Hydrophobic Soils

  • Modified on 22 July 2020

There are two main mechanisms that lead to the display of hydrophobic character in sands and soils. The first is the accumulation of waxy hydrophobic organic matter onto the soils from the crop being harvested, this material anneals over time, hardening over cycles of heating and cooling, to the point where the coating cannot be easily wetted nor removed. The second is the morphology of the sand particle that has a high surface tension due to its shape.

In areas where hydrophobic layers of soil are nested on clay or clay loams, the use of organic surfactants has been a common practice to promote water infiltration. For areas where there are deep reserves of hydrophobic sands, the use of conventional surfactants can be counterproductive as run off is shifted from the horizontal to the vertical planes, and greater reliance is placed on organic matter to retain water.

At CHT, with our focus on surface tension, we look at methods to reduce the surface tension of the sand particle, or to reduce the surface tension of the waxy build up as well as increasing the non-metallic cationic charge of the soil particle to rebalance the hydraulic conductivity of the soil.

POSTER OPTIMISING SURFACE TENSION 3With the modification of surface tension we improve the infiltration through the soil and within the CHT product concept, it is not enough to only reduce the surface tension of the soil using surfactants, but consequential drainage needs to be mitigated by increasing the cationic charge of the soil particle.

mossBy reducing the surface tension of the soil and imparting a cationic charge the surface tension and charge balance now become synergistic controls for the flow of water through the soil.

Examples of changes to surface tension of various surfactants may be found here:


Image at left used with permission © David Hall, Department of Primary Industries and Regional Development, WA

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