Plants on a wire of AGH University acousticians-- AGH UST

Image of a tomato plant placed on a surface in anechoic chamber with multiple microphones surrounding the plant

The stage of research performed in controlled conditions in the anechoic chamber of the Technical Acoustics Laboratory at the AGH University. Photograph: K. Chojnacka, B. Chojnacki

Plants on a wire of AGH University acousticians

20-08-2024

cooperation

Together with employees from the Department of Horticulture at the Wrocław University of Environmental and Life Sciences, AGH University researchers examine whether plants emit sounds, inaudible to the human ear, indicative of stress in cases such as water shortage, excessive dryness, or attack of pests. To help the plant specialists with the task come the acousticians from the AGH University who are able to register sounds generated by plants with the use of specialist microphones sensitive to ultrasounds.

The cooperation with the experimental glasshouse at the Centre of Advanced Horticultural Production Technologies of the Wrocław University has led to research which may be taken advantage of in plant diagnostics. Information and conclusions from further experiments may serve as an indication for horticulturists on how to take better care of large-scale crops and react more quickly to changes in irrigation or pest control.

Dr Janusz Mazurek from the Department of Horticulture admitted that the research on sounds emitted by plants has a practical aspect to it:

“We consider such a type of research to be innovative, and obtained results may be helpful for example in the research on stress in plants caused by physiological factors like water shortage, excessive temperature, deficiencies of nutrients, as well as those caused by diseases and pests. In horticultural production, recognising what is the problem quickly and in a non-invasive manner determines the effectiveness of actions undertaken by producers. This fits in with the broadly understood actions related to integrated production."

Plants generate sounds of frequencies which are inaudible to the human ear. The emitted ultrasounds may be registered solely by specialist microphones used by the researchers who work on a daily basis in the Technical Acoustics Laboratory in the Department of Mechanics and Vibroacoustics of the AGH University Faculty of Mechanical Engineering and Robotics.

Monitoring tomatoes in greenhouses

“The initial stage of our research was performed in experimental glasshouses of the Centre of Advanced Horticultural Production Technologies, where we studied small tomato seedlings which grow quite fast under the right conditions. It was crucial for the conditions for plant cultivation to be the best they possibly could be, and only competent staff could provide such, people who work in experimental glasshouses on a daily basis and know how to create such conditions. Each week, the increase in the height of tomatoes reached up to 30 cm according to our measurements,” Klara Chojnacka, AGH University doctoral student, explained.

The part of research performed in glasshouses in Wrocław. Photograph: Piotr Książek

Image of two scientist standing at microphones positioned to register audio from lines of tomato plants growing in an experimental glasshouse

“The glasshouse measurements have proven that the plants have in fact emitted ultrasound impulses and their frequency changed depending on the time of day. The plants generated more impulses during the day,” claimed Dr Bartłomiej Chojnacki from the AGH University laboratory.

The sounds generated by plants are the so-called impulse noise which, as explained by the AGH University team of acoustic experts, is easily distinguishable from the constant noise generated by lights, equipment, or people. Therefore, the results obtained in the greenhouses confirm the implications of few studies conducted thus far (the results of a study conducted on plants have been published by a team from Tel Aviv University).

Measurements in the anechoic chamber

The next step was to perform measurements in fully controlled conditions, namely in the anechoic chamber of the Technical Acoustics Laboratory at the AGH University with the use of microphones well-suited for bioacoustics studies. With such equipment the researchers are able to register sounds above 200 kHz, therefore the measuring range allows to experiments with various plants, ones that emit impulses of various frequencies. The tomatoes under study made noises in the range of 20–50 kHz.

„Nevertheless, grains or, for example, grape vine would call for different equipment with much higher sensitivity to ultrasounds and wider frequency range. As per the literature available, these plants emit impulses in the range of 80–150 kHz,” explained Dr Bartłomiej Chojnacki from the AGH University.

„We are able to attain stable acoustic conditions solely in our lab, in the anechoic chamber. Here we may be certain that nothing hinders the sound registration process. At the stage of work performed at the AGH University, we aimed to provide the right conditions in terms of the plants’ exposure to light, fertilisation, and irrigation. For this purpose, we consulted horticulturists from Wrocław,” Klara Chojnacka added.

The second stage of the measurement was carried out in the AGH University anechoic chamber. The researchers placed the plant in a controlled acoustic environment with acoustic background below 0 dB and without additional sound reflections, then they surrounded the plant with 8 specialist microphones.

„In addition to the registration of impulses, we could also examine the sound directivity, i.e. the direction in which the sound is emitted. It is a novelty in the research on sounds generated by plants. Based on studies conducted in such manner, we will be able to determine which element of the plant emits sounds and then analyse where it originates from,” Dr Chojnacki precised.

A few seedlings were studied, firstly they kept fertilising and watering them to obtain control data, then the plants were overdried until they became completely dry. The preliminary analysis of the data obtained in the laboratory indicates that the impulses of tomatoes reached 30–50 kHz, as in the case of glasshouses. The impulses intensified when the plant was dry.

The information obtained in research are to be verified by the researchers. In the following stage of the experiment, they will analyse the changes in signals emitted by the plant in dry conditions.

Objective – real-time plant diagnostics

The acoustic monitoring data may suggest the growers when the crops require taking additional steps on their part, all in real time. Owing to this type of diagnosis, plant growers will be able to care for their crops more diligently and react ahead of time.

“Acoustic research could find use in yet another, truly unobvious area that is controlled-environment agriculture, only gaining on popularity all over the world. Besides the data that relates to humidity or the temperature of the environment, cultivators could decide on enhancing fertilisation, watering more, protecting from pests without actually being there, just based on a signal from their plants,” AGH University scientists explained.

In this way, the research carried out with agriculture in mind is in line with industry 4.0 as it involves the support of human’s decision-making process. In the near future, the data delivered by acoustic experts may be of support for fruit growers and increase the quality of cultivated plants.

The measurement results can be of help in plant stress research. Photograph: Piotr Książek