Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.
Issue link: http://gcmdigital.gcsaa.org/i/234582
(up to speed) Irrigation, agronomics and playability Thomas A. Nikolai, Ph.D. email@example.com To summarize, most golfers incorrectly believe that withholding irrigation increases the speed of the green; however, that is only true if the greens are allowed to turn brown. At the other extreme, overwatering leads to soft greens and numerous longterm turfgrass health problems. 130 GOLF COURSE MANAGEMENT 01.14 "Proper turf irrigation is the most diffcult day-to-day agronomic decision the golf course superintendent makes" is the sentence James B. Beard, Ph.D., used to open Chapter 9 of "Turf Management for Golf Courses." That sentence is remarkable in its bluntness considering Dr. Beard is a pre-eminent turfgrass scientist, and one trait all scientists have in common is the desire to leave wiggle room for unexplained variables. Having said that, I have tested Dr. Beard's boldness at numerous conferences by displaying the quote on a PowerPoint slide and asking if anyone disagrees with the statement. To date, no superintendent has ever challenged it. Why is it so hard to make daily decisions about irrigation? Obviously, a lot of factors are involved, but it comes down to the fact that there is no simple method to measure the amount of plant-available water in the root zone. Now I am certain that "Soils" was your favorite class in college, but in case you have forgotten, plant-available water is the amount of water between feld capacity and wilting point and it is different in every soil. Addition of irrigation water above feld capacity results in water being pulled by gravity below the root zone — a saturated condition that wastes water and diminishes playing quality. A study performed by Rod Tocco at Michigan State University yielded results that demonstrate the interaction of irrigation on agronomics and playability. For three years, water was replenished on push-up research putting greens at evapotranspiration (ET) levels of 30 percent, 60 percent or 90 percent. In the frst two years of the study, there were suffcient and timely rain events resulting in no visual difference between any of the irrigation treatments. The third year was hot and dry, and the greens that received 30 percent ET water replenishment displayed signs of localized dry spot. It was not until these greens turned brown from lack of water that there were differences in green speed among irrigation treatments. Does that mean that the amount of irrigation applied on the putting surface has no impact on playability? No, not at all because irrigation directly affects the frmness or shot acceptance of the green. Now let's return to Tocco's results and consider irrigation quantity and its impact on shot acceptance. In the study, greens receiving 90 percent ET water replenishment consistently had the least amount of microbial activity. The lack of microbial activity suggests that those greens had less oxygen in the root zone, which is a result of overwatering. Long-term decreased microbial activity results in thatch accumulation, deeper ball marks, footprinting, scalping and diminished turfgrass quality and customer satisfaction. To summarize, most golfers incorrectly believe that withholding irrigation increases the speed of the green; however, that is only true if the greens are allowed to turn brown. At the other extreme, overwatering leads to soft greens and numerous long-term turfgrass health problems. Defning the proper amount of irrigation to replenish has always been diffcult, but fortunately technology has refned time domain refectometry (TDR), allowing superintendents to make more informed decisions on how much water to replenish on a daily basis. TDR moisture sensors (both hand-held and in ground) are the best tools to date for simple volumetric moisture content results. Given time (one year or so) and good record keeping, a superintendent can estimate the volumetric moisture content that correlates with the wilting point and feld capacity of his root zone(s). When this is accomplished, it becomes possible to irrigate within plant-available water parameters. This saves water, makes turfgrass healthier and improves playing conditions, which increases customer satisfaction. Putting this all together, it seems logical that golfers and superintendents can come together and embrace TDR technology. I don't think Dr. Beard would mind if he had to rewrite his frst sentence from Chapter 9. Thomas A. Nikolai, Ph.D., is the turfgrass academic specialist at Michigan State University in East Lansing, Mich., and a frequent GCSAA educator.