Soil Analysis

Lab#7: Soil Analysis
Asian University For Women
BIOL/ENVS 3003: ECOLOGY (Lab)
Fall 2022
Syed Mohammad Lokman
Instructor
Asian University for Women

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BIOL/ENVS 3003: ECOLOGY (Lab) Syed Mohammad Lokman (syed.lokman@auw.edu.bd)
● Students will understand the physical
properties of soil.
● Students will understand texture, moisture,
pH and water holding capacity of soil.
Learning Outcomes:

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● In general, Soil, also commonly referred to as earth or
dirt, is a mixture of organic matter, minerals, gases,
liquids, and organisms that together support life.
● A typical soil is about 50% solids (45% mineral and
5% organic matter), and 50% voids (or pores) of
which half is occupied by water and half by gas.
*Soil Organic Matter (SOM)
Soil

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Soil Profile

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Soil Profile
● Given sufficient time, an undifferentiated soil will evolve a soil
profile which consists of two or more layers, referred to as soil
horizons.
● Most agricultural soils are grouped into four main ‘master’
horizons: O, A, B, and C.
● These differ in one or more properties such as in their texture,
structure, density, porosity, consistency, temperature, color, and
reactivity.

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● The O horizon is an organic layer above the mineral soil that consists of fresh or
partially decomposed organic material and is most common in forested soils.
● The A horizon is the mineral soil surface layer and is the horizon most impacted
by biological and human activity. It usually has the highest percentage of SOM,
which often results in it being darker in color than the rest of the profile.
● The B horizon is the horizon of accumulation. Material from the A horizon, such
as clay and carbonates, leach downward and accumulate in the B horizon.
● The C horizon represents the weathered parent material.
● Bedrock (designated by R) or a deep accumulation of materials deposited by
wind, water, glaciers or gravity often lies below the C horizon.
Soil Profile

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● Various subcategories may occur within these horizons and are designated by a
lowercase letter following the master horizon capital letter (e.g., Ap or Bt).
● Below the A horizon will be either an E horizon, usually not present in grassland/
agricultural soils, or a B horizon, the horizon of accumulation.
● Not all soils will have every horizon or subhorizon present. For instance, a
poorly developed soil may lack a strongly defined B horizon or highly eroded lands
may have a thin, or nonexistent, A horizon.
● The biological influences on soil properties are strongest near the surface, though
the geochemical influences on soil properties increase with depth.
Soil Profile

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Soil Analysis
1. To Study the Texture of the Soil
2. To Study Moisture Content of Soil
3. To Study pH of Different Types of Soil
4. To Study Water Holding Capacity of Soil

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1. To Study the
Texture of the Soil
Soil Analysis

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● Soil texture 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 soil texture triangle is a tool used to visualise and
understand the meaning of soil texture names.

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% Sand
% Clay
% Slit

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● If we know the sand, silt, and clay percentages
of a soil, then the textural class can be identified
from the textural triangle.
● For an example, if a soil sample consists of 30%
clay, 55% sand and 15% silt:
○ From the intersection of lines in the soil
texture triangle; We can say the soil type is
sandy clay loam.

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● A clay soil is referred to as a fine-textured soil whereas a sandy soil is a coarse
textured soil.
● Numerous soil properties are influenced by texture including: Drainage, Water
holding capacity, Aeration, Susceptibility to erosion, Organic matter content, Cation
exchange capacity (CEC), pH buffering capacity.
● Soil texture determines the rate at which water drains through a saturated soil; water
moves more freely through sandy soils than it does through clayey soils. Once field
capacity is reached, soil texture also influences how much water is available to the
plant; clay soils have a greater water holding capacity than sandy soils.
Importance of Soil Texture

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● A soil with a high percentage of silt and clay particles has a greater erodibility
than a sandy soil under the same conditions.
● Organic matter breaks down faster in sandy soils than in fine-textured soils.
● The pH buffering capacity of a soil (its ability to resist pH change upon lime
addition), is also largely based on clay and organic matter content.
Importance of Soil Texture

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2. To Study Moisture
Content of Soil
Soil Analysis

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2. To Study Moisture Content of Soil
Procedure:
1. Take watch glass containing soil.
2. Weigh the watch glass with soil sample on a weighing
balance. Record it as Initial Weight (Wi).
3. Oven dry the sample at 105℃ until constant weight is
obtained. Record fully dried weight as Dry Weight (Wd).
4. Calculate the Moisture Content by using following formula:
Oven dry

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3. To Study pH of
Different Types of Soil
Soil Analysis

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Global variation in soil pH. Red = acidic soil. Yellow = neutral soil.
Blue = alkaline soil. Black = no data.
● The soil pH determine the availability
of soil minerals.
● Different plants have differing
optimum soil pH requirements.
● The majority of plants prefer a pH of
around 6 to 7, which is very slightly
acidic.
● A pH of 7.0 is considered neutral. An
acid soil has a pH value below 7.0
and above 7.0 the soil is alkaline.

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Procedure:
A. Let’s first prepare the soil solution.
1. Take soil from the watch glass and dissolve it into
the beaker containing water to make soil solution.
2. Take a funnel, place a filter paper in it and keep it on
a test tube.
3. Take soil solution and filter the solution through the
filter paper and collect the filtrates in a test tube.
4. The soil solution is now ready for testing pH.

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B.1. Using pH Paper:
1. Take a pH paper.
2. Using a dropper, take some soil solution from the
test tube. And put 1 to 2 drops of solution on the
pH strip on the tile.
3. Wait for some time for the pH paper strip to dry.
4. Note the colour and compare with the colour chart
given on the broad range indicator paper and get a
rough estimate of pH of the sample solutions.
B. 2. Using Universal Indicator Solution
1. Using a dropper, take some universal
indicator solution.
2. Put 5 drops of indicator solution into the
test tube that contain soil water sample.
3. Note the colour developed and compare it
with the colour chart.

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4. To Study the
Texture of the Soil
Soil Analysis

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4. Water Holding Capacity of Soil
● Water Holding Capacity of soil is 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 (the movement and filtering of fluids through porous materials)
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.

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Procedure:
1. Take 25 gm (Ws) of the sample soil in a watch glass.
2. Take a funnel, place a filter paper in it and keep it on a
measuring cylinder.
3. Transfer the soil from watch glass to filter paper.
4. Add 50 mL (W1) of distilled water to the filter paper.
5. The water filtration will start very soon. Wait 25-30 min
until the filtration is getting stopped fully.

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Calculation:
1. Record the level of water (W2) passed through the filter. Using the
below formula, calculate the water holding capacity of the soil:
Volume of water retained (Wr) = W1 - W2
Water Holding Capacity of Soil (WHCs) = [(Wr/Ws) ✕100] %

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Thank You!

Soil Analysis

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