GEM 4 model for soilless cultures: model description and parameterisation

Boesten, J.J.T.I.; Braakhekke, M.C.; Wipfler, E.L.; van Os, E.A.; Hoogsteen, M.J.J.


Experiences with previous versions of the Greenhouse Emission Model (GEM) for soilless cultures prompted the need for developing a revised version. GEM consists of a submodel for the water flows in the greenhouse (the WaterStreams Model, WSM) and a submodel for the pesticide behaviour in the greenhouse (the Substance Emission Model, SEM). The resulting emission fluxes are used by the TOXSWA model to simulate concentrations in surface water. This report describes the changes in WSM and provides a full description of the concepts and equations in the revised SEM version The main changes in WSM are the extension of options: (i) emission norms for nitrogen up to 2027 can be used, (ii) sodium levels can be set by the user, (iii) options for managing the discharge to the surface water are extended, (iv) a waiting time can be prescribed between a pesticide application and the next discharge. Option (ii) and (iv) are only available is used as a standalone model, i.e. outside GEM. There are two types of SEM: SEM-S for crops grown on slabs and SEM-P for crops grown in pots on tables. Main changes in SEM-S include: (i) the water in the slabs is divided into two equal parts with root uptake restricted to the first part, (ii) sorption to the slab material and the irrigation pipes is included, (iii) the amounts present in the air and condensation water immediately after spray or Low Volume Mister (LVM) application are strongly reduced, (iv) for spray and LVM applications direct contamination of the slabs, the drainage-water troughs, and the roof is added. Main changes in SEM-P include: (i) the amounts present in the air and condensation water immediately after an application are strongly reduced, (ii) the sorption equilibrium between the bottom 10 cm of the pots and the water on the tables was removed, (iii) for spray of LVM applications, the deposition on the tables is increased from about 10 to about 40%.