New turf plants require a different approach to irrigation.

As the northern regions of New Zealand install ever increasing areas of warm season (C4) turf across sports fields and golf courses, it’s important to look at how irrigation is managed, what the best practices might be, and what is required for the efficient use of water. Many Turf Managers operate under the misconception that no irrigation is required for warm season turf, while others irrigate small amounts daily to replace moisture lost through Evaporation and Transpiration (ET) – a practice that evolved around the maintenance of shallow-rooted, cool season turf species.

Know Your Site

In order to determine the best approach, you will need to have the following background information about the site you manage: plant species, root depth, development stage, soil type, nutritional status (growth rate), use (wear), temperature and rainfall. All of these factors combine to affect the required quantity and frequency of irrigation. As a Turf Manager, knowledge of your sites will help you weigh the importance of each factor when deciding what level of irrigation would be sufficient, but not excessive, for turf growth. Too much or too little can have detrimental effects, placing turf under stress and resulting in the poor performance of sports surfaces. For example, a couchgrass fairway on a well-structured soil, with low intensity use, will have a lower irrigation requirement (in quantity and frequency) than that of a high-use, sand-carpet, football field due to moisture retention in the soil rooting depth of the turf plant, and the amount of growth required.

Actively Manage

Based on your understanding of each site, develop a tailored, best practice methodology to warm season species irrigation. Rather than thinking of summer as a time to leave the irrigation on automatic daily applications, adopt an active management approach. First ask the following question: What am I trying to achieve with irrigation? Considerations may include:

• Growing the surface out of dormancy or transitioning from a cool season surface, ultimately achieving full coverage.
• Placing cool season grass weeds such as Poa annua under moisture stress to remove them from the sward.
• Reducing moisture in a saturated soil.
• Reducing moisture in a saturated soil.
• Maintaining a quality surface once full turf cover is re-established.
• Decreasing soil moisture coming into winter.

Use the tools available, such as soil moisture meters, weather stations and weather data from government sources such as MetService or NIWA, to maintain a soil water budget, recording rainfalls and daily ET to better schedule the frequency and quantity of irrigation applications. Once you understand the unique site factors and have decided on your objectives, segment the “irrigation season” into the following three periods with a specific goal for each.

Knowing all the factors affecting your site helps you decide how much irrigation is required for sufficient growth.

Proactively manage your turf’s moisture levels with the many tools now available.

The following table summarises strategies for a sand-carpet sports field:

1. Spring (September to November) – apply no irrigation.

In New Zealand, winter rainfall exceeds the ET and, in many cases, the drainage rate of the soil beneath our sports surfaces; consequently the soil becomes saturated. as spring weather patterns can vary from year to year, it’s important to monitor the moisture in the root-zone. Do not irrigate as average air and soil temperatures, Et and moisture loss will all be low. Watering at this time will favour cool season grasses, such as Poa annua or ryegrass, increasing competition and resulting in poor emergence from dormancy.

Also the 2 key drivers of the warm season grass dormancy break are soil temperature and increasing day length. Wet soils (saturated) are slower to warm up than dry soils, so irrigation could potentially slow the dormancy break and re-establishment of full turf cover.

2. Summer (December – February) – apply deficit irrigation.

Historic rainfall averages for Auckland and Northland show that, in a typical year, summer rainfall is sufficient to keep warm season turf alive without irrigation, but with a loss of quality. Irrigation applications during this period should be at a deficit to the recorded Et, to only just maintain turf quality. this results in soil moisture gradually reducing until either a rainfall event occurs or irrigation is applied.

irrigation will be by exception to top- up available soil moisture to a pre-determined level, e.g. 30% volumetric water content. No applications should be made until the soil moisture level reaches wilting point. this can be determined by visual cues, such as colour changes in the turf or the failure of the turf to spring back from foot traffic (known as footprinting), or by using a moisture meter in conjunction with site observations and your soil water budget. Following rainfall, no irrigation should be applied until the same wilting point is reached.

3. Late summer/early autumn (March – April) – apply no irrigation or increase the deficit.

Days are becoming shorter and temperatures are reducing by this time of the year, meaning the Et will be lower. turf plant uptake of water for cooling will also be reduced, leading to a smaller requirement for irrigation. For those managing couchgrass, the falling growth rate will be reducing water requirements also. the recommendation during this period is to turn off the irrigation or alternately, if this cannot be carried out without a reduction in turf quality, further reduce applications so that a greater water deficit is maintained.

Success from Change

The transition to warm season grasses makes sense for warmer regions. long term success will be dependant on correct irrigation. With warm season grasses, irrigation should be by exception rather than a normal daily event. this will minimise water use and increase turf quality.

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