Podzol

In soil science, podzols are common soils of coniferous or boreal forests. And they are also the typical eucalyptus forest soil and the heathlands of southern Australia. In Western Europe, podzols grow on the heartland, which is often built to be disturbed by a human for grazing(food) and burning. In some parts of the British like moorlands with podzolic soil, cambisols are stored under Bronze Age beetles (Dimbleby, 1962).

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Morphological Characteristics 

The typical Podzol in the zonal has a greyish-grey, highly leached eluvial horizon beneath the dark-skinned living atmosphere, and above a very dark brown surface. Most Podzols have a layer of the top layer (H-horizon) 1 to 5 cm thick, open and sponge, and grading into Ah-horizon with humified organic matter. According to the layer of debris, in particular, fragments of individual plants are still recognisable and the living roots can be exposed to mycorrhizae. Ah-horizon contains a dark mixture of grey organic matter and minerals (especially quartz). Basic bleached E-horizon has a single grain structure and the formation of brown to black illuviation soil varies from loose (unusual) through the firm, subangular blocky to very hard and large. 

At the end of the dry season of the zonal, Podzols usually have a high chroma indicating the accumulation of iron oxides (as well as aluminium oxides). In humid regions, Bhs-horizon is black and has a high content of organic transfer. The profile of the intrazonal tropical podzol has a top layer decomposed ('raw'), and the acid humus with a high carbon to nitrogen ratio. A-horizon below the hummus is poorly developed and it rests on the top of a light grey to white eluvial E-horizon of sand texture that can be from 20 cm to several metres thick ('Giant Podzols').

If you go still deeper in the illuvial horizon soil, it is commonly dark brown and irregular in-depth and you can rarely find the mottels or soft concentration and aluminium oxides. And slightly more clay in the illuvial horizon compared to the higher in the profile. Brightly coloured B(h)s-horizons with sesquioxides accumulates which occur in the temperate zone, which is uncommon in the tropics where podzolization is greatly restricted to iron-poor parent materials under the influence of ground-water.

Mineralogical Characteristics

The mineralogy characteristics of Podzols are somewhat different but it is nearly always marked by a predominance of quartz. In a cool, humid climate environment where the leaching is intense, and the parent material may be originally intermediate or even basic composition. Iron and aluminium can be found at maximum at different depths in the B-horizon, depending on the genetic history of a particular podzol soil. In the USA, the level of podzol tends to have the maximum iron content above the Aluminium maximum content. 

Well-developed intrazonal Podzols in Western Europe normally have the maximum amount of Aluminium content at the top of the B-horizon, with the iron maximum at a larger depth. Weathering processes in the A and E-horizons of well-developed Podzols on clay-poor materials will make the material transform clay to smectite (beidellite), and sometimes kaolinite. Whereas clays in the B-horizon may be Alumunium - interstratified. Allophane is the amorphous Aluminum- silicate which appears to accumulate in B-horizons having rich parent material.

Hydrological Characteristics

This podzol is generally wet because of its climate or terrain condition. The movement of the water through the soil will be impaired even in the dryland areas if the soil is having a dense illuviation horizon or an indurated layer at some depth of the soil. The formation of a thin iron pan takes place upon periodic water stagnation in the soil, either in the B horizon or below that some of the examples are Densic and Placic podzols. Podzols are even associated with the regions having annual precipitation surplus, the low water holding capacity of these soils may still cause drought stress in the dry periods. 

Physical Characteristics

Most of the Podzols have a sandy texture and weak aggregation of the structural elements. their bleached eluviation horizon contains normally less than 10 percent clay but the clay content could be slightly higher in the underlying illuvial horizon.

Chemical Characteristics

According to the chemical characteristics, the organic matter profile of Podzols shows two areas of concentration, one at the surface and another one is the spodic horizon. The carbon to nitrogen ratio is typically between 20 and 50 on the surface horizon of the soil, which decreases to 10 - 15 in the bleached horizon and then again it increases to 15 - 25 in the spodic horizon. The level of nutrients in the podzols have low consequences of a high degree of leaching. 

The plant nutrients are mainly concentrated in the surface horizons where the cycling elements are released on the decomposition of the organic debris but the phosphates may accumulate in the B-horizons (as the iron and aluminium phosphates). The surface region of the soil is generally acidic in nature with pHy150, which ranges between 3.5 and 4.5. As the depth of the zonal podzol increases, the pH value also increases to a maximum of about 5.5 in the deep subsoil, whereas the soil pH in the intrazonal podzols tends to be lowest in the top of the B-horizon.  

Biological Characteristics

In boreal and temperate climates, ‘large’ soil animals such as earthworms are scarce in most Podzols; decomposition of organic matter and surface soil homogenization are slow and are mainly done by fungi, small arthropods and insects. Many Australian Podzols show signs of earthworm activity. The activity of moles and earthworms increases rapidly when the podzols are fertilized.

Podzolization 

Podzolization is also known as podsolization is a process of complex soil formation by which the dissolved organic matter and ions of iron and aluminium are released through weathering of various minerals. These form organo-mineral complexes (chelates) and they are moved from the upper level of the soil profile and get deposited in the deeper parts of the soil. Through the process of podzolization, the eluvial horizon of the soil becomes bleached and of ash grey colour. The complexes of the soil move with the percolating water further below to the illuviated horizons of the soil, which is generally brown, red or black in colour as they accumulate and they consist of the cemented sesquioxides and organic compounds. It is a typical process of soil formation in the podzols. 

Preconditions

Podzolization usually occurs under forest or heath vegetation and is common in cool, humid areas as these climates prevent the activity of soil microbes in the topsoil. Overall, the formation of podzolization occurs when biological decay is inhibited and as a result, layers of acidic organisms (more) form. Under these acidic conditions, nutrient deficiencies continue to interfere with the microbial degradation of organic complexing agents. Medium to dark soils with poor parent material (usually rich in quartz) also promotes podzolization, as it promotes the flow of saturated water.

Key Steps

Mainly there are two steps in the process of soil formation of podzolization:

1. In the first step, mobilization and translocation of organic matter like Fe (Iron) and Al(aluminium) from the surface, the horizon takes place.

2. Further, Immobilization and stabilization of organic matter, Fe (Iron) and Al (aluminium) into the subsoil occurs.

In the topsoil of the acidic soils, organic matter (especially from plant waste, a layer of humus and roots exudates) along with the Aluminum and Iron ions, forming organo-mineral structures. These soluble chelates then move with percolating water from A (or E horizon) to B-horizon. As a result, horizon E (or Ae horizon in the Canadian soil classification system) has been left bleached and ash-grey in colour, while B-horizon is enriched with the relocation of organo-mineral structures. The colour of the B horizon is therefore red, brown, or black, depending on the iron ions of the metal or living organism. In general, the boundary between the B-line and eluvial Ae (or E) is very different, and sometimes hardpan (or Ortstein) can form, as Fe and Al transported with organisms increase mineral particles, cementing them into this compacted layer.

There are a number of reasons why these organo-mineral structures immobilize in the B-horizon. If Aluminium or too many iron ions bind to the organic compounds, the complexes might get fluctuated as the solubility decreases with the increasing metal to carbon ratio. Apart from that, a higher pH (or higher Calcium content) in the lower soil horizons can result in the breakdown of metal-humus complexes. In the lower layers of the soil, the organic complexing agents are degraded by the function of the microorganism. Some of the already established complexes in the B horizon will act as a filter, to absorb and travel the complexes from the upper soil horizons. A decreased water conductivity due to higher clay content can also result in the initial slope of organo-mineral complexes.

The substances relocated can separate the illuvial horizon soils sometimes. The uppermost part of the illuvial horizon is highly enriched in the organic substance, whereas Iron and Aluminium oxides are largely found in the lower parts of the illuvial horizon. Podzolization will also promote the relocation of some nutrients like (Cu, Fe, Mn, Mo and P) that brings them closer to the plant roots.

Did you know?

What is podzol in real life? In soil science, podzols are the typical soils of coniferous or boreal forests. They are also the typical soils of eucalypt forests and heathlands in southern Australia and In Western Europe, podzols developed on heathland are often used to construct human interference through grazing and burning.