The clay soils are those in whose particle composition (texture) particles smaller than 0.002 mm (called clays) predominate. When the predominance of clays is very high, they are considered heavy soils, due to their high density.
Clays are very important in soil fertility. They retain mineral salts by forming aggregates with humus (colloidal fraction of decomposed organic matter) and are good at moisture retention.
On the other hand, extremely clayey soils represent a problem for agriculture due to their poor infiltration. The most characteristic clayey soils are those of the order Vertisols (expandable clays).
This type of soils are distributed throughout the planet. Among the species that are most cultivated in these, rice stands out. Others like pineapple and rubber also have good production.
Article index
The large active surface and the high exchange capacity of the clays are their most relevant properties from the edaphological point of view. These properties are given by its small size, its negative electrical charge and its electrical conductivity..
Clays give the soil low permeability, high water retention and nutrient storage capacity. This makes your potential fertility high.
On the other hand, they confer poor aeration and have a low to medium susceptibility to erosion..
The physicochemical properties of clay soil depend on its mineralogical composition, particularly on the predominant type of clay. Thus, for example, allophane favors cation exchange capacity, porosity, moisture retention and structure..
While kaolinite has a low cation exchange capacity, low element retention and regular structuring.
The key category for a soil to be defined as clayey is texture. This refers to the proportion of sand, silt and clay in the soil. Each of these elements are categories of particle size.
If the clay particles represent 25% to 45% of the total particles present in the soil, it can be considered sandy-clay, coarse clay clay or silty clay. If the clays exceed 45% of the total composition, we are in the presence of a clay soil of fine clay.
To the extent that the clay content determines the texture and structure of the soil, it affects its porosity.
Due to their small diameter, the clay particles leave very small pores. This hinders the circulation of water and air in the soil matrix. These conditions generate soil saturation, which can lead to surface water stagnation as infiltration does not occur..
If the pores of the soil are saturated with water, the rhizosphere becomes anoxic (with a lack of oxygen). Under these conditions, most of the cultivated plants have serious difficulties to develop..
In the presence of humus, clay expresses its positive dimension. The clay-humic complex is formed and the aggregates are larger. Therefore the pores are also larger and improves permeability and aeration
If the clays and organic matter do not retain the cations, these will be dragged by the water towards lower horizons (leaching) affecting the fertility of the soil. The cation exchange capacity is due to the negative electrical charges that both humus and soil clays possess..
Soil pH can affect cation exchange capacity. This depends on the type of clay present in the soil..
When kaolinitic and allophane are present, the negative electrical charge varies depending on the pH. Whereas when expansive clays with a 2: 1 ratio are present, the load is constant at any pH value..
Soil microorganisms establish a close adhesion and separation relationship with the clay particles. On that surface, ion exchange processes occur that are captured or released by microorganisms..
Due to their low permeability, clay soils are ideal as natural or artificial water reservoirs. Some aquifers are established by the presence of a clay horizon at a certain depth.
Most clays belong to the group of phyllosilicates (silicates in flaky form). There are different types depending on the number of sheets that make up its structure. Among the most abundant are muscovite, kaolinite, biotite, chlorite, vermiculite and montmorillonite.
Other clay groups of medium abundance are quartz oxides. Among the less frequent we find feldspars, hematite, goethite, calcite, gypsum and halite..
Cristobalite and amorphous materials are found in clay soils of pyroclastic origin (volcanic ash)..
Due to the colloidal nature of its particles, clay soils retain a large amount of minerals. Clay soils have a tendency to retain iron (Fe) and to a lesser extent aluminum (Al).
Because clay soils retain a lot of moisture, oxidation processes occur. Hydrated iron oxides give these soils yellow or reddish colors
Clays, in combination with organic matter, contribute to the stability of the soil structure. In most cases it is the clay-humic complex that facilitates the formation of soil aggregates. Conversely, sodium makes clay unstable..
If a substrate is made exclusively of clay, it would have no structure and would not allow water infiltration. This would end up compacting and hardening.
A soil with expandable clays in a seasonal tropical climate undergoes drastic structural changes depending on the humidity conditions.
In the rainy season the clays expand and the soil tends to flood, it is soft, sticky and plastic. In the dry season the clays contract, showing the dry, hard soil with large cracks.
In a complete soil profile, clays are mostly located on the B horizon or the accumulation or precipitation horizon. This is due to their small size, which makes them wash from the surface..
In a landscape of settling in plains with large rivers, the overflows distribute the particles according to weight. In this sense, the clays, being the smallest, end up settling far from the shore in the lower areas..
Also in a landscape of mountains and valleys, the clays will tend to settle in the latter.
In geographical terms, its distribution is highly variable. Clay soils exist on all continents.
Vertisols are present in various latitudes and cover approximately 335 million hectares worldwide. A potential 150 million hectares of farmland is estimated. In the tropics they cover about 200 million hectares; a quarter of this is considered agricultural utility.
The main elements to take into account when using clay soils for agriculture are drainage and acidity..
The crop par excellence for clay soils is rice. Cotton, sugar cane and sorghum can also be grown, with proper management.
Some acid-tolerant and undemanding crops such as pineapple, rubber, or African palm, can be grown on some types of clay soils.
Within permanent crops, some fruit trees are adapted to clay soils. Among the fruit trees of temperate climate: apple, pear, quince, hazelnut and walnut. Forest plantations are equally viable.
For grazing, species of Brachiaria (Ex .: B. humidicola) and of Paspalum (Ex .: P. fasciculatum) tolerate excess water.
Yet No Comments