Exploring water droplet size as a sustainable farming tool

In the face of ongoing climate changes, which affect the destabilization of rainfall patterns and rising temperatures, agriculture faces serious challenges. It is becoming necessary to seek alternative, more ecological solutions that will improve crop health without increasing the amount of chemical pesticides.

A group of researchers from Huazhong Agricultural University in Wuhan, led by Man-Qun Wang, conducted experiments on tomato bushes to study how mechanical stimulation in the form of water spraying affects the growth of these plants.

The researchers particularly focused on two droplet sizes: small, with a diameter of 0.2 millimetres, comparable to a pixel on a computer screen, and large, with a diameter of 1 millimetre, equivalent to the head of a pin.

To ensure full control over the study, the soil under the bushes was covered with an impermeable layer, which eliminated the possibility that water reaching the roots could affect the experiment results.

The results were surprising. Plants sprayed with larger water droplets were shorter and more compact than those that received smaller droplets or were not sprayed. Interestingly, the differences in the quality and quantity of fruit among these three groups were small. However, what distinguished the plants exposed to larger droplets was their increased resistance to pests and diseases, including the cotton bollworm (Helicoverpa armigera) and grey mould (Botrytis cinerea).

Metabolic analysis showed that bushes sprayed with larger water droplets had elevated levels of hormones responsible for the plants' defensive responses. Researchers also observed higher levels of chlorogenic acid in the leaves, further strengthening the plants' resistance.

Moreover, there was a lower emission of volatile organic compounds, which normally attract butterflies that lay eggs on plant leaves. As a result, the number of eggs laid by insects decreased by 74 per cent compared to unsprayed plants.

In light of these promising results, the study's authors suggest that the development of water spraying technology could improve agricultural practices, making them more environmentally friendly and efficient. Mechanically stimulating plants, for example, by appropriate spraying, could be an alternative to using pesticides while supporting the crops' natural defence mechanisms.

This study marks another step in the search for methods to help agriculture adapt to increasingly challenging environmental conditions while minimizing negative environmental impacts.