What is soil moisture (tensio)?

What is soil moisture (tensio)?

We can determine the soil moisture by means of suction pressure or a vacuum. This suction pressure is measured by a tensiometer. This is a hollow tube with a porous ceramic on the bottom.

Porous means that the ceramic behaves as pores and the tube therefore functions as an artificial root of a plant. It allows moisture to pass through according to the environment. We will explain this further below.

The tube is closed at the top by a rubber stopper. Before it is closed, the tube is filled with demineralized water and placed into the soil or substrate. The water can now enter or exit the tube through the ceramic.

When the bottom or substrate becomes more dried out, water will be withdrawn out of the tube, which creates a vacuum in the tube. When this negative pressure is equal to the suction pressure of the bottom, no more water will be withdrawn from the tube.

If the soil or substrate gets moist, for example through rain or watering, the tensiometer will withdraw the water back from the soil due to the vacuum in the tube. This reduces the negative pressure until it is equal to the suction power of the soil.

When the soil or substrate contains so much water that it is saturated, the water can flow freely in and out of the tube. There is then no suction pressure from the bottom and the pressure in the tube will therefore be equal to the ambient pressure.

The tensiometer is therefore seen as an artificial root of a plant in which the negative pressure in the tube is always in balance with the suction pressure of the soil.

We can use this as a measure of the suction pressure that a plant or crop must exert to absorb water from the soil. The soil moisture is measured in hPa, which stands for Hectopascals.

The ideal soil moisture for you depends on your personal application. We are happy to help you accurately and reliably measure and monitor the desired soil moisture with one of our tensiometers. View our range here.