The STRI's Matthew Slinger looks at soil wetting agents, identifying the types, their uses and application.
Soil water repellency (SWR) occurs on many golf courses in the UK and Ireland. There are numerous causes of SWR, such as preferential flow of water, fungal activity, application of topdressing, presence of thatch and compaction, which may contribute to varying degrees.
Further to this, as soil dries, a critical moisture content may be reached below which soils become difficult to re-wet. Where soil water repellency occurs, the turfgrass may wilt and eventually die in the most severe case. Playability and the aesthetic appearance of the golf course can be affected. In addition, the use of water on golf courses is being discouraged throughout Europe as water shortages have occured in recent years.
Wetting agents have been used for many years to improve the wettability of soils on golf courses and, so, improve the efficacy of any water absorption. In the UK, numerous wetting agents are available. Each product may perform slightly differently depending on its mode of action, dose rate and suggested programme of use.
Soil wetting agents are based on three chemistries - non-ionic surfactants, block copolymers and organosilicones. A natural product - Yucca extract - is also available.
Hydrophobic soils are often coated with organic substances, which repel water making them difficult to rewet. Non-ionic surfactants work by binding to the organic coating allowing water to become attracted to the soil again. Block copolymers attach to the soil particles differently and may allow water to disperse or to be held in the rootzone. Organosilicones are very effective at achieving fast spreading of water.
To achieve the best from wetting agents any factors contributing to the dry patch should be addressed. Such as alleviation of compaction, removal of thatch and preventing the rootzone from reaching the critical moisture content by ensuring even and timely irrigation.
Best results are achieved by applying wetting agents in a programmed approach, starting early in the season before symptoms are observed. Blanket applications are also more effective than spot treatments.
The efficacy and longevity of each product depends on the dose rate. Therefore, subsequent applications should occur after the suggested period of effective control has elapsed for each product.
Attention should also be paid to the activity of each product. For example, Breaker Curative does not help water penetration but helps to remove the organic coatings on sand grains and flush them through the rootzone. Therefore, it should be used in a programme with another soil wetting agent that helps water distribution.