For over 30 years (Habeck and Christians 2000) the United States Golf Association recommendations for golf green construction have been accepted as the only widely recognised specification for construction throughout the world. Before the USGA specification golf greens were constructed with indigenous soils with possibly the inclusion of 'brought in' sand and some form of drainage system. However, there was no standard construction specification.
In recent years there have been alternative specifications used such as the Dutch or California system, and the STRI are currently working on a new construction guideline. But it is still the USGA system that is used as the standard method.
However, two of the most frequently asked questions are; does the USGA construction work? And is it an appropriate construction method for UK conditions?
Well I would answer yes to both questions. There is no doubt that the engineering principles behind the USGA construction method are sound and there is no reason why they should not work equally as well in the UK as in the USA.
So why are these questions being asked and why are so many new golf green constructions (built in the last 20 years) failing to live up to expectations.
In my opinion there are a number of reasons why so many new constructions are failing including:
1. The construction does not fit the USGA specification
2. Poor construction
3. Maintenance techniques have not been appropriate for USGA construction
4. The organic source has not been stable enough
5. Irrigation water quality has not been good enough
The following work looks at some of the above points in more detail.
This is probably the biggest influential factor responsible for the quality of the green not living up to expectation. The USGA construction method has extremely specific guidelines. If any one of these guidelines falls out of the parameter set by the USGA then you do not have a USGA construction green and more importantly the construction is likely to fail.
The USGA specification is based on engineering principles relating to the management of water movement within the rootzone. If any one component of the specification is different it is likely that the overall construction could fail (see charts below).
The Scotts company has recently built a USGA specification construction green at its Levington research station (see picture). Indigenous soil at the station is free draining and turf areas support a good mixture of fine turf grasses. It is therefore quite easy to simulate trial conditions for 'traditional' golf green or other sports areas. However, what we didn't have was a specific USGA construction for trial work.
The data from the trial work will be used throughout the world to support our products. It was therefore necessary to use the only world recognised construction specification. With the help of an accredited laboratory approved by the USGA we were able to produce a USGA rootzone. However, it was not an easy process to find/produce a rootzone mixture that adhered exactly to USGA specification. It was quite easy to find a sand that fitted the particle distribution criteria and we used Shamrock Superfine Peat which is a stable sphagnum peat and considered to be more suitable than other organic amendments (Hummel 1993).
We initially started off with 80% sand, 20% peat mixture. This specification gave us the correct overall particle distribution but the air filled and capillary porosity's were out of range. After a number of different mix ratios we found one where all the parameters could be met (approximately 85% sand, 15% peat).
The saturated conductivity was in the accelerated range, which is not acceptable for some experts, but we were happy to have the mix in this range, especially when you consider the research carried out by Habeck and Christians (2000) which found that percolation rates decrease dramatically after the green has been placed - see later.
As can be seen from the tables (see above) it is not only particle distribution that is important to meet USGA specifications, it is also essential to follow construction specifications. Guidelines are set out for drainage, stone carpet depth, blinding layer depth (if used) and rootzone depth. If these guidelines are not followed you will not have a USGA construction green - more importantly the construction is likely to fail.
Probably the two most common faults are incorrect depth of rootzone and poor rootzone consistency. If the depth of the rootzone is less than that recommended by the USGA the construction will not drain as efficiently as it should do. If the rootzone mix is poor and a homogenous consistent mix is not achieved, water movement through the rootzone can be disrupted. These problems can lead to excess moisture held within the rootzone, which can ultimately lead to anaerobic conditions (Black Layer) and the associated poor turf performance or even grass death.
Maintenance of the USGA Green
The maintenance of a USGA construction green is inevitably going to be different from a 'traditional' soil based green, especially in the first few years after construction. Factors influencing the way the green responds to maintenance treatments include: the organic source of the rootzone mix, conductivity range, grass species, amount of play, cutting height, top dressing used etc.
Probably the most important aspect of turf maintenance regarding USGA constructions (other than the type of top dressing used) is nutrient input.
Soil greens usually have a higher nutrient holding and exchange capacity (Cation Exchange) than USGA greens. This means that USGA greens need a frequent input of nutrients in order to provide the grass plants with enough nutrient for healthy growth. USGA greens are more prone to nutrient leaching (especially in first few years after construction) and generally have a lower 'buffering' capacity than soil based greens.
This means that the nutrient (and pH) status of the rootzone can change rapidly and therefore the health of the turf and overall quality of the green can also change quickly if nutrients inputs are not kept at sufficient levels.
On soil based constructions the annual Nitrogen input should be in the region of 8g - 14g N/M2 per year. On the USGA construction it can range between 25g - 30g per year. On soil based constructions other essential turf grass nutrients such as Potassium, Magnesium, etc. only need to be applied occasionally, whereas on USGA construction these nutrients need to be applied more frequently.
All essential nutrients (some text books state there are at least 13) are vital for healthy grass plant growth (Van Liebigs Law of Minimum). If one or more essential nutrients are deficient it will effect healthy grass plant growth.
Even trace nutrients can become low on USGA constructions whereas this is rare on soil based greens. Over time a USGA construction green will not require so much nutrient as the CEC of the green improves with increasing organic matter from dead grass leaves and roots.
Wilber (1999) found that the correct nutrient 'balance' within the rootzone is essential for efficient uptake and utilisation of nutrients by the turf grass plants and to maintain adequate movement of moisture through the soil.
Nutrients are constantly interacting with each other, if one nutrient is low (or high) it can affect the way other nutrients are taken up by the grass plant. It is quite difficult to keep the correct 'balance' of nutrients within a USGA rootzone, because nutrient status is constantly changing. This can influence the health of the grass plant with the obvious effect on the quality of the surface.
If the grass plant is weakened this can also lead to attacks by turf grass disease and increased wear and tear. If the grass sward is weak this can lead to invasion by undesirable grasses such as Annual meadow grass (Poa annua), although too much nutrient can also have this affect. It is a case of trying to get the balance right.
This is why it is important to carry out a regular comprehensive soil analysis of the rootzone (especially in the first few years after construction) in order to monitor nutrient status and apply necessary treatments - see below.
An organic portion of the overall USGA mix is recommended to help improve Cation exchange capacity and the water holding capacity of the rootzone (the USGA states 'the vast majority of sands must be modified with organic matter to meet the required physical characteristics'). The organic source can dramatically influence the way the overall rootzone performs. Some research shows this to be especially important once the rootzone has been placed.
Research carried out by Habeck and Christians (2000) found that changes do occur to USGA rootzone mixtures over a period of time. Greens were tested at 1, 6 and 19 years old. As the greens get older organic matter content increased as did clay and silt particles. Water movement through the rootzone was significantly less than recommended by the USGA even on the 1-year-old green. However, Maas and Adamson (1972) found that sphagnum peat (within the overall rootzone mix) was stable for a number of years after construction.
Peat can vary significantly in characteristics. Some have relatively fine particles such as reed sedge peat whereas some are more structured such as sphagnum peat. Sphagnum peat is a preferred (Hummel 1993) source of organic material for a USGA construction.
Because of the unique physical nature of the product, sphagnum peat has been shown to increase the moisture retention of the rootzone with only a slight affect on permeability. This is due to the fact that moisture is retained within the peat's cell structure. Nutrient holding and exchange capacity (Cation exchange) of the overall rootzone mix is also significantly improved. Other organic sources have been shown to decrease permeability significantly Blake et al. (1993).
Scotts Shamrock Superfine Peat is considered to be one of the most suitable organic sources for USGA construction (Tifdon Laboratories). Superfine is derived from coarse leafed sphagnum mosses. It is a very stable medium aged peat, resistant to excessive chemical and mechanical breakdown and shrinkage.
These characteristics are retained once the rootzone has been placed and long after construction has been completed. This allows the rootzone to maintain the USGA characteristics once construction has been completed. Superfine peat is a by-product of the Irish power industry and is not harvested from protected areas.
Other organic sources can meet USGA criteria, although the stability of these products during construction and after construction can be questioned (Hummel 1993).
Some soil amendments may become colloidal and breakdown very quickly during and after construction. If this happens finer particles can coat the sand particles or 'interpack' between the larger sand particles, this will have a serious detrimental effect on percolation rates. If percolation rates fall significantly, air within the rootzone will be replaced by water. If this happens the rootzone will become 'anaerobic'. When a rootzone is in this condition grass plants will become weak and the sward will 'thin' out. In extreme case large areas of turf can die back.
The quality of the water source can have a significant effect on the way the rootzone and turf performs, especially if the water source contains high levels of salts or carbonates and bicarbonates. Mitra (2000) states that most irrigation water contains salts.
Grass plants generally take up water and nutrients by osmosis, where water molecules move from a lower concentrated soil solution to a higher concentrated cell sap through a semi permeable cell membrane. When excess salts accumulate within the rootzone, the concentration of salts within the soil solution also increases. When this occurs the osmotic gradient changes and grass can not longer take up water through osmosis, leading to turf stress and drought symptoms.
It is fair to say that this situation occurs infrequently but it can become more common in the 'high stress' summer months, especially after summer applications of fertiliser.
Effects of high Sodium (Na)
Carbonates(Co3) and Bicarbonates(HCo3) are any acid salt of carbonic acid naturally occurring in water and soil to a greater or lesser extent. They form chemical relationships with Calcium and Magnesium to form Calcium and Magnesium carbonate or bicarbonate. Water high in carbonate and bicarbonates will increase the sodium hazard of the water. This is because reactions occur between Carbonate or Bicarbonate and Calcium and Magnesium in the soil to form Calcium (bi)carbonate and Magnesium (bi)carbonate. This reaction will precipitate (leach) out the Calcium and Magnesium ions leaving Sodium (Na) as the dominant ion forming an alkali (sodic) soil.
This situation does not occur frequently and is more likely to occur during hot summers where water is taken from a borehole.
Excess sodium can have a detrimental effect on the rootzone. Sodium creates a chemical reaction, which disperses soil colloids. This can create reduced infiltration rates due to the finer particles blocking pore spaces.
When high sodium levels are present within the rootzone, sodium ions can displace calcium and magnesium from the colloidal exchange complex. The calcium and magnesium ions can react with free carbonates and bicarbonates to form insoluble precipitates. In turn, sodium dominated soil particles are dispersed, leading to poor aeration and a general reduction in infiltration rates. It may be possible to reverse this situation by flocculating soil particles with the introduction of cations such as Calcium and Magnesium.
A good quality water analysis (assessed in conjunction with a soil analysis) can pick up the above problems so that remedial measures can be taken before damage is caused to the turf.
There are many courses with excellent USGA golf greens that are performing extremely well. However, there are greens constructed to a so-called USGA specification that are not performing well. I have highlighted some of the reasons above why these constructions are not living up to expectation, although there are obviously many influencing factors to consider. It is inevitable that when dealing with a dynamic environment such as fine turf, there will be situations when the surface does not perform as well as expected. However, if the green has been built to USGA specifications and is maintained correctly with good quality water there is absolutely no reason why that green will not perform well.