Nutrients: Nitrogen (N), Sulfur (S), Phosphorus (P ... · Nutrients: Nitrogen (N), Sulfur (S),...
Transcript of Nutrients: Nitrogen (N), Sulfur (S), Phosphorus (P ... · Nutrients: Nitrogen (N), Sulfur (S),...
Nutrients: Nitrogen (N), Sulfur (S), Phosphorus (P), Potassium (K)
Essential for all life, their availability (or lack thereof) controls the distribution of flora and fauna
Look into their:
Sources Pools (sinks) Fluxes
Nutrients must be in a specific form – specie - for use by organisms
leaching
+root uptake
microbial uptakesolid solution
Soil Organic Matter(CHONPS)
Nutrient Cycling: N, S, P, K
Primary Productivity
Leaves & Roots
SOM/Minerals
DecompositionHeterotrophic respiration
O
A
B
leaching of nutrients
Gas loss
plant nutrient uptake
Microbes
Minerals(P, S, K)
ions and molecules in solution (leaching)colloidal transporterosionrunoff
OU
T
gases and particulates to atmosphere (fossil fuel combustion (coal/oil); cycles; trees)
harvestingroot uptake
bedrock (1ry/2ry minerals in parent material)
Nutrients: natural & anthropogenic sources (IN) and outputs (OUT)
roots (exudates, biomass)
OU
T
IN
IN
N2fertilizers (chemical, manure, sludge)pesticideswet and dry deposition (acid rain, aerosols)plant tissue/residues
Fluxes (transformations)
Pools (sinks)(SOM/clays/oxides)
SOIL
The Nitrogen Cycle
+
Oxiczone
Suboxiczone
NO3-
Nitrogen evolution (gases)
NO
NO2-
N2O
N2
denitrification
nitr
ifica
tion
Organic-N NH3N-mineralization
immobilization
N o
xida
tion
stat
e
+5
-3
E h(m
V)
236
700
N-fixation
(-3)
(0)
(+1)(+2)
(+3)(+5)
imm
obili
zatio
n
Atmospheric N depositionFertilizer additions
(~90% of soil N) (-3)
Nitrification: NH3 to oxidized forms of N (NO2
-, NO3-)
(energy-releasing)
Oxidation of N2 does not occur except in a few
organisms (N-N triple bond)
N-fixation: enzyme-catalyzed reaction (occurs only in living organisms)
N2 (g) is prevalent in the air of soil pores
NO3- is the most stable
chemical form of N in aerated soil solutions
Denitrification: reduction of NO3
-
to reduced forms of N (N2) (energy-
consuming)
The Nitrogen Cycle
NH4+ sorption
The Sulfur Cycle
Oxiczone
Suboxiczone
Anoxiczone S2-
SO42-
oxid
atio
n/re
duct
ion
O2
A large variety of organic forms of S
M2+ + S2- = MS (pptation of metal sulfides)
metal sulfides tend to be “insoluble” (Hg, Ag, Cd, Cu, Pb, Zn, Fe(II))
Sulfate found in oxidized
environments
degradation of organic materials
(plant/animal)
H2S
The Sulfur Cycle
Oxidation states range from +6 to -2
Sulfur undergoes dramatic changes in redox cycling
reduced organic S (thiol)
sorption
In soil, SO42- originates from
• Organic matter mineralization
• Weathering of soil minerals
• Sulfur inputs from atmosphere
The Phosphorus Cycle
Mostly in organic P and inorganic P forms
PO43- is strongly retained by soils but can be transported in colloidal forms
P primarily as phosphate (PO43-), with an oxidation state of 5+
Al and Fe phosphates (acid mineral soils) Ca phosphates (non acid soils)
(variscite, AlPO4.2H2O ) (hydroxyapatite, Ca5(PO4)3OH )
PO43- sorption onto Al and Fe oxides is strong
Phosphate minerals (low solubility):
(strengite, FePO4.2H2O )
The Potassium Cycle
Sources: Primary and Secondary Minerals
Potassium as K+ with no changes in oxidation state
K+ flux controlled by CEC & chemical weathering ~ no organisms