ORIGINALARTICLE
Agronomicandenvironmentalimpactsofphosphorus
fertilizationoflowinputbahiagrasssystemsinFlorida
AugustineK.Obour•MariaL.Silveira•JoaoM.B.Vendramini•LynnE.Sollenberger•GeorgeA.O’Connor•JamesW.Jawitz
Received:11May2010/Accepted:30July2010/Publishedonline:19August2010ÓSpringerScience+BusinessMediaB.V.2010
AbstractPhosphorusmanagementinlowinput
bahiagrass(PaspalumnotatumFlugge)systemsrep-
resentsamajorchallengeofagronomicandenviron-
mentalimportance.ConcernsoveragriculturalP
transporttosurfacewatershavepromptedseveral
revisionsinthePfertilizerrecommendationsfor
bahiagrassinFlorida.Thisstudyevaluatedtheeffects
ofrevisedPfertilizerrecommendationsonforage
drymatteryield(DMY)andnutritivevalueandthe
potentialimpactsonwaterqualityinbahiagrass
pasturesgrowingonaSpodosol.Treatmentscon-
sistedofthefactorialcombinationofthreeNrates
(0,56,and112kgNha-1)andfourPrates(0,5,10,
and20kgPha-1),replicatedthreetimesandapplied
annuallyinMayof2007and2008.Foragewas
harvestedat28-dintervalsandDMY,tissuePand
crudeproteinconcentration,andPuptakewere
measured.TomonitorPleachingpotential,suction
cuplysimeterswereinstalledat15-,30-,60-,90-,and150-cmdepths.In2007,bahiagrassDMYwasnot
affectedbyP;however,in2008therewasalinear
increaseinDMYfrom6.9to8.2Mgha-1asPrate
increased.Inbothyears,tissuePincreasedlinearly
from2.1to2.5gkg-1asPratesincreasedfrom0to
20kgPha-1.Similarly,Puptakeincreasedfrom
14kgPha-1forthecontrolto19kgPha-1forthe
treatmentreceiving20kgPha-1.Duringthe2-year
study,PfertilizationhadnoimpactonsoilMehlich-1,
water-extractableP,andleachatePconcentrations.
LeachatePconcentrationsatthe15-and30-cmdepths
variedseasonally(from0.05to0.85mgPl-1),with
greaterspikesoccurringduringperiodsofhighwater
tableconditions.CurrentPfertilizationrecommenda-
tioncanincreasebahiagrassDMYwithnoadverse
impactsonwaterquality.
KeywordsLeachingÁPasturefertilizationÁ
SpodosolÁWaterquality
Introduction
Bahiagrassisthemostwidelyplantedperennialforage
grassinFlorida,occupyingabout2millionhainthe
state(MuchovejandMullahey2000).Bahiagrass
pasturesarepredominantlygrownonSpodosolsand
arewelladaptedtothesandysoilsofFlorida.Thegrass
tolerateslowsoilfertilityconditions,lowpH,and
intermittentwetconditionsandproduces
reasonableA.K.ObourÁM.L.Silveira(&)ÁJ.M.B.VendraminiRangeCattleResearchandEducationCenter,UniversityofFlorida,3401ExperimentStation,Ona,FL33865,USAe-mail:mlas@ufl.edu
L.E.SollenbergerAgronomyDepartment,UniversityofFlorida,2185McCarty,Gainesville,FL32611,USA
G.A.O’ConnorÁJ.W.JawitzSoilandWaterScienceDepartment,UniversityofFlorida,106NewellHall,Gainesville,FL32611,USA
123NutrCyclAgroecosyst(2011)89:281–290DOI10.1007/s10705-010-9393-1forageyieldsindroughtyconditions.Mostforage-
basedcow-calf(Bossp.)systemsinFloridarelyon
bahiagrasspastureasthemajorsourceofenergyand
proteinformostofthegrowingseason,therefore
adequateproductionofbahiagrassforageiscriticalfor
thesuccessofthecow-calfindustryinthestate.
Approximately80%ofcow-calfproductionin
Floridaisconcentratedinenvironmentallysensitive
areasinCentralandSouthFlorida(FDCAS1998),
wherePtransportfromagriculturalactivitiesrepre-
sentsaseriousthreattowaterquality(Reddyetal.
1999).Theprimarycow-calfproductionregioninthe
state,theLakeOkeechobeewatershed,facessignif-
icantproblemsassociatedwithnonpoint-sourcepol-
lutionofsurfacewatersbyagriculturalP.Although
dairyandbeefoperationshavebeensuggestedasthe
majorcontributorsofPtoLakeOkeechobee
watershed(Burgoaetal.1991),potentialPlosses
fromlow-inputcow-calfsystemsaresmallerthan
otherintensiveagriculturaloperationssuchascon-
finedanimalfeedingoperationsandintensiverow-
cropfarming.However,becauseoftheextensive
acreageoccupiedbygrazinglandsinFlorida,P
transportfrombeefranchingoperationscanpoten-
tiallyhavemajorimpactsonwaterquality(Allen
1988).Therefore,effectiveP-managementstrategies
thatbalanceproductivityandenvironmentalprotec-
tionarerequiredtosupportthecontinuedsuccessof
thecow-calfindustryandwaterqualityprogramsin
thestate.
Inrecentyears,concernsabouttheenvironmental
impactsofPfertilizationonbahiagrasspastureshave
promptedseveralrevisionsintheUniversityof
Floridabahiagrassfertilizationrecommendations
(Hanlonetal.2008).ThecurrentPfertilizerrecom-
mendationforestablishedbahiagrassinFloridais
basedonbothsoilandplanttissuePtesting
(Mylavarapuetal.2007).Phosphorusisrecom-
mendedonlywhentissuePconcentrationsare
below1.5gkg-1andsoiltestPlevelsareverylow
orlow(\15mgkg-1Mehlich-1P).However,there
arelimitedfielddatatovalidatetherevisedP
fertilizationrecommendationsforestablishedbahia-
grasspastures.
Theemphasisofmostpreviousstudiesonbahia-
grassPfertilizationhasbeenmaximizingbahiagrass
yieldatrelativelyhighlevelsoffertilizerP.Thus,
despitesignificantliteratureonbahiagrassresponseto
Pfertilization,thereislimitedinformationonstrategiesthatbalanceproductivitywithenvironmen-
talimplications.Fieldresearchisnecessaryto
determinetheminimumamountofPrequiredto
sustainbahiagrassyieldandpasturepersistence
withoutadverselyaffectingwaterquality.Thisis
particularlyimportantinFloridawherethehydrology
incombinationwithenvironmentalconditionsand
soilcharacteristicsacceleratenutrienttransportof
agriculturalPtosurfacewater.Theobjectivesofthe
studywereto(i)investigatebahiagrassresponseto
reducedPfertilizationratesand(ii)evaluatethe
potentialeffectsofbahiagrassPfertilizationonsoil-
testPconcentrationsandwaterquality.
Materialsandmethods
Theexperimentwasconductedonanestablished
bahiagrassfield(27°230N,81°560W)onSmyrnasand
(sandy,siliceous,hyperthermicAericAlaquods).
InitialsoilcharacterizationoftheAphorizon(toa
depthof15cm)showedanaveragesoilpHof5and
Mehlich-1extractableP,K,Mg,andCaof5,40,74,
and579mgkg-1,respectively.Bahiagrasswas
establishedin1990andhadnohistoryofNandP
fertilizationduringthepast15years.Plotsizewas
12.2912.2m,witha3.1-malleybetweenplots.
TreatmentswereafactorialcombinationofthreeN
applicationrates(0,56and112kgNha-1year-1)
andfourPrates(0,5,10,and20kgPha-1year-1)
arrangedinacompletelyrandomizeddesignwith
threereplications,foratotalof36plots.The56and
112kgNha-1ratescorrespondtotherecommended
UniversityofFloridaInstituteofFoodandAgricul-
turalSciences(UF-IFAS)lowandmediumbahia-
grassNoptions,respectively(Mylavarapuetal.
2007).Phosphorusapplicationratescorrespondto0,
0.5-,1-,and2-timestheUF-IFASPfertilizer
applicationrateof10kgPha-1.Nitrogenwas
appliedasammoniumnitrateandPaspotassium
phosphate.Eachplotalsoreceivedabasalannual
applicationof47kgKha-1(asKCl)and5kgha-1
ofmicronutrientmix(F503Gmicromix)containing
24gkg-1ofBandCu,144gkg-1ofFe,60gkg-1
ofMn,0.6gkg-1ofMo,and56gkg-1ofZn.Plots
receivedlimepriortotheinitiationofthestudyto
raisethesoilpHto5.5.Theexperimentwas
conductedfor2years(2007and2008),andtreat-
mentswereappliedinMayofeach
year.282NutrCyclAgroecosyst(2011)89:281–290
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