ponsored

Research f(JU Can Use

The Driving Force!Nitrogen - still an essential building block for sustaining healthy grass.BY MAX SCHLOSSBERG, PH.D.

Striving for perfection begins with promoting healthy grass. Meeting nutritional requirements of the turf is essential and should be the number-one priority ofthe maintenance program.aall the managed turf grass

areas comprising a golfcourse, none is more valued

or intensively maintained than theputting greens. Putting green squarefootage may represent less than 2% ofthe total managed golf course turf, yetputting green quality can make orbreak golfers' perception of playingconditions and, quite possibly, theirentire golfing experience.

Nitrogen (N) fertilization is animportant component of putting greenmanagement. Under optimal growthconditions and intermediate nutrientsufficiency, no other plant essentialnutrient has as powerful an influenceon turf grass canopy color and vigor,root-to-shoot growth relations, anddisease susceptibility. Likewise, whenapplied at rates commensurate withturf grass requirements, traditional fer-tilizer sources that provide any/all plantessential nutrient(s) besides N (except-

30 GREEN SECTION RECORD

ing acids or liming agents) do not havethe profound effect on soil biochemicalactivity as do N fertilizers.

Nitrogen fertilizers include numerousquick-release (QR; e.g. salts, urea) andslow-release forms (SR; e.g. naturalorganics, synthetic organics, coatedprills), each having its pros and cons.The advent of SR technologies may bethe most notable advance in recordedfertilizer history. However, because themost effective SR fertilizers are water-insoluble, coated, or both, most are onlyavailable in granular or sprayable-powderforms. Low-SGN (size guide number)SR granulars are effective putting greenfertilizers that minimize nutrient leach-ing loss and osmotic tissue desiccation,while steadily supplying available nutri-ents to turf grass. Nevertheless, the per-sistent nature of granular SR fertilizersrequires them to either be wateredthrough the canopy, stabilized in theupper soil profile (i.e., applied following

aeration or verticutting procedures) orfree to persist on the putting surface,potentially redirecting golfers' puttsbefore being carried away in the mowerclippings. This is one of several justifi-cations for liquid spray fertilizer appli-cation to putting greens during periodsof peak golfing activity. Other reasonsin support of this application methodare:• Frequent, light fertilizer applicationsoptimize plant health and nutrientrecovery (Bowman, 2003).• Regular spray applications are alreadybeing made to putting greens duringthe peak season.

RESEARCH INVESTIGATIONSThese things considered, independentfield studies were initiated on two putt-ing greens, purposefully cohabited bycreeping bentgrass (Agrostis palustris L.Pennn A4) and annual bluegrass (Poaannua L.). These experiments were

that showed most positive responses onthe TDPU green the previous year.These treatments were: 3 or 5 lbs.N/l,OOO sq. ft./year in one of fourQR-N forms: ammonium nitrate,ammonium sulfate, 9 parts NH4-N:1part N03-N, or 9 parts NH4-N:1 partdicyandiamide-N (DCD, an organicnitrification-inhibitor containing 67%N by mass), with or without bimonthlyPrimo MAXX (trinexapac-ethyl, 0.125oz./l,OOO sq. ft.) growth regulatorapplications, for the same TDPU-greenstudy purposes listed above.

As mentioned, these sites were main-tained as golf course putting greensthroughout the experimental periods.Corrective P20S and K20 fertilizerapplications were made prior to eachexperimental season. All plots wereequally mowed (0.125" height, 6-7 daysa week), irrigated, and treated withplant protectants when necessary. Out-side of the described treatments, nosystemic fungicides, growth regulators,fertilizers, or wetting agents wereapplied to either study. Measurementscollected for evaluative purposes were:

7.54.71.3

3.3

6731

1341,624

7.08.14.02.0

293141365

2,512

~ Ibs.nutrientlacre2 -

• Nitrogen (N) - no other plant essential nutrient has as powerful aninfluence on turfgrass canopy color and vigor, root-to-shoot growthrelations, and disease susceptibility.The research is clear; basic fertilityneeds must be met before the full benefit of fine-tuning fertility strategiescan be realized.

• Ammonium-based nitrogen is a catalyst that stimulates the uptake ofphosphorus (P) and manganese (Mn),two essential plant nutrients.There-fore, before corrective P or Mn applications are performed, considerincluding this nitrogen source in your fertility program, especially ifphosphorus or manganese is reported as deficient based on plant tissueanalysis.

• Rootzone soil organic matter and percolation rate are traits that shouldbe factored into decisions regarding N fertilizer type, rate, and frequencyof application. Perform soil analysis at least annually (physical andchemical) to assist in developing a fertility program that meets the needsof the turf.

• Limiting N inputs to achieve green speed is counter productive. IncreaseN fertility and frequency to satisfy N requirements of healthy turfgrass.This action, coupled with growth regulator application can furtherenhance plant health while still attaining the desired level of ball rolldistance. First and foremost, strive to maximize the natural defensemechanisms of the turf.

ft./year) and ammonium to nitrateratios (NH4 + as ammonium sulfate vs.N03- as calcium nitrate) to determinetheir influence on color, health, andnutrient content of the putting surface.

In 2004, the SB green experimentevaluated a narrow range of treatments

Table IPreliminary soil fertility/chemical properties of experimental putting green

rootzones (composite samples of upper 3", thatch removed).

Experimental Greenl

TDPU S8Soil Properties

Soil pH (I: I H20)CEC (meq/IOO g soilYSoil Organic Matter (% mass)3CaC03 equivalency (% mass)

'Topdressed pushup green (TDPU) and sand-based green (SB)2Determined using Mehlich 3 extractant3Determined by loss on ignition (LOI)

facilitated in 2003 and 2004 at the PennState University Valentine TurfgrassResearch Center (University Park, Pa.)for the purpose of identifying:• Annual N fertilization rate effect oncolor and health of putting greenscohabited by creeping bentgrass andPaa annua, and• The potential interactive effects ofQR-N form and/or systematic growthregulation on the first objectiveparameters .

METHODSThough creeping bentgrass/ annualbluegrass mixtures covered both experi-mental putting greens, their underlyingrootzones possessed dramatically differ-ent physical and chemical properties(Table 1). Likewise, the topdressedpushup green (TDPU) was more than20 years old at experiment initiation,while the sand-based green (SB) wasconstructed only two years prior. Inboth studies, fertilizer treatments (eachcomprising );\3 of the annual rate) wereapplied April to October with a CO2-

powered hand sprayer in a volume of2.2 gal./l,OOO sq. ft. (95 GPA), every 15::t 4 days. The 2-year experiment on theTDPU green evaluated a wide array ofannual N rates (1.5-8Ibs. N/l,OOO sq.

JULY-AUGUST 2006 31

Figure 2Average dark green coloration (by DGCI) of sand-based

putting green (58), by annual nitrogen fertilizer rateand trinexapac-ethyl application.

Figure IAverage daily clipping yield (shoot biomass production) by

experimental putting green, annual nitrogen fertilizer rate, andtrinexapac-ethyl (GR) application (sand-based green [58] only).

exceeding 5 lbs. N/l,OOO sq. ft., canopyDGCI levels significantly increasedwhen ammonium comprised half (4%increase) or >80% (6% increase) of thefertilizer N. Conversely, canopy coloron the SB green was affected most byN rate or GR (Figure 2), with GRtreatment increasing DGCI values 5%,regardless of N rate or form.

Shoot tissue nutrient concentrationdata, an integral requirement in thecomprehensive evaluation of turfgrasshealth, provided valuable information.In both greens, N fertilization ratedirectly affected N, K, Cu, and Zn levelsin tissue.However, the more interestingnutrient level responses to N-fertilizerapplications were observed on theTDPU green, particularly the directrelation of tissue P and Mn levels toincreasing ammonium content at everyN rate (Figure 3).

Of the treatments applied to the SBgreen, GR application decreased K andMn concentration in shoots by 5% and15%,respectively.As with the TDPUgreen, N rate and N form interacted toaffect shoot Mn levels significantly(Figure 4).

on the TDPU green. Though notshown here, a significant effect offertilizer ammonium content on DGCIwas observed over 2 years on theTDPU green. At annual N rates

0.8

- Sand-Based Green, 2004-----~ - - Sand-Based Green +-0 0.7 Growth Regulator, 2004L.cuQ. - TDPU Green, 2003-04.t!ci-

-0 III 0.6Qio.- 0>-0bO •c-.- L.Q.cu.9- Q. ",.""o III 0.5

cu ",.""~ ",."".!!! ",."">.. ",.""L.

-00.4 ",.""

vi",."".a= ",.""

",.""

",.""",.

0.32 3 4 5 6

Ibs. fertilizer N applied (per 1,000 sq. ft. per year)

turfgrass shoot growth/vigor (clippingyield, in lbs. dry clippings/l,OOOsq. it.!day), canopy dark green color index(DGCI, Karcher and Richardson, 2003),and tissue nutritional status (nutrientconcentration in dry clippings).Thesedata were collected 2-5 times perstudy/year, within 4 to 12 days of treat-ment application, and analyzed byregression and/or analysisof variancestatistical procedures.

RESULTSStatistically,shoot growth/vigorresponse was better correlated to rateof N fertilizer application than toform of the QR N (data not shown).Expectedly, growth response to N wasdirect. However, clipping yield measuredon the SB green lagged behind yieldsmeasured on the identically N-fertilizedTDPU green (Figure 1). Further,Primo MAXX (GR) application to theSB green depressed growth rate to 74%of the control plot growth rate inde-pendent of N rate or form.

Canopy color, measured by darkgreen color index (DGCI), was signifi-cantly affected by both N rate and form

xcu-0.£:L.o

(5-=:-UUc~cuOcu-...-L.

~.::lL.

'"o

0.50

0.48

0.46

0.44

- Sand-Based Green, 2004

- Sand-Based Green +Growth Regulator, 2004

2 3 4 5Ibs. fertilizer N applied (per 1,000 sq. ft. per year)

6

/

32 GREEN SECTION RECORD

150Ec..c...= 125

c cOL.p v 100'" :>....... In

c .!!!VI-u ___

75c0

U...c 50v.;:...:>Zv 0.68:>InIn

i=...0 0.660.-..ti~~.!:

OQ.. 0.64v:>InIn

E 0.62

0.60

8

6

-"--"

345Ibs. fertilizer N applied (per 1,000 sq. ft. per year)

2

........................................••••••.......••

34567Ibs. fertilizer N applied (per 1,000 sq. ft. per year)

Figure 4Average leaf tissue Mn concentration from

sand-based (SB) green, by quick-release N fertilizerformulation and annual nitrogen fertilizer rate.

2

- Ammonium Sulfate

- - - 9: I Ammonium Sulfate-N:DCD-N

-,- 9:1 Ammonium-N:Nitrate-N

............................•.................~.~~--------------

- - - Tissue P 9% NH.-N•••••• Tissue P 50% NH.-N- Tissue P 91 % NH.-N- - - Tissue Mn 9% NH.-N•••••• Tissue Mn 50% NH.-N- Tissue Mn 91 % NH.-N

•••••••• Ammonium Nitrate

.............-- - - - .----- :. .--- - - :.:..:. .---.

Figure 3Average leaf tissue P or Mn concentration from

topdressed-pushup (TDPU) green, by ammonium content ofquick-release N fertilizer and annual nitrogen fertilizer rate.

100

190

175

160

130

220

250

280

co.p'".......cvuco

Uc .-..1:Ec..v c..:> ---InIn

i=...oo.r:.In

>......o

SUMMARYThese data support previous researchresults and provide new insight intoputting green turfgrass nutritionalresponse to N. The difference observedin shoot growth between the twogreens was not expected, consideringsimilar conditions of light, temperature,and N fertilizer reapplication frequency.The lesser growth rate of the SB green,when compared to the TDPU green,illustrates the limited nutrient sequester-ing capacity and nutrient mineralizationactivity associated with young, low-OM, sand-based root media. Moreover,University Park received 29" of rainbetween May and October in 2004,and the relatively limited nutrient up-take in the SB green may have resultedfrom nutrient leaching. Thus, rootzonesoil OM and percolation rate are traitsthat should be factored into decisionsregarding N fertilizer type, rate, andfrequency of reapplication.

Nitrogen form played a significantrole in canopy color and tissue P on theTDPU green, and it affected Mn tissuelevels of both greens. The N formassociated with these enhancementswas ammonium. Exclusive use ofammonium sulfate for N fertilization isa well-recognized soil-acidifyingstrategy. In both greens, ammoniumsulfate fertilization resulted in significanttissue Mn increases, regardless of soilchemical properties (Table 1) or historicalmicronutrient fertilizer applications .

The observed effects of PrimoMAXX GR on putting green growthand color are in agreement with recentresearch (McCullough et al., 2005). Useof the GR did not interact with N rateor form, but consistently increasedcanopy color (5%) while suppressingshoot growth (26%), tissue K (5%), andtissue Mn (15%) in the 4- to 12-dayperiod following GR application .Ideally, these results will be consideredby golf course superintendents whohave not adopted GR use as a mainte-nance practice, yet fervently withholdnitrogen fertilizer from their bentgrass/Poa cohabited putting greens for the

JULY-AUGUST 2006 33

purpose of enhancing ball roll distance.An important message that can bederived from these results is this: Suit-able green speed can be mutuallyexcluded from suboptimal leaf Nanddisease susceptibility. Increase your Nfertilization frequency and rate tosatisfy the N requirements of healthyturfgrass (>4% tissue N). This action,coupled with initiation of GR appli-cations, is an effective and widely usedmethod to significantly enhance plant

health and canopy color (Figure 2)without an undesired concomitantincrease in shoot growth (Figure 1).

ACKNOWLEDGEMENTSThe author recognizes the Pennsylvania Turf-grass Council and the P&PIIFoundation forAgronomic Research for their invaluable supportof his research in turfgrass nutrition.

REFERENCESBowman, D. C. 2003. Daily vs. periodic nitrogenaddition affects growth and tissue nitrogen inperennial ryegrass turf. Crop Sci. 43:631-638.

Karcher, D. E., and M. D. Richardson. 2003.Quantifying turfgrass color using digital imageanalysis.Crop Sci. 43:943-951.

McCullough, P. E., H. Liu, and L. B. McCarty.2005. Trinexapac-ethyl application regimensinfluence creeping bentgrass putting greenperformance. HortScience 40:2167-2169.

DR. MAx SCHLOSSBERG is an assistantprofessor if tuifgrass nutrition in the Dept.if Crop and Soil Sciences at Penn StateUniversity.

Nitrogen - no other plant-essential nutrient has as powerful an influence on turfgrass color and vigor, root-to-shoot growth relations, and diseasesusceptibility.

34 GREEN SECTION RECORD