Lecture -7.jouyghhhhyyytfgggggggggiukyppt

.

1. SAC 301 Soil Fertility, Fertilizers and
Manures (2+1)
Lecture 7
P fertilizers-Rock phosphate, bone
meal, basic slag, single super phosphate,
diammonium phosphate, triple super
phosphate, properties and their
reactions in soil

2. P -Fertilizers
Discoveredin1669andwidelydistributedinthe
lithosphereasphosphates.
Occurmostlyascalciumphosphate{Tri-calcium
phosphate–{Ca
3(PO
4)
2}
Tri-calciumphosphateisthebasicmaterialforthe
manufactureofmanyphosphaticfertilizers
Morethan50countriesproducephosphaticfertilizer
TopfiveareU.States,China,Russia,IndiaandBrazil.

3. P -Fertilizers -Classification
Based on
Nature of source /
Manufacture
Based on
Solubility
Natural
Bones / Minerals / R.P
Treated / processed
S P / Bone char
Industrial byproduct
Basic slag
Chemical / Synthetic
Ammonium phosphate
Water soluble
SSP -16-18%, DSP -32%
TSP -46-48%
Amm.PO
4 -20%
Citrate soluble
Basic slag -14-18%
DCP -34-39%
Rhennia PO
4-23-26
Citrate insoluble
Rock. Phos.-20-40%
Raw B.M-20-25%
Steamed B.Meal-22%

4. I. Water soluble phosphate
Includeeithermono-calciumphosphateCa(H
2PO
4)
2or
otherwatersolublephosphateslikeammonium
phosphates.
Thesearereadilysoluble(solubility100gL
-1
)inwater
andabsorbedquicklybyplants(monovalentphosphate
ionH
2PO
4).
Thesefertilizersaresuitableforneutralandalkaline
soilsbutnotforacidsoils.

5. II. Citric acid soluble phosphates
Water–insolublebutsolubleinonepercentcitric
acid;Dicalciumphosphate-Ca
2(HPO
4)
2or{Ca
(HPO
4)}
2
Availability of P is slow (solubility 0.25g L
-1
)
Well suited for lateritic and acidic soils

6. III. Insoluble phosphates
Mainlyastricalciumphosphate-Ca
3(PO
4)
2
Availabilityisveryslow(solubility0.005gL
-1
)
Availableforprolongedperiodoftime.
Wellsuitedforstronglyacidicsoilsororganicsoils

7. Sl. No. Fertilizers Total P
2
O
5
(%)Form of PO
4
Avail.P
2
O
5
1. Ordinarysuperphosphate 16-18 Water Sol.16.5 -17.0
2. Concentratedsuperphosphate 46 –48 -do-
3. Monoammonium phosphate 48 (11 N) -do-
4. Diammoniumphosphate 53 (21 N) -do- 46 (18N)
5. Ammophos–A 48 (11 N) -do-
6. Ammophos–B 20 (20 N) -do-
7. Basicslag 14 –18 Citric .Sol
8. Dicalciumphosphate 34 –38 -do- 34.0
9. Fusedtricalciumphosphate 28 -do-
10. Rhenaniaphosphate 23 –26 -do-
11. Rawbonemeal 20 –25 Insoluble NA
12. Steamedbonemeal 22 –25 -do- NA
13. Rockphosphate 30 –40 -do- NA

8. Rock phosphate (mineral deposit)
Itoccursnaturally,asmineraldepositsconsisting
mainlyof[Ca
3(PO
4)
2]
3combinedwitheitherCaF
2,
CaCO
3,Ca(OH)
2orCaCl
2.
Thenaturallyoccurringmineraliscalled“Apatite”or
“Phosphorite”or“Phosphaterock”havingthegeneral
formula[(Ca
3(PO
4)
2)]
3CaX.
Thesenaturaldepositsserveasthebasicmaterialfor
thesynthesisofallotherphosphoricfertilizers.

9. Forms of apatite
Apatite -General formula (Ca
3(PO
4)
2)
3Ca xor Ca
10 (PO
4)
6x
where x= CO
3, Cl
2, F
2, SO
4or(OH)
2.
1.Carbonate apatite [Ca
3(PO
4)
2]
3CaCO
3 (Francolite)
2.Fluor apatite [ Ca
3(PO
4)
2]
3CaF
2 (most common)
3.Chlor apatite [Ca
3(PO
4)
2]
3CaCl
2
4.Hydroxy apatite [Ca
3(PO
4)
2]
3Ca(OH)
2
5. Sulphate apatite [Ca
3(PO
4)
2]
3CaSO
4

10. Predominant–Calciumcarbonateflourapatite(Francolite)
-Chlorapatite
HighgradeRP(55-80%P
2O
5)-Morocco(21,000m.t),Algeria,
Tunisia,USA(13,290m.t)
LowgradeRP(20-40%P
2O
5)–Trichy(TN),Singhbhum(Bihar),
(8,12,000t) Birmania&Udaipur(Rajasthan),
Mussoorie(UP),Laccadiveislands
GroundRPisinmarketpassesthrough200meshsieve

11. BiharRajasthan UP Tamil Nadu
P
2O
5 (%)20–4010-34.520-32 24-27
R
2O
3 (%)39.60About 2 3-10 4-9
F (%) 0.730.5-1.110.27-3.0 2-3
Composition Indian RP

12. Phosphate rock
Phosphoric acid TSP Super phosphate Nitro phosphate
Ammonium
phosphate
Solid mix. Fer.
a) Green or Wet process :
Ca
10F
2(PO
4)
6+ 10 H
2SO
4 + 20H
2O 6H
3PO
4+ 10CaSO
4+ 20H
2O + 2HF
b) White or Furnace process :
RP heated in an electric arc furnace to produce elemental P
then allowed to react with O
2to form P
2O
5and reaction with
water gives H
3PO
4

13. SingleSuper Phosphate
{Ca
3(PO
4)
2}
3.CaF
2+7H
2SO
4 +3H
2O 3Ca(H
2PO
4)
2.H
2O+7CaSO
4+ 2HF
Triple super
{Ca
3(PO
4)
2}
3.CaF
2+ 14 H
3PO
4+ 10H
2O 10Ca(H
2PO
4)
2.H
2O+2HF
2
Mono ammonium phosphate (11-52-0)
NH
3+ H
3PO
4 NH
4H
2PO
4
Di ammonium phosphate (18-46-0)
2NH
3+ H
3PO
4 (NH
4)
2HPO
4

14. Rock Phosphate
Total P
2O
5content -20 –40 % or 8.6 –17.2 %
Citrate solubility -5 to 17 % of total P
2O
5
Insoluble in water & effective only in acid & organic soils
Suitable for perennial crops
Partially acidulated RP is used for better solubility
Biosuper: RP + elemental S + Thiobacillus thioxidans
{Ca
3(PO
4)
2}
3.CaCO
3+ 6H
2CO
3 3Ca(H
2PO
4)
2+ 7CaCO
3
{Ca
3(PO
4)
2}.CaCO
3+ 14HNO
3 3Ca(H
2PO
4)
2+ 7Ca(NO
3)
2+ H
2CO
3

15. Super Phosphate
Water soluble phosphorus –18 % total & 16 % WSP P
2O
5
It contains about 20% Calciumand 12% Sulphur
Suitable for neutral soils & annual crops
In calcareous soils –converted to Tri-Ca-PO
4 (insoluble)
Strong acid soil –converted to Fe & Al-PO
4(insoluble) &
di-calcium-PO
4(insoluble)
Moderately acid soils –Fixed at the +ve sites of clay mineral
(not available for plants)
Alkali / sodic soils –converted to NaH
2PO
4(soluble)

16. Reaction of P fertilizers in soil
WhenSSPisappliedtoamoist(or)adrysoilbeforerainfall(or)
irrigation,themonocalciumphosphategetsdissolvedinthesoilwater.
Therootsofthegrowingplantstakeupthisformofphosphorus.
Butwithinaveryshorttime,thesolutionofmono-calciumphosphateis
precipitatedinthesoilpores.
DependinguponsoilpH,differentsoil-fertilizerreactionproductsare
formedthatarenotsolubleinwaterandbecomesunavailabletoplants.
Sothesuperphosphateisnotleachedfromthesoilbytherainfall.
WhenSSPisappliedtostrongacidsoils,itcombineswithFeandAlto
formtheirrespectiveinsolublephosphatesanddicalciumphosphatesas
follows

17. •WhenSSPisappliedtomoderatelyacidsoils,
phosphatefixationtakesplacebythesilicate
mineralspresentinsoilandbecomesunavailableto
plants.AlandFeareremovedfromtheedgesofthe
silicatecrystalsforminghydroxylphosphates.
•ApartofthereactedphosphatewithFeandAl
compoundsisalsoreleasedbyanionexchange
reactionwithOH

18. •WhenSSPisappliedtoneutralandcalcareoussoils,the
followingreactionwilltakeplaceandPbecomesunavailableto
plants.
Theinsolubletricalciumphosphateformed-convertedinthesoilto
moreinsolublecompoundslikehydroxylapatite[Ca10(PO4)5(OH)4],
carbonateapatite(Ca10(PO4)6(CO3)2andfluorapatite(C10PO4)6F2)
andultimatelyPbecomesunavailabletoplants.WhenSSPisappliedto
alkalinesoils(pH>8.5(or)9.0,Na+isthedominantcation),itreacts
withNa+andformsmono-sodiumphosphatewhichishighlysoluble
andbecomesavailabletoplants

19. Bone Meal
Bone meal
Total
P
2O
5(%)
CSP
P
2O
5(%)
Total N
(%)
Raw 20.0 8.0 3.0
Steamed 22.0 16.0 -
Similar in reaction as that of rock phosphate
Basic Slag
By product of steel industry –Citrate soluble in nature
13 % P
2O
5(as much as 17 % P
2O
5)
3 –8 % ( Indian steel industry slag)
Ca, Mg, Fe, Mn –additional advantage over SP (only Ca & S)
Suitable for meadows, pastures and acid soil
Slowly supplies P for many years

20. Super phosphate/Den super phosphate
Manufacture
TreatmentofRPwithacids,mainlyH
2SO
4toconvert
insolubletri-Caphosphatetomono-Caphosphates.
ConcentratedHNO
3,HCl,H
3PO
4andH
2SO
4canbeused
Sulphuricacidisfoundtobemoresuitablebecausewhen
itreactswiththeRP,CaSO
4isformed
CaSO
4actsasadehydratingagentandimprovesthe
physicalconditionofthefinalproduct.

21. The calculated quantity of H
2SO
4and ground RP
(material passing through a four-mesh sieve only has to be used)are
introduced and mixed thoroughly and then dropped in a pit
or den. Hence it is called asDen method.
Sufficient time of 24 to 36 hrsis allowed for the completion
of the reaction.
Temperature raised to100°Cand there is a loss of volume by
10% due to evaporation of water, CO
2and F.
{Ca
3(PO
4)
2}
3.CaF
2+ 7H
2SO
4 3Ca(H
2PO
4)
2+ 7CaSO
4+ 2HF

22. TheCaSO
4actasadehydratingagentandartificialdrying
isalsodonewherevernecessary
Thentheproductisgroundtoaveryfinepowderand
storedforsufficienttimeforthecuringofthematerial.
Precautions:
AnexcessquantityofH
2SO
4shouldnotbeused.
ThequalityoftheRPmustbepredecided.

23. Di-ammonium Phosphate manufacture
Both the DAP grade 16 : 48 : 0 and 18 : 46 : 0 (common)
are manufactured by wet process phosphoric acid method.
Wet phosphoric acid of 40-42 % P
2O
5equivalent is partially
neutralized to 89% by anhydrous ammonia at pH 5.6
Sulphuric acid is often used along with phosphoric acid to
control the grade of fertilizer
A temperature of 240 F
o
is maintained by adjusting acidulation
so that water evaporation may balance the heat of reaction.
2NH
3+ H
3PO
4 (NH
4)
2HPO
4