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Question 1: a. Present a nitrogen cycle within the earth system. b. Present organic matter classification in soils. c. Write a cellulose molecular structure with four sugar monosaccharides. a. Present a nitrogen cycle within the earth system. From the diagram of global nitrogen cycle, we can summarize key processes:  Stock of soil nitrogen depends on N fixation processes and decay processes of organic N compounds.  Major fixation processes consist of biological fixation and HaberBosh process.  Decay processes include ammonification (mineralization), nitrification, denitrification.  Biological N fixation:  HaberBoschindustrial N fixation: The Haber Process combines nitrogen from the air with hydrogen derived mainly from natural gas (methane) into ammonia. N2 + 3H2 > 2NH3 (ΔH = −92.4 kJ•mol−1)  Ammonificationmineralization: Nitrogen enters the soil through the decomposition of protein in dead organic matter Amino acids + 1 ½ O2 > CO2 + H2O + NH3+ 736kJ This process liberates a lot of energy which can be used by the saprotrophic microbes  Nitrification:  Denitrification: Denitrification is a natural soil microbial process where nitrate (NO3 ) is converted to nitrogen (N) gases that are lost to the atmosphere. b. Present organic matter classification in soils. There are many classifications of soil organic mater.  NONHUMIC SUBSTANCES • Carbohydrates  Carbohydrates consists of monosaccharides (single sugars), disaccharides, polysaccharides. The simplest carbohydrates are monosaccharides, or single sugars.  Carbohydrate macromolecules are polysaccharides, polymers composing of many sugar building blocks. • Proteins  Proteins account for more than 50% of the dry mass of most cells.

Question 1:

a Present a nitrogen cycle within the earth system

b Present organic matter classification in soils

c Write a cellulose molecular structure with four sugar monosaccharides

a Present a nitrogen cycle within the earth system

From the diagram of global nitrogen cycle, we can summarize key processes:

 Stock of soil nitrogen depends on N fixation processes and decay processes

of organic N compounds

 Major fixation processes consist of biological fixation and Haber-Bosh process

 Decay processes include ammonification (mineralization), nitrification, denitrification

+ Biological N fixation:

+ Haber-Bosch/industrial N fixation:

The Haber Process combines nitrogen from the air with hydrogen derived mainly from natural gas (methane) into ammonia

N2 + 3H2 -> 2NH3 (ΔH = −92.4 kJ·mol−1)

+ Ammonification/mineralization:

Nitrogen enters the soil through the decomposition of protein in dead organic matter

Amino acids + 1 ½ O2 -> CO2 + H2O + NH3+ 736kJ

This process liberates a lot of energy which can be used by the saprotrophic microbes

+ Nitrification:

+ Denitrification:

Denitrification is a natural soil microbial process where nitrate (NO3- ) is converted to nitrogen (N) gases that are lost to the atmosphere

b Present organic matter classification in soils

There are many classifications of soil organic mater

∗ NONHUMIC SUBSTANCES

• Carbohydrates

+ Carbohydrates consists of monosaccharides (single sugars), disaccharides, polysaccharides The simplest carbohydrates are monosaccharides, or single sugars

+ Carbohydrate macromolecules are polysaccharides, polymers composing of many sugar building blocks

• Proteins

+ Proteins account for more than 50% of the dry mass of most cells

+ Protein functions include structural support, storage, transport, cellular communications, movement, defense against foreign substances

Organic Carbon in soil

Organic Carbon in undecayed and partially decayed plant and animals tissues

Humus Soil organic matter

Biomass

Carbon in living organic

Humic substances Nonhumic substances

Humin Fulvic acid

Humic acid

+ Enzymes are a type of protein that acts as a catalyst, speeding up chemical reactions Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life

• Lipids

+ Fats are constructed from two types of smaller molecules: glycerol and fatty acids Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon A fatty acid consists of a carboxyl group attached to a long carbon skeleton

+ Fatty acids vary in length (number of carbons) and in the number and locations

of double bonds Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds Unsaturated fatty acids have one or more double bonds The major function of fats is energy storage

• Lignins

+ Lignin may be defined as an amorphous, polyphenolic material arising from enzymatic dehydrogenative polymerization of three phenylpropanoid monomers, namely, coniferyl alcohol, sinapyl alcohol, and p-coumaryl alcohol

It is most commonly derived from wood, and it is an integral part of the secondary cell walls of plants and some algae

+ In short, lignins compose of coniferyl alcohol (softwood), signapyl alcohol (hardwood), p-coumaryl alcohol (grasswood)

+ Lignin is a cross-linked racemic macromolecule with molecular masses in excess of 10,000 u

+ Nucleic acids are polymers called polynucleotides

+ Each polynucleotide is made of monomers called nucleotides

+ Each nucleotide consists of a nitrogenous base, a pentose sugar and a phosphate group

+ The portion of a nucleotide without the phosphate group is called a nucleoside

∗ HUMIC SUBSTANCES

Humic substances (HS) are complex and heterogeneous mixtures of polydispersed materials formed in soils, sediments, and natural waters by biochemical and chemical reactions during the decay and transformation of plant and microbial remains (a process called humification) Plant lignin and its transformation products, polysaccharides, melanin, cutin, proteins, lipids, nucleic acids, fine char particles, etc., are important components taking part in this process

c Write a cellulose molecular structure with four sugar monosaccharides.

Question 2

a Present soil colloid classification

b Present concepts of adsorption, absorption, desorption, adsorbate, adsorbent

a Present soil colloid classification.

Soil colloids can be classified by crystal structure

(a) Crystalline Silicate Clays

• Dominant colloid in most soils (not andisols, oxisols or organic soils)

• Crystals layered as in a book

• 2-4 sheets of tightly-bonded O, Si and Al atoms in each layer

 Kaolinite

 Smectite group

 Vermiculite group

 Mica group

 Chlorites

(b) Non-crystal colloids

 Salts:CaCO3 – calcite, aragonite

CaMgCO3 – dolomite CaSO4 – gypsum Ca5(PO4)3F, Ca5(PO4)3OH – flour – hidroxiapatite Ca3(PO4)2 – photphorite

• Not organized into crystalline sheets

• Both + and – charges can adsorbanions such as photphorite

• High water – holdingcapacity

• Malleable (charges in shape) when wet but not sticky

• Often form in volcanic soils (especially in Andisoils)

(c) Fe, Al oxides

Fe3O4 – magnetite Fe2O3 – hematite Al(OH)3 – gibbsite

(d) Humic colloids

Anon – crystalline, organic substance

Very large, organic molecules

≈ 50% C, 40% O, 5% H, 3% N and sometimes S

Structure highly variable

Very large negative charge due to three types of – OH groups

 carboxyl group COOH

 phenolic hydroxyl group

 alcoholic hydroxyl group

b Present concepts of adsorption, absorption, desorption, adsorbate, adsorbent

Adsorption is a physical process that involves the transfer of solutes from

the liquid phase to the surface of a solid matrix

Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid,

or dissolved solid to a surface

Absorption is the filling of pores in a solid.

When both adsorption and absorption processes take place simultaneously, the process is called sorption

Desorption: The process of removal of an adsorbed substance from the

surface on which it is absorbed

Adsorbent, adsorbate:

The substance on the surface of which adsorption takes place is called adsorbent

The substance which is being adsorbed on the surface of another substance, called adsorbate

Question 3

a Present Jackson-Sherman weathering stages

b State soil organic matter classification (ý b câu 1)

a. Jackson-Sherman Weathering

The relationship between weathering intensity and the mineral assemblages present in the clay fraction of a soil is described in the weathering sequence of Jackson et al (1948) and Jackson and Sherman (1953)

Jackson reasoned that the mineral composition of the clay-sized fraction could be employed to establish the weathering stage of a soil

Common minerals found in the clay fraction of a soil are identified by an index number Low numbers represent minerals easily weathered Whereas high numbers represent minerals relatively resistant to weathering and abundant in old soils The clay fraction of a soil is typically composed of three to five dominant minerals

Question 4

a Present the concepts of permanent structural charge, proton charge, inner-sphere complex charge, ouster-inner-sphere complex charge

b Present a structure of soil colloids

c Please explain differences between physical adsorption and chemical adsorption

a Present the concepts of permanent structural charge, proton charge, inner-sphere complex charge, ouster-inner-sphere complex charge.

a. Permanent structural change

Isomorphous substitution of layer colloids creates negative charge of particle surface This charge is termed permanent structural charge, σo

In addition, reaction between surface functional groups with solution ions generates proton charge σH, inner complex charge σis, oyster complex charge

σOS.

b. Inner sphere complex charge

adsorbed ions and molecules (other than H+ and OH-)

σis Inner sphere complex charge density

σis can be positive, negative or zero.

c. Ouster-sphere complex charge

Ions and molecules that are held at the surface σOS, the Ouster-sphere complex charge σOS can be positive, negative or zero.

b Present a structure of soil colloids.

Negatively charged colloidal particles:

− Nuclear

− Negative charge surface

− Fixed cation layer

− Exchangeable cation layer

∗ Positively charged colloidal particles:

− Nuclear

− Positive charge surface

− Fixed anion layer

− Changeable anion layer

∗ Negatively charged clay particles:

− Nuclear

− Negative charge surface (charge layer of colloidal particles)

d. Please explain differences between physical adsorption and chemical adsorption.

Physical adsorption: Van der Waals attraction between adsorbate and adsorbent The attraction is not fixed to a specific site and the adsorbate is relatively free to move on the surface This is relatively weak, reversible, adsorption capable of multilayer adsorption

Chemical adsorption: Some degree of chemical bonding between adsorbate and adsorbent characterized by strong attractiveness Adsorbed molecules are not free to move on the surface There is a high degree of specificity and typically a monolayer is formed The process is seldom reversible

physical adsorption chemical adsorption Cause Van der Waals forces, no

electron transfor

Covalent/electrostatic forces, electron transfer

Temperature

range

Low temperatures Generally high temperatures

adsorption Low, ≈ heat of fusion

(ca.10kJ/mol), always exothermic

High, ≈ heat of reaction (80 – 200 (600)kJ/mol), usually exothermic

Activation energy Low Generally high (unactivated: low)

Question 5

a Present soil phases in term of chemical composition

b Please write the structure of a ring phyllosilicate

a. Present soil phases in term of chemical composition

• Air

 Gases have atoms or molecules that do not bond to one another in a range of pressure, temperature and volume

 These molecules haven’t any particular order and move freely within a container

• Liquids

 Similar to gases, liquids haven’t any atomic/molecular order and they assume the shape of the containers

 Applying low levels of thermal energy can easily break the existing weak bonds

 Liquid crystals have mobile molecules, but a type of long range order can exist; the molecules have a permanent dipole Applying an electric field rotates the dipole and establishes order within the collection of molecules

• Solids

 Solids consist of atoms or molecules executing thermal motion about an equilibrium position fixed at a point in space

 Solids can take the form of crystalline,polycrstalline, or amorphous materials

 Solids (at a given temperature, pressure, and volume) have stronger bonds between molecules and atoms than liquids Solids require more energy to break the bonds

b. Please write the structure of a ring phyllosilicate.

Phyllosilicates, or sheet silicates, are an important group of minerals that includes micas, chlorite, serpentine, talc, clay minerals

The basic structure of the phyllosilicates is based on interconnected six member rings of SiO4 -4 tetrahedra that extend outward in infinite sheets

Each tetrahedra is bound to three neighboring tetrahedra via three basal bridging oxygens

Question 6

a Explain the origin of permanent structural charge of soil clay colloids

b Present adsorption types of soils

c Indicate the significances of soil adsorption in soil management

a. Explain the origin of permanent structural charge of soil clay colloids.

− Isomorphous subsitution of layer colloids creates negative charge of particle surface This charge is termed permanent oσstructural charge

• Each Mg2+ ion that substitutes for Al3+ causes a negative charge in a dioctahedral sheet

• Each Al3+ ion that substitutes for Si4+ causes a negative charge in a tetrahedral sheet

− In addition, reaction between surface funtional groups with solution ions generates proton charge σH , inner complex charge σis , ouster complex charge σcharge

b. Present adsorption types of soils.

Physical adsorption: Van der Waals attraction between adsorbate and adsorbent The attraction is not fixed to a specific site and the adsorbate is relatively free to move on the surface This is relatively weak, reversible, adsorption capable of multilayer adsorption

Chemical adsorption: Some degree of chemical bonding between adsorbate and adsorbent characterized by strong attractiveness Adsorbed molecules are not free to move on the surface There is a high degree of specificity and typically a monolayer is formed The process is seldom reversible

c. Indicate the significances of soil adsorption in soil management.

− Adsorption is a physical process that involves the transfer of solutes from the liquid phase to the surface of a solid matrix

− Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface

∗ the significances of soil adsorption in soil management is ability to retain water, nutrients and conditioner nutrition soil

• Chemical adsorption has meaning for properties and soil fertility This is the cause of accumulation of nutrients in the soil such as Al, P, Fe, S, in which the element beneficial to crops such as P,Ca,S, or reduce the tisicity of some other element like Al

• Because soil colloids have large specific surface and one layer of ions surrounded It can hold the opposite ions around That is the basic of calculation

of soil adsorption

• The relationship between adsorption capacity and the ions outside solution is the exchange relationship If concentrations of solution is high, soil colloids will adsorp ions in solution If the solution to low concentrations of ions from soil colloids are released out

• In addition to the absorption capacity of soil also through the attraction od food crops and microorganisms, capable of keeping the maater particle through small slit, rugged shores or retained for soil molecules precipitate, or air molecules, other water

Question 7

a Present soil element classifications

b State concepts of soil colloids, nanoparticles, clay particles, soil particles

c Please explain roles of surface functional groups of clay colloids

a. Soil element classifications:

− Metals

− Transition metals

− Nonmetals

− Noble gases

− Lanthanide series

− Actinide series

b. State concepts of soil colloids, nanoparticles, clay particles, soil particles.

• Soil colloids is a particle with a size of less than 1µm Any substance finely

dispersed in a gaseous, liquid, or solid medium, such that individual particles They are not visible in an ordinary microscope They do not settle out

• Nanoparticles is critical size range (or particle diameter) typically ranges from

nanometers (10−9 m) to micrometers (10−6 m) The term colloid is used primarily to describe a broad range of solid–liquid (and/or liquid–liquid)