Growth Factors I Water

Water is the most important and limiting growth factor of all. Its molecule is constituted by two atoms of Hydrogen and one of Oxygen united by a covalent bond.

These molecules have polar character, joining together through hydrogen bonds.

The interaction of these dipoles is responsible for the surface tension of the water, related to the ease with which the soil “gets wet”.

This is where surfactants come into play, widely used in the world of greenkeeping. With them, the surface tension of the water decreases, reducing the formation of dew on the surface of the greens and in turn the proliferation of fungal diseases, such as the “dollar spot” on greens coated with dew and low in nitrogen.

Areas without getting wet by water

Areas without getting wet by water.

Another very important effect of the use of surfactants is the elimination of hydrophobic zones, the “dry patches”. These are attributed to the decomposition effects of basidiomycete fungi. Fungi of the same group as the microorganisms that cause the typical “fairy ring” in the soil.

Hydrophobia is caused by the decomposition of mycelial remains of fungi and organic matter, Dernoeden. P.H, Creeping Bentgrass Management, 2002.

The amount of water that can be taken by the roots, is that surrounding them and therefore will depend on different soil characteristics such as:

  • Texture. The capacity of water retention follows this increasing order, depending on the type of soil: Sandy <Frost-Sandy <Limousine <Frosty-loamy <Clay.
  • Root length The greater the root length, the greater the water reserve.
  • Species and varieties, following the following increasing order of drought tolerance: Bahiagrass> Blue grass> Zoysiagrass and hybrid Bermuda, St Augustinegrass> Seashore paspalum> Fescue> Poa Pratensis> Rye grass> Agrostis> Poa annua.

VOLUMETRIC WATER CONTENT (VWC)

The volumetric content of water or moisture (VWC) is a numerical measure, percentage, of the soil moisture.

Any volume of soil will be occupied by a solid fraction, (either organic as plant material and mineral as sand particles). Another hollow fraction consisting of small and large pores, capable of being filled by air and water.

In the absence of water, all the pores are occupied by air (permanent wilting situation) and the water added to the soil fills the small pores (field capacity situation) and then the large pores (soil saturation situation) first. The difference between field capacity and permanent wilting point will give us the water available for the plant.

Soils of different textures like sands and clays, have saturation or field capacity at different whater percentages. It is common to find on USGA greens saturation percentages over 40% volumetric, field capacities around 25% volumetric and according to the species of grass C3 or C4 (with less or greater tolerance to dry situations), the grass will reach the point of permanent wilting below 10% volumetric.

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

 Moisture evolution in Tiloom sensors

Moisture evolution in Tiloom sensors

There are numerous sensors to measure the volumetric content of water or soil moisture. The TDR of the Spectrum brand to the FDR of the Decagon brand, through the coaxial impedance sensors of Stevens Waters, or the new POGO or Environmesh systems of Tiloom .

 

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