EDITOR’S NOTE: This entry is part of a series to highlight a new technology related to almond and tree nut production. The question/answer format is set to focus more on the technical aspects and application of the technology. In many articles, I discuss the importance of irrigation. With that in mind, I though I would reach out to a company that assists with irrigation scheduling based on site-specific data: Tule Technologies. Thanks to Valerie Bednarski for taking the time to answer my questions.

Tule is an irrigation technology that determines site specific water use for a specific crop. How does this technology work? Tule measures the actual evapotranspiration (ET) of your orchard. We are able to do this using the Surface Renewal Method that was developed at the University of California at Davis (Paw U et al. 1995; Snyder et al. 1996; Shapland et al. 2012a and 2012b; Shapland et al. 2014). ET is the process of evaporation from plant and soil surfaces and from within plant tissues (i.e., water movement through stomata). In most modern agricultural systems, ET is the dominant process of water loss from a field. (Editor’s note: more info on ET here)

What equipment is installed, and resources are used to determine water use?

The Tule Sensor is installed in the orchard and is positioned above the canopy. The sensor is able to measure the amount of evapotranspiration from the orchard based on air movement.  As the wind moves over your orchard, it picks up the water that transpires from the trees and carries it to our sensor. This is how we are able to measure the crop water use over a broad area.

An installed pressure switch is fitted to the irrigation system. This provides a direct measurement of irrigation durations. Using site specific irrigation specifications, we are able to turn the duration of each irrigation event into the amount of water applied.

What variables are measured?

Tule measures the actual, site-specific ET of your orchard using the Surface Renewal method. The sensor contains a thermocouple, which is a very thin wire that is able to measure minute changes in temperature in the air. With the sensor itself, we are measuring the heat that is transferred from the orchard to the air.

We take the energy balance approach to converting our sensor measurement into actual ET. The energy balance approach has been rigorously validated in research universities. We use remote sensing to measure the amount of sunlight your orchard receives. In short, the sunlight either warms the air or vaporizes water. We measure the sunlight, subtract from it our sensor-based measurement of the energy that warms the air, and what’s left is the energy that vaporized water. Because it takes a known amount of energy to vaporize a gram of water, we can convert the energy that vaporized water in the orchard into the amount of water that left the orchard.

We also measure the Crop Coefficient for your orchard. This is done similarly to the way researchers,  by comparing the Actual ET to the Reference ET. During the canopy development part of the season, Tule looks for the week with the maximum Actual ET compared to the Reference ET. We use this week to determine the size of the canopy because it is the time that the trees have the largest leaf area for transpiration. To learn more about how we measure the Crop Coefficient, check out our blog post here.

How does Tule correct itself? For example, let’s say there is a chronically underirrigated orchard. How does the system know how much water to apply to properly irrigate?

Tule creates irrigation recommendations based on the Actual ET we measure in your orchard.

To provide irrigation recommendations, we start by first measuring the water stress of your trees. Tule measures crop water stress by comparing the Actual ET to the Potential ET. If your trees are using less water than they could be using (i.e., Actual ET is less than Potential ET), then they are water stressed. The Potential ET is calculated by multiplying the Crop Coefficient for your field by the Reference ET. The Reference ET is sourced from our proprietary remote sensing model, which is similar to SpatialCIMIS.

Once we know the water stress of your trees, we can then provide irrigation recommendations. The grower provides us with water stress targets. If your orchard water stress is within your target water stress, then Tule recommends to apply 100% of the Actual ET. That is, Tule measures how much water your trees used (i.e., Actual ET), and recommends that you replace that amount of water with your next irrigation. If your trees are more water stressed than the target, then Tule recommends more water.

What if the grower wants to increase water applications to grow more canopy, can the tool assist in this process?

We also provide irrigation recommendations during the canopy development part of the season. One of the factors that determines the recommended amount is the grower’s input for their target Crop Coefficient. If the grower sets the target Crop Coefficient to a higher value than the Crop Coefficient for that orchard in previous years, then our irrigation recommendations will recommend the amount of water required to grow a larger canopy.

How does it know if it is applying too much or too little water?

Tule measures the Actual ET (i.e., the water use of the orchard), the water stress of the orchard, and the irrigation application amount. If you have been applying less than our recommendations and our water stress measurements show the trees getting more stressed, then you are irrigating too little. If you are applying more than our recommendation and more than the Actual ET (i.e, you’re applying more than the trees used), then you are applying too much water.

One of the unique things about Tule is that it provides the ability to determine site specific water use. Due to this specificity, Tule is believed to be more accurate than estimating crop water use (ETc) via CIMIS or other localized weather stations. What has been the observed difference in accuracy and precision of TULE in comparison to traditional irrigation scheduling? How much variability in water use/demand has been observed amongst installed Tule stations across the almond industry?

The almond industry in general has to choose from these three Kc’s that the research community has provided for almonds (Editor’s note: More info on Kc’s here). In reality the crop coefficient is different for every orchard, because the size of the canopy for each orchard is different. The graph provides a comparison of crop coefficients (Kc) measured in Tule customer orchards. We have observed a large variability across operations. If a grower is using the 1.17 Kc,, but their orchard actually has a Kc of 1, then the grower is overirrigating by (1.17 – 1) / 1.17 = ~15%. The opposite can also happen. The grower uses the Kc of 1.02, but the actual Kc for the block is 1.2, so the grower is underirrigating the trees and hurting their kernel weights. This is why it is important to know your specific orchard’s Kc. Knowing this information you will be able to build a site-specific water budget, which increases both water and nitrogen use efficiency

How does the software work during periods of planned deficit irrigation?

There are two ways you can approach deficit irrigation using Tule. First, you can apply your own pre-determined deficit irrigation amount. The Tule data can then be used to track the water stress level, making sure the trees do not become too stressed. If too much stress occurs, adjustments can be made to the pre-determined irrigation amount, applying more water to relieve the stress.

Second, water stress targets can be set to any desired range. If you set your water stress targets to a higher water stress range, then Tule will provide you with irrigation recommendations to stay within that target water stress range. The water stress level and date range for the water stress targets are customizable on our dashboard

Within the software, what information is provided to the farmer? What variables are they able to control? Are there features that they can take offline?

We provide the grower with four main deliverables: orchard water use (Actual ET), orchard water stress, applied irrigation amount, and recommended irrigation amount.

Our secondary deliverables are block-specific Crop Coefficient (i.e., Kc) measurements, annual water budget report, leaf-out soil water budget report, secondary irrigation line monitoring, benchmarking to similar fields, weather forecasts, canopy growth monitoring,  and an end of the season summary report.

The grower controls the Crop Coefficient target (i.e., how big of a canopy they want to grow) and the water stress targets.

Customers are able to download the Tule data (i.e., Actual ET, Reference ET, water stress, irrigation application time, irrigation application amount, etc.) from our dashboard to an Excel file.

What features of Tule are often overlooked? Why do these have value?

We think the site-specific Crop Coefficient is all too often overlooked. This is one of the main features that makes our product standout from traditional ET calculations. Using a general Crop Coefficient that is not specific to your orchard can drastically miscalculate the irrigation requirement for your orchard. We have found that Crop Coefficients can vary by more than 20%!

A new tool has been released that can determine stem water potential by taking a picture. Would it be possible to explain how this works? What equipment is needed? What aspects of the image are utilized to determine these values?

We trained a cutting-edge Artificial Intelligence model to develop Tule Vision in wine grapes.  The Tule Vision model was built on an unprecedented dataset using data from thousands of Tule sensor water stress measurements from our in-field sensors. These stress measurements were then correlated with 1000’s of pictures of vines taken by our field technicians. The strong correlation found, which we believed to be accurate, has been developed into a feature for wine grapes, although we are considering expanding it to almonds.

DISCLAIMER: Please note that the entry is not a recommendation of the product for use. This article contains facts and opinions, and is intended to provide information so that you can learn about new technology that may be of use for your farm. Furthermore, I did not receive any compensation for this article, I simply find the technology interesting.

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