by Stella Rixon, STRI agronomist
Golf clubs have many weapons in their armoury when it comes to luring new members to tackle their beautifully manicured courses. Challenging holes and magnificent locations are a couple of helpful chunks of bait, but sometimes ‘excellent drainage’ creeps into that promotional mix. Here I’m going to take a closer look at golf greens’ drainage rates and show how to make it something your club can be proud of.
Thatch issues are typically more obvious to the eye and easier to access now that we can accurately measure organic matter in the profile. Soil laboratory analysis, measured at four depths, commonly records organic matter content as a higher than desirable accumulation.
Depending on the environment and grass species, STRI conducted research suggests target values of 4-6% in the upper 0-20mm and <4mm in the lower profile. Levels higher than this will significantly negatively affect drainage rates and surface performance. Therefore, our attention is rightly focused on thatch management.
But beware! There are examples where courses came unstuck when they intensively dethatched and heavily topdressed over a three-year period.
In study cases, organic matter was successfully reduced to target levels but given heavy rainfall, the greens were wetter than ever, to the point of unplayable. In these examples, limited deep aeration had been carried out but not effectively enough to improve drainage sufficiently through the profile below the thatch. Whilst the thatch was present, it prevented water from penetrating too far into the profile and the excess surface water rolled down slopes or evaporated off more easily. With the thatch removed, the surface became more permeable to water, and once accepted into the upper profile, there was nowhere for it to go past 50mm. It therefore didn’t take much rain before the surfaces were saturated and unstable.
What about down below?
It is equally easy to blame poor drainage on less than desirable underlying soils. If a push-up green construction is sitting over clay or a silty sediment, then that may well be the case. However, if you have built up a depth of 200mm of freedraining rootzone above the poor soil, the surface should perform well enough in most instances, especially if there is a fall to allow water to shed. If you take an opportunity to measure drainage rate in the lower profile, you might be surprised.
Stuck in the middle
Drainage problems are commonly seen in this area of the profile. Changes in topdressing, layers of thatch or less visible broken down organic matter, compaction and iron pans are common place.
Mild, wet winters with cutting machinery out year-round, as well as foot traffic on wet soils spells disaster for soil structure. Horizontal breaks, poor rooting and pockets of anaerobic black layer indicate you have a problem in the mid-zone.
Pressure has dictated that clubs have become too fond of non-disruptive pencil tining to a maximum of 75mm depth, but have shied away from regular deeper work, as it is often deemed too disruptive. Instead, we put too much hope in a bottle of penetrative wetting agent, calcium flocculants and the like. But the crux of the problem is not biological or chemical in nature but a physical one.
The problem is highlighted when measuring speed of drainage down the profile. Consider the results of golf green from Course Y below, a heathland site (Fig. 2). Infiltration rate testing (Fig. 3) gave poor results from the surface, even with relatively low levels of organic matter (7% in 0-20mm and <4% below).
We want to aim for a drainage rate of 15-20mm/hr to cope with most UK rainfall. Therefore, further thatch reduction was an obvious target but what about further down the profile? An infiltration test at 95mm depth still gave an unsuitably low reading. However, infiltration rates were seen to improve significantly deeper in the profile at 200+mm depth.
I have found this to be a common occurrence, especially on heathland and downland sites, where natural site drainage is generally good. However, greens on a site can vary hugely, both between greens and within a green, so it is important to undertake sufficient testing replicates before deciding on a plan of action.
The devil’s in the detail
Once an accurate assessement of the issues are made, it makes it easy to decide on the best course of action. So for Course Y, it was obviously to undertake plenty of deep tine aeration to 200+mm, alongside surface dethatching techniques.
However, the implementation of this is key to success. Depending on the soil type and structure, solid tining in silty soils may not be sufficient and the holes quickly seal up again. Research has shown that narrow solid tining has a minimal and very temporary effect on infiltration rate, if at all.
To improve results, sand filling of holes is required to create more permanent channels through the profile. It is also essential that the sand-filled channels attain sufficient depth to reach the more free draining material.
In the case of Course X, the free-draining material was not found until you reached 28cm depth and previous deep tining had just missed the critical depth by 25mm.
The practicality of filling holes can be difficult and almost impossible if weather conditions turn wet during renovations. In an ideal world, we would want to achieve something as shown in Fig. 4 below where a sand-filled channel is connected to a more permeable horizon.
Of course, if you are unlucky enough to have a poorly draining profile throughout the depth attainable by aeration equipment, then your only viable option would be to look at drainage or reconstruction.
STRI is the leading, largest and most experienced professional body working specifically within golf. If you wish to engage one of our advisory team to discuss drainage, please email email@example.com or call 01274 565 131