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 problem. A robot picks out thirsty trees to use limited water more efficiently.
Elia Scudiero and colleagues at the University of California, Riverside (UC Riverside) said on the 2nd (local time), "We created maps of soil moisture that varies by tree in an orange grove so farmers can identify the right times and places to irrigate." The results were published in the international journal "Computers and Electronics in Agriculture."
◇Measuring moisture with magnetic sensors
The team developed a semi-autonomous robot that measures soil moisture. The base platform is the Jackal model from Clearpath Robotics of Canada; it measures 43 cm wide, 51 cm long, and 25 cm high. The robot can travel 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. Using the same principle, the EMI sensor identifies how well current flows with a magnetic sensor. When the ground is wet, electricity flows more easily.
To prevent the vehicle's metal parts from affecting measurements, the team attached a 35 cm nonmetallic rod to the front and mounted an EMI sensor at its tip. As the robot moves, it measures subsurface current and infers moisture from it. The researchers called it a "modern robotic divining rod."
In the university's research orange grove, the team had the robot move and measure soil moisture 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 below the surface. The researchers integrated the two datasets to create an orchard-wide soil moisture map. The map shows at a glance which trees are thirsty.
◇Prevents pests and protects groundwater from pollution
You can already measure soil moisture by inserting an EMI sensor into the ground, but you get only limited information. Scudiero said, "It only tells you what is happening right around where the sensor is installed underground." Installing sensors for every tree would be expensive. Using a robot, you can measure different soil moisture levels for hundreds or thousands of trees without underground sensors and irrigate accordingly.
California orchards use sprinkler systems that deliver the same amount of water at set times. UC Riverside researchers found through soil moisture maps that even within the same orchard, the amount of water available to each tree can differ. When soil particle density is high, there is more surface area for water to adhere to, increasing moisture, while sandy soils drain faster and hold less moisture. The team said, "We can identify the moisture distribution for each tree," adding, "By watering only the dry trees, agricultural water can be used efficiently."
Keeping soil at proper moisture levels is also crucial for plant health. Too little water stresses trees, making them more vulnerable to pests and disease. Conversely, too much water fills all the soil pores with water, preventing roots from taking up oxygen. Scudiero said, "If you give crops only the water they need, you can also reduce the risk of fertilizer being washed straight from the roots and polluting groundwater."
The team has been conducting research since 2019 to automatically measure soil moisture with robots. They have already applied for a patent on the related 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