2002: Superintendent News - Wetting agents help water infiltrate dry areas
By Tamson Yeh, Ph.D.
The popularity of wetting agents comes and goes, but for a golf course manager with a tough, highly variable site where the clientele expects consistent high quality, it can be a job or no-job situation.
Wetting agents are surfactants that increase the surface area for water to easily move on, thereby increasing its spreading and penetrating power. Many materials are used as wetting agents, including long chain alcohols, petroleum sulfonates, acid sulfates, sulfonated aromatic derivatives and esters of fatty acids.
Wetting agents are used as spreader stickers during pesticide application and to clean out spraying equipment afterward. But their widest use on the golf course is in the treatment of localized dry spots, which can be caused by natural variability in the soil, by fairy ring fungus or by compaction. When soils become dry past a certain point, organic acids in the soil will dry in a hydrophobic layer around the particles – water will bead up and not spread through this layer, but runoff.
The same thing happens in a thick thatch layer that dries out past a certain point. Basically, you have a molecular traffic jam – the road is closed and the water must detour. These localized dry spots can burn out quickly and make life a living hell for a superintendent who is trying to get water back into the system. The wetting agent changes the hydrophobic nature of these areas into a hydrophilic one – allowing water molecules again to spread through the dry spots by having their charges cling to both the soil particles and to each other.
A great example of the practical uses of a wetting agent on a regular basis would be a golf course on a heavy clay subsoil covered with extremely variable depths (1.5 inches to more than 8 inches in one small area) of slightly more friable topsoil also containing large amounts of clay. A course like this is found about 12 miles from my office. To my understanding, the chief complaint of the clientele is the quality of turf and playability after watering. Because of the uneven quality of the topsoil and the consequent rooting depths, automatic irrigation is inadequate for consistent quality. Areas with shallow depths of topsoil and shallow root systems dry out much faster than areas with deeper levels of topsoil, deeper roots systems and more stored water in the soil.
Compounding this problem is that if you water to suit the areas with shallow roots, other areas become boggy and unplayable, and you get turf decline and death because of saturated soil conditions. If the turf is watered on the basis of areas with deeper topsoil profiles, then shallow areas burn out. Clay soils, once they become very dry, are extremely difficult to rewet, resulting in an adobe brick effect. As the soil dries, cracks form, causing fingered flow of water when it is applied around large chunks of impervious clay soil. This was evident in several soil plugs I examined from this site. Further problems with soil and water infiltration result from the hilly topography of the course. When irrigation water or rainfall hits thinned turf, fine particles of soil wash out of those areas or are splashed up, resulting in runoff that can carry these fine particles to lower areas of the course, where they pack in between larger soil particles so that you essentially “Scotchgard” the soil surface. This makes it difficult for water and air exchange around the roots, resulting in poor turf quality.
In order to alleviate the situation without completely renovating the course, there are several slow but effective means of remediation. In the areas with the greatest variability of topsoil depth, a wetting agent used at the highest recommended rate on a consistent basis may improve wetability of the soil, requiring less water. This reduction in irrigation will benefit areas that become saturated when irrigation is geared toward shallower spots that burn out easily.
Research has shown that almost twice as much water is required to rewet untreated soils as those treated with the appropriate amounts of a wetting agent. This is merely an aid, not a cure. Better distribution and absorption of added water also will limit the presence of moss and algae, as well as the intrusion of annual bluegrass, whose shallow root system depends on the presence of large amounts of free water in the upper 2 inches of soil.
By reducing fingered flow of water, you will make the playing surface more even and firm, which should please golfers, not to mention the makers of wetting agents.