101 Questions answered
How Modern Wetting Agents Improve Soil Moisture: Penetration, Retention, and Nutrient Enhancement
Most broadacre soil wetting agents are typically non-ionic surfactants that work in two main ways:
1. Lowering the surface tension of the water – ‘penetrant’ property
Surfactants with penetrant properties contain long chain block copolymer compounds that act like detergent to reduce surface water tension, allowing water to better penetrate into a water repellent layer. These copolymer compounds have both hydrophilic and hydrophobic ends. The hydrophobic end binds to the coating on the soil particle while the hydrophilic end extends into the pore space allowing water to stick to it and move into the soil.
2. Retaining water in the root zone – ‘humectant’ property
Soil humectants are compounds that attract and retain moisture. They are large, complex molecules with many sites attracted to water and nutrients, and can counter the risk of leaching. These large molecules do not move within the soil and hence need to be applied where the water retention is needed, such as in the seed zone to enhance seed germination.
Modern broadacre wetting agents have both penetrant and humectant properties to allow both water penetration and retention.
Recent research in South Australia suggests that applying soil wetter to the seed zone leads to a more reliable response, especially when combined with stable press wheel furrows for effective water harvesting during the growing season. Press wheel furrow surface application requires soil wetters to be applied onto a firm surface free of loose repellent soil, and so are more susceptible to erratic responses following furrow in fill.
For more information see the fact sheet on managing water repellence at seeding: soil wetting agents.
Some have additional fulvic and humic compounds to enhance soil nutrient access and nutrient holding capacity.
