EVSC 590.N Cycle.mineralization Immobilization
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Transcript of EVSC 590.N Cycle.mineralization Immobilization
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7/30/2019 EVSC 590.N Cycle.mineralization Immobilization
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Nitrogen Cycle
n
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Nitrogen Mineralization and
Immobilization
Introduction;
Definition: N immobilization is defined as
the transformation of inorganic compounds(NH4+, NH3, NO3-, NO2-) into the organic
state.
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Nitrogen Mineralization and
Immobilization
1. Some organisms assimilate inorganic-N
compounds and transform them to
organic N constituents of cells, tissues ,and their soil biomass.
2. NH4+ salts are the most readily
assimilated nitrogen sources for mostbacteria, fungi and actinomycetes.
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Nitrogen Mineralization and
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3. Mineral N decreases in soil due to
synthesis of microbial biomass
(protein synthesis).
4. When C:N ratio > 30 N is taken from
mineral pool or degradation is slow(immobilization takes place).
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Nitrogen Mineralization and
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II. Calculation of Mineralization
/Immobilization Potential.
1. Consider decay of typical organicmaterial.
2. To estimate N needed for cell synthesis,
data on C assimilated and C:N ratio isrequired
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Nitrogen Mineralization and
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3. As a rule for mixed populations, carbon
assimilated is
Bacteria 5-10% Fungi 30-40%
Actinomycetes 15-30%
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Nitrogen Mineralization and
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4. C/N ratio of Microbial Tissues are as follows:
Bacteria 5:1
Fungi 10:1 Actinomycetes 5:1
5. Carbon content of microbial biomass is 45-
50% of dry weight.
6. % N varies with age. Hyphal cells in old
cultures have usually less N than young ones
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Nitrogen Mineralization and
Immobilization
Bacteria
Bacteria Assimilates 5-10% of carbon
and has C:N ratio of 5:1 100 units of carbon
5-10 units of carbon is assimilated
Needs 1-2 units of N regardless of source- If this is not present it will be taken from soil
solution.
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Nitrogen Mineralization and
Immobilization
Residue is not all carbon, approximately 40-50
% carbon
If residue has only 40% carbon Then100 units of residue will give 40 units of
carbon
Thus carbon which will be assimilated
40 X 0.05 = 2 units of carbon
40 x 0.10 = 4 units of carbon
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Nitrogen Mineralization and
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Since C/N ratio of bacterial tissue is 5:1, N neededis
- 2 x 0.2 = 0.4 units of N
- 4 x 0.2 = 0.8 units of N
If residue has 0.5% of N,100 units contains 0.5 unitsof N
Inefficient bacteria 0.4 units and thus will not havemuch problem.
Efficient bacteria will need 0.8 units of N and thuswill have to take extra 0.3 units from soil solution.
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Nitrogen Mineralization and
Immobilization
Actinomycetes
Actinomycetes assimilates 15-30 % of C
C:N ratio of actinomycetes tissue is 5:1 100 units of residue containing 40%
carbon and 0.5% N
Amount of carbon assimilated 0.15 x 40 = 6 units of Carbon
0.30 x 40 = 12 units of Carbon
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Nitrogen Mineralization and
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Fungi
Fungi assimilates 30-40 % of C
C:N ratio of fungal tissue is 10:1 100 units of residue containing 40% carbon and
0.5% N
Amount of carbon assimilated
0.3 x 40 = 12 units of Carbon
0.4 x 40 = 16 units of Carbon
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Nitrogen Mineralization and
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Amount of N assimilated
0.1 x 12 = 1.2 units N
0.1 x 16 = 1.6 units N
Thus fungi not great in mineralizing N.
Amount of N assimilated
6 x 0.2 = 1.2 units N
12 x 0.2 = 2.4 units N
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Nitrogen Mineralization and
Immobilization Amount of N in residue is 0.5 units
Therefore N will be taken from soil solution
i.e. N mineralization will take place. Fungi accumulates a lot of substrate in
excess of their needs.
When residue contains 40% C the C:N ratioshould be around 30:1.
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Nitrogen Mineralization and
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This is the critical C:N ratio (20-30:1).
This corresponds to 1.2-1.8% N
Material with this amount of N tends to bemineralized.
When ratio is narrow N tends to be released.
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Nitrogen Mineralization and
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III. Factors Affecting Immobilization
1. Availability of organic Molecule.
a. oxidized CHO is very rapidimmobilization.
b. Moderate to less suitable materials
c. Slow with extensively decayed materialsor resistant tissues such as lignin.
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2. pH
3. Available P
4. Temperature
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IV. Agronomic Significance
1. Plants are poor competitors with soilmicroflora when inorganic-N is inadequate.
2. Immobilization follow soil amendment of N-poor plant residue not desirable in growingseason since the nutrient is renderedunavailable.
3. Reaction may be beneficial by prevention ofleaching.