3. Role in Plants
• Protein
• Nucleic acid
• Chlorophyll
• Carbohydrate
utilization
Four nitrogenous bases –
adenine (A), thymine (T), guanine
(G), and cytosine (C) are
components in the DNA double
helix.
4. Forms Plants Uptake
Ammonia
• Plants uptake both forms.
• Uptake NO3
-
the most.
• NO3
-
is mobile, NH4 is not.
• NO3- prefers acidic pH.
• NH4
+
prefers neutral pH.
• Combination is better.
Which form is vulnerable to leaching losses?
Nitrate
5. Nitrogen Cycle
• N in soil enters, exits, and changes
forms in many ways.
• Can you name some of the processes
and pools in N cycles?
mineralization, immobilization,
nitrification, denitrification, nitrogen
fixation, nitrogen leaching…
12. Fertilizer Nitrogen
• Nitrogen fertilizer should be
added to the soil when the crop
will use it, adding excess N will
cause losses that may harm the
environment.
• Nitrogen is expensive and using
only what the crop needs for
adequate growth is important -
• THUS it becomes important to
give N - CREDITS for previous
management (legumes, manure or
other organic additions with low
C:N ratios).
Wheat with N response
13. Nitrogen soil testing
• Mobile nutrient
• In drier areas use a
fall or spring nitrate-N
soil test.
• In humid areas, use
spring nitrate-N test
or table value based on
previous crop and
organic matter.
14. Nitrogen soil testing
• After arriving at N
recommendation then
credits need to be taken
for:
– Previous crop
– Previous manure
applications or sludge
– 2nd
year after alfalfa
17. Chlorophyll
DNA and RNA
Protein
}
NH2
N molecules from
this amino group
NH2
NH2
NH2
When organic matter
decomposes, N-containing
molecules are released from
H
H
combine with H to
produce NH3 and NH4
NH3 + H = NH4
-
Ammonium
18. Chlorophyll
DNA and RNA
Protein
}
NH2
First they make
this gas, then
NH2
NH2
NH2 NH3
H
H+
H
+ NH4
AmmoniumAmmonia
(gas)
=
The simple steps in the mineralization process are now complete.
The process is also called ammonification.
When organic matter
decomposes, N-containing
molecules are released from
19. Denitrification
N2
Biologicaland
Chemical
Fixation
NH3 + H+
= NH4
Clay Fixation
and Release
NO3
N2
N2O
Immobilization
(use by the plant)
NITROGEN
Oxidation of NH4 to NO3 is
nitrification.
Nitrobactor
Nitrosomonas
Nitrification
NO2
Two kinds of bacteria are
involved in two steps.
20. Denitrification
N2
Biologicaland
Chemical
Fixation
NH3 + H+
= NH4
Clay Fixation
and Release
NO3
N2
N2O
Immobilization
(use by the plant) NITROGEN
In water-logged soil, NO3
transforms to gaseous N, and
this loss to air is denitrification.
Nitrobactor
Nitrosomonas
Nitrification
NO2
Steps: NO2--NO--N2O and N2
23. Sources of N in Wheat
• Organic – residue breakdown (slow)
• Organic manures (N content varies)
• Commercial
– Urea
– Ammonia
– Monoammonium phosphate (MAP)/diammonium
phosphate (DAP)
– Potassium nitrate
– URAN (urea + ammonium nitrate) solutions
– Ammonium nitrate
More discussion in Sections 4 and 5
24.
25. P Nutrition Principles
How the materials will be presented
P-cycle
Key
Factors
Sources
Forms
uptake
Role in
plant
P
26. P Essentiality
• Second most important
nutrient
• Its concentration in soil
solution is low
• Low solubility
• Low availability
• Low mobility
Nutrient Amount in
Solution (mg/L)
NO3
-
60
NH4
+
--
H2
PO4
-
, HPO4
2-
0.8
K+
14
Ca2+
60
Mg2+
40
SO4
2-
26
are key characteristics for
better management
27. Role in Plants
• ATP
• DNA/RNA
• Enhance crop maturity
• Root growth
Can you
justify how
P is
important
in these
28. Role in Plants
• ATP
• DNA/RNA
• Enhance crop maturity
• Root growth P is a critical component of
cell’s energy currency, ATP
29. Role in Plants
• ATP
• DNA/RNA
• Enhance crop maturity
• Root growth
P containing sugar
phosphate is the
backbone of DNA
30. Orthophosphate ions: H2PO4
-
& HPO4
2-
Plant Available Forms
7.2 pH
Availability is pH dependent
Both species are even at this pH
31. Phosphorus Cycle
• Not involved in atmospheric exchanges
• Cycles among various pools
– Soil solution
– Organic matter
– Inorganic minerals
• Interaction among pools is complex.
• Knowledge of each pool is necessary.
32. Phosphorus Cycle
Secondary
Minerals
Fe & Al PO4
CaPO4
Nonlabile P
Primary
Minerals
(Nonlabile P)
Solution P
H2PO4
-
HPO4
2-
Microbial-
P
bacteriaFungi
nematode
Plant residue
Labile P
Adsorbed
P
Dissolution
Dissolution
Precipitation
Adsorption
Desorption
Immobilization
Mineralization
Fertilizer-P
Soil Organic
Matter
Microbial P
(Nonalabile P)
(Labile P)
1. Soil Solution: plant uptake poolAdsorption and DesorptionPrecipitation and DissolutionMineralization and Immobilization
SOIL SOLUTION POOL
INTERACTIONS
33. Phosphorus Cycle
Secondary
Minerals
Fe & Al PO4
CaPO4
Nonlabile P
Primary
Minerals
(Nonlabile P)
Solution P
H2PO4
-
HPO4
2-
Microbial-
P
bacteriaFungi
nematode
Plant residue
Labile P
Adsorbed
P
Dissolution
Dissolution
Precipitation
Adsorption
Desorption
Immobilization
Mineralization
Fertilizer-P
Soil Organic
Matter
Microbial P
(Nonalabile P)
(Labile P)
Crop residue
and organic
matter release
P by
mineralization
Various factor
affects rate of
mineralization
including C/P
ratio
Net
immobilization
(available for
plant uptake) at
C/P >300
ORGANIC POOL
INTERACTIONS
What is good – high or low C/P?
Why?
34. Organic-P, quick facts
• P of organic matter range
between 1% and 3%
• Organic P is ~50% of total
P in soil
• Organic P decreases with
soil depth
• Organic-P increases with
increased organic-C (the
C/P, likewise N and C/N)
35. Phosphorus Cycle
Secondary
Minerals
Fe & Al PO4
CaPO4
Nonlabile P
Primary
Minerals
(Nonlabile P)
Solution P
H2PO4
-
HPO4
2-
Microbial-
P
bacteriaFungi
nematode
Plant residue
Labile P
Adsorbed
P
Dissolution
Dissolution
Precipitation
Adsorption
Desorption
Immobilization
Mineralization
Fertilizer-P
Soil Organic
Matter
Microbial P
(Nonalabile P)
(Labile P)
INORGANIC POOL
INTERACTIONS
Inorganic P fixed or released by
primary and secondary minerals
36. P
• Soil test for P (Bray pH<7.4 of soil)
• 0-5 ppm = very low
• 6-10 ppm = LOW
• 11-15 ppm = med
• 16-20 ppm = high
• > =21 ppm = very high
• No reason to have soil
test > 21
• environmental problems
when P >16
• ppm x 2 = lbs/acre
P deficient tomato
37. Soil P
• Crops need more P than is
dissolved in the soil solution at any
one time, therefore, this P in the
solution phase must be replenished
many times during the growing
season.
• The ability of a soil to maintain
adequate levels of phosphorus in
the solution phase is the key to
the plant available P status of the
soil. The solid phase P is both
organic and inorganic
Solid P Phase Solution Phase Root Hair
P deficiency reduces root growth
38. Inorganic-P, quick facts
• Low concentration & solubility of P due to slow
release and fixation
• Minerals mainly with Ca, in alkaline soils
• Minerals with Fe, Al, and Mg in acidic soils
•
39. Solubility of P-containing compounds
Compound Formula Compound type
Monocalcium phosphate
Dicalcium phosphate
Octacalcium phosphate
Tricalcium phosphate
Oxy apatite
Hydroxy apatite
Carbonate apatite
Fluorapatite
Ca(H2
PO4
)2
.H2
O
CaHPO4
.2H2
O
Ca8
H2
(PO4
)6
.5H2
O
Ca3
(PO4
)2
[3Ca3
(PO4
)2
].CaO
[3Ca3
(PO4
)2
].Ca(OH)2
[3Ca3
(PO4
)2
].CaCO3
3Ca3
(PO4
)2
].CaF2
Calcium
Strengite FePO4
-2H2
O Iron
Variscite AlPO4
-2H2
O Aluminum
• Ca-phosphate - major contributor in alkaline
soils
• pH determines its availability
• Solubility decreases in order of: mono >
di > tri calcium phosphates
43. P Essentiality Principles
• Plant absorbs larger amount of K next
only to N
• Plant tissue K: ~2.5% to 4.5% leaf dry
wt.
• Soil K: 0.5% to 2.5%
• Most soil K’s are tied up, availability is
often limited
44. Role in Plants
• Enzyme activation
• Water relations
(stomatal control)
• Energy relations
• Translocation (sugar
transport)
• Crop quality
Justify
how K is
important
in these
45. Role in Plants
• Enzyme activation
• K activates at least 60 enzymes in cell
• K level determines reactions catalyzed by enzymes
46. Potassium Fertility (Potash)
• Potassium (K+) is a problem
on acid soils, soils with low
CEC and with irrigation or
high rainfall where leaching
can readily occur.
• Potassium can be stored in
the soil from one year to
the next
• K is not a pollutant - even if
leached from soil, K does
not cause environmental
problems.
K deficient corn
47. Role in Plants
• Water relations
– K regulates stomatal
opening
K is critical to stomatal opening and closure in
regulating gas exchanges (CO2 in and H2O out)
48. Role in Plants
• Energy relations
– K is required for production of ATP
• Crop quality
– Increases root growth
– Enhances translocation of sugar
– Increase protein content in plant
– Reduces lodging
49. Forms uptake
K+
Soil K Pools and Concentrations
Mineral…………..… 5000 – 25000 ppm
Non-exchangeable…...….50 – 750 ppm
Exchangeable…………..400 – 600 ppm
Solution……………...………1 – 10 ppm
K-Cycle will show
interaction among pools
50. K forms - characteristics
1. Mineral – K : Minerals like
Mica, Feldspar, K is mainly
unavailable
2. Non-exchangeable – K : K in
secondary minerals like vermiculite
or colloidal-size mica, K is slowly
available
……more
51. In the non-exchangeable fraction of K
Most K
trapped
K slowly available K is widely
exchangeable
52. K forms - characteristics
3. Exchangeable-K: K on the cation
exchange sites of soil colloids is
readily available
53. K forms - characteristics
4. Soil solution-K: K is readily
available. Range in most cropland
soils ~ 1-10ppm.
~80% K plant uptake by diffusion,
availability depends of many
factors
54. Exchangeable K+
K+
K+
K+
K+
K+
K+
K+
Nonexchangeable K+
Plant &
animal
residues
2:1 Clay minerals
Soil solution
K+
Plant uptake
Desorption
Adsorption
Weathering
90-98%
0.1-0.2%
1-2%1-10%
ErosionLeaching
Feldspar
Mica
Primary
minerals
K
Mineral-K, mostly
unavailable, accounts
for majority of soil K
K
Non-exchangeable-K,
in secondary minerals, slowly
available, 2:1 clay
K
Exchangeable-K,
readily available, K
in cation exchange
site…
55. Exchangeable K+
K+
K+
K+
K+
K+
K+
K+
Nonexchangeable K+
2:1 Clay minerals
Soil solution
K+
Plant uptake
Desorption
Adsorption
Plant/
animal
residues
Weathering
90-98%
0.1-0.2%
1-2%1-10%
ErosionLeaching
Feldspar
Mica
Primary
minerals
K
K K
Residue K recovery is
minor, usually leach out
K leaching loss is often substantial
56. K Cycle Quick Fact
• K transfer from minerals is slow but
continuous
• Exchangeable and soluble K equilibrate
rapidly
• Fixed K equilibrate very slowly
• Transfer from mineral to other form is
very slow, usually unavailable (in one
crop year)
57. K Fixation – who is involved?
• Reentrapment of K ions between the layers of
2:1 clay (illite) is a major reason
• The 1:1 clay (kaolinite) do not fix potassium
• Major factor affecting K availability
– Clay minerals, CEC, nature of cations
– Soil moisture
– Soil temperature
– Amount of exchangeable K, capacity to fix K
58. Potassium Fertilizers
• Organic sources – K content varies with sources,
range in manure is 4-40 pounds
• Commercial sources – potassium oxide (K2O) is
guaranteed standard for fertilizer K
• Potash and Potassium names are used
interchangeably
• The world’s largest high-grade potash deposit is in
Canada
END OF SECTION 02 INSTRUCTION
59. Tools for detecting nutrient deficiency
• 1) Tissue testing -involves a complete
and detailed laboratory analysis of
nutrient elements in the plant leaves.
This is a very accurate way of assessing
how much nutrient the plant has
actually taken up from the soil.
• Recommendations are made on the
basis of these test results:
– Backed by research
– Dependent on plant growth stage and plant
part.
61. Calibration
• Process of ascertaining the degree of
limitation to crop growth or the probability
of getting a growth response to applied
nutrient at any soil test level.
• Soil test interpretation develops fertilizer
recommendations.
62. Correlation - process
• Exploratory
fertilization trial
– Greenhouse – a
controlled environment
with soil homogeneity.
• Trials in field with
selected soils.
