It's always best if farmers can detect drought stress before crop plants become wilted, weakened and lower-yielding. An experimental new portable device could help in that regard, as it uses ultrasound to spot such stress in its earliest stages.
The handheld tool was developed by scientists at Lithuania's Kaunas University of Technology, working with colleagues from the Spanish National Research Council. Unlike existing methods of measuring drought stress, it doesn't harm any part of the plant, and it delivers results instantly on the spot – not later on in a lab.
The device incorporates two disc-shaped ultrasound transducers which are set face-to-face with a gap between them. One of those transducers sends out an ultrasound signal, which is received by the other one.
When a leaf (which is still attached to the plant) is inserted into the gap, it affects the signal that is now passing through it. More specifically, the leaf's resonant frequency, thickness, density and other characteristics all alter the received ultrasound signal in a telltale fashion.
Therefore, by analyzing the signal data, software on a wirelessly linked smartphone is able to determine the plant's water potential and relative water content. Both of these metrics are traditionally used to assess drought stress.
If a significant amount of stress is detected, then the irrigation system (if applicable) can be activated. If not, then then the farmer can save water and avoid root damage by not overwatering. And as an added bonus, plant data and GPS coordinates are transmitted to a cloud-based server for use in a drought map of the area.
"[The device] is light, convenient, and results are obtained immediately," says the lead scientist, Prof. Linas Svilainis. "Using other devices, the leaves have to be cut and taken to the laboratory, which takes time, but here we can get the results right in the field."
Although the tool was originally designed for use on grape vines, it has been found to work equally well on any plants with leaves that are over 3 cm (1.2 inches) in diameter. A version for plants with smaller leaves is now in the works.
Source: Kaunas University of Technology
There are so many variations besides leaf size. The density an rigidity of the plant place a HUGE role in how ultrasound transfers through it. This is a waste of money for anything other than the specific plant species it is designed for.