What is the “Wetting Front?”

Posted by Robert Dailey Mar 16, 2008

The place where the water stops is called the “wetting front.”

In most soils, it is possible to scrape away the wet layer of soil and uncover dry soil underneath.

How far into the earth that water penetrates depends upon a number of variables.

Amount of Water

The most significant variable is the amount of water placed on the surface of the soil.

Permeability

Permeability of the soil also has a bearing on how deep and how fast water permeates layers.

Root Zones

In gardening and agriculture, it is not important to saturate all layers of soil. It is only necessary to wet the layers of soil through the root zones of plants.

If enough water seeps into the soil, and it reaches all levels of the root zone, then the plant can intake enough water to survive. If it only reaches one half of the root zone, plants will suffer and perhaps die. Even if the plants do not die, they will be stunted and their seed production will be reduced or eliminated.

Penetration

Ligh rains or irrigation may only penetrate a quarter to a half inch. Heavy rains will move much deeper through the soil, perhaps as deep as 10 to 20 inches. When water seeps into the soil a half inch or less, it’s easy to scrape aside the wet soil and find the wetting front. However if the wetting front has reached 20 inches or more, it becomes difficult to find the wetting layer.

Indicators

There are wetting front indicators which can be purchased. These work in various ways, but generally they are stuck into the ground and pop up when the wetting front passes the bottom of the device.