1. CS 351 SOIL MANAGEMENT & FERTILITY (SOIL FERTILITY COMPONENT)
Dr. Andrews Opoku

2. Course outline 1. Introduction-Growth & Yield factors
Definition of terms - soil fertility, soil productivity, soil quality
Units used in soil fertility work
2. The Nutrient elements
Nutrient cycling
Chemical forms, levels & factors affecting availability
Maintenance of Soil Fertility
Fertilizers/Manure & their use

3. Growth and yield factors
Maximum growth or yield is obtained when none of the
growth factors is present in less than the amounts required.

4. Growth and yield factors
Genetic factors.
The genetic constitution of a given plant species/ variety limits the extent to which that plant may grow and produce, and no matter how favourable the environmental conditions, these limits cannot be extended.

5. Growth and yield factors
Environmental factors
The physical environment is commonly grouped into 4 classes: 1. Climatic factors – temperature, rainfall or moisture supply, light, humidity, wind etc. 2. Physiographic factors – determined by the general geological strata, by topographical features – including relief & drainage ground water, attitude, slope and erosion. 3. Edaphic factors – including soil structure, composition of soil air, aeration, soil reaction (acidity & alkalinity) supply of mineral nutrient elements 4. Biotic factors – brought about by living organisms – like man, animals and plants.

6. The Concept of Soil Fertility
Is the quality that enables a soil to provide the proper nutrients, in the proper amounts and in the proper balance, for the growth of specified plants
when other growth factors – such as light, tempt, moisture and the physical condition of the soil are favourable.

7. The Concept of Soil Fertility
A soil can only be fertile if it is a favourable environment for root growth. And a soil can only be a suitable environment for plant roots if:
it is adequately drained and aerated.
if its salt content and content of exchangeable sodium ions are low
if its pH falls in a suitable range.

8. Soil Productivity
The capability of a soil to produce a specified plant under a specified system of management.
Soil productivity is basically an economic concept and not a soil property.
It involves :
Inputs ( a specified management system)
Outputs (yields of particular crops)
Soil type.

9. Soil Quality Concept

10. Soil Quality Concept
Soil quality is the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation
Soil quality is the capacity of a soil to:
Protect environmental quality
Sustain plant and animal productivity
Promote human health.

11. Units Types Laboratory units
1) Laboratory units: %, ppm, μg/g, μg/ml, mg/kg, mg/l, m.e./100g, cmol(+)/kg
2) Field units: lb/acre, kg/ha
Laboratory units
ppm – is a unit of conc. analogous to the % (percent) unit (i.e. parts per 100)
it is commonly applied to soil or solution concentration of nutrient elements.
E.g. 5 ppmK means 5 parts K per million parts soil

12. Units
Eg. A soil contains 0.112%N Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre, & v). kg/ha i) ppm % N = parts N/100 parts soil = x 104parts/100 x 104 parts soil = 1120 parts N/106 parts soil = 1120 ppm N

13. Units Eg. A soil contains 0.112%N
Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre, & v). kg/ha
ii. μg/g
0.112% N
= 0.112g N/100g soil
= g N/g soil
= 1.12 mg N/g soil
= 1120 μg N/g soil

14. Units Eg. A soil contains 0.112%N
Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre, & v). kg/ha
iii. mg N/kg
0.112 % N
= kg N/100 kg soil
= kg N/kg soil
= 1.12g N/kg soil
= 1120 mg N/kg soil

15. Units Eg. A soil contains 0.112%N
Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre, & v). kg/ha
iii. mg N/kg
0.112 % N
= kg N/100 kg soil
= kg N/kg soil
= 1.12g N/kg soil
= 1120 mg N/kg soil

16. Units
Eg. A soil contains 0.112%N Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre F.S, v). kg/ha iv. lb/ac F.S
Area = 1 acre
Depth = 6 in
Mass = 2 x106 ib

17. Units
Eg. A soil contains 0.112%N Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre F.S, v). kg/ha iv. lb/ac F.S % N = 1120 ppm N = 1120 parts N /106 parts soil = 1120 lbs N/106 ib soil = 1120 x 2lb N/2 x 106lb soil = 2240 lb N/ac. FS. (furrow slice)

18. Units
Eg. A soil contains 0.112%N Convert this to i). ppm, ii). μg/g , iii). mg/kg, iv). lb/acre F.S, v). kg/ha v. kg/ha 2240 lb N/ac = 2240 lb/ac x ac/1ha x kg/1lb = kg N/ha

19. Nutrient elements

20. 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.

21. MACRO NUTRIENTS Carbon Hydrogen Oxygen Nitrogen Phosphorus Potassium
Calcium
Magnesium
Sulphur

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

23. Nitrogen

24. 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

25. NITROGEN
Atmospheric N2
N fert
Immobilization
Nitrogen cycle

26. Nitrogen Transformations
Mineralization
Immobilization
Nitrification
Fixation
Denitrification
Volatilization

27. 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.

28. 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

29. 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+

30. 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

31. 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

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

33. 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+

34. 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.

35. 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

36. 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

37. 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 ↑

38. 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

39. 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

40. 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

41. 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

42. 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.

43. 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.

44. 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.

45. 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.

46. 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

47. 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

48. Forms of soil P

50. 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 )

51. 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

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

53. 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

54. P Fixation

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

56. 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)

57. Most Available P between pH 5.5 - 757

58. 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

59. 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.

60. Potassium Sources of K in Soils K-containing minerals. Eg:
Potash feldspars (KAlSi3O8)
Muscovite KAl3 Si3O10(OH)2
Biotite KAl (Mg, Fe)3 Si3O10 (OH)2
Micas

61. Fate of K+ in soil K+ ion liberated by weathering may
be lost through leaching
taken up by plants or other living organisms in the soil
be held on the cation exchange positions of the soil colloids; or
be converted to less available forms.

62. Factors affecting K Equilibrium in Soils
Conversion of soil and added potassium to less available forms is influenced by:
1. Types of Colloid
Humus and clay are the two major soil colloids
Humus
has high capacity to retain cations in the exchangeable form
has very low capacity for the fixation of K.

63. Factors affecting K Equilibrium in Soils
Clay mineral
Clays of the 2:1 type such as montmorillonite and illite fix K very readily and in large amounts.
Clays of the 1:1 type such as kaolinite fix little K
2. Wetting and Drying
The 2:1 type minerals fix K only upon drying (contraction).
Some release of the ions occurs upon rewetting of the soils (expansion)
3. pH
K fixation increases with application of lime or higher pH.

64. Luxury Consumption
Absorption of nutrient elements in excess of the amount required for optimum growth.
Luxury K
K content of plant
K required for optimum growth
Required K
Available K in soil

65. Leaching Losses of K
More K is lost by leaching in contrast to N & P (particularly P).
Leaching is common in heavily fertilized sandy soils.

66. Problem of K in soils
A very large proportion of K at a given time is relatively unavailable to plants.
K is subject to wasteful leaching losses since its available form is very soluble.
The removal of this element by crops is high, especially when high levels are available in the soil.

67. 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

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

69. 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

70. 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

71. 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)

72. 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

73. 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.

74. 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-

75. 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.
N deficiency

76. 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.
S deficiency

77. Thank you
Good LUCK

80. Soil aeration

81. Salinization