Alluvial Soil

Alluvial Soil

Alluvial soil are a large group of soils located in floodplains of rivers. Alluvial soil is also known as floodplain soil, their distinctive feature is periodic flooding with flood waters (floodplain process), not necessarily annual, but accompanied by the introduction and deposition of new mineral material on the soil surface (alluvial process). In addition, these soils are influenced by the close occurrence of groundwater.

The provision of alluvial soils with moisture and plant nutrients due to regular flood waters and alluvium deposits create favorable conditions for the cultivation of crops that are demanding fertility – vegetables, fruits and berries, sugar beets, etc. These soils are also used in meadow growing, growing forage crops, and under pastures.

Characteristics and colour of alluvial soil

The colour of alluvial soils usually ranges from light gray to ash gray, with browns mainly found in the northern plains, and in the coastal plains, it is reddish-brown due to the presence of iron oxide. Red soil is present in the eastern and southern parts of the Deccan plateau.

Alluvial soils are considered potentially fertile due to their characteristics and favorable location. They form quickly and accumulate humus, and are capable of producing large yields. Nevertheless, their use for the needs of agriculture should be accompanied by a number of agronomic measures. At the same time, it is especially important to monitor the water regime of the soil cover and hollow waters.

Characteristics of alluvial soil

The main characteristics of alluvial soil include:

  • Layering
  • Strict zoning
  • Young age
  • Formation on redeposited weathering crust from clastic rocks
  • Simultaneity of the ongoing processes of soil formation and the formation of the parent rock
  • The presence of large stone particles and pebbles in the composition
  • High population of living organisms
  • High humidity

Forming in different bioclimatic and geomorphological conditions on alluvium of different granulometric and mineralogical composition under the influence of ground and surface waters of different mineralization, alluvial soils differ markedly in analytical characteristics. Their reaction varies widely; they are subdivided into acidic, saturated (neutral), carbonate, and saline (saline). The composition and properties of organic matter, particle size distribution, cation exchange capacity, and the degree of saturation with bases also vary within the widest limits.

Alluvial soil depending on the nature of the deposit

Scientists classify alluvial soils according to different criteria. Thus, one of the typologies is based on the division of floodplain covers depending on the nature of the alluvial deposits. They may be:

  • Layered soils
  • Granular soils
  • Layered-granular

alluvial depositsAlluvial layered soils

  • Features of formation: They develop in the riverbed part of the floodplain, they are also found along the manes and in the central region of the floodplain. Sand and sandy loam deposits act as parent rocks.
  • Morphological features: A characteristic feature of the morphological structure of alluvial layered soils is a clearly pronounced layering of the profile (sandy, sandy loam, and light loamy layers of alluvium of different thickness alternate).
  • Fertility: The natural fertility of these covers is low due to the low humus content (about 0.2 – 1.5%). The thickness of the humus layer ranges from 3-5 to 10-30 cm.
  • Other features: They usually have a low nitrogen content.

Alluvial granular soils

  • Features of formation: They are formed in the lowered elements of the relief. The parent rocks for them are loamy and clayey alluvial deposits.
  • Morphological features: A feature of their structure is the alternation of light sandy structureless layers with darker layers of granular structure. Their formation is associated with the different nature of the deposition of alluvium in certain years in connection with the peculiarities of the flood.
  • Fertility: They occupy an average position in this indicator: they are more fertile than layered covers, but less than grain alluvial soils.
  • Other features: They have a high potential supply of batteries and a high absorption capacity. Their reaction varies widely (pH from 4 to 6 and above).

 Alluvial layered-granular soils

  • Features of formation: They are formed in the transitional part from the riverbed and central floodplain.
  • Morphological features: Their main morphological features are a well-defined humus profile with a distinct granular structure (hence the name). The profile also contains rusty and glue spots that appear due to excessive moisture.
  • Fertility: Granular soils are much more fertile than stratified soils due to their high humus content (2-6%). The humus layer is usually thick and well-developed.
  • Other features: They occupy an intermediate position, in one case or another, they can have the characteristics of both layered and grain alluvial soils.

Use of alluvial soils

alluvial soils

Floodplains are of particular value for agriculture. This is due to their good fertile properties (primarily in the central floodplain), as well as their proximity to water.

The most fertile soils in this group are alluvial meadow soils. They have a well-developed humus horizon – it is powerful, with a clear lumpy structure.

Various crops are cultivated on them:

  • Fodder
  • Cereals
  • Vegetable
  • Fruit
  • Berry

Thus, alluvial meadow soil covers are widely used as agricultural bases, hayfields, forage lands, and pastures.

To increase the fertility of these soils, the following agrotechnical measures are usually used:

  • Application of nitrogen, phosphorus, and potash mineral fertilizers
  • Organic fertilization
  • Liming acidic integuments
  • Sowing green manure plants
  • Planting one- and perennial grasses
  • Regulation of the water regime by means of irrigation and drainage
  • Creation of barriers against soil washout by hollow waters using earthen embankments (embankments, fences) and tree and shrub plantations

All these activities are aimed at preserving the qualitative characteristics of the soil cover. The construction of barriers also prevents water erosion and prevents hollow waters from eroding the soil.

Alluvial marsh soils can be used in agriculture only after draining. In this case, they become valuable agricultural land. But such reclamation is considered an expensive undertaking. It is much more profitable to extract peat in such areas.

Separately, it should be said about the construction of reservoirs and dams. Their creation negatively affects the quality characteristics of floodplain soils. First of all, their fertility deteriorates. The thing is that during the construction of reservoirs, the floodplain and alluvial processes are weakened, the groundwater level goes down, thereby degradation of the cover occurs. During the construction of dams, floodplain soils are flooded, eventually turning into swamps.

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