mod 3 princ. soil sc

8/3/2019 Mod 3 Princ. Soil Sc

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Chemical and

StructuralComposition ofSoilColloids


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Composition of SoilColloidsDefinition: What Does word colloid mean?

Colloid is a solid particles very small in size (infinitesimal size)Diameter varied between 1 nm to 1um.All Soil Colloidal particles lie in the clay -size fraction.Colloidal particles have two Important characteristics;1 High Specific Surface Area2 Electrified Surface (Electric charge)

{this charge are principally negative (). The positive

ones (+) are rare}

- These two characteristics are restricted for colloidal particlesonly. Neither silt, nor sand particles provide these

features.


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colloidal particles comparing with othersoil particles.

High reactivity of colloids mean:

1- High Adsorption CapacityAdsorption of H2O, cations, anions &

solublemolecules due to high surface area

2- High Cation Exchange Capacity(CEC). Due to negative electric chargeexists on the

surface of colloidal particles.Colloidal particles play an importantrole in:

1 - Physical and chemical

characteristics of soil.2 - Plant nutrition, and


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- According to their origin, soil colloids could be divided into two

types:

* Inorganic or Mineral Colloids: Originated from the decomposition

of rocks and mineral of the parent material. Inorganic colloidsinclude;

- Secondary clay minerals, aluminusilicates, phyllosilicates,

layer silicates (all are synonymous to the same object)

- Hydrous oxides (oxides, hydroxides and oxy-hydroxides) of Fe,

Al and Mn (Sesquioxide)

- Amorphous or non-crystalline materials (Allophane, Imogolite)

* Organic Colloids (Humus): Originated from the decomposition of

debris and bodies of all living organisms after their death. Among

all living organisms exist either on the surface or subsurface the

soil, green plants are the most dominant component of soil

organic colloid.


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Chemical and Structural Composition of

Secondary Clay Mineral

-Clay minerals present in clay fraction (


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STRUCTURAL UNITS OF SECONDARY

CLAY MINERALS

*All phyllosilicate minerals (clay minerals) are consisted of twostructural units:

(a) Tetrahedral unit (silica units) of formula (SiO4)4-.

Tetrahedron silica units

(SiO4)-4


8/109Tetrahedron silica sheet (Si2O5)

Tetrahedral units bounded together toform Tetrahedral Sheet (silicasheet) of formula )Si2O5)2-

-2


9/109{Al(OH)6}-3

(b) Octahedral unit (alumina unit)Formula is [Al(OH6]3-.

In this unit the central cation is Al that surrounded by 6 OH or 6 O

These units bounded together to form Octahedral Sheet (aluminasheet) of formula Al2(OH)6. This sheet called gibbsite Sheet. Another

octahedral sheet called brucite Sheet is exist.

In brucite sheet Mg2+ replacing Al3+ in the center of the octahedral

unit. The formula of brucite sheet is Mg3(OH)6.


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Octahedral sheet (alumina sheet)

{Al2(OH)6}

0


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ypes o secon ary c ayminerals (phyllosilicateminerals)

s Tetrahedral sheet bounded to octahedral one in differentways to form one layer.

s Secondary clay minerals consist of high number of layers.s Each layer contains certain number of sheets.s According to the number of sheets exist in the layer,

secondary clay minerals are typified to three groups:

- 1:1 type clay mineral

- 2:1 type clay mineral

- 2:1:1 (or 2:2) type clay mineral


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Types of secondary clay minerals (phyllosilicate minerals)

1:1 Type

Kaolinite

2:1 Type

Mica, Vermiculite

Montmorillonite

2:1:1 Type

Chlorite


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0.72 nm

Tetrahedral sheet

Octahedral sheet

Hydrogen bond exists

between oxygen atoms of the

upper layer and hydroxyl

groups (OH) of the lower

layer

Structural composition of

Kaolinite clay mineral


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1:1 Type clay mineral (Kandite group)

(OH)

O

Kaolinite mineral:Structural and atomic composition of 1:1 type clay mineralshowing that the layer consists of two sheets (tetra- and octa-hedral). The upper surface contains hydroxyl (OH) groups,whereas the lower surface contain oxygen atoms.1:1 type clay minerals are nonexpanding mineral due to hydrogenbound formed between layers.


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Hydrogen bond exists between

oxygen atoms of the upper layer

and hydroxyl groups (OH) of the

lower layer

Structural composition of

Kaolinite clay mineral

Characteristics of Kaolinite mineral:1- Non-expanded mineral due to hydrogen

bound between layers.2- CEC varied between 5-15 Cmol(+)/kg3- Specific surface Area ranged from 10-20m2/g


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Structural composition of 2:1

type clay mineral

(montmorillonite Mineral)

O

OO-O weak bond

Characteristics of Montmorillonite

mineral:1- Expanded mineral due to weak bond(O-O) between layers. Explain Why? 2-High CEC varied between 80-120Cmol(+)/kg. Give reason.

3- High specific surface area (700 m2/g).Give reason.


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OH

OOO

KaoliniteMontmorillonite

hydrogen bond (O-OH )O-O weak bond

None-ExpandedExpanded Mineral


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Sources of ElectricalCharge on Clay mineralsTwo sources are responsible for electrical charge created

on the surface of secondary clay minerals:

1- Permanent ChargeCreated from isomorphous substitution through:

- Replacing of Si4+ in tetrahedral sheet by Al3+- Replacing of Al3+ in octahedral sheet by Mg2+,

These replacements lead to a creation of negative charge on thesurface of clay mineral.

2 Variable Charge, or , pH dependent Charge, created from

dissociation of H+ ion on siloxane surface ( Silanole group , Si OH, or Aluminole group, Al-OH)

Si OH Si O- + H+

Al OH Al O- + H+


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Isomorphous

substitution

Unsatisfied bonds on

Broken- edges of thecrystal

SiO2

Si4O8

AlSi3 O8-Permanent charge

(ex. Mont.)

Si

Variable Charge

(ex. Kaolinite)

O

O

Sources of Electrical Charge on the surfaces of

Clay Mineral


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Kaolinite andMontmorilloinite minerals

Character Kaolinite Montmorllionite

Type 1:1 2:1

Expansion Nonexpanding Expanding

Charge

source

Variable charge(broken edges,

unsatisfied Valence)

Permanent charge(Isomorphoussubstitution)

CEC Low CEC ( 5 15Cmol+/kg)

High CEC (80 120Cmol+/kg)

Surface Area Low SA (10-20

m2/gm)

High SA (~ 700

m2/g)


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Clay

Minerals


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Inorganic Soil Colloids alsoinclude;

- Hydrous oxides (oxides, hydroxides and oxy-

hydroxides) of Fe, Al and Mn (Sesquioxide).Exist in highly weathered soil (tropicalregions)

- Amorphous or non-crystalline materials(Allophane, Imogolite)- Mainly exist insoil formed on volcanic rocks.


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Characteristics of Soil Colloids and theireffect on soil properties:

Soil colloids have high:- specific surface area.- cation Exchange Capacity- water retention capacity- elasticity when wet- chemical reactivity

So, soil contain considerable amounts ofsecondary clay minerals will . .


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II - ORGANICCOLLOIDS

SoilOrganic

Matter HUMUS

o rgan c Matter


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o rgan c Matter(SOM)

s Sources and chemical composition of organic

matters Decomposition of OMs Humus formations Chemical properties of humus:s Effect of humus on soil fertility


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Importance of organic matter to soil andplant

1 Plays an important role in determining physical andchemical

properties of soil

2- supply micro-organisms with food and energy which

support their rolein building up fertility of soil.

3 - Supply macro- (N, P, S,..) and micro-nutrients (Mn,Zn, Cu,) to

growing plants.

4 Increase soil water holding capacity.

5 It turns soil to dark color which increases absorptionof solar

radiation that increases microbial activity andchemical reactions.


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6 - Enhances formation of stable soilaggregates and overall

soil structure that affect air and water

relationships.7- Increase cation exchange capacity (CEC),and adsorption

capacity of soil.

8 Plays an important role indecontamination of heavy

metals and pesticides.

9 Increasing soil buffering capacity.

10- It protects the surface of soil fromerosion.


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Sources of Soil Organic matter (SOM)

Quantity of organic matter in soil


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Quantity of organic matter in soil- In mineral soils, the quantity of organic matter (OM)varied

between 0.5 5%.- In alluvial soils of Egypt, OM content ranged from 1 3%,

whereas, OMcontent in sandy soil is less than 0.5%- In organic soil, the quantity is usually higher than 18%.- Organic matter is determined in soil and calculated inform of

organic carbon (OC).- A conversion between SOM and SOC could achievedusing a factor

represent the percent of C in OM ( average about 58%)- SOM = OC * 1.72 ( also this factor could used as 1.8or 2 )- The quantity of organic matter in soil decreased withdepth ( Fig. ).


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Chemical composition of freshorganic matter:Compounds released in soil bythe death of plants and livingorganisms are;1 Carbohydrates:(polysaccrides, starch,

hemicelluloses and cellulose)

2 - Proteins3 - Tannins4 - Wax and fats

5 - Lignin.

i i f i


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Decomposition of organic matter

Micro-organisms attack organic residues freshly added to the soil to

gain food and energy required to their biological activities. Organic residues transform to intermediate components, then to finalsimple products.

Generally, the products of decomposition could be concluded in thefollowing points;

1- Carbohydrates decomposed and transformed to CO2 and H2O. 2 Proteins decomposed in different ways:

A Part transformed to amino acids, then to NH4 and NO3

B part combined with clay to be protected from microbial attack.

3- Lignin has high resistance to be decomposed by microbial attack, itjust submit to some chemical changes in structure.


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Degree of decomposition of organiccompounds:

Organic components could be arranged descendinglyaccording to their ability to decomposition as follows:

Saccrides, starch, simple proteins > crude protein >hemicelluloses > cellulose > wax, oil, fats> lignin.

** Micro-organisms as decomposers of organic residueshighly increased in number and mass, and also build up

many compounds inside their bodies. These compoundsrelease in soil and persist for long time after the death ofmicro-organisms.


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Humus formation:The modified lignin that resist microbialdecomposition combined with microbial proteinthat formed inside microbial cells and released tothe soil after the death of microbes, to formhumus. It is just one assumption or a theory forformation of humus in soil. (There are manytheories dealt with humus formation).


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Two important processes take place

during the decomposition oforganic residues.

These two processes areMineralization and

immobilization.They exist side by side, but thedominancy of one of them dependson chemical composition of organicresidues, particularly theratiobetween C and N in the residues(C:N ratio).

Minerali ation means transformation


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- Mineralization means transformationof nutrients from organic form(unavailable to plant) to simplemineral form available to plant.

- Nutrients are released in simplemineral form (e.g., NH4, NO3, K,..)available to plants when C:N ratio ofthe organic residues fall down to 20:1or lower.

W at o you now a out


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W at o you now a outimmobilization process?

In immobilization process, nutrients transformed form simplemineral form (e.g., NH4, NO3, K,..) available to plants to organicform unavailable to plant as a result of microbial activity to build uptheir bodies.

This process is dominant when C:N ratio of the organic residues ishigher than 33:1.

At this ratio the amount of nutrients released during thedecomposition of organic residues are taken up by microbes. Sogrowing plants suffer from nitrogen deficiencies.

So, it is not recommended to add organic residues of C:N ratiohigher than 33:1 to soil.


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So, organic residues with C:N ratiohigher than 33:1 should bedecomposed in piles before additionto soil until C:N ratio dropped to be

less than 33:1.Residues of C:N ratio of 20:1 orlower is most suitable for addition.


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Chemical Composition of humus:Chemical composition of humus are

not well known yet.Three components could beobtained from humus when submitto extraction using strong bases

and acids:1- Humin2- Humic acid (HA)3- Fulvic acid (FA)


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Model Structure of Humic acid

Model Structure of Fulvic acid

Properties of


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Properties ofHumus

1- Humus contains a large number of functional groups, including;

Carboxyl (COOH) > Ring- OH > Alcohol OH > Carbonyl (C=O ) >Amino (- NH2 ) > - SH

These functional groups are responsible for high reactivity ofhumus comparing with other particles exist in soil. They are

responsible for:1- Electrical charge created on humus.

2- Exchange and adsorption reactions, and

3- Chelation and complex formation between humus and

metal cations.


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S f ti h


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Sources of negative charges onhumus

- The charge of humus is variable (pHdependent charge).- This charge are created from ionizationof -COOH and

phenol (OH) groups as the following;

R-COOH R-COO- + H+

R-OH R-O- + H+

CEC of humus ranging from 200 to 400

Cmol(+)/kg


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Humus contains also amine groups (R-NH2)This group is amphoteric.This group has the abili ty to gain a proton (H+ion) and carries positive charge (+).

R-NH2 + H+ R-NH3+Also, this group can carry negative charge athigher pH values through ionization of H+ ion. R-NH2 + OH- R-NH- + H2O


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Sources of (-)-charges on Humus


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Effect of Humus on Soil-CEC


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Reactivity of Colloids &Chemical Properties of Soil

Reactivity of colloids


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Reactivity of colloidscould be explainedthrough the twoimportant reactions(processes) take placeon their surface;

1 Ion ExchangeReaction

2 Adsorption Reaction

Ion Exchange


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Ion ExchangeReactions


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IN SOILS-It has been demonstrated that soil colloids particles carry electric charges (mainlynegative charges. The positive charges are rare).

-Since charge balance must be maintained, counter ions (ions of opposite charge)attracted to the negatively charged sites to satisfy the surface charges.

-The ions attracted to the colloidal surfaces by electrostatic attractions calledExchangeable Ions.

-These ionscan be replaced by others have similar charges through a replacementprocess called Ion Exchange Reaction.


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-Definition: Ion exchange reaction isa reversible process, in which ioncould be changed between soilsolution and the surface of colloidalparticles.

- Characteristics of ion exchangeprocess are:

FastStoichiometric,Reversible, andNonspecific.

EXCHANGE REACTIONS IN SOILS


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Cation Exchange Reaction

-When positively charged ions attracted to the sites ofnegati e charges then the process specificall called


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negative charges, then the process specifically calledCation Exchange, and the ions called exchangeablecations.

The exchangeable cations in soils are usually bases like,Ca, Na, Mg and K. However, in acidic soils, Al3+ and H+are exist as exchangeable cations besides bases ones.- When negatively charged ions attracted to sites havepositive charge, the process called Anion Exchange, andions called Exchangeable Anions. Anion exchange

reaction is rare in soil, and may exist in acidic conditionsrather than normal or slightly alkaline soil.

-The sum of exchangeable cations satisfy the negativecharge sites on the surface of colloidal particles calledCation Exchange Capacity, CEC

Defintion: Cation exchange capacity is the sum of allexchangeable cations satisfy the negative charge of soilparticles at pH 7.0, or any other given pH, andcalculated in [Cmol(+)/kg]. (The old units wasmeq/100g).

Cation Exchange Capacity of soil increased as pH increased based on


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Cation Exchange Capacity of soil increased as pH increased based on

the fact that part of negative charge is variable, or, pH dependent

charge which is dependent on pH.

Factors Controlling Soil CEC


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Factors Controlling Soil CEC1 Clay Percent: The higher the clay content , the higher the

CEC

2 Type of clay mineral:

Kaolinite = 5 15 Cmol(+)/kg

Mica = 15 40 Cmol(+)/kg

Semectite = 60 - 100 Cmol(+)/kg

vermiculite = 100 150 Cmol(+)/kg

3 Organic Matter Content (CEC of humus ~ 200-300

Cmol(+)/kg)

4 Soil Acidity (pH) : As soil pH goes up, CEC increases.


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Cation Exchange Capacity of Different

Soils


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Soil Characteristics Basedon Ion Exchange Process &The Environmental

Significance of the Process


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Soil Characteristics Based on IonExchange ProcessI - Soil Acidity and Alkalinity (Soil pH)

II - Soil Buffering Action (SBA)

Environmental significance of SBC

Significance of Ion Exchange Processa Reclamation of Acidic and Alkali Soil

b - Availability of Exchangeable cations to plants

c - Protection of Nutrients from Loss

d - Pollution Abatement


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Soil Characteristics Basedon Ion Exchange Process

)


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I - Soil Acidity and Alkalinity (Soil pH)Definition: pH is a measure of hydrogen ion activityof the soil water system and express the acidity and alkalinityof soil.

pH = - [Log H+]In generally pH scale ranged from ( 0 14)

-But, soil pH varies between 4 -10.* Soils around the world have different pH values and could betypified according to pH value to:

I - Arid and semi-arid regions, like Egypt and all Arab countries,

soil usually have pH higher than 7 and up to 8.5. These soilscalled alkaline or slightly alkaline soil.

-(in some cases, pH gets higher than 8.5 and could reached 9or 10. This soil calledalkali soil or sodic soil. This soil cant be

cultivated (unproductive soil), and needs reclamation.


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I S il A idit d Alk li it (S il H)


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I - Soil Acidity and Alkalinity (Soil pH)

II - Humid regions: Soil are usually acidic and have

pH values significantly lower than 7 and down to 5.

III - Tropical regions: Soils have pH little lower than 7,and usually near 6. This soil called slightly acidic.

(Soils with pH around 7 callednormal or neutral soil.)


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Fuel and waste Burning:

Variable gases are produced through burning of fuel and wastes. These gases causeair pollution, so, the air of industrial regions and crowded cities is loaded byabnormal concentrations of CO2 , NO2 and SO2 which dissolve in rain water toproduce the phenomenon called "Acid Rain" according to the following equations.

CO2 + H2O H2CO3 CO3 + + 2 NO2 + H2O HNO3 NO3- + H+

These gases are additional sources of H+ ion in soil system

Factors controlling soil PH


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s Inside each group previously mentioned, Soil pH varied as the

following factors varied;

s 1-Soil organic matter: Soil pH decrease as OM% increased.

s 2 - CO2 concentration in soil air: Soil pH decreased as CO2 pressure in

soil-air increased, particularly in calcareous soil.

s 3 - Suspension effect: As soil: solution ratio increased, soil pH

increased.

s

4 - salt concentration: As salt content increased, soil pH desreased.s 5 - Kind of exchangeable cations:

Practical Issue


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Kind of Exchangeable CationsBase saturation percent (BS%)

BS% = { [Na + K+ Ca + Mg]ex /CEC )} X 1001 - If all exchangeable cations arebases (Na, K, Ca, Mg), soil pH ishigher than 7.Under this situation, If exchangeableCa is predominant (represent at least80% of all exchangeable cationsCEC), the pH usually lies between 7

8.5.


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If exchangeable Na percent (ESP) increased tobe 15% or more of CEC, the pH value willincrease to be higher than 8.5, and the soilbecamealkali or sodic soil.

(i.e., The magnitude of increases of pHdepend on the type of bases. Strongbases (e.g., Na+) highly increase pH.

Whereas, weak bases (e.g., Ca2+ &Mg2+) slightly increase the pH value.

On the other hand, if BS% decreased to beless than 100%. Which means that acidic

cations (H+ and Al3+) are exist asexchangeable, the soil pH decreases to belower than 7. Then, the soil is acidic.

N


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Na

Ca

PH

BS%So, Ca2+ is preferred than Na+ to be exchangedin soil.

Exchangeable sodium percent could be obtainedas follows:ESP = { [Na+]/ CEC} 100

As ESP increased to be 15%, soil-pH willincreases and exceeds 8.5. Then, the soilbecomes sodic or alkali.


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Problem on base saturation percent

(BS%)A soil containing the followingexchangeable cations (Cmole/kg)Ca = 8 , Mg = 3, Na = 8, k = 2

Calculate the following:1- CEC 2 BS%3 ESP 4 - How to modify its

pH?

II S il B ff i A ti


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II - Soil BufferingActions Definition:soil buffering action is the ability of soil to resist

changes in pH due to the addition of acids or bases.s Types & Mechanisms of soil buffering :s 1- chemical buffering: due to the reaction of soil

constituents with the added acids or bases.

-An example, by the addition of acid to calcareous soil, the

soil pH does not change due to the direct chemical reactionbetween the added acid and calcium carbonate as follows:

s CaCO3 + 2 HCl CaCl2 + H2O + CO2

So, calcareous soil has high buffering action for acids additives.


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SBAs

2- Compensation buffering:s this type of soil buffering is depending upon the presence of soil

colloids (humus & clay minerals) and the equilibrium between

active and exchangeable acidity (i.e., between H+ exist in

solution and exchangeable H+ as follows:

+

R

Base added

Acid added

OH- H2O

H+

active acidity0.1%

Compensation

Reservation

Hac+


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According to the "Law of mass action" theincreases of H+ concentration in solution as aresult of addition of acid, will shift the directionof the reaction to left side. This means that theexcess soluble H+ ions will be changed toexchangeable form (reservation reaction) andthe pH remains almost constant. On the otherhand, the decrease of active acidity by theaddition ofbases (OH), the reaction should be

shifted to wright side by compensation process.This means that some exchangeable acidity willbe released from DDL to the soluble form whichkeep the pH unchanged.


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Soil buffering capacity (SBC): Definition: SBC is the amount of acid or

base (mole or meq) required to change thepH of the mass unit of the soil by one unit.

Factors affecting SBC:1 - Soil texture: As clay percent

increased, SBC increased.2 - Organic matter content: The increase inOM content is accompanied by anincrease in SBC.3 - CEC: The higher the soil CEC , thehigher the SBC. This could be attributedto the high reserve acidity which cancompensate any shortage in soluble H+ .4 - Calcium carbonate content: Presence oflime in the soil increases SBC especiallyagainst acidic additions.


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Environmental significance of SBC:

1 - It prevents soil to be turned intoacidic or alkaline (prevents soildegradation).

2 - Decreases the hazardous of toxicchemicals through transformation ofsoluble forms into exchangeable oradsorbed forms.

3 - Regulates the release of nutrientsthrough compensating their lowconcentration in soil solution due toplant absorption.


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Environmental Significanceof Ion Exchange Process


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OHCOCCOCaH

H

a 223++=+ ++

+

+

I - Reclamation of acidic soils-Acidic soils characterized by high percent of exchangeable H+ andAl3+ which lead to sharp decrease in pH value. The soil becameunsuitable for plant growth.Acidic soils could be reclaimed by addition of lime as a source of Cacation this process called liming- lime dissolves in the acidic condition and produce Ca2+ cations. The

produced Ca2+ replaces H+ and Al3+ in surface of colloidal solidparticles which lead to a significant decrease in the pH value.The following equation represent this reaction.

-

2 pH >8.5, (usually pH raise to be 9 or 10)B- Remediation of +alkali soils requires reducg


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Na

SONaCaOHSOCaNa4224

2. +=+

B Remediation of +alkali soils requires reducgexchangeable Na

- It should be replaced by Ca- Gypsum [Ca(SO4)2. 2H2O] usually used as

source of calcium. So, addition of gypsum toalkali soil, then mixed well with soil, and followedby irrigation.- gypsum slightly dissolves in water and producecalcium ions (Ca++), then calcium ions replacesexchangeable Na.As the reaction proceeds, exchangeable Na+reduced and ESP gets lower than 15.Then, pHdecreased to be lower than 8.5, and physicalproperties of soil improved to be suitable forplant growth.


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s III - Plant Nutrition

Exchangeable cations are available to plant.

The higher the CEC values the higher the amount of nutrientsavailable to plant and reduction the amount lost by leaching. i.e.,

Protection of nutrients from being lost by leaching

Mass Excha nge a s a sou r ce o f nu t r i en t s t o p lan t

1- Exchange between solid particles and

hair roots.

2- Exchange between particlesthemselves.

IV Pollution Control


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IV - Pollution Control

Ion exchange process plays an important role in decreasing thehazardous of pollutants.

s Hazardous of pollutants increased as they exist in mobile formin soil solution. As these pollutants attracted to negative chargesexist on the surface of colloidal particles, they transformed toless mobile form, which reduces their down movement topollute ground water and reduces their uptake by plant andintroduction into food chain.


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Soil Fertility and

Plant Nutrition

Plant nutrition


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Plant nutrition

What is an essential element?Func t i ons o f e s sen t i a l e l emen t s i n p l an t s

Soil properties that influence nutrient availabil ity

Nitrogen PhosphorusPotassium Micronutrients

Essential Elements


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nutrients

An essential element is one that is:- Required for normal plant growth and reproduction,- Plant cant complete their life in the absence of this element,- Involved in one or more of biological activities carry out in

plant- Deficiencies symptoms appear on plant upon inadequate

supply of the element, and these symptoms disappear upontreating plants with the element,

- Cant be replaced by another element.

Essential Elementsnutrients


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nutrientss These elements called nutrients

s Nutrients : Elements essential for plant growth (e.g., Carbon, Hydrogen,Oxygen, Nitrogen, Phosphoresces, Potassium, Calcium, Magnesium,Slushier, Iron, zinc, Manganese, Coppor, Boron, Molybdenum andchlorine).

s

Scientists reported that, among all elements absorbed by plant and existin their tissues, only 16 elements are reported as essential elements tillnow.

s Other elements may added to this group in future.

s Elements such as, Ni and Co, are called beneficial elements. May betheir necessities to plant ascertain in near future.

Essential Element


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Nutrients

Exception for carbon(C) and oxygen(O), which aresupplied from

atmosphere, and(H) that suppliedfrom water, theessential elementsare obtained fromthe soil.

Essential elements and the chemical forms

most commonly taken up by plants.

Two elements (Ni and Co) are

approaching to be added to essentialelements.

Categories of


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Categories ofessential elements

Essential elements can be grouped into four categories based ontheir;

1- origin2- The relative amount a plant needs in order to grow properly.

Ni and Co

are

Functions of essentialelements in plants


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elements in plantss Carbon, Hydrogen, & Oxygens Directly involved in photosynthesis, which accounts for most of plant

growth:s 6 CO2 + 12 H2O 6 O2 + 6 (CH2O) + 6 H2O

s Nitrogens Found in chlorophyll, nucleic acids, and amino acids.s Component of protein and enzymes

s Phosphoruss Important for plant development including:s photosynthesis, respiration, cell division, and other processess Essential component of Adenosine Triphosphate (ATP), which is directly

responsible for energy transfer reactions in the plant.s Essential component of DNA and RNA, and phospholipids, which play

critical roles in cell membranes.

Functions of


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Functions ofessential elements

in plantss Potassium Found in ionic form in the cell, rather than incorporated in structure of organic

compounds.

Responsible for regulation of water usage in plants

Involved in photosynthesis , drought tolerance, protein synthesis

Calcium Essential for cell elongation and division.

Specifically required for root and leaf development

Magnesium

Primary component of chlorophyll and is therefore actively involved in

photosynthesis. Involved in phosphate metabolism, respiration, and the activation of several

enzyme systems.

Functions of essentialelements in plants


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elements in plantss Sulfur

Required for the synthesis of the sulfur-containing amino acids cystine,cysteine, and methionine, which are essential for protein formation.

s Boron

Essential for germination of pollen grains and growth of pollen tubes

Forms sugar/borate complexes associated with the translocation of sugars,starches, N, and P.

s Copper

Necessary for chlorophyll formation.

Catalyzes several enzymes.

s

Iron Serves as a catalyst in chlorophyll synthesis.

Involved in many oxidation-reduction reactions during respiration andphotosynthesis.

Functions of


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Functions ofessential elements

in plantss Manganese

Functions primarily as a part of the enzyme systems in plants.

Activates several important metabolic reactions (enzymes).

s Zinc

Essential for promoting certain metabolic/enzymatic reactions.

Necessary for the production of chlorophyll, carbohydrates, and growth hormones.

Molybdenum

Essential in the process of symbiotic N fixation by Rhizobia bacteria in legume rootnodules.

s Chlorine

Involved in: energy reactions in the plant

Serves as a counter ion in the transport of several cations in the plant.

Nutrient Availability to Plant


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Ion mobil ity in soilsAnions (negatively charged ions) usually leach more readilythan cations because they are not attracted to thepredominantly negative charge of soil colloids.

For example, NO3- , due to its negative charge and relativelylarge ionic radius, is not readily retained in the soil and is easilylost from soils by leaching.

An exception to this behavioris phosphorus anions(HPO4=,H2PO4-). These anionic forms do not easily leachedthrough the soil profile because of their specific complexingreactions with soil components.



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Effect of pH on nutrientavailabil ity The most important soil property influencenutrient availability is soil-pH:

Nutrients exist in soil in many chemical forms.Not all these forms are available to plant.Usually the soluble and exchangeable forms

are available to plants, the other forms arenot available to plant. Transformation ofnutrients from soluble to insoluble form andvice versa are affected by soil-pH value.



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Effect of pH on nutrient availabil ity

The relationshipbetween soil pHand the relative

plant availabilityof nutrients.

In general; except for Mo and B, the availabilityof most nutrients increased as soil pH decreased


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of most nutrients increased as soil pH decreasedto be lower than 7.

P: PhosphorusPlant availability of P isgenerally greatest in the pH range of 5.5 -

6.5. When soil pH falls below 5.5, P reactswith Fe and Al to produce insoluble Fe andAl phosphates that are not readilyavailable for plant uptake.

At pH higher than 6.5, P reacts with Ca toform Ca phosphates that are relativelyinsoluble and have low availability toplants.

K, Ca, and Mg: These nutrients are mostpresent in soils in available form at pHhigher than 6.0. Their availability to plantsdecreased in acid soil. They may have beenpartially leached out of the soil profile.


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Micronutrients: In general, mostmicronutrients are more available in

acidic than alkaline soils. As pHincreases, micronutrient availabilitydecreases.

An exception to this trendis Mo and B;their availability increase as soil pH

increases.Al, Fe, and Mn Toxicity: At pH values lessthan 5.0, solubility of Al, Fe, and Mnincrease and their concentrations insoil solutions increase to be toxic toplant.


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Fertilizers

Fertilizers


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s Expressions:-s - Fertilizer: Any organic or inorganic material of natural or synthetic

origin that added to soil to supply plant with one or more essential element.

s - Fertilization: The process in which nutrients are added to soil in the formof chemical fertilizers, animal manure, green manure or compost.

s Foliar fertilization : Application of a dilute solution contains

nutrient elements to plant foliage, usually, to supplement nutrients absorbedby plant roots.

s Fertigation: Application of nutrients through irrigation water.

ili


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Fertilizers

s Fertilizers are classified into two major groups:s 1- Organic fertilizers

2- Inorganic fertilizers (mineral fertilizer or

chemical fertilizer)- Inorganic fertilizers classified to 2 types;

- Simple (single) fertilizers: in which a fertilizer contain

only one nutrient (e.g., urea)

- Complete fertilizer: in which a fertilizer contain two ormore nutrients.

1- Inorganic fertilizers(mineral or chemical


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(mineral or chemicalfertilizers)

A chemical Fertilizers are fertilizers that contain nutrients in mineralform including either single or compound fertilizers.

- Single fertilizers include 3 main types;

I N- Fertilizers (Nitrogen fertilizers):-1- Ammonium Nitrate (NH4NO3): Contains 33% N.

- N exist in two forms NH4+ and NO3- . These two

forms are avoidable to plants.

2 - Ammonium sulphate [(NH4)2SO4]: Contains 21% N.3 - Urea [(CO(NH2)2]: Contain 46 % N.



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II P- Fertilizers (Phosphate fertilizers):-1- Single Supers phosphate {Ca(H2PO4)2: Contain 16-

22 % P2O5.2-Triple Superphaspate {Ca(H2PO4)2}: Contains 4452%

P2O5.

III -K- Fertilizers (Potassium Fertilizers)1- Potassium chloride (KCl): Contain 60-63% K2O.2- Potassium Sulplate (K2SO4): Contain 5053% K2O.

Potassium sulphate is much more preferable than

potassium chloride, particularly for crops sensitive to Cl

ions such as potatoes.



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s Useful Expression

Fertilizer analysis : The percentage composition of fertilizer,expressed in terms of nitrogen (N) , phosphors penta-oxide (P2O5 ) andPotassium oxide ( K2O )

- Fertilizer fixation : The process by which available plant nutrients arerendered less available or unavoidable in soil.

- Fertilizer requirement: The quantity of certain nutrient needed to increaseplant growth to optimum yield.



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s

IV - Micronutrient FertilizersMicronutrients are usually supplied in chelated form and added to plants by

foliar spraying. Also, they could be supplied in mineral form. However, mineralform is less soluble.

s Definition: Chelating agent are organic molecules such as EDTA, EDDHA,...

These compounds have the ability to make chemical bonds (co-ordinate covalentbond) with Fe, Mn, Cu, Zn. The chelates are readily soluble, even at higher pHvalues, which increase their suitability and high efficiency for plants. They couldbe added either to soil or by foliar applications.

s - Mineral Sources of micronutrient fertilizer: Micronutrients are usuallysupplied in sulphate form, such as; Ferrous sulphate, FeSO4.7H2O, Mn sulphate,Zn sulphate and Cu sulphate ..- Other micronutrients such as boron is supplied in form of Borax, andMolybdenum in form of ammonium molybdate.

2 Organic fertilizers


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2 Organic fertilizers

s

Organic fertilizers are the residues of plant and animals usuallycontain various macro- and micro-nutrients in an organic form andin different quantities. These fertilizers include, cow manure, chickenmanure, farmyard manure, compost and green fertilizer.

s Usually nutrients of organic fertilizers exist in an organic form not

available to plant. Organic manure should be decomposed bymicro-organisms to transform nutrients to simple ions in mineralform such as, NO3, K+, Mn++,.. Available to plant.

s Organic fertilizers have many advantages to soil and plant, besidesthey provides macro- and micro-nutrients to plant.

Term paper:You can Choose any agricultural issue to speak about. Or one ofthe following subjects:1- Physical weathering2- Chemical weathering


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2 Chemical weathering3- Biological weathering4- Time as soil formation factor5- Types of Egyptian soil6- Types of Somali soils7- Types of Nigerian Soils8- Types of Chad soils9- Sedentary soil10- Transported soil11- Organic fertilizers12- Compost13- Nitrogenous fertilizers14- Potassium fertilizers

15- Phosphate fertilizers16- Micronutrient fertilizers17-Chelating fertilizers18- Foliar fertilization19- Soil texture20- Soil structure21- Soil erosion22- Desertification23- Cation Exchange Capacity of Soil24- Soil Buffering action25- Soil pH26- Soil solution27- Role of Hydrogen ion in chemical weathering28- Soil formation processes29- Hydrous oxides in soil30- Amorphous material in soil31- Humus formation32- Major components of humus


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