'Waterstreams': A model for estimation of crop water demand, water supply, salt accumulation and discharge for soilless crops

Abstract: Closed growing systems are obligatory for soilless grown greenhouse crops in The Netherlands. It requires water sources of high quality as sodium (Na) accumulation is a potential risk and necessitates frequent discharge, which causes undesirable emission of nutrients and plant protection products. Rainwater as the primary water source, needs to be stored since precipitation and crop demand do not match. Large dry spells will become more frequent due to climatic changes and this necessitates the use of additional water sources, which will differ in quality and costs. The model ‘WATERSTREAMS’ was developed to estimate the total water demand and waste water flows from greenhouse crops and to optimize between options for water sources, concerning Na accumulation and nutrient emission. It describes all water flows in a greenhouse crop and the growing system. At the same time the Na concentrations in the input flows as well as the uptake are calculated, and if Na accumulates beyond a threshold value, a discharge event is programmed. The model calculations can be used to determine the total water demand from individual crops to clusters of greenhouses, as well as to optimize the size of rainwater collection tanks or the required capacity of additional water sources, using actual, historical or forecasted meteorological data. It also gives insight in the emission quantity.