soil texture and moisture

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Soil Texture and Moisture
Definition
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
Soil texture is defined as
the relative proportion of
sand, silt and clay.
The ranges of diameters of
the three separates are:
sand (2.0- 0.05 mm), silt
(0.05-.002 mm), and clay
(<0.002 mm).
http://science.kennesaw.edu/~jdirn
ber/limno/LecPhy/SiltSandClay.jpg
Feel test – Rub some moist soil
between fingers.
Sand feels gritty.
Silt feels smooth.
Clays feel sticky.
Diameter Ranges
Soil Fraction
Soil Separate
Diameter (mm)
Sand
Very coarse sand
1 to 2
Coarse sand
0.5 to 1
Medium sand
0.25 to 0.5
Fine sand
0.1 to 0.25
Very fine sand
0.05 to 0.1
Silt
Silt
0.002 to 0.05
Clay
Clay
< 0.002
Importance of Soil Texture
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Soil texture is one of the most important
properties of a soil, and it greatly affects land
use and management.
It affects the amount of water and nutrients that
a soil can hold and supply to plants.
Soil physical properties such as structure, and
movement of air and water through the soil are
affected by texture.
What affects soil texture?

The parent material, as modified by weathering
and soil- forming processes, determines a soil
horizon’s texture.
Residuum
(or bedrock)
Marine
Sediments
http://soils.ag.uidaho.edu/so
ilorders/aridisols_07.htm
http://soils.ag.uidaho.edu/so
ilorders/ultisols_01.htm
Can soil texture be altered?
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Texture is a relatively
permanent physical property
under natural conditions,
and, for most agricultural or
forestry uses, it is not
practical to change soil
texture.
In intensely managed
systems texture can be
changed by adding coarser
or finer material.
http://www.gov.mb.ca/iedm/prof
iles/images/alfalfa_lg.jpg
Determining Soil Texture - Lab
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
Soil textures can be determined in laboratory
analyses where the amount of sand, silt, and
clay are measured quantitatively.
We will do this in the laboratory activities.
http://earthobservatory.nasa.gov/N
ewsroom/NasaNews/ReleaseImage
s/20040730/06_LabTestingSoil.jpg
Soil Textural Class
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Soil textural classes are based on the
relative proportions of the various soil
separates (sand, silt, and clay).
There are 12 different soil textural classes.
We use the texture triangle to determine
the textural class.
Texture Triangle
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
The percentage units
(0-100%) of sand,
silt, and clay are listed
along the sides of the
triangle.
Also notice that the
relative proportion of
sand, silt, and clay
always adds up to
100%.
Texture Triangle Example #1
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
Tell me what the
textural class is if we
have: 42% sand,
35% silt, and 23%
clay.
We would have a
loam!!
Texture Triangle Example #2

What would we have if we had a soil with
8% sand, 32% clay, and 60% silt?
Texture Triangle Answer #2
http://www.public.iastate.
edu/~arossi/texture%20tr
iangle.jpg

We would have a silty clay loam!!
Organics in Soil Texture
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Sand, silt, and clay are the only particles
used to determine soil texture.
Soil texture refers only to the mineral
fraction of the soil.
Organic matter is not considered when
determining texture or textural class.
A precise analysis of soil texture requires
that organic matter be removed.
Experiment No. 6: DETERMINATION OF SOIL TEXTURE
AIM: To find out the contents of gravel , sand, silt and clay in the given
soil sample.
REQUIREMENTS: Soil sample, weighing machine, sieves of different
numbers of mesh.
THEORY:
PROCEDURE :-
1)Weigh about 20 g of the soil sample.
2)Pass the soil sample through a sieve with minimum number of
meshes per unit area.
3)Shake the sieve for 5-7 minutes.
4)Weigh the soil particle.
5)Pass the rest of the soil through other sieve with slightly higher
network of meshes. continue this with sieves with higher
number of meshes.
6)Calculate the percentage of each type.
7)Using the Texture triangle determine the soil texture type.
Experiment No. 7: DETERMINATION OF SOIL
MOISTURE CONTENT
AIM :- To determine the water content / moisture in the given soil
sample.
Definition:
The natural water content also called the natural moisture content is the ratio
of the weight of water to the weight of the solids in a given mass of soil. This
ratio is usually expressed as percentage.
Purpose
●
●
The knowledge of the natural moisture content
is essential in all studies of soil mechanics.
To sight a few, natural moisture content is
used in determining the bearing capacity and
settlement. The natural moisture content will
give an idea of the state of soil in the field.
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PROCEDURE :1. Clean the container dry it and weigh it (W1).
2. Weigh 5 gm of the soil and place in the container and weigh
(W2).
3. Dry the specimen to constant weight maintaining the
temperature between 105 0C to 110 0 C for a period varying
with the type of soil.
4. Record the final constant weight (W3) of the container with
dried soil sample.
Data and observation sheet for water content
determination
Sr no
Sample no
Can no
1
Weight of can, W1
(g)
2
Weight of can + wet
soil W2 (g)
3
Weight of can + dry
soil W3 (g)
4
Water/Moisture
content
W (%)
=
[(W2-W3)/(W3W1)]x100
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