Podsols and Latosols

What are podzols simply?

Acidic and have distinct horizons.

Where do podzols occur?

In cool temperate climates in the northern hemisphere, where there is more precipitation than evapotranspiration.

Where are podzols usually found?

Under coniferous woodland or a heather moorland.

What is the O horizon?

A layer of needles from the coniferous trees or heather leaf litter, and below this is a narrow, acidic A horizon.

Nutrients are leached from the A horizon by water.

What happens because of the acidity of podzols?

Water travelling through the soil is more able to dissolve certain minerals such as iron and aluminium compounds.

Leaching of these minerals creates a pale E horizon formed of mainly quartz sand and silt.

What letters are the 5 layers of soil?

• O

• A

• E

• B

• C

Where do minerals accumulate in podzols?

In the B horizon, forming a reddish brown layer.

In very well developed podsols, a ‘hard pan’ or ‘iron pan’ forms in the B horizon - this is a hard, continuous layer of deposited iron.

Why are podzols acidic?

Because the leaf litter from coniferous trees and heather is acidic, and they often form on acidic sandstones or clays.

What are podzols not good for?

Agriculture.

How do podzols impact livestock?

Some livestock can be grazed on areas with podzols.

How do podzols impact arable farming?

It is difficult;

• acidity and lack of nutrients means that few crops are able to grow.

• formation of a ‘hard pan’ can prevent water from draining away, making the soil vulnerable to waterlogging, damaging crops. Waterlogging also makes ploughing difficult because machinery sinks into the ground.

How does some arable farming take place on podzols?

This requires treatment with lime to reduce acidity, and extensive artificial fertilisation.

Why is forestry a common human activity on podzols?

Because coniferous trees typically grow successfully on podzols.

Low soil temperatures mean that it can take up to 100 years for a tree to reach maturity and be ready to harvest.

What are latosols simply?

Deep and red.

Where are latosols found?

Under tropical rainforests.

What do tropical conditions encourage for latosols?

High temperature and humidity in tropics encourage fast chemical weathering of the bedrock, forming soils up to 30-40m deep.

What does year-round plant growth mean for latosols?

The O horizon is quite thick.

However, as soon as leaf litter decomposes to humus, its nutrients are absorbed by vegetation rather than staying in the soil - means the fertile A horizon is very thin.

What is rainfall like in tropical rainforests?

Rainfall is higher than evapotranspiration, causing a soil moisture surplus.

Means there is a lot of leaching - silicate minerals are leached from the B horizon, but less soluble iron and aluminium compounds are left behind.

Iron compounds give B horizon a red colour.

What can the build up of minerals in latosols lead to?

Can form a laterite horizon, which acts like clay.

What can latosols influence?

Human activity.

What are latosols like for agriculture?

Poor for agriculture due to low nutrient content. Once rainforest trees are removed, soil has no protection from heavy rainfall - leaching increases and latosol becomes even more nutrient poor.

How have humans living in the rainforest adapted to latosols?

• Traditional agriculture using ‘slash and burn’ clears one small area for growing crops at a time.

• Burning vegetation to clear the plot adds nutrients to the soil. After one growing season, a new plot is cleared, and the first one is left to recover fully.

How has farming expanded in areas with latosols?

Large areas of land are cleared for agriculture, and soil isn’t given a chance to recover - this has led to permanent soil degradation.

What is the laterite horizon like?

Soft when its moist, but hard when it dries out - this makes it useful for building.