Volumetric Water Content (VWC): Measure your irrigation better

The volumetric water content or Volume Water Content (Volume Water Content) is a numerical, percentage measurement of the soil moisture.

The VWC measures the ratio between the volume of water in a soil and its total volume.

Any given volume of soil will be occupied by a solid fraction(either organic as plant material or mineral as sand particles). and another hollow fraction consisting of small and large pores, which can be filled with air and water.

In the absence of water all pores are occupied by air (permanent wilting situation) and the water supplied to the soil first fills the small pores (field capacity situation). Then the large pores (soil saturation situation). The difference between field capacity and permanent wilting point gives the water available to the plant.

Soils of different textures, such as sands and clays, show saturation or field capacity at different percentages.

It is common to find in USGA greens saturation percentages above 40% volumetric, field capacities around 25 % volumetric. Depending on whether the grass species is C3 or C4 (with less or more drought tolerance) they will reach the permanent wilting point below 10% volumetric.

It is intuitive to see how the different irrigation cycles coincide with the field capacity of the green (26% volumetric), see attached graph.

Numerous sensors are available to measure the volumetric water or moisture content of the soil. From Spectrum TDRs to Decagon FDRs, from Stevens Waters' coaxial impedance sensors to the innovative POGO o Environmesh by Tiloom.