UC Riverside robot maps orchard soil moisture tree by tree to cut water use

A University of California, Riverside research team has developed a robotic system that maps soil moisture tree by tree across an orchard, giving growers a way to water only the trees that need it as drought and groundwater limits tighten across the U.S. West.

The approach targets a costly blind spot in irrigated agriculture. Most growers rely on a handful of buried soil-moisture sensors and then irrigate uniformly, even though water availability can swing sharply from one tree to the next. Beyond wasted water, overwatering pushes nitrogen and other nutrients below the root zone and into groundwater, turning an irrigation problem into a fertilizer-loss and pollution problem.

From buried sensors to a moving map of the orchard

The system, described in the journal Computers and Electronics in Agriculture, was developed by the group of Elia Scudiero, associate professor of precision agriculture and director of UC Riverside’s Center for Agriculture, Food, and the Environment. A robot drives through the orchard measuring soil apparent electrical conductivity, then combines those readings with data from a small number of fixed moisture sensors to build a statistical model that predicts water content across the entire field.

The output is a tree-by-tree picture of how much water is actually available, rather than a single average for the block. Soil texture is a key reason conditions vary so much: fine soils hold water tightly, while sandy soils drain quickly, so neighboring trees under identical sprinklers can experience very different moisture levels.

What is soil electrical conductivity?

Soil apparent electrical conductivity measures how easily an electrical current moves through soil. It responds to moisture as well as to clay and salt content, so when it is paired with direct readings from buried sensors it can be translated into accurate, spatially detailed estimates of soil water content without installing a sensor at every tree.

Why overwatering is also a fertilizer problem

Keeping moisture in a narrow band matters for more than yield. Too little water stresses trees and leaves them open to pests and disease, while too much starves roots of oxygen and drives nutrients past the root zone. “There’s a sweet spot,” Scudiero said. Applying only what each tree needs reduces the risk of washing fertilizer into the environment, a growing concern as states tighten groundwater rules and nitrate limits.

From research plots to commercial farms

The project has been in development since 2019 and was tested at UC Riverside’s Citrus Research Center and Agricultural Experiment Station. The team has filed a patent covering how the robot interacts with sensors without disturbing their readings. Next steps include trials with commercial growers and ruggedizing the machines for varied crops and weather conditions, with private partners potentially turning the technology into a commercial product. For growers facing tighter water supplies and rising costs, the payoff could be significant, or, as Scudiero put it, “More crop per drop.”

Source: UC Riverside

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