The talk "Aspects to Consider in the Use of Soil Sensors: Calibration and Interpretation" was held at the President Pedro Aguirre Cerda Museum and Cultural Center in the Calle Larga commune. It was given by researcher Carlos Zúñiga Espinoza, Ph.D., from the Agricultural Research Institute INIA La Cruz (Chile).

The activity was part of the Technological Absorption for Innovation (PATI) Program, funded by CORFO, titled "Efficient Water Use in New Table Grape Varieties and Rootstocks in Central Chile through the Demonstration and Use of Sensor Technology."

The project was born in response to the challenges faced by 10 table grape producers affected by reduced water availability due to the incorporation of new varieties and rootstocks into their orchards, whose water behavior is still unknown. These water needs have been poorly studied, and little information is available. Therefore, this initiative will allow producers to optimize their irrigation strategies, incorporate new technologies, and improve their production capacities.

Dr. Zúñiga explained to the farmers the importance of understanding the soil-water-plant relationship as a key aspect for efficient irrigation management. “Understanding how the soil, the plant, and the atmosphere interact is essential for efficient water management in agriculture. These three components form a continuous system, in which the atmosphere acts as a driver of water demand. Water, captured from the soil, is transported through the plant to the leaves through transpiration, following a water potential gradient that runs from the soil to the atmosphere.”

This process is fundamental for irrigation decision-making, since the water available in the soil varies according to its retention capacity and plant demand. The critical levels that allow water availability to be characterized are: saturation, field capacity, irrigation threshold, and permanent wilting point. “Understanding these values ​​allows us to establish optimal ranges for applying irrigation without wasting resources or affecting production.”

Soil sensors allow for indirect measurement of water content in soil profiles at different depths, based on the determination of the frequency of the electromagnetic field or the time it takes for an electrical signal to propagate through the soil.

The INIA specialist emphasized that simply installing sensors is not enough; they must be properly calibrated to obtain reliable data adapted to the specific conditions of each soil type on the property. He explained that there are two types of calibrations: with absolute values ​​and with relative values.

Absolute calibration, he said, “allows us to establish a direct relationship between sensor readings and the actual volumetric water content in the soil, which requires obtaining accurate measurements at different depths and moisture contents, correlating them with the sensor readings. Meanwhile, relative calibration, which is simpler, is based on reference values ​​such as field capacity and permanent wilting point.”

In addition, fundamental concepts such as Readily Available Water (RAW) were highlighted, a relevant concept for determining irrigation thresholds. Examples of soil moisture curves under different conditions and depths were presented, illustrating how information obtained from sensors allows for timely and efficient irrigation scheduling.

The project "Efficient Water Use in New Table Grape Varieties and Rootstocks in Central Chile" includes the installation of demonstration units on beneficiary farmers' properties, where different sensor-based irrigation strategies will be evaluated in comparison with each producer's conventional practices. These experiences will generate local evidence of their effectiveness, assess production and quality impacts, and disseminate the results to other farmers in the region.

Alberto Espinoza, a project professional, explains that "the demonstration units have precisely that purpose: to demonstrate that the use of sensors allows for improved irrigation efficiency without affecting production and, in many cases, even increasing it."

This initiative is expected to reduce energy costs associated with inefficient water use, estimated at approximately $60,000 per hectare per season. It also seeks to prepare producers for potential water restrictions, reduce the risk of production losses, and improve competitiveness, especially for small and medium-sized farms, in the face of water shortages.