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Summer Deficit Irrigation of Bermudagrass
An In-depth Study

Robert Green, Ph.D., Alan Moss, M.S., Emma Rae McDonough, B.S., Kelly Parkins, M.S., Ramesh Kumar, Ph.D., Eudell Vis, M.S., Valerie Mellano, Ph.D., Grant Klein, M.A.
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Over the course of two summers, plots of bermudagrass were subjected to varying degrees of deficit irrigation to help determine the minimum amount of irrigation needed to maintain acceptable turfgrass quality for the entire warm season, and the minimum amount of irrigation required if lower turfgrass quality is suitable.


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The amount of weekly irrigation for each plot was at a level of 100%, 75% or 50% calculated crop evapotranspiration under standard conditions (ETcrop). Additionally, adjustments were made for the lack of irrigation distribution uniformity (DU) for each plot, causing a small increase in the amounts. These photos taken on the same day show the turf quality at 50% optimal irrigation (top), 75% optimal irrigation (middle) and 100% optimal irrigation.


(Editor's note: The following article was excerpted from a research paper from a team led by Robert Green, Ph.D., the entirety of which can be found at https://tinyurl.com/yd2l2cxy.)

Common bermudagrass and hybrid bermudagrass are very popular turfgrass species in warm climates across the United States. The growth characteristics, overall appearance and adaptation of bermuda-grass to these climates deliver a quality turf that will respond well to a range of maintenance levels.

"Deficit irrigation," the practice of irrigating below optimal conditions helps conserve water, maintain water budgets, save on operating costs and more. Depending on the degree of deficit, bermudagrass can continue to provide sufficient growth and recuperative ability, and acceptable turfgrass quality during the entire warm season. But what is the minimum amount of irrigation needed to maintain acceptable turfgrass quality for the entire warm season, and what is the minimum amount of irrigation required if lower turfgrass quality is suitable?

The Study
The primary objective of this study was to begin to define irrigation requirements for a range of bermudagrass visual quality and color ratings during the warm season. Ratings were on a scale of 1 to 9 (where 1 = dead or brown; 5 = minimally acceptable; 6 = acceptable; and 9 = maximum quality or color). This study was conducted over two summers on 12 well-established GN-1 hybrid bermudagrass plots located at the Center for Turf, Irrigation and Landscape Technology at California State Polytechnic University, Pomona. Plots were located in full sun. Each plot was individually zoned and controlled. Prior to the study, plots were well irrigated to ensure uniform soil water content in the 0- to 12-inch root- zone depth.

The amount of weekly irrigation for each plot was calculated based on several factors including monthly warm-season turfgrass crop coefficient (Kc) developed in Irvine, Calif.; and a treatment level of either 100%, 75% or 50% calculated ETcrop. Additionally, a scheduling multiplier was used to adjust for the lack of irrigation DU for each plot; this caused a small increase in the amount of applied irrigation.



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During both years the study was conducted, overall average visual turfgrass quality and color were greater than 6.0 (acceptable) for the 100% and 75% optimal treatments. Even the 50% optimal treatment was almost always higher than the minimally acceptable rating of 5.0 for both ratings.


Plots were mowed two days per week with a walk-behind reel mower. Height of cut was 0.75 inch (1.9 cm) during the first summer, and 0.87 inch (2.2 cm) during the second one. Plots were fertilized by hand once every two weeks at a nitrogen rate of 0.30 pound/1,000 square feet with a 16N-6P2 O5 -8K2 O granular fertilizer. Visual turfgrass quality and color ratings were taken once every two weeks (nine days after fertilization and two days after mowing).

Results and Conclusions
During both years, overall average visual turfgrass quality and color were greater than 6.0 (acceptable) for the 100% and 75% optimal treatments; the 50% optimal treatment average was not lower than 5.7, which is considerably higher than the minimally acceptable rating of 5.0.

In the study, total salts did not build up appreciably in the 0- to 12- inch soil profile because they were irrigated with a high-quality recycled water. In other situations, salt buildup could be a problem. Fortunately, bermudagrass has been reported to possess the highest salt-tolerance rating.

Results from deficit irrigation will vary because of multiple factors, but these results show that 75% to 50% optimal (63% to 41% ETo, respectively, for the duration of the warm season) can be used while maintaining acceptable to minimally acceptable bermudagrass quality and color. But the 50% optimal treatment could be too low for many situations, such as desert areas.



As seen in LC/DBM magazine, July 2018.






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September 21, 2018, 9:10 pm PDT

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