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Tom Shapland, PhD

About Tom Shapland, PhD

Posts by Tom Shapland:

An Introduction to FieldStat

As a grower, you know that irrigation management is your highest leverage tool for influencing your crop value. Water stress significantly impacts your crop yield and quality. That’s where Tule’s FieldStat comes in. FieldStat is a revolutionary technology that measures crop water status directly in your field, giving you crucial insights into the water stress of your plants daily, remotely, and without the hassle of using a pressure bomb. In this post, we’ll discuss the science of FieldStat and how you can use it to optimize your crop yields.

Factors that Influence Plant Water Use

The amount of water a plant can use, or Actual Evapotranspiration (ETa), is influenced by three main factors. 

1.) Weather. Plants use more water on warm, sunny days than on cool, overcast days. Reference ET (ETo) tells us about the weather. 

2.) The size of the plant. A larger plant with more sunlit leaf area uses more water than a smaller plant with less sunlit leaf area. The Crop Coefficent (Kc) tells us about the canopy size. 

3.) Water stress. When plants encounter water deficits, they regulate their water use and use less water. The Water Stress Coefficient (Ks), or as we call it, FieldStat, tells us about water stress. 

What is FieldStat and How Does it Work?

FieldStat, also known as the Water Stress Coefficient or Ks, is a measure of the actual water use of the plants compared to their potential water use. If the plants are not using as much water as they could be using, then they are water-stressed. To calculate the Water Stress Coefficient (Ks), we need to know Actual ET, weather (ETo), and canopy size (Kc).

Screen Shot 2023-04-27 at 1.26.34 PM

Tule places sensors in farm fields to measure the actual water use of the plants. To calculate the potential water use of the field, Tule uses remote sensing models to obtain the Reference ET (i.e., the influence of the weather). In addition, Tule uses the same method to determine the Crop Coefficient (i.e., Kc) that research scientists use to determine the standard, generalized Crop Coefficients. 

FieldStat correlates with leaf water potential, which is typically measured using a pressure chamber. This has been demonstrated in numerous academic studies by university researchers, such as this winegrape study (see chart below) and this almond study. Unlike the pressure chamber, which only tells you about the water status of one plant, FieldStat measures the water status of a one to ten-acre area. This gives you a powerful tool to see the water stress of every field, every day, from anywhere, over many plants at a time. 

Note that the Water Stress Coefficient (i.e., FieldStat) for monitoring plant water stress has been studied and validated for sixty years. FieldStat is an established science. In fact, it was first introduced in FAO 56 Evapotranspiration manual, which was written in the 1960s, ten years before the invention of the pressure chamber! 

LWP_Ks

The above figure shows the relationship between the pressure chamber readings (i.e., leaf water potential) and the Water Stress Coefficient (i.e., FieldStat). In this paper, the authors omitted the Crop Coefficient term. Because the Crop Coefficient is a constant for any given field, omitting the Crop Coefficient shifts the curve up or down but does not influence the linear slope between pressure chamber readings and the Water Stress Coefficient. 

Visualizing FieldStat Over Time

The chart below from an almond orchard shows how FieldStat changes over time. The horizontal black line is the weekly average value for FieldStat. The vertical blue lines are the irrigation applications. 

Tule places sensors in farm fields to measure the actual water use of the plants. To calculate the potential water use of the field, Tule uses remote sensing models to obtain the Reference ET (i.e., the influence of the weather). In addition, Tule uses the same method to determine the Crop Coefficient (i.e., Kc) that research scientists use to determine the standard, generalized Crop Coefficients. 

FieldStat correlates with leaf water potential, which is typically measured using a pressure chamber. This has been demonstrated in numerous academic studies by university researchers, such as this winegrape study (see chart below) and this almond study. Unlike the pressure chamber, which only tells you about the water status of one plant, FieldStat measures the water status of a one to ten-acre area. This gives you a powerful tool to see the water stress of every field, every day, from anywhere, over many plants at a time. 

Note that the Water Stress Coefficient (i.e., FieldStat) for monitoring plant water stress has been studied and validated for sixty years. FieldStat is an established science. In fact, it was first introduced in FAO 56 Evapotranspiration manual, which was written in the 1960s, ten years before the invention of the pressure chamber! 

FieldStat_Example

At the beginning of the season, FieldStat is 100%, which tells us the plants are using as much water as they could use. Starting in late June, the grower cuts back on the irrigation amount for hull split. We can see that the plants become more stressed each day as they go from around 100% FieldStat to about 80% FieldStat. In September, the water has been cut off to facilitate harvest operations, so FieldStat falls to around 40%. In October, the grower applies water to the orchard again, the plants start using more water compared to what they potentially could use, and FieldStat rises back up to around 80%. 

How to Use FieldStat

To use FieldStat, all you need to do is place a Tule sensor in your field. On our web and mobile apps, you will see daily FieldStat readings from the sensor. The sensor will tell you the water use of your field compared to the potential water use (i.e., the Water Stress Coefficient, or FieldStat). 

Once you have this information, you can use it to make informed decisions about your irrigation practices. You can quickly see which blocks are showing more stress than your target stress level and which blocks are on track. If your FieldStat readings show that your plants are more stressed than your target, follow the Tule irrigation suggestions to get them back on track. Conversely, if your FieldStat readings show that your plants are less stressed than your target, then you may be able to delay your next irrigation.

Conclusion

FieldStat is a powerful tool that allows you to measure crop water status directly in your field, remotely, and without the hassle of using a pressure bomb. It is based on established science that predates the pressure chamber. With FieldStat, you can see the water stress of every field, every day, from anywhere. 

Interested in learning more about Tule sensors for your farming operation? Click here to schedule a quick demo!

 

Spring Water Budget Report 2023

 

Great growers start irrigation planning now!

Tule sensors measure the soil water budget in hundreds of fields throughout California for our customers. At the start of each water year (October 1), we measure the water inputs (i.e., irrigation and rain) and subtract the water outputs (i.e., field-scale orchard water use measured with Tule sensors, runoff, and deep percolation).

evapotranspiration

The Spring Water Budget Report tells growers the amount of water in inches that they can expect to have in their soils as of February 28. Every year, our customers rave about how much they appreciate and rely on the report. 

“With every winter seeming to be so different with how much rain we get and when we get it, the spring water budget has allowed us to have a better idea of irrigating before we have canopy growth.” said David Ilsley of Shafer Vineyards. “It’s allowed us to delay irrigations that gut instinct and weather reports would have triggered an irrigation in the past. Now, by having data, we can see that yes, we do need to irrigate or no, we can let it ride a few more days and that’s helped us save water.” 

The data from our sensors also provides interesting insights into the “State of the Soil” of California’s fields. Here’s a look at the average soil water budget in orchards, vineyards, and other fields in different growing regions:

Screen Shot 2023-03-03 at 7.20.16 AM

At Tule, we’re optimistic that 2023 will be a great year for California growers. But to get there, they will have to irrigate to the water needs of their crops. Our Actual ET sensors provide the most important information you need to maximize your production. Don’t take it from us. Here is what our customers say.

“Tule makes me a better grower because I am able to validate my irrigation schedule with actual tree water usage,” said James Nichols, VP of Farming Operations at Nichols Farms. 

Good luck with the farming season!

Tom and Team Tule

Tule Acquired by CropX!

Tule a part of CropX

I’m excited to announce that Tule has been acquired by CropX Technologies! CropX is an Ag Tech company with about 100 employees, including a deep bench of agronomic, product development, and engineering talent. The hardware and software development team at CropX is about 35 people! The CropX system offers its users real-time mobile and desktop insights and advice on irrigation, disease control, nutrient management, and more, based on above-ground crop sensing data and below-ground soil monitoring. Although CropX has a robust set of agronomic decision support tools and offices worldwide, CropX is very similar to Tule. Both companies are veteran agriculture businesses that have thrived by staying focused on supporting their customers and building simple, science-based products. 

Tule and CropX combined offer everything there is to love about Tule and more. We will continue to support and improve Tule’s products. In addition, we will integrate soil moisture sensing and evapotranspiration monitoring into one platform. CropX’s other capabilities, including their disease management tool, will also be available in their complete agronomic farm management platform. I will continue as the leader of the Tule business unit within CropX while working to build upon our existing product offerings and expand globally. 

Ten years ago, I started Tule as a spin-out of my research at UC Davis. At the time, I had thought nothing could be more rewarding than to see a fundamental science innovation out of the lab and in production agriculture. How naive of me that I thought productizing my research would be the most meaningful part! The most rewarding part of my journey at Tule has been getting to know and work with many growers I admire and consider my friends. I look forward to embarking on the next stage of the Tule journey!

Please feel free to reach out to us if you have any questions. As always, we love hearing from you!

Tom Shapland, PhD
CEO
Tule, a part of CropX

Tule’s Four Deliverables

 

Tule sensors offer growers four main deliverables:

1 Daily Actual Evapotranspiration (ETa) of your field

2 Daily water stress measurements of your field

3 Real-time irrigation monitoring in your field

4 Irrigation suggestions for your field 

Let’s take a deeper dive into each of these deliverables so you know exactly the type of information you’ll get as a Tule customer.

 

1 Daily Actual Evapotranspiration (ETa) of your field  

Evapotranspiration (ET) is the process of evaporation from plant and soil surfaces and from within plant tissues. In most modern agricultural systems, ET is the dominant process of water loss from a field.

Tule sensors are a UC Davis research-based innovation for directly measuring the Actual Evapotranspiration (ETa) of your field. I developed the technology during my PhD work. Understanding the Actual Evapotranspiration of a given field can serve as an excellent tool when making important irrigation decisions.

evapotranspiration

Knowing the ETa means you know the water use of your field – not just one point in the soil or just one plant.

Measuring ETa shows you how much water is being used by your crop. That helps you understand how much you should irrigate to replace water lost and achieve optimal plant water stress. 

ETa will decrease when there is an inadequate supply of water in the soil. If the daily ETa decreases, it’s time to irrigate!

Having daily ETa records tell you how your crop is responding to your irrigation decisions, providing feedback on your irrigation strategy.

ETaREcords

2 Daily Water Stress Measurements

In addition to measuring Actual Evapotranspiration (ETa) every day, Tule sensors also measure the daily water stress of your crop. We show water stress in a graph that we call FieldStat. With FieldStat, a grower knows the status of all of their fields – at any time, from any place, and with confidence.

Before Tule, scientists measured ETa with lysimeters, which are basically giant pots on a buried truck scale. Using ETa data collected with lysimeters, scientists developed the water stress coefficient over fifty years ago. The water stress coefficient is a measure of the amount of water the plants are using (i.e., ETa) compared to the amount of water they could use, given the size of the plants and the current weather conditions. In other words, if the plant is using less water than it could use, then it’s water stressed.

Researchers have demonstrated in numerous peer-reviewed articles that the water stress coefficient, which we call FieldStat, correlates with crop yield, as well as various other measurements of plant water stress like leaf water potential (i.e., pressure bomb readings). But unlike the bomb, which only tells you about one plant, FieldStat measures the plant water status for a 1- to 10-acre area. As your crop becomes more water stressed, FieldStat decreases (as seen in the graph below).

FieldStat

3 Real-time Irrigation Monitoring

Each Tule sensor comes with a pressure switch that monitors irrigation applications. The irrigation  data is reported and tracked on the Tule app and web dashboard. We use your irrigation data and sensor-based Actual ET measurements to build our irrigation suggestions. 

With the pressure switch, you can see exactly when water turned on and off within minutes of it happening. Not only can you check irrigation events using the Tule app or web dashboard, but you can also now receive notifications to your phone! Extra peace of mind, right in your pocket.

Tule-notification copy

4 Irrigation Suggestions

So you have a Tule sensor that measures the water use and water stress of your crop. And you have the pressure switch that tracks your irrigations. 

Now what? What are you supposed to do with this information?

We’ve got you covered! Using the data collected by your Tule sensor and pressure switch along with contextual information about your field, we suggest the amount of water to apply to achieve your targeted level of water stress. For example, if you want to maximize yield, then we suggest the amount of water to apply to keep your plants experiencing water stress.

You can easily access your Tule information on the Tule web dashboard, email reports, or iPhone app. Suggestions are reported in hours as well as inches or gallons per vine, depending on your crop type.

 
TotalRecommended

Tule’s Four Main Deliverables

There you have it! Those are our four main deliverables! Our customers use our Actual ET, water stress, irrigation monitoring, and irrigation suggestions to make irrigation decisions. If you’re ready to learn more, please reach out to us!

The Importance of Distribution Uniformity

Distribution uniformity values most growers consider “good enough” could still be costing $700 per acre.

This fall, Team Tule was pleased to join the Almond Board of California on their Irrigation Workshop Series. We spoke to growers all over the state about the differences between Reference Evapotranspiration (i.e., the water use of a lawn) and Actual Evapotranspiration (i.e., the water use of your crop field) and the importance of irrigating to Actual Evapotranspiration.

I enjoyed learning from the other speakers at the ABC workshops. My favorite was the presentation by the Almond Board’s Tom Devol called, “Importance of Distribution Uniformity and Cost of Leaks.” In the presentation, ABC’s Field Outreach & Education Senior Manager discusses the hidden cost of poor distribution uniformity.

At Tule, we’ve long touted the importance of monitoring and improving distribution uniformity along with measuring and irrigating to Actual Evapotranspiration. They’re both important tools when it comes to irrigating efficiently and maximizing the profitability of your operation.

 

Putting a Number on Issues

ABC_MissingSprinkler

Missing Sprinkler

.87 GPH 

52.2 GPH

46,771 gallons in a season of irrigation.

ABC_ImproperRepair

Improper Repair

.21 GPH

12.6 GPH

11,290 gallons in a season of irrigation. 

ABC_LeaksAtFilter

Leaks at Filter

.61 GPH

36.6 GPH

20,773 gallons in a season of irrigation.

ABC_CloggedScreens

Clogged Screens

Lose of 12 PSI in system pressure. 

Source: ABC Presentation Uniformity and Leaks Presentation

What’s more, if you’re using an in-line pressure switch to monitor irrigation applications, like the one on the Tule sensor, having good distribution uniformity is key to getting the most from the data.

Take a look at Tom Devol’s Distribution Uniformity presentation here.

A leak here and a leak there can add up to significant water costs and crop loss. But did you know that poor distribution uniformity can cause overall over-irrigation to overcompensate for under-irrigated areas? That can lead to excess water bills, pumping costs, and nutrient leaching.

In one of Tom’s examples, he shows that a distribution uniformity reduction from 100% to 85% in a 100-acre almond orchard can cost a grower up to $70k in a year. And that’s where water is cheap! And not including ineffective nutrient applications!

Simple Math on 100 Acres

Lost Yield

$655.00 per Acre x 100 Acres…..$65,500.00   

Additional Water Applied

$36.00 per Acre x 100 Acres………..$3600.00

__________________________________________

TOTAL……………………………………………..$69,100.00     

Source: ABC Presentation Uniformity and Leaks Presentation

Tom Devol’s presentation is geared toward almond growers, but the pitfalls of low distribution uniformity plague any irrigated crop. Now is a great time to conduct a distribution uniformity test on your ranch! Need help monitoring your distribution uniformity? Many Resource Conservation Districts conduct DU tests for free!  Contact your local RCD here or contact Meras Water Solutions.

What should my FieldStat targets be?

 

Tule’s best growers use the Season Summary Report to guide their decision.

The Tule 2022 Season Summary Reports are live! I love the reports for their agronomic overview of the annual cropping cycle. But did you know you can also use the Season Summary Reports to answer that perennial question: “What should my FieldStat targets be?” 

FieldStat is Tule’s evapotranspiration-based water stress measurement. Growers set target levels of water stress for each irrigation block. FieldStat tells the grower if the block has too little water stress, too much water stress, or the desired amount of water stress.  

Many of our customers ask us what water stress level is right for their blocks. Generally, we advise that it’s best to start with the business model for the block. If quality doesn’t nudge the crop price and yield is king, then growers should set the FieldStat targets to no stress or very low levels of stress. If the crop can fetch a better price with increased quality, like we see in some winegrape vineyards, then there is some amount of stress the grower wants the plants to experience.  

But how much stress is the correct amount? And when is the right phenological window for the water stress? We tell growers the general range we see for their crop, production goal, and region. But farming is site-specific. General ranges can only go so far.

Our most agronomically sophisticated customers use their Season Summary Reports to set their targets. They set aside time each winter to plan their irrigation strategies for the next year. They review how their blocks performed with response to yield, quality, and response to heat events. Then, they examine the FieldStat chart on the Season Summary Report.  

Did some of the crop get sunburned during the late summer heat wave? Consider setting your targets to less stress in the period running up to harvest.  

Did my berry weights come in higher than expected?  Consider lowering your FieldStat targets (i.e., aim for more stress) and drive more quality. 

Were my kernel weights less than they’ve been in previous years? Consider raising the lower threshold of my FieldStat targets so the trees experience less water stress.

 
Season Summary FieldStat Chart

In this winegrape vineyard, the winemaker wanted smaller berries. For next season, the grower will decrease the FieldStat targets (i.e., aim for more water stress) to achieve lower berry weights. 

There is a trove of other valuable agronomic information in the Season Summary Reports. You’ll find a historical review of your canopy size, summaries of your block’s Actual Evapotranspiration and irrigation applications, a comparison between your irrigation regime and the timing and amount of irrigation at similar fields in your area, winter soil water budgets, and more. At Tule, we provide our customers with valuable information for every stage of the annual cropping cycle. 

Each fall when the reports are ready, our customers receive an email with directions for downloading them. Customers can access the report for last season and for previous seasons on the Web app. Watch this video to learn how to download the reports 

We’re excited to share the latest Season Summary Reports with you!

 

How To Correct Pressure Chamber Readings for the Influence of Vapor Pressure Deficit

Last summer, I was talking to a viticulturist about the water stress level of one of his blocks.

The midday leaf water potential says 14 bars, but it is 104 degrees out,” He said. “It’s probably more like a 12. I’m not going to irrigate yet.”

I’ve heard many growers make similar statements. Vapor pressure deficit, which is a measure of the dryness of the atmosphere and tends to increase during high temperature events, has a strong influence on pressure chamber readings. The phenomenon is well-documented in the academic literature and commonly observed among grape growers. Like the viticulturist I was speaking to last summer, many growers intuitively adjust their pressure chamber readings on hot and dry days. But even the most talented viticulturists have a story about getting a 16 bar reading on a hot day, turning the water on in a panic, and later regretting the decision.

The tree nut industry adjusts pressure chamber readings for the influence of vapor pressure deficit as a standard protocol. The method tree nut growers have adopted from academia requires learning a new scale (i.e., 6 bars is the new 14 bars). I think the grape industry has been reluctant to adopt a similar VPD correction because the existing scale is deeply entrenched in viticultural practices.

Here is an approach to correcting pressure chamber readings for the influence of VPD that preserves the existing scale.

  • First, we determine the baseline VPD. The baseline VPD is the typical VPD for the time of day and the time of year for a particular region.
  • Next, we compare the VPD at the time of the pressure chamber reading to the baseline. If the VPD at the time of the reading is higher than the typical VPD (i.e., higher than the baseline), then we would expect the pressure chamber to show too much stress.
  • Then, we calculate how much the elevated VPD is influencing the pressure chamber reading.
  • Lastly, we remove the influence of VPD from the pressure chamber reading.

In the past, I haven’t concerned myself much with this issue and other issues with the pressure chamber. It would be like performing CPR on a pterodactyl. If the cardiac arrest doesn’t kill it, then surely the asteroid will. Labor costs will soon enough exterminate the pressure chamber. But the pressure chamber is something of the gold standard in the grower community, so let’s endeavor to improve our use of the device.

Moreover, the dinosaur-slaying asteroid that Tule created, Tule Vision, already corrects for the influence of VPD. The Tule Vision model was trained on FieldStat readings from our sensors, and FieldStat measurements are corrected for the influence of weather. If you want to compare Tule Vision readings to pressure chamber readings, then you will need to correct the pressure chamber for the influence of VPD.

Method

Determine The Baseline

vpd-adjust-fig-1-47eed56d4aef717014bf67876192798d232bcf5c544588050a75df834d8bd3ad

The above figure from Williams and Baeza 2007 shows the relationship between midday leaf water potential and vapor pressure deficit for vines without water stress. Note that the leaf water potential units are in megapascals. Because most growers speak of water potential in terms of positive bars, I will use the same convention. The figure tells us, “For vines without water stress, you will get a leaf water potential of 5 bars when the VPD is very low (i.e., generally the air temperature is cool), and you will get a leaf water potential of 12 bars when the VPD is very high (i.e., generally the air temperature is hot).

Depending on the weather, your pressure chamber readings can be off by up to 7 bars.

This reminds me of something else I once heard a grower tell me. “I don’t use the pressure chamber because it’s just a labor-intensive way of checking the weather.”

The baseline VPD should be region specific because one grower’s high VPD event may be another grower’s routine VPD. If you farm in an area where the VPD is always at a high value (e.g., 6 kPa), then you are used to what the pressure chamber readings say for 6 kPa conditions. That is, you have calibrated your interpretation of the pressure chamber for the local conditions. When you get a 12 bar reading, you know that, where you farm, 12 bars means the vines are still looking lush. But for another grower, who farms in a milder climate where the VPD is typically around 2 kPa, 12 bars means the vines are showing more stress and it’s time to turn on the pump.

During any particular day, the highest VPD tends to correspond to the highest air temperature. That is, the VPD changes throughout the day. Also, VPD changes throughout the year. The highest VPD on a typical day in May is lower than the highest VPD on a typical day in August. Therefore, in addition to being region specific, the baseline VPD should also be specific for a time of day and specific for the month.

For our baseline VPD, we take the last three years (2017, 2018, and 2019) of VPD data for one location per California county. We use CIMIS data because it’s readily available to everyone on the internet. We calculate the average VPD over the last three years for June at 10 am, for June at 11 am, for June at 12 pm, and so on. We run the calculation for the hours of x am to y pm and for the months of June through September. The result is the average VPD for a region for a particular time of day and for a particular month.

Calculate the Baseline VPD and the VPD at the Time of the Pressure Chamber Reading

For the next step, we want to see how much higher or lower the VPD is from the baseline VPD. This is a fairly straightforward calculation. We calculate the baseline VPD for the time of day and month of year that we took the pressure chamber reading, as described in the previous section. Next, we calculate the VPD at the time of reading. If you’re unsure on how to make these calculations, then you can request a copy of our sample Excel file.

Calculate the Influence of VPD on the Pressure Chamber

Rather than taking an intuitive guess at how much error VPD has caused in the pressure chamber reading, let’s put some numbers to it. Let’s start with the regression model that Williams and Baeza developed for relating VPD and leaf water potential (LWP) in the figure above.

Equation 1.

LWP = -0.49 - 0.079 * VPD

We can take this equation, and use it to see what the LWP would be at our baseline VPD and what the LWP would be at the VPD of the time of the pressure chamber readings.

Equation 2.

LWP_bomb_time = -0.49 - 0.079 * VPD_bomb_time

Equation 3.

LWP_baseline = -0.49 - 0.079 * VPD_baseline

We want to know how much the current VPD increased or decreased the LWP compared to the baseline. If we know the influence of the VPD on the reading, then we can use it to correct our leaf water potential reading.

Equation 4.

LWP_error = LWP_bomb_time - LWP_baseline

If you substitute equations two and three into the right side of equation four, then the intercept term (i.e., -0.49) drops out, and you get this.

Equation 5.

LWP_error = -0.079 * (VPD_bomb_time - VPD_baseline)

The above equation would give us the leaf water potential in negative megapascals. Growers speak of leaf water potential in terms of positive bars, so the error looks like this in terms of bars.

Equation 6.

LWP_error = 0.79 * (VPD_bomb_time - VPD_baseline)

Remove the Influence of VPD from the Pressure Chamber Reading

We know the error that VPD caused in the pressure chamber reading. Let’s subtract the error from the pressure chamber readings to get the corrected reading.

Equation 7.

LWP_corrected = LWP_bomb_time - LWP_error

A hypothetical vine, a hypothetical intern, and a data-savvy viticulturist

Let’s imagine we have a vine in Napa where the actual leaf water potential is always 12 bars. The hypothetical vine always stays at 12 bars, no matter how much water it gets.

vpd-adjust-fig-2-4a7be1e1bffa2bc152828fa1787edc5efe0d6059aee36a8853ff75a9e23028c7

In the above figure, we have the baseline VPD in Napa County at 3 pm Pacific Daylight Time (2 pm Pacific Standard Time) for the months of June through August in red. We also see the actual VPD at 3 pm PDT in Napa for June 2019 through September 2019 in black.

vpd-adjust-fig-3-de84f04bc3641e186fa509df895275bb119ced419be2f028cf60594836440de6

Using “Equation 6” above, the figure above shows the error caused by the influence of VPD.

vpd-adjust-fig-4-fe8478189ada568a026a37d34def627e34e7bbc02093ce43c9416f2c25e50dd3

If you were to send your hypothetical intern out to take pressure chamber readings of this hypothetical vine every day at 3 pm PDT from June through September in 2019, the above figure shows the readings he would get.

Even though the vine is actually 12 bars every day, that is not what the pressure chamber tells your hypothetical intern. On September 7, 2019, your hypothetical intern gets a pressure chamber reading of 11. Your hypothetical intern looks at the value, looks at the vine, and puts his hand to his brow to soothe his hangover (“3 pm! I can’t drink like I used to.”, he says to himself. “Being 23 is the worst.”). On September 13, 2019, your hypothetical intern gets a 14. Perplexed, he writes 12 down on his clipboard, finds some air-conditioned bar, and spends the rest of the afternoon contemplating a career in banking.

You take your hypothetical intern’s readings, and you decide you’re going to correct the values for the influence of VPD. You requested a copy of our sample Excel file that has the baseline VPD values and above calculations in it. You go to the CIMIS website to look up the air temperature in Celsius and vapor pressure in kPa for your county. You enter the weather data and pressure chamber readings into the spreadsheet, and, as expected, you get 12 bars.

vpd-adjust-fig-5-9e446f8d5f99cf6eb655207e8cbd32c89c2345955cf48c00cc52e288e7909529

But wait, what about the influence of water stress on the influence of VPD on pressure chamber readings?

vpd-adjust-fig-6-af5ef952e035a5a989311c4ab083fe4c65bec0c7a6ed5d35873762f0f60b55bc

The above figure from Williams and Baeza 2007 shows that the relationship between VPD and leaf water potential changes with water status. In other words, the water status of the vines influences the pressure chamber error caused by VPD. The more water-stressed the vines, the less the VPD influences the pressure chamber reading.

This blogpost presents a method for correcting pressure chamber readings for the influence of VPD. It is a starting point for trying to quantifiably correct the pressure chamber. To correct the pressure chamber more rigorously, you would first need to know the water status of the vines. And that’s quite the quandary, isn’t it? To use the pressure chamber to get the water status of the vine, first you need to know the water status of the vine… so that you can correct for the influence of VPD on the pressure chamber reading.

You’re in a vineyard, standing in the sun. It’s 104 degrees and the VPD is 6 kPa. You’re staring at the petiole of a leaf in your pressure chamber. You’re wondering how you can get the water status of the vine, so you can use the pressure chamber to get the water status of the vine. Just then, your hypothetical intern walks down the vine row towards you. He’s dressed like a banker, and he’s wearing a Panama hat. You rest your hand on the pressure chamber. He puts his hand on your shoulder.

“This dinosaur is never gonna make it,” he says. “Just get yourself Tule Vision already.”

California Almond Productivity:The Road to 4,000 Pounds Per Acre

almond yield history
  • Introduction Phase (1900 – 1935)
    1. Cross-pollination requirement established.
    2. Cross-pollinated and late-blooming varieties developed.
    3. Trees grown on hillsides without irrigation.
  • Establishment Phase (1935 – 1960)
    1. Almond yields shown to respond well to irrigation.
    2. Plantings spread to flat ground in Sacramento and San Joaquin Valley.
  • Transition Phase (1960 – 1985)
    1. State Water Project and Central Valley Project bring irrigation to more orchards.
    2. Introduction of Nemaguard rootstock.
    3. Agrichemical advancements increase fertilizer availability and improve pest control.
  • Expansion Phase (1985 – 2014)
    1. Micro-irrigation shortens periods of water stress between irrigation events.
    2. Increased canopy size from higher planting density and reduced pruning.
    3. Within-season fertigation improves tree nutrition.
  • Maximization Phase: (2014 – Onwards)
    1. Yields increase to the biological maximum achieved in highest performing orchards.
    2. Research-based field-specific Actual ET measurements, water stress monitoring, and irrigation recommendations from Tule (Founded 2014) enable growers to maximize production.

How will you achieve 4,000 pounds per acre?

Technology and management practices have always driven yield gains in California almond production. To an almond grower from the 1970s, our current almond yields would be unfathomable. In the future, statewide yields will be 4,000 pounds per acre, like we see today in the highest performing orchards.

almond_water_production_function-b14583fe17c59a8b8e4183c56981e3f2bb45f5ef5a172274fc2feefa21676d1e

By irrigating to exactly the orchard’s need, you can maximize production (see figure on left). Tule provides irrigation recommendations based on measurements of the plants needs (i.e., Actual ET). Contact Tule to learn how our research-based irrigation advancements are driving the future of California Almond yields.

CONTACT TULE TO SCHEDULE A DEMO

Deficit Irrigation Strategies For Almonds

As you may know, monitoring and minimizing plant stress during postharvest is one of the most important things you can do to ensure fruitful future yields. Using Tule’s FieldStat, you can monitor the crop stress of your field daily and remotely during this critical time. Below, we quickly review the effects of water stress for each growth stage of almonds, as supported by current academic research. 1

  • Early Season
    In general, stress should be entirely avoided during the early stages of the season (specifically from leaf out until the onset of hull split, including nut set). During early season canopy growth, any stress-induced water deficit will hamper photosynthesis and limit growth. This will have direct, negative effects on current and future yield. During the subsequent period of nut set, any significant water deficit will lead to increased nut drop and smaller kernel size. 2 (Tule recommends Target FieldStat set to Low Stress)
  • Hull Split
    From the beginning of hull split until 90% hull split, research indicates that moderate levels of stress may help conserve water and have only negligible effects on yield. Specifically, maintaining a midday stem water potential between -14 and -18 bars has been shown to decrease total water consumption by 15% without affecting nut size or total nut load. 3 (Tule recommends Target FieldStat set to High Stress)
  • Pre-Harvest / Harvest
    Following hull split through harvest, it is critical that you irrigate to maintain as little stress as possible. During these phases, water deficits will result directly in decreased nut weight and quality. 4 ( Tule recommends Target FieldStat set to Low Stress)
  • Postharvest
    During this stage, the buds for next season’s nut growth begin to set and develop; water stress here has been proven to have a greater effect on yield than any pre-harvest deficits. 5 (Tule recommends Target FieldStat set to Low Stress)

With Tule, you can easily and remotely monitor your crop stress over an entire field to ensure irrigation doesn’t limit yield potential throughout the season. Tule allows you to track your performance as compared to the research above by setting different stress targets for each phenological stage. With your targets set, Tule will alert you if your crops exceed your stress threshold and provide an irrigation recommendation to get you back on track.

To learn more about tracking strategic deficit irrigation and irrigation management with Tule, please contact us.

1. For more detailed information on various SDI techniques please see the California Almond Board’s guide.

2. Prichard et al. 1996; Lampinen et al. 2007

3. Shackel et al. 2004

4. Goldhamer and Viveros 2000

5. Goldhamer and Viveros 2000

Tule Target PRI: Achieve Full Canopy and Yield Potential

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One of the most important milestones for a successful growing season is sufficient canopy growth to support your yield targets. The new Tule Target PRI helps you get your field to its full canopy size and yield potential.

How Do I Use the Tule Target PRI?

The Tule Target PRI gives you a goal PRI for achieving full canopy size. To use the Tule Target PRI, log into your Tule dashboard and compare your current PRI to the Tule Target PRI .

To use this tool, we assume you are familiar with the Plant Response Index (PRI). For our purposes in this article, it is important to remember the PRI increases as the canopy develops in your field.

If the PRI from your field is already equal to or greater than the Tule Target PRI, then your canopy has already reached a sufficient size. In the figure below from 2014, we see that the PRI reached the Tule Target PRI — hence, the canopies were fully developed — by the middle of May.

canopy_dev_pri

If your PRI is below the target, but steadily progressing towards the Tule Target PRI, like we see below in the example from 2015, then the current irrigation strategy will likely produce the full canopy size. Proceed with your current irrigation strategy as informed by your Tule Actual ET monitoring.

canopy_dev_pri_2

How does the Tule Target PRI work?

The Tule Target PRI is based on the largest canopies that you have grown in your field over the last three years. The Tule Target PRI is calculated from historic satellite imagery from your field. We obtain the maximum Normalized Difference Vegetation Index (NDVI) between June and July for the previous three years. We transform the NDVI values into the Tule Target PRI, which is the maximum potential PRI for your field.

The Tule Target PRI also takes into account the largest canopies grown in similar fields throughout your region. The canopy in your field may not have reached its full potential size over the last three years — if, for example, you may have replanted your perennial crop three years ago. We calculate the maximum PRI for similar fields (i.e., fields planted with the same crop, on the same row spacing, etc.) in your region. The Tule Target PRI is the greater of value of either: 1) the maximum PRI in your field over the last three years, or 2) the maximum PRI of similar fields in your region over the last three years.

How does the Tule Target PRI work?

The Tule Target PRI is designed to help you achieve full canopy development in your field and help you meet your production goal. We at Team Tule are thrilled to release this new feature! If you have any questions, please email support@tuletechnologies.com. We’d love to hear from you!

[Update from April 2016: You now have the ability to choose a Target PRI based on historical data from the last five years. See this blog post for more information about this new improvement.]