Soil Moisture

Understand the soil moisture and the VWC mesure (Volumetric Water Content)

Rafael Ferreira avatar
Written by Rafael Ferreira
Updated over a week ago

This article is part of a series with technical content that we did to help younderstand how our products work. This refers to the product Irrigation Management. Below you get a list with all the articles written by us about this theme.

We recommend you to read the article Analysis of soil data before start the reading of this article

Soil Moisture

The soil moisture related to FC (Field capacity) and PWP (Permanent wilting point) are extremely dependent on the soil structure. So the FC and PWP are directly affected by some soil variables like organic matter, the source rock, the granulometry (amount of sand, silt and clay), the soil compaction, etc. So, it’s common in a soil profile that each depth has a different moisture of FC and PWP.

How the soil has different values of FC and PWP, the same measure can be higher to one kind of soil and lower to another. So comparing two different soils, not always the one with more moisture is the soil with more water available to the plant, or the one with less moisture needs to be irrigated. It’s very important the relation between this and the FC and PWP values.

There’s a lot of techniques that allow us to measure the soil moisture. One of them is through the sensors that measure the soil moisture content by soil volume, as known as Volumetric Water Content (VWC). This content is the ratio of water volume by the volume of soil and water (cm³/cm³ ou m³/m³), so the VWC is equal to a percentage (%).

For example, the components of a known volume of soil are shown in the above picture, How the VWC is the volume of water divided by the total volume, in this case we have a VWC of 40%.

In the normal situations of the field we never see soil moisture equals to zero or 100%. The soil is made in addition to water, air, particles of rock, sediment, etc. So, a saturated soil will never measure 100% of VWC, because if not, it will be pure water.

Examples of soil moisture data in two different depths and their respectives values of FC and PWP.

Previous article -Soil analisys data

Next article -Soil tension

Did this answer your question?