Golf Greens Irrigation

Irrigation can be easily overapplied and is a major contributory factor in the gradual deterioration of golf greens, creating ‘target golf’, which does not provide the challenge which can be gained from well managed golf greens. The finer desirable grasses will manage well on low amounts of water, but this must be supported by a good depth of root growth and other correct maintenance practices, including not mowing too short, otherwise the sward will suffer.

Irrigation management is a much-underused resource (primarily because it is over applied) in the drive to maintain dry and firm, good performing, golf greens, with much reduced pest, disease and weed attacks and infestations.

As spring approaches and progresses slowly into summer the soil profile will typically start to dry. If rooting depth is poor and very dry conditions are allowed to develop for a prolonged period of time in the surface 50mm, or so, then a moisture break can typically occur which creates dry patch conditions, making the soil extremely difficult to rewet.

The use of a wetting agent before this situation arises is typically undertaken, helping to ensure adequate soil moisture is available to a plant. It is important that any wetting agent is thoroughly watered in to prevent scorching of the grass but also to ensure the material is spread out to encompass the entire rootzone area for uniform coverage.

Applications vary depending upon the product, but if monthly applications are considered from March onwards over the summer period then this would equate to 7 applications. If a product required about 3 litres per application for a bowling green, then this would equate to 2 x 10litre bottles. The use of wetting agents, where required, should be considered a short to medium term practice, with the aim being to adjust maintenance practices to encourage a situation where they are no longer needed. Where limited use of wetting agent is desirable, then two applications possibly in May and then July might be a consideration.

The finer desirable grasses will manage well on low amounts of water, but this must be supported by a good depth of root growth and other correct maintenance practices, otherwise the sward will suffer. Watering to a good depth (this will depend upon how much rootzone is present) and then let the roots explore for moisture in the lower profile as the surface gradual dries through evapotranspiration. The actual amount of water lost through evapotranspiration is less than the potential (theoretical) calculated rate.

Where water availability is not an issue, for example, probably during April and certain periods during the summer, when rainfall is plentiful then the theoretical potential evapotranspiration is most likely to be at or near the actual rate because water supply is not limiting water usage. However, as it becomes depleted and scarcer the plant will start to adapt to these changing, more stressful, conditions.

There is clearly a delicate balance to be had to ensure playing surfaces continue to perform well, but at the same time to not apply water unnecessarily. Using the natural drying of a rootzone and drier conditions to advantage can help to reduce the need for fertilisers, plant growth regulators and fungicide applications in particular. The more water that is applied, the more of everything else will essentially be needed, resulting, for example, in increased mowing and additional verticutting as well as increasing the risk of disease attack.

If a sward can be maintained in a dry and firm condition, then the height of cut can often be relaxed slightly, to maybe 6mm, and still produce smooth putts, as well as true and fast surfaces during the main growing season. A similar smooth surface which plays true and fast might also be achieved where a sward is well-watered on a regular basis, mown very tightly at 3.5mm, with plant growth regulator applied to reduce annual meadow grass seed head production, regular feeding and with more frequent mowing. The question would be when considering these two examples might be either, ‘Which one is best’? and/or ‘Which one contributes most to the sustainability of our course’?

The importance of good root growth cannot be overemphasised when it comes to effective irrigation practices and water consumption. For example:

• if a green typically has a sandy rootzone of just 100mm (although in practice for many greens this will be much greater) it may potentially have available water at 12% within the profile (meaning 12mm of water will be retained within the soil if at field capacity).

• the roots will ideally explore to all of this depth.

• water usage for a strong growing sward is estimated as a potential evapotranspiration rate of 25mm per week, during the summer period. As available water becomes harder to extract from the soil the grass plant will actually start to reduce its need, so this figure is often quoted where continued, relatively strong, growth is assumed to be maintained, but this is not necessarily in the best interest of the production of a fine turfgrass surface during the summer period – some element of natural stress from water restriction can produce a more resilient sward. With reduced need for water due to adaptation to drying conditions the actual evapotranspiration rate is reduced.

• the supply of water to the grass sward, from within the soil, in the above example would last about half a week, meaning irrigation would be needed (assuming no rainfall occurs) about twice a week. All 12mm would not be used up as usage would occur at a decreasing rate.

• if, however, the root depth was only 50mm, then available water would typically be down to just 6mm, meaning irrigation might be required on about four times per week.

• more frequent irrigation can lose some of the benefits of intervals of rainfall which would otherwise top-up the available water for a deeper-rooted green but would be wasted on shallow rooted greens.

Where the golf greens have been overseeded, then the aim of watering will be to aid germination and to prevent newly germinated seed from rapidly drying out, yet at the same time encouraging roots to gradually explore deeper into the rootzone. A lighter watering will be required than on an established green because the roots are shallow and just developing.

The edges of greens which adjoin bunkers as well as the tops of slope and slopes within greens can dry out more rapidly than the main flatter body of a green. Hand watering, which can be quite time consuming but which can provide a much more focused and appropriate degree of application for these types of localised areas, will usually be needed to complement any automatic irrigation programme if a uniform sward surface is to be achieved.

Insufficient watering during prolonged dry periods can result in the green drying out, resulting in the disorder of localised dry patch, which can be especially pronounced where thatch is also a problem. To reduce the chance of this happening it is important to manage irrigation practices correctly and this includes ensuring the system is properly maintained and serviced, which includes decommissioning over the winter and then recommissioning in the spring.

A different disorder, black layer, can often result from excessive irrigation, especially on sand-dominant greens, and also where thatch and compaction have become a problem, resulting in poorly drained profiles. Monitoring the pH of irrigation water is a good practice as this can help to identify potential problems where the water has a high pH (especially pH 7.5 or higher) as this will encourage black layer, which is favoured by more alkaline conditions, as well encourage many turfgrass diseases, in particular take-all patch.