Understanding and Managing Turf Stress
Moisture meters, such as the new Fieldscout TDR 350 that AGS supply, are becoming more common in turf management and I firmly believe that if you can manipulate soil moisture to the exact level you require as a turf manager, you are 90% of the way to producing a quality surface and massively reducing turf stress.
Maintaining that moisture at the level you require is the tricky part. Firstly, you need good drainage to enable excess rainfall to drain away quickly. This is the biggest problem for many golf courses and sports pitches. Secondly, you need a good irrigation system that can apply water evenly across the surface. Even the most perfect state of the art irrigation system will over-water and under-water in certain areas and many systems up and down the country are old and inefficient.
Course Managers/Head Groundsman will know the frustration of greens/pitches soaking wet and soft in one area and dry and wilting in others due to a dodgy watering system (if you even have one!).
How ‘Wet’ Should Soil Be?
What is the ideal soil moisture level? There’s no single answer to that. It changes with soil types, grass species and whether it’s a golf green, golf tee, football pitch or cricket wicket. STRI recommend 15-30% for golf greens which is a pretty wide range. Personally in my greenkeeping days, I liked my sand-modified soil-based parkland greens around 18-20%, some Golf Course Managers are happy at 25-30%, I know many Championship Links venues try to get it around 10% for competitions and the professional level football stadiums I visit range from high teens/low 20’s up to early 30’s.
Some golf greens will be kept as dry as possible that keeps the grass alive in order to promote the growth of bents and fescues and push out or deter Poa (Fescue and Bent are much more tolerant of drought than Poa). Some golf clubs will ‘over-water’ to make their greens look healthy and to keep golfers happy who like to thin a rescue wood out of the semi-rough and still get a bit of backspin. The punishment for this will be thatch development and increased disease and the days of being able to paper over the cracks with this style of management with a full fungicide programme may be coming to an end.
What is Plant Stress?
Seaweed has been used for many years in turf management and research is starting to understand how it benefits plants in stress situations. But what actually happens to the plant when it starts to be affected by stress?
When growing normally, molecular oxygen will take on electrons during metabolic processes such as photosynthesis, combining to form harmless by-products such as water. Under stress-induced conditions such as drought, this oxygen-accepting electron process struggles to function efficiently, resulting in the production of a number of alternative oxygen species known as ‘free radicals’.
These free radicals will cause major damage to cell walls and their contents and lead to a breakdown in the production and stability of pigment (loss of colour) and if stress conditions continue, ultimately cell and plant death. Plants produce anti-oxidants that react with free radicals to prevent these damaging effects. Under continued stress conditions plants struggle to produce enough anti-oxidants to balance out the increase in free radicals. The plant effectively tries to go into dormancy to protect itself from increasing stress.
This is the point where sports turf performance really starts to decline. An increase in the plant hormone ethylene occurs, which is a signal to certain plant cells to shut down and die so more energy is concentrated on essential parts of the plant only. Once the hormone ethylene is produced in greater quantities production of other hormones, notably cytokinins and auxins, are reduced. Seaweed and humic acids are rich in cytokinins and auxins and re-dress the balance of these hormones in the plant and enable the production of anti-oxidants to increase the plants ability to combat damaging free radicals. Quality biostimulants effectively help the plant defeat stress using their own systems and maintain turf performance at a higher level.
Benefits of Seaweed
Pure Kelp SA is a pure seaweed product (as the name implies!) and forms part of one of the summer stress packages and it is reassuring to know we have scientific research confirming that this will reduce plant stress effects. THE key trigger for anthracnose is lack of nitrogen and it is now known that seaweed extracts will affect plant genes involved in nutrient uptake: – it upregulates the expression of a nitrate transporter gene NRT1.1 that improves nitrogen sensing and auxin transport which results in enhanced root growth and improved nitrogen take up.
Height of cut will have a big effect on drought tolerance. Going down below 3mm on golf greens means the plant can very quickly start to shut down in hot, dry weather. There is much less total water within each plant and, generally speaking, a smaller root mass, so if evapotranspiration (ET) rates are high then a larger percentage of the total moisture in that plant can be lost in a day. (Evapotranspiration is the combined loss of moisture from the plant/soil due to evaporation from soil and surfaces and transpiration via plant leaves.)
Use of Wetting Agents
Don’t forget the value of wetting agents/surfactants in these conditions. The right product for your site will not hold on to excess water in the soil but ensures a more even distribution throughout the rootzone to prevent the combination of wet and dry spots. We have conducted trial work at a Championship Football Stadium over the past few months and the right choice of product has produced daily moisture readings that are significantly more consistent: it holds on to moisture better when the weather is drier and pushes it through quicker when they have had the severe downpours over the last few weeks. Don’t be afraid to contact us for advice on the best surfactant for your site.
If your golf club or any turf area suffers from localised dry spots from sand splash areas around bunkers or other awkward to spray areas, then the granular wetting agents can really help. Some products last longer than many liquid formulations, so it can have a valuable use where spraying is not done regularly such as awkward tees, lawns and bowling greens. It can be applied to localised problem areas such as slopes or high spots/ridges where a blanket spray of the area would be beyond the budget.