Soil formation

what are the organic soil horizons

L - fresh litter, F - partly decomposed litter, H - well decomposed litter, O - organic horizon containing humus in a damp environment

what are the mineral horizons

A - surface/topsoil,

E- elluviated subsurface, less organic matter, paler colour,

B - subsurface, no rock, illuviation/accumulation,

C - partialy weathered parent material,

R - Rock

what are the 3 soil formation models

Environmental product, soil material flux, dynamic rate model

What is pedology?

The study of soils in their natural environment, including formation, classification, and distribution.

What are the five soil forming factors in CLORPT?

Climate, Organisms, Relief, Parent material, Time.

Which soil forming factor controls weathering and leaching most strongly?

Climate.

What does parent material influence in soils?

Texture, fertility, mineralogy, and weathering rate.

What is a pedon?

The smallest 3D unit that represents a soil.

What is a polypedon?

A group of similar pedons forming a soil unit.

What is the solum?

The weathered and biologically active part of soil including A, E, and B horizons.

What is found in the O horizon?

Organic litter and decomposing material.

What characterises the A horizon?

Mineral soil mixed with organic matter.

What characterises the E horizon?

A pale eluviated horizon depleted in clay, Fe, and Al.

What occurs in the B horizon?

Accumulation (illuviation) of clay, Fe, Al, or organic matter.

What is the C horizon?

Partially weathered parent material.

What is the R horizon?

Unweathered bedrock.

What is eluviation?

The removal of material from an upper horizon.

What is illuviation?

The accumulation of material in a lower horizon.

What process creates an E horizon?

Eluviation.

What is hydrolysis?

A chemical weathering reaction where water breaks down minerals to form clays.

Give an example of hydrolysis.

Feldspar weathering to kaolinite clay.

What is oxidation in soils?

Loss of electrons, commonly Fe²⁺ becoming Fe³⁺.

What colours are associated with oxidation?

Red, yellow, and brown colours.

What is reduction?

Gain of electrons under anaerobic conditions.

What soil conditions favour reduction?

Waterlogged or anaerobic conditions.

What is topdown pedogenesis?

Soil development downward from the surface.

What is upbuilding pedogenesis?

Soil development through addition of new material at the surface.

What is developmental upbuilding?

Thin additions incorporated into the existing soil.

What is retardant upbuilding?

Large additions bury old soils and slow development.

What is the environmental product model?

A model where soil is the product of interacting environmental factors.

What is the dynamic-rate model?

A model recognising soils change progressively or regressively through time.

What is a progressive soil pathway?

Increasing soil development over time.

What is a regressive soil pathway?

Soil simplification caused by erosion or disturbance.

What are additions in soil systems?

Inputs such as organic matter, dust, or volcanic ash.

What are removals in soil systems?

Losses through erosion or leaching.

What are transformations in soil systems?

Changes such as weathering or decomposition.

What are translocations in soil systems?

Movement of material within the soil profile.

How does relief affect soil depth?

Steep slopes generally have shallower soils.

How do organisms influence soil acidity?

Some vegetation, especially conifers, produces acidic litter.

Why are volcanic ash soils often fertile?

They contain reactive minerals and good structure.

How long can soil formation take?

Thousands to tens of thousands of years.

What happens to soils as they age?

They become more weathered and more strongly leached.

What does NZSC stand for?

New Zealand Soil Classification.

What is the purpose of NZSC?

To classify and predict the behaviour of NZ soils.

List the hierarchy of NZSC.

Order, Group, Subgroup, Family, Sibling.

What is a diagnostic horizon?

A horizon used for soil classification.

What does a Bt horizon indicate?

Clay accumulation.

What does a Bh horizon indicate?

Humus accumulation.

What does a Bs horizon indicate?

Fe and Al accumulation.

What does a Bg horizon indicate?

Gleying/reducing conditions.

What is a lithologic discontinuity?

A boundary between different parent materials.

How are lithologic discontinuities shown?

Using prefixes such as 2Bw or 2Cu.

What are Allophanic soils associated with?

Volcanic ash and allophane minerals.

Name key features of Allophanic soils.

Low bulk density, high P retention, excellent structure.

What are Gley soils?

Soils affected by prolonged saturation and reducing conditions.

What are Podzol soils?

Strongly leached acidic soils with E and Bh/Bs horizons.

What are Granular soils?

Strongly weathered clay-rich soils with granular structure.

What does “Orthic” mean in NZSC?

Typical or common expression of a soil.

What does “Typic” mean in NZSC?

Default subgroup lacking special features.

What are soil families based on?

Texture, permeability, mineralogy, and profile material.

What are soil siblings used for?

Detailed land management distinctions.

What properties define siblings?

Depth, drainage, texture, stoniness, and functional horizons.

What are functional horizons used for?

Predicting soil behaviour such as drainage and rooting.

What is the main clay mineral in allophanic soils?

Allophane.

What is the Horotiu soil?

A Typic Orthic Allophanic Soil.

What are characteristics of Horotiu soil?

Well drained, volcanic ash derived, highly productive.

What is Te Kowhai soil?

A Typic Orthic Gley Soil.

What are features of Te Kowhai soil?

Grey colours, poor drainage, reducing conditions.

Why are diagnostic horizons important?

They indicate pedogenic processes and aid classification.

What is the benefit of NZSC?

It reflects NZ-specific soil conditions and processes.

Why are soil siblings useful?

They help guide land use and management decisions.

What is leaching?

The downward movement of dissolved ions through soil.

Which ions are commonly leached?

Ca²⁺, Mg²⁺, Na⁺, and K⁺.

What causes increasing soil acidity during leaching?

Loss of base cations and replacement by H⁺ and Al³⁺.

What is ionic potential?

Ionic charge divided by ionic radius.

Which ions are most easily leached?

Ions with low ionic potential.

Name two easily leached ions.

K⁺ and Na⁺.

Name two less mobile ions.

Fe³⁺ and Al³⁺.

What is base cycling?

Nutrient recycling through vegetation and litter decomposition.

Which vegetation type promotes strongest base cycling?

Grasslands.

Which vegetation type promotes strong acidification?

Coniferous forests.

What is podzolisation?

Movement of Fe, Al, and organic matter downward under strong leaching.

What horizon is characteristic of podzolisation?

E horizon.

What does “Podzol” mean?

“Ashes underneath.”

What horizons define Podzol soils?

Bh and/or Bs horizons.

What is a Bh horizon?

A humus-rich illuvial horizon.

What is a Bs horizon?

A horizon enriched in Fe and Al oxides.

What conditions favour podzolisation?

Acidic, humid, free-draining conditions.

What vegetation commonly promotes podzolisation?

Conifers and kauri.

What is allophane?

A nanocrystalline aluminosilicate mineral.

What is ferrihydrite?

An Fe oxide mineral.

What is gibbsite?

An aluminium hydroxide mineral.

What causes the pale colour of E horizons?

Strong eluviation of Fe, Al, and OM.

What is a humus pan?

A cemented Bh horizon.

What is ortstein?

A cemented Bs horizon.

Why are podzol boundaries often sharp?

Limited biological mixing due to acidity.

What type of parent material commonly develops podzols?

Sandy or coarse-textured parent material.

What process often accompanies podzolisation?

Argillisation.