practical manual for soil chemistry, soil fertility


Post on 07-Jan-2017




7 download

Embed Size (px)






    (S.CHEM. 4121)


    Dr. R. VERMA

    Dr. K.K. SHARMA




    (Shri Karan Narendra Agriculture University, Jobner)

    Campus: Jobner 303 329, Distt. Jaipur





    The main aim of preparing this practical manual is to provide simple guide

    line in lucid and concise manner to under graduate students while performing

    their practical excises. It is primarily designed to cover the syllabus of soil

    chemistry, soil fertility and nutrient management. (SCHEM 4121). This manual

    has been compiled from the point of view of the students requirement and to give

    them thorough training in the principles and methods of soil and plant along with

    calculations and interpretation of the results. This manual contains details about

    concept, instrumentation, and principle of instruments soil analysis for available

    N, P, K, S, Fe, and Zn in soil, rapid plant tissue test for NPK and analysis of

    NPK in plants.

    We are thankful to Dr. B.L. Yadav, Professor and Head, Deptt. of Soil

    Science and Agricultural Chemistry, S.K.N. College of Agriculture, Jobner for

    his encouragement for preparation and publishing of this manual.

    It is hoped that teachers imparting this undergraduate course of soil science

    will find the manual useful. Any suggestion for the improvement will be highly


    Place: Deptt. Of Soil Science & Agril. Chemistry.

    S.K.N. College of Agriculture, Jobner

    January, 2014 Authors

  • 3


    S.No. Particulars Page Date Signature of


    1. Concepts of chemical analysis 1-5

    2. Instrumentation in the laboratory 6-7

    3. Basic principles of the instruments 8-11

    4. Determination of available nitrogen in soils

    (Subbiah and Asija, 1956)


    5. Determination of available phosphorus in

    soil (Olsen et al., 1954)


    6. Determination of available potassium in

    soil (Metson, 1956)


    7. Determination of available sulphur in soils

    (Chesnin and Yien, 1950)


    8. Estimation of available (DTPA

    extractable) iron, manganese copper and

    zinc in soil (Lindsay and Norwell, 1978)


    9. Determination of nitrogen in plant (Snell

    and Snell, 1949)


    10. Determination of Phosphorus in plant

    (Jackson, 1973)


    12. Determination of Potassium in plant

    (Bhargava and Raghupathi, 1993)


    13. Rapid plant tissue test for NPK (Cook and

    Wheeler, 1978)


  • 4


    Object: Concepts of chemical analysis

    1.1 Analytical reagents:-

    Chemical reagents are supplied in different grades and each grade has a distinct purpose

    and range of uses. The purest grade is analytical reagent (AR), the second is laboratory reagent

    (I.R.), the third is guaranteed reagent (GR) and fourth is technical grade. Second and third form

    of reagents, have a lot of impurities of micronutrients. Therefore, for the determination of

    micronutrients, AR grade reagent should be used.

    1.2 Concentrated acids and bases:-

    Strength of acids and bases are expressed on the basis of their normality. The strength of

    some concentrated acids and bases are presented in table 1.

    Table-1. Strength of concentrated acids and basis

    Reagent Concentration Approximate specific gravity

    Normality Per cent by weight

    HCl 11.6 37-38 1.19

    H2SO4 35-36 97-100 1.84

    HOAC 17.5 99.5 1.13

    HNO3 16 70-71 1.42

    HCLO4 9-11.6 60-70 1.51-1.67

    H3PO4 45 85 1.71

    NH4OH 15 28-29 0-90

    HOH 55 100 1.00

    1.3 Distilled water:-

    Distilled water is always used in chemical analysis. The quality of distilled water varies

    from single distilled to double or triple depending upon the requirement of analytical

    technique(s) e.g. double distilled water (glass distilled) is always recommended for micronutrient

    and heavy metal analysis.

  • 5

    1.4 Filter Paper:-

    Several types of filter papers are available in the market depending on their ash content,

    porosity and elemental composition. The commonly used filter papers are Whatman, Munktells,

    Schleicher and Schuell. These filter papers are available in different number(s) ranging from No.

    1 to 60. The pore size decreases with their increasing numbers.

    1.5 Preparation of cleaning solution

    1.5.1 Chromic acid cleaning solution:-

    Chromic-sulphuric acid cleaning solution is very important for final cleaning of

    glassware. Visible materials and organic solvents should be removed with water before using

    cleaning solution. The cleaning solution can be prepared either by dissolving 80g of K2Cr2O2 or

    Na2Cr2O2 in about 300 ml of water (with heating) in a 2000 ml of corning/ borosil beaker. To the

    beaker, add one litre of technical/commercial grade H2SO4 Considerable red chromic oxide

    (Cr2O3) precipitates.


    A cleaning solution that does not involve Cr2O3 crystallization is made by dissolving 5g

    of K2Cr2O2 in a minimum of water and add one litre of technical/ commercial grade H2SO4 to

    this solution.

    1.5.2 Aqua regia:-

    Another cleaning solution used is aque regia. The aqua regia is prepared by mixing

    concentrated HCl and H2SO4 in a rato of 3:1.

    1.6 Laboratory apparatus

    1.6.1 Glass wares:-

    Corning/borosil glass that contains arsenic is preferred for most of the laboratory


    1.6.2 Sieve openings v/s meshes per inch:-

    The size of sieve openings in mm approximately based on the assumption that opening is

    0.63 of the meshes interval. Hence

    mm per opening = 16

    Meshes per inch

    For example, a 100-mesh screen has opening of 0.16 mm.

  • 6

    1.7 Preparation of standard solutions/expression of solution concentration

    1.7.1 Molar solution/ Molarity (M):-

    A one molar solution contains one mole or one gram molecular weight of a chemical

    substance in one litre of the solution. This expression is written as:

    Molarity = No. of moles per litre

    No. of moles = .()

    Mol . wt .

    Problem-1: Calculate the molarity of a 100 mi of a solution containing 0.32 g of NaOH

    Problem-2: Calculate the weight of NaOH in 5 litres of 0.65 M NaOH.

    1.7.2 Molal solution/ Molality (m):-

    The molality of a solution is the number of moles per 1000 g of the solvent. Molal

    solutions are prepared by dissolving gram mole(s) of chemical substance in 1000 g of the


    Molality = No. of moles per 1000 g of the solvent.

    Problem-1: Calculate the molality of a solution which contains 10% K2CO3 by weight.

    Problem-2: Calculate the weight KOH in 1056 g of 1 molal KOH solution.

    1.7.3 Normal solution/ Normality (N):-

    The chemical reactions occur on chemical equivalent basis. Thus, one gram equivalent

    weight of chemical compound is equivalent to one gram equivalent weight of the other. When

    one gram equivalent weight is dissolved in a solvent and volume made 1000 ml, the solution is

    referred to as normal solution and concept is called normality (N).

    Normality = No. of g equivalent per litre

    = Mol . wt .


    Gram equivalent weight = Weight in gram

    Equivalent weight

    Problem-1: Calculate the normality of a solution containing 1.70 g of AgNO3 per 100 ml of the


  • 7

    Problem-2: Calculate the weight of HCl in 2 litres of 0.1 N HCl.

    1.7.4 The Milliequivalent weight:-

    When equivalent weight is expressed in milligrams i.e.

    Milliequivalent weight = Equivalent weight

    1000 x 1000

    Number of milliequivalents = Normality x 1000

    Milliequivalent (meq/litre) = ppm (parts per million )

    Eq .wt .(Equivalent weight )

    ppm = meq./litre x Eq.wt.

    ppm to % = ppm


    1.8 Standardization of solutions:-

    The exact standardization of solution is done with primary standard solution of

    approximate strength. Most commonly used primary standard solutions are:

    (i) Acids: Potassium hydrogen phthalate

    Benzoie acid

    Constant boiling Hydrochloric Acid

    Sulphamic acid

    Potassium acid iodate

    (ii) Bases: Sodium carbonate

    Mercuric oxide


    (iii) Oxidising agents: Potassium dichromate

    Potassium bromate

    Potassium iodate

    (iv) Reducing agents: Sodium Oxalate

    Arsenious oxide

    Iron metal

    Potassium ferrocynide

    (v) Others: Sodium chloride

  • 8

    Potassium chloride

    1.9 Preparation of standard solutions

    1.9.1 Standard solutions of acids:-

    The standard acid solutions can be prepared by using the equation given below

    V1N1 = V2N2

    where V1 = Volume of concentrated acid required

    N1 = Normality of the concentrated acid

    V2 = Total volume of the acid to be prepared

    N2 = Normality of the acid to be prepared

    Problem-1: Preparation of 100 ml of 4 N HCl solution. From concentrated.


View more >