Late-season bermudagrass nutrition and cold tolerance ... - GCSAA

081-092 Sept04Techwell 8/17/04 5:19 PM Page 81Late-season bermudagrassnutrition and cold tolerance:Time for a paradigm shift?Instead of applying less nitrogen and more potassium on bermudagrass as fall approaches,perhaps some superintendents should be doing the opposite.E.H. Ervin, Ph.D.; J.M. Goatley Jr., Ph.D.; M.D. Richardson, Ph.D.;and G. Munshaw, Ph.D.RESEARCHSCIENCE FOR THE GOLF COURSEdedicated to enriching the environment of golfAs bermudagrass growth begins to slow inlate summer and early fall, superintendentsoften generously apply potassium while curtailingthe use of nitrogen. Why? Plainly,because turfgrass textbooks say ample potassiumwill improve cold hardiness, whereaslate-season nitrogen may reduce it. Let’sexamine some textbook quotations that supportthis paradigm.In his 1973 volume, “Turfgrass: Scienceand Culture” (2), Beard writes: “Nitrogenstimulates growth causing increased hydrationof the tissues and a decrease in the carbohydratelevel. The result is decreased low temperaturehardiness. The inhibitory effects ofhigh nitrogen nutrition on low temperaturehardiness can result from (a) excessive nitrogenapplications or (b) a late nitrogen applicationmade during the hardening period.KEY pointsMore Info: www.gcsaa.orgFigure 1. The color response of a Tifgreen bermudagrass putting green on Oct. 19, one week after ammonium nitratewas applied at 2.0 pounds nitrogen/1,000 square feet (97.6 kilograms/hectare).Photo courtesy of M. GoatleySome prominent turfgrass textbookssupport the notion that fertilizingbermudagrass in the fall can lead to aloss of cold hardiness.Recent research has shown thatbermudagrass fertilized in late summerand early fall often remains greenlonger without losing its cold hardiness.High soil-test levels of potassium asopposed to moderate or sufficient soiltestlevels do not improve cold hardinessin bermudagrass.Be cautious in applying late-seasonnitrogen to avoid the risks of nitrateleaching and spring dead spot.Adequate levels of potassium and phosphorusare important in ensuring low temperaturehardiness . . . It is not just a low nitrogen levelor a high potassium level that is critical inmaximum low temperature hardiness but theinterrelationship between the two nutrients”(p. 239-240).Beard supports these statements by citingtwo studies about Kentucky bluegrass coldhardiness (3,4) and one about commonCoastal bermudagrass (1). The quotationabove appears to have led to similar views inmany of the more recent turfgrass textbooks.In “Best Golf Course ManagementPractices,” McCarty writes: “Late fall nitrogenfertilization promotes succulent or ‘lush’ turfgrassgrowth and reduced root carbohydrateformation by forcing shoot growth over thatof root or rhizome growth” (8).In “Turfgrass Management,” Turgeonwrites: “[L]ate summer and early fall fertilizationof warm-season turfgrasses mayreduce their cold-hardiness and result in somewinterkill where cold winters are encountered”(14).Bermudagrass growthConsiderable recent research has providedextensive empirical evidence that does notsupport the statements in these references.September 2004GCM 81

081-092 Sept04Techwell 8/17/04 5:20 PM Page 82RESEARCHBefore we review this evidence, let’s frame thediscussion by reviewing bermudagrass growthduring the hardening period. Specifically, is itreasonable to think that lush shoot growthcan be promoted on transition zonebermudagrass (Cynodon species) once hardeningtemperatures are occurring? What arethese temperatures?When average daytime temperatures ([dailylow + daily high]/2) drop below 60 F (15.6 C),bermudagrass growth slows dramatically, withleaf discoloration (and the onset of dormancy)occurring in earnest once they drop below50 F (10 C) (5). In an upper transition zone climatesuch as in Roanoke, Va., average temperaturesof 60 F (15.6 C) are reached aroundSept. 30, with the first hard frost occurringabout Oct. 15, leading to almost complete leaftissue browning by early November.Thus, this mid-September to early-November hardening period is when textbooksadvise greatly reducing or actuallyeliminating the use of nitrogen. How doesbermudagrass respond to the lower temperaturesand shorter days of this period? Untilone or two hard frosts have occurred, thebermudagrass is still green and photosynthesizing,but little leaf elongation is occurring.But where is this photosynthate going?We contend that, as in cool-season grassesin late fall, most photosynthate is goingtoward root, stolon and rhizome growth orstorage. During this hardening period, itwould be almost impossible to promote alarge flush of succulent growth with an applicationof soluble nitrogen fertilizer. Try it, andthe result is most often a greening responsewithout significant vertical growth.If the turf remains green later in the fall,the results should be greater photosynthesisand net energy gain. Loss of this re-greenedleaf tissue to a hard frost most likely has littleconsequence for overwintering becausethe status of the stem tissue (crowns, stolonsand rhizomes) determines winter survival.Based on this reasoning, we hypothesizethat applying nitrogen late in the season inthe transition zone on bermudagrass that hasnot been overseeded will:• enhance color retention before frost events• encourage re-greening after mild frostevents• have no effect on cold hardiness• promote early spring green-upBelow we present supporting data fromfour late-season nitrogen studies conductedover the last 15 years.Study 1: Schmidt and ChalmersAt the Virginia Tech Turfgrass ResearchCenter in Blacksburg, mature Tifgreenbermudagrass was managed at 0.625 inch(15.88 millimeters) on a silt loam (pH 6.2and moderately high soil-test level of potassiumat 274 pounds/acre [307.1 kilograms/hectare]).[Researchers (5) havepresented the following potassium sufficiencyrankings: very low = 0-60 pounds/acre (0-67.3 kilograms/hectare); low = 61-120pounds/acre (67.3-134.5 kilograms/hectare);moderate = 121-280 pounds/acre (135.6-313.8 kilograms/hectare); high = greater than280 pounds/acre (313.8 kilograms/hectare).]The bermudagrass was treated with 0, 2.5pounds or 5.0 pounds nitrogen/1,000 squarefeet (0, 122.1 or 244.1 kilograms/hectare)from urea in split applications on Aug. 30and Sept. 27 of 1989, 1990 and 1991.The results in Table 1 clearly show thatlate-summer through early-fall nitrogenapplications to Tifgreen bermudagrass, amoderately winter-hardy cultivar, providedextended color in fall 1989. Similar resultswere found in 1990 and 1991. At no timeduring the three years of the study wasbermudagrass recovery from dormancyimpaired because of late-season nitrogen(13). This was true even though conditionsin December 1989 were unusually cold,with a record low for Dec. 23 of -10 F(-23.3 C). Temperatures were normal inBlacksburg, Va., during the winters of 1990-1991 and 1991-1992.Study 2: Goatley et al.Mature Tifgreen bermudagrass, managedat 0.18 inch (4.57 millimeters) on aloam (pH 6.0 and a high soil-test level ofpotassium of 300 pounds/acre [336.3kilograms/hectare]) in Starkville, Miss.,received 0, 1.0 or 2.0 pounds nitrogen/1,000 square feet (0, 48.8 or 97.6 kilograms/hectare)from ammonium nitrateand 0, 0.8 or 2.0 pounds potassium (0, 39.1or 97.6 kilograms/hectare) from potassiumchloride (in all combinations) during the secondweek of October in 1989, 1990 and1991. On this soil, which contained sufficientsoil-available potassium (5), fertilizingwith potassium did not measurably changebermudagrass color or levels of total nonstructuralcarbohydrate (TNC) at any timefor any level.LATE NITROGEN ON TIFGREENNitrogen application rate 1989 color rating (9 = darkest) % greenhouse regrowth*Pounds/1,000 sq. ft. Kilograms/hectare Oct. 3 Oct. 16 Oct. 23 Feb. 15, 1990Control (no nitrogen applied) 5.8 b 4.4 b 4.3 c 28.6 a2.5 122.1 7.2 a 5.3 a 4.9 b 24.7 a5.0 244.1 7.3 a 5.3 a 6.3 a 26.1 a*Percentage of greenhouse regrowth of dormant plugs that are subjected to controlled freezing to 23 F (-5 C). Plugs were sampled and frozen on Jan. 25, 1989.Table 1. Influence of 1989 late-summer and early-fall applications of nitrogen on fall color and cold hardiness of Tifgreen bermudagrass.Values followed by the same letters within a column are not significantly different from each other.82 GCMSeptember 2004

081-092 Sept04Techwell 8/17/04 5:20 PM Page 83RESEARCHThe only measurable response was a linearincrease in concentrations of leaf-tissuepotassium as potassium applications increasedfrom 0 to 2.0 pounds/1,000 square feet (0 to97.6 kilograms/hectare). However, the nitrogenprovided longer fall color retention(Figure 1) and quicker spring green-upwithout reducing rhizome TNC levels inwinter or early spring (Table 2). The dataindicate that the 1-pound rate was sufficientfor enhanced color retention and green-up.No winterkill occurred in the field during thethree years of the study, even following anunusually cold spell in late December 1989.(7). The winters of 1990-1991 and 1991-1992 were normal.Study 3: RichardsonIn the third study, mature Tifwaybermudagrass was managed at 0.5 inch(12.7 millimeters) on a silt loam (pH 6.4,with phosphorus and potassium levelsmaintained at sufficiency levels according tosoil tests) at the University of ArkansasResearch and Extension Center in Fayetteville(1998-1999) and at Springdale (Ark.)Country Club (1999-2000). Both sitesreceived either no nitrogen after Aug. 1 or 1.0pound nitrogen/1,000 square feet (48.8 kilograms/hectare)(from urea) on Aug. 15 and onCOLOR AND RHIZOME TNC, 1991-1992Nitrogen rateRating date Control (no nitrogen applied) 1 pound/1,000 sq. ft. 2 pounds/1,000 sq. ft.(48.8 kilograms/hectare) (97.6 kilograms/hectare)ColorColor rating (9 = darkest)Oct. 17, 1991 5.3 6.2* 6.3*Oct. 31, 1991 5.8 7.1* 7.3*April 6, 1992 6.3 6.9* 6.8*RhizomesRhizome TNC (grams/kilogram)December 1991 14.2 14.4 13.2March 1992 14.6 14.2 13.6*Significantly different from the control.Table 2. Tifgreen bermudagrass color ratings and rhizome total nonstructural carbohydrate (TNC) levels during the 1991-1992 winter period.COLOR AND FREEZING TOLERANCENitrogen application datesTurf color (9 = darkest)September October November AprilNone after Aug. 1 (control) 6.2 5.8 4.5 4.5Aug. 15 and Sept. 15 6.8 6.3 6.1* 5.7*% rhizome survival following freezing, 199928 F (-2.2 C) 25 F (-3.9 C) 21 F (-6.1 C) 18 F (-7.8 C)None after Aug. 1 (control) 53.6 49.7 42.2 0.0Aug. 15 and Sept. 15 53.4 44.4 38.5 0.0*Significantly different from the control.Table 3. Fall and spring color ratings of Tifway bermudagrass and rhizome freezing tolerance as affected by late-summer nitrogen applications.September 2004GCM 83

081-092 Sept04Techwell 8/17/04 5:21 PM Page 84RESEARCHSept. 15. Both winters of the study (1998-1999 and 1999-2000) were mild for theregion, and no winter injury was observed inany of the plots. Thus, controlled freezing testswere used to determine the low temperaturesurvival of field-harvested rhizomes. Additionallate-summer nitrogen enhanced fall colorretention and spring green-up without affectingcold hardiness, as determined by rhizomesurvival after controlled freezing (11) (Table 3).Study 4: Munshaw and ErvinThis study used two-year-old Tifwaybermudagrass managed at 0.63 inch (16.0millimeters) on a silt loam (pH 6.8 andmedium-low soil-test levels of potassium of120 pounds/acre [134.5 kilograms/hectare])at the Virginia Tech Turfgrass ResearchCenter in Blacksburg. All plots received 1.0pound nitrogen/1,000 square feet (48.8kilograms/hectare) monthly from Maythrough July in 2001 and 2002. BeginningAug. 15 of each year, the nitrogen treatmentreceived additional nitrogen from ammoniumnitrate at 1.0 pound nitrogen/1,000square feet (48.8 kilograms/hectare) everythree weeks, with the last application aboutOct. 17. Therefore, annual nitrogen rates forthe control were 4.0 pounds/1,000 squarefeet (195.3 kilograms/hectare), and the nitrogentreatments received 7.0 pounds/1,000square feet (341.8 kilograms/hectare).The data show that the extra nitrogen didnot provide a large late-season color benefit.We may have applied the nitrogen, seen aquick greening response (although data werenot collected) and then had a frost before ourscheduled visual rating date, thereby losingthe data that showed the benefit. However,the most important point is that additionallate-season nitrogen enhanced Novembercolor retention without affecting cold hardiness,as determined by rhizome survival aftercontrolled freezing (Table 4) (11).The 2001-2002 winter was normal, andno field winterkill was noted. The 2002-2003winter was colder than normal, and Tifwaywinterkill of approximately 30% was noted.However, winterkill percentage was the sameregardless of late-season nitrogen rate.Study 5: Miller and DickensThe second standard practice of the lateseasonbermudagrass management scenario isto apply potassium liberally with the intentionof promoting plants that are more coldhardy.Researchers at Auburn Universityconducted a study to answer this question:How much potassium is enough?Mature Tifway bermudagrass, managed at0.5 inch (12.7 millimeters) on a loamy sand(pH 6.0) at the Auburn University TurfgrassResearch Center in Auburn, Ala., was used inthis 1992-1994 study. The objective was toevaluate the effects of high annual potassiumapplication rates on cold resistance inbermudagrass (10). Initial soil-available potassiumwas very low at 36.0 pounds/acre (40.4kilograms/hectare).Potassium was applied from April throughOctober to cover a low to very high range ofmonthly rates: 0, 0.25, 0.5, 1.0, 2.0 and 4.0pounds potassium/1,000 square feet (0,12.2, 24.4, 48.8, 97.6 and 195.3 kilograms/hectare).Only the three highest potassiumrates were chosen for determination ofcold resistance. The most significant resultsare outlined below.• At the end of the study (September1994), soil-test potassium levels wereapproximately 80 (low), 115 (low) and160 (moderate) pounds/acre (89.7, 128.9and 179.3 kilograms/hectare) for the 1.0,2.0 and 4.0 pounds potassium/1,000square feet/month (0, 48.8, 97.6 and195.3 kilograms/hectare/month) treatments,respectively.• The amount of potassium in bermudagrassleaf tissue increased until the 1.0 poundpotassium/1,000 square feet/month (97.6kilograms/hectare) level was reached. Atthis monthly potassium level and above,leaf-tissue potassium flat-lined at approx-COLOR AND FREEZING TOLERANCE, 2001-2002Nitrogen applicationTurf color (9 = darkest)August September October NovemberControl 8.2 8.0 7.0 3.6Late-season 8.2 7.9 7.2 4.3*% rhizome survival following freezing †39 F (3.9 C) 27 F (-2.8 C) 23 F (-5 C) 19 F (-7.2 C)Control 57.5 23.3 8.6 0.0Late-season 50.7 23.2 6.9 0.7*Significantly different from the control.†The percenages for rhizome survival following freezing are the averages of the data from Jan. 2 and Feb. 3, 2002.Table 4. Color ratings of Tifway bermudagrass and rhizome freezing tolerance as affected by late-summer and fall nitrogen applications averaged over 2001 and 2002.84 GCMSeptember 2004

081-092 Sept04Techwell 8/17/04 5:21 PM Page 85RESEARCHimately 1.1%. This indicates that plantuptake of potassium was saturatedat monthly application rates of 1.0 poundor above.• Greenhouse, lab and field observationsindicated that applied potassium had noeffect on cold resistance.ConclusionsA 1971 trial (6) demonstrated that adequate,balanced ratios of nitrogen and potassiumwere more effective in promotingwinter survival of two bermudagrass cultivarsthan either high-nitrogen or high-potassiumfertilization programs. All of the studies summarizedin this paper, in which potassiumwas maintained at approximately moderatesoil-test sufficiency levels throughout theexperiments, support these earlier reports andsuggest that continuing nitrogen fertilizationinto the later months of the growing seasondoes not significantly affect freeze toleranceof bermudagrass, as long as other macronutrientssuch as potassium are not limiting.The last 15 years of research in the uppersoutheast and the transition zone of theUnited States indicate the possibility of aparadigm shift in our late-season nutrientmanagement of bermudagrass. Keepingbermudagrass green later in the fall has notresulted in a loss of cold-hardiness.We have two recommendations, withthree added precautions.If soil tests indicate potassium levels are inthe moderate to high range (121-400pounds/acre [135.6-448.3 kilograms/hectare), high rates of potassium do not needto be applied late in the season to improvebermudagrass cold hardiness.Applications of soluble nitrogen at 0.5 to1 pound nitrogen/1,000 square feet (24.4-48.8 kilograms/hectare) at two- to four-weekintervals, until hard frosts have resulted incomplete dormancy, will prolong fall colorretention and may enhance spring green-up(Figure 2).• Precaution 1. Apply lower rates of nitrogenon sandy soils where the risk of nitrateleaching is greater.• Precaution 2. Prove the benefits of late-seasonnitrogen to yourself and your constituentson a small scale beforeimplementing on the whole course.Experiment with rates and timings foryour location on one fairway or nurseryarea for at least one year.• Precaution 3. Be especially skeptical whenFigure 2. Late-October color resonses of Tifway bermudagrass three weeks after treatments were applied. From top tobottom, the treatments were: no nitrogen treatment, ammonium nitrate, IBDU (Isobutylidene Diurea, a slow-release nitrogensource) and methylene urea.considering the implementation of lateseasonnitrogen on areas of the course historicallyprone to spring dead spot, as someresearch and experience has indicatedhigher late-season nitrogen causes greaterincidence of spring dead spot (9).Literature cited1. Adams, W.E., and M. Twersky. 1959. Effect of soilfertility on winter killing of Coastal bermudagrass.Agronomy Journal 52:325-326.2. Beard, J.B. 1973. Turfgrass: Science and culture.Prentice-Hall, Englewood Cliffs, N.J.3. Beard, J.B., and P.K. Rieke. 1966. The influence ofnitrogen, potassium and cutting height on the lowtemperature survival of grasses. AgronomyAbstracts 58:34.4. Carroll, J.C., and F.A. Welton. 1939. Effect of heavyand late applications of nitrogenous fertilizer on thecold resistance of Kentucky bluegrass. PlantPhysiology 14:297-308.5. Carrow, R.N., D.V. Waddington and P.E. Rieke. 2001.Turfgrass soil fertility and chemical problems. AnnArbor Press, Chelsea, Mich.6. Gilbert, W.B., and D.L. Davis. 1971. Influence of fertilityratios on winter hardiness of bermudagrass.Agronomy Journal 63:591-593.7. Goatley, J.M. Jr., V. Maddox, D.J. Lang and K.K.Crouse. 1994. ‘Tifgreen’ bermudagrass response tolate-season application of nitrogen and potassium.Agronomy Journal 86:7-10.8. McCarty, L.B. 2001. Best golf course managementpractices. Prentice-Hall, Upper Saddle River, N.J.9. McCarty, L.B., L.T. Lucas and J.M. DiPaola. 1992.Spring dead spot occurrence in bermudagrass followingfungicide and nutrient applications.HortScience 27(10):1092-1093.10. Miller, G.L., and R. Dickens. 1996. Potassium fertilizationrelated to cold resistance in bermudagrass.Crop Science 36:1290-1295.11. Munshaw, G., and E.H. Ervin. 2004. Nutritional andPGR effects on lipid unsaturation, osmoregulantcontent, and relation to bermudagrass cold hardiness.Ph.D. dissertation, Virginia PolytechnicInstitute and State University: ETD-01162004-171301.12. Richardson, M.D. 2002.Turf quality and freezing toleranceof ‘Tifway’ bermudagrass as affected bylate-season nitrogen and trinexapac-ethyl. CropScience 42:1621-1626.13. Schmidt, R.E., and D.R. Chalmers. 1993. Late summerto early fall application of fertilizer and biostimulantson bermudagrass. International TurfgrassSociety Research Journal 7:715-721.14. Turgeon, A.J. 2002. Turfgrass management, 6th ed.Prentice-Hall, Upper Saddle River, N.J.E.H. Ervin, Ph.D. (ervin@vt.edu), is an assistant professorand J.M. Goatley Jr., Ph.D., is a turfgrass specialistin the department of crop and environmental scienceat Virginia Polytechnic Institute and State University,Blacksburg; M.D. Richardson, Ph.D., is an associateprofessor in the department of horticulture, Universityof Arkansas, Fayetteville; and G. Munshaw, Ph.D., is anassistant professor in the department of plant and soilsciences, Mississippi State University, Starksville.September 2004GCM 85