Using CFD modeling to assess the impact of water input restriction on an impatiens crop grown inside a greenhouse

In greenhouses, it is possible to increase water use efficiency by reducing water inputs to plants while maintaining them in a good physiological state. This requires however a better quantification of plant response to water restriction conditions. Modeling tools may help assess water transfers in the substrate-plant-atmosphere continuum but up to now, they were mostly established for well-watered conditions. The aim of this study is to implement a CFD model to evaluate the impact of water reduction onto the crop and microclimate conditions at the scale of a greenhouse. The CFD model solves the 2D transient equations for conservation of mass (water vapour in particular), momentum, and energy. The crop is considered as a porous medium exchanging latent and sensible heat with its environment. Latent heat or transpiration is strongly dependent on the stomatal resistance, which itself is affected by water restriction. This effect was considered through a specific stress function of the substrate water potential. This latter was calculated using the van Genuchten model combined with a water balance between irrigation and transpiration, considering the water transfers in the whole substrate-plant-atmosphere continuum. First, in a former study for the same conditions, the model was successfully validated against experiments conducted inside a 100 m² impatiens glasshouse for both well-watered and restriction regimes. Then in the present study, different irrigation scenarios were tested by reducing progressively the water supply. Simulations showed the ability of the model to quantify the impact of water restriction on the leaf temperature, stomatal resistance, evapotranspiration, substrate water potential and microclimate distribution inside the greenhouse. From results, it was established that the water supply could be reduced by about 30% compared with a reference case (water input equal to the substrate water capacity) without significantly affecting the leaf temperature and transpiration rate, and therefore potentially the plant growth.