An aerial view of the experimental field. Small plots with white outlines indicate the areas treated with or without soil surfactant. Photos courtesy of Emily Merewitz
Editor’s note: This research was funded in part by GCSAA through the Environmental Institute for Golf.
As putting green species, creeping bentgrass (Agrostis stolonifera) and annual bluegrass (Poa annua) often endure water and traffic stresses on golf courses. Water stress includes conditions that may result in a water deficit to the plant or a water surplus.
Far more research has been done on water stress and/or the potential benefits of surfactant use for creeping bentgrass than for annual bluegrass. Growth habits and rooting characteristics — which can affect water uptake and usage and thereby affect irrigation rates, frequencies and timings — in annual bluegrass are different from creeping bentgrass (1, 3). Additionally, research that combines water stress with traffic stress will more accurately reflect real golf course conditions compared with a singular experimental stress.
Most information available regarding use of surfactants on annual bluegrass also incorporates plant growth regulators or other chemical treatments with a goal of removing annual bluegrass, as it is often viewed as a turfgrass weed species. For superintendents who actively culture annual bluegrass putting greens, a better understanding of the effects of surfactants on physiological responses and turfgrass performance under specific irrigation regimes is needed.
The role of soil surfactants
Soil surfactants and wetting agents are primarily used in turfgrass management to manage localized dry spot, which is often caused by hydrophobicity, or water repellency, which is the result of organic coatings on sand or soil particles.
Root zones of golf course greens commonly have a high sand content because the greens have been treated with sand topdressing or because they were originally constructed of sand. Organic coatings on sand or soil particles can lead to several problems, including lack of available water to plant roots, uneven water flow through the soil, and increased susceptibility to abiotic and biotic stresses such as wear stress (4).
In addition to alleviating localized dry spot, surfactants can also improve various other issues in water relations in sand and soils. In many cases, soil water content may not be adequate or may exceed turfgrass requirements. For instance, water deficiencies or excess may occur because of the amount of precipitation, breaks in irrigation equipment, poor placement or coverage of irrigation heads, and many other reasons. Even in the absence of hydrophobic sands or soils, research is needed on how surfactants can be used in turfgrass management to optimize soil water content, particularly for high-value putting green species such as creeping bentgrass and annual bluegrass.
Wear or traffic stress
Wear or traffic stress, which occurs primarily on tee boxes and putting greens, is a significant problem on most golf courses and is caused by scuffing, tearing or crushing of the turfgrass plants by feet, vehicles or other mechanical objects. Over time, this damage, under either optimal conditions or periods of environmental stress, can compromise turfgrass health and degrade playing surfaces. It can also compact soils, leading to impaired root growth and damage (1).
The amount of traffic can vary widely among golf courses and within a single putting green, calling for research involving different levels of traffic stress. Simulating real turfgrass field conditions by including traffic stress as a factor has yet to be performed in research studies of water use or surfactants. The objective of this study was to determine whether a surfactant treatment would promote tolerance to overwatering, insufficient irrigation, and traffic stress for individual stands of annual bluegrass and creeping bentgrass on a sand-based green.
Materials and methods
Turfgrass plot maintenance
In 2013, research plots received total nitrogen (N) of 130.25 pounds/acre (146 kilograms/hectare), total phosphorus (P) of 14.27 pounds/acre (16.0 kilograms/hectare), and total potassium (K) of 52.28 pounds/acre (58.6 kilograms/hectare). Plots were fertilized with 21.76 pounds N/acre (24.4 kilograms/hectare) on May 5, Aug. 2 and Oct. 1, using an 18-9-18 (N-P-K) granular fertilizer (Andersons Golf Products). Nitrogen was applied as a foliar spray weekly from June 14 to Sept. 26, using a 28-0-0 (N-P-K) liquid fertilizer at a rate of 4.37 pounds N/acre (4.9 kilograms/hectare).
During 2014, total nitrogen applied was 117.76 pounds/acre (132 kilograms/hectare), and total potassium applied was 44.4 pounds/acre (49.8 kilograms/hectare). Plots were fertilized with 21.76 pounds N/acre on May 5, June 10 and Sept. 26, using a 19-0-15 (N-P-K) granular fertilizer (Andersons Golf Products). Nitrogen was applied as a foliar spray weekly between June 9 and Aug. 29, using a 28-0-0 (N-P-K) liquid fertilizer at a rate of 4.37 pounds N/acre. Granular treatments were applied and irrigated with 0.15 inch (3.8 mm) of water to avoid fertilizer burn. Fungicides were applied preventively and curatively to avoid turfgrass loss.
The surfactant (Revolution, Aquatrols) was applied as a foliar spray to Penn A-4 creeping bentgrass and annual bluegrass field plots at the recommended label rate of 2 gallons/acre (18.5 liters/hectare). The soil surfactant was applied monthly from May through October in 2013 and 2014. The spray application volume was 10.35 gallons/acre (96.9 liters/hectare) applied with a CO2 backpack sprayer. After application of the soil surfactant, 0.03 inch (0.76 cm) of water was used to incorporate the surfactant into the soil. The surfactant treatments were small plots within larger blocks of watering treatments.
Surfactant-treated plots (white outline) were located within larger drought-stressed plots (6% soil moisture) of annual bluegrass (Poa annua).
The treatments included three watering treatment regimes based on soil volumetric water contents (SWC) (8%, 12% and 16% SWC). The entire field plot included an automated irrigation system that tracked SWC, temperature and soil salinity every 20 minutes (Integrated Sensor System, Rain Bird). The irrigation system tracked those parameters with soil sensors (TSM-1, Rain Bird) that were installed horizontally in each plot at a depth of 3 inches (7.62 cm).
Low-traffic (5,688 rounds of golf), moderate-traffic (11,376 rounds of golf) and no-traffic (control) treatments were applied in summer 2013 and 2014. Traffic treatments were implemented using a golf traffic simulator (110 pounds; 49.9 kilograms) modified with extra weight (150 pounds; 68 kilograms). It consisted of a 21-inch (0.53-meter) long roller, covering 2.86 square feet (0.266 square meter) with each revolution. Golf cleats (Black Widow Softspikes) were attached to the roller, which was manually pushed across plots to simulate traffic.
The three traffic treatments were applied to each 7-foot-by-8-foot (2.2-meter-by-2.4-meter) plot three times weekly, simulating 237 rounds of golf at the low traffic rate and 474 rounds of golf at the moderate traffic rate each week, from June 1 to Sept. 15 of each year. The rounds of golf were based on a golf shoe containing an average of 12 spikes per shoe, with the average golfer taking about 26 full steps (52 paces) per putting green.
Time-domain reflectometry (TDR) was used to measure SWC at two depths of 1.5 and 4.8 inches (3.8 cm and 12.2 cm) (FieldScout TDR 300; Spectrum Technologies). These depths were chosen based on probe size availability and rooting characteristics of both species. Visual turf quality ratings were taken on a scale of 1 to 9, where 1 is poor, 9 is best and 6 is acceptable (2). Canopy reflectance was determined by measuring NDVI (normalized difference vegetation index) with the use of a turfgrass color meter (FieldScout TCM 500, Spectrum Technologies). This instrument calculated an index value range from 0.000 to 1.000, with values closer to 1.000 indicating greater green color. All measurements were recorded weekly after turfgrass mowing on non-cloudy days between May 13 and Sept. 23 in 2013, and May 28 and Sept. 16 in 2014.
Results and discussion
Application of the surfactant decreased SWC in the 12% and 16% SWC target turf when compared with SWC in the control turf (Figure 1). Excessive soil water can cause a lack of oxygen to roots, which can lead to poor nutrient uptake; stomatal closure, which reduces carbon fixation; and the accumulation of certain metabolic intermediates, which can be toxic to plant cells.
Conversely, application of the soil surfactant increased SWC at the 8% SWC target when compared with turf areas at the 8% SWC target that were not treated with surfactant (Figure 1). Drought stress is an important factor even in irrigated turf. As golf course putting greens are often maintained on the dry side for playability, drought stress conditions can cause susceptibility to secondary stresses such as traffic and increased susceptibility to pathogens. Thus, surfactants may improve water availability to grasses when turf is receiving too little or too much water.
Creeping bentgrass and annual bluegrass responded similarly to the water and traffic stress treatments, with overall reductions in turf quality and NDVI. In creeping bentgrass, plots with 16% SWC had lower turf quality in 2013 compared with turf quality in the 8% and 12% SWC treatments (Figure 2). Application of the soil surfactant resulted in higher turf quality compared with the untreated control in plots at 16% SWC in 2013.
In 2014, creeping bentgrass at 8% SWC had lower turf quality than the turf in the plots at 12% and 16% SWC. However, adding a soil surfactant increased turf quality in plots at 8% SWC compared with the turf that was not treated with a surfactant. As an example, the untreated control turf had a quality rating of 4.6, and turf treated with a surfactant had a quality rating of 6.8 at 8% SWC (Aug. 19, 2014, in creeping bentgrass).
In both 2013 and 2014, a soil surfactant improved the turf quality of annual bluegrass at 8%, 12% and 16% SWC when compared with the control. In creeping bentgrass, soil surfactant treatments affected NDVI measurements in both 2013 and 2014. Turf treated with soil surfactant had overall greater NDVI values in 2013 and 2014 when compared with the control turf at 8%, 12% and 16% SWC (Figure 3). This shows that, with the addition of a soil surfactant, less irrigation water was required to maintain annual bluegrass NDVI when compared with plots that received more water. Traffic treatments did not affect NDVI values within creeping bentgrass in 2013 or 2014.
Compared with the untreated control, the surfactant treatment improved turf quality and NDVI in late summer of both years. The surfactant increased annual bluegrass and creeping bentgrass turf quality during water deficit, excessive water, and/or foot traffic conditions. The surfactant treatment decreased moisture retention when plots were overwatered and increased moisture when plots were underwatered.
Automated irrigation can be set to below-optimal levels to conserve water without sacrificing turf quality when turfgrass has been treated with a soil surfactant and if traffic is present. Trafficked or non-trafficked areas with drainage issues or areas prone to high soil moisture may benefit from surfactant applications.
The authors would like to thank the National Institute for Agriculture, Michigan State University AgBioResearch, Project GREEEN, and GCSAA for financial support of this project through the Environmental Institute for Golf. We also thank Aquatrols Corp. for financial support and product donations. Thanks also to the Rain Bird Corp. for donation of automated irrigation equipment.
The research says ...
- This research attempted to determine how surfactants can be used to optimize soil water content, particularly for putting green species such as creeping bentgrass and annual bluegrass.
- The surfactant treatment improved turf quality and NDVI in late summer of both years of the study, and increased annual bluegrass and creeping bentgrass turf quality during water deficit, excessive water, and/or foot traffic conditions.
- The surfactant treatment decreased moisture retention when plots were overwatered and increased moisture when plots were underwatered.
- Beard, J.B. 1973. Turfgrass: Science and culture. Prentice Hall, Englewood Cliffs, N.J.
- Krans, J.V., and K. Morris. 2007. Determining a profile of protocols and standards used in the visual field assessment of turfgrasses: A survey of National Turfgrass Evaluation Program-sponsored university scientists. Applied Turfgrass Science 4:1. doi:10.1094/ATS-2007-1130-01-TT
- Lyons, E.M., P.J. Landschoot and D.R. Huff. 2011. Root distribution and tiller densities of creeping bentgrass cultivars and greens-type annual bluegrass cultivars in a putting green. HortScience 46:1411-1417.
- Wilkinson, J.F., and R.H. Miller. 1978. Investigation and treatment of localized dry spots on sand golf greens. Agronomy Journal 70:299-304.
Kevin Laskowski is a graduate student, Kevin W. Frank is an associate professor and Extension turf specialist, and Emily B. Merewitz is an assistant professor in the Department of Plant, Soil and Microbial Sciences at Michigan State University, East Lansing, Mich.