For a number of crops, the availability of rainwater is less than the total water demand of the crop, while there is pressure on the use of groundwater. This forces growers to look for alternative water sources or reduce water demand.
A study used model calculations to investigate whether it is possible to grow tomatoes year-round without using supplementary water by limiting evaporation, recovering evaporation water, or using water derived from energy production via hydrogen.
For their scenario study, the researchers chose a dry weather year (885 mm/year, 2019; not a low total amount, but very poor distribution with hardly any precipitation from January to June) to detect extreme situations earlier. In addition, a scenario was described with an exposed crop from September to July so that it can also be used as a reference.
Larger rainwater basin
A larger rainwater basin of up to 3000 m3/ha reduces the need
of supplementary water greatly, the researchers observed. Screens from 600 W/m2 irradiation and higher RH (measures from Het Nieuwe Telen) reduce water demand. Measures to recover evaporation water (balanced ventilation, active dehumidification, and closed greenhouse) also reduce the use of supplementary water.
Water use efficiency (WUE), or the number of liters of water needed to produce 1 kg of product, is improved with all scenarios. In the reference, 13.6 L/kg is used for tomatoes, in a closed greenhouse,
5.1 L/kg.
Dehumidifying
In a fully closed greenhouse, no additional water is needed, but energy consumption for dehumidification increases sharply. Investing in this is only financially interesting if the energy picture also
is also correct, say the researchers. Hydrogen as a fuel has potential, but the production of water from it should be seen as a by-product and not as the main reason for applying this technology.
Market prices for the product and cost prices for gas, electricity, and fertilizers now seem to determine the economic feasibility. Calculations were done before the sharp increase in energy prices (2022), so there is still some stability. Where it will go is not predictable and, therefore, not included.
The scenario study to minimize the use of supplementary water was published by WUR. The study was made possible by contributions from TKI Tuinbouw & Uitgangsmaterialen, Greenport West-Holland, Stimuleringsbudget emissiebeperking glastuinbouw (STOWA) and Stichting Kennis in je Kas.
