ISHS Acta Horticulturae 313: III International Symposium on Computer Modelling in Fruit Research and Orchard Management
THE SIMPLIFIED DRY MATTER PRODUCTION MODEL FOR APPLE: ESTIMATION OF CANOPY PHOTOSYNTHESIS IN DISCONTINUOUS CANOPIES |
| Author: | A.N. Lakso |
| Abstract:
A simplified dry matter production model, constructed with the user-friendly "Stella" dynamic simulation automatic programming language on a Macintosh computer, was described in the last symposium (Lakso and Johnson, 1990). The simplified model uses a daily time step and thus estimates daily integrals of canopy photosynthesis, leaf area development and respiration. A major limitation of the model for fruit crop modelling is that it originally dealt with canopies as continuous. An evaluation is made of a method of dealing with discontinuous canopies is simplified ways that do not require the inclusion of a diurnal radiation geometry model in the basic daily iterations. The method is adapted from Jackson and Palmer (1979), and separates the incident light into two fractions; viz. that which penetrates directly to the ground without passing through any volume allotted to tree canopy, and that which is the maximum potentially intercepted by a solid tree canopy (Fmax in the model of Jackson and Palmer (1979)). These two factors are estimated according to solid tree models that assume infinite leaf area (i.e. zero transmission) in the canopy allotted volume. The tree canopy photosynthesis from the original model is then adjusted by (i) reducing the incident light to that would could potentially hit the canopies, and (ii) increasing the original whole-orchard LAI by dividing by the fraction of light actually incident upon the canopies (LAI' = LAI/Fmax). These adjustments have opposing effects, as the total light intercepted decreases, but the interception within the canopies increases. Although simulated canopy photosynthesis decreases as Fmax declines, greater changes occur at higher LAI values since increasing an already high LAI has little additional effect on light interception for photosynthesis. | |
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