chemical solubility and agricultural performance of p...

S. Kratz, S. Haneklaus, E. Schnug / Landbauforschung - vTI Agriculture and Forestry Research 4 2010 (60)227-240 227

Chemical solubility and agricultural performance of P-containing recycling fertilizers

SylviaKratz*,1SilviaHaneklaus*andEwaldSchnug*

*1 JuliusKühn-Institut,FederalResearchCentreforCultivatedPlants,InstituteforCropandSoilScience,Bundesallee50,38116Braunschweig,Germanycorrespondingauthor:[email protected]

Abstract

158P-containingfertilizers,standardmineralandrecyc-lingproducts,wereanalyzedfor theirchemicalsolubilityusing10differentmethods.Correlationsbetweenmethodswerehighlysignificant,indicatingthatareductionofof-ficialmethodsisviable.AmodifiedNeubauerpottrialwascarriedoutwithdifferentP-recyclingproductsto investi-gatewhichmethodwasbestsuitedtodescribetheirplantavailability.Thebestcorrelationbetweenshort-termplantPuptakeandchemicalsolubilitywasfoundforwaterex-traction,whilemidtolong-termPavailabilityisbetterde-scribedbyextractionswithammoniumcitrate.ForreasonsofpracticabilityitisrecommendedtousetheEUmethodof neutral ammonium citrate extraction to evaluate thenutritivevalueofP-recycling fertilizers.The tradable (so-calledtotal)PcontentofafertilizercanbedescribedbytheEUmineralacidextractionwithH2SO4+HNO3oraqua regiadigestion.

Keywords: Recycling fertilizers, P solubility, chemical ex-traction methods, P plant availability, Neubauer pot trial

Zusammenfassung

Löslichkeit und agronomische Qualität von P-hal-tigen Recyclingdüngern

158 phosphorhaltige Düngemittel, darunter Standard-mineraldünger und Recyclingprodukte, wurden mit 10verschiedenenMethoden auf ihre chemische Löslichkeituntersucht.HochsignifikanteKorrelationenzwischendenMethoden legtennahe,dassesmöglich ist,dieVielzahlderoffiziellenMethodenzurBeschreibungderP-Löslich-keitzureduzieren.MithilfeeinesmodifiziertenNeubauer-KeimpflanzenversucheswurdeunterEinsatzverschiedenerP-Recyclingprodukte untersucht, welche Methode ambesten zur Beschreibung der Pflanzenverfügbarkeit die-serProduktegeeignetist.DiebesteKorrelationzwischenkurzfristiger Pflanzenaufnahme und chemischer Löslich-keitwurde fürdieWasserextraktiongefunden,währendsichdiemittel-bislangfristigeP-Verfügbarkeitbessermit-tels Extraktionen mit Ammoniumcitrat beschreiben ließ.AusPraktikabilitätsgründenistdieEU-MethodezurExtrak-tion mit neutralem Ammoniumcitrat zu empfehlen, umdasDüngepotentialvonP-Recyclingdüngernzubewerten.Der marktfähige (“so genannte totale”) P-Gehalt einesDüngers kann mittels Mineralsäureextraktion nach EU-Vorschrift (H2SO4 + HNO3) oder Königswasseraufschlussbeschriebenwerden.

Schlüsselwörter: Recyclingdünger, P-Löslichkeit, chemische Extraktionsmethoden, P-Pflanzenverfügbarkeit, Neubauer-Keimpflanzenversuch

mailto:[email protected]

228

1 Introduction

The German Fertilization Ordinance (Düngeverord-nung–DüV)holds anobligation for farmers to fertilizetheir crops according to Good Agricultural Practice, i.e.accordingtocropnutrientdemands.In§5DüV,thebal-ancesurplusforphosphateislimitedto20kgP2O5/ha*yr.PrerequisiteforthisisanefficientPfertilizationwithmini-mizedPlosses.Inordertorealizethis,apreciseestimateof theplant available (“efficient”) shareof fertilizer P isneeded.Theextractionwithchemicalsolventsgivesafirstorientationabouttheefficiencyoffertilizers.TheGermanFertilizerOrdinance(Düngemittelverordnung–DüMV,An-nex2, Table4)offers11options todescribephosphatesolubility, most of them identical to themethods givenby theEU regulation2003/2003on fertilizers.The largenumberofdifferentmethodshashistoricalroots.Itisim-perativethatmethodsarecomparableinordertocalculatereliablefertilizerrates.Forthisreason,theGermanFederalMinistryforNutrition,AgricultureandConsumerProtec-tion(BMELV)initiatedaresearchprojectonthe“Standard-izationofphosphateanalysisandcharacterizationoffertil-izers”,whichwascarriedoutbytheJuliusKühn-Instituteintheyears2008and2009.Theprojecthadthreemainaims:

• to reduce the multitude of chemical extraction me-thodsforcharacterizingphosphatesolubility,

• tofindaclearandsimpledefinitionofmethodswithregardtotheirexplanatorycontentaboutthesolubilityofthefertilizer,i.e.

- Water:immediatelyavailable(initialeffect) -Weak acid: available within the first vegetation period

- Strongacid(mineralacid):maximumamountofP whichmaypotentiallybecomeavailable/tradable totalcontent,

• toexaminethecorrelationbetweenchemicallyextrac-tablePcontentandagronomicalefficiencyusingare-presentativeselectionofPcontainingfertilizerswhicharecurrentlymarketedincludingorganicfertilizers(far-myardmanure,sewagesludge,compost,animalresi-dues)and„new“products(suchasfertilizersbasedonsewagesludgeash).

2 Material and methods

2.1 Laboratory screening of fertilizers

P-containingfertilizersweremainlysuppliedbybranchesofthegovernmentalfertilizercontrol(Düngemittelverkehrs-kontrolle). Further samples of „new“ products such asthose fromwastewater treatmentoranimalwastepro-

ductswereprovidedbyBerlinerWasserbetriebe(BWB),awastewatertreatmentplantinGifhorn,theFederalInsti-tuteforMaterialsResearchandTesting(BAM)Berlin,Ash-DecUmweltAG,ReFoodGmbHandtheAssociationforTechnologyandStructuresinAgriculture(KTBL)DarmstadtaswellasfromthecollectionsofJKI.Table1givesanover-viewofthesamplesanalyzedinthisproject.

Table1:

Overviewoftheanalyzedfertilizersamples(N=158)

Group Type descriptionNo. of

samples

Mineral fertilizers 77

StraightPfertilizersSingle(SSP)andTripleSuper-phosphate(TSP)

2+6

(Soft)groundrockphosphate 4

Partiallyacidulatedrockphosphate

7

Compoundfertilizers NPKfertilizer 30

NPfertilizer 15

PKfertilizer 11

LimewithP 2

Organic and organo-mineral fertilizers and products based on them

81

Sewagesludge OrganicNPfertilizer 11

OrganicPandNP(MAP)fromwastewaterprecipitation

1+1

Sewagesludgeash 6

P,PKandNPKfromthermo-chemicallytreatedsewagesludgeash

22+5+2

Biowastecompost OrganicNPK/PKfertilizer 5

Fermentationresidues OrganicNPKfertilizer 4

Slurry(cattleandpig) OrganicNPKfertilizer 16

Meatandbonemeal(+ash)OrganicNP(+mineralP)fertilizer

6+1

Vegetableresidues(vinasse/melasse)

OrganicNPKfertilizer 1

Total: 158

Samplepreparation:Inthecaseofmineralfertilizersandmineralproductsfromsewagesludgeash/meatandbonemealash,theoriginalsubstance,conditionedat40°Candfine-groundtoaparticlesizeof<60µminaRetschRS1vibratingdiscmillwithzirconiumoxidegrindingequip-ment,wasusedforallextractionsanddigests.Fermenta-tionresiduesandslurriesdeliveredas liquidsamples (ex-ceptforonesolidsample)weredriedinaventilatedovenat60°Candfine-groundtoaparticlesizeof<60µminatungstencarbidemortarorvibratorydiscmillwithzirco-niumoxidegarniturebeforeextraction.


Thefollowingmethodswereusedtodescribethesolu-bilityofthefertilizersamples(Table2).Fortheslurries,onlyaselectionof theabove listedmethodswasapplied (W,CAL,CA,AR).

Table2:

ChemicalextractionmethodsusedforthedescriptionofPsolubility

Code Method

MinALUFA MineralaciddigestaccordingtoVDLUFAII4.1.1.2(HNO3+H2SO4+CuSO4)

MinAEU MineralaciddigestaccordingtoEU-method3.1.1(HNO3+H2SO4)

AR Aqua regiadigestaccordingtoDINEN13346/2001-04

FA Extractionwith2%formicacid(VDLUFAII4.1.2)

CA Extractionwith2%citricacid(VDLUFAII4.1.3)

NACEU ExtractionwithneutralammoniumcitrateaccordingtoEU-method3.1.4

W+NACFN ExtractionwithwaterandneutralACaccordingtoFresenius-Neubauer(VDLUFAII4.1.4)

AAC ExtractionwithalkalineammoniumcitrateaccordingtoPetermannat20°C(VDLUFAII4.1.5)

W Extractionwithwater(VDLUFAII4.1.7)

CAL ExtractionwithcalciumacetatelactateaccordingtoSchül-ler(1969)/BGKeVbookofmethods

P determination was done colorimetrically (Molyb-denum-Blue) according to Murphy & Riley (1962) with(NH4)6Mo7O24x4H2O.TheLUFA-andtheEU-methodformineralaciddigestion

yieldedcomparableresults(R2=0.999,p<0.01),there-foretheEU-methodwasusedexclusivelyforthecompletesampleset.Highlycorrelatingresultswerealsoobtainedfor AR andMinAEU digestion (P-AR (mg/kg) = 0.986*P-MinA(mg/kg)+1595(withp<0.0005;R2=0.993)).ThusexistingdataforARdigestionofsewageslusdgeashprod-uctscouldbeusedforcalculatingtheMinAEUcontent.

2.2 Modified Neubauer trial

TheaimoftheNeubauertrialwastoexaminethecor-relationbetweenchemicalPsolubilityofPrecyclingfertil-izersandPuptakeandeffectsonyield,respectively.Thequestion tobeansweredwaswhichchemicalextractionmethodisbestsuitedtoassessthebioavailabilityofPinrecycling fertilizers. To answer this question, amodifiedshort-termNeubauer trialwassetup:PrincipleoftheNeubauermethodistouseplantroots

as “reagents” to determine the amount of “root solu-ble” and thus plant available nutrients.A largenumberofplants(100ryeseeds)onasmallamountof(fertilized)substratemakessurethatrootsolublenutrientsareusedupwithin a short periodof time (14 to18days), given

thatabioticfactorsareoptimum(NeubauerandSchneider,1923;Neubauer,1931).450 g of fertilized substratewere filled into transpar-

entpolystyrolvessels(diameter12cm,height6cm)andseededwith100ryeseeds.Theexperimentwasdesignedasan“exhaustiontrial”,meaningthatafterafirstcutofshootsafter16days(atBBCH12/13)(Straußetal.,1994)plantswerefurthercultivateduntilvisiblesymptomsofnu-trientdeficiencywereobserved,accompaniedbyretardedgrowth.Asecondandathirdcutwerecarriedoutafter29(BBCH12)and43days(BBCH11/12),togetherwitharecoveryofroots.Astestplant,thesummerryecultivarArantes (thousand

grainweight:41.3g,germinability:89%),wasusedun-dressed.ThetestsubstratewasP-freequartzsand[grad-ing:“fine“sand:0.1to0.4mm,coarsesand0.7to1.2mm].Quartzsandwasfilledintothevesselsinthreelayers:Thebottomlayerconsistedof50gcoarseand100gfinesand,whichwasmixedwith the ground test fertilizers.Thislayerwasalsosprinkledwiththesupplementalfertiliz-ersolutions.Ontopofthis,alayerof150gfinesandwasplaced.Ryeseedswereevenlyspreadontopofthesecondlayerandcoveredwithathirdlayerof150gfinesand.SeedingdatewasMay20,2009.Thefirstcutwashar-

vested16dayslateratBBCH12/13(Straußetal.,1994)onJune5,2009.Thesecondcutwasperformed29daysaftersowingatBBCH12onJune18,2009andthethirdcutafter43daysatBBCH11/12onJuly2,2009.Allpotswerebrought toapproximately65%offield

capacitywithde-ionizedwater.Duringthetrial,waterwassuppliedindividuallyaccordingtopotweight.

Fertilizationstrategy:• Definedamountsof P coming fromdifferent P recy-cling fertilizers seeTable3+4 (calculationbasedontotalPsolubleinMinAEU)

• Plevels(severePdeficiency–optimum–Psurplus):20–40–60mgP(determinationofoptimumratewascalculatedbasedonPuptakeofshootdrymatterinapilottrialatanassumedPutilizationof20%)

• Supplementationof liquidN forall treatmentsup totheNamountsuppliedbyanN-containingtestfertili-zer(withoutconsiderationoffertilizerno.7)(Table5).Additionally,Nwasappliedatarateof10and5mg/potN,respectively,aftereachcut.

• UniformsupplementationofK,Ca,MgandSinliquidform(calculationbasedondrymatteryield fromthepilotexperimentandaveragenutrientcontent,consi-deringnutrientinputbytestfertilizers)(Table5)

• No micronutrients (as indicated by the pilot experi-ment)

• Controltreatmentswithseveralstandardmineralfer-tilizers(singlesuperphosphate,fullysolubleNP,partly

230

digestedrockphosphate),analyticalgrademonocalci-umphosphate(MCP)andazeroPtreatment,suppliedwithallothermacronutrientsinliquidformlikethetestfertilizers

Table3:

TestfertilizersusedintheNeubauertrial

Tr.1 Sample name

Description

ZeroP

1 OrgNPBM OrgNPfrombonemeal(Beckhornbonemealsteamed)

2 OrgNPMBM OrgNPfrommeatandbonemealcat.3(AntonKnollcompany)

3 MBMA Ashfrommeatandbonemealcat.1(Rethmann/ReFood)

4 OrgNPSS OrgNPfromsewagesludge(precipitation,WWTPGifhorn)

5 Struvite MAP(struvite)fromwastewaterprecipitation(BerlinerWasserbetriebe)

6 P-SSATC StraightPfromthermochemicallytreatedsewagesludgeash(MgCl2-type,BAM)

7 NPK-SSATC NPKfromthermochemicallytreatedsewagesludgeash(MgCl2-type,AshDec)

Controls:

8 MCP Monocalciumphosphateanalyticalgrade(p.a.)

9 SSP Singlesuperphosphate

10 DAP Diammoniumphosphate

11 paRP Partlyacidulatedrockphosphate

1Tr.=treatment

Table5:

Fertilizersolutionsandnutrientdosageappliedperpot intheNeu-bauertrial

Nutrient Compound used Dosage (mg pure nutrient per pot)

N NH4NO3,KNO3,Ca(NO3)2 89.5

K KNO3,K2SO4 60.0

Ca Ca(NO3)2 20.0

Mg MgSO4 4.0

S MgSO4,K2SO4 5.3

ForthedeterminationofP,theplantmaterialwasdriedinaventilatedovenat60°Cuntil constancyofweight.Then thematerial was fine-ground to a particle size of< 0.12 mm employing an ultra-centrifugal mill (RetschZM1)withtitaniumgrindingequipment.0.5gplantmate-rialwasdigestedwith4mlHNO3+1mlH2O2inamicro-wave(CEM/Mars)at600Wattfor27minutes,raisingthetemperatureupto200°C.Aftercoolingdownthedigestwasfilledupto50mlwithdeionizedwater.Pconcentra-tionwasdeterminedbyICP-OES(SpectroM120S).

3 Results and discussion

3.1 Laboratory investigations

Figure 1 showsmedian, quartiles and ranges of P2O5contents of the different fertilizer types determined inmineralacid(MinAEU)andaqua regia(AR).Pcontentsintheseextractantsaregenerally termed“so-called total”,

Table4:

Pcontentandrelativesolubility(in%ofMinA-P2O5)ofthefertilizersusedintheNeubauertrial

Tr. Type MinA-P2O5 (%) Relative solubility (in % of MinA-P2O5) in ...

FA CA NACEU W+NACFN AAC W

1 OrgNPBM 15.0 76 34 27 33 8.5 0.93

2 OrgNPMBM 17.4 91 74 48 65 16.0 0.99

3 MBMA 25.9 48 50 15 15 7.0 0.01

4 OrgNPSS 8.9 57 84 88 86 80.0 0.40

5 Struvite 27.6 97 100 92 51 6.3 0.73

6 P-SSATC 21.4 75 65 21 21 4.8 0.13

7 NPK-SSATC 7.4 101 103 92 92 70.0 73.00

8 MCP 57.4 97 98 97 98 95.0 96.00

9 SSP 20.9 101 88 84 87 83.0 76.00

10 DAP 45.8 115 101 102 103 107.0 87.00

11 paRP 41.6 76 69 65 71 66.0 53.00

FA-formicacid;CA–citricacid;NACEU-neutralammoniumcitrate;W+NACFN-waterandneutralAC;AAC-alkalineammoniumcitrate;W–water(Tr.=treatment)


Figure1:

Mineralacid(MinA)andaqua regia(AR)solubleP2O5contentsoftheanalyzedfertilizers(%oforiginalsubstance)–median,quartilesandranges

(1=organicfertilizers,2=solublemineralfertilizers,3=rockphosphates(RP),4=Pfertilizerswithlime,5=productsfromsewagesludgeash(SSA),6=productsfromwastewater(WW)treatment,7=meatandbonemealash)=outlier,*=extremevalue,numbersrefertoBMELV-samplenumberandthusareonlydescriptive

60

50

40

30

20

10

0

Fertilizer type

1-org2-m

inPK

5-SSA-P

6-WW

-P

2-minN

P

3-paRP

5-SSA

7-MBM

A

2-minN

PK

3-RP

5-SSA-N

PK

2-minP

4-P-lim

e

6-WW

-NP

124

60

50

40

30

20

10

0

Fertilizer type

1-org2-m

inPK

5-SSA-P

6-WW

-P

2-minN

P

3-paRP

5-SSA

7-MBM

A

2-minN

PK

3-RP

5-SSA-N

PK

2-minP

4-P-lim

e

6-WW

-NP

7015

12

3

1***P

O_

Min

A(%

)2

5

PO

_A

R(%

)2

5

becauseonlynon-destructivemethodssuchasXRFdeter-mine the real total content (Haneklausetal.,1994).Ex-pectedly(seeabove)bothmethodsyieldedsimilarresults.Similarly, therewas a strong relationship between the

GermanandEU-method forextractionwithneutralam-moniumcitrate(Table6).

Table6:

PearsoncorrelationcoefficientsfortherelationshipbetweenGermanandEU-methodforthedeterminationofPsolubilityinneutralammo-niumcitrate(W+NACFNandNACEU)

Group of samples n r p

Allsamples 143 0.993 0.01

Mineralfertilizersonly 75 0.999 0.01

Organicfertilizersonly 27 0.983 0.01

Sewagesludgeash(products)only 35 0.676 0.01

While there was a very strong and highly significantcorrelationbetweentheGermanandtheEU-methodformineralaswellas fororganic fertilizers, itwasdistinctlyweakerforsewagesludgeashesandtheirproducts.Ascanbeseenfromthecorrelationmatrices(Table7to

10),therewerecloserelationshipsbetweenallexaminedextractionmethodswhenallfertilizerswereviewedasonegroup. However, when the different types of fertilizersweregroupedseparately,therewereobviousdifferences:Whilecommonmineralfertilizersshowedverystrongandhighlysignificant(p<0.01)correlationsinallcases,sew-

agesludgeashesandtheirproductsshowedaheteroge-neous picture,with only occasionally significant correla-tionsbetweendifferentextracts.Itisspeculatedthatthismightbeduetotheheterogeneityintheproducts.Incon-trasttotheashproducts,thegroupoforganicfertilizersshowedformostextractions–exceptwater–mediumtovery strong, significant to highly significant correlations.Thereasonfortheunpredictableresultsforthewaterex-tractionisprobablythefactthatthedriedorganicsampleshadhydrophobicsurfacesandwerethereforedifficulttomoisteninwater.Figure2givesanoverviewofrelativePsolubilitiesoffer-

tilizertypesindifferentextractants.Sincethelargegroupofash-basedfertilizerswasnotdigestedinmineralacid,relativesolubilitiesarereferredtoaqua regiahere.Relativesolubilityinthegroupoforganicfertilizers(1-org)showedahighvariability.Acomparablebehaviorwasalsofoundinotherextractstestedinthisstudy(figuresnotshownhere).Thiswasnotonlybecause thisgroupwas composedofdifferentsubtypes(farmyardmanure,biowastecompost,sewagesludge,meatandbonemeal, fermentation resi-duesandvegetableresidues)butalsoduetotheinternalheterogeneityofeachofthesesubgroups,whichdidnotallowapreciseevaluationoftheirquality.The products from sewage sludge ash also showed a

highlyvariablesolubility(type5:SSA,SSA-P,SSA-PK,SSA-NPK), inparticular thegroupofP fertilizers fromunpro-cessed thermochemically treated ash. This group com-prised22samples(SSA-P).Obviously,thismaterialwasstill

232

Table7:

Pearsoncorrelationcoefficientsfortherelationshipbetweendifferentextractionmethods,calculatedforallfertilizers(seeTable1)

MinAEU AR FA CA W+NACFN NACEU AAC W

MinAEU 1

AR 0.992** 1

FA 0.967** 0.942** 1

CA 0.958** 0.942** 0.981** 1

W+NACFN 0.944** 0.877** 0.961** 0.956** 1

NACEU 0.941** 0.890** 0.960** 0.962** 0.993** 1

AAC 0.902** 0.838** 0.911** 0.918** 0.969** 0.966** 1

W 0.889** 0.827** 0.923** 0.923** 0.964** 0.959** 0.966** 1

CAL 0.920** 0.926** 0.961** 0.966** 0.974** 0.976** 0.957** 0.973**

MinALUFA-Mineralaciddigest;MinAEU-Mineralaciddigest;AR-Aqua regia;FA-2%formicacid;CA-2%citricacid;NACEU-neutralammoniumcitrate;W+NACFN-waterandneutralAC;

AAC-alkalineammoniumcitrate;W-water;CAL-calciumacetatelactate;Significances:**=p<0.01,*=p<0.05,n.s.=notsignificant

Table8:

Pearsoncorrelationcoefficientsfortherelationshipbetweendifferentextractionmethods,calculatedformineralfertilizers(seeTable1)


MinAEU 1

AR 0.997** 1

FA 0.974** 0.978** 1

CA 0.959** 0.962** 0.987** 1

W+NACFN 0.954** 0.958** 0.984** 0.994** 1

NACEU 0.948** 0.953** 0.983** 0.994** 0.999** 1

AAC 0.922** 0.924** 0.948** 0.967** 0.970** 0.972** 1

W 0.924** 0.926** 0.957** 0.977** 0.979** 0.981** 0.968** 1

CAL 0.912** 0.918** 0.949** 0.958** 0.969** 0.971** 0.947** 0.967**


AAC-alkalineammoniumcitrate;W-water;CAL-calciumacetatelactate;Significances:**=p<0.01,*=p<0.05,

n.s.=notsignificant

Table9:

Pearsoncorrelationcoefficientsfortherelationshipbetweendifferentextractionmethods,calculatedforproductsfromsewagesludgeash(seeTable1)


MinAEU 1

AR n.c. 1

FA n.c. n.s. 1

CA n.c. 0.341* 0.820** 1

W+NACFN n.c. n.s. 0.550** 0.467** 1

NACEU n.c. 0.378* n.s. n.s. 0.676** 1

AAC n.c. n.s. -0.472** -0.414* n.s. 0.515** 1

W n.c. -0.503** n.s. n.s. n.s. n.s. 0.416* 1

CAL n.c. n.c. n.c. n.c. n.c. n.c. n.c. n.c.



n.s.=notsignificant,n.c.=notcalculated


Figure2:

Relativesolubility(referredtoaqua regia(AR))ofdifferentfertilizertypesinwater(W),neutralammoniumcitrate(NACEU),citricacid(CA)andformicacid(FA)–median,quartilesandranges

(1=organicfertilizers,2=solublemineralfertilizers,3=rockphosphates(RP),4=Pfertilizerswithlime,5=productsfromsewagesludgeash(SSA),6=productsfromwastewater(WW)treatment,7=meatandbonemealash)=outlier,*=extremevalue,numbersrefertoBMELV-samplenumber

120

100

80

60

40

20

0

Fertilizer type

CA

(%A

R)

1-org2-m

inPK

5-SSA-P

6-WW

-P

2-minN

P

3-paRP

5-SSA

7-MBM

A

2-minN

PK

3-RP

5-SSA-N

PK

2-minP

4-P-lim

e

6-WW

-NP

120

100

80

60

40

20

0

Fertilizer type

NA

C(%

AR

)E

U

1-org2-m

inPK

5-SSA-P

6-WW

-P

2-minN

P

3-paRP

5-SSA

7-MBM

A

2-minN

PK

3-RP

5-SSA-N

PK

2-minP

4-P-lim

e

6-WW

-NP

Fertilizer type

120

100

80

60

40

20

0

W(%

AR

)

1-org2-m

inPK

5-SSA-P

6-WW

-P

2-minN

P

3-paRP

5-SSA

7-MBM

A

2-minN

PK

3-RP

5-SSA-N

PK

2-minP

4-P-lim

e

6-WW

-NP

2

104

3198

1926

2427

39

98

5999

70

61

17

28

99

19

13117

170

22

19

17

33

3359

27

26

19

* *

**

*

140

120

100

80

60

40

20

0

Fertilizer type

FA

(%A

R)

1-org2-m

inPK

5-SSA-P

6-WW

-P

2-minN

P

3-paRP

5-SSA

7-MBM

A

2-minN

PK

3-RP

5-SSA-N

PK

2-minP

4-P-lim

e

6-WW

-NP

103

23

23

33

61

rather heterogeneous in its speciationdespite the treat-mentandmilling.Thestandardmineralfertilizers(types2,3and4)stood

outwiththeir inmostcasescomparably lowvariationindifferentextractants.Formineralfertilizersandsewagesludgeashproducts,

thewaterextractdidnotfollowthetrenddescribedhere:While the ash products showedmostly a uniformly low

watersolubility,thestandardmineralfertilizersdisplayedvaryingwater solubilitydependingon theirdifferentde-greeofacidulation.Duetotheobservedvariation insolubilitybothwithin

andbetweengroupsitwasnotpossibletoderivereliablestatisticalparameterssuchasconfidenceintervalsormeansolubility factorsfromthissampleset.Thiswill requirealargersetofsamples.

234

Table10:

Pearsoncorrelationcoefficientsfortherelationshipbetweendifferentextractionmethods,calculatedfororganicfertilizers(seeTable1)


MinAEU 1

AR 0.984** 1

FA 0.951** 0.952** 1

CA 0.933** 0.900** 0.834** 1

W+NACFN 0.945** 0.899** 0.844** 0.977** 1

NACEU 0.897** 0.825** 0.744** 0.958** 0.983** 1

AAC 0.755** 0.631** 0.505* 0.875** 0.866** 0.934** 1

W n.s. n.s. n.s. n.s. n.s. n.s. n.s. 1

CAL 0.777** 0.584** 0.878** 0.821** 0.741** 0.692** n.s. 0.902**



n.s.=notsignificant

3.2 Modified Neubauer trial

3.2.1 Dry matter yield

Thetotalyieldofallthreecutsincludingrootsdifferedsignificantlybetweenzerocontrolandallothertreatments(Table11).Ingeneral,differencesbetweenPformsprovedtobenotsignificant.Acleardifferentiationbetweencon-ventionalandrecyclingfertilizerswasnotpossible.Treat-ment7(NPK-SSATC)displayedloweryieldsatcut2and3,whichmightbeduetotheexcessiveNsupplyforcedbytheparticularcompositionofthisfertilizer(unsuitableN:P-ratio)1.Inaddition,supplementationofpotassiumbyuseofKClmighthaveweakenedtheplantsinthistreatment,since therewas no buffering in the sand substrate (salteffect). Surprisingly, treatment 8 (MCP) produced loweryieldsthanallothertreatmentsalthoughitsPcontentwascompletely water-soluble. Treatment 10 (diammoniumphosphate)showedsignificantlyhigheryieldsthansomeoftheothertreatments.

1 Treatment7wasamultinutrient(NPK)fertilizerbasedonsewagesludgeash.InordertotestthequalityofthePcomponent,itwasdecidedtosupplyPsolelyfromthatfertilizerdespitethefactthatthismeantanexcessiveNsup-plyatthesametime(Plevel20:126mgN,Plevel60:378mgNperpot).Whileplantswereabletotoleratethisuptothefirstcut,therewasaclearyielddepressionatPlevels40and60atcut2,followedbyatotalcollapseoftheplantsbeforecut3.

Table11:

Meandrymatter yields (gDM/pot) of the different fertilizer treat-mentsintheNeubauertrial,cuts1to3(shoots)+roots(drymatteryieldzeroP:1.78g/pot)(Tr.=treatment)

P level 20 P level 40 P level 60

Tr. DM (g/pot) Tr. DM (g/pot) Tr. DM (g/pot)

6 3.53a 7 2.80a 7 3.01a

11 3.61ab 8 2.83a 6 3.30ab

3 3.74abc 9 2.93ab 8 3.68ab

5 3.82abc 4 3.73bc 9 3.72b

9 3.98abc 11 3.74bc 11 3.81b

2 3.99abc 6 3.87c 4 3.82b

4 4.00abc 1 3.91c 5 3.82b

7 4.06abc 5 3.95c 10 3.88b

8 4.11abc 10 4.00c 2 3.89b

1 4.25bc 2 4.11c 3 3.90b

10 4.42c 3 4.11c 1 3.93b

differentlettersindicatesignificantdifferencesbetweentreatments(Tukey,p<0.05)

3.2.2 P content of plants

IncreasingPlevelsfrom20to60mgperpotweredis-playedinanincreasingPcontentofshoots(Table12).Thiseffectwasnotclearintreatment3:cuts1to3,treatment4:cut3,treatment6:cut1andtreatment9:cut2.In the treatments suppliedwith recycling fertilizers (tr.

1to7),Pcontentsofshootsincreasedconsistentlyfromcut1tocut3.Incomparisontothisfinding,thePcontentin the treatments fertilizedwith standardmineral fertil-izers (fully water-soluble products aswell as rock phos-phatebasedproducts, tr.8 to11) remainedconstantordecreased.


Table12:

MeanPcontentofshoots inthedifferentPfertilizertreatmentsoftheNeubauertrial


Tr. P (mg/kg) Tr. P (mg/kg) Tr. P (mg/kg)

Cut1(ContentofzeroPtreatment:4019mg/kgP)

1 3182a 1 3181a 1 3072a

5 3253a 3 3603a 3 3650ab

2 3523ab 2 3853a 2 3856ab

3 3570ab 5 3859a 5 4194bc

4 4079bc 4 4654b 6 5010cd

6 4649c 6 4983b 4 5248d

7 6025d 9 7916c 11 9040e

8 6101d 7 8090c 9 9432e

11 6201d 11 8457cd 7 10562fg

9 6466d 8 8527cd 10 10649g

10 6475d 10 9319e 8 11061g

Cut2(ContentofzeroPtreatment:5229mg/kgP)

1 3682a 1 4102a 3 4216a

3 4340ab 3 4190ab 1 4410a

2 4512bc 2 5256bc 6 5750b

7 4591bcd 6 5515cd 2 6043b

4 4658bcd 4 5712cd 4 6083b

10 4720bcde 5 6240cde 5 6753bc

5 4921bcde 7 6632def 9 7881d

9 5038bcde 11 6956efg 11 7887d

6 5146cde 10 7227efg 7 8254de

8 5301de 9 7678fg 8 9105e

11 5455e 8 7871g 10 9359e

Cut3(nomorebiomassproductionfromzeroPtreatment)

1 4226 3 4408 3 4450

3 4666 1 4590 1 4691

7 4729 6 5732 6 5913

2 4858 2 6498 4 6493

10 5032 11 6617 2 7430

9 5086 4 6619 9 7442

6 5134 10 6948 11 7779

4 5291 9 7027 5 8755

8 5408 8 7294 8 8793

11 5489 5 7578 10 9311

5 6557


(forcut3,noanalysisofvariancewaspossible,becauseduetoscarceplantbiomass

repetitionswerejoinedintoamixedsampleforchemicalanalysis)

Drymatter yieldsof all 11 treatmentsdecreased fromcut1tocut3(Table11).Thus,theobserveddifferencesinPcontentbetweenrecyclingandmineralfertilizerscannotbeexplainedbyadilutioneffectduetoincreasingbiomass

production.Rather,adifferentqualityorPavailabilityofthefertilizercanbeassumedasthemainreason.Thestan-dardmineralfertilizerswereinstantlyavailableandthere-foretakenuptoalargerextentbeforethefirstcut,whilePinrecyclingfertilizerswasmoreslowlyavailable,yetre-leasedandtakenupcontinuouslybytheplantsthrough-outtheentireexperimentof43days.

3.2.3 Plant P uptake

Tables13to15giveanoverviewofthenetplantPup-take (roots, shoots and total produced biomass). Net PuptakewascalculatedbysubtractingthePuptakeofthezeroP treatment (representingP reserves in seeds) fromthatofthefertilizedtreatments.ThePutilizationratewascalculatedforcut1andtotalyield(includingroots).PlantssuppliedwithmineralPfertilizersclearlyshowa

highertotalPuptakethanthosewhichreceivedrecyclingfertilizers (Table13).Graded ratesof standardmineralPfertilizerswere reflected in increasingPuptake. In com-parison,Pwastakenupatlowratesfromrecyclingfertil-izersandresponsestothedoseweremarginalatbest.ThisindicatesthelimitedPpotentialoftherecyclingfertilizers.In thegroupofmineral fertilizers,diammoniumphos-

phate(tr.10)showedthehighestPuptake,while inthegroupof recycling fertilizers, struvite (tr.5)was theonewith the highest P uptake. However, the difference be-tween treatment 5 and treatments 4 (org NPSS), 2 (orgNPMBM) and6 (P-SSATC)proved tobenot significant (seeTable13).Bonemeal(tr.1)andmeatandbonemealash(tr.3)displayedthelowestPuptakeofalltestedproducts.OneexceptiontothegeneraldifferencebetweenmineralandrecyclingfertilizerswasNPK-SSATC(tr.7),ahighlysol-ubleproduct,whichcontainedTSPtoadjustitsPcontent.ThisproductyieldedasimilarPeffectasstandardmineralPfertilizersatthefirstcut.ItsunsuitableN:Pratio,however,increasinglyimpaireditsperformancewithgradedPlevels(seefootnote1).Withreferencetothetotalproducedbiomass(rootsand

shoots), utilization rates were extraordinarily high withup to 92%of the P supply. This ismore than 4 timeshigher than theaverage valueof20%given in the lit-erature(Finck,1992).Thisdifferencecanbeexplainedbytheparticular set-upof theNeubauer testwith its largenumberofseedsonasmallamountofsubstrate,whichisexplicitlydesignedtoachievecompleteutilizationofPoranestimateofthetotalpotentiallyavailableP.Theresultsofthisexperimentsuggestthatthepotentialofthetestedfertilizers should preferably be evaluated and comparedbasedontheresultsforPlevel20ashighutilizationrateswerealreadyrealizedatthatlevel.Lookingindividuallyatthedifferentcuts(Table14),the

first harvest reflected differences between treatments in

236

Table13:

MeannetPuptakeandutilizationrate(UR,in%ofPsupply)oftotaldrymatteryield(cut1to3includingroots)inthedifferentPfertilizertreat-ments(Tr.=treatment)


Tr. P uptake (mg) UR (%) Tr. P uptake (mg) UR (%) Tr. P uptake (mg) UR (%)

1 07.9a 40

3 08.1a 40 1 08.0a 20 1 08.3a 14

2 09.4a 47 3 09.4ab 23 3 09.1ab 15

6 09.5ab 47 6 11.5ab 29 6 10.9abc 18

5 10.0ab 50 4 11.8ab 30 2 12.5abc 21

4 10.3ab 51 2 12.1b 30 4 13.9bc 23

11 13.0bc 65 5 12.7b 32 5 15.1c 25

7 14.9cd 74 9 17.8c 44 11 24.0d 40

9 15.7cd 78 8 18.4c 46 9 24.7d 41

8 16.0cd 80 11 21.5cd 54 8 25.5d 42

10 18.3d 92 10 24.2d 61 10 29.3d 49


thesamewayasthesumofallcuts.Thismirrorsthead-vantageofthewater-solublePfertilizersduringtheinitialgrowthstage.Incut1,theplantsfertilizedwithNPK-SSATC(tr.7)werestillperformingextraordinarilywell.Thiswasthe only recycling fertilizer reaching the same level of Puptake as themineral fertilizers. Following treatment 7,thesecondhighestPuptakeofrecyclingfertilizerswasob-servedforP-SSATC(tr.6)andorgNPSS(tr.4),respectively.Bonemeal(tr.1)displayedthelowestPuptake.With15to52%atPlevel20and5to23%ofPsupplyatPlevel60,Putilizationratesatcut1wereratherhigh.Atthesecondharvest(cut2,after29days)differences

between standard mineral and recycling fertilizers wereconsiderably smaller. The reasonmightbe thatby then,thenon-water solubleportionof the recycling fertilizershadbecomeavailable.Apparently,theinitialadvantageofthewater-solublePwasover timecompensatedat leastpartiallybynonwater-solubleP forms (particularly thosesolubleinneutralammoniumcitrate).However,Puptakeintherecyclingfertilizertreatmentswasstillbelowthatinthestandardmineral fertilizerstreatments, thoughthesedifferenceswerenotsignificantinallcases(Table14).Thistime,therecyclingfertilizerwiththehighestPuptakewasstruvite(tr.5),followedbymeatandbonemeal(tr.2).Intreatment7 (NPK-SSATC), P uptake at P level 40 and60was clearly reduced due to the yield depression,which,asdiscussedabove,hadbeencausedpresumablybytheunsuitableN:PratioresultinginanexcessiveNsupply.

Atthethirdharvest,thedifferenceinPuptake2betweenstandardmineralandrecyclingfertilizerswasinmostcasesnolongersignificant,ornotobservedatall.Obviously,theinitialadvantageofthemineralfertilizersbytheirwater-solublePwasalmostleveledoutbytheslowlyavailablePportionoftherecyclingfertilizersbythen(Table14).How-ever,comparedtocut1withPuptakesupto15mgperpot, Puptake at cut3was comparably low in all treat-ments.ThisindicatesthatplantavailablePreservesweremoreor lessusedupat that time.Thisassumptionwasstrengthened by the observation of signs of root decay(browncolor)ofdifferentextentfrompottopot,andbyamassivelyreducedbiomassproductioncomparedtocut1.The P content in the substrate determined by CAL-P,however,deliverednoadditionalevidence(seeFigure2).Recyclingtreatment7didnotproduceanybiomassafter

cut2.Thebestrecyclingtreatmentwasagainstruvite(tr.5) followedbyorgNPMBM (tr.2).Bonemeal (tr.1),meatandbonemealash(tr.3)andP-SSATC(tr.6)alldisplayedaverylowPuptake.Like changes in root morphology, P uptake of roots

variedconsiderablybetweenthedifferent fertilizer treat-ments(Table15).ThereexistedacleardifferencebetweenstandardmineralandrecyclingfertilizerswithregardtoPuptakeinrelationshiptothePlevel:Exceptfortreatment7(NPK-SSATC),onlythestandardmineralfertilizersshowedanincreaseinPuptakewithincreasingPlevel.

2 SincethezeroPtreatmentdidnotproduceanymorebiomassaftercut2,netPuptakeofshootsatcut3isidenticalwithgrossPuptake.


Table14:

MeannetPuptakeandutilizationrate(UR,in%ofPsupply,onlyforcut1)ofdrymatteryieldinthedifferentPfertilizertreatmentsfortheindi-vidualcuts


Tr. P uptake (mg) UR (%) Tr. P uptake (mg) UR (%) Tr. P uptake (mg) UR (%)

Cut1

1 2.92a 15 1 2.82a 7 1 2.95a 5

5 2.95a 15 3 3.99a 10 3 3.81a 6

3 3.63a 18 5 4.07a 10 2 4.87a 8

2 3.64a 18 2 4.58a 11 5 5.1a 8

4 4.37a 22 4 4.83a 12 6 5.3a 9

6 5.00ab 25 6 5.3a 13 4 6.4a 11

11 7.2bc 36 9 10.1b 25 9 12.3b 21

8 8.2cd 41 7 10.7b 27 11 12.3b 21

9 8.7cd 43 8 10.9b 27 8 13.0b 22

7 8.7cd 44 11 11.9bc 30 7 13.1b 22

10 10.4d 52 10 14.2c 36 10 14.1b 23

Cut2

3 1.59a 7 1.01a 7 1.22a

6 1.60a 1 1.92ab 3 1.86ab

1 1.67ab 3 1.95ab 1 1.94ab

4 1.88ab 6 1.96ab 6 2.17abc

7 2.02abc 4 2.05b 4 2.49abcd

2 2.09abc 2 2.63bc 2 2.67bcde

9 2.12abc 5 2.83bcd 5 3.50cde

11 2.14abc 8 3.32cd 9 3.65def

5 2.23abc 9 3.46cd 11 3.87def

8 2.49bc 10 3.58cd 8 3.97ef

10 2.77c 11 3.74d 10 4.94f

Cut3

6 1.98a 7 0 7 0

3 2.11a 6 2.44a 3 2.37a

1 2.36ab 3 2.48ab 1 2.46a

7 2.49ab 1 2.57ab 6 2.63a

9 2.53ab 4 2.81ab 4 3.07a

11 2.54ab 12 3.37ab 9 3.80ab

4 2.57ab 8 3.43ab 2 3.81ab

2 2.68ab 9 3.51ab 12 4.02ab

12 2.76ab 2 3.74ab 11 4.22ab

8 2.95ab 10 3.82ab 8 4.25ab

10 3.38b 5 3.94ab 5 5.1b

5 3.48b 11 3.97b 10 5.3b


Since the test substrate did not contain any P, P-CALcontentsattheendoftheexperimentshouldgiveanindi-cationifandtowhichextenttheplantavailableamounts

ofPsuppliedbyfertilizationwereinfactexhaustedbytheplants(seeabove).ThenetP-CALcontentwascalculatedbysubtractingtheP-CALcontentofthezeroPtreatment.

238

Figure3demonstratesthatPwasmoreorlesscompletelytakenupbyplantsonlyatP level20.Adirect compari-sonshows that,asexpected, standardmineral fertilizersdeliveredhigheramountsofCAL-solublePthanrecyclingfertilizers.TheonlyexceptionwasNPK-SSATC(tr.7),whichshowedveryhighCALcontents.Asexplainedabove,thissewagesludgeashbasedfertilizerwasenrichedwithtri-plesuperphosphatetomaintainapredefinedPcontent,inadditiontheproductcontainedKCl,whichexplainsitshighersolubility.Thewitheringoftheplantsaftercut1inthis treatmentcausedthehighexcesssubstrate-Pat theend of the trial. Apart from this treatment, the highestamount of plant-available P among the recycling fertil-izerswas supplied byOrgNPMBM, Org NPSSand struvite,whilethelowestamountsofplant-availablePcamefromP-SSATC,MBMAandorgNPBM.

Table15:

MeannetPuptakeofrootsinthedifferentfertilizertreatments


Tr. P uptake (mg) Tr. P uptake (mg) Tr. P uptake (mg)

3 0.72a 8 0.21a 6 0.83a

6 0.89a 1 0.67ab 1 0.90a

2 0.94a 9 0.70ab 3 1.08a

1 0.99a 3 0.97abc 2 1.11a

11 1.19ab 2 1.19abc 5 1.48a

5 1.38ab 7 1.45abcd 4 2.03a

4 1.44ab 6 1.78bcd 11 3.55b

7 1.67ab 5 1.82bcd 7 3.81b

10 1.73ab 11 1.97bcd 8 4.23b

9 2.35b 4 2.11cd 10 4.94b

8 2.37b 10 2.60d 9 4.98b


3.2.4 Relationship between chemical solubility and P up-take in the Neubauer trial

ThehighestPuptakeswererealizedbythoserecyclingfertilizerswhichdisplayedthehighestsolubilityinneutralammoniumcitrate(andcitricacid).Acorrelationanalysiswas performed to investigate the statistical relationship

Figure3:

Plant-availablenetPcontent(P-CAL)inthesubstrateofdifferentfertilizertreatmentsafterthefinalharvest(soiltestlevelA=low;fertilizerde-scriptionseeTable3)

0

5

10

15

20

25

30

35

40

45

50

55

60

65

org NP (BM) org NP (MBM) MBMA org NP (SS) Struvite P-SSA(TC) NPK-SSA(TC) MCP SSP DAP pa RP

Fertilizer type

NetP

-CA

L(m

g/k

g)

P level 20 mg

P level 40 mg

P level 60 mg

upper limit of soil test level A


betweenchemicalsolubilityofthefertilizersandPuptakeintheNeubauertrial.Table16showsthat–lookingatthemeanofall11testedtreatments–thestrongestcorrela-tionwas found betweenwater-soluble P and P uptake.Also,astrongcorrelationwasfoundbetweenPsolubilityin alkaline ammonium citrate (AAC) and P uptake, fol-lowed by solubility in water+neutral ammonium citrate(W+NAC).ThiswastruefortotalPuptake(allcuts)andPuptakeatcut1. Incontrasttothis,atcut2thestron-gestcorrelationwithPuptakewasfoundforPsolubilityinmineralacid,followedbywaterandammoniumcitrate,whileatcut3,extractionwithNACEUshowedthebestcor-relation,followedbythestrongerextractantsformic(FA)andcitricacid(CA).Thisresultmirrorsthestrongerinitialeffectofwater-solublefertilizersandtheslowreleaseofnon-watersolublePforms.Lookingseparatelyatstandardmineralorrecyclingfer-

tilizers, the extracts with ammonium citrate correlatedbestwithPuptake inthecaseofmineralfertilizers.Sig-nificantcorrelationswerefound,however,theywereonlyweak(Table17).

Table16:

Pearsoncorrelationcoefficients(r)fortherelationshipbetweenabsolute(MinA)/relativePsolubilityindifferentchemicalextractsandPuptakeinthepottrial,calculatedforall11testfertilizersincommon

Shoots cut 1 Shoots cut 2 Shoots cut 3 Roots Shoots cut 1 to 3 + roots

n 142 139 134 141 133

MinA-P(%) 0.494** 0.565** 0.368** 0.292** 0.619**

FA(%MinA) 0.541** 0.435** 0.472** 0.362** 0.552**

CA(%MinA) 0.489** 0.352** 0.458** 0.392** 0.503**

NACEU(%MinA) 0.590** 0.453** 0.488** 0.473** 0.615**

W+NACFN(%MinA) 0.704** 0.450** 0.402** 0.501** 0.684**

AAC(%MinA) 0.773** 0.451** 0.285** 0.531** 0.724**

W(%MinA) 0.849** 0.469** 0.310** 0.520** 0.777**

Significances:**=p<0.01,*=p<0.05

Table17:

Pearsoncorrelationcoefficients(r)fortherelationshipbetweenabsolute(MinA)/relativePsolubilityindifferentchemicalextractsandPuptakeinthepottrial,calculatedformineralfertilizers(Types9to11)


n 48 48 48 48 48

MinA-P(%) 0.289* 0.193 0.257 0.025 0.239

FA(%MinA) 0.228 0.197 0.215 0.195 0.250

CA(%MinA) 0.180 0.217 0.239 0.181 0.230

NACEU(%MinA) 0.293* 0.218 0.243 0.202 0.295*

W+NACFN(%MinA) 0.295* 0.221 0.248 0.202 0.297*

AAC(%MinA) 0.278 0.247 0.281 0.195 0.297*

W(%MinA) 0.227 0.186 0.201 0.196 0.245


For the recycling fertilizers, the strongest correlationswithnetPuptake(shootsandroots)wereobservedforex-tractionswithcitricacid(CA),followedbyneutralammo-nium citrate (NACEU orW+NACFN).However, therewerealsocleardifferencesbetweenthefirstandthefinalyield:Whilethepositiveinitialeffectofwater-solublefertilizerswasseenatcut1,atcut3therewerestrongerrelation-shipsbetweenPuptakeandthemorepowerfulextract-antscitricacid(CA),NACEUandformicacid(FA)(Table18),confirming again that the prompt advantage of water-soluble P forms can be at least partly compensated byslowlyavailablePformswithtime.

240

Table18:

Pearsoncorrelationcoefficients(r)fortherelationshipbetweenabsolute(MinA)/relativePsolubilityindifferentchemicalextractsandPuptakeinthepottrial,calculatedforrecyclingfertilizers(Types1to7)


n 84 81 76 84 76

MinA-P(%) -0.550** 0.303** 0.222 -0.365** -0.150

FA(%MinA) 0.414** 0.241* 0.469** 0.249* 0.395**

CA(%MinA) 0.590** 0.277* 0.488** 0.530** 0.722**

NACEU(%MinA) 0.479** 0.271* 0.480** 0.540** 0.625**

W+NACFN(%MinA) 0.588** 0.086 0.283* 0.518** 0.550**

AAC(%MinA) 0.611** -0.170 -0.060 0.516** 0.385**

W(%MinA) 0.865** -0.323** -0.093 0.461** 0.387**


4 Conclusions

Itcanbeconcludedfromtheclosecorrelationsbetweenvariouschemicalextractionmethodsfoundformineralaswellasorganicfertilizersthatitiseasilypossibletoreducethenumberofstandardmethodstothreeorfour.Thiswillbemuchmoredifficultforproductsfromsewagesludgeash.However,withregardtotheheterogeneityofthesematerialsitisquestionablewhethertheirqualitycanasyetbedefinedwithsufficientaccuracytomakethematrad-ablefertilizer,i.e.moredevelopmentandresearchontheproductionengineeringside(stabilityandabilitytocontrolthethermochemicalprocess)isnecessary.Thisshouldin-cludethequestiontowhichextentnewconstituentsun-predictablydevelopingduringthethermochemicalprocessimpairthedeterminationofPsolubilitywithconventionalchemicalextractionmethods.The statistical calculations on correlations between

chemical solubility and agricultural performance in theNeubauerpottrialconfirmedarelationshipbetweenwa-tersolubilityofafertilizerandits initialeffect,whilethemid-termeffectofnon-watersolublefertilizerswasbestdescribedbyanextractionwithammoniumcitrate.Sinceitiseasiertohandleinthelaboratory,theEUmethodofneutralammoniumcitrateextractionwithoutaprecedingwaterextractionisrecommended.Inordertoestimatethetradable total P contentofa fertilizer, it is suggested tomaintainthemineralacidextractionalreadypracticedonEUlevel.However,sincethismethodshowsclosecorrela-tionwith theaqua regiaextraction, it isalsopossible tochoosethelatteroneforso-calledtotalP.Anadvantageoftheaqua regiaextractisthefactthatthisisatthesametime thestandardmethod toquantify totalheavymetalcontentsinfertilizersandsoils.

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Legal norms

Düngemittelverordnung(DüMV)vom16.12.2008,BGBlI(60):2524-2581,ge-ändertam03.11.2004,Bundesgesetzblatt:Teil1/BundesministerderJu-stizI:2767

Düngeverordnung (DüV)–VerordnungüberdieAnwendungvonDüngemit-teln, Bodenhilfsstoffen und Kultursubstraten nach den Grundsätzen dergutenfachlichenPraxisbeimDüngenvom27.02.2007,Bundesgesetzblatt:Teil1/BundesministerderJustiz,p221

EU-VerordnungüberDüngemittelVO(EG)2003/2003v.13.10.2003,EU-Amts-blattL304,mitÄnderungsverordnungenVO(EG)Nr.2076/2004,EU-Amts-blattL359,S.25ff.undVO(EG)Nr.162/2007,AmtsblattderEuropäischenUnion2007/L51:7

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