Foliar fertilization maintained higher seedling nitrogen levels and increased root ... Nursery managers can improve seedling viability by adding foliar fertilizer.
Foliar Fertilization During Bud Initiation Improves Container-Grown
Ponderosa
Pine
SeedlingViability Mark E. Montville, Plum Creek Forest Nursery, Box 188, Pablo, Montana, 59855; David L. Wenny and R. Kasten Dumroese, Departmentof Forest Resources,ResearchNursery, Universityof Idaho, Moscow, Idaho 83844-1137.
ABSTRACT. Ourobjectivewastodetermineif avoidingnutrientstressduringbudinitiationofponderosa pine (Pinusponderosa vat. ponderosa) grownin a containernurserywouldenhanceseedlingviability.Nitrogen stresswas avoidedby applyingfoliar fertilizer at rates between324 and 972 ppm N to greenhouse-grown seedlings. Foliarfertilizationmaintainedhigherseedlingnitrogenlevelsandincreasedrootcollardiameter by45%. Heightwasslightlyincreased, cold-hardiness slightlyreduced,androotgrowthpotentialunaffected byfoliar fertilizer applications. Nurserymanagerscan improveseedlingviabilitybyaddingfoliar fertilizer applicationsto their growingregimes.West.J. Appl.For. 11(4):114-119.
thetimingof seedlingbudset,seedlingmorphological charGrowers ofcontainer seedlings forreforestation commonly
manipulatefertilizer applicationrates,especiallynitrogen (N), to regulategrowthof theircrops(Landiset al. 1989).In general,seedlings receiveabout50 ppmN duringestablishmentandhardening,andabout150 ppmN duringtherapid growthphase(Tinus and McDonald 1979, Landiset al. 1989).Theabruptreduction fromhighN ratesto lowerrates, waterstress, andfurtherreductionof nutrientuptakebecause of reducedrootgrowthandlowermassflow anddiffusionof nutrients(TimruerandArmstrong1989)areintendedto stop heightgrowthandinitiatebudformation.However,continuingapplications oflowlevelsofN duringtheremainder ofthe hardening phasemayneverallowseedlings torecoverprebud formationN concentrations(Montville and Wenny 1990). Seedlings requirepropernutrition,especiallyN, to develop carbohydrate reserveslate in the growingseasonfor optimum survivaland growth after outplanting(Tukey and Meyer 1966,Ericssonet al. 1983,Miller andTimmer 1994). Because Douglas-fir (Pseudotsuga menziesii var. menziesii) (Miller 1981) and slash pine (Pinus elliotii) (Eberhardtand Pritchett1971) treesabsorbfoliar applied nutrients, we hypothesized thatfoliar-appliedN absorbed by container-grown ponderosa pine(Pinusponderosavar.ponderosa) seedlingscould be used to avoid nutrient stress duringbud initiationand subsequent seedlinghardening, thus improvingseedlingviability (Langerud1991). Our objectivewasto determinetheeffectof foliar-appliedN on 114
WJAF11(4)1996
acteristics,root growthpotentialand cold-hardiness, and seedlingnutrition,particularlyfoliar N concentration. Methods
Ponderosa pineseeds, collectedat900m elevation,15km northeast of Moscow, Idaho, were sown the first week of
April (week0) into21 trayseachcontaining 200RayLeach© pinecells(66 ml) filled witha 1:1peat:vermiculite medium. Trays were randomizedon greenhousebencheswithin a productioncrop.Duringeveryirrigation,phosphoric acid wasadded(41 ppmP) to lowerpH. Fromweek2 through5, all seedlingsreceived Peters' Conifer Starter© (N:P:K = 4:25:35) at 42 ppmN twiceper weekas soil drenches(see Table 1 and Wenny and Dumroese1987). During weeks6 through9, all seedlings werefertilizedtwiceper weekas a soil drench; Peters' Conifer Grower© (N:P:K = 20-7-19) at
120ppmN wasalternated withcalciumnitrate(N:P:K:Ca= 15.5-0-0-19)at 92 ppmN. Throughoutthe growingseason, duringeachfertilization with a Peters'fertilizer, micronutrients were added at the rate of 0.5, 2.25, 31, 18, and 35
mgL-1 of B, Fe,Mn,Mg, andS, respectively. When seedlingsattained a target height of 12-15 cm (week 10) intermittentall-night lighting was suspended Eighteentraysof seedlingswere randomlyassignedto receive Peters' Foliar Feed© (N:P:K = 27:15:12) twice each
Table I Weight proportions of the various elemental nutrients applied, expressed as percentages of the total weight of the fertilizer.
Starter
Nutrient N
(7-40-17)
P K B Cu Fe
7 17.5 14.1 0.015 0.03 0.2
Mg Mn Mo Zn
Grower
(20-7-19) 20
Finisher
Foliar
(4-25-35) (27-15-12)
3.1 15.8 0.025 0.06 0.4
4 10.9 29.1 0.025 0.06 0.4
27
0.15
0.3
0.3
0.0625
0.03 0.03 0.03
0.06 0.005 0.06
0.06 0.005 0.06
0.0625 0.0006 0.0625
6.5 10 0.025 0.0625 0.125
week at 324, 648, or 972 ppm N (six traysper rate). These applicationrateswere recommendedon the label. R-11©, a spreader-activator,was addedto thesefoliar fertilizer solu-
tions(0.15 mlL-1) to reducewatertensionandenhance fertilizerpenetrationinto needles.Foliar fertilizerwas applied with a sprayernozzleattachedto a gardenhoseconnectedto a 1:100 injector.Each foliar fertilizer rate was appliedjusttothepointof needlerunoff(2.5ml perseedling). Seedlings thatreceivedfoliar fertilizerwereirrigatedwith micronutrients, at ratespreviouslydescribed,when their growingmediumreached75% of saturated trayweight(see Landiset al. 1989). Control seedlings(the remainingthree trays) received Peters'ConiferFinisher©(N:P:K= 4:25:35)at24 ppmN and micronutrients whentheirgrowingmediumreached75% of saturatedtray weight. The "setting,"or initiatinganddevelopment of terminal budsby seedlingsin the nurseryis a functionof cultural practice,seedlingmorphology,and genetics(MacDonald andOwens1993).Budinitiationandgrowthoccursalonga continuum. Alongthiscontinuum, nurserymanagers referto theappearanceof brownbudscales,whichenclosethe shoot apexandarevisiblewith theunaidedeye, as"budset."This definitionof budsetidentifiesa discernible phenotypic state in operationalseedlingproduction,usefulfor determining whento modify culturalpractices. Budsetwasvisibleatweek14andfoliarfertilizerapplications were suspended for half the seedlings(designated Duration1)(threetraysperrate,ninetraystotal).Duration1 seedlingsandthecontrolseedlings receivedPeters'Conifer Finisherat 24 ppm N andmicronutrientsalternatedwith 92 ppm N suppliedvia calcium nitrate when their growing mediumreached75% of saturated trayweight.Theotherhalf (designated Duration2)(threetraysperrate,ninetraystotal) receivedPeters'ConiferFinisherat 24 ppmN andmicronutrientsevery time their growingmediumreached75% of saturatedtray weight,alongwith foliar fertilizeronceevery 4 wk until theendof the growingseason. Measurements
We measuredroot collardiameter(RCD), height,terminal budlength,percentbudbreak,andshoot-rootratio. Ten seedlings pertreatment/tray combination hadtheirRCD and height measuredmonthly from just before bud initiation
treatments(week 9) until the growing seasonended(week 34). RCD was recorded5 mm above medium-surface,and height was measuredfrom medium-surfaceto bud tip. At week 34, theseseedlingsalsohad their terminalbudsmeasured(baseof the most basipetal,contiguous,brown bud scaleto the tip). Percentbudbreakwasdeterminedby evaluatingall seedlingsin eachtreatment/traycombinationduring weeks 16 and 18. During week 34, 10 randomly selected seedlingsfrom eachtreatment/traycombinationwere dried 24 h at 65øC and shoot-rootratioscalculatedby dividing shootweightby root weight(Thompson1985). Seedlingnutrientconcentration, root growthpotential, and cold-hardiness were also examined.Twenty seedlings from eachtreatmentwere compositedinto a singlesample andanalyzedfor foliarN, P, andK concentrations; justbefore bud initiation treatmentsbegan (week 10), after seedling budset(week 14), at the endof thegrowingseasonimmediatelybeforecoldstorage(week 34), andafterfour monthsof cold storage.Foliar analysiswas doneby W.R. Graceand Company(Fogelsburg,PA) usinga Carlo Erba CHN Analyzer for N concentrations,and acid digestionand an ICP Spectrometerfor the otherelements. To determineseedlingroot growthpotential(RGP), 16 randomly selected seedlings from each treatment were grownin a growthchamberasdescribedby Ritchie(1985). Root growth was evaluated accordingto Krugman and Stone(1966). Cold-hardinesswas evaluated,following 4 monthsof cold storageat 1.5øC,by subjecting3 groupsof 15 seedlingsper treatment(5 randomlyselectedseedlings from each treatment/traycombination)to one of three differentfreezingtemperatures(-10, -20 or-40øC). Seedlings were planted in 3.8 liter pots filled with a 1:1
peat:vermiculitemedium.Potswereinsulatedwith perlite to preventroot freezing.Coolingrate to the testtemperature was 5øC/hr, and after a 2 hr soak at the desired
temperature,the warming rate was 10øC/hr. Following exposureto test temperatures,seedlingswere placed on greenhousebenchesat room temperature(22øC) with a 16 hr photoperiod.After 10 days, needle, bud, and stem damagewas evaluated,and temperaturesrequiredto kill
50%of theseedlings calculated (LT5o). StatisticalAnalysis We usedmultivariateanalysisof variance(MANOVA) techniquesas describedin Johnsonand Wichern (1988) to assess the effectsof the seventreatments(threefoliar fertil-
izerrates,two durations plusa control)onRCD, height,dry shootandrootweight,shoot-root ratio,budlength,budbreak, number of new roots, and cold-hardiness. Because of the
unbalancednatureof the treatmentstructure,a meansmodel approachas describedin Milliken and Johnson(1984) was
used.Significantmultivariatetestsbasedon Wilks' criteria werefollowedby Fisher'sprotectedLeastSignificantDifference(LSD) at a 0.05 level of significanceto isolatewhich univariatemeansdiffered amongthe treatments(Milliken and Johnson1984). DifferencesbetweenRCD and height immediatelybeforetreatment,andat subsequent measurements, were used to assesstreatmenteffects. SAS (SAS Institute,1985) wasusedfor all analyses. WJAF11(4)1996 115
Results Bud Formation
and Growth
Multivariate analysisshowedterminal bud length was significantlyinfluencedby treatments (P = 0.025);theapices of bothfoliar fertilizedseedlings andcontrolseedlings were coveredwith brown bud scalesfollowing 4 wk of bud initiation (week 14). In someseedlings,shootsand needles elongatedthroughthebudscalesabout2 wk later(week 16); percentageof seedlingsinitiating shootgrowth increased fromzerofor controlseedlings toninefor seedlings receiving 972 ppmN (? = 0.083), butby mid-August(week18),visible brownbudscaleswereagainevidentat the shootapex. For the univariate bud length, foliar fertilizer rate was significant(Table 2). Contrastbetweenmeanbudlengthof all foliar fertilized seedlingsandthe controlwasalsosignificant,with controlseedlingshavingshorterbuds. Root Collar Diameter and Height Multivariateanalysisof RCD andheightdatawassignificant(P = 0.005) for treatments,andtreatmentshada significanteffect (P = 0.0007) on the univariateRCD. Subsequent
contrasts showed significant differences between foliar-treated andcontrolseedlings, fertilizerrate,andduration(Table 2). At growingseason conclusion, meanincremental RCD growth increasedsignificantlyasfoliar fertilizerrateincreased,with seedlings receiving972 ppmN havingthelargestRCD. Both fertilizer durationsproducedseedlingswith significantly larger RCD than the control. Effectsof treatmentsontheunivariateheightweresignifi-
cantat P = 0.05. Subsequent contrastsshowedseedlingsof eachfoliar fertilizerratedisplayedsignificantlymoreincrementalheightgrowththan controlseedlingsbetweenbud initiation(week 10) andbudset(week 14) (? = 0.0001)(data not shown).Seedlingheightincrementbetweenbud initiation and the end of the growing season(week 34) was significantly increasedby foliar fertilizer rate (Table 2). Contrastsshowedcontroland seedlingsgiven 324 ppm N
exhibited equivalentheight growth, but s•gmficantlyless incrementalheightgrowththanseedlingsof the two higher foliar fertilizerrates.At theendof thegrowingseason, mean heightof all foliarfertilizedseedlings(all ratesanddurations) was similarto controlseedlings(? = 0.06). Shoot Weight, Root Weight, and Shoot-RootRatio Multivariate analysis showed shoot dry weight and shoot-rootratioswere significantlychangedby treatments (P = 0.0001); however,the univariatedry root weight was unaffected(? = 0.1)(data not shown).Shoot dry weight was significantly changedby the treatments(P = 0.0001) Further contrastsrevealed all foliar fertilized seedlings had significantly different shoot biomass than control seedlings(Table 2), and shootbiomasswas significantly changedby foliar fertilizer rate andduration.The interaction between rate and duration was also significant (P = 0.01) for shootdry weight. Shoot dry weight increased with increasing rates of foliar fertilizer but Duration 2 seedlingswere significantlylighter than Duration 1. The univariateshoot-rootratio was significantlychanged(P = 0.0001) and further contrastsshowedfoliar fertilizer rate anddurationinfluencedratios.Duration 2 seedlingshad a lower ratio than Duration 1 becauseof differencesin dry shootweight.Shoot-rootratio increasedsignificantlywith foliar fertilizer rate, but ratios were low (_
