A Golf Digest poll was conducted in two segments – all golfers (350 respondents) and a combination of golfers and non-golfers (650). Over 1000 interviews were conducted over the phone and a telling statement reflected some differing opinions (Barton, 2008):
“Golf is an environmentally friendly / compatible sport”.
- 91% of golfers agreed
- 66% of non golfers agreed
Many believe golf courses use too much water, leach excessive amounts of fertilizer to the groundwater and surface water, and use synthetic chemicals such as pesticides (herbicides, insecticides, and fungicides) indiscriminately. Again, this is the perception and if anything, it’s probably become more pronounced today.
In this article we are going to discuss new technology that has been developed that can directly impact chemical inputs and the environmental footprint of golf courses. Our focus is on the water used on turf, more specifically, the oxygen in the water.
Water Use and Water Quality
Water is the largest input applied to a golf course and so it has a significant impact on all aspects of agronomy. The best quality water available for turf comes from the sky – void of most problematic chemicals and with a good oxygen level. Once rainwater is captured and stored or contacts the ground, it becomes contaminated with minerals, chemicals, organics, etc. and can begin to negatively impact soil health.
When superintendents are asked how their turf quality looks after a good soaking rain – most reply it’s the best they’ve seen in a long time. Why? Rainwater is generally slightly acidic in pH and has no bicarbonates or salts that inhibit soil microbiology. In fact, rainwater can effectively flush green complexes – washing away many soil chemistry problems such as high sodium content.
Rain has between 8-10 ppm of dissolved oxygen (DO) which is obtained as it passes through the atmosphere on its way to Earth. It’s the dissolved oxygen in the water that is the critical measurement of water quality as it impacts almost all the biological activities in the soil. And yet, few measure the DO in their water. Water chemistry is the focus, driven by the need to adjust ions and molecules to change soil conditions – maybe driving the overdosing chemical perceptions of golf?
Irrigation water sources used in golf courses include city/potable water, well water, reclaimed water, rivers, ponds, and lakes. Each of these sources has their own unique water chemistry and impact on soil health. For this discussion we’re going to focus on the dissolved oxygen levels of these irrigation sources – most of which are low and problematic compared to rain water.
US golf courses use approximately 2.1 billion gallons of irrigation water per day. Many courses have more than one source of water for irrigation, over 50% is sourced from ponds or lakes and another 46% from groundwater or wells. Municipal reclaim water from wastewater treatment plants accounts for only 12% of all irrigation water supply (Lyman, 2012) With most of the irrigation water coming from potentially low dissolved oxygen sources, it’s important to understand what low DO levels are and how they impact soil health.
Water dissolved oxygen level is expressed as parts per million (ppm) or milligrams per liter (mg/L). Ranges of DO and the impact on plant health are:
- Highly saturated > 15 ppm. Great for plant health. Hard to obtain with air. Normally use oxygen or ozone injection to achieve this level of DO. Can occur in upper portions of ponds with full algae blooms (photosynthesis).
- Good quality = 8 ppm. Oxygen can be released into the root zone and raise plant metabolic activity. Plants are generally healthy. Low disease pressure.
- Acceptable = 6 ppm. Oxygen will keep plants alive. Some pockets of concern if water fills soil air pore space. Can create favorable disease conditions.
- Hypoxic < 4 ppm. Severe oxygen deficiency that is very harmful to plant health and can be fatal to turf. Creates significant disease pressure.
- Anoxic <1 ppm. Oxygen-deficient and negatively impacts soil life. Should not be used for irrigation purposes.
Typical irrigation water dissolved oxygen @ 20 deg. C
Related: Superintendent Predict the Future of Your Irrigation Ponds with Bathymetric Mapping
| Irrigation Sources | DO level |
|---|---|
| Well water/groundwater | 0-2 ppm |
| Pond/lake (surface) | 4-10 ppm |
| Pond water (bottom) | 0-2 ppm |
| Reclaimed water | 1-6 ppm |
| Streams/rivers (moving) | 6-8 ppm |
| City/potable water | 5-8 ppm |
Surface water intakes are recommended on ponds that are stratified to reduce the potential for low DO water and sediment from the bottom to be sent to the turf. (Smart, 1999). During the daylight hours when algae are producing oxygen, irrigation water DO is elevated (along with algae levels). At night algae consume the oxygen they made during the day – resulting in lower DO irrigation water still being sourced from a floating intake system. This is especially acute if a course is irrigated just before daybreak when dissolved oxygen is at its lowest.
How does low DO water impact turf?
Turf respiration enables plant roots to absorb soil oxygen, water and nutrients and transport them to plant tissue. Soil is made up of roughly 50% solid material/minerals and the rest water and air or pore space. Plant roots absorb oxygen from the pore space and oxygen dissolved in soil moisture, using it like animals do in breathing.
The soil environment is impacted when soil pore (air) spaces are filled with water. When the water contains high levels of dissolved oxygen, it is more suitable to support soil health and plant growth. If water oxygen is low, oxygen can be displaced from the root zone, the pore spaces become saturated and plant health starts a serious decline. Studies have shown that when irrigation water is low in DO, soil oxygen will pass into the water and DO can actually be lost to the soil profile and drained away – making the problem even worse.
Anaerobic soil generally has a black color and can emit a hydrogen sulfide / rotten egg odor. As free oxygen is lost, sulfates in the soil are reduced to sulfides and can form what is commonly referred to as “black layer”. This anaerobic zone in the soil causes a loss of root mass, poor nutrient uptake, and declining turf health. Turf thinning, especially in the summer, can be a direct result of black layer. High plant respiration rates during periods of higher temperatures and humidity cause an oxygen demand in the soil that can’t be achieved with low DO water.
Once the root zone oxygen level is depleted, and turf health declines, it only rebounds when the soil dries out and the pore spaces are reopened or when higher dissolved oxygen water is provided (rainfall). This cycle continues on many irrigated golf courses and has a significant impact on the increased use of fertilizers and pesticides to combat this anaerobic soil condition.
Many irrigation ponds contain blue green algae or cyanobacteria. This is especially a problem in the summer months when nutrients in the bottom muck are released into the water column, feeding the algae. When this water is used for irrigation, cyanobacteria are spread on the turf and cause yellow spot and other issues.
Thin turf can be crusted or matted with blue green algae which negatively impacts turf recovery. Additionally, blue green algae create an anaerobic environment and directly cause black layer as sulfides are reduced in the soil. Cyanobacteria release toxins into the soil that cause chlorosis. Efforts to reduce cyanobacteria should start with the source – reducing the blue green algae levels in the irrigation pond by introducing oxygen that migrates to the bottom and reduces phosphorus release. (Tredway, 2006)
How Low Water Dissolved Oxygen Levels Impact Chemical Use
Fertilizers
Nitrogen, Phosphorus, and Potassium are required by plants in order to ensure healthy and sustainable growth. Soil bacteria are aerobic organisms. They need oxygen to survive and respire. Soil oxygen levels determine and impact bacteria population levels. Both bacteria and fungi microbes utilize soil nitrogen to decompose carbon in the soil. Protozoa and nematodes consume these microbes – releasing nitrogen to the plant in the form of ammonia.
Under oxygen rich environments, Nitrosomonas and Nitrobacter bacteria convert ammonia into free nitrates in the soil. Free nitrate is then utilized by the plant. This has to be done in an aerobic environment and is the primary pathway for nitrogen assimilation into plants.
If the soil is oxygen deficient, denitrification occurs. Soil microbes use nitrate and nitrite as the terminal electron acceptors for respiration (instead of oxygen) and even sulfate when no more nitrate is available (black layer) . Again, when turf is watered with low DO water, soil pores become filled, and the soil profile can become oxygen limiting (Horgan, 2003). As soil temperatures rise, nitrogen losses increase as the turf’s elevated respiration triggers more denitrification and a decreased efficiency in fertilizer use. The result of this biochemical reaction is evolution of the nitrogen as N2 gas – resulting in loss of N from the soil to the atmosphere.
Phosphorus is used in a plant for collecting the sun’s energy and completing photosynthesis by converting it into plant energy that is used for cell development and reproduction. It is an essential element for plant growth and is a component of RNA and DNA.
Approximately 30-60% of phosphorus in the soil is in an organic form which is not plant available. Organic phosphorus includes dead plant and animal residue, soil microorganisms, and stored P in algae and other decaying material. Aerobic soil organisms are used to process organic forms of P into inorganic forms which can be used by the turf – a process called mineralization.
The form of phosphorus most readily accessed by plants are orthophosphate ions that are assimilated into the plant via diffusion. This requires a higher level of P in the soil than in the roots to drive the P into the plant. By ensuring a healthy microbial community in the soil to assist in efficient orthophosphate conversion, less supplemental P is required to be added to turf.
Golf courses must manage inorganic phosphorus fertilizers closely. Insoluble phosphorus that is not taken up by the plant is typically washed down the soil profile and drainage system or into the water table, stormwater pond, wetlands, or adjacent stream. In that case – this nutrient runoff can be a major cause of algae blooms and deteriorating surface water quality, sometimes negatively impacting a golf course’s own irrigation pond.
Another reason for turf managers to ensure good water quality and adequate dissolved oxygen is to avoid the high cost of supplemental fertilizers. Since the beginning of 2020 the cost of nitrogen fertilizers has increased nearly 4 fold with P & K up nearly 3 fold. Improving soil health is an economic necessity in today’s golf economy.
Pesticides
Pesticides, insecticides, and fungicides are commonly used on golf courses to deal with unwanted pests. Chemical manufacturers have modified and reformulated these products over time to improve safety and impact on the environment. Early products contained high levels of arsenic, cadmium, lead, and other heavy metals. These are now gone and replaced with synthetic chemicals such as organophosphates that raise new concerns in regard to bioaccumulation and human health.
Excellent training and application techniques have helped courses successfully use these products with few major incidents. However, mortality studies have shown an elevated incident rate of brain, Non Hodgkins lymphoma, prostate and large intestine cancers in golf course superintendents who are exposed to these chemicals (Kross, 1997).
Not only do pesticides kill unwanted pests, but they also negatively affect beneficial soil microorganisms, and in doing so, halt or decrease the amazing work these microbes do within soils. For example, nitrogen-fixing and phosphorus mineralizing microorganisms have been observed to become inactive in soils contaminated with pesticides.
Finding ways to reduce pesticides should be an important initiative in golf. Courses, such as the Vineyard Golf Club, Martha’s Vineyard, MA and Rivermont Golf Club, Atlanta, GA have leveraged reducing chemical inputs into a more organic approach to turf management. This requires a significant change in the perspective of golfers to accept a more natural look on the course vs. the “Augusta Look” of deep green and white sand bunkers over the entire property.
Fungi is an essential soil component that sequesters carbon and breaks down complex organic matter such as cellulose and lignin (thatch control). But some species of fungi are pathogenic and can cause plant disease in turf. Two options to treat pathogenic disease are to apply fungicides to kill the fungi or promote healthier soil so that healthier fungi can outcompete pathogenic species.
Healthy turf can fight pathogens fairly well by protecting the plant roots. But once the plant becomes stressed, it’s much more difficult to resist pests and disease. Fungal spores can be dormant for many years in soil and be activated by a number of factors:
- Too much moisture.
- Pesticides that kill off beneficial bacteria and fungi
- Lack of oxygen in the soil
Increasing the dissolved oxygen in the irrigation water and in the soil can reduce the potential for pathogenic fungi to grow and can also stimulate the beneficial microbe community to increase dominance in the soil. Focusing on this approach vs. applying fungicides can stop the cycle of “treating the symptom instead of the cause”.
Improving soil oxygen with water
Existing cultural methods in golf to increase soil oxygen have focused on modifying the soil surface to introduce more air and re establish a larger pore space – literally punching holes in the soil. Various mechanical tools are used – Air2G2, DryJect, Hydroject, core aerification, drill and fill, etc.
The common practice of mechanical aerification impacts only about 10 percent of the soil volume in exposing it to atmospheric air after these treatments. This process requires a significant investment in time and money to complete and leaves putting surfaces in poor condition while they heal – resulting in loss of revenue for greens fees courses and unhappy golfers.
When discounting hydrophobic regions, water will deliver oxygen to 100 percent of the turf’s soil volume. This is one of the main benefits of using water’s natural ability to transport dissolved oxygen. Plus, by filling both the water space and the pore space with highly oxygenated water, the soil microbial community benefits greatly.
Golf superintendents haven’t focused on enhancing the oxygen content of water because the technology to maintain O2 in water (especially warmer water) for extended periods, was unavailable. Efforts to increase irrigation DO by increasing pond aeration have failed because the bubbles float.
Floating bubbles, or buoyancy, is a natural consequence of conventional aeration. When air is mixed into a water source through a fountain, aerator, mixer, etc. the resulting air bubbles formed are at least 1 micron in size and they float. The bubbles rise up into the pond until they reach the surface, then break open and release their cargo of oxygen back into the atmosphere. Thus, DO increase with these methods is limited.
Research into making bubbles that don’t float was started in Japan and South Korea a number of years ago. In early experiments these ultra fine bubbles, called nanobubbles, were formed with pressurized dissolution, electrolysis, or by mixing liquids in a chamber and then feeding them through a shear point.
Many advances in these technologies have resulted in a recent adoption of nanobubble water in hydroponics and other agriculture to improve plant oxygen. Nanobubbles are also gaining widespread interest in improving fish farms and for algae control in ponds and lakes. The golf industry is just beginning to implement nanobubble technology to improve irrigation water quality.
The latest nanobubble oxygen technology utilizes cavitation to shear the oxygen bubble into a particle size of less than 200 nm (essentially smaller than a virus and just larger than DNA). The process works by utilizing a sophisticated pattern of cavitation chambers and shear planes to initiate a controlled endothermic reaction which produces a high concentration of oxygen nanobubbles (over 240 million / gallon) with a mean particle size between 50 -100 nm. A series of partial plates is housed in a pipe that is installed inline. The plates are oriented in a way that forces flowing water to expand and contract under shear stress many times while flowing through the pipe.
The expansion and contraction in the nanobubble processor creates cavitation, which is the formation of gas bubbles within a liquid due to rapid pressure changes. The processor is designed in a way that the voids are small enough to form nanobubbles, and shift the zeta potential of the particles in the water toward zero or negative.
Because cavitation operates at low pressure, oxygen nanobubbles tend to stay in solution much longer than conventional aeration. This allows oxygen to be deposited on the bottom of lakes and ponds where it can transform the bottom muck into an aerobic environment and consume nutrients – curtailing algae production. Irrigation water can hold oxygen longer and transport it to the root zone and to the plant roots at levels of 18-30 ppm of DO – nearly 2-3 times higher than rainwater.
Another key feature of nanobubble oxygen is the large surface area (because of the tiny bubble size) and the highly negative charge each bubble has.
This negative charge is responsible for improving cation retention in the soil (increasing CEC for calcium for instance) and for reducing the surface tension on the soil surface.
Because of the protective action of soil microbes to generate a polysaccharide “slime” layer around them and increase surface tension and contact angle, hydrophobic areas can develop in stressed soil. Those areas are not wettable and can become oxygen deficient. If water is not able to adequately penetrate the depths of a 2-inch to 8- inch root zone, soil gases are trapped as well and oxygen deficiencies emerge.
Wetting agents / surfactants can be used in treating hydrophobic areas and returning moisture to sections of the green that are dry. They also transport oxygen dissolved in water to the turf root zone (Roberts, 2002). But they are expensive and subject to overuse. Instead, by utilizing nanobubble oxygen water, the highly negative charge of the oxygen bubbles and extremely high surface area virtually eliminate the need for these expensive wetting agents – resulting in a much more sustainable and consistent infiltration rate.
Injecting ozone ahead of the cavitation unit creates ozone nanobubbles that can oxidize biofilm and organic material throughout the irrigation system. Cleaner pipes and sprinkler heads help maintain a higher DO level as well as decreasing the spread of disease in the turfgrass and reducing maintenance requirements of irrigation systems. Ozone is also effective in killing spores and molds in irrigation water, further reducing pathogens (Warwick, Avondale Golf Club, Sydney).
Continuing research
Research in Australia has been conducted on both Couch grass (warm season) and Rye grass (cool season). This work, by P. McMaugh, has shown that cool season grasses treated with high DO nanobubble water are able to better handle the stress of infrequent watering in hot conditions. Also, root loss was markedly less in turf treated with high DO water – in fact, cool season grass root mass increased in hot conditions, even when the turf was under stress.
Related: Australian Golf Courses Recognized in Global List
Water infiltration testing in Australia, where there are now three golf courses using nanobubble oxygen water full time to improve irrigation water quality, has shown a dramatic increase without using wetting agents. These same golf courses have documented 50+% reductions in fungicide and fertilizer while using nanobubble oxygen and ozone in their irrigation water.
Warm season grasses also benefit from nanobubble oxygen water with significantly less stress and better root mass with higher DO water. Manly Golf Club, Sydney, has confirmed better root mass development and reduced fungicide and fertilizer use with nanobubble oxygen irrigation water. Avondale Golf Club, Sydney, has significantly increased water quality and plant disease in bent grass by incorporating both nanobubble oxygen and ozone in their treatment system.
The University of Arkansas (Richardson, De Boer) has documented increased turf DGCI (Dark Green Color Index) levels on bent grass using nanobubble oxygen water. This research was conducted using membrane generated nanobubble oxygen water. Higher nanobubble generation rates of cavitation technology would yield additional bent grass benefits in terms of root mass increase as previously shown by McMaugh’s work.
The University of Georgia is using cavitation to generate nanobubble oxygen water for testing on warm season turf growth rates, root mass development, color, nutrient uptake, water infiltration rate and pathology. An 18% reduction in dollar spot was observed. UGA is also studying the impact of displacing salts in the soil profile caused by improved infiltration. M. Hoban (Rivermont GC) has reported improved color response in field plots irrigated with nanobubble oxygen water and tested by UGA.
REFERENCES
- Barton, John. (March 2008). “Golf and the Environment”. Golf Digest.
- Berndt, Lee, Joe Vargas Jr., and Brad Melvin, (March 1989). “Sulfur, Organic Matter And the Black Layer.” Golf Course Management, p 48.
- Horgan, Brian. (March 2003) “Denitrification Impedes Fertilizer Effectiveness.” Turfgrass Trends, p 52-57.
- Kross, BC, (May 1996) “Proportionate Mortality Study of Golf Course Superintendents”. American Journal of Medicine. P 501
- Lyman, Gregory T. (November 2012). “Golf’s Use of Water: Challenges and Opportunities. USGA Summit on Golf Course Water Use”
- Morgan, Lynette PhD. (May/June 2000). “Are Your
- Plants Suffocating? The importance of Oxygen in Hydroponics.” Practical Hydroponics & Greenhouses, p 52.
- Roberts, Eliot C. PhD. (April 1990) “Soil / Air / Water Plant Relationships.” Landscape & Irrigation, pp 72-76.
- Simojoki, Asko. (2001) “Oxygen Supply to Plant Roots in Cultivated Mineral Soils.” Department of Applied Chemistry and Microbiology, University of Helsinki.
- Smart, Bud. PhD. (Jan/Feb 1999) “Maintain the Best Irrigation Water Quality on the Golf Course.” USGA Green Section Record, p1
- Tredwell, Lane, PhD,Stowell, Larry PhD, Gelenter, Wendy PhD , (November 2006) “Yellow Spot and the Potential Role of Cyanobacteria as Turfgrass Pathogens”. GCM p83
Ron Pote is owner of Byo-Gon, Inc. and NanoOxygen Systems an environmental company based in Charleston, SC. His passion for golf is a big part of his efforts to improve the environmental footprint of the game.
