practical manual for soil chemistry, soil fertility
Post on 07-Jan-2017
Embed Size (px)
SOIL CHEMISTRY, SOIL FERTILITY AND
Dr. R. VERMA
Dr. K.K. SHARMA
DEPARTMENT OF SOIL SCIENCE AND AGRICULTURAL CHEMISTRY
S.K.N. COLLEGE OF AGRICULTURE
(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
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
12. Determination of Potassium in plant
(Bhargava and Raghupathi, 1993)
13. Rapid plant tissue test for NPK (Cook and
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.
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
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
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.
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
Problem-1: Calculate the normality of a solution containing 1.70 g of AgNO3 per 100 ml of the
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
Constant boiling Hydrochloric Acid
Potassium acid iodate
(ii) Bases: Sodium carbonate
(iii) Oxidising agents: Potassium dichromate
(iv) Reducing agents: Sodium Oxalate
(v) Others: Sodium 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.