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BIOLOGICAL TRANSFORMATIONS OF NITROGEN IN SOIL
Animal residuesPlant residues
Animals
Plants
Plant roots
Nitrate
Ammonia
Microorganisms
Humus
NitrogenNitrous oxide
Nitrite
N.E.R. Campbell and H. Lees
<
NITROGEN CYCLENITROGEN CYCLE
Nitrogen Distribution in 10 Virgin Soilsand Their Cultivated Counterparts
Nitrogen Distribution in 10 Virgin Soilsand Their Cultivated Counterparts
Virgin Soil Cultivated SoilVirgin Soil Cultivated Soil
Nonhydrolyzable ( 6N HCl )
Hydrolyzable
Nonhydrolyzable ( 6N HCl )
Hydrolyzable
Total
Ammonium
Hexoseamine
Amino Acid
Unidentified
Total
Ammonium
Hexoseamine
Amino Acid
Unidentified
25.4 24.0
74.6
22.2
4.9
26.5
21.0
74.6
22.2
4.9
26.5
21.0
76.0
24.7
5.4
23.4
22.5
76.0
24.7
5.4
23.4
22.5
1 to 3 % of this N is mineralized each year.1 to 3 % of this N is mineralized each year.
Approximately 0.02 to 2.5 % of soil is as Nitrogen.
In a 2 % OC soil ( Ohio ) the value would be about 0.2% Nitrogen.
Approximately 0.02 to 2.5 % of soil is as Nitrogen.
In a 2 % OC soil ( Ohio ) the value would be about 0.2% Nitrogen.
<
NITROGEN MINERALIZATIONNITROGEN MINERALIZATION
Conversion of organic nitrogen to the moremobile, inorganic stateConversion of organic nitrogen to the moremobile, inorganic state
AMMONIFICATON
Formation of ammonia from organic matterFormation of ammonia from organic matter
NITRIFICATION
Oxidation of ammonium to produce nitrateOxidation of ammonium to produce nitrate
N = Inorganic Nitrogen
N = Nitrogen Assimilated by microorganisms
N = Nitrogen removed by Plants
N = Nitrogen lost via Leaching
N = Nitrogen lost via Denitrification
N = Inorganic Nitrogen
N = Nitrogen Assimilated by microorganisms
N = Nitrogen removed by Plants
N = Nitrogen lost via Leaching
N = Nitrogen lost via Denitrification
N = Organic matter mineralized - (N + N + N + N )N = Organic matter mineralized - (N + N + N + N )
i
i
A
A
P
P
L
L
D
D
The disappearance of N following the addition
of a nitrogen - poor crop residue is called immobilization .
Immobilization is the result of microbial assimilation
of inorganic nitrogen and is the converse of
mineralization .
The disappearance of N following the addition
of a nitrogen - poor crop residue is called immobilization .
Immobilization is the result of microbial assimilation
of inorganic nitrogen and is the converse of
mineralization .
I
Ammonium is the most readily assimilated N source
for soil microorganisms.
Ammonium is the most readily assimilated N source
for soil microorganisms.
NH > NO > Organic NNH > NO > Organic N4 3+ -
Whether immobilization or mineralization of Nitrogen occurs
depends on the C:N ratio. The C:N ratio where the two
processes are in equilibrium is approximately 30 ( 1.5 % N )
Whether immobilization or mineralization of Nitrogen occurs
depends on the C:N ratio. The C:N ratio where the two
processes are in equilibrium is approximately 30 ( 1.5 % N )
C:N > 30 N is taken from mineral
pool or degradation is slowed
C:N > 30 N is taken from mineral
pool or degradation is slowed
C:N < 30 Mineral N is releasedC:N < 30 Mineral N is released
I
I
I
Immobilization
Mineralization
Nitrogen Factor
The number of units of N immobilized for each 100
units of material being decomposed, i.e. the amount
of N that must be added to avoid immobilization.
Nitrogen Factor
The number of units of N immobilized for each 100
units of material being decomposed, i.e. the amount
of N that must be added to avoid immobilization.
N? =100
Changes in inorganic N in soil receiving
various quantities of glucose
Changes in inorganic N in soil receiving
various quantities of glucose
Weeks
mg
Ino
rgan
icN
per
gS
oil
mg
Ino
rgan
icN
per
gS
oil
75 mg75 mg
0 mg0 mg
0
8
16
24
32
5 10 15 20
300 mg
300 mg
Changes in C:N ratio during the decomposition
of plant residues
Changes in C:N ratio during the decomposition
of plant residues
Weeks
C:N
Rati
oC
:NR
ati
o
Wheat
Polygonium
0
10
20
30
40
4 8 12 16
Alfalfa
C:N
SUMMARY
The lowering of the C:N ratio from an initailly high
value to a lower value occurs during decompostion.
The lowering of the C:N ratio from an initailly high
value to a lower value occurs during decompostion.
1
2
3
4
The rate and extent of immobilization through microbial
assimilation depends on the carbonaceous substances
undergoing decay.
The rate and extent of immobilization through microbial
assimilation depends on the carbonaceous substances
undergoing decay.
Whether N is immobilized or mineralized depends on
the nature of the microbial population.
Whether N is immobilized or mineralized depends on
the nature of the microbial population.
( BACTERIA < FUNGI < ACTINOMYCETES )( BACTERIA < FUNGI < ACTINOMYCETES )
NN
Mineraliztion
Organic Mineral formMineral form
Immobilization may be both harmful and beneficial.Immobilization may be both harmful and beneficial.
Harmful if crop plants also are competing for NHarmful if crop plants also are competing for N I
I
I
Beneficial in serving as a store for N during times
of low N requirements by plants
Beneficial in serving as a store for N during times
of low N requirements by plants
-+
FACTORS INFLUENCING MINERALIZATIONFACTORS INFLUENCING MINERALIZATION
Oxygen status
- Ammonifying population includes both
aerobes and anaerobes
Oxygen status
- Ammonifying population includes both
aerobes and anaerobes
1
2
3
4
5
Moisture Status
- Wet / dry cycles
Moisture Status
- Wet / dry cycles
pH
- greatest when the soil pH is near neutral
pH
- greatest when the soil pH is near neutral
C:N ratioC:N ratio
Temperature
- Optimum is at 40 - 60 C , which is higher
than most biological processes
Temperature
- Optimum is at 40 - 60 C , which is higher
than most biological processes
o
FATES OF NH PRODUCEDFATES OF NH PRODUCED4+
1. Taken up by plants
2. Taken up by microorganisms
3. Held onto the soil cation exchange sites
1. Taken up by plants
2. Taken up by microorganisms
3. Held onto the soil cation exchange sites
4. Is fixed within the clay lattice
5. Reacts with organic matter to formquinone - NH complexes
6. Lost to the atmosphere through volatilization
7. Used as an energy source by chemoautotrophs
4. Is fixed within the clay lattice
5. Reacts with organic matter to formquinone - NH complexes
6. Lost to the atmosphere through volatilization
7. Used as an energy source by chemoautotrophs
NH
NH
NH
NH
NH
NH
4
4
4
4
4
4
+
+
+
+
+
+
2
+ =
MIneralization of organic nitrogen and organic carbon are
closely related to one another. The ratio of CO - C to N
produced in an unamended soil is relatively constant,
ranging from 7 to 15 : 1 .
MIneralization of organic nitrogen and organic carbon are
closely related to one another. The ratio of CO - C to N
produced in an unamended soil is relatively constant,
ranging from 7 to 15 : 1 .
Techniques Used to Predict N ProductionDuring a Growing Season
Techniques Used to Predict N ProductionDuring a Growing Season
Determine the quantity of N producedduring a short laboratory incubationperiod.
Establishing what fraction of totalorganic nitrogen is correlated withnitrogen mineralization rate.
Determine the quantity of N producedduring a short laboratory incubationperiod.
Establishing what fraction of totalorganic nitrogen is correlated withnitrogen mineralization rate.
NO - N (at time of planting ) prior toside - dressingNO - N (at time of planting ) prior toside - dressing
1
2
2
3 3
i
i
i
-
DECOMPOSTION OF AMINO ACIDSDECOMPOSTION OF AMINO ACIDS
( removal of amino group )( removal of amino group )
Transamination (some directly enter TCA cycle )Transamination (some directly enter TCA cycle )1
2 Oxydative deaminationOxydative deamination
+ +3
2
R C COOH + NAD NADH ( H ) + R C COOH + NHR C COOH + NAD NADH ( H ) + R C COOH + NH
H
NH
H
NH
H OH O2
R C COOH + NADH (H ) RCH COOH + NHR C COOH + NADH (H ) RCH COOH + NH
H
NH
H
NH
H
NH
H
NH
H OH O2
O
R C COOH + O H O + R C COOH + NHR C COOH + O H O + R C COOH + NH
O
amino acid dehydrogenaseamino acid dehydrogenase
3
2 2 3
2
H
NH
H
NH2
H
NH
H
NH2
Reductive deaminationReductive deamination
2
2
32+
4 Hydrolysis
2
H
OH
R C COOH + H O R C COOH + NHR C COOH + H O R C COOH + NH3
R C CH COOH R CH CHCOOH + NHR C CH COOH R CH CHCOOH + NH3
5 Desaturation
2
DECOMPOSITION OF NUCLEIC ACIDS
N
NH
CN
N
HC
C
CHC
N
N
HC
CH
CHHC
Purine Base Pyrimidine Base
(Base - Sugar - P) Base - Sugar - P Base - Sugar Sugar + Purine
or Pyrimidine BaseN
Nucleic Acid Mononucleotide
Pathway of Metabolism of Purines and Pyrimidines
Purine bases Pyrimidine bases
Adenine
Hypoxanthine
Cytosine
Guanine Uracil
XanthineBarbituric
acid
Uric acid
Urea
Allantoin
Allantoic acid
Glyoxylicacid
Malonicacid Alanine
Urea
Ureidopropionicacid
NH3
B-
B-
NITRIFICATION
The biological formation (oxidation) ofammonium to produce nitrite and nitrate
NITRIFICATION
The biological formation (oxidation) ofammonium to produce nitrite and nitrate
NH NO NONH NO NO4 2 3- -
MICROORGANISMS INVOLVEDMICROORGANISMS INVOLVED
1 Obligate aerobes
2 Derive their carbon solely from CO or carbonates
3 Derive their energy from oxidation of NH or NO
1 Obligate aerobes
2 Derive their carbon solely from CO or carbonates
3 Derive their energy from oxidation of NH or NO
2
24
4
-
3-
2-
2-
+
+NITROSOMONAS NH NO
NITROBACTER
NITROSOMONAS NH NO
NITROBACTER NO NONO NO
Nit
roso
mo
nas
Nit
rob
acte
r
GValance
StateValance
State
-3
+3.9
-68.9
-1
+1
+3
+5
-18.2
Postulated Steps in NitrificationPostulated Steps in Nitrification
NH OHhydroxylamine
NH OHhydroxylamine
2
NHammonium
NHammonium
4+
(NOH)nitroxyl radical
(NOH)nitroxyl radical
2 2N O + H ON O + H O
2NOnitriteNO
nitrite
-
3NOnitrateNO
nitrate
-
+
21/2 O
H
1/2 O
H
2H OH O
+
21/2 O
H
1/2 O
H
2 2NO H Ohydrated nitrite
NO H Ohydrated nitrite
-.
2
2
1/2 O
H O
1/2 O
H O
2
2
1/2 O
H O
1/2 O
H O
1 Hydrazine ( HN = NH ) strongly inhibits NH OH NO
but weakly inhibits NH NH OH.
1 Hydrazine ( HN = NH ) strongly inhibits NH OH NO
but weakly inhibits NH NH OH.
BIOCHEMICAL MECHANISMS
OF NITRIFICATION
BIOCHEMICAL MECHANISMS
OF NITRIFICATION
NH + 1/2 O NH OH + H NONH + 1/2 O NH OH + H NO4 2 2
2
4
2
2
2+ + -
EVIDENCE FOR HYDROXYLAMINE INTERMEDIATEEVIDENCE FOR HYDROXYLAMINE INTERMEDIATE
-
+
2
2 2
2 Results have shown that NH OH can accumulate in small
amounts in Nitrosomonas treated with hydrazine.
2 Results have shown that NH OH can accumulate in small
amounts in Nitrosomonas treated with hydrazine.
3 Oxidation of ammonium is blocked by copper enzyme poisons
such as thiourea. However, NH OH NO is not
affected by thiourea.
3 Oxidation of ammonium is blocked by copper enzyme poisons
such as thiourea. However, NH OH NO is not
affected by thiourea.
-
R
R
R
R
NH + NO N - N = O + OHNH + NO N - N = O + OH
R
R
R
R
-
and dehydrogenation ( hydrogen removal ) reactionand dehydrogenation ( hydrogen removal ) reaction
NITROSAMINE FORMATIONNITROSAMINE FORMATION
Secondary Amine NitrosamineSecondary Amine Nitrosamine
2
21 The oxygen in the nitrate product is from H O,
not molecular oxygen
2 This is an example of a hydration ( water addition )
1 The oxygen in the nitrate product is from H O,not molecular oxygen
2 This is an example of a hydration ( water addition )
-
-3
-2
2
2H O NO 2NO + 4H
4H + O 2H O
2NO + O 2NO
2H O NO 2NO + 4H
4H + O 2H O
2NO + O 2NO
--2 32
2
2
.
NH OH + O HNO + H ONH OH + O HNO + H O2
2
2 2
( NOH ) NO NO( NOH ) NO NO -
2 21/2 N O + 1/2 H O1/2 N O + 1/2 H O
1 Incubation of hydroxylamine and Nitrosomonas
causes production of NO and N O
1 Incubation of hydroxylamine and Nitrosomonas
causes production of NO and N O2
2
2
2
2
2
2 N O is not an intermediate in nitrification
because it is not converted to NO
2 N O is not an intermediate in nitrification
because it is not converted to NO
3 Mechanisms are speculative. N O may be
produced from NO still present in the
Nitrosomonas
3 Mechanisms are speculative. N O may be
produced from NO still present in the
Nitrosomonas
-
-
Chlorate ( Dinitrophenol ) inhibits the formation of nitrate
from nitrite by Nitrobacter. This can be used to study the
Chlorate ( Dinitrophenol ) inhibits the formation of nitrate
from nitrite by Nitrobacter. This can be used to study the
reaction facilitated by Nitrosomonas.reaction facilitated by Nitrosomonas.
NH NO NONH NO NO4 2 3+ - -chlorate
blocks reaction
chlorate
blocks reaction
The formation of nitrite from ammonium can thus be measured.
This reaction is important because it is the rate limiting step.
The formation of nitrite from ammonium can thus be measured.
This reaction is important because it is the rate limiting step.
FACTORS AFFECTING NITRIFICATIONFACTORS AFFECTING NITRIFICATION
NITRIFICATION
1 Acidity
2 Aeration
3 Moisture
4 Temperature
5 Organic Matter
1 Acidity
2 Aeration
3 Moisture
4 Temperature
5 Organic Matter
Beneficial or Harmful?Beneficial or Harmful?
Increases loss of N due to leaching
Increases loss of N due to denitrification
Increases risk of NO toxicity
Increases loss of N due to leaching
Increases loss of N due to denitrification
Increases risk of NO toxicity
Increases soil acidity
May allow easier uptake of N by plants
It is a necessary intermediate in returningN to the atmosphere
Increases soil acidity
May allow easier uptake of N by plants
It is a necessary intermediate in returningN to the atmosphere
3-
1
2
3
4
5
6
1
2
3
4
5
6
The end product of fertilizer N is nitrate whether the fertilizeris added as urea, anhydrous ammonia, or ammonium nitrate.The end product of fertilizer N is nitrate whether the fertilizeris added as urea, anhydrous ammonia, or ammonium nitrate.
CONTROL OF NITRIFICATIONCONTROL OF NITRIFICATION
DESIRABLE CHARACTERISTICSOF NITRIFICATION INHIBITORSDESIRABLE CHARACTERISTICSOF NITRIFICATION INHIBITORS
1 Control of nitrification inhibitors
2 Use of nitrogen compounds that release N slowly
1 Control of nitrification inhibitors
2 Use of nitrogen compounds that release N slowly
because of limited solubility in water or slow rate
of microbial decomposition
because of limited solubility in water or slow rate
of microbial decomposition
3 Use of nitrogen compounds coated with material
that will delay the release of N
3 Use of nitrogen compounds coated with material
that will delay the release of N
1 Specific in blocking NH NO
2 Able to move with fertilizer through soil
3 Non-toxic to plants
1 Specific in blocking NH NO
2 Able to move with fertilizer through soil
3 Non-toxic to plants
4 Non-toxic to plant root micro-environment
5 Not easily bio- or chemical degradable
4 Non-toxic to plant root micro-environment
5 Not easily bio- or chemical degradable
4 3+ -
NITRIFICATION INHIBITORSNITRIFICATION INHIBITORS
POTENTIAL ADVANTAGES
DISADVANTAGES
1 Reduced gaseous loss of N
2 Reduced loss of NO by leaching and runoff
3 Reduced risk of NO toxicity
1 Reduced gaseous loss of N
2 Reduced loss of NO by leaching and runoff
3 Reduced risk of NO toxicity
1 Increased gaseous loss of N ( NH Volatilization )
2 Increased fixation or immobilization of NH
3 Some plants do not use NH , but primarily NO
1 Increased gaseous loss of N ( NH Volatilization )
2 Increased fixation or immobilization of NH
3 Some plants do not use NH , but primarily NO
3
3
34
-
-
-
-
4+
4+
+
NCl CCl
3
MOST EFFECTIVE INHIBITORS OF NITRIFICATIONMOST EFFECTIVE INHIBITORS OF NITRIFICATION
1 N - SERVE1 N - SERVE
2 - Cloro - 6 - ( Trichloromethyl ) - Pyridine2 - Cloro - 6 - ( Trichloromethyl ) - Pyridine
2 - Amino - 4 - Cloro - 6 - Methyl - Pyrimidine2 - Amino - 4 - Cloro - 6 - Methyl - Pyrimidine
2 3( or Na CS )( or Na CS ) Sodium TrithiocarbamateSodium Trithiocarbamate
4 - Amino - 1, 2, 4 - Triazole4 - Amino - 1, 2, 4 - Triazole
3 ATC
2 AM
N
2NHH CH C
Cl
3N
N N
HC CH
N
N N
HC CH
N
NH2
24 CS4 CS
2Na CS + 2H O + 5CO 4NaHCO + 3CS2Na CS + 2H O + 5CO 4NaHCO + 3CS2 2 2 23 3
5 DWELL5 DWELL
S
H C OC N
N C CCl
S
H C OC N
N C CCl
5 2
3
N
DENITRIFICATION
The reduction of nitrate to nitrite and then to gaseous nitrogen
products which are lost from the aquatic or soil system. It is
The reduction of nitrate to nitrite and then to gaseous nitrogen
products which are lost from the aquatic or soil system. It is
a dissimilatory reduction reaction.a dissimilatory reduction reaction.
ASSIMILATORY NITRATE REDUCTIONASSIMILATORY NITRATE REDUCTION
NO NHNO NH3 4
+
The ammonium is used for cell growth. This reaction is oxygen
insensitive and is inhibited by reduced N compounds
The ammonium is used for cell growth. This reaction is oxygen
insensitive and is inhibited by reduced N compounds
DISSIMILATORY NITRATE REDUCTIONDISSIMILATORY NITRATE REDUCTION
NO N , N ONO N , N O3 2 2
This reaction provides energy for growth, but the nitrogen
is not used directly for synthesis of microbial products.
This reaction provides energy for growth, but the nitrogen
is not used directly for synthesis of microbial products.
This reaction is very oxygen sensitive and ammonium insensitive.This reaction is very oxygen sensitive and ammonium insensitive.
IMPORTANCE OF DENITRIFICATIONIMPORTANCE OF DENITRIFICATION
1
4
Represents a major loss pathway of nitrogen from soils ( 30% )Represents a major loss pathway of nitrogen from soils ( 30% )
2 Nitrous oxide, a product of denitrification, may lead to
destruction of the ozone layer
Nitrous oxide, a product of denitrification, may lead to
destruction of the ozone layer
3 Importance in commercial wastewater treatment plants
to reduce nitrate levels
Importance in commercial wastewater treatment plants
to reduce nitrate levels
A key intermediate, nitrite, readily reacts with secondary
amines to produce carcinogenic nitrosamines
A key intermediate, nitrite, readily reacts with secondary
amines to produce carcinogenic nitrosamines
5 N cycling on global basisN cycling on global basis
R
RR
R
NH + NO N NO + OHNH + NO N NO + OH2
A key feature distinguishing denitrification from asssimilatory nitrate reduction
is the formation of a nitrogen - nitrogen bond in denitrification.
A key feature distinguishing denitrification from asssimilatory nitrate reduction
is the formation of a nitrogen - nitrogen bond in denitrification.
Note!
ASSIMILATORY REACTION
DENITRIFICATION
4+
3
3
2
2
2NO 2NO 2NH OH 2NH2NO 2NO 2NH OH 2NH
2NO 2NO ? N O N2NO 2NO ? N O N
2
+5 +3 -1 -3
2 2
Time
Normal Sequence of EventsNormal Sequence of Events
mg
of
Nit
rog
en
mg
of
Nit
rog
en
3NO 2N
N ON O2
2NO
+5 +3 +1 0
1
2
3
4
5
Nonrecovery of total N or N nitrogenNonrecovery of total N or N nitrogen
Disappearance of denitrification intermediatesDisappearance of denitrification intermediates
METHODS OF DETERMINING DENITRIFICATION RATESMETHODS OF DETERMINING DENITRIFICATION RATES
A. Sensitivity of detection losses are low
B. Short term studies not possible
C. Analytical errors are important
A. Sensitivity of detection losses are low
B. Short term studies not possible
C. Analytical errors are important
A. NO or NO disappearance
( works only if nongaseous N losses are minimal )
A. NO or NO disappearance
( works only if nongaseous N losses are minimal )
3 2
B. N O disappearance
- nondisturbing to soil system and specific to
one step of denitrification pathway
B. N O disappearance
- nondisturbing to soil system and specific to
one step of denitrification pathway
2
- difficult to calculate data ( on a soil basis )- difficult to calculate data ( on a soil basis )
Production of N O and NProduction of N O and N2
A. Sensitive and very precise
B. Background of N is high, making a natural system
difficult to use
A. Sensitive and very precise
B. Background of N is high, making a natural system
difficult to use2
Inhibition of N O reduction by acetyleneInhibition of N O reduction by acetylene2
N O N is inhibited by C HN O N is inhibited by C H2 2 2 2
Denitrification is measured by the accumulation
of N O in the presence of C H
Denitrification is measured by the accumulation
of N O in the presence of C H2 22
Isolation and enumeration of denitrifiersIsolation and enumeration of denitrifiers
15
FACTORS WHICH CONTROL DENITRIFICATION IN SOILFACTORS WHICH CONTROL DENITRIFICATION IN SOIL
1 Oxygen and redox potential
2 Water content
3 Concentration of NO or NO
4 Organic C
5 pH ( optimum is 7.0 - 8.0 )
6 Temperature
1 Oxygen and redox potential
2 Water content
3 Concentration of NO or NO
4 Organic C
5 pH ( optimum is 7.0 - 8.0 )
6 Temperature
3 2- -
3-
2-
First order to zero order reaction ratesoccur at low concentrations of NO or NOKm = 4 - 7 uM
First order to zero order reaction ratesoccur at low concentrations of NO or NOKm = 4 - 7 uM
3-NO inhibits NO N so that early
intermediates accumulateNO inhibits NO N so that earlyintermediates accumulate
22-
2
23-NO inhibitions cause greater N O production
relative to NNO inhibitions cause greater N O productionrelative to N
Optimum occurs between 60 - 75 C. Whether chemicalprocesses are of great importance in this temperaturerange is still not known.
Optimum occurs between 60 - 75 C. Whether chemicalprocesses are of great importance in this temperaturerange is still not known.
o
2-
At low pH, more N O is produced relative to N
NO can accumulate at low pH
At low pH, more N O is produced relative to N
NO can accumulate at low pH2 2
DECOMPOSITION OF UREA
AllophanicAcid
Urea
Urease
AmmoniumCarbamate
2 2 2 232H OH O
H N - C - NH H NCONH 2NH + CO2
O
2 2 2 23H N - C - NH + CO H NCNHCOOH 2NH + CO2
O O
Advantages
Disadvantages
USE OF UREA AS A N SOURCE IN SOILS
Rapid hydrolysis to ammonium carbamate
1 Raises pH and causes voloatilization losses of N
2 Nitrite toxicity
3 Seedling germination can be inhibited
1 High N content (45-46% N)
2 Low cost of manufacture, transport, storage, and distribution
3 High solubility in water
4 Ease in handling (nonexplosive, noncaking)
5 Suitable for dry blends or in solution blends
6 Can be applied as a foliar spray
7 Used in production of compound fertilizers (Urea phosphates)
FACTORS PROMOTING NH VOLATILIZATION LOSSESFACTORS PROMOTING NH VOLATILIZATION LOSSES3
1 pH values > 6
2 Low moisture content
3 High temperatures
1 pH values > 6
2 Low moisture content
3 High temperatures
4 Low CEC of soils
5 Addition of highly nitrogenous fertilizerN sources without incorporation
4 Low CEC of soils
5 Addition of highly nitrogenous fertilizerN sources without incorporation
APPROACHES USED TO DECREASE VOLATILIZATION
LOSSES FROM UREA
APPROACHES USED TO DECREASE VOLATILIZATION
LOSSES FROM UREA
1 Urease inhibitors
2 Slow release urea fertilizers
3 Addition of divalent cations with application of urea
1 Urease inhibitors
2 Slow release urea fertilizers
3 Addition of divalent cations with application of urea
Hg, Ag are the most effective inorganic inhibitors
Catechol, hydroquinone - most effective organic inhibitors
Hg, Ag are the most effective inorganic inhibitors
Catechol, hydroquinone - most effective organic inhibitors
Conversion to acidic derivative (urea phosphate )Conversion to acidic derivative (urea phosphate )
Formation of water insoluble urea compounds ( urea-forms )
Coat urea granule with an inert or water resistant
material (sulfur-coated
Formation of water insoluble urea compounds ( urea-forms )
Coat urea granule with an inert or water resistant
material (sulfur-coated urea )urea )
+ =
Phosphorodiamides,
NBPT N ( n - butyl ) thiophosphoric triamide
(oxon form is active form )
Phosphorodiamides,
NBPT N ( n - butyl ) thiophosphoric triamide
(oxon form is active form )
(NH ) X + CaCO (NH ) CO H O + CaX
where X = SO or HPO
(NH ) X + CaCO (NH ) CO H O + CaX
where X = SO or HPO
4
4
4
4
4
4
4
4
4
4
4
2
2
2
2 2
2
2 2
2 24 2
4 2
22
2
2
2 2
2
2
2
4 23
3
3
3
3
3
3
3
3
3
23
42 -
- -
-
43 -
(NH ) CO H O 2NH OH + CO and
NH + OH NH OH NH + H O
(NH ) CO H O 2NH OH + CO and
NH + OH NH OH NH + H O
.
.
.
.
.
+
at alkaline pH the reactiongoes to the right
at alkaline pH the reactiongoes to the right
2NH X + CaCO ( NH ) CO H O + CaX
X = Cl , NO , H PO
2NH X + CaCO ( NH ) CO H O + CaX
X = Cl , NO , H PO- -
CO ( NH ) + 3H O ( NH ) CO H OCO ( NH ) + 3H O ( NH ) CO H Ourease
soluble salt ofdivalent cationssoluble salt of
divalent cations
urea
(NH ) CO H O + 2H 2NH + CO + 2H O(NH ) CO H O + 2H 2NH + CO + 2H O+ + 6
7
5
4
3
2
1
(NH ) CO H O + CaX CaCO + 2NH X(NH ) CO H O + CaX CaCO + 2NH X
From Fenn, Taylor, and Matocha, SSSAJ, 1981, 45:777From Fenn, Taylor, and Matocha, SSSAJ, 1981, 45:777
CaCO precipitation and pH depression ( exchange of Ca for H on exchange
sites ) as mechanisms of ammonia volatilization reduction!
CaCO precipitation and pH depression ( exchange of Ca for H on exchange
sites ) as mechanisms of ammonia volatilization reduction!
+3
[ see equations 6 and 7 ][ see equations 6 and 7 ]
