Dr Samuel Stacey, ICL Specialty Fertilizers

Uneven wetting of the soil can have a significant negative effect on turf health. Turf roots need a consistently moist environment for normal functioning, both to absorb nutrients and to help the shoots maintain an adequate rate of photosynthesis. Root health is an important driver of turf resilience to environmental stresses and turf roots do not grow into dry soil.

Established sand profiles are prone to developing dry patches that do not re-wet evenly during normal rainfall and irrigation cycles. In times of heat and moisture stress, uneven wetting will leave turf more prone to colour loss as well as loss of density. When irrigated, water may preferentially flow downwards via narrow channels instead of moving horizontally to fully wet the soil (Figure 1 ‘Water only’). Root growth can suffer and the playing surface may be negatively affected. Under extreme conditions, this can begin to look like patchy growth and uneven, mottled colour. 

Sand profiles with dry patch issues will support less root growth, hold less available water and require more frequent irrigation. The good news is that dry patch can be virtually eliminated by regularly applying a high quality wetting agent.

Wetting agents and their effect on water
Water (H₂O) is a really interesting molecule. What makes it interesting is the way that water molecules interact together. Each water molecule contains two hydrogen atoms (positively charged) and one oxygen atom (negatively charged). While the overall molecule is uncharged, the oxygen side is slightly more negative and the hydrogen side is slightly more positive. This causes an attraction between water molecules that chemists call ‘hydrogen bonding’. It is the attraction between the hydrogen of one water molecule with the oxygen of another. This attraction is the reason why pure water has a strong surface tension, why it rises in capillary tubes and also at the side of a glass. The attraction between molecules is the prime reason why water doesn’t easily absorb into hydrophobic sand and why moisture that does absorb prefers to form narrow channels rather than evenly wet up the soil profile.

What does a wetting agent do? It interferes with the hydrogen bonding and reduces the water’s surface tension. As a result, the water quickly absorbs into sand profiles and, instead of channelling, will spread horizontally and more evenly wet up the soil profile (Figure 1). In side-by-side comparisons it is amazing to see how much of an effect a good wetting agent can have. 

The best quality wetting agents often contain multiple surfactants, are biodegradable, will not burn turf roots and are highly effective at eliminating dry patch and improving water distribution. On established fine turf on USGA profiles, wetting agents can significantly improve the soils water holding capacity and create an optimal environment for root growth.

Figure 1. Wetting agents such as H2Flo Trismart improve water infiltration and lateral movement in sand profiles that naturally develop hydrophobicity.

Proven performance
H2Pro Trismart was designed specifically for fine turf grown on USGA sand profiles. It was developed at ICL through a collaboration between surfactant and turf specialists and has been independently tested by the STRI Group under Australian conditions. 
In 2017-18 a replicated trial was conducted at STRI’s Redlands research facility. Surfactants were applied to mature ultradwarf hybrid bermudagrass (cv. TifEagle) grown on a USGA profile and maintained as a golf green.
H2Pro Trismart was applied at relatively low application rates (monthly applications of 10 l/ha following an initial application of 25 l/ha). Other comparison wetting agents were applied at their recommended label rates. Other plots were left untreated (control) so that the trial would also quantify the full benefit that wetting agents can provide on established USGA sand profiles. The trial was run for six months beginning in November 2017 and wetting agent performance was evaluated over the spring, summer and early Autumn period.

The Results
The trial showed clear beneficial effects from using wetting agents and from H2Pro Trismart in particular. The performance of H2Pro Trismart versus an alternative wetting agent and the control has been summarised in Table 1. H2Pro Trismart showed the greatest effect between the months of November and March, coinciding with the peak period of moisture and heat stress in Australian grown turf. H2Pro Trismart reduced the incidence of dry patch by an average of 86% compared to the control (Table 1). Compared to the comparison wetting agent, Trismart reduced dry patch by an additional 67% and increased volumetric soil moisture by an average of 15% (Table 1). Differences between treatments were statistically significant (P  0.05).

Table 1. The performance of H2Pro Trismart versus both untreated turf and turf treated with a comparison wetting agent from November 2017 to the end of March 2018.

Turf colour and quality was also significantly (P  0.05) improved by H2Pro Trismart (Table 1 and Figure 2). While the average turf colour score was improved by 43% versus the control, it was also 19% higher than the alternative wetting agent. Turf treated with H2Pro Trismart maintained better and more even colour throughout the trial period by reducing dry patch and improving the storage and distribution of soil moisture (Figure 2, Table 1).
 

Figure 2. Turf colour and quality when treated with H2Pro Trismart (left) and an alternative wetting agent (right). Photo taken on 6th November 2017 in plots irrigated to 100% Evapotranspiration replacement using supplementary irrigation.

The trial also measured the effect that wetting agents have under restricted irrigation management. Half of the trial site was managed so that irrigation only replaced up to 60% of the calculated evapotranspiration rate. The turf was also protected from heavy rainfall events using covers. 
The results showed that H2Pro Trismart had a significant beneficial effect when irrigation availability was restricted. At this site, H2Pro Trismart allowed a 40% reduction in irrigation inputs without detrimental effects on turf colour or quality. This has important implications for turfgrass management, especially given the extended dry conditions that are currently being experienced in many parts of Australia. Where irrigation availability is restricted, the regular use of a high quality wetting agent can help to optimise turf quality by minimising the effects of moisture stress on the playing surface.

Main findings
• H2Pro Trismart significantly increased turf colour and quality, increased soil moisture availability and reduced dry patch versus a comparison wetting agent and versus untreated fine turf.
• H2Pro Trismart protected turf that was managed under a restricted irrigation regime (60%ET replacement). 
• H2Pro Trismart showed excellent safety and produced no burning or phytotoxicity effects. 
• By improving moisture infiltration and storage in sand profiles, high quality wetting agents help to provide an optimal environment for root growth. The result is more resilient turf that is less susceptible to environmental stresses and maintains a better quality playing surface.