If you're trying to produce crops that require less water, then you need to know how much water those plants are using. Scientists at Iowa State University have taken an interesting new approach to finding out, by producing graphene-based moisture sensors – they take the form of strips of tape that are applied to the leaves.

Graphene consists of carbon atoms linked together in a honeycomb pattern, in a one-atom-thick sheet. Among other things, it is highly electrically-conductive.

Led by associate professor Liang Dong, the researchers made the sensors by first creating a row of indented patterns on the surface of a polymer block, then filling those indentations with a liquid solution containing graphene. After the solution dried, a strip of tape was laid along the row and then pulled off, taking the graphene with it.

According to Dong, the process is quite simple, and the sensor strips are very inexpensive to produce.

When one of the strips is adhered to the leaf of a plant, the electrical conductivity of the graphene is affected by water vapor being naturally released from that leaf. Those changes in conductivity can be measured, in order to ascertain the rate at which the leaf transpires (gives off water vapor). The more that it does so, the more water the plant uses.

The technology has already been successfully field-tested on plants such as corn.

"The concept of wearable electronic sensors for plants is brand new," says Dong. "And the plant sensors are so tiny they can detect transpiration from plants, but they won't affect plant growth or crop production."

A paper on the research was recently published in the journal Advanced Materials Technologies.