WINTER HYDRATION OF GREENS WITH OARS PS

For all our customers who are expecting snow or freezing temperatures; scientific research has shown that applying OARS PS just before the snow hits, allows for an improved spring greenup and improves infiltration deeper in the root zone.

Read on to find the ins and outs of this research.

Objectives

•  Do winter applications of OARS PS influence water repellency and retention of greens in spring?
•  What effects do winter applications of OARS PS have on spring quality and color of turf?
•  Is the playing surface firmness changed with these applications?

Materials and Methods

The study was conducted form November 2015 until April 2016 on a ‘T‐1’ creeping bentgrass (Agrostis stolonifera L.) putting green mowed at 3,5 mm at The Ridge Golf Course in Salt Lake City, Utah. The rootzone was sand with 0.6% organic matter, a pH of 8.4, CEC of 7.4 and low salinity (0.2 dS/m). OARS PS was applied at 25,4 L / Ha. before expected snow cover (pre‐snow timing), or before snow cover and again after snow melt (post‐snow timing). The pre‐snow application was made on November 22, 2015 and the post‐ snow application was made on February 18, 2016. An untreated control was used for comparison. Applications were made to three replicate 2,25 m2 completely randomized blocks with a backpack sprayer operating at 2,75 bar through a boom with four TeeJet AI11002VS nozzles calibrated to deliver 87 GPA of water. Pre‐snow applications were watered in with overhead irrigation after application, and post‐snow applications were watered in with rainfall.

A fungicide was applied to the green in late November 2015 to protect against snow mold diseases. Little other management was done to the trial given the time of year, except for mowing that resumed in March 2016 when turf began actively growing.

Water repellency, or hydrophobicity, effects were measured by water droplet penetration tests (WDPT) performed on soil cores pulled from the putting green. Cores were collected at initiation in November and again the following spring in April. Five soil cores in each plot were removed using a 2 cm diameter soil probe (Figure 1). Cores were air‐dried and a 35 μl droplet of distilled water was dispensed on the core using a pipette at 1 cm intervals, starting at the surface 0 cm and ending at 6 cm. The length of time it took for the water droplet to completely penetrate the soil at each interval was recorded with a stopwatch. Droplets that did not penetrate the soil after 10 minutes (600 seconds) were recorded as 600 seconds. Water penetration times for each core at each depth were averaged for the mean. The water penetration means were separated into four repellency classes of wettable, or non‐water repellent (<5 seconds); slightly (5–60 seconds); strongly (60–600 seconds); and severely (>600 seconds) water repellent.

Moisture retention effects from the treatments were determined by measuring the volumetric water content (VWC) of the soil using a dielectric permittivity probe (POGO; Stevens Water Monitoring, Portland, OR) before snow cover and after snow melt. Eight measurements were taken within each plot averaged for the water content mean. Surface firmness was measured the same days with a TruFirm impact hammer (Spectrum Technologies, Plainfield, IL) that measures the penetration force of a golf‐ball shaped weight dropped from a consistent height. This force is correlated to a firmness value of 0 to 1, with higher values equaling a softer putting surface. Three measurements were taken in each plot and averaged for the firmness mean. Turfgrass quality and color were also visually assessed on a 1‐9 scale, with 9 having the best quality and darkest green color. Turfgrass color was also measured with a chlorophyll meter (CM‐1000, Spectrum Technologies, Plainfield, IL) that estimated the chlorophyll content in the leaves by measuring reflected wavelengths of light. This reflectance was captured in the meter as a chlorophyll index value of 0 to 999, with higher numbers equaling darker green plots. Three measurements were taken in each plot and averaged for the chlorophyll mean. All data was analyzed for differences using ARM with means compared using Fishers’ LSD and a 90% confidence interval. Data that was not homogeneous or skewed were subjected to appropriate transformations to normalize the data.

Water Repellency Results

The treatments had significant effects on rootzone water repellency in spring (Table 1). Specific effects include:

•  Water penetration times were similar between treatments at all depths going into winter, with strong water repellency in the top 2.5 inches of the rootzone (Table 1).
•  An application of OARS PS before snow cover significantly improved wettability of the playing surface during winter, but making another application after snow melted resulted in greater reductions in water repellency deeper in the rootzone.
• The rootzone of untreated turf became more hydrophobic during winter. A single application of OARS PS before snow cover improved wettability at the surface by 40%, but did not greatly influence wettability at lower depths between 1 to 3 cm. Interestingly, wettability was improved at 4 cm in the rootzone from the single application.
• Making two applications of OARS PS in winter, one before snow cover and another after snow melted, improved surface wettability of the putting green by 85%. Wettability was also significantly better deeper in the profile at some depths compared to making a single application.
• Future work should look at higher rates of OARS PS, plus combinations of other surfactant chemistries applied with OARS PS, to further improve rootzone hydration during winter as soil hydrophobicity was still slightly repellent despite the improvements measured in this study.

Moisture Content Results

The treatments did not have significant effects on rootzone water retention in spring (Table 2). Specific effects include:

• Rootzone water content was not influenced by OARS PS immediately after snow melted, or in spring when temperatures increased and wind blew imposing drought and desiccation stress. However, water content was numerically higher in April in turf receiving both applications of OARS PS, indicating the need for further study.
  • While environmental conditions caused the rootzone to dry down in March and April, access to irrigation water was limited. Localized dry spot (LDS) symptoms developed in April comprising 50% of untreated turf. OARS PS treated turf had some LDS symptoms, but were significantly less than untreated turf. A single application of OARS PS in winter reduced LDS by 38%, while making two applications reduced 78% of the symptoms (Figure 2).

Surface Firmness Results

The treatments did not have significant effects on putting green firmness in spring (Table 2). Specific effects include:

• Applications of OARS PS in winter did not cause a softer or firmer playing surface compared to untreated turf.

Turf Quality and Greenup Results

The treatments had significant effects on turf quality and greenup in spring, but not for leaf chlorophyll content (Table 3). Specific effects include:

• Turf quality and greenup were improved in spring from applying OARS PS before snow cover. Making an additional application of OARS PS after snow melted, significantly improved turf quality and greenup over the single application. However, leaf chlorophyll levels were similar for treated and untreated turf in spring.

Discussion

Applications of OARS PS before snow cover improved wettability of the putting green surface in spring. Making another application of OARS PS after snow melted further improved putting green hydration deeper in the rootzone. Two applications of OARS PS in winter lessened soil hydrophobicity, allowing the playing surface to accept more water, and water to move down through the rootzone easier. The use of OARS PS on greens in winter did not greatly influence water retention of the putting green rootzone, but did reduce localized dry spot symptoms that developed in spring. Turf quality and greenup were improved in spring from winter applications of OARS PS, but the firmness of the putting surface was not greatly changed.