A laboratory assessment of wetness sensors for leaf, fruit and trunk surfaces

A laboratory assessment has been made of the performance and applicability of several different conductimetric wetness detectors for use in monitoring water distribution on different plant surfaces in a tree canopy. Leaf surfaces were monitored using parallel electrode clip sensors and grid sensors. Fruit and trunk wetness was monitored using parallel electrode sensors encircling fruit and trunk samples. Modifications to the fruit sensors to facilitate fitting and reduce the risk of epidermal damage have been investigated. Generally, the simplest parallel electrode designs performed better than the sensors with intended design refinements, in terms of instantaneous signal onset sensitivity, the matching of sensor signal profiles with weighed water loss profiles, and the accuracy of the determination of wetness persistence on the sampled surfaces. Factors affecting the drying profiles obtained using the sensors include the previous wetting history, the distribution of water on the surfaces, and the surface texture.