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Edaphic factors and their relationship with living beings (long)

 The physical and chemical characteristics of the soil.

Soil constituents

image 1 soil constituents

Soil constituents separate according to their mass; they are said to be sediment.
The soil seems to consist of a solid fraction which includes:
 A mineral part (pebbles, gravel, sand...).
 An organic part (animal and plant remains)
The legend of figure 1: 1= remains of animals and plants, 2= cloudy water, 3= clays, silts, 4= fine grains of sand, 5= coarse grains of sand 6= gravels.
2) We observe bubbles escaping from the ground in the tube, and droplets of water that form on the wall of the tube. This means that the soil contains water and gas


The floor is made up of:

 A solid part: is made up of mineral and organic elements.

 A liquid part: is made up of water and dissolved substances.

 A gaseous part.

 A living part: the living beings of the soil.

Soil characteristics

a- The physical characteristics of the soil:

a1: Soil texture

To determine the texture of a soil sample, the following action:
- Hydrogen peroxide is added to a soil sample which is placed
in a beaker; to remove organic matter.
- Hydrochloric acid (HCl) is then added to remove the
- The sample is rinsed with water, then the mineral part is dried remaining.
- The mineral part thus isolated by sieving is separated into several categories of grains of different and decreasing diameters using a series of sieves mounted in a column
- We weigh each category of grains and calculate their percentages.

Image 2: Grain size scale of soil texture

- The texture of the soil is determined according to the percentages of clays, silts, and sands it contains, we use this as a texture triangle.

texture triangle
Image 3: texture triangle

1= clayey texture, 2= clayey-loamy, 3= fine silty clay, 4= silty clay, 5= clayey-sandy, 6= Fine clay loam, 7= very fine loamy, 8= fine loam, 9= loamy, 10= clayey-sandy loam, 11= sandy loam, 12= sandy

a2: La structure du sol

Soil structure is the way sand, silt, and clay particles are
arranged relative to each other.
There are three main structures which are:
- Particle structure: consists of sandy elements of variable size,
piled up without any clay bond. This structure is characterized by the
presence of a large number of pores.
- Glomerular structure (lumpy): consists of a set of
lumps (grains of sand and silt bound together in aggregates by the clay-humic). It contains many gaps.
- Compact structure: consists of sandy elements linked by a mass
of clay. It is a non-porous structure (absence of pores).

a3: Permeability and water holding capacity

Permeability is expressed by the amount of water that passes through the soil by filtration.
It can be expressed by the rate of filtration of water in a given time in
cm3/min: P = Vg/(t2-t1)
Water holding capacity is the volume of water retained by the soil after filtration (water drainage by gravity): Vr = V-Vg

Image 4: Permeability and water holding capacity

It can be seen that the permeability is greater in sandy soil than in
in clay soil rich in humus; it is even less important in clay soil, in contrast to the water-holding capacity.
This can be explained like this:
- For sandy soil, the grains are relatively coarse and structurally
particles, which allows the easy flow of water, and reduces the capacity for water retention.
- For clay soil, the grains are very fine and of compact texture, which
prevents water run-off and increases water-holding capacity.
- For clay soil rich in humus, is characterized by a structure
lumpy, the grains are very fine, forming lumps with the humus, and
contains many gaps allowing the flow of excess water.
- The most interesting type of soil for plants is clay-humic soil
because its water retention capacity is average, which favors the
ideal plant development

a4: The distribution of water in the soil

- Gravity water: water that flows easily under the effect of gravity. She occupies the lacunar spaces. 
- Capillary water: water held in the soil around soil particles. This water is easily usable by the plant.
- Hygroscopic water: Water that remains too well retained by the particles of the floor. This water is not absorbable by plant roots.

a5: Variation in the water retention capacity of the soil and the point

Water retention capacity: this is the volume of water retained by the soil after gravity water flow (water drainage by gravity).
The wilting point determines the minimum water content of the soil below which the plant cannot overcome the capillary tension of the water (can no longer absorb water).

Variation in the water retention capacity of the soil and the point
Image 5: Variation in the water retention capacity of the soil and the point

It can be seen that the smaller the grain size, the greater the retention capacity. water and wilting point increase. In the presence of humus, there is an improvement in the capacity of water retention for different soil types.
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