Articles
LOW-COST SYSTEM FOR ON-LINE MEASUREMENT OF PLANT TRANSPIRATION AND PHOTOSYNTHESIS IN GREENHOUSE PRODUCTION
The development of new control strategies and the widening of control systems to include new technical systems therefore is closely linked with the development of new sensor systems (Schmidt, 1994).
In recent years, the development of commercial sensors has resulted also in the improvement of sensors for use in horticultural practice.
New and cheaper instruments have been developed, for example, for measuring in-house CO2 concentrations, substrate moisture, nutrient concentrations in solution, etc.
Regarding laboratory tests and scientific experiments, a large number of methods is available for measuring and calculating plant physiological quantities, such as leaf temperatures, sap flow velocities, transpiration, photosynthesis and stomatal dynamics (Stanghellini, 1987; Bakker, 1986; De Graaf, 1988, Baille, et al., 1991).
However, no sensors for data logging right on the plant have been used so far in practical horticulture.
This has been mainly due to the high price of such measuring instruments and to the difficulty of attaching them to the plant.
Recording of representative means has been another problem.
Plant physiological measurings are highly inhomogeneous, which means that a large number of sensors will be required for getting reliable means.
This is why a process sensor that supplies a maximum of information with a minimum of measuring instruments was developed at Humboldt University of Berlin (Schmidt, 1991).