class12

1. ANALYSIS OF SOIL SAMPLES

2. Introduction
Soils are a complex combination of organic
matter, gasses, minerals, organisms, and liquids, that altogether
support our life. Earth's body of soil is called the pedosphere,
which has four important functions. It is a medium for plant
growth, it stores water, supplies, and purifies, it is a modifier of
the earth's atmosphere, it is a habitat for organisms. Soil is one
of the principal substrata of life on earth, which is a participant
in the cycling of carbon and other elements through the global
ecosystem. To study the texture of soil samples and a few more
go through the experiment below.
Soils are a complex combination of various organic matter,
gasses, minerals, organisms, and liquids, all of which support
our life. The Earth's body of soil is known as the pedosphere,
which has four important functions:
Soil is used for the growth of plants. Soil helps to store water.
Soil is said to be the modifier of the earth's atmosphere and also
is a habitat for organisms.
Soil analysis is a set of various chemical processes that
determine the amount of available plant nutrients in the soil, but
also the chemical, physical and biological soil properties
important for plant nutrition. Chemical soil analysis determines
the content of plant nutrients; nitrogen (N), phosphorus (P2O5),
potassium (K 2 O), pH, humus content, total CaCO3, available

3. lime, organic matter, total sulphur (S), Sodium, micro nutrients,
and other physical characteristics (capacity, permeability,
density, pH value).
Reasons for doing soil analysis
1. To determine the level of availability of nutrients or the need
for its introduction.
2. To predict the increase in yields and profitability of
fertilization (poor soils do not always provide yield increase
due to fertilization because of possible limiting factors).
3. To provide the basis for calculating the required fertilizing of
each crop.
4. To evaluate the status of each nutrient element and
simultaneously determine how to manage the nutrients.
5. To improve economic planning and decision making for a
farmer.
According to the content of nutrients in the soil obtained by soil
analysis and the requirements of a particular crop, it is easier to
determine the amount of required fertilizers to achieve high and
quality yields. High quality soil analysis is the basis of planning
of fertilizing (what fertilizers to use, what amount and when to
use) and thus the quality of the entire production cycle, which
results in a high quality and yield and better farm managerial
decisions.
When is the best time to do a soil analysis?

4. Taking soil samples for analysis is greatly advised to be done
after harvesting of crops and before any fertilizing, at optimum
soil moisture. The soil must not be depressed, along the edge of
the farm or where mineral fertilizers are unevenly scattered,
because the sample will not be representative of the whole field
and the resulting data will not be a reflection of the real status of
the soil in the entire field. In the case of permanent crops such as
orchards and vineyards analysis is carried out periodically.
How to properly perform sampling
Samples are taken using an auger, but can also be taken using a
shovel.
Important factors to put into consideration when taking soil
samples:
Depth of sampling.
Depth of sampling is critical because tillage and nutrient
mobility in the soil can influence nutrient levels in different soil
zones. Sampling depth depends on the crop, cultural practices,
tillage depth and the nutrients to be analyzed.

5. Theory
Soil is the upper humus, containing a layer of the earth,
consisting of rock and mineral particles mixed with decayed
organic matter. Soil sustains plant life and contains numerous
living organisms. Soil, along with air and water, is one of the
three most important natural resources, which we cannot live
without. A productive soil contains approximately 46% mineral
matter, 4% organic matter, 25 % water and 25% air.
An approximate composition of soil shown below
Let’s see the physical characteristics of soil.
The physical characteristics of a soil are due to the size of its
soil particles. Soils are classified according to their particle size
as follows:

6. Texture of Soil
Soil texture is an important physical characteristic of soil which
is used in both the field and laboratory to determine classes for
soils based on their physical texture. The soil texture depends
upon the proportion of the constituent solid particles of different
sizes. The terms sand, silt, and clay refer to particle size; sand is
the largest and clay is the smallest. The size of sand particles is
0.05–2 mm, silt particles are 0.002–0.05 mm, and clay is smaller
than 0.002 mm.
The term loam refers to a soil with a combination of sand, silt,
and clay sized particles. Each texture corresponds to specific
percentages of sand, silt, or clay.
The soil texture triangle is a tool used to visualize and
understand the meaning of soil texture names. The below figure
shows each of the 12 textural classes based on the percentage of
sand, silt, and clay in each.

7. If we know the sand, silt, and clay percentages of a soil, then the
textural class can be identified from the textural triangle. Say for
an example soil consists of 12% clay, 55% sand and 31% silt,
we will see how to determine the textural class of the soil.
Here, the sample soil has 12% clay, so draw a line
corresponding to percent clay. Similarly draw the lines for
percent sand (55%) and percent silt (31%). The lines which
intersect indicate the soil type we have. From the above sample,

8. soil consists of 12% clay, 55% sand, and 31% silt; hence the soil
type is sandy loam.
PH of Soil
The chemical property of the soil depends upon the presence of
different types of nutrients and pH of the soil. The soil pH is an
indication of acidity or alkalinity of soils. The soil pH is
important in determining the availability of soil minerals.
Different plants have differing optimum soil pH requirements.

9. The majority of plants prefer a pH of around 6 to 7, which is
very slightly acidic.
Water Holding Capacity of Soil
One of the main functions of soil is to retain water and make it
available for the plant to access. All of the water in the soil is
not available to plants. The amount of water available to plants
is therefore determined by the number and size of the soil’s pore
spaces. Water holding capacity of the soil is the amount of water
held by the capillary spaces of the soil after the percolation of
gravitational water into the deeper layers. Fine sandy loam, silt
loam and silty clay loam soil store the largest amount of water,
whereas sand, loamy sand and sandy loam have limited water
storage capacity.

10. Aim
To study soil samples from two different sites and analyses their
properties such as texture, moisture content, water-retaining
capacity and ph. Also, the study aims to correlate the plants
found in such soil.
Materials required
For this experiment, soil collected from
the roadside and garden are to be used. Apart from the soil
samples, other required materials are:
 Tile.
 Beaker.
 Funnel.
 Burner.
 Dropper.
 Crucibles
 Petri dish.
 Glass rods.
 Test tubes.
 Wire gauze.
 Filter Paper.
 Distilled water.
 Mortar and Pestle.
 pH paper booklet.
 Measuring cylinder.
 Universal pH indicator solution.

11.  Tin Box with a perforated bottom.
 Weighing scale or electronic balance.
Procedure
The following are the steps taken to prepare the soil samples for
experiments to analyses various properties.
To study the pH of the Soil Samples
 Take the collected roadside soil and garden soil into two
different beakers containing water.
 Mix the test tubes with the soil solution slowly
 Now into a clean and dried two test-tube, arrange a funnel
spread covered with a filter paper.
 Now gently pour the soil solutions into the test tubes
separately.
 Let the water to completely filter off from the filter paper.
 Take the collected filtrates (soil) into the two different test
tubes for testing the pH values.
 With the help of a dropper, add a few drops of universal
indicator solution to both the test tubes.
 Observe the changes.
Observation
When the universal pH indicator is added to the test tube
containing the soil solution, the color changes. These color
changes can be tracked using the pH color chart. Roadside soil
has a pH level of 7 while garden soil has a pH level of 6. Most
crops grow between pH levels of 6.0 and 7.0.

12. To study the texture of Soil Samples
 Collect 50 gm of any soil sample in a beaker.
 Take a clean and moisture-free measuring cylinder and the
collected soil sample into it.
 Now pour little water into the same measuring cylinder and
shake well.
 Keep the apparatus undisturbed for a few minutes and wait
for the particles to settle down.
 After a while, observe the changes in the measuring
cylinder.
 The soil particles in the measuring cylinder will start to
settle down in layers.
 Record the thickness of these layers.
Observation
Using a soil textural triangle, draw the corresponding percentage
of the soil components (silt, clay & sand). The resultant lines
which, intersect indicate the type of soil.
To study the Moisture Content of Soil Samples
 Collect two different soil sample in two different crucibles.
 Weight the soil samples using a weighing balance.
 Make a note of the reading.
 Place the two crucibles over the Bunsen burner and heat it
until it becomes dry.
 Now again weigh the soil samples and record the weight of
the dry soil samples.

13.  The samples are now ready to be used to determine the
moisture content of the soil.
 Calculate the two different readings to know the moisture
content of soil samples.
Observation
The sample where the initial and final weight is the larger
indicates a higher moisture content. Lower values mean the
moisture content is quite low.
To study the Water Holding Capacity of Soil Samples
 Collect a garden soil sample in a beaker.
 To a clean and dried mortar pestle add the collected soil
sample.
 Now slowly grind the soil sample into a fine powder using
a pestle.
 Place a filter paper at the bottom of the tin box.
 Weigh the entire contents of the tin box.
 Now, add the powered soil into the tin box.
 Use the glass rod to press and tap the box, so that the soil is
uniformly layered.
 Now, the weight of the tin box is measured and to be
recorded.
 Next, take two glass rods and place them parallel to each
other. Ensure that the distance between the two is not long.
 Position the tin on the two glass rods in such a way that the
bottom is in contact with the water.

14.  The complete setup should be left undisturbed until the
water seeps through the upper surface of the soil.
 Now, remove the tin and allow all the water to flow out
from the bottom.
 Wait until no more water percolates from the tin.
 Now wipe the bottom dry and use the weighing machine to
note down the weight.
 Calculate the two different readings to know the water
holding capacity of the given soil samples.
Observation
The water holding capacity of the soil is determined by the
quantity of water held by the soil sample versus the dry weight
of the soil sample.
Result and conclusion
Compare % water holding capacity of soil collected from
different habitat conditions. The variation in water holding
capacity is due to varying proportion of sand, silt and clay in the
soil of different habitats. Soil with very high proportion of sand
have very low water holding capacity due to large pore spaces

15. between the particles which enables the water to percolate freely
into deeper layers leaving upper layers practically dry. In clay
soil, due to very small size of the pore spaces (fine capillaries)
the water is retained in the capillary spaces as capillary water. In
this soil the water does not percolate freely. Soil with more or
less equal proportion of sand, silt and clay (loam soil) combines
the properties of sand and clay and therefore has optimum water
holding capacity and optimum soil-air for root growth.
Based on the pH values obtained, categories the samples into
acidic, basic, neutral type