Rectangular containers were each filled with 12 litres of a peat:perlite substrate (60:40), planted with 24 seedlings of Petunia 'Velvet Carpet' and placed in a greenhouse.
Irrigation of a container was triggered when the substrate's water content fell below a threshold value ranging from 0.05cu m to 0.40cu m of water per cubic metre of substrate.
At each irrigation, 63ml of a solution containing 200mg per litre of a fertiliser (20N; 4.4 P: 16.6 K) was applied. The water contents of the substrates were monitored and controlled by two pre-calibrated capacitance sensors per container.
The sensors kept very accurate control, despite changes in plant size and solar radiation, and no water escaped from the containers. Furthermore, plant dry weight decreased in proportion to the decrease in water content of the substrate from 0.25cu m to 0.05cu m per cubic metre.
These results suggest that the system could be used both to conserve water and to control plant size.
Growth and Water Use of Petunia as Affected By Substrate Water Content and Daily Light Integral by Van Iersel, Dove, Kang and Burnett (2010). HortScience 45 (2): 277-282. ISHS members can view HortScience from the website at www.ishs.org.