THERMAL-CONDUCTIVITY SENSING FOR ONLINE MONITORING AND CONTROL OF THEMOISTURE-CONTENT IN ROCKWOOL SLABS

On-line measuring and controlling the climate in a greenhouse is daily practice and can easily be done with climate computers. An automatic on-line and direct measurement of the moisture content of a substrate with growing plants is a major lack in the general automation of horti culture on substrates. The use of thermal conductivity sensing, makes it possible to measure and control the moisture content on-line in ine rt substrates like rockwool. Ln this way it is possible to supply nutr ient solution to plants according to their demands. The thermal conduc tivity of a homogeneous substrate increases if its moisture content in creases. Thermal conductivity measurements are fully controlled by a c omputer, connected with the irrigation system of the greenhouse. Examp les of automatic irrigation in a tomato crop on rockwool slabs, where the computer decides if it is necessary to irrigate or not are elabora ted. (C) 1998 Elsevier Science B.V.