New technology for more precise soil moisture management

Water availability is a significant challenge for growers in California and other dry regions. While soil moisture sensors provide some insights for irrigation scheduling, their usefulness is limited.  

Current soil moisture sensors only provide information at the spot where a grower installed them. So, the data represents soil moisture at a single point or a handful of points when the reality is that there tends to be a lot of soil moisture variability in an orchard, explained Elia Scudiero, associate professor of precision agriculture and the Director of the University of California, Riverside’s Center for Agriculture, Food and the Environment (CAFE). 

“A handful of sensors per field, when a grower can afford them, are not adequate tools to provide information on when and how to apply irrigation,” he said. “Plus, a lot of the growers that have micro irrigation systems are spending a lot of time driving around the field to check the system for leaks and damage by wildlife like coyotes.” 

Scudiero and his team are working on a robotic sensor divining rod to provide growers with a tree-by-tree understanding of their orchard’s water needs.  

“Water is a big issue here in California in terms of limiting crop production,” he explained. “More and more we have growers that are asking for better technologies to be able to manage water resources.” 

Mapping orchard-wide soil moisture levels  

Scudiero’s team developed a robotic platform that can travel under each tree to measure soil apparent electrical conductivity. When it passes locations where growers already have soil moisture sensors installed, the system learns the moisture levels and converts soil electrical conductivity measurements to soil water content estimations. 

UCR describes apparent electrical conductivity as, “how easily electricity moves through the soil and is influenced by factors including moisture as well as salt and clay content.” Combined with soil sensor data, this creates a more complete picture of soil moisture variability across the orchard.   

“For the first time, you’re able to get a number of soil moisture for every single tree in your orchard with very high accuracy,” he said. 

Testing the prototype was the first step in the research, and he looks forward to studying how to apply this new data to irrigation scheduling. 

“This is the first application to use an electromagnetic sensor and the type of modeling that we employ to map soil moisture,” he said. “Globally, there are very few applications that can give you these levels of soil moisture with high accuracy.” 

The sensor and modeling approach is especially important for tree crop operations where drones aren’t effective due to canopy obstructions. That makes undercanopy, groundbased sensing particularly valuable. 

“This type of sensing technology is a novelty because it can give you the soil moisture for every single tree,” he added. 

For growers, that could translate into smarter zoning, more precise irrigation schedules and a clearer picture of how water moves across their orchards. 

Water precision increases cost efficiency 

More precise soil moisture mapping goes beyond sustainable water use; it also helps growers manage fertilizer and environmental risk. 

“Water is key to many processes,” Scudiero said. “Nitrogen and water go hand in hand here in California, especially in microirrigated orchards, where a lot of the growers in California are adding fertilizer to the irrigation line so that they can fertigate.” 

Any time a fertigated block is overirrigated, there is a risk of washing nutrients away from the roots, giving no nutrients to the plants. Once fertilizer is lost, growers absorb the cost and excess nutrients can move into unintended areas, creating environmental and potential health risks. 

With fertilizer prices rising, the payoff from targeted irrigation and fertigation becomes even more critical. 

“With the current events, we are expecting fertilizer prices to go up,” Scudiero said. “So, finding ways of using them more wisely is probably going to be a higher and higher priority.” 

Photo source: Aritra Samanta, UC Riverside