Turfgrass Fertilization:A BASIC GUIDE FOR PROFESSIONAL TURFGRASS MANAGERSCOLLEGE OF AGRICULTURAL SCIENCESAGRICULTURAL RESEARCH AND COOPERATIVE EXTENSION
3Soil and TissueTestingSOIL TESTINGSoil testing is an importantfirst step in developing aturfgrass fertility program.For some nutrients, it is theonly way you can accuratelydetermine how muchfertilizer your turf needs.Most land grant universitiesand many commerciallaboratories provide soiltesting services, althoughprices and services varyamong labs. For a nominalfee, Penn State offers astandard soil test forphosphorus, potassium,calcium, magnesium, andlime requirements. Morecomprehensive soil analysesare available upon request.Typically, nitrogen is notanalyzed as part of astandard soil test becauselevels fluctuate too rapidlyin soil to provide meaningfulrecommendations.A soil test programinvolves sampling, laboratoryanalysis, interpretation,and recommendations. Theresults obtained from a soiltest are only as good as thesample submitted. Samplingdirections vary fromlab to lab, so follow instructionson the test kit carefully.Instructions shouldtell you how manysubsamples are required pertest, the sampling pattern,the sampling depth, andwhether thatch should beincluded in the sample.Penn State soil testsampling instructionssuggest collecting 12 ormore subsamples perlocation in a regular gridpattern (Figure 1). If the sitevaries in soil type, previouslime or fertilizer treatment,or other past maintenancepractices, take separatesamples accordingly. Testkit instructions suggestsampling soil 2 to 3 inchesin depth and discardingthatch. Mix all subsamplestogether to make onesample, then take about 1/3pint of this mix and place itin the mailing kit (Figure 2).Be careful not to contaminatethe sample with limeor fertilizer during samplingand mixing.Typically, soil testsshould be taken every threeyears. If you wish to monitornutrient levels overmany years, take thesamples at about the sametime of year every time yousample. Always test the soilbefore establishing orrenovating a lawn.Soil test labs vary in howthey analyze soil andinterpret test results. Thegreatest variation in analysisis usually among labsfrom different areas of thecountry. Be sure to sendyour samples to a laboratorythat is familiar with thenutrient requirements andgrowing conditions ofturfgrasses in your region. Ifyou are sending samples toa national commerciallaboratory, note yourlocation.Figure 1. Soil sampling patternfor turfgrass areas. Take soilsamples 2–3 inches in depthfrom 12 or more locations persite.Figure 2. Penn State soil test sampling instructions suggest mixingall subsamples together to make one sample.● ● ● ●● ● ● ●● ● ● ●
4Interpretation of soil testresults allows your nutrientlevels to be placed intocategories such as low(deficient), adequate, orhigh based on the researchand experience of turfgrassspecialists. Recommendationsare usually providedas pounds of fertilizer per1000 square feet (also basedon research and the experienceof turfgrass specialists).Make sure you understandthe recommendationsbefore applying the fertilizer;that is, determine if therecommended amount offertilizer is to be applied inseveral separate applicationsor if it can be providedin one application.Recommendationsoffered by Penn State’s soiltest lab are based on researchwith lawn grasses inPennsylvania and on theexperience of turf specialistsat the University. It is notsurprising that recommendationsfrom other statesdiffer, since soils, researchprocedures, and specialists’opinions differ from thoseof Penn State specialists. Tomaintain consistent soil testresults and recommendations,work with one labthat is convenient to useand whose recommendationsyou can understand.TISSUE TESTINGTesting of turf leaf tissueallows you to monitornutrient levels, which canbe related to the need forfertilizer. Leaf tissue testingis also a means of diagnosingnutrient deficiencies,verifying diagnosis madefrom visual deficiencysymptoms. Tissue nutrientlevels can be determined formost or all nutrients, or foronly one or two. It isbecoming more popular tosample leaf tissue fornitrogen to determinefertilizer nitrogen requirements.As with soil testing,proper sampling of leaftissue is critical. Samplesmust be representative ofthe area, collected accordingto lab instructions and,above all, free from soil andother contaminants.Fertilizer BasicsCost is a primary concern indeciding which fertilizerproduct to use. Selecting theleast expensive fertilizer,however, does not necessarilymean you have foundthe best value. Fertilizershould be purchased on thebasis of quality rather thanon bag size or price. Qualityis determined by theamounts and types ofnutrients contained in thebag and by the product’sphysical characteristics.Figure 3. The three numbers onfertilizer containers indicate thepercentages by weight ofnitrogen, phosphate, and potashin the fertilizer.NUTRIENTS INFERTILIZERSTurfgrass fertilizers usuallycontain three plant nutrients:nitrogen, phosphorus(designated on labels asavailable phosphate, orP 2O 5), and potassium(designated as water solublepotash, or K 2O). These threenutrients are represented onthe fertilizer container asthree numbers, indicatingthe percentages by weightof nitrogen, phosphate, andpotash—always in thatorder (Figure 3). The threenumbers are referred to asthe fertilizer grade.
5When nitrogen, phosphorus,and potassium are allpresent in the container, thefertilizer is called a completefertilizer. Sometimesone or two of these nutrientsare not present, and themissing nutrient(s) aresimply listed as “0” in thegrade. Occasionally,turfgrass fertilizers containother nutrients such assulfur, iron, and/or calcium.These are usually listed onthe label but are not part ofthe fertilizer grade.A fertilizer grade is usedto determine the percentageby weight of plant nutrientsin the product. For example,a 100-lb bag of fertilizerwith a grade of 30-0-10contains 30 lb of nitrogen,no phosphate, and 10 lb ofpotash. A 50-lb bag of thesame product would yield15 lb nitrogen, no phosphate,and 5 lb of potash.Knowing the fertilizer gradeis important in determininghow much fertilizer toapply to your turf.Sometimes, a fertilizerratio is specified on soil testreports or in fertilizerrecommendation sheets.The fertilizer ratio indicatesthe proportion of nitrogen,phosphate, and potash inthe product. For example,an 18-6-6 fertilizer containsthree parts nitrogen to onepart phosphate to one partpotash. Thus, this fertilizerhas a 3-1-1 fertilizer ratio.NITROGEN SOURCES INFERTILIZERSThe source of nitrogen in afertilizer is important fordetermining your turf’sgrowth rate, density, andcolor. Nitrogen fertilizerscan be divided into twocategories—quick releaseand slow release. Quickreleasenitrogen sources aresoluble in water; hence,How much phosphorus and potassium are really inyour fertilizer?The chemical formulas P 2O 5and K 2O are the traditionalmeans of expressing the amount of phosphorus (P) andpotassium (K) in fertilizer. In fact, no such compoundsexist in fertilizers. In the rare event that you have todetermine the actual amounts of phosphorus andpotassium in your fertilizer, use the following formulas:% P 2O 5x 0.44 = % P% K 2O x 0.83 = % KExamples:A fertilizer containing 20% P 2O 5has about 9% P(20% P 2O 5x 0.44 = 8.8% P)A fertilizer containing 10% K 2O has about 8% K(10% K 2O x 0.83 = 8.3% K)NOTE: Typically, you do not need to perform thesecalculations because fertilizer recommendations arealmost always provided as lbs P 2O 5/1000 sq ft andlbs K 2O/1000 sq ft.How to calculate a fertilizer ratioIf your soil test report recommends applying 1.5 lb ofnitrogen, 0.5 lb of phosphate, and 0.5 lb of potash per1000 sq ft, you should apply a fertilizer with a ratio of3-1-1 since you need three times as much nitrogen asphosphate and three times as much nitrogen as potash.The simplest method of determining a ratio is to dividethe weights of nitrogen, phosphate, and potash by thelowest weight of the three.Example:To determine a fertilizer ratio for a recommendation of1.5 lb of nitrogen, 0.5 lb of phosphate, and 0.5 lb ofpotash, divide the weight of each of the three nutrients(1.5 lb, 0.5 lb, 0.5 lb) by the nutrient with the lowestweight (0.5 lb).1.5 ÷ 0.5 = 30.5 ÷ 0.5 = 10.5 ÷ 0.5 = 1Thus, the fertilizer ratio that best fits this recommendationis 3-1-1.You can also determine fertilizer ratios from fertilizergrades by dividing the percentage of nitrogen, phosphate,and potash by the lowest percentage of the threenutrients.Example:Determine ratios for the following fertilizer grades:21-7-7, 22-6-8, and 18-5-9.Grade = 21-7-7 Grade = 22-6-8 Grade = 18-5-921 ÷ 7 = 3 22 ÷ 6 = 3.7 18 ÷ 5 = 3.67 ÷ 7 = 1 6 ÷ 6 = 1.0 5 ÷ 5 = 1.07 ÷ 7 = 1 8 ÷ 6 = 1.3 9 ÷ 5 = 1.8Ratio = 3-1-1 Ratio = 3.7-1-1.3 Ratio = 3.6-1-1.8nitrogen is available toplants immediately. Theyalso can burn turf moreeasily than slow-releasesources. Slow-releasenitrogen sources typicallyrelease a portion of theirnitrogen over relativelylong periods (several weeksto several months).The relative amounts ofquick- and slow-releasenitrogen in a fertilizerproduct are listed on thelabel as percentages of thetotal nitrogen (Figure 4).Quick-release nitrogen isdesignated as ammoniacalnitrogen and/or urea. Slowreleasenitrogen is designatedas water insolublenitrogen (WIN) or controlled-releasenitrogen. Fora more detailed explanationof nitrogen sources, see“Turfgrass NitrogenSources” (page 10).
6Figure 4. A fertilizer bag maycarry the following label:Guaranteed Analysis:Total Nitrogen .................................. 20%10% Ammoniacal Nitrogen3% Urea7% Water Insoluble NitrogenAvailable Phosphate (P 2O 5) ............. 10%Water Soluble Potash (K 2O) .............. 10%PHYSICALCHARACTERISTICS OFFERTILIZERSA fertilizer’s physicalcharacteristics determineshow easy it is to handle andhow evenly it is applied toturf surfaces. Granularfertilizers that containsignificant amounts of dustand broken particles makefor poor distribution ofnutrients, especially whenapplied through rotaryspreaders. Similarly, productscontaining differentsizedgranules are notevenly distributed by rotaryspreaders because thelarger, heavier particles arethrown further from thespreader than smaller,lighter particles. Whenpurchasing a fertilizer, lookfor a product with uniformparticle sizes and minimalamounts of dust and brokengranules.The density of granularfertilizers is also an importantphysical characteristic.Lightweight fertilizers arethrown for only a shortdistance by rotary spreaders,resulting in narrowswaths and, thus, the needfor more passes by thespreader operator. Also,lightweight particles areeasily carried by wind,resulting in poor distributionpatterns on windydays. Most professionalfertilizer applicators preferhigh-density fertilizersbecause of their improvedspreading characteristics.Some turfgrass fertilizersare sold as liquids or as dryformulations that can bedissolved in water for sprayapplications. Some liquidfertilizer formulationsseparate into layers whenstored for extended periodsin cold temperatures. Besure to follow storagedirections carefully whenusing liquid formulations.Dry fertilizers used forspray applications shouldnot contain impurities thatcan clog or abrade spraynozzles.CALCULATIONS USED INTURFGRASSFERTILIZATIONProper fertilization practicesrequire that preciseamounts of nutrients bedelivered to the lawn. Smallmistakes in area measurementsor fertilizer ratecalculations can producepoor results and, sometimes,serious turf injury.Sample problems on page 7are designed to provide thesimplest methods of solvingthe most frequently encounteredquestions regardingarea measurements andfertilizer rates.Determining the area of a site to fertilizeSquare:Rectangle:w (100 ft)Right triangle:Circle:b (30 ft)a (100 ft)b (100 ft)l (200 ft)r (5 ft)h (40 ft)Area = a x bArea = 100 ft x 100 ftArea = 10,000 sq ftArea = l (length) x w(width)Area = 200 ft x 100 ftArea = 20,000 sq ftArea = 0.5 x b (base) xh (height)Area = 0.5 x 30 ft x 40 ftArea = 600 sq ftArea = (always 3.14) xr 2Area = 3.14 x 52Area = 3.14 x 25 ftArea = 78.5 sq ftTo calculate the area of irregularly shaped lawns,divide the lawn into common shapes, calculate theareas of the shapes, then add the areas together.
7Calculations used in turfgrass fertilization1. A fundamental problem in turfgrass fertilizationinvolves determining how much fertilizer is needed tosupply a specified amount of nitrogen (or any othernutrient) per 1000 sq ft. Use the following examples tolearn how to solve this type of problem.Example:You have a 50-lb bag of 26-5-10 fertilizer that you wantto apply to a lawn at a rate of 1.0 lb nitrogen per 1000sq ft. How much of the 26-5-10 fertilizer will you needto apply per 1000 sq ft?The quickest way to solve this problem is to ignore theweight of the fertilizer bag and simply divide theamount of nitrogen desired (1.0 lb nitrogen per 1000 sqft) by the percentage of nitrogen in the bag (26%).When using percentages in calculations, convert thenumber to its decimal form (for example, 26% = 0.26;5% = 0.05).(1.0 lb nitrogen per 1000 sq ft) ÷ 0.26 = 3.8 lb of a26-5-10 fertilizer is needed to supply 1.0 lb nitrogenper 1000 sq ftExample:Find out how much phosphate and potash you areapplying to the turf when you apply 3.8 lb of the26-5-10 fertilizer per 1000 sq ft.Multiply the amount of fertilizer you are applying(3.8 lb per 1000 sq ft) by the percentage of phosphate inthe bag (5%). Do the same for potash (10%). Rememberto convert the percentages of phosphate and potash totheir decimal forms.(3.8 lb fertilizer per 1000 sq ft) x 0.05 phosphate = 0.19 lbphosphate per 1000 sq ft(3.8 lb fertilizer per 1000 sq ft) x 0.10 potash = 0.38 lbpotash per 1000 sq ft2. Another common problem involves determining thearea that a bag of fertilizer can cover and how manybags are needed to cover large sites.Example:How much area can be covered with a 50-lb bag of26-5-10 at the rate of 1.0 lb nitrogen per 1000 sq ft?Now that you know 3.8 lb of 26-5-10 fertilizer willcover 1000 sq ft, determine how many times 3.8 lb goesinto 50 lb.50 lb ÷ 3.8 lb = 13.2Now multiply 13.2 by 1000 sq ft :13.2 x 1000 sq ft = 13,200 sq ft.Thus, a 50-lb bag of 26-5-10 covers 13,200 sq ft at a rateof 1.0 lb nitrogen per 1000 sq ft.Example:How many 50-lb bags of 26-5-10 will you need tofertilize a 30,000 sq ft lawn at 1.0 lb nitrogen per 1000sq ft?If a 50-lb bag of 26-5-10 fertilizer covers 13,200 sq ft at1.0 lb nitrogen per 1000 sq ft, determine how manytimes 13,200 goes into 30,000.30,000 ÷ 13,200 = 2.3 bags of 26-5-10 will cover30,000 sq ft.3. Occasionally, fertilizer recommendations given as lbnitrogen per 1000 sq ft must be converted to lb fertilizerper acre.Example:You are treating a large sports turf complex and wouldlike to determine how many lb of a 16-8-8 fertilizershould be applied per acre if the recommendation callsfor 0.75 lb nitrogen per 1000 sq ft.First: Find out how much fertilizer will be needed per1000 sq ft (see examples in problem 1).(0.75 lb nitrogen per 1000 sq ft) ÷ 0.16 = 4.7 lb fertilizerper 1000 sq ftSecond: Since there are 43,560 sq ft in an acre, multiplythe amount of fertilizer needed per 1000 sq ft by 43,560,then divide by 1000.(4.7 lb fertilizer x 43,560) ÷ 1000 = 205 lb of a 16-8-8fertilizer per acre
8Nitrogen in TurfNitrogen is an essentialelement for all living thingsand the mineral elementneeded in the largestamounts by turfgrasses.Although nitrogen isabundant in the atmosphere(about 80 percent of the airsurrounding us is nitrogengas), it is in limited supplyin soils and available toplants only after it has beenconverted to nitrate (NO 3-)or ammonium (NH 4+) bymicroorganisms or industrialprocesses. In mostcases, nitrogen fertilizermust be applied regularly tomaintain high quality turf.Although nitrogenfertilizer is required forhealthy lawns, it can alsocontaminate ground- andsurface waters throughleaching and runoff. Excessivenitrate concentrationsin drinking water are ahealth risk, especially forinfants, pregnant andnursing mothers, andyoung children. Nitrogenmovement into water canalso accelerate degradationof ponds, lakes, coastalbays, and estuaries througha process called eutrophication.Eutrophication refersto the addition of nutrientsto surface waters, resultingin algae blooms, denseaquatic plant growth,depletion of oxygen, and, inadvanced stages, fish kills.The goal of a nitrogenfertility program is tooptimize plant uptake whileminimizing leaching,runoff, and gaseous losses.To achieve this goal, youshould understand hownitrogen behaves in theenvironment and know theconditions that influenceits fate.OPTIMIZING NITROGENUSEAlthough soil testing canprovide guidelines for howmuch phosphorus, potassium,and lime turfgrassesneed, it does not givereliable information aboutnitrogen requirements. Justhow much nitrogen shouldbe applied depends on thespecies you are attemptingto maintain (and, in somecases, the cultivar), the soilconditions at the site, howthe turf is managed, andhow the site is used. Also,the amount of nitrogen thatturfgrasses take up isinfluenced by applicationtiming, the source(s) ofnitrogen, and the amount ofnitrogen applied perapplication. Designingfertilizer programs formaximum uptake and useof nitrogen by turf isdiscussed in “FertilizerPrograms” (page 19).LEACHINGLeaching occurs whenirrigation or rainfall carriesnitrogen, primarily in thenitrate form, downwardthrough the soil profile. Asnitrate moves below plantroot systems, it continues tomove downward, eventuallyending up in groundwater.How much nitrogenis leached from a lawndepends on the soil type;the amount and rate ofprecipitation; and thenitrogen source, rate, andtiming of application.The greatest potential forleaching is in sandy soilsduring periods of wetweather or under excessiveirrigation, and followingapplications of quick-releasenitrogen at high rates.Leaching can be reduced byusing slow-release nitrogensources on high-sandcontentsoils or by usinglow rate applications ofquick-release nitrogensources. Leaching can alsobe curtailed by restrictingnitrogen applications whenplants are not activelygrowing (during midsummerand winter) and/orduring extremely wetperiods of the year. Sinceleaching of nitrogen cansometimes occur even inloam soils, be sure always tofollow good fertility andirrigation practices.RUNOFFWhen nitrogen is applied toturf, some may be carried inrunoff into surface orgroundwater. Runoff iswater that reaches the turfsoilsurface and is notabsorbed into the ground oraccumulated on the surface,but runs downslope. Therate of runoff is determinedby the amount and rate ofprecipitation, slope, infiltrationcapacity of soil, geologicalfeatures of the site,vegetation cover, andcultural practices.Runoff is most likely tooccur following sudden,heavy rainstorms on soilswith poor infiltration
10TurfgrassNitrogenSourcesDeveloping a nitrogenfertility program is animportant decision that canaffect the quality anddurability of your turf.Because of differences insite conditions, uses of turf,level of turf quality desired,and cost considerations, nosingle program will fit allsituations. Fortunately,there are many differentturfgrass nitrogen sourcesthat you can use to developa program to fit your needs.Before selecting a nitrogensource(s) for yourprogram, understand howquickly the nitrogen in theproduct is released andunder what conditions thisoccurs. It is also helpful toknow how the product isformulated and its potentialfor burning turf.QUICK-RELEASESOURCESQuick-release nitrogensources are also called“quickly available,” “fastacting,”“soluble,” “readilyavailable,” and other termsthat indicate rapid availabilityof nitrogen to turf afterapplication. This groupincludes compoundscontaining ammonium,nitrate, or urea. Quickreleasesources have nitrogencontents ranging from11 to 46 percent (Table 3)and generally are lessexpensive than slow-releasesources. Being watersoluble, they may beapplied in liquid as well asin dry form. They give arapid green-up response,and frequent applications atlow rates are suggested forreducing excessive growthand fertilizer burn.Ammonium and nitratecontainingsalts (ammoniumnitrate, ammoniumsulfate, monammoniumphosphate, etc.) are availablein granular and, insome cases, sprayableformulations. In water,these nitrogen sourcesreadily dissolve into theirpositively and negativelycharged components. Forexample, ammonium nitrate(NH 4NO 3) fertilizer mixedwith water forms ammonium(NH 4+) and nitrate(NO 3-). In soils, bacteriaconvert ammonium intonitrate through a processcalled nitrification. Plantsmay use nitrogen in eitherthe ammonium or thenitrate form, but mostnitrogen is taken up asnitrate.Urea is a syntheticorganic fertilizer thatcontains 46 percent nitrogen.It is available ingranular and prilled formsfor dry applications and,since it is water soluble, itcan be applied as a liquid.Provided there is adequatemoisture following application,it reacts quickly withwater and the naturallyoccurring enzyme urease toform ammonium-nitrogen.This reaction usually takesplace within 7 to 10 days.Under high pH (alkaline)conditions, volatilization ofnitrogen as ammonia mayoccur from urea and ammonium.Volatilization is alsofavored by low soil-cationexchangecapacity (sandysoils), drying of moist soil,and high temperatures.Volatilization of ammonia isTable 3. Some quick-release nitrogen sources used in turfgrassfertilizers.Chemical FertilizerSource formula grade Salt index*Urea CO(NH 2) 246-0-0 75Diammonium phosphate (NH 4) 2HPO 420-54-0 34Monammonium phosphate NH 4H 2PO 411-48-0 30Ammonium nitrate NH 4NO 333-0-0 105Ammonium sulfate (NH 4) 2SO 421-0-0 69Calcium nitrate Ca(NO 3) 216-0-0 53Potassium nitrate KNO 313-0-44 74* Salt index is a relative measure of the salinity of fertilizers andindicates the relative burn potential of nitrogen sources (a high salt indexindicates a high potential to burn turf). Sodium nitrate is the benchmarkvalue against which all other materials are compared, with a salt indexof 100. Salt indices may vary with formulation.
11greatest on grass areas, andlosses as high as 30 percentof the applied nitrogen havebeen reported. Watering-infertilizer keeps such lossesto a minimum.SLOW-RELEASESOURCESSlow-release nitrogensources, also called “controlled-release,”“slowlyavailable,” “slow acting,”and “water insoluble,” arean important part ofturfgrass fertility programs.They provide a longerduration of nitrogen releasethan the quick-releasesources and are safer to useon turf because of theirlower burn potential. Recentstudies have shown thatunder certain conditions,slow-release nitrogensources are less likely toleach into groundwater thanquick-release sources.Disadvantages of slowreleasenitrogen sourcesinclude their high price perunit of nitrogen and reducedefficiency (a lowerpercentage of the appliednitrogen is used by turf inthe first year or two of use)compared to quick-releasesources. The higher cost andlow efficiency haveprompted many manufacturersand turf managers tomix or blend both slow- andquick-release sources.Slow-release nitrogensources can be grouped intoseveral categories, includingthe natural organics,ureaform, urea-formaldehydeproducts, triazones,IBDU, sulfur-coated urea,and polymer-coated nitrogen(Table 4).Natural organicsFor the most part, naturalorganics are by-productsfrom the plant and animalprocessing industries orwaste products. Examplesinclude hoof, horn, andfeather meal; fish scrap andmeal; seed meals (cottonseed,linseed, castor pomace);dried and compostedTable 4. Some slow-release nitrogen sources used for turfgrass fertilization.Product Form* Grade %WIN** %CRN**Natural organicsMilorganite G 6-2-0 92 —Sustane G 5-2-4 66 —Nature Safe G 8-3-5 85 —Ringer Turf Restore G 10-2-6 90 —Harmony 3-6-3 G 3-6-3 60 —UreaformNitroform G,P 38-0-0 67 —METH-EX 38 G 38-0-0 67 —Urea-formaldehyde reaction productsNutralene G 40-0-0 36 —METH-EX 40 G 40-0-0 36 —HD Super Fairway G 35-3-7 83 —Coron L 28-0-0 0 70TriazonesFormolene Plus L 30-0-0 0 60N-Sure L 28-0-0 0 72IBDUPar-Ex IBDU (coarse) G 31-0-0 90 —Par-Ex IBDU (fine) G 31-0-0 85 —Sulfur-coated ureasLebanon Pro G 37-0-0 — —Polymer-coated nitrogenmanures; activated andcomposted sewage sludges;and process tankage.Considerable variationexists in the physical andchemical properties ofdifferent natural organicfertilizers.The natural organics canbe characterized by relativelylow nitrogen contents(usually below 10 percent),the presence of waterinsoluble nitrogen (WIN),and nitrogen release intermediatebetween that ofquick-release nitrogensources and extremely slowreleasenitrogen sourcessuch as ureaform. Release ofnitrogen is dependent onmicrobial activity and isPolyon G 43-0-0 — —Sulfur Kote II G 41-0-0 — —LESCO Poly Plus Std. G 39-0-0 — —Poly-S G 40-0-0 — —Poly-S G 38-0-0 — —Poly-X Pro G 37-0-0 — —*Form refers to physical state of product, G = granular, P = powder, and L = liquid.**%WIN is the percentage water insoluble nitrogen of the total nitrogen; %CRN is the percentage controlled releasenitrogen of the total nitrogen.
12highly variable amongproducts. Factors influencingnitrogen release are thechemical composition of thematerial and environmentalconditions that influencemicrobial activity. Environmentalconditions affectingbreakdown of naturalorganic fertilizers includetemperature, soil moistureand oxygen, and soil pH.UreaformUreaform is made byreacting urea with formaldehydein ratios of about 1.3to 1. Ureaform fertilizersshould contain at least 35percent nitrogen, with atleast 60 percent of the totalnitrogen being WIN. Ureaformaldehydeproducts notfalling within these guidelinesare referred to by otherterms such as methyleneurea and methylol urea.Ureaform is divided intothree, almost equal fractionsbased on solubility. FractionI is soluble in cold waterand contains urea, methylenediurea, anddimethylene triurea.Nitrogen availability in thisfraction is similar to that ofquick-release nitrogensources, but the nitrogen isnot as quickly available.Fraction II is insoluble incold water but soluble inhot water; it is made up ofthe slow-release compoundstrimethylene tetraurea andtetramethylene pentaurea.Fraction III, the mostslowly available, is insolublein both hot and coldwater and is made up ofpentamethylene hexaureaand longer chain polymers.Studies have shown thatover a 6–7 month periodabout 4 percent of FractionI, 25 percent of Fraction II,and 84 percent of FractionIII remain in the soil. Theslow breakdown of FractionsII and III accounts forthe low efficiency ofureaform during the firstyears of use. With continueduse and buildup ofureaform, recovery ofapplied nitrogen improves.Release of nitrogen fromureaform depends onmicrobial activity, and thesame environmental factorsthat affect release fromnatural organics also affectrelease from ureaform.Because of low nitrogenrecovery (efficiency) in thefirst years of use, you willusually need to use higherrates or supplementureaform with solublesources in these years. Thislow recovery and slowresponse during coolperiods support the conceptof fertilization with combinationsof ureaform andquick-release nitrogensources.Other urea-formaldehydeproductsThese are also reactionproducts of urea andformaldehyde but are madewith wider ratios of urea toformaldehyde (more urea)than ureaform; thus, theyrelease nitrogen faster.These products contain 30–35 percent nitrogen and areclassified “slowly available.”However, somecontain enough watersolublenitrogen to give aresponse closer to quickreleasenitrogen sources,such as urea, than to slowreleasenitrogen sources.Others can be expected togive a quick initial response,but they have a slightlyslower release rate than thequick-release nitrogensources. Any urea-formaldehydeproduct that does notclaim WIN or claims CRN(controlled-release nitrogen)and not WIN as a percentageof the total nitrogen,will release nitrogen quickly(similar to urea).Some urea-formaldehydeproducts are available inliquid form, whereas othersare available only as granularfertilizers. They containmostly water solublecompounds such asunreacted urea, methylolurea, and short polymermethylene ureas (methylenediurea and dimethylenetriurea). The amount of eachcompound in a product islargely dependent on theurea/formaldehyde ratioand the conditions underwhich the reaction takesplace during manufacture.These nitrogen sources aretypically more expensivethan urea and ammoniumand nitrate products, butthey are safer since theyhave reduced fertilizer burnpotential.TriazonesTriazones are water-solublecompounds containing atleast 41 percent nitrogen.Triazone mixtures areproduced through a reactioninvolving urea, formaldehyde,and ammonia. On adry weight basis, triazoneproducts are about 30–36percent triazones, about 40–50 percent urea, and theremainder, methylol andmethylene ureas. Triazonesare classified as slow-releasenitrogen sources, eventhough their nitrogenreleasingproperties arecloser to those of urea thanto slow-release nitrogensources. Although moreexpensive than urea,triazone products are saferbecause of their reducedburn potential. Productscontaining triazones areliquids.IBDUIBDU is made by reactingisobutyraldehyde and urea.It contains 31 percentnitrogen, with 90 percent ofthe total nitrogen beingWIN in the coarse (0.7–2.5mm) product and 85 percentWIN in the fine (0.5–1.0mm) product. IBDU breaksdown slowly in soilsbecause of low solubility,but once in solution, it ishydrolyzed and releasesnitrogen. Particle size has alarge effect on the release ofnitrogen, with smallerparticles releasing morequickly. The release rate isfaster with higher soil-watercontent and, to a limitedextent, higher temperatures.In tests at Penn State, wehave observed a three- tofour-week delay beforeobtaining a response fromIBDU applications onKentucky bluegrass, but notafter applications to anaerated and topdressedputting green. Probably theclose contact with wet soiland more liberal irrigationpractices enhanced releaseon the putting green. If the
13delay in response is consideredobjectionable, a solublenitrogen source can be usedto supplement the IBDU.We have observed earlyspring greening with IBDU,and nitrogen recovery fromIBDU exceeded that fromureaform during the firstand second years of use. Wehave gotten a quickerresponse and greaternitrogen recovery from finethan from coarse IBDU.Sulfur-coated ureaSulfur-coated urea (SCU) ismade by spraying preheatedurea prills or granuleswith molten sulfur. Asealant, such as wax or amixture of oil and polyethylene,is often applied toseal pores and imperfectionsin the sulfur. Nitrogencontent is usually in therange of 32–38 percent anddepends on coating thickness.Increasing the thicknesslowers the nitrogencontent.Nitrogen is released fromSCU by microbial degradationof the sealant anddiffusion of soluble nitrogenthrough pores and cracks inthe sulfur coating. Therelease rate quickens ascoating thickness decreasesand as temperature increases.Also, breakage ofthe coating as a result ofmechanical damage oraging enhances the releaseof nitrogen.Particles within a SCUproduct are not identical. Ifthey were, one might expectall of them to releasenitrogen at the same time.Quick release occurs withimperfectly coated particles;an intermediate rate ofrelease takes place withparticles in which thesealant has covered imperfections;and the greatestdelay in release occurs withthe more thickly and moreperfectly coated particles.Once release begins from agiven particle, it is quiterapid. Thus, the slowreleaseproperties of SCUcome from the variability incoatings among the individualparticles. SCU withsealants have given goodresponse from two applicationsper year on Kentuckybluegrass turf, and nitrogenefficiency has equaled thatof quick-release nitrogensources. Sealant-free SCUproducts typically releasenitrogen at a slower ratesince they have thickersulfur coatings.Polymer-coated nitrogenPolymer-coated nitrogenfertilizers consist of urea,SCU, or other nitrogensources coated with a thinlayer of polymer (plastic)resin. They typically containabout 40 percent nitrogen.Several types of polymercoatednitrogen fertilizersare available. For nitrogenrelease to occur frompolymer-coated urea, wateris absorbed through thecoating and dissolves thenitrogen. Nitrogen is thengradually released throughthe coating by osmosis.Different coating thicknessesmay be used toobtain different nitrogenrelease rates. The thicker thecoating, the slower therelease. Release increaseswith a higher temperatureand is not significantlyinfluenced by soil moisturelevels, volume of waterapplied, soil pH, or microbialactivity.For the polymer-coatedSCUs, water passes throughthe polymer coating first,then through pores andcracks in the sulfur coating.Since these products do nothave wax sealants, nomicrobial degradation isneeded. Nitrogen is releasedthrough the openings in thesulfur and diffuses throughthe polymer to the soil. Aswith polymer-coated ureas,release rates can be controlledby varying thecoating thickness.
14Phosphorusin TurfPhosphorus is one of threeprimary nutrients neededby turfgrasses as a regularfertilizer addition. Althoughit is present in smallamounts in turfgrass tissues(0.3–0.55 percent on a dryweight basis), phosphorusis extremely important forrooting, seedling development,cell division, and thesynthesis of various compoundsused by plants.Phosphorus is available toturfgrasses as H 2 PO 4-andHPO 4=and is mobile inplants (meaning that it canmove from one portion ofthe plant to another).Phosphorus deficienciesin turf are usually expressedin the early stages ofseedling development,appearing as a purple or redcoloring of leaf blades andas reduced growth andtillering. Research at PennState has shown that at least60 lb of plant-availablephosphorus per acre isrequired for normal growthand development of lawngrasses.Phosphorus is present ininorganic and organic formsin mineral soils, and bothare important sources forplants. Although the totalamount of phosphorus insoils can be large, much isunavailable to turf becauseit forms insoluble complexeswith other elementsand/or because it is “fixed”to clay particles.The most importantfactors affecting phosphorusavailability to turfgrassesare soil pH and concentrationsof iron, aluminum,manganese, and calcium insoils. In acid soils, theH 2 PO 4-form of phosphoruspredominates and combineswith iron, aluminum, ormanganese to form insolublecompounds that areunavailable to turfgrasses.When the soil pH drops to5.5 and below, enoughphosphorus can be renderedunavailable to cause deficienciesin turf. Also, underacid conditions, somephosphorus can be “fixed”by silicate clays, resulting inreduced availability toplants.In high-pH soils, HPO 4=is the most common form ofphosphorus. In these soilsphosphorus combines withcalcium to form insolublecalcium phosphates. As thesoil pH approaches 8.0 orabove, significant amountsof phosphorus are unavailableto turfgrasses. Maximumamounts of plantavailablephosphorus (bothinorganic and organicforms) are obtained bykeeping the soil pH between6.0 and 7.0.Phosphorus can besupplied to turf as inorganicand/or natural organicfertilizers (Table 5). Inorganicphosphorus fertilizersinclude superphosphatesand ammonium phosphatesand are manufactured bytreating rock phosphatewith various acids. Naturalorganic fertilizers typicallycontain phosphorus derivedfrom plant or animal byproducts.These fertilizerscan contain as much as 13percent phosphorus.Phosphorus is largelyimmobile in soils—meaningthat it takes a long time tomove from the turf surfaceinto the root zone. Phosphorusmay take weeks ormonths to move just a fewinches in soil. Because of itspoor mobility, phosphorusshould be incorporated intothe soil prior to seeding orsodding at the amountrecommended on your soiltest report. Apply thephosphorus to the surface,then incorporate it 4–6inches deep with a rototillerso that developing roots canuse the fertilizer. On estab-Table 5. Some sources of fertilizer phosphorus.Approximate %Sources of available P 2O 5% PhosphorusInorganicOrdinary superphosphate 16–21 7–9Triple (treble) superphosphate 40–47 17–21Monammonium phosphate 48 21Diammonium phosphate 46–53 20–23Natural organicSteamed bone meal 23–30 10–13
15lished turf, some phosphoruscan be incorporated intosoil either just before or justafter cultivating with a coreaerator. Perhaps the bestapproach to phosphorusfertilization of establishedturf is to soil test every threeyears to monitor yourphosphorus levels and touse phosphorus-containingfertilizers periodically tomaintain adequate levels.Phosphorus, along withnitrogen, is one of the majornutrient sources contributingto surface- and groundwaterpollution in theUnited States. Althoughphosphorus is not readilyleached from turf soils intogroundwater, recent studiesof phosphorus fate oncropland have shown thatthis nutrient can entersurface waters via erosionand runoff. Avoid applyingphosphorus fertilizer whererunoff is likely—such as onfrozen soils and pavedsurfaces.Potassiumin TurfPotassium is a primaryturfgrass nutrient and isusually supplied annuallyas fertilizer to lawns. Itmakes up about 1.0–2.5percent of the plant’s dryweight, and its primary roleinvolves regulating severalimportant physiologicalprocesses. Potassiumactivates plant enzymesused in protein, sugar, andstarch synthesis. It alsoplays a key role in maintainingturgor pressure inplants. Thus, it has a stronginfluence on droughttolerance, cold hardiness,and disease resistance ofturfgrasses. Deficiencies ofpotassium in turf may beexpressed as increasedsusceptibility to drought,winter injury, and disease.Although large quantitiesof potassium are present insoils, only a small fraction isavailable to plants. Mostsoil potassium is in unavailableforms as feldspar,muscovite, and biotiteminerals. Potassium isavailable to turfgrasses inthe ionic form (K + ) andoccurs in the soil solutionand on negatively chargedsoil particles. In general,more plant-availablepotassium is present in finetexturedmineral soils (soilsthat contain high amountsof clay) than in sandy soils,especially in areas thatreceive high amounts ofrainfall or are regularlyirrigated. The best way todetermine potassium needsfor turfgrass is through soiltesting.Potassium is mobile inplants and sometimes canbe taken up in amountsgreater than needed foroptimum growth. Thisphenomenon, called“luxury consumption,” isgenerally consideredinefficient use of the nutrient.It is difficult to determineif luxury consumptionis a problem in turf culturesince very little informationis available on the optimumconcentrations of potassiumin turfgrasses.Potassium can be suppliedto turf using inorganicfertilizers, natural organicfertilizers, or both (Table 6).However, most fertilizerpotassium is derived frominorganic sources, inparticular, muriate ofpotash (potassium chloride)and sulfate of potash(potassium sulfate). Both ofthese fertilizers are watersoluble.Table 6. Sources of fertilizer potassium.Approximate %Sources of available K 2O % PotassiumMuriate of potash (KCl) 60–63 50–52Sulfate of potash (K 2SO 4) 50–53 44
16Although it is readilyleached into groundwater,potassium is not a majorpollutant in surface- andgroundwater in the UnitedStates. It rarely is present inconcentrations toxic topeople or aquatic life, and itdoes not deplete water ofoxygen.SecondaryNutrients inTurf: Calcium,Magnesium,and SulfurCalcium, magnesium, andsulfur are consideredsecondary nutrients becausein most cases they onlyoccasionally need to besupplied to turf in the formof fertilizer. Applications ofcalcium and magnesium areusually only necessarywhen your soil pH is belowoptimum for turfgrassgrowth. By liming soil whenyour soil test indicates aneed, you are supplyingyour turf with calcium orcalcium- and magnesiumcontaininglimestone. Whenyour soil test indicates aneed for calcium but notmagnesium, you can use alime source containing onlycalcium carbonate. If thesoil is low in magnesium,however, use dolomiticlimestone since it containsboth calcium carbonate andmagnesium carbonate(Table 7).In the rare event thatcalcium is recommended fora lawn with an adequatepH, you can use gypsum asa source of calcium. Keep inmind that gypsum is not aliming source. Also, despiteclaims on some gypsumlabels, it will not relieve soilcompaction or break up claysoils in the northeast UnitedStates. Gypsum improvessoil structure in sodic andhigh-salinity soils found insome areas of the westernUnited States.Sulfur is sometimes usedto lower soil pH where ahigh soil pH can cause turfproblems. Sulfur is usuallyonly necessary in westernstates where arid conditionslead to alkaline soils. In thenortheastern United States,high pH values are rarely aproblem and there isusually enough sulfur insoils to supply turf needs.Table 7. Some common sources of calcium, magnesium, and sulfur.ApproximateSourcesnutrient content*Calcium carbonate (agricultural limestone)32% calciumMagnesium/calcium carbonate (dolomitic limestone) 22% calciumGypsum22% calciumCalcium nitrate19% calciumMagnesium/calcium carbonate (dolomitic limestone) 12% magnesiumEpsom salt (magnesium sulfate)10% magnesiumAmmonium sulfate24% sulfurFerrous sulfate19% sulfurGypsum19% sulfurPotassium sulfate18% sulfurElemental sulfur90% sulfur*Actual percentages of nutrients may vary depending on purity and source ofproduct.
17Micronutrientsin TurfThe seven micronutrients(sometimes called traceelements) required byturfgrasses include iron,manganese, zinc, copper,molybdenum, boron, andchlorine. As mentionedearlier, micronutrients areneeded by turfgrasses onlyin minute amounts andrarely need to be suppliedto turfgrasses growing inmineral soils. However,when turfgrasses are grownin high-sand-content soils(golf course putting greensand some tees) or high-pHsoils, micronutrient applicationscan be beneficial.IRONIron is an important componentof plant enzymes andproteins involved in respiration,nitrogen metabolism,and chlorophyll synthesis.In individual turfgrassplants iron deficienciesappear as chlorosis (yellowing)of the youngest (upper)leaves. Turf deficiencysymptoms show up asyellow mottling, rather thanthe uniform yellowingobserved in nitrogendeficientturf.Most soils in the northeasternUnited Statescontain adequate levels ofiron, and deficiencies arerare. In unusual cases whereexcessive liming hasoccurred or irrigation watercontains high bicarbonatelevels, the uptake and/ortranslocation of iron by turfmay be reduced. Thisproblem, sometimes referredto as lime-inducedChelated micronutrientsIron, zinc, manganese, and/or copper often occur informs that are not taken up by plants. This problem isespecially marked if the soil has a high pH (8.0 orabove). One way of correcting this problem is to applythe nutrient as a chelate. Chelate comes from the Greekword “clawlike” and denotes a soluble and stableproduct formed when an organic compound called achelating agent bonds to the nutrient. The chelatingagent keeps the nutrient in solution and releases it atthe root surface where it is absorbed into the plant.Chelated nutrients can also be absorbed through turffoliage.The most common commercial chelating agents used inthe turfgrass industry are EDTA(ethylenediaminetetraacetic acid) and DTPA(diethylenetriaminepentaacetic acid). EDTA chelatesiron at a pH of less than 6.3; above a pH of 6.8 it reactswith calcium, rendering it ineffective. DTPA chelatesiron up to a pH of 7.5; above 7.5, calcium interfereswith solubility, making it ineffective.Chelates have been shown to be superior sources ofiron, zinc, manganese, and/or copper since lower ratesof chelated micronutrients can achieve the same resultsas higher rates of inorganic sources. Because lowerrates can be used, the potential for plant injury isreduced. However, the cost of chelated micronutrientsmay be considerably higher than that of inorganicsources.chlorosis, can be correctedby acidifying the soil and bysupplying iron-containingfertilizers.In the northeasternUnited States, iron fertilizeris applied by turfgrassmanagers to enhance turfcolor without stimulatingexcessive leaf growth. Ironapplications can producedarker green turf evenwhen levels are adequate inplant tissues before applicationsare made. By reducingthe rate of nitrogen fertilizerand supplementing withsmall amounts of iron, anoticeable turf green-up canbe achieved with fewer ofthe negative aspects associatedwith excessive nitrogenfertilization, such as frequentmowing and outbreaksof certain diseases.The most common formsof iron fertilizer forturfgrasses are inorganiciron salts and organic ironchelates (chelated iron)(Table 8). An inorganic ironsalt is a water-soluble formof iron that contains iron oriron and ammonium pairedwith sulfate (e.g., ferroussulfate, ferric sulfate, orferrous ammonium sulfate).Since turfgrasses can absorbiron from these productsthrough foliage, the prod-
18ucts are typically applied asfoliar sprays. In soil applications,much of the iron frominorganic sources is convertedto insoluble ironhydroxides, iron phosphates,or iron carbonates—compounds that are unavailableto turfgrasses.Chelated iron sources areusually more efficient atsupplying plants with ironthan inorganic iron salts.Recent studies have shownthat about 2 lb of iron peracre from iron chelateprovides the same colorenhancement of Kentuckybluegrass as 4 lb iron peracre from inorganic ironsulfate. Since lower rates ofchelated iron can be used toobtain a dark green turf,there is less chance ofinjuring turfgrass with aniron application.Rates of iron fertilizer forlawn grasses can varydepending on the source,time of year, and number ofapplications. Generally, arate of 2 lb of iron per acrefrom chelated iron isadequate for a noticeableturf green-up. Turf green-upfrom iron applications canlast between several weeksand several months,Table 8. Some common fertilizer sources of iron.ApproximateSourceiron content*Ferrous sulfate 19%Ferric sulfate 23%Ferrous ammonium sulfate 14%Iron chelates:NaFeDTPA 10%NaFeEDTA 5–9%depending on weatherconditions followingapplication. Applicationsduring cool, wet periods(when turf is growingrapidly) enhance color foronly two to three weeks,whereas applicationsduring cool, dry periods(when growth of turf isslow) may last for severalmonths.Excessive amounts ofiron can cause noticeablediscoloration (a black-greencolor) in turfgrasses and, insome cases, may injurethem. The degree of injurydepends on the type of turf,the rate of iron, and theenvironmental and managementconditions at the timeof application. Sometemporary blackening ofKentucky bluegrass foliagehas been observed with aslittle as 4 lb of iron per acre,from both inorganic andchelated sources. Somedieback of Kentuckybluegrass foliage can occurwith rates higher than 15 lbiron per acre.*Actual percentages of iron may vary depending on purity and source ofproduct.Table 9. Some common fertilizer sources of micronutrients(manganese, zinc, copper, molybdenum, boron, and chlorine).ApproximateSourcesnutrient content*Manganese:manganese sulfate and manganese oxide 0.05–7.27% manganesemanganese EDTA0.05% manganeseZinc:zinc sulfate and zinc oxide0.05–1.3% zinczinc EDTA0.05% zincCopper:copper oxide0.05–0.5% coppercopper EDTA0.05% copperMolybdenum:sodium molybdate 0.0005–0.026%molybdenumBoron:boric acid0.02% boronChlorine:potassium chloride< 10% chloride*Actual percentages of nutrients may vary depending on purity and source ofproduct.OTHERMICRONUTRIENTSUnless your soil has a highpH (greater than 8.0) andthe texture is extremelysandy, micronutrientfertilizer applications areprobably not needed. Infact, micronutrients otherthan iron are rarely beneficialand are sometimesharmful when applied toturfgrasses. Boron, forexample, is toxic toturfgrasses even whenapplied in small amounts.Indiscriminate use ofcopper can lead to deficienciesof iron in turfgrasses. Ifyou are managing turf inhigh-sand-content soils,work with a reputable soiland tissue testing lab todetermine if micronutrientsupplements are needed. Ifthey are, use high-qualityturfgrass fertilizers containingonly the micronutrientsthat you need to correct thedeficiency (Table 9).
19FertilizerProgramsNo single turfgrass fertilizerprogram is ideal for alllawns, athletic fields, andgolf courses. The type andamount of fertilizer you useand the timing of yourapplications will depend onmany factors, includinggrass species and cultivars,soil type, managementpractices, how the turf isused, and the users’ expectations.Turfgrass species differ inthe amount of fertilizer,especially nitrogen fertilizer,that they require for bestperformance (Table 10).Kentucky bluegrass andperennial ryegrass typicallyneed 3–4 lb nitrogen per1000 sq ft per year, whereasthe fine fescues respondbest to about 2–3 lb nitrogenper 1000 sq ft per year. IfKentucky bluegrass turf isfertilized only with 1 or 2 lbof nitrogen per 1000 sq ftduring the growing season,it will usually become lightgreen or yellow, thin, andmore susceptible to pestdamage.Table 10. Annual nitrogen requirements for turfgrass species used inthe northeastern United States.Amount of nitrogen required each growingTurfgrass speciesseason* (lb/1000 sq ft)Kentucky bluegrass 3–4Rough bluegrass 3–4Perennial ryegrass 3–4Annual ryegrass 2–3Tall fescue 2–3Fine fescues (creeping red,Chewings, hard, and sheep) 2–3Creeping bentgrass 3–6* Use rates in the high range for turf grown in infertile soils, when clippingsare removed from the site, and in high traffic areas. Rates in the low rangecan be used for turf grown in inherently fertile soils and when clippings arereturned to the turf.In contrast, if a finefescue turf receives nitrogenin amounts required byKentucky bluegrass (3–4 lbnitrogen per 1000 sq ft peryear), it can become moresusceptible to drought, heatstress, and some diseases.Therefore, be sure toidentify the species you aremanaging and to adjustyour fertility programaccordingly. With lawnscontaining mixtures ofspecies, fertility programsare usually designed tofavor the most desirablespecies.Turfgrass cultivars canalso vary in their nitrogenrequirements. However,specific recommendationsfor individual cultivars areseldom made becausenitrogen requirements havenot been determined formost new cultivars. Inaddition, many managershave no way of knowingwhich cultivars are presentin the turf.Turfgrass fertilizerprograms will vary with soilquality and type.Turfgrasses growing onsites where much of thetopsoil has been removed orin sandy soils usuallyrequire more fertilizer thanturf growing in goodqualitytopsoils. This isbecause of the loweramounts of nutrients foundin poor-quality soils and thefact that nitrogen is moreeasily leached from sandysoils. Improving poorqualitysoils with additionsof organic amendments,such as good-qualitycompost, can improve soilstructure, add nutrients,and enhance nutrientretention, thus reducingfertilizer needs.Management practicessuch as mowing andirrigation can significantly
20influence the amount offertilizer that turfgrasseswill need. By returninggrass clippings to your lawnyou can reduce nitrogen,phosphorus, and potassiumfertilizer needs by up toone-third. Lawns irrigatedoften during the summermonths will use morefertilizer than those notirrigated.How the turf is used alsodictates how much fertilizeris needed. For instance,turfgrasses growing in hightraffic areas, such as athleticfields, usually require morefertilizer for better recoveryfrom wear than low trafficareas. Roadside turf, used tocreate a buffer betweenlanes on highways and tocontrol erosion on banks,generally receives little orno fertilizer since aestheticsis not a primary goal andmowing must be kept to aminimum.Ultimately, users willhave differing expectationsconcerning the function andaesthetics of turfgrass areas.Thus, fertilizer programswill vary according to theseexpectations.APPLICATIONFREQUENCYThe number of fertilizerapplications you makeduring the growing seasonis just as important as theamount and type of fertilizeryou use. To maintainhigh-quality turf, two ormore fertilizer applicationsper year are generallyrequired. If only twoapplications are made,higher rates of nitrogen(1.25 to 1.5 lb nitrogen per1000 sq ft per application)are usually necessary. In thiscase, fertilizers containingslow-release nitrogensources are desirable sincethe nitrogen is releasedgradually over extendedperiods and turf burning isless likely.In most cases, fertilizerprograms involve morethan two and as many asfive applications per year.These programs allow moreflexibility in application rateand nitrogen source thantwo-application programssince there is less timebetween applications. Afour application per yearprogram, for example, caninvolve rates less than 1 lbnitrogen per 1000 sq ft perapplication. These lowerrates allow the use of quickreleasenitrogen sources.SCHEDULINGFERTILIZERAPPLICATIONSThe best times of year tofertilize cool-seasonturfgrasses are in latesummer, late fall, and midto late spring. Sometimes,two spring applicationsmay be desirable—one inearly spring and another inlate spring. Fertilizersapplied to turf duringperiods of heat and droughtin midsummer can stressplants and lead to injury.The most important timeof year to fertilizeturfgrasses is late summer(early to mid September).Fertilizer is very necessaryat this time because itpromotes recovery fromdrought and heat-relatedinjury sustained duringmidsummer. Late summerto early fall is also the timeof year that cool-seasongrasses begin to manufactureand store carbohydrates.Carbohydrates areused by turfgrasses for rootand rhizome growth,disease and stress tolerance,and protection from winterinjury. Nitrogen appliedduring late summer stimulatesfoliar growth, but notto the extent that occurs inspring. Thus, slightly higherrates of nitrogen (1.0–1.5 lbnitrogen per 1000 sq ft) canbe used for late summerapplication.An application of fertilizerin late fall can serve as areplacement for an earlyspring application. Late fall,in this case, is the time thatfoliar growth slows orstops, but soils are notfrozen. In most areas ofPennsylvania, late fallfertilization should takeplace in mid to lateNovember.The advantages of latefall fertilization over earlyspring fertilization are: (1)nitrogen taken up by turf inlate fall is used primarily forand by roots (before the soilfreezes); (2) little, if any,foliar growth occurs; and (3)carbohydrates are notexhausted as quickly whenlate fall fertilizer applicationsare made in place ofearly spring applications. Ifdone correctly, late fallfertilization provides earlyand noticeable turf green-upin spring with less foliargrowth. Excess growth isoften associated with highrates of nitrogen applied inearly spring.The main disadvantageof late fall fertilization isthat, in some situations,nitrogen leaching mayoccur. Consequently, thispractice should not beperformed on sandy soilswith quick-release nitrogenfertilizers. Slow-releasenitrogen sources, such asnatural organics and IBDU,are ideal for late fall applicationsmostly because theyare not as likely to leach asquick-release sources.If late fall fertilizerapplications are not made, asmall amount of fertilizermay be desirable in earlyspring. Applying high ratesof nitrogen to turf in earlyspring produces excessivefoliar growth and forcesplants to use up valuablefood reserves needed forroot growth and diseaseresistance. Thus, lower ratesshould be used. Typically,rates of 0.5 to 0.75 lb nitrogenper 1000 sq ft allowearly spring green-up oflawns without excessivefoliar growth. Since 0.5 lbnitrogen per 1000 sq ft doesnot supply enough nitrogento carry the turf through thesummer months, a latespring application isprobably needed. A latespring application can bemade in late May or earlyJune; rates can vary from0.75 lb to 1.5 lb nitrogen per1000 sq ft. A fertilizercontaining some slowreleasenitrogen is desirableat this time of year becauseit can supply limitedamounts of nitrogen to turfin early to midsummer.
21 3POTASSIUM ANDPHOSPHORUSRecommendations from asoil test lab should specifythe amounts of phosphorusand potassium (usually inlb phosphate and potashper 1000 sq ft) your turfneeds. The rate of phosphateapplied in a singleapplication should besimilar to rates of nitrogen(0.5–1.5 lb per 1000 sq ft) orslightly higher (2 lb phosphateper 1000 sq ft), but itshould not exceed 5 lbphosphate per 1000 sq ft.Potassium is usuallyapplied at rates of 0.5 to 2.0lb potash per 1000 sq ft.EXAMPLES OF LAWNFERTILIZER PROGRAMSThe three sample fertilizerprograms at right aredesigned for medium- tohigh-maintenance lawnsgrowing under environmentalconditions andsoils found in centralPennsylvania.Example of a fertilizer program for a perennial ryegrass and/or kentucky bluegrass lawn (clippingsreturned)*Dates of application Nutrients/1000 sq ftMay 1–June 101.25 lb nitrogen (20% or more as WIN, CRN, or a coated nitrogen source**)0.5 lb phosphate0.5 lb potashSept. 1–Sept. 201.5 lb nitrogen (20% or more as WIN, CRN, or a coated nitrogen source**)0.5 lb phosphate0.5 lb potashNov. 10–Nov. 301.25 lb nitrogen (50% or more as WIN, CRN, or a coated nitrogen source**)0.75 lb potash* If soil test indicates high levels of phosphate and potash, omit from program and use nitrogen sources only. If soiltest indicates phosphate and potash are needed, use fertilizer with high proportions of each nutrient.** WIN = water insoluble nitrogen, CRN = controlled release nitrogen; coated nitrogen sources can include sulfurcoatedurea or polymer-coated nitrogen.Example of a fertilizer program for a fine fescue lawn (clippings returned)*Dates of applicationMay 1–June 10Sept. 1–Sept. 20Nutrients/1000 sq ft1.0 lb nitrogen (20% or more as WIN, CRN, or a coated nitrogen source**)0.5 lb phosphate0.5 lb potash1.0–1.5 lb nitrogen (20% or more as WIN, CRN, or a coated nitrogen source**)0.5 lb phosphate0.5 lb potash* If soil test indicates high levels of phosphate and potash, omit from program and use nitrogen sources only. If soiltest indicates phosphate and potash are needed, use fertilizer with high proportions of each nutrient.** WIN = water insoluble nitrogen, CRN = controlled release nitrogen; coated nitrogen sources can include sulfurcoatedurea or polymer-coated nitrogen.Example of a fertilizer program for a tall fescue lawn (clippings returned).*Dates of applicationMay 1–June 10Sept. 1–Sept. 20Nov. 10–Nov. 30Nutrients/1000 sq ft1.0 lb nitrogen (20% or more as WIN, CRN, or a coated nitrogen source**)0.5 lb phosphate0.5 lb potash1.0 lb nitrogen (20% or more as WIN, CRN, or a coated nitrogen source**)0.5 lb phosphate0.5 lb potash1.0 lb nitrogen (50% or more as WIN, CRN, or a coated nitrogen source**)0.75 lb potash* If soil test indicates high levels of phosphate and potash, omit from program and use nitrogen sources only. If soiltest indicates phosphate and potash are needed, use fertilizer with high proportions of each nutrient.** WIN = water insoluble nitrogen, CRN = controlled release nitrogen; coated nitrogen sources can include sulfurcoatedurea or polymer-coated nitrogen.
PREPARED BY PETER LANDSCHOOT, PROFESSOR OF TURFGRASS SCIENCEFunding for Urban Nutrient Management is provided by theChesapeake Bay Program through the Pennsylvania Department ofAgriculture.Visit Penn State’s College of AgriculturalSciences on the Web: www.cas.psu.eduPenn State College of Agricultural Sciencesresearch, extension, and resident educationprograms are funded in part by Pennsylvaniacounties, the Commonwealth ofPennsylvania, and the U.S. Department ofAgriculture.This publication is available from the PublicationsDistribution Center, The PennsylvaniaState University, 112 AgriculturalAdministration Building, University Park, PA16802. For information telephone 814-865-6713.Where trade names appear, no discriminationis intended, and no endorsement byPenn State Cooperative Extension is implied.Issued in furtherance of Cooperative ExtensionWork, Acts of Congress May 8 andJune 30, 1914, in cooperation with the U.S.Department of Agriculture and the PennsylvaniaLegislature. T. R. Alter, Director ofCooperative Extension, The PennsylvaniaState University.This publication is available in alternativemedia on request.The Pennsylvania State University is committedto the policy that all persons shallhave equal access to programs, facilities,admission, and employment without regardto personal characteristics not related toability, performance, or qualifications asdetermined by University policy or by stateor federal authorities. It is the policy of theUniversity to maintain an academic andwork environment free of discrimination,including harassment. The PennsylvaniaState University prohibits discriminationand harassment against any person becauseof age, ancestry, color, disability orhandicap, national origin, race, religiouscreed, sex, sexual orientation, or veteranstatus. Discrimination or harassmentagainst faculty, staff, or students will notbe tolerated at The Pennsylvania StateUniversity. Direct all inquiries regarding thenondiscrimination policy to the AffirmativeAction Director, The Pennsylvania StateUniversity, 328 Boucke Building, UniversityPark, PA 16802-5901, Tel 814-865-4700/V, 814-863-1150/TTY.© The Pennsylvania State University 2003Produced by Information and CommunicationTechnologies in the College of AgriculturalSciencesCAT UC1845M11/03cp4609