Photosynthesis is the basis for crop growth and production. Measuring crop photosynthesis is therefore important to monitor the status of the crop. Since this process responds very rapidly to changes in the greenhouse climate (light, CO2, vapour pressure deficit and to a lesser extent temperature), photosynthesis is very suited to monitor whether the climate is set according to the needs of the plant. The ideal monitoring system provides continuous measurements, is robust, cheap and can measure a large area. Wageningen UR Greenhouse Horticulture is currently developing measuring systems that fulfil these demands.
The first sensor is the crop photosynthesis monitor. This is a soft sensor that calculates the CO2 uptake of the entire greenhouse. The monitor is based on the CO2 balance of the greenhouse. On the one hand, CO2 is added to the greenhouse via CO2 supply. On the other hand CO2 is lost via ventilation, changes in CO2 concentration and crop photosynthesis. By measuring the CO2 concentration and determining the ventilation loss, crop photosynthesis can be calculated. By doing manual measurements of leaf photosynthesis as well, and scaling these up to crop photosynthesis by a crop growth model, the crop photosynthesis monitor can be validated.
Furthermore, a new fluorescence sensor is developed, which determines the efficiency of photosynthesis. This new sensor provides short light pulses from the top of the greenhouse. The fluorescence signal is then measured by the sensor, which is programmed to measure various spots in a surface of 3 x 3 m. Since the measurements are fast, the sensor provides a good image of the crop photosynthesis in a short period of time. The results of the sensor will be compared to data of small fluorescence sensors which will be placed at different heights in the canopy to give a picture of the efficiency of crop photosynthesis.