Fertiliziilg;,ligh- Traffic TurfBy Stephen T. Cockerham, Victor A. Gibeault and Mf;J.tff]f3w K. Leonard

S'ports fields are stomped on, kicked,scuffed, dug out, and otherwisegenerally and thoroughly beat up.

More often than not, through all of this, thefield still has turfgrass on it.

Well-managed turfgrass sports fields are'safe, durable, and aesthetically attractive,but they are not 100 maintenance. Turfgrassunder the 'pressures of high traffic shouldbe sustained at their optimum vigor. Correctfertilization of the turf is a key factor in thatprocess.

Fertilizers - When selecting fertilizers foruse on sports turf, consider the turfgrassspecies, the nutrients needed, the effect ofthe nutrients on the plant, the nutrient.sources available, the characteristics ofdifferent nutrient sources, time of year, andthe requirements and limitations of the facil-ity (budget, manpower, equipment, eventsschedule, and maintenance schedule).

There is not a particularly wide range ofgrasses grown as sports turf. In the Sunbeltit is pretty well limited to cultivars of onewarm-season grass, bermudagrass, plusvarious cool-season species that might bewinter overseeded. In the North, three coolseason species are used alone or in mix-tures: Kentucky bluegrass, tall fescue, andperennial ryegrass.

Nitrogen (N), phosphorus (P), and potas-sium (K) are the primary nutrient elementsused in large quantities by plants. Fertilizerlabels contain the nutrient analysis indi-cated by the percent by weight of N-P-K inthe package.

As a fertilizer, phosphorus is referred toas phosphate and shown as the chemicalnotation P205. Potassium as a fertilizer isknown as potash and is shown by thechemical notation K2o. For simplicity wewill use P and K, meaning P205 and K20.Nitrogen is designated as N in fertilizeranalysis.

Nitrogen is a major ingredient of theplant. As a component of chlorophyll, nitro-gen deficiency first shows up as a yellowingof the turf. The deficiency is corrected bythe application of nitrogen as a turf fertilizer.Nitrogen fertilizer sources are separatedinto three groups: inorganic, naturalorganic, and synthetic organic.

Inorganic nitrogen fertilizers producequick plant response, are not very sensitiveto temperature, and are low in cost per unitof nitrogen. However, they are highly solu-ble in water, so the response doesn't lastmuch longer than four weeks.

The most commonly used inorganicnitrogen fertilizers are ammonium nitrate,ammonium sulfate, and calcium nitrate.

Sports fields canhave.,a' dark uniform color with the correct application of fertilizer.

'. . ,: I . '.' '" ' . ~ , .'

Ammonium !~ ta~en up bythe roots,' butmost of it is apSQrged by soil particles. Soilmicrobes cq'rvertit into the nitrate form,release it frqrnthesoilparticles and makeit available ~~aff!.C06Itemperatures slowthe soil mj~rpq~~, making the ammoniumlessavailableto tpeplant. Nitrate, also eas-ily absorbeppy'ih~ roots, is not sensitive totemperatures- ',!"'. .

Ammonium s~!fa~e (21-0-0) in addition tonitrogen in the ammoniumform contains 24percent sulfpr:'Hecausesulfur reacts toacidify soil,th~stE~'rtilizer is recommendedfor use on ~ik~nn~soils.

Calcium DWq!~ (15-0-0) lis a good coolweather tiJrfqerHlize,r,but it absorbsmoisture e.·~~;i!{9~USi~g it to cake in thebag. Therefore'; it should be stored in air-tight t:ontq!fl~rS.;':' : .

Natural orQa,nJenitrogen turf fertilizers arederived mO~1'yffprnanirnal wastes (manureand sewag~ ~!99Qe). Thesernaterlals typi-cally are i1ot;·~oluble.· The plant growthresponse i~'sIQ~~l1d they are only effectivefor four to eigHf months.

The low nni6Q~nanalysis (two to 15 per-cent) ofnat~ral prganics makes their costper 'unit of NhJ~her than the inorganics.Even though 'tt1~yare expensive N sources,many turf rnR-hfigers L!se natural organicsdue to the ~r~~~nce of a number of othernutrients. Sincesoit microbes break downthe.natural qr~a,nl~~to release the nitrogen,effectiveness f~, poor in cool weather.

Activated §~»,age sludge is the primarynatural orgqDi~nitr?gen fertilizer used rou-

tinely on turf. Activated sewage sludge,produced from treated, processed sewage,contains four to seven percent N. Manuresare occasionally applied as a preplant fer-tilizer for turfgrass establishment, but thehigh soluble salt content can beundesirable.

Synthetic organic nitrogen fertilizers areprimarily urea and urea-based compounds,both soluble (quick-release) and slow-release. Soluble synthetic organic fertiizersgive quick turf growth response that maylast four to six weeks.

Soluble urea (45-0-0) is by far the mostpopular soluble sythetic organic nitrogensource for use on turf. The prills are con-venient to apply dry through a spreader, orcan be dissolved in a sprayer tank for liquidapplication. The very high N content meansthat less total quantity must be handledcompared to other fertilizers.

Besides leaching as rapidly as a solublefertilizer, a large percentage of N is lost tovolatilization in warm weather, which hap-pens when the ammonium in the urea turnsto free ammonia and evaporates. Cool-season use of urea minimizes volatilization.

Slow-release insoluble synthetic organicnitrogen fertilizers have little turf burn risk,and plant growth response is slow. Theyrelease N over an extended period, makingplant growth more consistent and reducingthe number of applications. However, theslow-release materials are more expensivethan other sources.

continued on page 22

October, 1988 21

Fertilizing High-Traffic Turfcontinued from page 21

Slow-release N fertilizers are made byeither combining urea with other com-pounds to produce water-insolublematerials, or coating a readily soluble Nsource. The most commonly used water-insoluble urea compounds for turf areureaformaldehyde (UF) and isobutylidenediurea (IBDU).

UF (38-0-0) fertilizer is packaged withabout 25 percent N in the soluble form toprovide a quick turf response. Nitrogen isreleased from the insoluble fractions of UFthrough microbial breakdown and is depen-dent upon temperature. It isn't very effectivewhen temperatures fall below 50 degrees F.

The rate of N release from UF is con-trolled by the size of particles and the fer-tilizer chemistry. A smaller particle sizeincreases the number of particles, thusincreasing the surface area of the fertilizerthat is exposed to microbial activity.

IBDU (31-0-0) releases N as the particlesslowly dissolve in soil moisture. Sincerelease is 'not influenced by microbialbreakdown or temperatures, IBDU is goodfor cool season use. Like UF, the rate of Nrelease depends on the size of the particle.Turf response may take as long as fourweeks, but can last as long as 16 weeks.Turf managers, often anxious for a quickresponse, sometimes add soluble N toIBDU for immediate impact.

Slow-release sulfur-coated urea (SCU) isproduced by spraying molten sulfur ontogranules of urea. The rate of N release fromSCU is determined by the thickness of thesulfur coating and the particle size. The Nanalysis varies, but 32-0-0 is a common for-mulation, and sulfur (12 to 22 percent) isavailable to the plant.

Response to common turf formulations ofSCU lasts eight to ten weeks. SCU usuallyprovides a better initial growth responsethan other slow-release fertilizers, and thecool season activity of SCU is acceptable.It is the least expensive slow-release syn-thetic organic fertilizer per unit of N.

Resin-coated materials are produced bycoating urea, or other compounds, with awater-permeable plastic resin. Theseproducts usually are 26 to 34 percent N.The permeability of the coating is sensitiveto temperature. LONer temperatures slow Nrelease by causing the resin to contract, soresin-coated fertilizers are primarily forwarm season use.

Resin-coated fertilizers do not cause turfto produce a flush of growth. Instead, theinitial response is a gradual increase ingrowth without the rapid spurts commonwith other fertilizers. This growth can besustained for four to six months. Resin-coated fertilizers are the most expensive Nsource.

Forcing growth-Sports turf fields havethe same normal maintenance require-ments of any turfgrass sward. The uniquedemands of the sports field often call forforcing extraordinary qrowth. Frequent,22 sportsTURF

high N-rate applications will cause a rapidflush of growth. Most of the response isfoliage, but the roots also grow. Thisresponse is useful in peaking for a certainevent or recovering from a particularlydamaging event. However, forced growthcreates a risk of long term problems withthe turf, because the growth flush tends todeplete carbohydrate reserves and reducelater injury recovery potential.

Phosphorus is used to make proteinsand help transfer energy within the plant. Itis especially important in the developmentof roots, rhizomes, stolons, and tillers. Theroots are vital to the sustenance of thegrass plant. If there are no roots, then thereis no growth. Rhizomes, stolons, and tillersare the mechanisms that established turf-grasses use to spread.

Traffic is the mostsignificant stress on

sports fields, andpotassium increases

traffic tolerance.

Two common sources for P are super-phosphate (0-15-0) and triple super-phosphate (0-45-0). Monoammonium phos-phate (11-48-0) and ammoniumphosphate-sulfate (16-20-0 plus 15 percentsulfur) are common N fertilizers that arehigh in phosphate.

Injury recovery- Turf density can be afunction of the vigor and efficiency of theroots, rhizomes and tillers. Recovery frominjury is most certainly a function of theirvigor and efficiency. Excess P in the rootzone allows the plant to utilize it.

Low solubility makes phosphorus veryimmobile, and repeated application causesit to accumulate in the upper soil layers.This has not been a problem and may pro-vide excess P on demand to the plantunder stress. If the sports field is beingresodded, putting one of the phosphate-nitrogen fertilizers under the turf and on topof the soil or sand enhances sod knitting.

Potassium is involved in several plantmetabolic processes, many of which arerelated to water use. It is highly soluble anddoes not stay in the root zone very long.Sports turf on sandy soils and pure sandslose K rapidly and requires applicationsnearly as frequently as N.

Common fertilizer sources are potassiumchloride or muriate of potash (0-0-60) andpotassium sulfate (0-0-50). Both are inex-pensive. Often a nitrogen plus potash fer-tilizer product mixture is used to assure thatboth nutrients are available to the plant.

Stress resistance- Turf does not usuallyrespond visibly to added potassium. It is theincreased stress resistance that is impor-tant. Drought, heat, and cold tolerance are

improved and disease resistanceincreased. Traffic is the most significantstress on sports fields, and potassiumincreases the turfgrass traffic tolerance.

Sulfur deficiency stunts the growth of theturf plant. Common sulfur sources areammonium sulfate (24 percent S), potas-sium sulfate (18 percent S), sulfur-coatedurea (12 to 22 percent S), superphosphate(12 percent S), ferrous sulfate (19 percentS), and elemental sulfur (99 percent S).

Occasional use of sulfur-containing nitro-gen fertilizers (e.g. ammonium sulfate)usually takes care of the sulfur needs ofsports turf. Many sports fields are built inmarginal soils, including land fill, where sul-fur applications may be beneficial. Sulfurfertilizers tend to lower pH due to their acidreaction in the soil and are usually preferredfor alkaline soils.

Iron (Fe), essential for chlorophyll synthe-sis, is important to turf color. Turf sufferingfrom iron deficiency is chlorotic, and doesnot respond to nitrogen. Iron is usuallypresent in the soil, but has a tendency toform insoluble compounds.

Iron can be applied either as a salt or ina chelated form. Salts include ferrous sul-fate (20 percent Fe) and ferrous ammoniumsulfate (15 percent Fe). Chelates are chem-icals that bind iron to prevent insolublecompounds from forming, while still allow-ing uptake by plants. Modifying the pH ofalkaline soil with repeated sulfur use or anacid soil with lime can cause a turfresponse from released iron.

Turf color-As any sports turf managerknows, nitrogen is not the only way to maketurf a uniform dark green. Iron is a valuabletool for providing that color.

If nitrogen is in adequate supply, anapplication of soluble iron (0.25 lb. Fe/1000sq ft) such as ferrous sulfate will almostalways darken the color of the turf withintwo to three days. Because ferrous sulfatewill easily burn the turf, irrigation should fol-low application immediately, Application ona hot day or at a high rate will cause burnwhere the applicator tires scuff the turf.

The primary plant nutrient elements (N,P, and K) are seldom applied singly. Whenall three are in one fertilizer product, it iscalled a complete fertilizer.

In the fertilizer product, the nutrients arebalanced in ratios to each other dependingupon the local climate, soils, and grassneeds. A starter or preplant fertilizer mayhave a ratio of about 1:2:2, which might bean analysis such as 5-10-10or 10-20-20. TheN is low, while the P and K are high tostimulate seedling development. A com-mon maintenance ratio for complete fer-tilizers might be about 3:1:1, which might bean analysis such as 15-5-5.

Sports turf, regardless of species, shouldbe fertilized with N every month of the grow-ing season. One or two of these applica-tions should be with a complete fertilizerwith a 3:1:1 or 2:1:1 ratio. The rate is usuallycalculated using the percent N in the formu-lation.

continued on page 24

Fertilizing Hlgh·Trafflc Turfcontinued from page 22

Application rates:"'" For maintenance ofsports fields with any of the grasses, nitro-

, gen is applied at the rate of one pound per1,000 square feet per month of growing sea-son. If slow re~ase nitrogen fertilizers areused, apply one pound N per 1,000 squarefeet/month of release period. A rate of 2.5 to3.pounds per 1,000 square feet of productshould be a minimum applicationof slow-release materials.

In the early spring, it is often possible to"jump start" bermudagrass with a one-timeapplication of two to three pounds N per1,000 square feet in a soluble form.

The overseed species seldom rootthrough the thatch of the base species anddraw from whatever nutrients are availablein the thatch. Light, frequent N applications(0.5 pounds N/1,000 square feet monthly)may be adequate. If a vented plastic tarp isused to maintain soil temperatures, careshould be exercised in the use of N fer-tilizers. Free ammonia released by fer-tilizers under a tarp will cause considerableinjury to the turfgrass foliage.

Winter use of fertilizers depends uponthe growth of the turf. As soil temperaturesdrop below 50 degrees F, bermudagrassstops needing fertilizers. For the cool sea-son species the magic soil temperature isaround 40 degrees F. When the trend of thesoil temperatures is up in the spring and

• : <. / ;.' ~:?~_:; ,;i .~.passes these tempe~f.u~es, It is time tobegin fertilization .aqat :,~i,. '.

On cool- aridwa,.ni3~~~~~9riJurfgrasses,phosphorus is applied,~(,t~~ ,r~te of one totwo pounds of P per J,OOO, .~qu,are feet peryear. Potassium'appfI9$llt9rll? on sportsfields can be a little Ii .ij~~L~~~m on otherturf. Potassium is aPl>IJ~.s!;~t; 0.5 to onepound o~K per l~OOOS~Q~~;.r.#-etpe~ monthof growing season"Orn:(sandy, SOilS andsands ~se t.~e higher r~-t~~!;~''~ "

Application or.N'r.,{fZ~: J~ possiblethrough the irrigatioh~~s(ej;t;i.:Using liquidfertilizers a~d. inje~~6rR~t#Q~ ,pe nU,trien!scan be applied ,eveyt,;;t.fQl¢}the held ISirrigated. Theriuttieili:,~:~pi?JiGation rateshould be verydituts A~ti.;~\ti~)ntentof put-ting on about one lb.: f~~cti nutrient per:1000 sq. ft. over the p riQd:.ofa month.

Sports turf fields r qU(J:~\a.'erification torelieve compaction. -ThereJs~some benefitto fertilizing' imrnediatefW~~~f~er:aerifying.'S,ome fertilizer.will ,~ ~fP9(~,r:,)~nthe, holeseither as a wh()lepar '~~J~~/q:h~tnsolution asit dissloves in 'r.airjdtiO-lg'aJI9h' water. I

Turf can visibly}e~p0H~:,iA.~tes 'of iron aslow as 0.1' up to '1.0P(f(rn~~9,(::Fe per 1',000square feet within·aJe'ot'thOV,rs,after an iron'application, paf.tiCJf~ri:~~4i-f:~nitrogen isapplied at the same Ii '~~:!Jro.riJ~ppliedat thehigh rate has a '~erynl'9H;~~t.n risk, and itshould be used only witl:Y9f~tcare-don'tuse it in hot weather; cJoo'Jf;,Walkor drive onthe sprayed area until It ha\s been watered,

and water immediately after application.All sports turffacilitTes have budget limi-

tations, but it is important that the budgetnot skimp on fertilizer. For the benefits itprovides to a sports field, fertilizer is a lowcost supply item.

For example, a sports field of 2.5 acres,which is a reasonable size for one field(football or baseball), would use less than$4,000 per year (four cents/squarefoot/year) for the highest application rates ofthe most expensive coated slow-release fer-tilizer. A good fertilizer program, dependingupon field demands, might spend ten to 25percent of that on fertilizer.

SCheduling fertilizer appucanons aroundevents can be a major challenge. A set pro-gram for maintenance including fertilizertreatments is often impossible to keep, Thesports turf manager seldom has any inputinto events scheduling. Events that requirecovering the field, such as concerts, cancause irrigation and fertilization to be post-poned, or a very heavy schedule of athletic

I events may not leave time for field work.The sports turf manager must be flexible,decisive, and opportunistic to get the workdone and to maintain a safe, attractive field.

Editor's Note: The authors from the Uni-versity of California, Riverside, (in order)are superintendent of Ag. Operations,extension environmental horticulturistand staff research associate.

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