(written as technical paper for ITRC 2022, but withdrawn)
Previously existing recommended target values for organic material (OM) in golf greens are difficult to use. No practical strategies have been found when measuring OM in golf greens in Sweden since 2012. In 1428 samples from golf greens in Sweden 2020-2021, the average level of organic material at 0-25 mm is 7,4 % (w/w). 90% of samples were higher than 4,2% (w/w) and could be a minimum level for sustainable organic material (MLSOM).
A new target for OM is argued to be: get as much OM as you get away with.
Background
Managing organic material (OM) in golf greens is complex and not fully understood. Sampling and analysis is not standardized so comparison of values is difficult. Recommendation for target values depends on local conditions (Gaussoin 2013). Laboratory methods for analysis of compliance with USGA recommendations for putting green construction use equipment that requires preparation of samples in a way that it would not work with undisturbed samples. Much of the OM was removed when verdure and thatch was cut away (Sandell 2012). Using traditional standardized methods for measuring soil organic matter is a reason for differences in target values when comparing reported research results (USGA 2021). Asian Turfgrass Center has developed a method where five samples on a green once a year, at 0-20mm, 20-40mm and 40-60mm depth, verdure is intact when doing the loss on ignition at 440 C (Woods 2021). There are many benefits of OM: shear strength, hardness, wear tolerance, protecting from environmental variation, increase CEC and moisture holding capacity (Gaussoin 2013).
Sweden
South part of Sweden is almost snow free in winter, and north of Sweden is experiencing many dead greens after each winter, so conditions of growth season is very different for managing turfgrass. The peak of soil temperature and daylight is separated and spring start up get all the light but low temperature. In autumn soil is warm but light could be very limited and cloudy conditions make all the difference in winter preparations. Most of the golf courses in Sweden are built in the “golden era” 1980-2005 where 50% of all golf courses were built in Sweden, and most of them took many short cuts in construction (SGF 2011).
Measured values in Sweden
In 2020, 250 samples were taken from 75 golf courses with 30 yr + old greens at both beginning, mid and in late summer.
Follow up on all 18 greens at a golf course after nine years did not help in management strategies. Following OM yearly in the same golf green for ten years did not lead to any clear strategy, but was good for reflection on budget and yearly variation in weather and amount of play.
Variation
Management, growth zone, budget and ambition, sampling method, sampling time and frequency were common issues when discussing practical strategies with course managers.
The OM values from golf greens are very dependent on where the samples are taken. On a local dry spot, an old fairy ring, a low spot where Annual Poa is established after a winter kill, odd patches or a returfed area would show different values. When taking samples at a good performing creeping bent USGA golf green in seven positions and eight samples at every position, it showed variation within a position is almost as big as the variation between positions. No matter how small area of interest, multiple samples need to be taken.
At the same time and in same green a moisture meter (Spectrum TDR350) was calibrated and 32 points measured with 75 mm probes. The variation in moisture was very similar with OM variation. If moisture is found varying more than 20% on a green maybe ten samples for OM analysis is required for that specific green to make conclusions about significance of differences on separate measurements.
When to sample and how often
Since spring start up is very different every year in Sweden and inputs and management have a huge impact on opening date, it could be wrong to always use the same date for measurements once a year. Especially in northern Sweden most greens are reestablished every year after sever winter kill and OM is not following the calendar when in hands of a skilled Superintendent.
At Hofgård GC in south Sweden three greens where measured every month April-October 2021 and show very small variation but similar development over the year following the management practices. It is a low input golf course and use most resources in early spring to establish full cover on greens and then in May focus to get good playability with topdressing, solid tine aeration and rolling to get proper green speed coming into the busy period June-Aug. Later in autumn depending on weather, sand is applied to diluting OM (Pettersson 2021).
To keep down costs and still capture how management is having an impact on OM, three times per year would be enough if first occasion is after opening day when a period of pushing turfgrass been done, second time is in summer when greens are optimized to be the best and then in autumn to adopt management practice to weather conditions. This means measuring OM is not a tool for what to do to get good greens, more a follow up on impact on management practices.
Suggested method for sampling and analysis of OM
Three measurements per year, seven samples on each green, top 25 mm individual values, and pooled samples and lower levels. Undisturbed samples could be taken with 30-40 mm diameter probe. Verdure should not be removed and no sieving at 2 mm when preparing sample in lab.
Look for inconsistencies with sand in channels from coring, if any clay is present, chemical reactions (mostly iron oxidation/reduction), layering from topdressing and take photo of the cores. Since samples are less than 50 g drying five hours in crucibles at 105 C is enough. Burning at 550 C for one hour is similar to the Swedish standard for Soil organic matter.
If 0-25 mm and 25-50 mm is of interest, eight samples per green three times per year would at three greens be 72 samples. Cost is around 20 EUR per sample, so lab cost is 1500 EUR per years. If you build your own lab 4000 EUR will get you the equipment to burn 24 samples at the same time and only cost electricity. This inaccuracy of this process is way less than variation in samples.
Two cases of calibration
Hills S&GC is a tournament golf course in Göteborg, south west of Sweden with European Tour events 2017 and 2018. Lycke GC was also built for tournaments and had a Ladies European tour event in 2012, and also situated in Göteborg close to the sea. The course manager at Hills also supervises Lycke GC as agronomy advisor. It makes the cases great for comparison.
All 18 greens were measured three times at Hills 2021 in May 10, June 26 and Oct 6. The greens were returfed in 2017 with Creeping Bent (007) from Spain. Turf was optimized for transport so the thatch was strong and it created a layer and made the greens troublesome and there was a need of extra attention coming years to get a harmonic profile. In 2021 most greens showed similar development of OM over the year and they perform well. There are four greens showing deviating pattern with low OM and no significant increase over the year.
According to the course manager it is exactly the four weak greens that are low and have little response over the year. The level of 5-6% is working fine at Hills S&GC (Andersson 2021a).
At Lycke GC all greens were measured may 12, July 1 and Aug 29 in 2021. Greens are 15 years old and seeded with Creeping Bent, Penn A2/A4. Budget is low and no sand or aeration been applied in previous four years.
Playability is high, mowing on 2 mm, but 2020 OM of 11% average at 0-25mm was considered too high and topdressing and aeration been applied in 2021 with some extra fertilizer to meet the need for recovery of turfgrass. OM show 2021 that all but one green has had significant development of OM over the year, only changes in green no 2 is not significant. Even with top dressing and aeration program greens are increasing 25-45%. It could be a natural response from aeration and more fertilizer. Some weak greens have improved 2021 and 25-40% increase is a great response. Lycke GC monitor ClipVol closely and is satisfied with playability even with high OM numbers. Next year diluting OM with sand will be in focus (Andersson 2021b).
Discussion
Measuring hardness and smoothness is a great compliment to measure OM. A way forward could be to extend measurements with clip volume and amount of sand applied. I would be terrific if any biology measurement was reliable to get an even better overview.
Old school say high OM is a problem, and we should aim for low numbers. Experiences from Asian Turfgrass Center report the best greens always are high in OM (Woods 2021). Maybe a Minimum Level of Sustainable Organic Material (MLSOM) would be 3,8% (w/w) in Sweden.
”The greens are talking to you. Are you listening” (Zontek 2008).”Superintendents know when OM has gone too far away. There are many indicators, and one of the best is ball marks. Ball marks are strongly connected to how the course is played. A green at a tournament links course with fescue get very different ball marks from an inland wet Poa green in Sweden.
References
Andersson, C. (2021a). Interview. December 2021
Andersson, C. (2021b). Interview. December 2021
Gaussoin, R. E., Berndt, W. L., Dockrell, C. A., Drijber, R. (2013). Characterization, Development, and Management of Organic Matter in Turfgrass Systems. In John C. Stier, Brian P. Horgan, and Stacy A. Bonos (Ed.), Turfgrass: Biology, Use, and Management (vol. 56). Agronomy Monograph.
Sandell, B. (2012). Fysikalisk analys av golfgreener. Rapport 2012:22. SLU, Alnarp
SGF (2011). Golfbanan – Bygga om helt delvis eller inte alls. www.golf.se
Petterssson, P. (2021). Interview. November 2021
USGA (2021). Developing a Consistent Approach to Organic Matter Testing. USGA Green Section Podcast
Woods, M. (2021). ATC Office Hours: OM246 report discussion. www.youtube.com
Zontek, S.J. (2008). The Anatomy of a pitch mark. USGA Green Section Record.