Key Takeaways

• Salinity problems are typically driven by a combination of elevated salinity in the irrigation water and poor drainage, more so than “bad water” alone.
• High salinity in putting greens is very often a surface problem. The vast majority of cases show the highest salinity in the top half inch of the soil profile, driven by higher organic matter content and poor surface drainage that causes salts to accumulate there.
• Leaching is a critical salinity management tool, but it only works if done correctly. True leaching requires 3-5 inches of water, not just a deep watering. 
• Stop chasing chemical fixes – salinity management in putting greens is a physical water management issue. Real solutions rely on improving surface drainage, improving infiltration, and matching the turf species to the salinity of the irrigation water. 
• Sodium does not cause structural issues in sand-based putting greens when clay levels are very low. However, sodium and other specific ions can cause toxicity to turf leaves, roots and stems at elevated levels.
   

Potential damage from salinity and direct ion toxicity varies widely between turf species and even among cultivars within the same species. Some of the differences may surprise you. For example, creeping bentgrass is more salt tolerant than it is often given credit for. With high-salinity irrigation water, bentgrass will perform better than other cool-season grasses such as perennial ryegrass, Poa trivialis and Poa annua. Bermudagrasses, including ultradwarf varieties, are very salt tolerant. In fact, in over 20 years of working with golf courses throughout the West, I have not seen high enough salinity in a putting green rootzone to significantly harm bermudagrass. However, there are instances where salinity is high enough to act as a growth regulator. Zoysiagrass offers similar salinity tolerance to bermudagrass. Seashore paspalum is the most salt-tolerant grass used on putting greens and in my observation can perform well with irrigation water EC equal to 10.0 dS/m and perhaps higher. As a sidenote – in my experience it is very rare to see irrigation water exceed 7.0 dS/m in the continental U.S. Higher-salinity irrigation water is more common in Hawaii.

Salinity Thresholds

I would like to offer guidance on salinity thresholds that I believe are a good indicator for when to initiate leaching with various turf species. Leaching can be defined as applying enough water to push existing soil water out of the rootzone to reduce overall salinity. I recommend using a portable EC meter such as the FieldScout EC Soil Meter to measure bulk soil salinity at specific depths in the profile and monitor when leaching is necessary. I start by inserting the tip of the meter into the rootzone to measure salinity in the top half inch of the soil and then I like to take readings in approximately half-inch increments down through the profile. Another option is to use a soil moisture meter capable of measuring salinity, such as the USGA Moisture Meter. But it is important to recognize that moisture meters typically measure salinity in an elliptical zone around the length of the metal probes and therefore can’t measure salinity at shallow or specific depths like a portable EC meter.

Information about salinity at specific depths is very valuable because the readings usually vary significantly through the soil profile, and an average over several inches may not allow you to identify a problem near the surface. In well over 90% of cases, a portable EC meter will show higher salinity in the top inch of the soil profile than 2 or 3 inches down and salinity most often will decrease significantly beyond that depth. This pattern is commonly seen in sand-based putting greens where higher organic matter content in the upper portion of the rootzone will tend to hold more water and trap salts.

When using a portable EC meter to monitor salt content in the rootzone, take readings until you find the depth with the highest salinity, which will very likely be in the top half inch. If the soil is extremely dry, the meter will not provide an accurate result and irrigation water should be added to moisten but not saturate the soil. When the highest EC reading is at or above your threshold for leaching, it is time to take action. In my experience, the threshold values below are good indicators that salts are high enough to potentially cause problems. Salinity values approaching or exceeding these values may result in issues such as growth regulation, turf thinning and rapid blight disease. The values are expressed in milliSiemens per centimeter (mS/cm), which is the typical unit of salinity measurement on portable EC meters and is numerically equivalent to dS/m.

• Poa annua and Poa trivialis (> 1.5 mS/cm)
• Creeping bentgrass (2.5-3.0 mS/cm)
• Bermudagrass (10.0-12.0 mS/cm)
• Seashore paspalum (15.0-16.0 mS/cm)
• Perennial ryegrass (4.5-5.0 mS/cm)
  
  

These threshold values are conservative. I have seen numerous bentgrass greens in good health with EC values ranging from 4.0-5.0 mS/cm. In cooler climates, or in cooler months, turf will perform better at higher salinity and conversely will experience greater stress at similar salinity levels during hotter months. Young seedlings, sprigs or even sod will show stress at lower values.

Management Strategies

A successful salinity management program for putting greens requires understanding the characteristics of the irrigation water and the soil profile, and then determining how best to move water through the soil. If the turf has appropriate salinity tolerance for the water applied, managing salinity should focus on moving water through the profile. In general, most mature putting green rootzones drain in excess of 1.5-2 inches per hour. Observations reveal that this is enough to move salts past the rooting depth with a proper leaching program. That is why, in most cases, salinity can be successfully managed in putting greens. However, even with water containing only moderate salinity, salts can accumulate to harmful levels in localized areas. For example, the highest salt readings are commonly found along the perimeters of putting greens, especially near the front of the green where water tends to gather. Even with proper subsurface drainage, if surface drainage is poor, water will accumulate and evaporate, leaving salts behind.

Managing surface issues that contribute to salt accumulation

Salt content of the irrigation water is often the first concern that comes to people’s mind when thinking about salinity in putting greens, but basic drainage issues often play a key role by trapping excess water that evaporates and results in increased salinity. Collar dams that trap water and salts in low areas along the green perimeter are a common issue. As are V-shaped troughs along the edge of the green where the putting surface doesn’t tie in properly to the surrounds. Such areas are sure to hold water and accumulate salts. While a combination of deep and shallow aeration, spiking, and even drill-and-fill will help, they won’t fix problems with surface drainage. Ultimately, the solution is regrading to create positive surface flow off the green. Here are a few tips for successfully regrading around putting green perimeters:

• For warm-season courses, especially those with bermudagrass, annual or biannual scarification or fraise mowing will help. These tactics may not remedy a steep collar dam, but they are great ways to prevent collar dams from forming and to lower slightly raised turf around greens. 
• Regrading and regrassing will improve surface drainage, but a project of this scale may require a significant amount of disruption in the area around the green. In some instances, it is necessary to disrupt an area that extends 15-20 feet outside of the green perimeter to produce positive surface flow and a smooth tie-in with surrounding areas. 
• For minimally raised turf around the edge of a green, aeration and rolling may be all that is needed. Aggressive core aeration, followed by irrigation and rolling with a greens roller or preferably a 1-ton roller has been shown to work surprisingly well for lowering minimally raised collars.
  
  

The highest salinity values I have observed in putting green soils are in the top 1 mm of the soil profile where turf density has thinned and an algae crust has formed. The algae crust is nearly impermeable and after irrigation water evaporates, salts accumulate on top of this crust. The salts are very often not the primary or even secondary cause of turf loss in these areas. The road to recovery starts with eliminating the algae which will then facilitate leaching. The algae crust can be mitigated by using a spiker, slicer, aerator or hand tools. Sand should be applied to smooth the surface and plugging, sodding or seeding performed as needed to expedite turf recovery. Many times, areas where algae crusts form are also too low and regrading is necessary to improve surface flow.

Implementing a leaching program

Leaching is an important management practice for courses that have salinity issues in their greens – especially in areas where rainfall is infrequent. The first step in successful leaching is accurately measuring soil salinity so you can use this data to determine when leaching is necessary. Years ago, a multicourse property I worked with would conduct leaching twice per month throughout the year. It turned out after evaluating the soil salinity data that this was unnecessary and they were not only wasting water, they were also leaching valuable nutrients from the profile. Once they began using a portable EC meter to guide leaching, they discovered that they only needed six to eight events per year. The moral of this story is to use the salinity thresholds provided above (or create your own based on how your turf performs at various salinity levels) as an initial guide to schedule leaching events. Over time, with routine data collection, you will very likely find that these thresholds are more conservative than necessary and you can conduct leaching on a less frequent interval.

Keep in mind that deep watering and leaching are two different things. A deep watering event that is meant to replenish water in the rootzone and bring the soil back to field capacity usually involves adding ½ to 1 ½ inches of water. A leaching event is meant to fill the rootzone with irrigation water and drive most of the resident water containing higher salinity down through the soil profile and into the subsurface drainage system, if there is one. Therefore, a leaching event typically requires 3-5 inches of irrigation water applied over one or two evenings to minimize runoff and maximize flushing.

If you are looking for a smart way to leach those salts away, consider using small microsprinklers and/or small impact rotors on roller bases to add water slowly and only to the green surface itself. Superintendents in Southern California have been using these techniques successfully for decades to leach salts from Poa annua greens. These small sprinklers work especially well where only full-circle sprinklers are available around putting greens. Full-circle sprinklers can be used for leaching greens, but the surrounds and greenside bunkers will get a heavy dose of water in the process, which will have a negative impact on playing conditions and maintenance operations the following day. Even part-circle sprinklers that are dedicated to the putting surfaces will unnecessarily add water to greenside bunkers and surrounds during leaching events, so investing the time to deploy smaller sprinklers is worthwhile. 

I recently led an experiment at a golf course in Arizona to evaluate the leaching efficacy of three different strategies. All greens in the study were aerated with 1/8-inch solid tines prior to the leaching treatments. Two greens received 45 minutes of runtime from the part-circle overhead sprinklers, two greens received 120 minutes of runtime from the part-circle overheads and one green was irrigated with small, portable sprinklers that ran nearly 13 hours overnight.

Salinity was measured using the FieldScout Soil EC Meter as well as the USGA Moisture Meter. Prior to leaching, FieldScout EC readings in the top half inch of the profile ranged from 1.0 to 5.0 mS/cm and the USGA Moisture Meter readings ranged from 1.5 to 2.0 mS/cm (remember that these tools measure salinity differently). Average salinity in the two greens that received 45 minutes of irrigation increased the following morning by 1.5 to 3.0 mS/cm. Salinity decreased in one green that received 120 minutes of irrigation and remained the same in the second green. The greatest salinity reduction was observed in the green where the microsprinklers were placed. Furthermore, there was little to no impact on green surrounds with the microsprinklers while there were bunker washouts and wet surrounds with the 120 minutes of irrigation treatment, although the impact on the surrounds was not unacceptable and would have likely gone mostly unnoticed by golfers. The 120-minute runtimes used about 16,000 gallons of water per green while the greens that received 45 minutes used 6,500 gallons of water per green and the green with the microsprinklers received about 8,000 gallons of water. The average moisture content in the rootzone was about 2% higher (35% versus 37% using 3-inch probes) with the microsprinklers and the 120 minutes of runtime compared to the greens that received 45 minutes of irrigation. This does not represent a significant difference from an agronomic or playability standpoint.

The clear winner in the test was the microsprinklers. However, there is an investment involved in purchasing microsprinklers and it does take a considerable amount of time to set them up behind play in the afternoon. If you are using full- or part-circle sprinklers to leach, try to only run one sprinkler per green at a time. If you must run two at a time on a single green, set the schedule so that the heads are on opposite sides of the green to minimize overlap and potential runoff. Cycling the runtimes and including soak times of at least 20 minutes before a particular head runs again is recommended if possible. Adding all that water just to have it sheet off the green is not useful, so you should expect to run the greens heads for eight to 10 hours to allow enough time for water to soak into the profile, and you may need to run a second night to apply the amount of water needed without creating excessive amounts of runoff.

Some courses will conduct venting operations in conjunction with leaching. This usually involves small-diameter solid or hollow tines, or some form of spiking/slicing to encourage water penetration and infiltration. Leaching is also often scheduled following larger hollow- or solid-tine aeration. Any practice that reduces compaction and improves water infiltration will likely add value to leaching events. Research at UC Riverside supports the idea that core aeration improves leaching efficiency. There is some concern that aeration prior to leaching will result in preferential flow, meaning that water will find the aeration holes and not effectively move salts from the soil between the holes. However, research shows that regardless of whether the green is aerated or not, there will be some preferential flow due to soil hydrophobicity. This can be minimized by using wetting agents and avoiding leaching when the soil is very dry. Any type of aeration or slicing that maximizes the amount of water moving through the profile and not sheeting off the green offsets any preferential flow that may occur.

If a leaching program is working, the EC of the soil should be significantly less than the electrical conductivity of the water (EC_w). For example, if the EC_w is 2.0 dS/m, a putting green soil that drains well and is leached appropriately should have an EC from saturated paste extract (EC_e) less than 2.0 dS/m and ideally only around 1.0 dS/m. If soil EC_e is substantially higher than the irrigation water, it likely means there are soil physical problems and/or surface drainage issues that need to be addressed. In this type of scenario, there are likely bigger problems to fix than just salinity challenges.

Adjusting the turf species, water source, or soil profile

In cases where salinity is still problematic in spite of a solid leaching program, take a closer look at the soil physical characteristics and make sure the turfgrass species is able to tolerate the salinity in the irrigation water. If the irrigation water salinity is too high for the turf but the soil drains adequately, resurfacing greens with a more salt-tolerant variety is very likely needed. Another idea is to use an alternative water source for the greens or to blend the current water with one that has lower salinity. Other courses employ a hybrid approach where they use low-salinity water during strategic periods, such as during the overseed season in Southern states to facilitate healthy cool-season turf growth. Then, they switch back to higher-salinity water (that is typically less expensive) during the summer months when bermudagrass is the dominant species on their greens. Adjusting the water source for key playing surfaces is an effective way to manage salinity, but if the irrigation system infrastructure needed to make this possible is not in place, there could be a significant investment required to separate or blend water sources.

If the salinity of the irrigation water is suitable for the turf on the greens but soil salinity is high despite efforts to leach, some form of soil modification is likely necessary. Use solid deep tines and perhaps the drill-and-fill technique to mitigate compaction and improve soil water infiltration deep into the profile. These practices are likely necessary four to six times annually to address serious infiltration issues, and in some cases even that number of treatments is still not enough. If these efforts don’t succeed after several years, it is likely that the greens need to be rebuilt or the putting green soil needs to be substantially modified to improve water infiltration. In such instances, start by collecting undisturbed soil cores and sending them to an accredited laboratory for guidance about the soil physical properties.

Soil and water amendments

Adding calcium (typically in the form of gypsum) is most likely ineffective and unnecessary to help reduce salts and improve leaching in putting green soils. Calcium applications may be beneficial in soils containing greater than 6%-8% clay when that clay is expansive, but most putting green soils have less than 6% clay and therefore are not susceptible to soil dispersion and swelling. Applying gypsum or other calcium sources to manage salinity is likely a waste of time and money. Adding some form of weak acid to the irrigation water is sometimes done in an effort to enhance leaching and reduce soil salinity. I hate to be the bearer of bad news, but this approach is futile. Acid products can be used to lower the water pH and reduce carbonates and bicarbonates, therefore reducing the sodium permeability hazard. This is recommended where sodium levels are high and the soils are susceptible to dispersion. However, in most all putting green situations there is no risk of soil dispersion from sodium.

There is a narrative in the golf industry that bicarbonates and carbonates may precipitate and create impermeable layers within the rootzone and/or at the sand and gravel interface in a layered putting green system. There is no evidence to support these claims. The topic of bicarbonate or carbonate layering has been studied and a direct quote from the abstract tells the story: “Our findings from this study do not provide evidence that bicarbonate from irrigation will cause formation of layers or zones of accumulation in putting green soils, contrary to this widely-held belief in the turfgrass industry.”

Keep It Simple

The overarching message on how to successfully manage salinity in putting greens is to keep it simple. Don’t search for answers in a bag or a jug. Grow turf that has suitable salinity tolerance for the irrigation water, maintain good internal and surface drainage, and conduct leaching on an as-needed basis determined by measured EC thresholds. If that doesn’t work, give your regional USGA agronomist a call and we’ll figure it out together!

References

Ayers, R.S., & Westcot, D.W. (1985). Water quality for agriculture (Vol. 29, p. 174). Rome: Food and Agriculture Organization of the United Nations.

Carrow, R., Duncan, R.R., & Huck, M.T. (2008). Turfgrass and landscape irrigation water quality: Assessment and management. CRC Press.

Harivandi, M.A., Guo, X., Brown, J., Waters, R., & Wu, L. (1999). A screening model to evaluate landscape plants’ response to municipal recycled water irrigation. In 3rd International Symposium on Irrigation of Horticultural Crops (pp. 719-724).