Scientia horticulturae vol:74 issue:4 pages:307-312
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 horticulture on substrates. The use of thermal conductivity sensing, makes it possible to measure and control the moisture content on-line in inert substrates like rockwool. Ln this way it is possible to supply nutrient solution to plants according to their demands. The thermal conductivity of a homogeneous substrate increases if its moisture content increases. Thermal conductivity measurements are fully controlled by a computer, connected with the irrigation system of the greenhouse. Examples of automatic irrigation in a tomato crop on rockwool slabs, where the computer decides if it is necessary to irrigate or not are elaborated. (C) 1998 Elsevier Science B.V.