LONG TIME PLANT RESPONSE MEASUREMENTS FOR YIELD PREDICTION, WATER USE AND CLIMATE CONTROL OPTIMIZATION USING GAS EXCHANGE MEASUREMENTS IN SEMI CLOSED AND VENTILATED GREENHOUSES

An advanced prototype of a phytomonitor was developed at Humboldt University in the frame of the national ZINEG project for low energy greenhouses (www.zineg.de). Ten leaf cuvettes were allocated to different tomato leaves in the canopy to get a representative average of the gas exchange of younger and older leaves under shaded and non-shaded conditions. The cuvettes were constantly attached to several plants for the whole cultivation period, with a seven-day interchange period. Two instruments were used in two greenhouses with different climate control systems (semi-closed and a ventilated greenhouse as reference) to show the differences in the climate – canopy interaction. With the help of the Mollier Plot Analyzer software, developed at Humboldt University, the climate comfort zone of the canopy for maximum photosynthetic light use efficiency was found. With the calculation of the accumulated CO₂ and transpired water, the differences in the yield expectation for the next four weeks and the plant consumed water was estimated.
From the result of the light use efficiency evaluation with the Mollier Plot Analyzer, the comfort zone for tomato growing in the semi-closed greenhouse was estimated to be in a temperature range from 20 to 28°C, with a relative humidity of 75 to 95%. In the ventilated greenhouse most of the condition points with lower light use efficiency were found to have higher temperature and lower relative humidity. The difference in the yield between the semi-closed and ventilated greenhouse was shown by the difference in CO₂ uptake measured by the phytomonitors and the difference in the photosynthetic light use efficiency of the canopy in both greenhouses. The calculated water consumption using the gas exchange measurement data showed a high correlation to the measured water consumption. With this result it should be possible to apply gas exchange measurement systems not only for climate control but also for irrigation control.