Moisture sensors useful for optimizing greenhouse strategies

A technique developed in viticulture, in which sensors directly read off the moisture situation in the plant, can provide valuable information for fine tuning the greenhouse climate. It is one of the new methods explored by eight greenhouses in the Dutch Practice Network “Limits to evaporation and water” in an attempt to bring efficient energy consumption to a next level. Their main conclusion: "you have to let go of old patterns and start listening to the crop".

All participants of the trial network already invested heavily in new technologies such as double screens, fresh air and greenhouse dehumidification, as well as in new tools such as pyrgeometers and infrared cameras. The idea is to minimize crop evaporation, thereby minimizing the amount of moisture to be drained. A humid climate in the greenhouse also creates problems with fungal diseases.

But how to minimize evaporation? Network Supervisor Peter van Boekel, "For instance, it’s not known exactly how many grams of moisture per square meter per hour a crop must evaporate overnight to maintain nutrient intake levels. What we did establish is that a behavioral change is needed. Traditionally, growers tend to think in terms of relative humidity. But those joining the network are looking at absolute amounts of moisture, the moisture in the plant and moisture balance in the greenhouse.”

Innovative research in arboriculture and viticulture brought them on the track of sensors that allow for more ‘intimate’ crop information. Four of the eight growers had measuring units installed with sensors that directly measure the plant-sap flow in the plant and record the changes in stem thickness (LVDT). Thus, both the water absorption and the drying of the plant is measured. The computer links such values to leaf temperature, light quantities and other physiological measurements. For the first time, it is possible to actually "listen" to the crops.

Source: Praktijknetwerken in de Landbouw