SIMULATION OF THE DIURNAL RATE OF CO2-ASSIMILATION OF A ROW CROP IN A VENLO GREENHOUSE
On days with large amounts of direct radiation the transmissivity of the glasshouse cover varies considerably. At low solar elevations crop gross photosynthesis is significantly reduced due to low transmissivities. On bright days the instantaneous gross photosynthetic rate of row crop can be highly dependent on the position of the sun. On these days a significant reduction in the rate of photosynthesis occurs at midday dependent on the path width, with glasshouse and rows orientated North-South (row direction is equal to the glasshouse direction). With an East-West orientated glasshouse the decrease in the rate of photosynthesis compared with a horizontally homogeneous crop is enhanced by increasing solar elevations. It is evident that for bright days a more detailed model is necessary for calculation of the rate of photosynthesis of a row crop for the purpose of dynamic optimization.