The science behind the surfaces

 

ATM expert columnist John Neylan, who played a key role as an agronomic consultant for the Peninsula Kingswood redevelopment, outlines the lengthy and detailed research and investigation that went into ensuring the new greens provide an optimum playing surface.

The putting surfaces at the redeveloped Peninsula Kingswood Country Golf Club (PKCGC) are setting a very high standard and it is doubtful that any golfer that plays the courses even thinks about how they were achieved, let alone understand the numerous elements involved.  They may associate the excellent surfaces with the new bentgrass variety chosen or the excellent greenkeeping practices of director of courses Glenn Stuart and his team, but are unlikely to understand the detail behind the greens construction process. 

The finished product the golfer experiences involves numerous basic elements including surface contouring, profile design, sand selection and bentgrass selection.  While these elements are critical, there is also the maintenance practices including machinery, manpower, the skill of the greenkeeeping staff and understanding the performance characteristics of the profile and turf.  If any aspect is deficient it is unlikely that the playing surfaces will achieve the expected high standard.

From my perspective the greens at PKCGC are a product of detailed research including the selection of the rootzone mix, designing the profile and selecting the bentgrass.  It wasn’t a result of guess work or popular opinion, but a lot of work put into understanding the desired outcomes and then using the available science to make the most informed decisions. 

The overall objective at PKCGC was to develop greens that had the characteristics of the best of the Melbourne sandbelt golf course greens.  That is, they were to be firm, dry and fast and not to be perched water table profiles.  It also meant that the greens were going to challenge convention with several innovations.   This article reflects two components of the project and the detailed analysis and data collection associated with selecting the rootzone sand and deciding on the most appropriate creeping bentgrass cultivar.

 

Sand selection and the putting green profile


The requirement of putting surfaces has always been about being firm and reasonably fast. In the AGCSA’s 2012 benchmarking study, it was determined that the elite level clubs provided greens that were firmer, drier and smoother and were considered to be superior putting surfaces.  The issue of surface firmness and how to achieve it has become a frequent discussion point in recent years. 

With the focus on surface hardness, the way greens are being constructed has been questioned and whether there should be a return to the finer sands and loamy sands that are the basis of the sandbelt greens.  The AGCSA study mentioned demonstrated that a sandbelt green constructed using a fine loamy sand soil with a profile depth of several metres, consistently provided firmer surfaces throughout the year.

 

Sand research project


Based on my observations over many years, it was apparent that there was much that was not known regarding sand type, moisture retention and its relationship to stability and hardness. For this reason I commenced a research project that examined the influence of proportion of silt and clay, moisture retention, moisture release, particle shape and particle size distribution and their effects on surface hardness (reported in ATM 16.5).  This research had been well underway at the time the PKCGC project was in the planning phase and the results of the research became a key source of information in deciding on the sand selection.

The research involved selecting eight different sands representing manufactured sands commonly used in greens construction, coastal dune sands and a loamy sand that is typical of the Melbourne sandbelt.  The sands varied in particle size distribution and the proportion of fines.  The testing regime involved saturating each of the profiles and then once drainage had ceased a series of measurements was undertaken as the profile dried out including;

  • Volumetric water content;
  • Surface hardness using the 0.5kg Clegg Impact Soil Tester (CIST). The hardness readings were taken at regular increments that related to the rate of reduction in soil moisture.

The conclusions from the research were that sands that have about 3-4 per cent by weight of silt and clay tend to produce a harder surface and even as the sand dries the firmness is maintained at higher levels than the sands with very few fines.  With the finer sands, it is the frictional forces produced by the smaller particles fitting within the voids of the larger particles that maintain the harder surface. 

The sands with no fines had maximum surface hardness when the moisture content was near field capacity and this firmness diminished relatively quickly as the sand dried out.  The influence of moisture on the sands with a low silt and clay content most probably assists in ‘holding’ the particles together or, more accurately, when the voids are filled with water there is less opportunity for particle displacement.  This characteristic of the sands with a low silt and clay content makes them difficult to manage as a consistently firm surface.  The ‘ideal’ sand had the characteristics detailed in Table 1. 
 

Table 1: Reference sand sample from sand research project

Sieve size (mm) Reference sand 
2.000 0
1.000 0.3
0.500   5.4
0.250 36
0.150 45.3
0.053 11
Pan 2
Total fines (<0.250mm) 58.3
Fineness modulus 0.87
Total Porosity (%v/v) 35
Air-filled porosity (%v/v) 11.5
Capillary Porosity (%v/v) 23.5
Saturated Conductivity
16 drops (mm/hr)
280
Saturated Conductivity
32 drops (mm/hr)
190

 

Based on this research, there were 11 sands tested to determine what sands were commercially available and whether the selected sand could be produced in sufficient quantities to construct 36 greens and practice putters at PKCGC.  Of the sands tested, a sand based on the fine topdressing sand from Rocla (now Hanson’s) was selected. 

While the sand had the desirable characteristics for producing a firm surface due to the fine soil particles present, it was also important that all of the other physical characteristics were considered such as capillary porosity, aeration porosity and hydraulic conductivity.  The other aspect of selecting the sand was whether a consistent sand could be produced over the life of the project. 

 

Sand selection and quality control


Once the preferred sand was identified, discussions were undertaken with Rocla regarding the practicality of producing the sand over the potential life of the project.  It was important for the consistency of the profiles that each green was constructed using a sand that was similar to the selected material regardless of whether it was in year one or year four. 

The sand was based on the fine topdressing sand and there were several samples tested before establishing the benchmark sample and the acceptable range for future testing (Table 2). The skill of Rocla’s Langwarrin quarry manager Jack Jaskolowski was critical in coming up with a blend that was expected to be achievable over the long-term.  Jack’s knowledge of the raw materials and how to blend them was a key factor in being able to achieve such an ambitious process.  It was decided to test every 700-tonne stockpile for approval and before it was delivered to site.  From July 2015 through to January 2019 there were about 60 samples tested. 

The greatest challenge in producing a consistent blend was maintaining the proportion of silt and clay.  In particular, it takes a relatively small change in this fraction to reduce the drainage rate to an unacceptable level.  Over the period of the project there was a relatively small number of stockpiles rejected and highlighted the quality of the production process.  
 

Table 2: Benchmark sample and the acceptable range 

Sieve size (mm) Acceptable range
2.000 0.1
1.000 0.1
0.500 3.4 – 4.0
0.250 32 – 41
0.150 39 – 53
0.053 8 – 14
Pan 1.4 – 2.4

Greens profile


The profile of the greens was discussed in considerable detail involving OCCM lead golf course architect Michael Cocking, Glenn Stuart and myself.  The primary objective was to create a profile based on the ‘best of the sandbelt’ greens.  The key elements were the physical characteristics of the sand, the depth of the profile and the attention to the surface shape and surface drainage. 

Based on the characteristics of the selected rootzone sand, the general profile specification was 400mm of rootzone sand over at least one metre of native site sand.  The depth of the greens profile was considered to be important in providing the ‘draw down’ of moisture that we typically observe on deep, native sand profiles.

The PKCGC site does not have a consistent soil type with areas of the course having a relatively shallow sand layer over a clay subsoil.  In areas where greens were to be constructed on such soils, the profile was over excavated, subsoil drainage installed, at least a metre of site sand placed over the drains and then the selected rootzone sand.  As added insurance there was some additional subsoil drains installed at the interface of the imported rootzone sand and the underlying site sand.

 

Bentgrass selection


From a science perspective, selecting the creeping bentgrass (Agrostis stolonifera) cultivar was an involved process that examined all of the available data and practical installations.  At the time of the project planning, Penn A1 and Penn A4 were the industry benchmark grasses with MacKenzie also being introduced into Australian golf greens. 

PKCGC had selected Penn A4 for the resurfacing of greens some years earlier and based on an assessment of the greens in 2014 the Penn A4 was still considered to have the general characteristics required to form a high quality putting surface. 

Around the same time, I was involved in establishing a bentgrass trial in conjunction with Matt Merrick of Heritage Seeds.  The replicated trial was funded by Heritage Seeds and established on a sand profile at the Keysborough Golf Club in April 2014.  The trial was primarily set up to assess the characteristics of several new creeping bentgrass cultivars imported by Heritage Seeds and not previously seen in Australia. 

Amongst the grasses in the trial were Pure Distinction, Pure Select and Crystal Blue Links which were an unknown entity under southern Australian conditions.  These new cultivars were compared against the industry standards at that time including Penn A4 and Penn G2.

The trial was assessed for the parameters detailed below and where practical the NTEP Turfgrass Evaluation Guidelines (http://www.ntep.org) were used to rate the trial;

  • Germination and establishment;
  • Visual turf quality;
  • Visual turf density;
  • Visual turf colour;
  • Pest and disease (0 = nil, 5 = 100 per cent plot infected).
  • Poa annua invasion. 

In the first eight months of the trial there was not a lot of difference between the cultivars though the Pure Distinction was starting to demonstrate significantly greater turf density than most of the other cultivars.  At that time the Pure Distinction was not particularly remarkable though it was showing promise. 

The trial area was subjected to moisture stress in February 2015 due to an irrigation failure with Pure Distinction being the least affected and had significantly better turf quality than Penn A4, Penn G2, MacKenzie and Crystal Blue Links (Table 3).  From my perspective this was a turning point in terms of what Pure Distinction may have to offer.  Interestingly, a trial being undertaken in Sydney also had a similar issue with moisture stress and the Pure Distinction was again the least affected cultivar.

Over the two years of the trial the Pure Distinction continued to be the standout variety with significantly better turfgrass quality 10 out of 12 assessment dates (part of the data is detailed in Table 4).  The results indicated that the new cultivars were as good as the industry standard cultivars with Pure Distinction being a denser cultivar that was exhibiting better turfgrass quality compared to Penn A4, Penn G2, MacKenzie and Crystal Blue Links.
 

Table 3: Visual turfgrass quality following moisture stress

Variety Turfgrass Quality (4/2/15)
Penn A4 4.7
Penn G2 5.0
MacKenzie 4.3
Crystal Blue Links 5.0
Pure Distinction 7.3
Pure Select 6.7
LSD (P<0.05) 2.1

 

Table 4: Visual turfgrass quality for bentgrass cultivars

                                                            Turfgrass Quality

Variety 19/6/15 15/7/15 7/8/15 23/10/15
Penn A4 7.0 6.8 6.2 6.3
Penn G2 6.7 6.2 6.0 6.2
MacKenzie 6.3 6.5 6.2 6.2
Crystal Blue Links 6.5 6.5 6.2 6.2
Pure Distinction 7.3 7.0 6.7 7.0
Pure Select 7.3 7.0 6.7 7.0
LSD (P<0.05) 0.8 0.7 0.6 0.7

 

Table 5: % Poa annua (visual rating)

 

                                                                27/10/16

Variety Turf Quality Turf Density % Poa annua
Penn A4 6.0 6.0 5.0
Penn G2 5.3 5.7 13.3
MacKenzie 5.5 6.0 15.0
Crystal Blue Links 5.7 5.8 15.0
Pure Distinction 7.7 7.7 1.7
Pure Select 7.8 7.5 2.0
LSD (P<0.05) 0.7 0.7 6.2

 

The trial area was continued to be maintained after the official assessment period was completed with an assessment undertaken six months after the trial was completed (Table 5).  The most notable aspect on this occasion was that Pure Select and Pure Distinction had significantly less Poa annua compared to all other cultivars except for Penn A4.

When a bentgrass had to be selected for PKCGC, there was a large amount of NTEP data reviewed in addition to the data from the trial plots at Keysborough GC.  Based on the NTEP data, Pure Distinction had similar or better turf quality and density than Penn A1, Authority and T1.  The only negative was the susceptibility to dollar spot (sclerotinia homoeocarpa). 

Colleagues in the US were also consulted in order to gain their impressions of Pure Distinction versus Penn A1 and Penn A4 and if there were any obvious weaknesses.  The feedback from colleagues was on balance very positive.  From my perspective at the time, based on the available information, Pure Distinction was considered to be a good choice. 

In addition to my agronomic review of the available grasses, Glenn Stuart was making an independent assessment of the Pure Distinction being maintained at Royal Canberra Golf Club and making his own enquiries as to the suitability of the grass. 

 

Conclusion


From my perspective, the construction and grassing of the greens at PKCGC has been a challenging and innovative project.  It has challenged convention in terms of profile construction and bentgrass selection, but it was tackled in a methodical and scientific manner.  Using the available research information provided a sound basis for the decision-making process.

This project emphasises the importance of research and the need for ongoing investment in turf research projects in Australia.  The sand research project was funded by me and the information collected provided the best guide as to the selection of the most appropriate sand type and the expected performance characteristics.  The bentgrass trial was funded by Heritage Seeds and while there was a commercial interest, the trials were properly conducted and the data was invaluable in the decision-making process.  
 

Words: Brett Robinson

Photos: PKCGC/Gary Lisbon and John Neylan

Originally published in Volume 21.5 (Sept-Oct 2019) Australian Turfgrass Management Journal. To subscribe to the journal click here.