Sensor information provides a crucial source of information for the autonomous control of a greenhouse. In the AGROS project, a large number of sensors is applied to measure greenhouse climate, plant status, water uptake and crop growth. Intelligent algorithms can use this information and the crop traits derived to control the greenhouse autonomously.
The “Winter light greenhouse” is a greenhouse designed to have a high light transmission in winter. This greenhouse is located at the site of the business unit Greenhouse Horticulture of Wageningen University & Research in Bleiswijk, The Netherlands. A high wire cucumber crop is grown there. The “Winter light greenhouse” hosts several demonstration trials, that aim for a reduction in CO2 emission. In the summer cultivation of 2021, an efficient CO2 supply strategy was demonstrated, in which the CO2 supply was reduced to 20 kg/ha/year, which is considerably lower than in commercial practice. In the current winter cultivation, the electricity consumption of the LED lighting is reduced by using them less hours than in previous years. The LED lighting is better tuned to the predicted amount of natural light to balance the light sum and yield.
The Winter light greenhouse & AGROS
The public-private partnership project AGROS “Towards an autonomous greenhouse” makes use of the cucumber trials in the “Winter light greenhouse”. Ilias Tsafaras, responsible for the work package on sensors explains: ‘Various sensors were installed in the greenhouse, which collect data on climate and crop growth. Some of these sensors were kindly supplied by the partners of the AGROS project’.’
In the greenhouse, Ilias points out some of the sensors: ‘These 2Grow sap flow and stem diameter sensors are attached to the stems of the plants in the greenhouse. The sensors provide information about sap flow and diameter variation over time and allow us to record the response of the plants to for example irrigation. IMEC One Planet Research Center supplied measuring boxes that measure the temperature and relative humidity of the greenhouse air. These are important parameters in the greenhouse climate. They have also installed infrared cameras and RGB cameras at different heights in the crop. These provide information about the crop temperature.’ Ilias then points to a couple of orange sensors: ‘Cultilene provided us with these CARA MET sensors that can be inserted into rock wool slabs. They measure substrate temperature, E.C. and water content. This information can be used to determine and evaluate the fertigation strategy.’
Other sensors
In addition to the sensors that come from partners of the AGROS project, a number of other sensors have been installed to collect data that may be required for autonomous greenhouse control. A set of cameras is installed facing the crop. ‘We are trying to extract plant parameters from the images automatically, such as leaf initiation rate and fruit growth duration. Nowadays, these plant parameters are still measured manually.’ Net radiometers at different heights measure the long- and short-wave radiation. This information is relevant for the energy balance of a greenhouse/plant and can be used to determine the screening strategy. On his computer screen, Ilias points at the data of the PAR line sensors that measure the amount of photosynthetically active radiation (PAR) at different heights in the crop. ‘These line sensors provide information on the light interception of the crop. The weighing systems in the greenhouse can determine slab and plant weight. Together with data on irrigation and drainage, they provide us with estimates of crop transpiration, crop weight and predicted yield.’