1. Nutrient elements

2. Plant nutrients A plant nutrient is said to be essential if:
A deficiency of the nutrient makes it impossible for the plant to complete its life cycle.
Such deficiency can be prevented or corrected only by supplying this element.
The element is involved directly in the nutrition of the plant.

3. MACRO NUTRIENTS Carbon Hydrogen Oxygen Nitrogen Phosphorus Potassium
Calcium
Magnesium
Sulphur
These are obtained from atmospheric
CO2 and soil water.
These are obtained by plants from the soil

4. Plant nutrients Micronutrients Iron Manganese Boron Molybdenum Copper
Zinc
Chlorine
These are obtained by plants from the soil

5. Nitrogen

6. Nitrogen N is extremely important for Agriculture
N should be managed carefully
Plants need it in large amounts
It is fairly expensive to supply
It is easily lost from the soil

7. NITROGEN
Atmospheric N2
N fert
Immobilization
Nitrogen cycle

8. Nitrogen Transformations
Mineralization
Immobilization
Nitrification
Fixation
Denitrification
Volatilization

9. NITROGEN N – Mineralization Amino acid NH4+ NO3- N – Immobilization
The microbial conversion of organic N to mineral-N
Amino acid NH NO3-
immobilization
Nitrosomonas / nitrobacter
Bacteria/ fungi
mineralization
N – Immobilization
This is the conversion of inorganic N to organic form in microbial tissue.

10. Mineralization of N-compounds
The process takes place in essentially 3 steps:- aminization, ammonification and nitrification.
Aminization
Conversion of proteins and allied compounds to amines and amino acids by heterotrophic bacteria and fungi.
Proteins R–NH2 + CO2 + Energy
Heterotrophic
Fungi/bacteria

11. Ammonification
It is conversion of amines and amino acids to NH4+ by heterotrophic bacteria and fungi
R – NH2 + H2O NH3 + R –OH + Energy
Heterotrophic
Fungi/bacteria
R-NH NH3 + H NH4+

12. Ammonification Fates of NH4+ 1) fixed by clay minerals,
2) may be converted to NO2- or NO3- by nitrification
3) used by plants (NH4+),
4) volatilization
High pH Soils > 7.5

13. Soil conditions affecting Ammonification
1) C:N ratio
Material C:N ratio
FYM (composted)
FYM (Fresh)
Saw dust
2) Aeration: well – drained aerated soil
3) pH :Generally fungi act best in pH < 5.5; Bacteria in pH >5.5

14. Nitrification
Nitrification is the biological oxidation of ammonia to nitrate.
2 NH → 2NO2- + 2H2O + 4H+ + Energy
2 NO2- + O2 → 2NO3- + Energy

15. Nitrification 2 - step process
1. 2NH O2 ---> 2NO2- + 4H H20 + E
Nitrosomonas/Nitrosococcus
2. 2NO2- + O2 --> 2NO3- + E
Nitrobacter
Process is acid causing due to release of 4 H+

16. Nitrification Reactions require molecular oxygen
Reaction releases H+ ions resulting in the acidification of the soil.
Reactions involve microbial activity and therefore soil conditions (moisture supply, temperature & pH) should be optimum for microbial activity.

17. Gaseous Losses of Soil N
Gaseous losses of N occur mainly as N2 N2O, NO and NH3.
Mechanisms for the losses are:
Denitrification
Chemical reactions involving nitrites under aerobic conditions
Volatilisation of ammonia

18. Gaseous Losses of Soil N
a) Denitrification:
is the biochemical reduction of nitrates under anaerobic conditions to gaseous N-compounds.
NO NO NO N2O N2 O O O O
Factors Affecting Denitrification
i) Soil moisture and oxygen supply
ii) Availability of organic substrate
iii) Soil pH and temperature

19. Gaseous Losses of Soil N
Reaction of nitrites under aerobic conditions
Nitrites in a slightly acid solution will evolve gaseous N when brought in contact with certain ammonium salts, with simple amines such as urea, and even with Non-nitrogenous sulphur compounds and carbohydrates.
Possible reaction:
2HNO2 + CO(NH2)2 → CO2 + 3H2O + 2N2 ↑

20. Biological nitrogen fixation
Conversion of N2 in the soil atmosphere into NH4+ by specialized groups of micro-organisms.
Non-Symbiotic (free living microbes):
Clostridium – anaerobic
Azotobacter – aerobic,
blue-green algae

21. 2. Symbiotic N Fixation Bacteria invades host plant root
Rhizobium
Bacteria invades host plant root
Response of host plant root is to grow a nodule for the bacteria to live in.
Bacteria takes N2 from the air and converts it into R-NH2 in bacteria and some is in the form of NH4+
Fate of N Fixed by Rhizobium:
1) used by host plant,
2) leaks out of root to become available to surrounding plants,
Cowpea
Nodulation
Host plant-bacteria complex

22. Non-Biological Fixation
1) Atmospheric electrical discharge (lightning)
Oxidation of N
N2 + 3O NO-3
2) Industrial process
10-20% of NO3- via atmospheric
deposition

23. N - balance Available soil N Commercial fertilizers immobilization
Non Symbiotic fixation
immobilization
Crop removal
Symbiotic fixation
Available soil N
Rainfall
Crop residues and manure
Atmosphere
Gaseous losses
Erosion losses
Soil organic matter
Leaching losses
Fixation by clay minerals

24. Distribution of N in soils
1) Drainage : Under poor drainage, decay of O.M. is very slow
Organic N is high, Mineral N is low
2) Topography: On slopes, N content is lost faster than that on summit or valley bottom.

25. Distribution of N in soils
3) Texture: N, content decreases as texture becomes coarser.
4) Seasonal effect:
Nitrate level slowly increases during the dry season due to low leaching.
Nitrate levels increase rapidly at the beginning of the rainy season due to increased bacteria activity and mineralization in the presence of low leaching.
During the rainy season level of N falls and remains fairly constant until the next dry season due to leaching of N compounds from the soil.

26. N in Plant Nutrition is an essential constituent of all living matter.
important in the formation of protein.
forms an integral part of chlorophyll molecule.
an adequate supply of N is associated with vigorous vegetative growth and deep green colour.

27. N deficiency Symptoms A stunted yellowish appearance
Yellowing or chlorosis, usually 1st appearing on the lower leaves, the upper leaves remaining green
In severe shortages – leaves will turn brown and die.

28. P -cycling

29. Phosphorus Discovered by Hening Brand in 1669
Name Origin: phôs (light) and phoros (bearer) “phosphorus = light-bearer”
Atomic number 15
Atomic weight
One isotope 32P

30. Soil Phosphorus Lithosphere is the main source and reservoir of P
Lithosphere – 0.12% = 1200ppm
Soil solution – 0.2 to 0.3ppm
Total P content of soil depends
O.m content
Parent material
Degree of weathering

31. Forms of soil P

33. Inorganic P Insoluble or nearly insoluble P compounds Acid soils
Free Fe and Free Al combine with phosphate
Al3+ + H2PO4- + 2H2O H+ + Al(OH)2H2PO4
(soluble) (insoluble)
Alkaline soils
Free Ca and Mg combine with Phosphate
2PO Ca Ca3(PO4)2
(soluble) (Insoluble )

34. Inorganic P 2) Insoluble phosphate-clay complexes 4 5 6 7 8 Al3+ +
Al (OH)2
+ 2H+
Precipitated form
Dissolved form
Fixation by Al and Fe
Fixation by Ca
Reaction with clays 4 5 6 7 8
Soil pH

35. Soluble phosphate forms
H3PO4 = phosphoric acid, H2PO4- = 1º orthophosphate,
HPO4-2 = 2º orthophophate, PO4-3 = phosphate

36. Calcium Phosphate Compound
â Ca(H2PO4)2
â monocalcium phosphate
â CaHPO4
â dicalcium phosphate
â Ca3(PO4)2
â tricalcium phosphate
â Ca5(PO4)3OH2
â hydroxyapatite
â Ca5(PO4)3F
â Fluorapatite 6 pH 8

37. P Fixation

38. P Fixation
P “Fixation” – refers to the processes whereby available phosphorus forms combinations with other soil constituents and thus becomes unavailable to plants.

39. Mechanisms for P fixation
1) Precipitation reaction between P and other ions in soil solution to form hydroxy-phosphates
Al(OH)2+ + H2PO Al(OH)2H2PO H+
(soluble) (insoluble)
Ca2+ + HPO CaHPO4
(soluble) (Insoluble )
2) Adsorption reaction between soluble P and insoluble soil components
Al2O3.3H2O + 2H2PO Al(OH)2H2PO OH- (soluble) (insoluble)

40. Most Available P between pH 5.5 - 740

41. Factors affecting P fixation
Type of clay minerals and amount of clay in soil
Presence of OH- of Fe, Al and Mn
Soil reaction
Presence of organic matter

42. The presence of Organic matter in the soil
Om reduces P fixation;
the formation of phospho-humic complexes which are more easily assimilated by plants
anion replacement of the phosphate by the humate ion.
the coating of sesquioxide particles by humus to form a protective cover.

43. Secondary Macronutrients
Ca Mg and S are secondary macronutrients
They are required by plants in lesser amounts than NPK but in larger quantities than the micronutrients.
They are essential for correcting the reaction of soil.
Ca,Mg for reclaiming acid soils
S for reclaiming alkaline soils
They are prone to leaching

44. Magnesium
Mg is the only mineral element in the chlorophyll molecule

45. Magnesium It is absorbed by plants as the ion Mg 2+.
Sources of soil Mg
Weathering of rocks such as:
Dolomite , Ca Mg (CO3)2 or
Olivine , MgFeSiO4
Biotite , K (Mg Fe)3 Al Si3 O10 (OH)2

46. Calcium Weathering of rocks such as: Ca is absorbed by plants as Ca2+
Source of Soil Ca
Weathering of rocks such as:
Dolomite Ca.Mg (CO3)2
Calcite CaCO3
Apatite Ca5(PO4)3·(Cl, F, OH)
Calcium feldspars

47. Sulphur
S is an essential element particularly associated with protein synthesis.
Plant available form of S = SO42-.
Sulphur fertilization is becoming important because of changes in the use of some fertilizers
SSP (18% P2O5; 8-10% S) to TSP (45% P2O5; <3% S)
AS (NH4)2SO4 (21%N; 24%S) to CO(NH2)2 (urea) (46%N)

48. Micronutrients
Nutrient elements required by plants in relatively small amounts.
Iron
Manganese
Boron
Molybdenum
Copper
Zinc
Chlorine
These are obtained by plants from the soil

49. Micronutrients Source of micro nutrients soil parent material
2) organic matter
In uncultivated lands there is a greater concentration of micronutrients in the surface soil where O.M. levels are high.

50. Micronutrients Plant available forms of micro nutrients Nutrient
Iron
Fe2+ or Fe3+
Manganese
Mn 2+
Boron
BO33-
Copper
Cu 2+
Molybdenum
MoO42-
Zinc
Zn 2+
Chlorine
Cl-

51. Nutrient mobility and deficiency symptoms
For nutrients which are mobile in plants deficiency symptoms 1st appears on the lower and older leaves.
Eg: N, P, K, Mg, and Zn.
Mg deficiency

52. Nutrient mobility and deficiency symptoms
Nutrients with limited mobility in plants produce symptoms on new leaves or growing points.
Eg: calcium, sulphur, boron, iron, copper, and Mn.
Fe deficiency

53. Thank you
Good LUCK