soil 3 - soil composition.ppt

7/25/2019 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

soil 3 - soil composition.ppt

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