Testing of the Greenhouse Emission Model for application of plant protection products via drip irrigation in soilless cultivation

An experiment was conducted to test the Greenhouse Emission Model (GEM) performance. The model simulates fate of plant protection products in soilless systems for a various combinations of application types, substrate and crop types in Dutch greenhouses. Pymetrozine and imidaclorid are applied withthe nutrient solution in sweet pepper growing on stone-wool. Measured and simulated concentrations were compared for (i) simulations with experimentally derived water flows, (ii) simulated water flows based on weather conditions and based on computer settings of the automatic control system and (iii) a predefined scenario in GEM3.3.2 for sweet pepper. GEM is able to simulate water flows well, when these flows are based on weather conditions and computer settings. Also, the concentrations in the mixing tank were simulated well. Simulated concentrations in the used water reservoir were higher than measured concentration. The model performance improves when the cultivation compartment is simulated with two reservoirs instead of one, with the rationale that no complete mixing occurs in the cultivation compartment. The effect of plant uptake and degradation could not be assessed. The concentration in the recirculation water in greenhouse is sensitive to the volumes of the various reservoirs in the greenhouse system. It is recommended to update the reservoir volumes according to the latest insight on commercial greenhouse systems.