Droughts are worsening around the world due to global warming. More places are running short of water for agriculture. Scientists have developed technology to solve agriculture's water shortage. A robot picks out thirsty trees to use scarce water more efficiently.
Elia Scudiero and a research team at UC Riverside said on the 2nd (local time) that they "created a map of soil moisture that differs for each tree in an orange orchard to determine the right time and place for irrigation." The study was published in the international journal "Computers and Electronics in Agriculture."
◇Measuring moisture with a magnetic sensor attached
The team developed a semi-autonomous robot that measures soil moisture. The base platform is the Jackal model from Clearpath Robotics of Canada. Its dimensions are 43 cm wide, 51 cm long, and 25 cm high. The robot can drive over uneven terrain such as unpaved roads and farms.
The robot's core technology is an electromagnetic induction (EMI) sensor that measures soil moisture. In 1831, British physicist Michael Faraday discovered the law of electromagnetic induction, which says that a changing magnetic field induces an electric current. An EMI sensor detects how well electric current flows inside soil as the magnetic field changes. When the ground contains more water, current flows more easily.
To prevent the vehicle's metal parts from affecting the sensor's readings, the researchers mounted a 35 cm nonmetallic rod on the front of the vehicle and attached the EMI sensor to its tip. As the robot moves, it measures subsurface current and, based on that, infers moisture content. The team called it a "modern robotic dowsing rod."
In the university's research orange orchard, the team had the robot move around and measure soil moisture content with the EMI sensor. At the same time, they inserted 12 cm EMI electrode rods at 20 locations to measure moisture at a depth of 12 cm from the surface. The researchers integrated the two datasets to create a soil moisture map for the entire orchard. The map shows at a glance which trees are thirsty.
◇Blocking pests and preventing groundwater pollution
It is already possible to measure soil moisture by inserting an EMI sensor into the ground, but that yields only limited information. Scudiero said it "only tells you what is happening right near where the sensor is installed underground." Installing sensors in the soil for every tree would be costly. Using a robot, it is possible to measure different soil moisture for hundreds or thousands of trees without underground sensors and irrigate accordingly.
Orchards in California use sprinkler systems to apply the same amount of water at set times. The UC Riverside team found through the soil moisture map that even within the same orchard, the water available to each tree can differ. When soil particle density is high, the greater surface area holds more water, raising moisture levels; when soil is sandy, water drains faster, lowering moisture. The team said, "Using the robot we developed this time, we can grasp the moisture distribution status for each tree," adding, "We can water only the dry trees, which should improve the efficiency of agricultural water use."
Maintaining adequate soil moisture is also important for plant health. If under-watered, trees become stressed and more vulnerable to pests and disease. Conversely, overwatering fills all the soil's pore spaces with water, preventing roots from absorbing oxygen. In effect, the crop suffocates in water. Scudiero said, "If you water as much as the crop needs, you can also reduce the risk of fertilizer being washed straight off the roots and causing groundwater pollution."
Since 2019, the team has been conducting research to automatically measure soil moisture with robots. They have already filed for patents related to the technology and said they plan to test the newly developed system in real farms beyond the university's research orchard.
References
Computers and Electronics in Agriculture (2026), DOI: https://doi.org/10.1016/j.compag.2026.111540