The
secondary particles arrangement of the building blocks called (peds) within the
soil mass together within the pore size distribution.
CHARACTERISTICS OF SOIL STRUCTURE
Same
experience and researches have rise to multitude of descriptions in soil structure.
The term soil tithe is often used to describe the quality of soil structure for
crop growth. A soil considered to posse’s good tilt is one that readily
fractures whether the stress arise from tillage, emerging seedlings or growing
root and plants or micro-organisms.
1. Description
of the aggregate: This refers how the
shape, stability, size, and durability in the water, but in this Aggregates
description are four basic areas in this.
(a) Rounded
aggregates and spherical: This is the circles arrangements of particles in
soil they are of two types; Crumb and Granular structure
(i) The crumb arrangement this has large
gravels, pore space between the aggregates which has same shape with angular
but are more porous because there are found in topsoil.
(ii) Spheroidal
arrangement: (granular arrangement/the particles are lamented or bound
together in circular form with lots of air spaces it is found in topsoil.
(c) Aggregate
arrangement: This is clay soil containing > 15% tend to form structural
aggregate in both physical and biological processes, it may very in size from
crumbs (2 mm) to polyhedorons or sub-angular <0.005-0.02m to prism columns
> 1.0m,
This primary individual particles
form aggregate and are arranged in the profile, like (loamy) this arrangement
is desirable for agriculture license it has good air, and water movement for
plant growth. E.g are
(1)
plate-like
(2) block-like and
(3) Prismatic
(CI) Plate
like aggregate arrangement: The primary soil particles are arranged in horizontally
and flat resembling plates or leaflets on top of each other. Whish is found in
the sub-soil.
Plate-like aggregate arrangement
(iii) Prismatic
arrangement: Is the vertical axis is
long than the horizontal axis with air spaces
Prismatic
arrangement: The vertical axis is
long than the horizontal axis with air spaces, when the top ones are round
columnar but they are flat found in the sub-soil.
(iv) Block like arrangement: The arrangement of
particles whose edges are irregular and may either shape or round, it is found
in rich clay soil at the sub-soil.
2. Description
of pore size distribution
Here the wide range of soil are the
pore space exist in inevitable gaps in packing of soil particles the
disturbances is due to roots, tillage, swelling, soil animal, which allow soil
to act as a medium for air and water transport can be grouped into some
categories.
(a) Large pores (macro-pores) this pores are
large mainly used for air and water conduction which is active in drainage with
Demeter of range 5.000-0.1 micron.
(b) Litho spores (mesopores) this used to
condition and to a limited extent for water retention, it has size range of 0.1
-0.005 microns in diameter cylindrical range and it is intermediate between
macro and Micro-pores
© Micro- pores (capillary or very small
pores
It
is mostly used for storage and retention of water, while the size range are
<0.005-microns.
3. Quantifying the pore volume-are the
formation of soil structure aggregates, they are formed in two ways processes.
1. Cementation: Of soil material: Is the
binding of micro-aggregate with other primary soil particle like (sand, clay
and silt) which has same cementing or building agents, it has headiness,
brittleness caused by the building or cementing agent than clay with the following
cementing or building agent are e.g clay organic matter, sesquoxides (like Fe
and AL oxide) and calcite.
2. Flocculation : This is getting together
of clay particles to form clay domains, tactoids or floccules, micro-aggregate
forms the factoids, while foclutation occur when the soil is witty or
flocculation can be encourage through the following ways.
(i) High concentration of salt in soils.
This encourage flocculation equal discourages it when it dilute concentration.
(ii) Polyvalent cations: This are di and all
trivalent cation as mg2+, Fe2+, Ca2+ AL3+,
Fe3+ this will improve flocculation:
The
persent of monovalent cations in dilute amound discourage flocculation and
encourage detoloccuation or dispersion e.g are Na+,L1+, K+.
Management of soil structure
1. It ensuring optimal porosity in crop
growth for maximum yield under good conditions.
2. It help in decourased transportation
and detachability by water and wind in soil conservation, erosion and runoff
reduced while infiltration and percolation rate increased) it can be improved
by the
3. Crop rotation
4. Proper tillage
5. Addition of organic matter
6. Quality irrigation water
7. Soil amendments
Before
we go on there are some agent that can destroyed soil structure both physical
and chemical properties.
Physical
compaction of soil is (tillage, trampling by animal, practices)
Chemical
dispersion
1. Irrigating with high sodium
2. High salt content
Tillage and it effect on soil structure
The word tillage can be defined as
the mechanical method of the soil manipulation for any purpose in crop
production. Tillage particles can be reducing it operation on land for e.g.
(i) Plow and plant
(ii) Plow – plant
(iii) Strip cropping
All this type can reduce tillage in
the land while weeds are controlled by using chemical.
Importance of soil structure
1. It support aeration for roots and
micro-organism
2. Adequate water
3. It eases root penetration, permitting
through exploitation of soil for water and nutrients.
4. Seed germination in rapid and uniform.
5. It resistance of soil slaking surface
sealing and acceleration erosion by water and wind.
In
this are two most useful indices of soil structure
(1) Bulk density
(2) Aggregates stability
(a) Bulk density is: Is the measurements
which relevant to conditions of (i) (ii) and (iii) above this increase with
high value sandy texture while
(2)
Aggregates stability is the coherence of soil from iv and v above while
aggregate decreases with declining organic matter and silty fine sandy loam.
Aeration and water support depend on
soil pre size distribution in air capacity and available water capacity, water
logging is susceptibility in others.