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).
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!
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.
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!
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!