New research shows that cool-season varieties can thrive with less water

Dr. Brian Horgan discusses the sustainability of turfgrasses with reduced inputs.
Photos courtesy of Dr. Brian Horgan.

Turfgrass research is providing new information that indicates cool-season turfgrass can be maintained at peak performance with less irrigation than previously thought necessary. Water use has long been a major concern in arid climates, and reducing water use a major focus for turf managers due to the availability and cost of irrigation water. Increased focus is now being placed on water availability and runoff water that can carry chemical residue. Interest in stormwater management is increasing, and various municipal, state and federal regulatory requirements have been mandated.

In response to the concern about availability, cost and regulatory requirements, researchers have looked at various ways to reduce water use in growing turfgrass while maintaining the quality of the turfgrass. Studies at the University of Minnesota (UMN) indicate that irrigation amounts can be reduced while keeping cool-season turfgrass performing well.

Dr. Brian Horgan is an associate professor in turfgrass management with the UMN department of horticulture. He has been at UMN since 2001, and his research is directed primarily toward finding grasses that can be sustained with fewer inputs of every type.

Horgan said, “Water use in turfgrass culture is under intense scrutiny and has been identified by regulatory agencies and environmental groups as a focal point for reducing consumption of water. In addition to concerns over the scarcity of water supplies, the increasing monetary cost of water, electricity and irrigation system components are factors in the push for conserving water resources.”

Irrigation input was measured by volumetric jars.

Although the studies were conducted primarily for water conservation, Horgan noted, “Because nutrient and pesticide fate follow the water, using less irrigation water may reduce off-site movement.” Minnesota is among the states that have recently issued mandates restricting the use of fertilizers containing phosphorus.

These studies determined that turfgrass can perform well with substantially less water than is normally applied, and work continues to further define cool-season turfgrass cultivars that will perform best with the fewest inputs.

Overwatering issues

Horgan noted that turfgrass is sustainable in many settings only with extensive inputs. He is interested in finding ways that turfgrass can survive in more settings without the high number of inputs. Reducing inputs will help turfgrass managers keep overall management costs down, as well as help cut back on any environmental impacts that may occur from runoff associated with turfgrass.

Horgan said that homeowners and professional turfgrass managers frequently use much more water than required for the designated function of the turfgrass. He said, “Homeowners are not versed enough in irrigation controllers and turfgrass irrigation needs. Therefore, they set their systems in the spring and turn them off in the fall. During this growing season, they water the same amount each week regardless of need.”

While professional turfgrass managers usually have a thorough understanding of irrigation, Horgan feels that they tend to overwater as well. He said, “Professional turfgrass managers tend to irrigate to the least common denominator. In other words, they irrigate for the weak, which keeps the weak turf weak, and overwater the better performing turf. This cycle continues until all species and cultivars are used to higher water inputs.”

Evapotranspiration (ET) is an empirical number of water loss. Although ET is discussed more in arid climates, such as the Southwest, it is an essential part of water management in any location. Horgan said, “In the Midwest, we tend to see ET losses exceed rainwater inputs during the summer months. This is when supplemental irrigation is required. Unfortunately, irrigation systems are turned on too early in the spring, which affects root growth and predisposes plants to summer stress.”

Ongoing research has been conducted at the UMN Research Outreach and Education Center at the St. Paul campus. The project was designed in the following manner.

Six 5-by-5-foot plots were set up with quarter-circle spray heads on each corner and an individual station at a satellite controller. A series of four 10-day experiments were conducted on these plots with ET replaced at 100 percent and at 80 percent. Turf quality was measured using various sensors, and root development was assessed. Rainfall was prevented from reaching the plots by a polypropylene rain cover, which could be installed within five minutes, so that only irrigation water provided moisture to the turfgrass.

Horgan said, “There were no statistical differences in turf quality that received different irrigation treatments in any experiment, suggesting that replacement of 80 percent of actual ET is sufficient. Turfgrasses in the Midwest can be well managed with about 80 percent of ET, or 0.8. We also know that during the spring and fall this number is even lower, 40 to 60 percent; in the middle of summer, this number may be closer to 90 to 100 percent.”

A permanent rain shelter now prevents rainfall from reaching turfgrass at the test plots.

Horgan emphasized that the results indicate that irrigation systems cannot be set once during the year without overwatering or underwatering turf. He said, “Different times of the year require different amounts of water.”

The Minnesota Golf Course Superintendents Association and Toro Corp. provided primary funding for the studies.

Looking ahead

An NTEP (National Turfgrass Evaluation Program) study begun in 2009 will focus on evaluating 25 cool-season species to determine which ones can be sustained with the fewest inputs. Data from this study will be collected and evaluated through 2011.

A permanent rain shelter has been constructed at the test plot site. Horgan said, “The rain shelter allows us to keep rainfall off the turfgrass so we can irrigate in the amount that the plant needs to determine water use rates by species and cultivars.

“This is a commercially available trial of cool-season grasses on which we will impose acute drought, and determine what lives following extended drought periods. It is a two-year study being conducted through NTEP at several sites across the country where cool-season grasses are grown,” Horgan said.

Horgan can be contacted via email at bphorgan@umn.edu for more information on the completed studies and the recently instituted NTEP study on the performance of different turfgrass species.

Nancy Riggs is a freelance writer and has been covering the green industry for Turf for almost 20 years. She resides in Mt. Zion, Ill.