Irrigation distribution uniformity (DU) measures how evenly water is applied across an irrigated area. Careful head spacing with consistent flow and pressure are key factors that help to deliver good DU. A well-designed irrigation system can deliver greater than 80% DU when wind speed is less than 5 mph. For decades, golf course superintendents have strived to optimize DU through leveling and raising sprinkler heads, replacing nozzles and changing system pressure, among other strategies. These measures have been reported to deliver more-efficient water use with fewer wet and dry areas. But does a high DU really result in consistent moisture across tees, fairways, roughs and putting greens?
Years of performing irrigation water audits and comparing that data to soil moisture consistency, which we can call moisture uniformity (MU), has shown me that DU and MU are not always related. For example, courses that have recently installed new irrigation systems – that theoretically have very high DU – spend several years adjusting run times on hundreds (if not thousands) of sprinklers to decrease wet and dry areas in pursuit of improved soil moisture consistency. In fact, there are plenty of instances where we have seen that the fairways with the best MU do not have the best DU. Why is this? It is because there are so many factors in the field that influence MU – e.g., wind, sun exposure, slope, soil compaction, variable surface organic matter, shade patterns, soil textural changes, soil depth, soil and water chemistry, and turf height of cut.
What can superintendents do to improve what matters most to turf quality and playability – adequate but not excessive soil moisture across playing areas? Running an irrigation audit can identify where problems exist, and conducting practices like raising and leveling sprinklers and replacing worn nozzles will improve DU. But the focus should be on optimizing MU, which is more difficult and requires a great deal of time and effort, especially for courses that depend heavily on irrigation for large parts of the year. Below are some actions superintendents can take to improve MU:
- Use hand-held moisture meters or other tools emerging in the marketplace to measure soil moisture and respond as often as daily to these data through sprinkler run time adjustments.
- Program the system for multiple short cycles of irrigation (cycle/soak) to prevent irrigation runoff.
- Apply wetting agents routinely to improve water penetration.
- Regularly utilize spiking, solid- and hollow-tine aeration or slicing machines to decompact soils.
- Utilize hand watering and portable, low-precipitation sprinklers to address isolated dry spots.
Another excellent strategy is to set expectations that firm and fast conditions are the goal, rather than lush and green turf. The USGA is committed to helping golf course superintendents improve MU, reduce water use and produce firmer playing surfaces. Please have a read through the USGA Water Conservation Playbook for more information on optimizing water use.
West Region Agronomists:
Brian Whitlark, regional director, West Region – bwhitlark@usga.org
Ross Niewola, agronomist – rniewola@usga.org
Information on the USGA’s Course Consulting Service
Contact the Green Section Staff