Modelling the stomatal resistance under water comfort and restriction to assess the transpiration of a greenhouse New Guinea impatiens crop

Abstract : In greenhouses, reducing water consumption by increasing water efficiency is of high interest. To reach this goal, predictive models of soil-plant-atmosphere water transfers may be used. Such models are however presently mainly developed for open field conditions and very few models exist for greenhouse plants grown in pots. Implementing these models requires an accurate estimate of the stomatal resistance Rs. The aim of this work is to implement and adapt the multiplicative Jarvis model (1976) to calculate Rs for greenhouse potted plants not only under water comfort but also under water restriction, through the introduction of a new multiplicative function depending on the growing media matric potential. The obtained model could then be tested to evaluate transpiration. To establish the model parameters, an experiment was conducted during sixteen weeks inside a greenhouse with ornamental plants grown in containers on shelves. Both water comfort and water restriction conditions were applied. The peat matric potential, radiation, temperature and humidity were continuously recorded while Rs was measured and transpiration was assessed with scales. Data collected on four weeks were used to fit the parameters of Rs depending on radiation and water pressure deficit under water comfort. The multiplicative matric potential function was then deduced from Rs measured on stressed plants. The model was validated against data and showed its ability to assess Rs both under comfort and restriction conditions. The developed model of Rs could therefore help assess transpiration under various irrigation regimes.