The Nitrogen CycleAtmospheric

nitrogen

Atmosphericfixation

and deposition

Animalmanures

and biosolids

Industrial fixation(commercial fertilizers)

Crop harvest

Volatilization

Denitrification

Runoff anderosion

Leaching

Organicnitrogen

Ammonium(NH4)

Nitrate(NO3)

Plant residues

Biologicalfixation by

legume plants Plantuptake

Immobilization

Immobilization

Mineralization

Mineralization

Input to soilComponent Loss from soil

-+

The Phosphorus Cycle

Animalmanures

and biosolids Mineralfertilizers

Crop harvest

Runoff anderosion

Leaching(usually minor)

Organic phosphorus•Microbial•Plant residue•Humus

Primaryminerals(apatite)

Plant residues

Plantuptake

Soil solutionphosphorus•HPO4

-2

•H2PO4-1

Secondarycompounds

(CaP, FeP, MnP, AlP)

DissolutionDissolution

PrecipitationPrecipitation

Mineralsurfaces

(clays, Fe and Al oxides,

carbonates)W

eath

erin

g

Wea

ther

ing

AdsorptionAdsorption

Mineralization

Mineralization

Immobilization

ImmobilizationDesorptionDesorption

Input to soilComponent Loss from soil

Atmosphericdeposition

The Potassium CycleAnimal

manuresand biosolids

Mineralfertilizers

Crop harvest

Runoff anderosion

Leaching

Soil solution potassium (K+)

Plant residues

Plantuptake

Mineralpotassium

Fixedpotassium

Exchangeable potassium

Input to soilComponent Loss from soil

The Sulfur Cycle

Animalmanures

and biosolids

Mineralfertilizers

Crop harvest

Runoff anderosion

Leaching

Absorbed ormineral sulfur

Plant residues

Plantuptake

SulfateSulfur(SO4)

Atmosphericsulfur

Elementalsulfur

Organicsulfur Immobilization

Immobilization

MineralizationMineralization

Bacterial reduction

Bacterial reduction

Bacterial oxidation

Bacterial oxidationOxid

atio

n

Oxid

atio

n

SOSO22 gas gas

Reduced sulfur

Input to soilComponent Loss from soil

VolatilizationAtmosphericdeposition

-