Quick Tip

Creeping bentgrass is the most widely used cool-season turfgrass species on putting greens in the United States. When grown on sand-based putting greens, such as those built to United States Golf Association specifications, bentgrass summer decline and occurrence of localized dry spots (LDS) quickly become one of the most overwhelming hurdles for superintendents. The use of wetting agents or soil surfactants has gained recent popularity with turf managers by increasing water infiltration and retention of drought stricken putting greens.

Localized dry spots are thought to be caused by the Basidiomycete fungi (McCarty, 2005). As the fungi decompose, they release organic and hydrophobic fulvic and humic acids (Miller and Wilkinson, 1978; Roberts and Carbon, 1972). Localized dry spots are areas several inches to several feet across and irregular or serpentine in shape. They are characterized by having soils that are extremely hydrophobic and very difficult to re-wet upon drying.

Wetting agents have been used to increase water-holding capacity of turfgrass soil media for some time. Wilkinson and Miller (1978) determined the severity of localized dry spot caused by hydrophobic soil can be reduced by improving moisture retention and infiltration when under wetting agent treatments. Karnok and Tucker (2001) reported that one application of a wetting agent significantly reduced the MED (molarity of ethanol droplet, a test for water repellency) of a hydrophobic soil for up to 12 weeks.

The study

Figure 1

A two-year field study was conducted in 2006 and 2007 at Clemson University to evaluate effects of a wetting agent (Revolution by Aquatrols Corp.) and both liquid and granular potassium (K) fertilization on the alleviation of summer stress associated with creeping bentgrass during summer months. Plots were arranged in a randomized split-block design with four replications.

The wetting agent was applied monthly from May to October each year at a rate of 6 ounces per 1,000 square feet (oz/ft² ). Applications of the wetting agent were immediately watered in by hand.

Potassium (K) was supplied to the research plots as either liquid or granular sources. Liquid K was applied every two weeks from May to October each year at 0, 2 pounds, or 4 pounds K/1,000ft² . Liquid K was applied using a carbon dioxide backpack type sprayer. Granular K was applied at times of aerification; one spring and two fall aerification dates each year. After aerifying and removing cores, a granular K was swept by hand into each plot in order to incorporate fertilizer into soil. Granular K was also supplied at 0, 2 pounds, or 4 pounds K/1,000ft² annually.

Parameters measured included leaf and root tissue nutrient concentrations, clipping yield, root weight, volumetric soil water content, soil hydrophobicity using the water droplet method at 1.5-centimeter (cm) and 3-cm depths, and turf quality (TQ). Turf quality was measured on a 1 to 9 scale; 1 being dead turf, 7 being acceptable, and 9 being of optimal turf color and quality.

Figure 2

For soil hydrophobicity testing, two cores were removed from each plot two weeks after each wetting agent application. Cores were allowed to air dry for four weeks, and a droplet of water was placed at 1.5-cm and 3-cm depths. Time taken for core to fully absorb the droplet was recorded in seconds.

All statistical computations were conducted using the analysis of variance (ANOVA) procedure within the Statistical Analysis System (SAS Institute, 1999). Means were separated using Fisher's Least Significant Difference (LSD) test at an alpha level of 0.05.