“When a growth site dries out, it is difficult to get it wet again.
It is dry in the Netherlands, so dry that the soil can become water-repellent. René Voogt, who helps greenkeepers monitor the water level of their plants through data interpretation using ConnectedGreen’s technology, explains what is happening.
Author: Karlijn Klei
Voogt has been observing the drought in the Netherlands for some time through the data from the sensors that the company has distributed across the country. “Despite the relatively wet winter,” Voogt explains, “many growth sites never fully recovered from last year’s drought.”
“The soil contains pores,” Voogt explains. “The size of these pores can vary, from large pores in sand to very small pores in clay. This is useful because it allows the soil to supply trees and plants with moisture and oxygen. However, when the soil dries out, the pores fill up with air. The soil becomes so dry that it becomes hydrophobic, or water-repellent. This is a very common phenomenon with long-lasting adverse effects.”
To recover from the drying out, the soil needs not only water but also time. Normally, this recovery occurs during the winter when there is less evaporation and more rain compared to the preceding months. “However, this winter was not wet enough to fully replenish the growth sites after last year’s dry period,” Voogt explains. “Especially in places with a sandy subsoil, the hanging and ground water has disappeared or sunk deeper due to the drought.” René compares the dried-out soil to a sponge. “If you throw a bone-dry sponge into a bucket of water, it doesn’t absorb the water immediately. It regains its water-absorbing function only after soaking for a while.”
“Drought makes the soil hydrophobic, or water-repellent.”
If you are dealing with hydrophobic soil, it is important to give it smaller amounts of water more frequently rather than a large amount at once. “If you pour a large amount of water on it at once, it simply washes away,” Voogt explains. This leaching occurs either through the surface, such as rainwater flowing over paved streets, or directly through the growth site towards the groundwater. However, the water level has become so low in many places due to the drought that the roots can no longer reach it.
“We need to give water more frequently in smaller amounts instead of occasionally giving a lot,” Voogt emphasizes once again. This wisdom is not new, of course, but with the drought of recent years, it is more important than ever. “In practice, people often drive a tractor to a tree and fill the watering ring once or twice. Unfortunately, only 10 to 20 percent of the water remains in the hydrophobic growth site – and that is a waste, of course.” Not only of water and labor, but also of the nutrients and salts in the soil, as they are washed away with the water.
The degree of leaching can be visualized with the data collected and analyzed by Voogt using ConnectedGreen. Voogt says, “The steeper the peak on the moisture graph, the more leaching is occurring. This can be observed with a large water application to a dried-out growth site: the moisture content rises very quickly but also decreases almost as rapidly. When you perform smaller, more frequent water applications, the peak is less steep: water is added more slowly but also stays in the growth site better. By carefully observing this, it is possible to find the optimal amount of water to maintain the average moisture percentage. In practice, this can save up to 70 percent of the water volume. In a medium-sized municipality, that can quickly save several hundred thousand liters per season.
The essence of the story is: if you let the growth location dry out, it becomes very difficult to moisten it again. Voogt says, “So it is important not only to water correctly but also to properly construct growth locations and planting areas.” Here, the reuse of rainwater plays an important role. The drought we are facing is alternating with another extreme: short but very heavy downpours. By using structures such as water buffers or crates around and under the planting areas, you achieve two goals at once. Voogt explains, “On one hand, you capture peak water that may otherwise cause waterlogging. Hydrophobic soil behaves more or less like pavement. By capturing the water, you prevent waterlogging and have water available for use when needed. This creates micro-systems that are independent of whether groundwater is available or not.”
Unfortunately, such structures cannot be installed just anywhere. In those cases, according to Voogt, it is crucial to maintain everything very well through monitoring. “You need to intervene before the soil dries out. If it has already dried out, then you have to provide water in a cautious manner. It is really time to reconsider watering practices and the construction of growth locations,” concludes Voogt. “I believe the growth location of the future will be a combination of innovations like those we have seen at the Gouden Gieter.”
“The growth location of the future is a combination of innovations like those we have seen at the Gouden Gieter.”
Bullying the Roots
Watering is a complex issue. Although you need to keep an eye on the water needs of your trees and plants, you shouldn’t “spoil” them, as Voogt explains. “If you serve plants their every wish, they can become ‘lazy.’ This means that a tree or plant no longer needs to develop its roots further to reach water, and therefore doesn’t do so.” If you then skip watering once, the tree is in trouble. Due to its underdeveloped or less developed root system, it cannot access the ground or subsurface water. “Nursery growers are aware of this. Trees on nurseries are watered in a way that encourages root development. We call it ‘bullying,'” says Voogt. “You need to tease the roots a little so that they develop properly.”