Soil Formation and Composition

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Questions and Answers

Soil composition is mainly influenced by what factors?

Topography and altitude

Vegetation and wildlife

Climate and land use

Parent material and formation conditions (correct)

What is characteristic of sandy soils?

High mineral material content

High organic matter content

Low organic matter content (correct)

High water content

Which of the following is NOT a main component of soil?

Living organisms (correct)

Mineral materials

Organic matter

Microorganisms

What is unique about peats?

Almost exclusively organic matter Signup and view all the answers

Why do air and water content vary heavily in soil?

Due to parent material and formation conditions Signup and view all the answers

What is the main factor influencing soil texture?

Parent material and formation conditions Signup and view all the answers

What happens to root biomass when the plant or parts of the plant die?

It turns into dead organic matter Signup and view all the answers

What is the purpose of mechanical degradation of biomass by organisms like earthworms?

To make the biomass more accessible to terminal degraders Signup and view all the answers

What is pedoturbation caused by?

Movement of soil within a profile caused by animals and plants Signup and view all the answers

What is the term for organisms that contribute to pedoturbation?

Ecosystem engineers Signup and view all the answers

What happens to hardly degradable organic compounds in the soil?

They form humic compounds Signup and view all the answers

What is the role of earthworms in soil ecosystems?

They mechanically degrade biomass Signup and view all the answers

What is the significance of organic matter in the soil?

It is necessary to release crucial nutrients Signup and view all the answers

What do ants and termites contribute to the soil ecosystem?

They create underground networks of tunnels Signup and view all the answers

What is the function of sticky mycelia in nematophagous fungi?

To sense the movement of nematodes and trap them Signup and view all the answers

What happens to soil organisms when oxygen is present in the soil?

They live by aerobic respiration Signup and view all the answers

What is the result of denitrification in soil?

Conversion of nitrate into N2 Signup and view all the answers

Why is nitrate more abundant in soils compared to aquatic habitats?

Due to the use of fertilizers in soil Signup and view all the answers

What type of microorganisms are able to switch between aerobic respiration and fermentation?

Facultative aerobes Signup and view all the answers

What is the term for the use of nitrate as an electron acceptor for respiration?

Denitrification Signup and view all the answers

What happens to soil microorganisms when conditions become anoxic?

They switch to fermentation or denitrification Signup and view all the answers

Why do soil organisms fluctuate between oxic and anoxic conditions?

Due to the periodic waterlogging of soil Signup and view all the answers

Study Notes

Soil Formation and Composition

Soil formation is influenced by the type of parent material and the conditions under which it is formed.
Sandy soils have little organic matter, whereas peats are almost exclusively organic matter with little mineral material.
Air and water content can vary heavily in soils.
The four main components of soil are:
Mineral materials
Organic matter (including root biomass)
Dead organic matter (formed when plant material dies)
Water and air

Soil Biocenosis

Dead organic matter is fed on by the entire soil biocenosis, which degrades it to release crucial nutrients like phosphorus and nitrogen.
Hardly degradable organic compounds form humic compounds, similar to kerogen.
Soil organisms have different ecological roles, such as earthworms, which mechanically degrade biomass and excrete undecomposed organic matter.

Soil Mixing and Pedoturbation

Pedoturbation is the movement of soil within a profile caused by animals (and some plants), which can reduce the presence of soil horizons by mixing.
Organisms that contribute to pedoturbation, such as ants, termites, and earthworms, are ecosystem engineers.
These organisms create tunnels, burrows, and networks that allow air access to deeper layers, contributing to soil mixing.

Soil as an Ecosystem

Soil organisms play a major role in biogeochemical cycles beyond carbon, including nitrogen and water.
In waterlogged soil, anaerobic conditions can lead to the establishment of an anaerobic food web similar to aquatic sediments.
Facultative aerobes, like yeast, can switch between aerobic respiration and fermentation/denitrification depending on oxygen availability.
Denitrification can lead to a loss of bioavailable nitrogen from the soil, particularly during rainy periods.