Podzolic soil, also termed as podzol, or called the lessive soil, is a soil that is usually formed in a broadleaf forest and is mostly characterised by the average leaching, which is also highly susceptible to compaction.
The eluvium horizon is usually 4 cm to 8 cm thick, and is low in iron and aluminium oxides and humus. It is generally formed under moist, cool, and acidic conditions, and only where the parent material, like the granite or the sandstone, is present and is rich in quartz. It is usually found under a huge layer of organic material during the process of decomposition, which has a thickness of 5 cm to 10 cm. Sometimes, the middle region often has a thin horizon of 0.5 cm to 1 cm. When the soil horizon gets bleached, it goes over into another red or red-brown horizon, which is also known as the so-called Podzolic B. The colour is normally strongest in the upper region, and the changes occur at a depth of 50 cm to 100 cm, and it progresses to the part where the soil is mainly unaffected by any of the processes, which is the part of the parent material. The solid profiles are named by the letters A, which is the topsoil, E, which is the eluviated soil, B, which is the subsoil, and C, which is the parent material. The red yellow podzolic soil is a poor soil with many limitations, including low soil pH, low clay content, low aggregate stability, low nutrient content, and susceptibility to compaction. Organic matter is the only indicator of fertility in these soils.
In some of the Podzols, the E horizon is absent, which can be because of being masked by the biological activity or being obliterated by the disturbance. The podzols that have very little or almost no E horizon development are often classified as the brown podzolic soils, which are also called Umbrisols and Umbrepts.
The process of podzolization is a complex soil formation process due to which the organic matter is dissolved and ions of iron and aluminium are released through the weathering of various minerals from the organo-mineral complexes, and are moved from the upper parts of the soil profile. It goes and deposits in the deeper regions of the soil. Via this process, the eluvial horizon of the podzol becomes bleached and it turns into an ash-grey colour. The complexes move along with the percolating water and move further down to the illuviated horizons, which are usually brown or are coloured red or black when they accumulate, and are made up of cemented sesquidoxes and/or organic compounds. Thus, podzolization is typically a soil formation process in the podzols.
The above-mentioned process of formation of podzol soil, known as podzolization, can be simplified into two main steps:
The mobilisation and the translocation of the organic matter, iron and aluminium, from the surface horizon
The immobilisation and the stabilisation of the organic matter, the iron and aluminium, into the subsoil
Finally, podzolization also promotes the relocation of some of the nutrients, such as copper, iron, manganese, molybdenum, and phosphorus, bringing them closer to the plant roots.
Process of soil formation results in the formation of Podzols and Podzolic soils. Podzolization consists of the downward migration of Al and Fe elements. It happens together with organic matter, from the surface areas, and their accumulation in the profile's deep areas. The bases, other than Calcium, are generally removed and the whole soil becomes very acidic (which implies acid leaching). This process is characterised generally by a strong acidity that causes slow organic development. It releases acidic nature compounds and so the extreme alteration of the mineral phase takes place, because the medium is enriched with insoluble elements, such as Fe and Al. So they are generally migrated towards lower portions by the organic compounds.
A favourable combination of environments of podzolization include the following:
i) Ideal climatic conditions: The humid and cold climatic conditions are ideal for it.
ii) Parent material: Sandy materials have poor reserves of weatherable minerals. Hence, they generally favour the operation of podzolization because it helps in easy percolation of water.
iii) Acid Product Vegetation: Acid-producing vegetation such as coniferous pines are essential.
iv) Leaching and Translocation of Sesquioxide: Due to becoming mobile of hummus and Sesquioxide, they leach out from the upper horizon and deposit in the lower one.
As iron and aluminium move about, the horizon gives a bleached grey and ashy appearance. The Russians used the term Podzols (pod means under, and the meaning of Zola is ash-like, i.e., ash-like horizon appearing beneath the surface horizon) for such soils.