What does podzolic soil mean?
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.
Podzolization Process
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.
Podzolization
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.
FAQs on Podzolic Soil
1. What is podzolic soil?
Podzolic soil, also known as Podzol, is a type of infertile, acidic soil primarily found in cool, humid climates, especially under coniferous or boreal forests. Its name originates from the Russian words for "under" (pod) and "ash" (zola), referring to its characteristic light grey, ash-like subsurface layer created by intense leaching.
2. What are the main characteristics of podzolic soils?
Podzolic soils have several distinct characteristics that make them unique. Key features include:
High Acidity: They have a very low pH value, making them one of the most acidic soil types.
Low Fertility: They are naturally infertile due to a lack of essential plant nutrients and a high concentration of toxic aluminium.
Distinct Horizons: They exhibit a clearly defined profile with a bleached, ash-grey 'E' horizon below the topsoil and a dark, reddish-brown 'B' horizon where leached minerals accumulate.
Coarse Texture: They typically form from sandy or coarse-grained parent material, leading to poor water and nutrient retention.
3. How is podzolic soil formed?
Podzolic soil is formed through a process called podzolization, which occurs in cool, wet environments. Acidic water, enriched by decaying pine needles and other organic matter, percolates through the soil. This acid dissolves and leaches minerals like iron, aluminium, and humus from the upper soil layer. These materials are then washed downwards and redeposited in a lower layer, creating the soil's distinct, multi-coloured horizons.
4. Where are podzolic soils found in India and around the world?
Globally, podzolic soils are widespread across the vast boreal forests (taiga) of North America, Scandinavia, and Russia. In India, their occurrence is limited to specific high-altitude regions of the Himalayas, particularly in states like Himachal Pradesh and Uttarakhand, where the cool, moist climatic conditions required for their formation are present.
5. What is the specific process of 'podzolization'?
Podzolization is the intense soil-forming process that creates podzols. It involves rainwater becoming highly acidic as it passes through the surface layer of pine needles and organic litter. This acidic solution leaches (a process called eluviation) soluble minerals and organic compounds, especially iron and aluminium, from the topsoil. This leaves behind a bleached, ash-like layer of silica. The leached materials are then deposited in the subsoil (a process called illuviation), forming a dense, dark layer known as a spodic horizon.
6. How do podzolic soils differ from laterite soils?
Although both are formed by leaching, podzolic and laterite soils are fundamentally different. The primary distinction lies in the climate:
Podzolic Soil: Forms in cool, humid climates. The leaching process removes iron and aluminium from the topsoil, depositing them below.
Laterite Soil: Forms in hot, wet tropical climates. The intense leaching process removes silica and other bases, leaving a high concentration of iron and aluminium oxides at the surface, which results in its characteristic reddish colour.
7. Can podzolic soils be used for agriculture?
In their natural state, podzolic soils are generally unsuitable for agriculture due to high acidity and poor nutrient content. However, they can be improved through specific management practices. A key method is liming, which involves adding crushed limestone or chalk to the soil to raise the pH and neutralise the acidity. Additionally, heavy application of organic matter and fertilisers is necessary to supply the nutrients required for crop growth. Only acid-tolerant crops like potatoes, rye, oats, and some berries can be cultivated with success.
