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Wetting agents for soil reduce repellence effects by lowering surface tension, which increases infiltration. Wetting agents can be applied in broadacre farming as narrow bands over the furrow, or even within the furrow itself near the seeds to save money by using lower rates. Some formulations contain water and nutrient-retention compounds to reduce wetting agent leaching. These newer formulations can be applied as a blanket to the entire soil surface.
Property of soil wetting agents
The soil wetting agent are chemical combinations that can allow water to enter and remain in soils resistant to water.
Penetrants
Penetrants reduce the surface tension and spread water over the soil particles. Penetrants can also encourage the leaching of nutrients and water. Some penetrants are designed to break down faster to reduce leaching risks.
Water-retaining compounds
These compounds can be used to reduce soil leaching. They attach a part of their molecules to the soil surface, and another part to water or nutrients. Water repellent soils are best managed with products that combine penetrants with water retaining chemicals.
Wetting agents with bands
The wetter is sprayed into the row of crops at seeding at a cost-effective rate of 0.5-2 litres/hectare (L/ha). It is usually sprayed on the soil surface behind the press wheel at the bottom of the furrow to increase the efficiency of water harvesting. This also reduces the “gapiness” of the crop establishment. The use of banded wetting agent is more difficult to manage than many other repellence methods.
There are a number of problems that can occur when wetter is applied to the furrow behind the press wheel.
- Some designs of presswheels can cause soil to be disturbed and the band to be broken. The recessed rims on wheels of flat or square cross-section encourage soil to be thrown and the sides of the furrow to be ripped up. Presswheels with smooth sides and a ‘V” or ‘U” cross-section are best.
- Spraying too close to the wheel of the presswheel can cause the soil in the furrow at the bottom to stop moving.
- The wind can blow away the spray from the furrow.
- After seeding, wind and rain can fill the furrow.
Water retention chemistry has been absent and the crop yield response ranges from 0-20%. The best results are usually achieved with dry seeding, some subsoil water and moderate rainfall within days or weeks of seeding. In the south-west part of WA, banded wetters are more effective on soils with repellent forest gravel.
Recently, some soil-wetter products have been applied in the furrow next to the seed. These products can be used with other liquids, such as UAN or fungicides. They are usually applied using the liquid banding kit on the seeder. This placement has been shown to be effective for certain products, but on deeper sands this can be less reliable.
Wetting agents for blanket application
Using a boom spray, soil wetters are applied to the entire soil surface at rates between 20 and 50 litres per hectare. They are usually sprayed onto stubble or dry soil, and then washed in with the opening rains.
As they are applied over the entire soil surface, blanket wetting agents can improve germination. The results of trials and farm evaluations were highly dependent on the soil type and the season. The most successful soils are forest gravel soils found in the south-west agricultural area. Some of these products have a longer life span and can be used on soils that are responsive for up to two seasons.
It is important to test blanket wetting agents on farms. They may be the most effective on weed “hot spots” such as gravel hills and sheep camps, where weeds are more likely to emerge in soil that repels water.
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