Soil Science – agriinfo.in https://agriinfo.in Sun, 14 Apr 2019 13:11:12 +0000 en-US hourly 1 https://wordpress.org/?v=5.1.1 Requirement of Details on Lable of Soil Sample https://agriinfo.in/requirement-of-details-on-lable-of-soil-sample-1781/ https://agriinfo.in/requirement-of-details-on-lable-of-soil-sample-1781/#respond Tue, 15 May 2018 20:01:47 +0000 http://agriinfo.in/index.php/2018/05/15/requirement-of-details-on-lable-of-soil-sample/ Requirement of Details on Lable of Soil Sample 1. Name of the farmers 2. Full address 3. Exact location of the field. 4. Irrigation 5. Drainage 6. Soil type 7. Soil slopes 8. Cropping history and yields 9. Manures applied to the preveious crops. 10. Salinity and sodicity 11. Size of the area representing sample […]

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Requirement of Details on Lable of Soil Sample

1. Name of the farmers
2. Full address
3. Exact location of the field.
4. Irrigation
5. Drainage
6. Soil type
7. Soil slopes
8. Cropping history and yields
9. Manures applied to the preveious crops.
10. Salinity and sodicity
11. Size of the area representing sample
12. Crop and variety to be grown and
13. Date of sampling

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Plant Proteins and their Quality, Essential Amino Acids and Limiting Amino Acids https://agriinfo.in/plant-proteins-and-their-quality-essential-amino-acids-and-limiting-amino-acids-1556/ https://agriinfo.in/plant-proteins-and-their-quality-essential-amino-acids-and-limiting-amino-acids-1556/#respond Thu, 10 May 2018 10:04:48 +0000 http://agriinfo.in/index.php/2018/05/10/plant-proteins-and-their-quality-essential-amino-acids-and-limiting-amino-acids/ Plant Proteins and their Quality, Essential Amino Acids and Limiting Amino Acids   (1) Between 10 and 30 % of the protein in forage is converted into human food by ruminants, whereas 40 to 60 % of the protein can be extracted. The approximate consequences of fractionating forage crop rather than using it as fodder. […]

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Plant Proteins and their Quality, Essential Amino Acids and Limiting Amino Acids

 
(1) Between 10 and 30 % of the protein in forage is converted into human food by ruminants, whereas 40 to 60 % of the protein can be extracted. The approximate consequences of fractionating forage crop rather than using it as fodder.

(2) Leaves are the main site of protein synthesis and there are losses during translocation to other parts of a plant.

(3) When LP is made, the crop is harvested when less mature than when silage is made, and much less mature than when hay is made or a conventional crap is taken, the cost of harvesting is greater but an immature crop is not at risk for so long from diseases and pests.
 
(4) Crops that regrow several times after being cut young, or perennial crops, maintain cover on the ground, this enables fuller use to be made of sunlight and protects the ground from erosion.
 
(5) The fibrous residue contains the protein that was not extracted. Depending on the processing conditions, it can have two to five times as great a percentage of dry matter as the original crop and can therefore be dried to produce conserved ruminant feed economically.

Crops:
 
Species and varieties selected for seed production or for a use other than LP extraction have been the source of most of the LP made in bulk. If varieties, possibly of species not at present used in agriculture, were investigated, yields would probably be greater than those so far attained.

Cowpea (Vigna unguiculata) gave 895 kg/ha in 80 days i.e., more than 4 tons if that rate could have been maintained for a year. In short term experiments yields as great as 17 kg of extracted protein per ha per day have been claimed.

Separation of Extract from Fiber:
 
The yields given above were measured on 4 to 5 kg samples of leaf taken from within a crop, pulping them in the unit designed for IBP (Davys & Pixie, 1969), pressing a sample in the unit similarly designed (I3avys, Pixie & Street, 1969) and measuring the amount of protein perceptible from the extract with trichloroacetic acid. In large-scale work it is usually advantageous to re-extract the fiber, this can give half as much protein again as a single extraction, but it would be difficult in the laboratory to get quantitative and repeatable results from a double extraction. The manner in which increasing skill in agronomy and processing have increased yields at Rothamsted

Separation of Protein from Extract:

Heat coagulation is generally accepted as the most satisfactory method for making a protein curd. Green, predominantly ‘chloroplastic’, protein coagulates at 50 to 60 °C, if that is separated; colourless ‘cytoplasmic’ protein separates at 70 °C. No more protein coagulates on further heating, but heating to 100 °C is probably advantageous in other ways it ensures a more nearly sterile product and it inactivates leaf enzymes more completely. When steam is injected into a stream of juice, heating takes place in 1 or 2 seconds; this produces had, easily filtered cured, and there is less enzyme action before inactivation. Chlorophyllase rich plants such as lucerne and wheat show the importance of this; the chlorophyll in LPs made by heating to 80 °C was almost completely hydrolysed to chlorophyllide, whereas there was little hydrolysis during quick heating to 100 °C (Arkcoll & Holden, 1973).

Bengal Gram:

The Bengal gram or chick pea (Cicer arietinum) has two principal cultivated types; the brown or yellow   brown deshi type and, the white seeded Kabuli type. Variation in their nutritive values are presented in table.

Table: Composition of two types of Bengal Gram:

 

Crude Protein (%)

Ether Extracts (%)

Crude Fiber (%)

Ash (%)

Carbohydrates (% by Difference)

Phosphorus (mg % / 100 g)

Calcium (mg/100 g)

Iron (mg/100 g)

Kabuli Type

21.64

5.78

5.49

2.67

64.42

305.8

167.4

8.36

Deshi Type

20.91

4.56

10.06

2.6

61.78

308.8

231.1

6.90

Red Gram:

Red gram or pigeon-pea is the second most widely cultivated pulse in India. Based on morphological characters, two forms, namely Cajanus cajon var. flavus, commonly known as tur and Cajanus cajan var. bicolor, known as arhar, have been described. The former type includes the commonly cultivated varieties, which are relatively dwarf and  bear yellow flowers and plain pods; the latter type includes most of the perennial types, which are generally late maturing, tall and bushy varieties.

Table: Methionine and Sulphuric Content of varieties of Red Gram

Variety

Methionine (mg/g)

Sulphur (mg/g)

P.2780

3.00

1.30

P.3758

2.40

2.50

P.4768

2.20

2.90

P.4415

2.60

1.90

P.4657

2.30

1.72

R.24

2.05

1.92

S.32

2.05

1.32

S.34

2.03

1.72

 

 

 

Commercial Varieties

 

 

T-21

1.33

1.52

C-II

1.80

1.70

N-84

1.55

1.50

T-15-15

1.60

1.50

Phaseolus Group:

Moong beans, urd beans and moth bean are considered to be native to India, having been originated from Phaseolus sublobatus which grows wild in India.

Moong Bean or Green Gram (Phaseolus aureus):

The research work on the improvement of moong beans was started in India in 1925 with large collections of seed samples from different districts of the country and also from Burma. Pure line selection from the local materials resulted in some promising varieties, e.g., GG-127, GG-188, Krishna – 11, Khargone-1, Co. 1, Kopergaon, NP-23 and Jalgaon 781.

Urd Bean or Black Gram (Phaseolus mungo):
 
The earliest attempts to improve urd bean started in 1925, when 125 strains were isolated from the local bulks. Systematic improvement of urd was started in 1943. These efforts resulted in a number of promising varieties, both for dry areas, e.g. BG-379, B.R. 61, Mash-48, Mash 35-5, Khargone-3, T-27, T-65 and Sindh Kheda 1-1, and also for wetlands, e.g., ADT-1.
 
Moth Bean (Phaseolus acontifolius):
 
A breeding program on this crop was started in 1943 and 150 collections were made from the cultivated areas of the country. From single plant selections, two types, namely B-15 and B-18, were identified as good grain types and T-3 as a good fodder variety. Another variety No. 88, was identified as a better grain type, maturing in 120 days. These lines showed some improvement in yield, by 10-15 %, but no varieties resistant to diseases have been identified. Disease resistance and quality aspects are being considered in future breeding program.

Dolichos Beans:
 
Two major species of Dolichos, are commonly cultivated in India. One is Dolichos lablab, commonly known as walve or avare and the other Dolichos biflorus, known as horse gram or kulthi.

Walve or avare (Dolichos lablab):
 
Research work on improvement of avare has been carried out with the object of developing drought resistant, high yielding types with good quality pods. Some of the varieties e.g. Co. 1, Co. 5 and Co. 6, have shown wide adaptability and are being popularized in rotation with late paddy in areas where winters are mild.

Horse Gram or Kulthi (Dolichos biflorus):

Very little work has been done on the improvement of horse gram; however, as a result of single plant selections from the local bulks, a number of varieties recording 15-20 % more yield than local bulks have been developed. Some of the varieties e.g. BGM 1-1, No. 35, D.B. 7 have been found promising. Variety BGM-1 exhibited a high degree of virus resistance.

Cowpea:
 
A breeding program for improvement of this crop (Vigna sinensis) has been in progress since 1940. A number of grain, fodder and vegetable varieties have been identified from time to time largely from collections made within the country or from abroad of the grain types, N.P. 2, N.P. 7, C-32, T-I, K-11, K-14; of the fodder varieties.

Pea or Matar:
                                            °
There are two main types of cultivated pea (Pisum sativurn), namely the large, smooth or wrinkled seeded garden pea and the small, round or dimpled seeded field peas. While the former type is used as a table variety, the latter is used as pulse, whole or split.

Garden Pea:
 
A breeding program on the garden pea was initiated at the Indian Agricultural Research Institute in the thirties. Through single plant selection, the medium-tall, wrinkled-seeded variety NP-29 was developed which is still popular in the country for its quality. During the same period, green-seeded Hara Bauna and white round seeded Lucknow Poniya were popularized for general cultivation in northern India. In central India, where the winters are comparatively short, the variety Khapar Kheda became more popular. In the warm-temperate zone around the Himalayas, a smooth, white-seeded variety was popularized under the name Kala Nagini or Kanawari. In recent years, a few more varieties, e.g., Early Badger, Boneville and Perfection with very attractive pod size have been introduced for general cultivation.

Lentil:

Varietal improvement programs for this species (Lens esculntus), were initiated in India in 1924 by collecting mixed samples bought in bazaars all over the country. Single plant selections were picked up from the bulk population and sixty-six types were isolated. Some of these varieties e.g., N.P. 11, N.P. 47 (IARI), T-36, T-8 (UP), L-9-12 (Punjab) and B.R. 25 (Bihar).

Khesari or Teora:
 
The consumption of this pulse (Lathyrus satiyus), in large quantities leads to lathyrism because of the presence of, l-N- oxalyl amino alanire (βOAA). It is a very hardy crop and comes up well even under water logging and extreme drought conditions. Therefore in areas which are completely dependent on the monsoon, farmers insist on growing it.

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Biomolecules – Definition, Types, Structure, Properties and Its applications https://agriinfo.in/biomolecules-definition-types-structure-properties-and-its-applications-1549/ https://agriinfo.in/biomolecules-definition-types-structure-properties-and-its-applications-1549/#respond Tue, 01 May 2018 18:39:57 +0000 http://agriinfo.in/index.php/2018/05/01/biomolecules-definition-types-structure-properties-and-its-applications/ Biomolecules – Definition, Types, Structure, Properties and Its applications Definition of Biomolecule: An organic compound normally present as an essential component of living organism.   Characteristics of Biomolecules: 1) Most of them are organic compounds. 2) They have specific shapes and dimensions. 3) Functional group determines their chemical properties. 4) Many of them arc asymmetric. […]

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Biomolecules – Definition, Types, Structure, Properties and Its applications

Definition of Biomolecule:

An organic compound normally present as an essential component of living organism.
 
Characteristics of Biomolecules:

1) Most of them are organic compounds.
2) They have specific shapes and dimensions.
3) Functional group determines their chemical properties.
4) Many of them arc asymmetric.
5) Macromolecules are large molecules and are constructed from small building block molecules.
6) Building block molecules have simple structure.
7) Biomolecules first gorse by chemical evolution.

Important Biomolecules of life:

1) Water: Being the universal solvent and major constituents (60%) of any living body without which life is impossible. It acts as a media for the physiological and biochemical reactions in the body itself. Maintain the body in the required turgid condition.

2) Carbohydrates: It is very important for source of energy for any physical body function.

3) Proteins: These are very important from body maintenance point of view,helps in tissue, cell formation.

4) Lipids: These are very important from energy source as well as human nutrition point of view.

5) Nucleic Acids: Nucleic acids are very important as DNA carries the hereditary information and RNA helps in protein formation for the body.
 
6) Enzymes: Enzymes are simple or combined proteins acting as specific catalysts and activates the various biochemical and metabolic processes within the body.

Table: Fundamental Biological Molecules (Biomolecules):

Sr. No.

Small Molecule

Atomic Constituents

Derived Macro – Molecule

1

Amino Acid

C, H, O, N (S)

Proteins

2

Sugars

C, H, O

Starch, Glycogen

3

Fatty Acids

C, H, O

Fats, Oils

4

Purines and Pyrimidine

C, H, O, N

Nucleic Acids

5

Nucleotide

C, H, O, N, P

Nucleic Acids (DNA and RNA)

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Proteins – Definition, Classification, Properties and Functions https://agriinfo.in/proteins-definition-classification-properties-and-functions-1555/ https://agriinfo.in/proteins-definition-classification-properties-and-functions-1555/#respond Tue, 01 May 2018 05:13:39 +0000 http://agriinfo.in/index.php/2018/05/01/proteins-definition-classification-properties-and-functions/ Proteins – Definition, Classification, Properties and Functions Definition of Protein: Polymeric compounds the monomeric units of which is amino acid. Classification of Protein (with examples): A) Based on composition    B) Based on structure A) Based on Composition: i) Simple Proteins ii) Conjugated Proteins iii) Derived proteins i) Simple Proteins: Classified according to solubility a) Albumins […]

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Proteins – Definition, Classification, Properties and Functions

Definition of Protein:

Polymeric compounds the monomeric units of which is amino acid.

Classification of Protein (with examples):

A) Based on composition    B) Based on structure

A) Based on Composition:

i) Simple Proteins
ii) Conjugated Proteins
iii) Derived proteins

i) Simple Proteins: Classified according to solubility

a) Albumins
b) Globulins
c) Glutelins
d) Histories
e) Protamine
f) prolamines
g) Scleroproteins

ii) Conjugated Proteins: Contain amino acid + prosthetic group.

a) Glycoproteins
b) Chromoproteins
c) Lipoproteins
d) Nucleoproteins
e) Phosphoprotein

iii) Derived Proteins: Derivatives of proteins due to action of heat,   enzymes, or chemical reagents.

a) Primary Derived
b) Secondary Derived

B) Based on Structure:

i) Fibrous
ii) Globular

Function of Protein:

1) Storage
2) Transport
3) Structural Material
4) Metabolic Growth Regulator
5) Control of Physiological Functions
6) Catalytic Activity
7) Hormonal
8) Toxicity by Foreign Proteins

Properties of Proteins:

i) Optical Property
ii) Colloidal
iii) Solubility
iv) Amphoteric Nature
v) Denaturation of Proteins etc

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Measurement of Electric Conductivity https://agriinfo.in/measurement-of-electric-conductivity-1786/ https://agriinfo.in/measurement-of-electric-conductivity-1786/#respond Tue, 24 Apr 2018 12:58:42 +0000 http://agriinfo.in/index.php/2018/04/24/measurement-of-electric-conductivity/ Measurement of Electric Conductivity Principle of Salt Bridge: In salt bridge 2 fixed the resistance R1 and R2 and variable resistance Rv are connected in a branched circuit with the conductance cell having resistance Rx. An AC potential is applied at C and D. An AC potential is employed to prevent electrolysis of the solutions […]

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Measurement of Electric Conductivity

Principle of Salt Bridge:

In salt bridge 2 fixed the resistance R1 and R2 and variable resistance Rv are connected in a branched circuit with the conductance cell having resistance Rx. An AC potential is applied at C and D. An AC potential is employed to prevent electrolysis of the solutions and polarization of electrode in the conductance at Rx. Ordinarily 1000 cycle source. As the frequency arises, capacitance effects become important and are compared for which the variable condenser in paralledl wih R2. the variable resistance by Rv is adjusted until there is no current pain the phone circuit from A to B as indicated by a minimum shadow or shift in the electric eyes.

There A and B are at the same potential and the voltage drop. IRX between BD must b equal to I’R2 the voltage drop between Ad.

IRx = I’R2

Also, Irv= I/R

IRx/Irv= I’R2/ IR1,

Hence,

Rx= I’R2/I’R1 x Irv.

Since R1 and R2 are fixed, the dial on Rv can be calibrated to read Rx the resistance of the test sample or the dial on Rv can be calibrated to read I/Rx that is directly in conductance of the solution.

% salts in soil= EC (mmhos/cm) X 0.064

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Preparation of Soil Test Summaries and Soil Fertility Maps https://agriinfo.in/preparation-of-soil-test-summaries-and-soil-fertility-maps-1806/ https://agriinfo.in/preparation-of-soil-test-summaries-and-soil-fertility-maps-1806/#respond Fri, 06 Apr 2018 23:08:53 +0000 http://agriinfo.in/index.php/2018/04/06/preparation-of-soil-test-summaries-and-soil-fertility-maps/ Preparation of Soil Test Summaries and Soil Fertility Maps Besides their use in making individual fertilizer recommendation to the farmers, soil test data usually are summarized for a respective block and district and on an all India level. Such soil fertility summaries are useful to administrators and planner in deciding the kind and amount of […]

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Preparation of Soil Test Summaries and Soil Fertility Maps

Besides their use in making individual fertilizer recommendation to the farmers, soil test data usually are summarized for a respective block and district and on an all India level. Such soil fertility summaries are useful to administrators and planner in deciding the kind and amount of fertilizer most suitable in each area or district and determining the policy of fertilizer, distribution and consumption in different region. The data also are of use to fertilizer association, fertilizer industries and extension workers in promoting their respective programme and to research workers, particularly from the point of view of changes in fertility levels, conditioned by different fertilizer use or by different soil and crop management practices. Its satisfactory soil test summaries of any unit have been sufficiently large and the samples are representative of the whole area. For district summaries there should be at least one sample for one every 500 acres for block summaries one sample for every 50 acres and for village summaries one sample for every 5 acres.
            
Many soil test summaries include tables giving percentage of the total number of samples falling in different categories of classification. E.g . Low, medium and high.

Parker’s Nutrient Index:

In order to compare the levels of soil fertility of one area with those of another it is necessary to obtain a single value for each nutrient. Here the nutrient index introduced by Parker et. Al. (1951) is useful. The percentage of samples in each of the three classes, low, medium and high is multiplied by 1,2 and 3 respectively. The sum of the figures thus obtained is divided by 100 to give the index or weighted average.

Three Tier System: 

PI = No .of samples (low) X 1 + No of samples (medium) X 2 +
                               No. of samples ( high) X 3
       _________________________________________________
                                Total number of samples

Six Tier System :

No. of samples (V.L) X 0.5 + No. of samples (L) X 1.0 + No. of samples
(Medium) X 1.5 + No of sample (M high) X 2.0 + No. of sample ( High) X
2.5 + No of samples (V. high) X 3.0                                                               

PI=    _______________________________________________________________
                                         Total number of sample

Rammoorthy and Bajaj ( 1969) modified the index classification as low 1.67 , medium 1.67 – 2.33 and high above 2.33 to avoid under weight age to the medium categories.

The use of nutrient indices in preparation of soil summarises and for fertilizer recommendations.

The nutrient indices permit a comparison of soil conditions within a given region, clearly reflects management effects and tell at a glance the nutrient sufficient and deficient area. The indices are used in preparing the nutrient index map which serve many useful purpose.

Following samples should be avoided for to purposes:

1. Unusual area, saline, sodic etc.
2. Only samples from one common crop should be grouped together. E.g. for making recommendation to rice soil test values for rice soils should be taken in to consideration. Preparation of soil fertility maps and fertilizer based on indices: Village wise, Taluka wise, District wise and State wise.

1. Use of concentric circles to depict indices.
2. Use of different colour combination.
3. Use of other symbols used for the purpose by the local soil testing laboratories of government of Maharashtra.

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Soil Air https://agriinfo.in/soil-air-272/ https://agriinfo.in/soil-air-272/#respond Fri, 06 Apr 2018 06:07:04 +0000 http://agriinfo.in/index.php/2018/04/06/soil-air/ Soil Air Soil air is a continuation of the atmospheric air. Unlike the other components, it is constant state of motion from the soil pores into the atmosphere and from the atmosphere into the pore space. This constant movement or circulation of air in the soil mass resulting in the renewal of its component gases […]

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Soil Air

Soil air is a continuation of the atmospheric air. Unlike the other components, it is constant state of motion from the soil pores into the atmosphere and from the atmosphere into the pore space. This constant movement or circulation of air in the soil mass resulting in the renewal of its component gases is known as soil aeration.

Composition of Soil Air: The soil air contains a number of gases of which nitrogen, oxygen, carbon dioxide and water vapour are the most important. Soil air constantly moves from the soil pores into the atmosphere and from the atmosphere into the pore space. Soil air and atmospheric air differ in the compositions. Soil air contains a much greater proportion of carbon dioxide and a lesser amount of oxygen than atmospheric air. At the same time, soil air contains a far great amount of water vapour than atmospheric air. The amount of nitrogen in soil air is almost the same as in the atmosphere.

Composition of soil and atmospheric air

Percentage by volume

 

Nitrogen

Oxygen

Carbon dioxide

Soil Air

79.2

20.6

0.3

Atmospheric Air

79.9

20.97

0.03

Factors Affecting the Composition of Soil Air:

1. Nature and condition of soil: The quantity of oxygen in soil air is less than that in atmospheric air. The amount of oxygen also depends upon the soil depth. The oxygen content of the air in lower layer is usually less than that of the surface soil. This is possibly due to more readily diffusion of the oxygen from the atmosphere into the surface soil than in the subsoil. Light texture soil or sandy soil contains much higher percentage than heavy soil. The concentration of CO2 is usually greater in subsoil probably due to more sluggish aeration in lower layer than in the surface soil.

2. Type of crop: Plant roots require oxygen, which they take from the soil air and deplete the concentration of oxygen in the soil air. Soils on which crops are grown contain more CO2 than fallow lands. The amount of CO2 is usually much greater near the roots of plants than further away. It may be due to respiration by roots.

3. Microbial activity: The microorganisms in soil require oxygen for respiration and they take it from the soil air and thus deplete its concentration in the soil air. Decomposition of organic matter produces CO2 because of increased microbial activity. Hence, soils rich in organic matter contain higher percentage of CO2.

4. Seasonal variation:
The quantity of oxygen is usually higher in dry season than during the monsoon. Because soils are normally drier during the summer months, opportunity for gaseous exchange is greater during this period. This results in relatively high O2 and low CO2 levels. Temperature also influences the CO2 content in the soil air. High temperature during summer season encourages microorganism activity which results in higher production of CO2.

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Soil Colloids https://agriinfo.in/soil-colloids-261/ https://agriinfo.in/soil-colloids-261/#respond Thu, 29 Mar 2018 06:59:02 +0000 http://agriinfo.in/index.php/2018/03/29/soil-colloids/ Soil Colloids The colloidal state refers to a two-phase system in which one material in a very finely divided state is dispersed through second phase.   The examples are: Solid in liquid – Clay in water (dispersion of clay in water) Liquid in gas -Fog or clouds in atmosphere The clay fraction of the soil […]

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Soil Colloids

The colloidal state refers to a two-phase system in which one material in a very finely divided state is dispersed through second phase.
 
The examples are:

Solid in liquid – Clay in water (dispersion of clay in water)
Liquid in gas -Fog or clouds in atmosphere

The clay fraction of the soil contains particles less than 0.002 mm in size. Particles less than 0.001 mm size possess colloidal properties and are known as soil colloids.

General Properties of Soil Colloids

1. Size: The most important common property of inorganic and organic colloids is their extremely small size. They are too small to be seen with an ordinary light microscope. Only with an electron microscope they can be seen. Most are smaller than 2 micrometers in diameter.

2. Surface area: Because of their small size, all soil colloids expose a large external surface per unit mass. The external surface area of 1 g of colloidal clay is at least 1000 times that of 1 g of coarse sand. Some colloids, especially certain silicate clays have extensive internal surfaces as well. These internal surfaces occur between plate like crystal units that make up each particle and often greatly exceed the external surface area. The total surface area of soil colloids ranges from 10 m2/g for clays with only external surfaces to more than 800 m2/g for clays with extensive internal surfaces. The colloid surface area in the upper 15 cm of a hectare of a clay soil could be as high 700,000 km2/g

3. Surface charges: Soil colloidal surfaces, both external and internal characteristically carry negative and/or positive charges. For most soil colloids, electro negative charges predominate. Soil colloids both organic and inorganic when suspended in water, carry a negative electric charge. When an electric current is passed through a suspension of soil colloidal particles they migrate to anode, the positive electrode indicating that they carry a negative charge. The magnitude of the charge is known as zeta potential. The presence and intensity of the particle charge influence the attraction and repulsion of the particles towards each other, there by influencing both physical and chemical properties.

The negative electrical charge on clays comes from
i) Ionizable hydrogen ions and
ii) Isomorphism substitution.
 
i) Ionizable hydrogen ions: Ionizable hydrogen ions are hydrogen from hydroxyl ions on clay surfaces. The -Al-OH or -Si-OH portion of the clay ionizes the H and leaves an unneutralized negative charge on the oxygen (-Al-O- or – Si-O). The extent of ionized hydrogen depends on solution pH; more ionization occurs in more alkaline (basic) solutions.
 
ii) Isomorphous substitution: The second source of charge on clay particles is due to the substitution of one ion for another of similar size and often with lower positive valence. In clay structures, certain ions fit into certain mineral lattice sites because of their convenient size and charge. Dominantly, clays have Si4+ in tetrahedral sites and A13+ in octahedral sites. Other ions present in large amounts during clay crystallization can replace some of the A13+ and Si4+ cations. Substitutions that are common are the Si4+ replaced by A13+, and even more extensive replacement of A13+ by one or more of these: Fe3+, Fe2+, Mg2+ or Zn2+ Since the total negative charge from the anions (the oxygen) remains unchanged, the lower positive charge because of substitution results in an excess negative charge at that location in the structure.

4. Adsorption of cations: As soil colloids possess negative charge they attract the ions of an opposite charge to the colloidal surfaces. They attract hundreds of positively charged ions or cation such as H+, A13+ Ca2+ , and Mg2+. This gives rise to an ionic double layer.

The process, called Isomorphous substitution and the colloidal particle constitutes the inner ionic layer, being essentially huge anions; with both, external and internal layers that are negative in charge. The outer layer is made up of a swarm of rather loosely held (adsorbed) cations attracted to the negatively charged surfaces. Thus a colloidal particle is accompanied by a swarm of cations that are adsorbed or held on the particle surfaces.

5. Adsorption of water: In addition to the adsorbed cations, a large number of water molecules are associated with soil colloidal particles. Some are attracted to the adsorbed cations, each of which is hydrated; others are held in the internal surfaces of the colloidal particles. These water molecules play a critical role in determining both the physical and chemical properties of soil.

5. Cohesion: Cohesion is the phenomenon of sticking together of colloidal particles that are of similar nature. Cohesion indicates the tendency of clay particles to stick together. This tendency is primarily due to the attraction of the clay particles for the water molecules held between them. When colloidal substances are wetted, water first adheres to the particles and then brings about cohesion between two or more adjacent colloidal particles.

6. Adhesion: Adhesion refers to the phenomenon of colloidal particles sticking to other substances. It is the sticking of colloida1 materials to the surface of any other body or substance with which it comes in contact.

7. Swelling and shrinkage: Some clay (soil colloids) such as smectites swell when wet and shrink when dry. After a prolonged dry spell, soils high in smectites (e.g. Vertisols) often are crises-crossed by wide, deep cracks, which at first allow rain to penetrate rapidly. Later, because of swelling, such soil is likely to close up and become much more impervious than one dominated by kaolinite, chlorite, or fine grained micas. Vermiculite is intermediate in its swelling and shrinking characteristics.

8. Dispersion and flocculation: As long as the colloidal particles remain charged, they repel each other and the suspension remains stable. If on any account they loose their charge, or if the magnitude of the charge is reduced, the particles coalesce, form flocs or loose aggregates, and settle out. This phenomenon of coalescence and formation of flocs is known as flocculation. The reverse process of the breaking up of flocs into individual particles is known as deflocculation or dispersion.

9. Brownian movement: When a suspension of colloidal particles is examined under a microscope the particles seem to oscillate. The oscillation is due to the collision of colloidal particles or molecules with those of the liquid in which they are suspended. Soil colloidal particles with those of water in which they are suspended are always in a constant state of motion. The smaller the particle, the more rapid is its movement.

10. Non permeability: Colloids, as opposed to crystalloid, are unable to pass through a semi-permeable membrane. Even though the colloidal particles are extremely small, they are bigger than molecules of crystalloid dissolved in water. The membrane allows the passage of water and of the dissolved substance through its pores, but retains the colloidal particles.

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Soil Water Potential https://agriinfo.in/soil-water-potential-266/ https://agriinfo.in/soil-water-potential-266/#respond Wed, 28 Mar 2018 06:09:12 +0000 http://agriinfo.in/index.php/2018/03/28/soil-water-potential/ Soil Water Potential The retention and movement of water in soils, its uptake and translocation in plants and its loss to the atmosphere are all energy related phenomenon. The more strongly water is held in the soil the greater is the heat (energy) required. In other words, if water is to be removed from a […]

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Soil Water Potential

The retention and movement of water in soils, its uptake and translocation in plants and its loss to the atmosphere are all energy related phenomenon. The more strongly water is held in the soil the greater is the heat (energy) required. In other words, if water is to be removed from a moist soil, work has to be done against adsorptive forces. Conversely, when water is adsorbed by the soil, a negative amount of work is done. The movement is from a zone where the free energy of water is high (standing water table} to one where the free energy is low (a dry soil). This is called soil water energy concept.

Free energy of soil solids for water is affected by

i) Matric (solid) force i.e., the attraction of the soil solids for water (adsorption} which markedly reduces the free energy (movement} of the adsorbed water molecules.

ii) Osmotic force i.e., the attraction of ions and other solutes for water to reduce the free energy of soil solution.

Matric and Osmotic potentials are negative and reduce the free energy level of the soil water. These negative potentials are referred as suction or tension.

iii) Force of gravity: This acts on soil water, the attraction is towards the earth’s center, which tends to pull the water down ward. This force is always positive. The difference between the energy states of soil water and pure free water is known as soil water potential. Total water potential (Pt} is the sum of the contributions of gravitational potential (Pg), matric potential (Pm) and the Osmotic potential or solute potential (Po).

Pt = Pg + Pm + Po

Potential represents the difference in free energy levels of pure water and of soil water. The soil water is affected by the force of gravity, presence of soil solid (matric) and of solutes.

Methods of expressing suctions: There are two units to express differences in energy levels of soil water.

i) PF Scale: The free energy is measured in terms of the height of a column of water required to produce necessary suction or pressure difference at a particular soil moisture level. The pF, therefore, represents the logarithm of the height of water column (cm) to give the necessary suction.

ii) Atmospheres or Bars: It is another common mean of expressing suction. Atmosphere is the average air pressure at sea level. If the suction is very low as occurs in the case of a wet soil containing the maximum amount of water that it can hold, the pressure difference is of the order of about 0.01 atmospheres or 1 PF equivalent to a column of water 10 cm in height. Similarly, if the pressure difference is 0.1 atmosphere the PF will be 20. Soil moisture constants can be expressed in term of PF values. A soil that is saturated with water has PF 0 while an oven dry soil has a PF 7.

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Electrical Conductivity https://agriinfo.in/electrical-conductivity-1785/ https://agriinfo.in/electrical-conductivity-1785/#respond Fri, 16 Mar 2018 12:38:44 +0000 http://agriinfo.in/index.php/2018/03/16/electrical-conductivity/ Electrical Conductivity All soils contains varying amount of salts in solution form as carbonate bicarbonates, sulphate, chlorides etc. determination of these salts in soil solution is very important in connection with interpretation of their harmful effects, on plant growth , seed germination etc. The electrical conductivity of water extract of soil gives a measure of […]

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Electrical Conductivity

All soils contains varying amount of salts in solution form as carbonate bicarbonates, sulphate, chlorides etc. determination of these salts in soil solution is very important in connection with interpretation of their harmful effects, on plant growth , seed germination etc. The electrical conductivity of water extract of soil gives a measure of these salts in the soil. Pure water as it doesn’t contains salts is a poor conductor of electric current where as water containing ample amount of salts conducts electric current approximately in proportion of amounts of salts.

Electrical conductivity or electrical conductance is the reciprocal of resistance ( R) in ohms.

C= I /R

Where, I= Current in atmosphere, R= Resistance in Ohms.

Conductance is expresses as millions (1000 times mhos)

Specific Conductance:

Specific conductance ( L) of a solution is the conductance that would be measured at 25 0C between electrode 1 cm2 cross section and placed one cm apart and may be visualized as the conductance across a cm3 or mhos/cm. specific conductance may e measured with a cell of various dimension by means of cell constant. Because of number obtained expressing specific conductance of the solution are generally small it has been convenient to express specific conductance as millimhos/cm (1000 times mhos/cm,) and this unit is adopted widely.

1. AC potential application
2. Potentiometer resistance
3. Resistance cell
4. Ear phone or electric eye.

Significance of Electrical Conductivity:

The EC of the soil has direct relationship with growth of different crops.
Rating chart of soil EC:
Where, less than 1 dSm-1 Normal.

1-2 dSm-1: Critical for germination
2-3 dSm-1: Critical for salt sensitive crops.
Above 3.0: Injurious to most of crops.

Factors Affecting the Electrical Conductivity:

Temperature:

The EC meter is standardize at 25 0C and rise or decrease in temperature of solution needs correction. The correction factor should be multiplied with observed values.

EC at 25 0C = EC t X ft.

ECt = EC at temperature t, ft= correction factor at temperature.

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