The formulations that we have presented now are sufficient to describe the radiatif climate inside an intercropping systems formed by three vegetal levels: date palms, fruit trees and market gardening at any time and location. Special attention is given to light sharing between the three crop stories and spatial variability of light transmitted through them. As the detailed geometrical structure of the oasis in the region of North Africa is largely unknown, the equations presented above can help for the proposal of a best architecture for an efficient use of resources when thinking to install new oasis with tolerant species. Also, for the projects of rehabilitation and the biodiversity arrangement of the existing oasis in the region the cited equations are very useful. But the challenge is to extrapolate a results found for one oasis to the others and to scale up a model applied for a limited field to a vast region.
5.2.2 Formulating Heat and Mass Transfer Inside the Oasis
An important method to analyse and monitor the heat and mass transfer inside the vegetation is to consider a formulation that introduces many specific parameters concerning plant physiology and leaf microenvironment (Chen, 1984). I cite here the stomata conductance, stomata resistance, leaf area index, photosynthesis rate for all the plant component, leaf temperature, turbulent transfer resistance, aerodynamic resistance, boundary layer resistance, wind velocity, net and global solar radiation, air temperature (Jarvis and Mc Naughton, 1986). In the same meaning, we can consider an electrical analogy with circuits for the sensible and latent heat exchanged between the different farming stories inside the oasis (Sellami and Sifaoui, 2008). The net radiation absorbed within each layer of the oasis canopy represents its current source. Sensible and latent heat flux supplied by the layer inside the canopy are considered as intensity of the electric current. Potential sources, analogy of tension for the electric current, were air temperature at a reference height for sensible heat circuit and the water vapour pressure of the air at a reference height for latent heat circuit. Inside the oasis, in the vertical direction, the driving forces (potential) is determined from difference in temperature between layers for sensible heat density and from difference in water vapour pressure between layers for latent heat flux. Applying the analogy of electrical circuit theory and using the energy balance equations permit to formulate the latent heat flux, the sensible heat flux, the set of resistances to heat and mass transfer and the biomass productivity inside the oasis with the following equations:
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