Nitrogen Forms

1
Nitrogen Forms

• Nitrogen Gas (N2)
• Ammonium N (NH4)
• Nitrate N (NO3-)
• Ammonia (NH3)
• Nitrous (N2O) and Nitric (NO) Oxides
• Organic N

2
Nitrogen Transformations

• Fixation
• Mineralization
• Immobilization
• Volatilization
• Nitrification
• Leaching
• Denitrification

3
Behavior of Ammonium N

• Ammonium N NH4
• Cation, therefore adsorbed on CEC
• Won't leach or denitrify
• Can be fixed in certain clay minerals micaceous
  clays
• Plant uptake
• Very common source of N
• Volatilization at high pH
• Rapidly converted to NO3-N under most conditions,
  therefore doesnt accumulate in soil

4
Volatilization

• NH4 OH- ? NH3? H2O
• Requires very high pH
• pH N as NH3
• 7 0.5
• 8 5.0
• 9 35

5
Volatilization

• Reaction of urea in the soil
• Urease
• CO(NH2)2 2 H2O ? 2 NH4
  CO32-
• Urea Ammonium N
  Carbonate
• CO32- H2O ? HCO3- OH-
• NH4 OH- ? NH3?
  H2O

6
Volatilization

• Urea nitrogen Source of NH4-N and High pH
• Includes
• Urea Fertilizer
• Urea-Ammonium Nitrate Solution (UAN)
• Manure
• Incorporation of Urea
• With no soil incorporation the NH3 gas is free to
  go off into the air.
• With incorporation same reaction occurs but the
  NH3 gas is trapped and reabsorbed.
• Loss of 30 of the N possible within a week with
  no incorporation
• Immediate incorporation by injection, tillage, or
  rain minimizes the losses.

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Volatilization

• Other conditions that affect urea volatilization
• Higher temperatures increase volatilization loss
• Wind increase volatilization loss
• High soil moisture to dissolve the urea speeding
  up volatilization loss
• Lower CEC reduces adsorption of NH4 thus
  increases volatilization

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Volatilization

• Management related to urea volatilization
• Incorporation
• Incorporate with tillage as soon as possible
  following application
• Apply urea immediately before rain
• Dribble liquid nitrogen (UAN)
• Reduced exposed surface area
• Achieve significant amount of the benefit of
  incorporation
• Dont use urea based fertilizers
• Ammonium nitrate
• Ammonium sulfate

9
Volatilization

• Dribble liquid N

140
Dribble
Spray
120
Corn Yield (Bu/A)
100
80
0 45 89 134 178 lb N/A applied
10
Volatilization

• Management related to urea volatilization
• Use extra fertilizer to compensate
• Urease inhibitors

11
Volatilization

• Urease Inhibitors reduce Breakdown of UreaUrea
  NH4 CO32-NH4
  NH3 ?
• Urease enzyme rapidly breaks urea down and
  results in ammonia volatilization if on the
  surface
• Urease inhibitor inhibits breakdown allowing time
  for urea to be incorporated
• The slowing of conversion of urea to ammoniacal N
  can significantly reduce the potential for NH3
  volatilization

Urease
High pH
12
Urease Inhibitors

• N-(n-butyl)thiophosphoric triamide (NBPT)
• Agrotain
• Effective urease inhibitor
• Can be used with Urea and UAN
• Cost ?

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Effect of N placement, source, and NBPT on
irrigated no-till corn yieldKansas, Crete silt
loam
Broadcast
Gordon. KSU Fertilizer Report. 2006. 2-year
average
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Apparent N fertilizer recovery in no-till
cottonMississippi, Marietta fsl
Surface dribble
Broadcast
Earnest and Varco. 2006.
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Urease Inhibitors

• Ammonium Thiosulfate (ATS)
• Exhibits urease inhibition in laboratory
  incubations
• Inconsistent results in the field
• No benefit in surface spray application of UAN in
  experiments in
• Pennsylvania
• Ohio
• North Dakota
• Missouri

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Nitrification

• Nitrification of Ammonium N
• 2NH4 4O2 ? 2NO3- 4H H2O
• Nitrification carried out by obligate autotrophs
• Nitrification is fairly rapid under favorable
  conditions

17
Nitrification

• Nitrification is a two step process
• 2NH4 3O2 ? 2NO2- 4H
  2H2O
• Nitrite
• 2NO2- O2 ? 2NO3-
• 
  Nitrate
• 2NH4 4O2 ? 2NO3- 4H H2O

18
Nitrification

• Moisture Level
• Optimum _at_ Field Capacity
• Temperature
• Optimum 25 - 35 C (75 - 95 F)
• Aeration
• O2 necessary for nitrification

19
Nitrification

• pH
• Nitrification bacteria sensitive to soil pH
• Nitrification will be slower at low pH
• At high pH free NH3 is toxic to nitrobacter which
  may result in buildup of toxic levels of NO2-
• Nitrification lowers pH

20
Behavior of Nitrate N

• Nitrate N NO3-
• Anion, therefore not adsorbed on CEC
• Very susceptible to leaching and denitrification
  losses
• Plant uptake
• Most common mineral form of N in most soils

21
Nitrate Leaching

• Public Health Standard for nitrate in drinking
  water 10 ppm NO3-N
• Nitrate nitrogen (NO3-) is negatively charged
  therefore it is not adsorbed by on the soil CEC
  and thus will move with soil water.
• High soil moisture
• High infiltration and percolation of soil water

22
Nitrate Leaching

• Management related to Nitrate Leaching
• Rate
• Match N application to plant needs
• N not taken up by plants susceptible to leaching
  loss
• Significant leaching loss even at economic
  optimum N rate

23
Nitrate Leaching

• Management related to Nitrate Leaching
• Timing
• Apply N as near to time of crop utilization as
  practical
• Avoid times when potential for loss is high

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Nitrification Inhibitors

• Nitrification Inhibitors
• Nitrosomonas
• 2NH4 3O2 ? 2NO2- 4H
  2H2O
• Nitrite
• Nitrobacter
• 2NO2- O2 ? 2NO3-
• 
  Nitrate

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Some patented nitrification inhibitors
Frye. 2005.
26
Effect of nitrification inhibitor on no-till
corn yield Kentucky
Frye, 2005. Urea or UAN surface applied
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Denitrification

• 2NO3- ? N2O N2
  3O2 Nitrate Anaerobic
  Nitrogen gases Oxygen
• Microbes
• Nitrate Nitrogen
• No oxygen - wet soil
• Energy source for bacteria - organic matter
• Warm temperatures
• Favored by higher pH
• Form of N lost varies with pH
• pH lt 5.5 NO
• pH lt 5.5-6.0 N2O
• pH gt 6.0 N2

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Denitrification

• 2. Denitrification
• Anoxic process (ie. occurs in absence of oxygen)
• Catalysed by facultative anaerobes called
  denitrifiers - a diverse group of heterotrophic
  bacteria.
• Electron acceptor NO3-, NO2- and nitrogen oxides
• Electron donor Organic carbon source (e.g.
  acetate, glucose etc.) (i.e. COD)
• Biological reduction of NO3- and NO2- to gaseous
  N2 is a four-step process
• NO3- ? NO2- ? NO (g) ? N2O (g) ? N2 (g)
• (5) (3) (2) (1)
  (0)
• Not all denitrifiers contain all the enzymes
  needed
• ? entire reduction is carried out by different
  microorganisms.

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Denitirification

• 2. Denitrification
• Reduction of nitrate to nitrite
• NO3- 2 H 2 e- ? NO2- H2O (nitrate
  reductase)
• Reduction of nitrite to nitric oxide
• NO2- 2 H e- ? NO H2O (nitrite
  reductase)
• Reduction of nitric oxide to nitrous oxide
• 2 NO 2 H 2 e- ? N2O H2O (nitric oxide
  reductase)
• Reduction of nitrous oxide to dinitrogen gas
• N2O 2 H 2 e- ? N2 H2O (nitrous oxide
  reductase)
• Most denitrifiers will use O2 (if available) to
  oxidise their carbon source, in preference to
  NO3- as the electron acceptor. This is possiby
  because slightly more energy is available from
  the reduction using oxygen as the e- acceptor
  (?Go - 78.6 kJ mol-1) instead of nitrate (?Go
  - 72.1 kJ mol-1).
• Whether denitrification can occur in presence of
  O2 is unclear

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Denitrification pathway
32
Surface water
Low NH4
Oxidized layer
Reduced soil layer
Biodegradation
Slow Diffusion
C/N lt20
C/N gt20
NH4 HIGH
33
Surface water
nitrification
Low NH4
Oxidized layer
NO3 high
Reduced soil layer
Slow Diffusion
NH4 HIGH
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Denitrification

• Denitrification losses can be very high
• Denitrification occurs very rapidly once soil is
  saturated with water
• Very little denitrification once nitrate is in
  the groundwater because no energy source for
  microbes
• Growing plants can increase denitrification by
  using up soil oxygen
• Increased potential for denitrification when
  organic materials such as manure are applied.
• Increase potential for denitrification in
  conservation tillage systems
• Avoid denitrification losses by not applying N
  prior to the wet periods of the year.
• Denitrification used in wetlands to remove NO3-
  from water.

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Denitrification

• Denitrification used in wetlands to remove NO3-
  from water.

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Dewatering Centrate/Filtrate Rich in Ammonia
Nitrogen
Influent
Sec. Clarifier
Primary Settling Tank
WAS
Waste primary sludge
Gravity Thickener
Anaerobic Digestion
20-40 of Influent N Load TKN 600 1200
mg/L Alkalinity 50 needed for full
nitrification Relatively low carbon rbCOD/TKN0.4
0
Centrate / Filtrate
Dewatering
Biosolids
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InNitri Process was the first bioaugmentation
scheme
Sec. Effluent
PC
Activated Sludge Tank
RAS
WAS
Nitrifiers NO3-N
Centrate (NH3-N)
Nitrification Reactor 250C
Expected benefit not fully realized Temperature
change Poor capture of recycle stream
nitrifiers Predation Change in total dissolved
solids content osmotic pressure
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Biotechnology

• unstable nitrification
• carry out routine monitoring of microbial
  community structure and function within
  bioreactors restriction fragment length
  polymorphism (T-RFLP) assays qPCR
• stable denitrification as the complete reduction
  of nitrate to nitrogen gas without the
  accumulation of the intermediates of the
  denitrification pathway (nitrite, nitric oxide,
  nitrous oxide) the use of bioaugmentation to
  increase stability, and the effect of diversity
  on stability

42
Anammox

• Anaerobic Ammonium Oxidation (Anammox)
• The oxidation of ammonium to dinitrogen gas (N2)
  with nitrite as the electron acceptor by
  autotrophic bacteria.
• Discovered at the Kluyver Laboratory, Delft, The
  Netherlands in 1995.
• For the first time, ammonium was discovered to be
  oxidised in the absence of oxygen by a rare
  species of bacteria Planctomycetes, Candidatus
  Brocadia anammoxidans.
• NH4 NO2- ? N2 2 H2O (?Go -357 kJ
  mol-1)
• Ammonium can be oxidised directly to dinitrogen
  gas, without the need for the multi-step process
  of aerobic nitrification and heterotrophic
  denitrification.

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Anammox
The electron donor is ammonium, the electron
acceptor is nitrite. Ammonium (ox. state -3) gets
oxidised to N2 (0), and nitrite (3) is reduced
to N2. Autotrophic ? avoids the need for addition
of a carbon source, which is sometimes a cost in
conventional systems. All original attempts to
isolate the responsible microorganism failed
organism grows extremely slowly (?max 0.003
h-1), probably lives in nature at the oxic/anoxic
interface. Advent of molecular microbiological
techniques, eg. molecular probing ?greater
insight into natural habitats.
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Anammox 4.3.1
Process only known from one species
chemolitho-autotrophic planctomycete Brocadia
anammoxidans Energy generation NH4 NO2- ?
N2 2 H2O Carbon fixation CO2 2 NO2- H2O
? CH2O 2 NO3- Measured overall growth at r
0.0014 h-1 (Strous, 2000) 1 NH4 1.32 NO2-
0.066 HCO3- 0.13 H ? 1.02 N2 0.26 NO3-
0.066 CH2O0.5N0.15 2.03 H2O Known N2
comes from NH4 and NO2- N in biomass comes
from NH4
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Cannon
CANON (Completely Autotrophic Nitrogen removal
Over Nitrite) Cooperation between aerobic and
anaerobic ammonium oxidisers under oxygen
limitation. Completely autotrophic ? promising
opportunity for wastewaters with a very low
organic carbon content (eg. landfill leachates,
aquaculture waste). Ammonium is oxidised to
nitrite by aerobic ammonium oxidisers
(Nitrosomonas, Nitrosospira etc.)
NH4
1.5 O2 ? NO2- 2 H H2O The nitrite
produced can be used by anammox

NH4 1.3 NO2- ? N2 2 H2O Overall
nitrogen removal by CANON 1 NH4 0.75 O2 ?
0.5 N2 1.5 H2O H Advantages of CANON system
low aeration costs (60 less than traditional
systems), requires no addition of a carbon source
(process is autotrophic) and the only end product
is N2.