Soil surfactants - Using soil temperatures to determine application timing in order to maximise results
Could there be a better way to know when to reapply soil surfactants, so the product works as well as possible? Dr Christian Baldwin, The Aquatrols Company, explains...
Soil surfactants are essential tools for turfgrass professionals implementing turfgrass management programmes. They offer many benefits such as; reducing localised dry patch formation, enhancing soil moisture uniformity, improving water infiltration, increasing root growth, minimising nutrient leaching and boosting turf physiological fitness.
Given these advantages, soil surfactant chemistries vary widely and include formulations such as straight block, reverse block, methyl-capped polymers and alkyl polyglucosides (APG), as well as combinations of these chemistries. Ultimately the choice of surfactant depends on turfgrass conditions, management goals and specific agronomic needs.
Using a calendar to time applications
Even though there are different types of soil surfactants (wetting agents), they all share one thing: they need to be reapplied based on a calendar schedule. Depending on the product, the label might say to reapply every few weeks or every few months.
But this raises a question - could there be a better way to know when to reapply, so the product works as well as possible? Recently, more people have started to investigate the use of a Growing Degree Day Model to help decide the best timing for applying wetting agents, instead of using the calendar.
Understanding Growing Degree Day models
A Growing Degree Day (GDD) model is a simple way to measure how much warmth has built up in the soil over time. Plants need a certain amount of heat to grow, and GDD helps to track that.
To calculate GDD:
- Take the day’s highest and lowest temperatures
- Find the average
- Subtract a base temperature - the point where plant growth stops. For turfgrass, this base temperature is usually around 6°C.
GDD models are commonly used in farming to help predict plant growth and decide the best times for carrying out practices such as fertilising, spraying or mowing.
Turfgrass managers are starting to use GDD models more often to help make better decisions based on how the grass is actually growing, rather than letting the month or week dictate application timing. These models can help predict how and when the grass will respond to different treatments.
Right now, GDD models are mainly used in turfgrass management to help determine timing for applying plant growth regulators, making fertiliser applications, controlling weeds, managing annual meadow grass seedheads in spring, and predicting when diseases might appear.
Why use a Growing Degree Day model?
There are two main reasons why these models are popular:
- They’re easy to use. All you need are daily high and low temperatures, and you can plug these into the model using a recommended base temperature based on what you are trying to achieve.
- GDD tracks heat buildup, and temperature is one of the biggest factors that affects how grass grows. When temperatures get too high, it can throw off the plant’s balance between making and using energy. This can lead to problems like poor root growth, less nitrogen uptake, and a higher risk of disease.
In the end, using GDD makes a lot of sense - because grass responds to temperature changes, not to calendar dates.
Potential benefits of using GDD models
- Data-driven decision making
- Cost efficiency
- Improved turf health
- Adaptability to climate variability
The effect of temperature on surfactant breakdown in the soil
Even though soil surfactants are widely used, there hasn’t been much research on how temperature affects how long they last in the soil. To explore this, researchers at the University of Minnesota ran two studies.
In the first study, Sam Bauer looked at how well a surfactant applied in the autumn held up into the following spring. He found that in spring (about five months later), water moved into the soil faster in treated areas compared to untreated ones, showing that the surfactant was still working.
Building on that, Ryan Schwaub, also from the University of Minnesota, studied how soil temperature affects water repellency, aiming to better understand how temperature plays a role in surfactant performance.
The results showed that soil temperature seemed to affect how quickly water soaked into the soil (measured by WDPT), but it’s still unclear if temperature really affects how long surfactants last in the soil.
At the University of Arkansas, Eric DeBoer studied how applying surfactants in late autumn impacted ultradwarf bermudagrass during winter. Like the University of Minnesota’s results, his study found that late-season surfactant applications helped the grass recover better, reduced winter damage and improved how fast water moved into the soil in spring. However, the results weren’t always the same every year.
Overall, there’s no clear answer yet on how temperature affects surfactant breakdown - likely because there hasn’t been enough research, and the variability of soil make-up adds to the complexity.
New research
To better understand how temperature impacts the longevity of surfactants, The Aquatrols Company has launched a new research project. The initial phase of this study is being conducted at the University of Tennessee, with plans to expand it across various climatic zones. This research explores how different surfactant types and application rates influence soil moisture retention and turf performance, particularly in the spring following winter
To track what’s happening in the soil, moisture sensors were placed at different depths to collect daily data. This will give a detailed look at how moisture levels through the profile change over time.
The research began in late 2024 and will continue through 2025, wrapping up in 2026. Stay tuned for updates and results!
Using Growing Degree Days to time the application of soil surfactants
Right now, there are three soil surfactants with GDD models that are available to the public on the website greenkeeperapp.com. While it’s still a small selection of products, it’s a positive step toward better timing of surfactant applications for improved results.
These models are still in testing (Beta) mode, but ongoing research is working to expand them to include more types of surfactants and different application rates. Over time, with more data and research, these models will become more accurate and even more helpful for turfgrass managers around the world who maintain golf courses, sports fields and other turf areas.
For more information, please contact your local Aquatrols Account Manager.
The Aquatrols Company develops technology to optimise soil – water - plant interactions. Aquatrols strongly believe we should take responsibility to protect our soil and water environment by delivering high performing, safe and environmentally responsible surfactant products for our end users, distributor partners and the wider community.