Irrigated crops need a supply of water matched to the plants’ changing demands. Even a briefly inadequate supply can decrease crop yields by up to 40 %. Ideally, farmers would provide exactly as much water as plants need, precisely when they need it. However, in practice, this is difficult to achieve. Therefore many farmers tend to overwater to be safe. The extent varies depending on region and crop, but 20–50 % overwatering is common. Overwatering causes numerous environmental problems, plus unnecessary extra costs for farmers. Matching the water supply to plants’ needs would increase yields and save money. With this goal, the EU-funded StemSense project developed a sensor that measures fruit trees’ and vines’ demand for water. The current project is a continuation of an earlier EU-funded project of the same name, which studied the device’s feasibility and validated the production. The new project miniaturised the sensor, finalised the software and industrial processes and demonstrated the technology in the marketplace.
Stem water potential
Key to the operation of the sensor is the physiological principle of stem water potential (SWP). “This is a direct measurement of the water tension force in the plant’s xylem tissues, its upward water transport channel,” explains Anat Halgoa Solomon, project coordinator. “Expressed simplistically, SWP describes the energy that the plant needs to pull water from the soil to the leaf.” The less energy the plant exerts getting water, the more will be available for the development of fruit. SWP has been conventionally measured using a manual device called a pressure chamber or pressure bomb. This method has two main disadvantages – it only measures SWP during a short window each day and requires a trained technician – so it is limited and inconvenient. Nevertheless, SWP is the best indicator of real-time water need in plants.
New, convenient way to measure SWP
To overcome the problems, the StemSense team developed InTree, a unique, automatic SWP monitoring system. “We embed an innovative miniature sensor into a tree’s trunk, directly connected to the plant’s vascular tissue,” adds Halgoa Solomon. “The sensor includes an osmometer: a very small volume of concentrated fluid sealed with a semipermeable membrane. Once the sensor is attached to the plant tissues, water passes via osmosis from the tissues into the unit.” Monitoring the unit’s pressure gives a continuous indication of the tissues’ water potential. The StemSense team was the first to achieve such direct monitoring. To employ this innovative technology, farmers pay for a subscription. Company agronomists consult with the farmers about their goals, determine the optimal positioning of sensors in a field (usually one per 1–2 hectares), and finally install the sensors into individual plants. The project’s sophisticated online system combines continuous SWP data with environmental parameters to determine the plants' water status and adjust the irrigation accordingly. Following a successful product launch in 2020, 100 % of customers have been retained, and the company has established more than 15 international distributors. The project will target orchard and vineyard markets worldwide. StemSense allows farmers to use less water to achieve a better product. This saves costs and increases profits while also stretching the world’s limited water supply.
StemSense, water, sensor, SWP, monitoring, stem water potential, irrigation, InTree, orchard, vineyard