Soil 3 - Soil Composition.ppt
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Transcript of Soil 3 - Soil Composition.ppt
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Soil 3 Soil Composition
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The ideal composition of soil,25% Air,25 % H2O,
45% Mineral Matter5% Organic Matter
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Particles The te!t"re of a soil depends on the relati#e
mi!t"re of sand, silt and cla$ particles The most common method of classif$ing soils is
ased on the percentage cla$ in the oil &g Soils that contain ' 5 % cla$ are (no)n as
sand$ soils
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The particles in the soil are classed on their si*e An$thing o#er 2mm in diameter is referred to as
gra#el, peles or stones +articles from 2 mm to '5 mm are called sand
particles rom '5 mm to '''2 mm are called silt
particles An$ particle "nder '''2 mm is referred to as
cla$
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Sand and Silt are similar in composition and areformed $ ph$sical rea(do)n of roc(s
Cla$ particles are formed $ oth ph$sical andchemical rea(do)n of roc(s
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As mentioned efore soils are classified $ theamo"nt of cla$ in the soil- ' 5 % Cla$ Sand$ Soil
- 5 .' % Cla$ Sand$ /oam
- .' 2' % /oam- 2' 3' % Cla$ /oam
- 3' 4' % Cla$ Soil
- 4' % 0p Hea#$ Cla$ Soil A more common and acc"rate )a$ at loo(ing at
the t$pe of soil is $ "sing a soil triangle
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Mineral matter is composed of inert solids, gra#el,coarse and fine sand, and silt and cla$ particlesThese different names come ao"t eca"se of thesi*e of each is different
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Soil Texture
1ra#el 2mm
Coarse Sand 2mm
ine Sand '2mm
Silt ''2mmCla$ '''2mm
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The % of each particle in a soil can e estimated"sing sie#es
. A (no)n )eight of a dr$ soil particle is placed in
the top sie#e2 Sha(e #igoro"sl$3 eigh the cla$ fraction4 6es"lt7
Cla$ 8 .'' 9 % Cla$ Total .
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The cla$ particle is the most important soilparticle as it is the onl$ particle, )hich ischarged
:t holds a negati#e charge and is called an anion :t is ale to attract positi#el$ charged ions
to)ards it ;cations< hen lime is spread on land it replenishes the
Ca2=;calci"m< in the soil and flocc"lation occ"rs
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This is the gathering together of cla$ particlesforming aggregates
:t is responsile for gi#ing soil its str"ct"re A )ell>flocc"lated soil )ill ha#e a desirale
cr"m str"ct"re :t )ill e friale
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An "ndesirale str"ct"re is referred to as eingplastic or loc($
/ime promotes flocc"lation :t is recommended that it e spread on a#erage
e#er$ 5 $ears locc"lation in soil promotes aeration
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hen a soil sample is r"ed et)een $o" fingersit rea(s "p into cr"ms
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This is the ailit$ of cla$ articles to s)ap positi#el$charged ions ;cations< from one to another
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Sandy Soils Ha#e large air holes ree ?raining soils :s eas$ to )or( )ith ;light< ?ries o"t @"ic(l$ Minerals are easil$ leached +oor soil )ith little or no n"trients :s a )arm soil
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Clay Soils Holds )ater easil$ This protects from leaching of minerals :s nat"rall$ fertile soil er$ poor drainage, )hich can lead to )ater
logging :s a cold soil
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Loam Soils :ntermediate characteristics of oth cla$ and
sand$ soils More ad#antages and fe)er disad#antages than
sand$ or cla$ soils A good mi!t"re is 4' % Sand, 4' % Silt and 2' %
cla$ hile the nat"re of soil depends on the particle
composition, the amo"nt of h"m"s in the soil isalso a maBor factor