germination, flowering, new leaf emissions
from terminal buds tales place beyond a specific sum of temperatures.
Thermal time therefore drives development sequences in plants.
Thermal time thus defines the growth cycle steps (rather than a calendar schedule) in
most agronomic crop models.
Light interception
The other point to consider in the production of dry matter (DM) is the relationship
between growth and light interception.
In its simplest form, this relationship can be expressed by the following equation:
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DM = LUE . PAR . (1 - e k . LAI ). (Eq. 1)
where
LUE is Light Use Efficiency, i.e. the efficiency of light conversion to dry matter for the active part of the radiation (PAR) received by the cover.
LAI is the Leaf Area Index, i.e. the leaf area per m2 in the crop.
The higher this index is, the more light is intercepted by the foliage.
The coefficient k is determined empirically. The exponential term models how the leaves cover each other, reducing light efficiency.
This formalism based on the light intercepted by the foliage is the Beer-Lambert law.
Notes.
1. Beyond a LAI value of 4, all the light is intercepted and dry matter production saturates.
Additional leaves are no longer effective and increasing the planting density is pointless.
2. Under favourable conditions barely more than 20 grams of dry matter can be produced per day per m2.