How to Optimize Vineyard Water Use through Hands-off Evapotranspiration Monitoring
Deciding how much water to apply for irrigation is as challenging as it is important to producing healthy vines and quality wines. The age old questions of when, where and how much to irrigate will not be getting less important any time soon. If anything, with climate change and increasingly drier and hotter conditions both on and off season, they are going to get more and more prevalent. Even in regions where water supply and cost are not pressing issues, optimizing water inputs is crucial for more sustainable vineyard management.
So how to go about answering these questions? In this blog we discuss one method of determining your vineyard’s water needs and how technology could help make it more efficient and accessible.
The Evapotranspiration Method of Irrigation Scheduling
Figure 1. A diagram showing water use through crop evapotranspiration (ETc), surface runoff and deep percolation and replenishment of water supply through precipitation and irrigation. Image courtesy of University of Minnesota Extension
To start off, let’s define evapotranspiration (or ET). ET is the total water lost through evaporation from soil surface and transpiration (loss of water vapor) from leaves over time (see Figure 1). So in essence, evapotranspiration reflects vineyard water use (assuming groundwater recharge and runoff are negligible). Water lost in ET is replenished through rainfall and irrigation. This means, the amount of wate r that’s required for irrigation can be calculated given the amount of rainfall and ET. Rainfall data can be easily accessed from local weather stations.
But how is evapotranspiration measured?
Given that different plants have different rates of water loss, grapevine evapotranspiration (ETc) is calculated by multiplying a reference ET value (ETo) by a crop-specific coefficient (Kc).
Grapevine ET (ETc) = Reference ET (ETo) x Crop-specific coefficient (Kc)
ET for a reference crop (ETo) - a standard plot of irrigated grass - can be obtained from local weather stations. The method of calculating Kc is manual and involves estimations of canopy cover and the percentage of vineyard area that is shaded (for details see this article by Texas A&M).
By now the initial impression of evapotranspiration as a simple metric to inform irrigation decisions is probably starting to give way to concerns over the additional work that all these manual estimations and calculations create. If you are thinking “Surely there’s a way to make this automated?”, we are with you.
Hands-off ET monitoring
Figure 2. Remote evapotranspiration monitoring on Deep Planet’s VineSignal platform
In-field sensors to measure ET have been used in research but not commercially as these are expensive and difficult to install. Local weather stations are not a suitable alternative either - they provide data on reference ET values, as mentioned above, but these need to be adjusted with a crop-specific coefficient which requires further manual measurements and calculations.
A more user friendly and cost effective approach is to use signals from satellite imagery and to analyze these signals using machine learning algorithms to create evapotranspiration maps of vineyards. This approach is the basis of VineSignal’s new hands-off ET monitoring tool by Deep Planet. It visualizes evapotranspiration across the vineyard using heat maps, as well as displays cumulative ET per block across the growing season. Data is generated weekly to allow dynamic monitoring and to feed into irrigation decisions. This fully remote tool and the ‘Notes’ feature on the platform help vineyard managers and growers make data-based decisions on irrigation.
Benefits for growers
Using manual calculation of ET fails to reflect two very important factors of vine growth:
Grapevine water use and needs change during the growing season, depending on the developmental stage of the vines and on environmental factors
There is spatial variability in water use, depending on soil type and other factors, so a single number cannot accurately represent water use throughout the entire vineyard
One approach to addressing the first of these shortcomings is to use a varying-rate coefficient (Kc). This means that a different Kc value is used at every developmental stage during the growing season. For example, Washington State University has estimated varying-rate Kc which is dependent on growing degree day accumulation (see article here). However, this still leaves a number of factors unaccounted for:
Not optimized for different regions - geography has a major impact on vineyard behavior
Not optimized for different grape varieties - different varieties have different water needs and characteristics when it comes to water use
Fails to address spatial variability within vineyards
Remote monitoring of ET with VineSignal not only addresses these limitations, but is also easy to set up and use, cost-effective and does not involve maintenance of in-field equipment.
Other methods of monitoring vineyard water use
Figure 3. Sub-terrain soil moisture map showing soil moisture interpolation across the vineyard and to a depth of 5 feet (1.5 meters).
Given the importance of soil water content and irrigation to grape growth, it is no surprise that there are a number of approaches to monitoring vineyard water use. Perhaps the most common approach is using soil moisture sensors that continuously generate data on soil moisture status. To get more meaningful insights from these soil moisture readings, VineSignal’s sub-terrain soil moisture interpolation feature provides 3D maps of soil moisture across the vineyard and 5 foot deep. For more proactive decision-making, the platform also gives two-week predictions of soil moisture at 90% accuracy and can incorporate irrigation data to provide dynamic irrigation scheduling recommendations. All of this information is easily accessible on desktop or mobile devices through the VineSignal platform and important alerts are communicated through the ‘Notes’ function and email notifications.
The bottom line
Although evapotranspiration is not a new concept when it comes to plant water use and soil moisture status, it has not had commercial appeal because of the technical and technological drawbacks discussed earlier. However, with satellite data becoming more abundant and the development of AI and machine learning technologies, these drawbacks can be overcome, giving access to an easy-to-use tool to effectively monitor vineyard water use and to incorporate these insights into irrigation decisions. For growers and vineyard managers this translates into more optimized irrigation water use which means savings in the cost of water and improved sustainability in their vineyards, especially for those who cannot afford expensive soil moisture sensors.
To learn more about how this and other features on VineSignal could drive value for your vineyard, visit our website or register to be a beta tester by clicking the button below.