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Cal Poly Pomona Examines Deficit Irrigation

Bermudagrass can be watered at a deficit, a team of researchers found.


By studying Bermudagrass, a research team at Cal Poly Pomona determined that during the warm season, the turf can maintain an acceptable look and quality while being irrigated at a deficit.

Severe drought conditions across California led the state legislature to pass laws requiring a 20 percent reduction in urban water use by the end of 2020. Turfgrass researchers at Cal Poly Pomona saw this as an opportunity to study deficit irrigation, as their research indicates landscape water use accounts for about 30 - 50 percent of total urban water use, including at parks, on golf courses, and in other public spaces. (However, a study done by Dennis Pittenger calculated that "Landscape water use in California accounts for only 9 percent of the total statewide developed water use." Read more about this at

Deficit irrigation is the practice of irrigating below optimal levels to allow soil and turfgrass tissue to gradually dry during the summer. The process helps conserve water, maintain water budgets, save on operating costs and more.

Bermudagrass was the turf of choice, as it is frequently used on golf courses, sports fields, lawns and parks. The study was conducted over the course of two summers with twelve 10'x10' plots of GN-1 hybrid Bermudagrass randomly selected to be irrigated weekly at one of three optimization levels: 100 percent, 75 percent, or 50 percent.

The results were ranked on quality or color on a scale from 1 to 9, where 1 is brown/dead, 5 is the minimally acceptable quality, 6 is acceptable, and 9 is the highest quality.

During both years of the study, the overall average visual turfgrass quality and color for the 100 and 75 percent optimal treatments were ranked at 6.0 or greater. The 50 percent optimal treatment was not lower than 5.7, though the results from the second study would have been rated lower if it had not been terminated early due to unseasonal rainfall.

These results indicate that 75 to 50 percent optimal irrigation can be used during the warm season to maintain minimum acceptable Bermudagrass quality and color, a decrease from what is typically used across Southern California. Robert Green, one of the researchers on the study, emphasized that "You've got to go with Bermudagrass, not cool season grass like tall fescue" when using deficit irrigation. "Cool season grasses will just turn brown," he said.

The research was conducted by R. Green, E.R. McDonough, A. Moss, K. Parkins, R. Kumar, E. Vis, and V. Mellano of the Plant Science department at Cal Poly Pomona. It was supported by a California State University Agricultural Research Institute grant.

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August 24, 2019, 2:33 pm PDT

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