Soil structure is an arrangement of soil particles (sand, silt, clay) into large units
called aggregates. Soils are aggregated together by binding agents such as
organic matter, clay, caco3, iron oxides and biological factors such as hyphae.
Naturally formed aggregate
are called peds. Aggregates are also formed artificially during plowing or
digging. They are called clouds.
Peds are considered as the
soil structural unit. Peds has a distinct shape. There are well-defined planes of
weakness between the aggregates.
Soil structure is created by
combing several peds together.
Different types of peds
can be found in soil.
Aggregation of soils
Soil particles may be present either as single individual grains
or as aggregate. When a group of particles bound together into granules or
compound particles. These granules or compound particles are known as secondary
particles.
A majority of particles in a sandy or silt soil are present
as single individual grains while in clayey soil they are present in granulated
condition.
The
individual particles are usually solid, while the aggregates are not solid but
they possess a porous or spongy character.
Sand consists of only macrospores which are between
aggregates but clay soils have macrospores between aggregates and microspores
within the aggregates.
Degree of water movement
Soil structure affects water movement. Soil structure
affects how quickly water moves through the soil. Water moves quickly through soils
with many small grains. Soil with larger aggregates in the form of blocks or prismatic
have moderate drainage.
Single grain,
Granular >Blocky, Prismatic>Platy, massive
Factors affecting soil structure
1) Kind of clay (With increasing of
amount of clay, soil particles are well aggregated.)
2) Amount of organic matter(When soil
has a high amount of organic matter, soils are well-bounded together and
increase pore spaces )
1) Freezing and thawing (Freezing and
thawing effects on soil formation. When parent material is frozen and thawed
regularly, new minerals are formed therefore soil profile is developed)
2) Wetting and drying (With wetting of
soil, soils are relatively well aggregated. With the drying of soil, soils are
relatively less aggregated)
3) The action of burrowing organisms (Soil the structure is always changed with burrowing animals. They mix soils. Lower
layers are taken onto the surface. Soils are well aerated because soils are opened
to the external environment. Stability of soil aggregates is also increased)
4) Growth of root systems of plants (With
the growth of roots systems of the plant, soil particles are bonded together very
strongly)
Importance of Soil Structure
Influences
many important soil properties:
1) infiltration rate
2) water retention
3) aeration amount of
pores are affected
4) drainage
5) Germination of seeds-When soil has relatively
loose soil structure and a considerable amount of pores which are contained the optimum level of water and air, it is very suitable for germination.
6) Soil
erosion-When stability of soil aggregates are relatively weaker, soil particles
are tended to detach from the surface.
Stable soil aggregation is a very valuable
property of productive soil. Yet, the stability of soil aggregation is very
reliant on the type of minerals present in the soil. Certain clay minerals form
very stable aggregates, while other clay minerals form weak aggregates that
fall apart very easily.
Highly
weathered silicate clay, oxides, and amorphous volcanic materials tend to form
the most stable aggregates. The presence of organic matter with these materials
improves stable aggregate formation. In nutrient management, aggregate
stability is important because well-aggregated minerals are well-drained and
quite workable.
In contrast,
less weathered silicate clay, such as montmorillonite, form weak aggregates.
Some silicate clay is said to have shrinks well potential. This means that
the soil minerals expand or swell, when wet, causing the soil to become sticky
and drain poorly 
Post a Comment