Controlling of irrigation systems of greenhouse plants by using measured transpiration sum.

摘要

A newly developed device for measuring transpiration flows on several leaves in a plant stand was used to test the possibility for controlling the water supply of greenhouse plants. For this, the time integral is formed for the measured transpiration mass flow density. That integral is then extrapolated to the entire area of the plant stand, using the leaf area/floor space index (LAI). As soon as a defined transpiration sum is reached, an irrigation run is triggered to give that amount of water back to the plants. For testing the method, the water balance was determined for plant stands. Measurement on strongly transpiring plants (Capsicum annuum) indicated regular variations of the water balance at night. Errors due to differences between cuvettes and reference sensor were eliminated after the measuring system was modified. Good agreement between the amounts of water supplied and the sum of transpiration rate and excess water were found in gerbera plants grown in perlite. As a second stage of the experiment, plant stands were controlled with the help of the measured transpiration. In stands with constant leaf area/floor space ratios, the trend of tension oscillations in the substrate was kept constant over several days. Variations appeared whenthe leaf area index changed due to plant growth. To eliminate that effect, irrigation based on the measured transpiration was adjusted with a growth model, or the trend of tension was recorded for adjustment of the leaf area index.