A method to analyse the radiation transfer within a greenhouse cucumber canopy (Cucumis sativus L.)

In cucumber with its distinct row structure, leaf area and light are unevenly distributed in space. The aim of this work is to conceptualise a radiation transfer model and to describe the set up of the related experiments. The parametersation of the radiation transfer model will be done based on static structural models of cucumber plants obtained from digitalisation. To analyse the radiation transfer for each leaf, the sunlit and shaded areas and the corresponding light intensities on them will be calculated as functions of sun position, incoming light, plant and canopy architecture. To distinguish sunlit and shaded leaf area a projection algorithm will be used to get a measure for the fraction of sunlit leaf area. The intensity of direct light on the sunlit leaf area will be calculated by the incoming PAR intensity depending on the angle between irradiance vector and area normal. PAR intensity on shaded leaf parts (diffuse light) will be calculated based on the approach of Monsi & Saeki. Input parameters will be leaf area index, leaf optical properties of the surrounding leaves and empirical factors describing plant distribution. Output variables of the radiation transfer model will be the sunlit and shaded areas of each leaf with the corresponding light intensities. Future versions of the of radiation transfer model will need to be coupled with functional models of photosynthesis and assimilate allocation. A further step will be to link the model with a dynamic structural model of cucumber plant growth to obtain a functional-structural plant model of cucumber on organ basis. Such models allow improving the understanding of relationships between plant architecture and plant growth and may help to identify optimised plant manipulations regimes.