Dynamics of micronutrients in soil

1. Lecture 14
Micronutrients’ dynamics inSoil

2. micronutrients
 Importantlysevenoreightandmorenow.
 Requiredbyplantsinppmlevel.
 Mostoftheminfluenceenzymaticactivities.
 Alsofunctionascatalysts.
 Deficienciesobservedinlighttexturedandcalcareoussoils.

3. In general, forms of mironutrients
Forms Influence of
availability
• In the soil solution Immediately available
• on the exchange complex
• Adsorbed on soil surfaces
• Inorganic compounds
Available pool replenish soil
solution forms
• In organic matter
• In living organisms
Available on decomposition
• In secondary minerals
• In primary minerals
Potential medium – long term
sources of available form

4. otherwise
 solubleform,
 Complexform,
 Precipitatedform,
 Oxidationandreductionformand
 Chelate form(complexwithOM)

5. Soil Solution
Soil
Organism
s
Chelates
Clay
minerals
Soil
Minerals
(insoluble
Forms)
Organic
Matter
(bound
forms)
Leaching
Animals &
Humans
Fertilizers
MICRO
NUTRIENTS
CYLCE

6. SOIL
SOLUTION
Exchange &
Surface adsorption
Organic matter &
microorganisms
Nutrient uptake
by plants
Solid phase
Minerals
&
Precipitates
Absorption
Exudation
Precipitation
Dissolution
Adsorption
Desorption
Immobilization
Mineralization
Relationship between
the various forms of
Fe, Zn, Cu & Mn
(Metal micronutrients)
in Soil

7. iron
Sources
◦ commonlyfrom primary andsecondaryminerals
 Olivene((Mg,Fe)2SiO4),Pyrite(FeS),Hematite(Fe2O3),
Goethite(FeOOH),Limonite
(FeO(OH).nH2O+Fe2O3.nH2O)andMagnetite(Fe3O4).
 Mostlyasoxides,hydroxides,sulphidesandsilicates.

8. forms
Fourmajorforms
1. PrimaryandSecondarymineralFe
2. Adsorbed Fe
3. OrganicFe
4. SolutionFe-Fe(OH)2
+

9. Factors affecting availabilty of IRON
 Soil pH–IncreaseinpHdecreasestheavailabilty
◦ Foreveryunit, Fe3+ decreases1000foldand Fe2+ 100 fold
 EffectofHCO3 andPO4:
◦ HCO3 increasesthesolubilityofPO4 andinduceprecipitationofFePO4
◦ CausesHCO3 inducedchlorosis.
 PresenceofCa&K:Antogonisticeffect.
 Organicmatter:Increasestheavailabilityandforms chelates.
 Soil texture:
◦ FinetexturedsoilshavemoreFe.
 Waterlogging :
◦ AnaerobicFe3+ toFe2+ -increasesavailability
◦ chelatesareformedwithOM.

10. manganese
Sources
 Minerals:
Pyrolusite(MnO2), Hausmanite(Mn3O4),
Manganite(MnOOH), Rhodochrosite(MnCO3)and
Rhodonite(MnSiO3).
Forms
1.solutionMn2+,
2.exchangeableMn2+,
3.organicallyboundMnand
4.mineralMn.
◦ EquilibriumamongtheseformsdeterminesMnavailability.

11. Factors affecting Manganese availability
 SoilpH:Mn2+ decreases100foldfor eachunitincrease inpH.
◦ Similartobehaviourof otherdivalentmetalcations.
 OM:stronglyinfluence.LowavailabilityinhighOM.
 CaCO3: Decreasessolutionandexchange Mnduetoprecipitation as
MnO2.
 Water logging:Increasestheavailability

12. Continued…
 Soiltexture:Finetextured hasmore total, exchangeableandactiveMn.
 Soiltype:
◦ RedandLaterite soilhavemore availableMn.
◦ Montmorillonite clayhashightotal Mn.
◦ Kaoliniteclayhasmore exch.andwatersolubleMn.
 Interactionwithothernutrients:
◦ highlevelsofCu,FeorZn,reduce Mnuptake byplants.
◦ AdditionofacidformingNH4
+ enhanceMnuptake
◦ NeutralKCl,NaCl,CaCl2 applicationincreaseMnavailability.

13. zinc
 Sources:
◦ Igneousrockscontainabout70ppm.
◦ Sedimentaryrocks(shale)containmoreZn(95ppm).
◦ Limestone (20ppm), sandstone (16ppm).
 Zncontainingminerals:
◦ Sphalerite(ZnS),Smithsonite (ZnCO3),Willemite(Zn2SiO4),Hemimorphite
(Zn4(OH)2Si2O7H2O)andFranklenite(ZnFe2O4).
 Forms:
◦ SolutionZn2+,adsorbedZn2+,organicallycomplexed ZnandZninprimary
andSecondary minerals.

14. Factors affecting Zinc availability
 SoilpH:
◦ DecreaseswithincreasedpH.
◦ Availabilitybetween5and7.5
◦ Above8,ZnformZincateionasprecipitate (insolubleandunavailable)
 OM:
◦ Increasetheavailabilityaschelate.
◦ Immobilisebyhighmol.wt- organicsubstanceslikelignin.
 CaCO3:
◦ Leadsto fixationofZnasZnCO3 precipitate.

15. Continued…
 Interactionwithothernutrients:
◦ Cu,Fe&MninhibitZn2+ uptake.
◦ Antagonistic effectespeciallybyCu2+ &Fe2+.
◦ HighPavailabilityinduceZndeficiency.
◦ SO4 andNincreasestheavailabilityanduptake.
 Flooding:normallydeficientinflooded soils.
 Climate:
◦ Zndeficienciesaremoreduringcool,wetseasonanddisappearinwarmer
weather.
◦ Increasingsoiltemperature increasestheavailability.

16. copper
Sources:
◦ ImportantCu containingminerals.
 Chalcopyrite(CuFeS2),
 Chalcocite(Cu2S)and
 Bornite(CuFeS4)
Oxides,carbonates,silicates,sulphates andchlorides ofCu.
◦ Manures,fertilizersandCucontainingfungicides.

17. Forms
 soilsolutionCu– inionic andcomplexedform.
 ExchangeableCu– oncationexchangesitesofclayand
OM.
 Occludedand co-precipitatedinsoiloxidematerials.
 SpecificallyadsorbedCuonspecificadsorptionsites.
 OrganicallyboundCu-inOMand livingorganisms.

18. Factors affecting Copper availability
 SoilpH
 CaCO3 asaffectinginthe
 OM caseofZn
 Phosphates
 Clayminerals:
◦ BentoniteandMontmorilloniteheldCu tightly.
◦ Al2O3 fixhighamountofCu andreduce availability.

19. boron
Sources
◦ Tourmaline-aborosilicate.
◦ Borosilicateisinsoluble,resistanttoweathering.
◦ ReleaseofBisquite slow.
◦ Alkalineearthboratesareplentifulinsoilsofaridclimate.
◦ Balsoaddedthroughorganicmanures,fertilizersandirrigationwater.
Forms
 Existsinfour forms asothermicronutrients.
◦ SoilsolutionB,AdsorbedB,organicallycomplexed BandBinminerals.

20. Factors affecting B availability
 SoilpH.
 CaCO3
 OM
 Irrigationwater-Btoxicity mayoccur, ifcontainhigh.
 Saltconcentration-increaseswithincreasingEC.
 Soiltexture
 Typeofclay:Badsorption capacitiesfollowthe order -mica>mont.>
Kaolinite
 InteractionwithCaandK.

21. molybdenum
Sources
◦ Mostlythrough organicmanuresandfertilizers.
◦ Lesscontribution through mineralwulfenite (PbMoO4).
Forms
◦ Asothermicronutrients.
◦ Soilsolution Mo-asMoO4
2-,HMoO4
- andH2MoO4.

22. Factors affecting availability
 soilpH:increaseswithincreasingpH(unlikeother micronutrients).
 Liming:increasetheavailability.
 OM:increasethe availability
 Texture:Moavailabilityincreasedwithclay content.
 Amountof FeandAloxides: stronglyadsorbed andbecomes available.
 Interactionwithotherelements:
◦ Penhances,SO4 depresses.
◦ CuandMnreduce,butMgencourages.
◦ NO3-Nencourages butNH4-N reduce.

23. chloride
 Sources:
◦ Originatesfromsaltstrapped inparentmaterial
◦ Frommarineaerosolsandvolcanicemissions
◦ Byoceanicsaltspraycarriedinrainandsnow.
◦ 2ppm Cl- inprecipipation nearseacoasts.
 Forms:
◦ SolubleCl- andexchangeableCl-.
◦ pHdependant positive charge(AEC).

24. cobalt
 CO2+ adsorbed on exchangecomplex.
 Occurs asclay-OMcomplexes similartoothermetalions.
 Orderof adsorption
muscovite> hematite>bentonite=Kaolin.
 Coavailabilityfavoured byincreasingacidityandwaterlogging
conditions.