A three-dimensional approach to modeling light interception in heterogeneous canopies

The accuracy of plant growth models depends strongly on a precise calculati on of radiation uptake, Numerous approaches exist to estimate light absorpt ion in spatially heterogeneous canopies, but these either have restrictions with respect to canopy structure or involve complex and inflexible calcula tions. The objective of this study was to develop a simulation tool to asse ss radiation penetration into canopies that should (i) give details on ligh t absorption in heterogeneous canopy architectures and (ii) comprise simple and easily adaptable routines. In the model, the complete canopy volume is subdivided into cubic units that are either empty or filled with leaf area . Leaf area can be distributed in an arbitrarily chosen geometric solid pos itioned anywhere in the model domain. Transmission through the cubes is cal culated by following the path of solar rays from the top of the canopy to g round level, Daily canopy absorption is calculated separately for direct an d diffuse radiation, taking reflection and scattering of the direct beam in to account. Using only a few readily obtainable parameters, a close agreeme nt between simulated and measured canopy transmission of a cauliflower (Bra ssica oleracea var. botrytis L.) crop sas found (r(2) = 0.97). Comparing di fferent canopy structures ranging from single-plant canopies to a closed ca nopy gave detailed information on the absorption characteristics and the di stribution of light absorption in individual plants. Results for closed can opies and row crops were consistent with those of earlier models It is thus useful as a reference model to identify possible simplifications in the qu antification of light interception by heterogeneous crops.