Last summer was incredibly challenging and many golf courses suffered with loss of grass cover, including to our frustration, our more drought resistant species. STRI consultant, Stella Rixon, investigates why?
The disturbance theory
Interestingly, if we look at the research work of Grime, Hodgson & Hunt (1988) Comparative Plant Ecology – A functional approach to common British species on which ‘The Disturbance Theory’ is based, you will see it predicted the outcome of the drought pretty well. This study mapped the presence/absence of plant species, including some of our turf species, according to their environment. Each environment was rated in terms of its level of stress, disturbance and competition, defined as:
- STRESS – anything that restricts growth, ie temperature, lack of light, low nutrients or moisture
- DISTURBANCE – anything that physically breaks/reduces plant material, ie pests, disease, wear, mowing/brushing/verticutting etc, loss of rooting due to compaction, wind or frost damage and also desiccation.
- COMPETITION – is an environment which has good growing conditions for plants (moisture, nutrients, warmth, light). In this environment, the most competitive plants (fastest growing, best able to capture the available resources) will dominate.
In the diagram (Fig 1) of where our key turf species sit within this environmental triangle, you can see that if stress is high (ie lack of water, high temperatures) and we increase the disturbance (keep mowing, traffic, increasing desiccation as the ground dries out) then the grass species left will be ryegrass and annual meadow-grass, which establishes from seed once a break in the stress/disturbance allows.
This is largely what has been observed on courses across the country – turf death where stress and disturbance were extreme with ryegrass being one of the most resilient grasses to withstand the stresses. The resulting thinned turf quickly became colonised with annual meadow-grass once moisture returned in the autumn.
Factors affecting drought survival
There were some courses that managed to retain their fine grasses, sometimes without irrigation! Most notable were the chalk downland sites, where the soil drains well but also have good moisture reserves. In addition, the higher pH favours plenty of microbial (and worm) activity to break down thatch and the waxy substances that cause hydrophobicity in soils: Suberin, a waxy substance produced by roots, is thought to be a key contributor to hydrophobic conditions.
Research shows hydrophobicity is more likely on sandy soils, soils with low pH and soils that dry down to a critically low moisture level, below which they quickly become hydrophobic (see videos below). This perfectly our heathland sites, which explains why they had such a hard time of it last summer.
How much thatch is too much?
Thatch can obviously be an issue in preventing good water infiltration through the surface, but we do need some present. Vigorous dethatching to the point of thinning the sward is undesirable – remember the Disturbance Theory triangle – fescue likes a settled environment.
I would suggest around 20mm of thatch is acceptable in fescue/bent dominated fairways, provided water can pass through it. This can easily be checked via infiltration testing at the surface and/or checking for hydrophobicity using the Water Droplet Test.
This will quickly show you whether water is passing through the surface to where roots can access it. Hydrophobic conditions may be below ground rather than at the surface and therefore our efforts need to be directed at getting water deeper into the profile.
Case Study: A Heathland Survivor!
To understand the issues more fully, I returned to a heathland site, where we had undertaken a previous fairway study, to see how they fared. You may remember my initial article published in a previous Bulletin. Let me recap:
Heathland Club X is set on freedraining, acidic sandy loam soil. In May 2011, the club asked STRI to undertake a turf quality benchmarking study of three of their weakest fairways prior to installation of an automatic irrigation system, (in use from spring 2012). Three sample areas were marked on each fairway and assessed for % grass cover/ bare ground, turf quality and sward species composition.
When first assessed prior to irrigation installation, the fairways were prone to severe drought stress causing significant loss of grass cover and thinned, patchy swards (see Fig 2) that were dominated by annual meadow-grass (Poa annua) (Fig 3).
This grass species is ubiquitous in the environment and highly present in the soil seedbank. It can quickly exploit bare areas left by drought stress, once moisture becomes available again in the autumn, but it also has poor drought tolerance and so dies out again in the summer.
Hence an undesirable vicious circle occurred each year. Once irrigation was installed, it was used judiciously in combination with overseeding to maintain suitable moisture levels to promote desirable fine grasses and prevent extreme drought and loss of grass cover, hence keeping the opportunistic Poa out.
In June 2016, after four years of using fairway irrigation, the same sample areas on the fairways were re-assessed and the results compared, which were very favourable (see Figs 2 and 3).
This spring, I returned to the same sampling areas again to see how they had come through the drought. As you can see from Figs 2 and 3 and Images 1–9, the fairways had coped very well indeed with no loss of grass cover to drought stress and retention of fescue dominant swards. The 16th fairway recorded a little more Poa annua than previously.
However, it should be noted that this testing date was two to three months earlier in the season and this fairway is more shaded and moister in the winter months when the sun is low, due to trees along the south side. Therefore, it is likely that Poa increases in this particular fairway in the autumn and then reduces again in the summer as it dries out again.
Images 1-9 taken pre and post irrigation installation demonstrate the difference in quality that watering has made to this site.
So, an excellent outcome for the club and one that we can learn from. I convinced ‘Heathland Club X’s’ Course Manager, David Murdoch (Liphook Golf Club) to stop hiding his light under a bushel and talk us through his success! We came up with the following:
Secrets to success
- The right site – Good drainage is essential for successfully growing fescue dominant swards. Even on a dry site such as Liphook, low-lying or flat areas that are shaded and therefore damper are more prone to compaction and meadow-grass invasion. Being able to avoid the extremes of too moist and too dry is a necessity
- Automatic irrigation – Installation of an automatic irrigation system helped Liphook to break the drought induced die-back and Poa annua succession cycles that used to occur on this dry site
- Overseeding – Once irrigation was installed, overseeding took place with desirable grass species (dominated by creeping red fescues) to fill in the thin swards. Irrigation was used to ensure successful germination, when rainfall was insufficient
- Retain full cover but avoid excess growth – Once full grass cover was re-established, it has been carefully managed to maintain existing cover but not produce excess growth and therefore avoid thatch build up. Fairways do not receive any nutrition so that clippings are not excessive and can be recycled back to the ground. This helps prevent drought stress. Due to the slow growth, there is very limited need to scarify, hollow core or top dress, as thatch is not excessive, and the low pH (5.0 or less) and dryness keep worm activity low. Regular divotting is undertaken with fescue but large scale overseeding is no longer necessary
- Wetting agent – A necessity for a dry site, we apply wetting agent monthly from late March to early September on fairways
- Watering – Irrigation is used carefully, aiming to provide a less frequent, deeper soak, as opposed to daily light irrigation that will evaporate off. We are lucky that we have a summer abstraction borehole licence that provides sufficient water for this
- Decompaction – Thorough and deep aeration is essential to ensure good water infiltration and rooting depth. Due to our good drainage, the soil does not become overly compacted, in addition to this we have less than 30,000 rounds per year. We generally do this this once, but sometimes twice, a year and ensure that full depth of 250-300mm, with a small amount of heave is achieved
If you have any questions or comments about this article, contact Stella Rixon on Twitter here.
For agronomic assistance on your golf course, call +44 (0) 1274 565131 or email firstname.lastname@example.org.