Soil Science Module 5

What are the 4 types of macrofauna in soils?

Vertebrates, Arthropods, Annelids, and Mollusks

These are soil invertebrates, such as mites, dung beetles, and sow bugs, that physically break down coarse plant litter into smaller fragments, increasing the surface area for microbial decomposition.

Shredders

These are specialized organisms, ranging from microscopic protozoa and nematodes to larger invertebrates like centipedes and spiders, that hunt and consume other soil life to regulate population levels and facilitate nutrient cycling.

Soil Predators

These are soil organisms, such as certain springtails and turtle mites, that use specialized mouthparts to pierce or scrape fungal hyphae, thereby controlling fungal populations and stimulating new hyphal grow

Fungal Feeders

These are annelids that stimulate microbial activity, mix and aggregate soil, provide channels for roots, bury and shred plant residue, and create borings which improve aeration and drainage.

Earthworms

True/False

Earthworms prefer moist soil

True

True/False

Earthworms prefer coarse-textured soils

False

What pH is ideal for earthworms?

Around 6.5

These are permanent or temporary underground tunnels made by earthworms that improve soil structure by increasing aeration, enhancing water infiltration, and creating pathways for root growth.

Burrows

These are nutrient-rich waste products excreted by earthworms that stabilize soil aggregates and significantly increase the availability of minerals for plant uptake.

Casts

This is the process of using specific earthworm species, such as Eisenia fetida, to accelerate the decomposition of organic waste into a nutrient-dense, humus-like bedding material.

Vermi-composting

This is the final, nutrient-dense organic fertilizer produced through the breakdown of organic matter by earthworms and microorganisms.

Vermicompost

What are the types of microfauna in soils?

Nematodes and Protozoa

Threadworms and Eelworms belong to what category of microfauna?

Nematodes

True/False

Nematodes are eukaryotic and unicellular

False

Amoeba belongs to this category of microfauna

Protozoa

True/False

Protozoa are eukaryotic and unicellular

True

These are single-celled soil organisms characterized by hair-like projections called cilia, which they use for locomotion and to sweep bacteria into their oral grooves for consumption.

Cilliate Protozoa

These are single-celled soil organisms that use one or more whip-like appendages called flagella for movement and are essential for nutrient cycling as they primarily consume bacteria.

Flagellate Protozoa

What types of microflora are found in soils?

Bacteria, Actinomycetes, Fungi, and Algae

These microflora are simple, single-celled prokaryotic and mostly heterotrophic with some being phototrophic which prefer near-neutral pH.

Bacteria

These are engineered vessels or systems that provide a controlled environment for the growth of microorganisms or cells to facilitate the biochemical processing of substances.

Bioreactors

These microflora look similar to fungi and have spores but they are also like bacteria because they are prokaryotic and their walls are like that of bacteria.

Actinomycetes

What is the second most abundant organism in the soil?

Actinomycete

What gives soil its rich earthy smell?

Actinomycetes

Preferred pH for actinomcyetes

6-7.5

Actinomycete that fixes atmospheric nitrogen

Frankia

These microflora are important because they can decompose resistant organic compounds such as: cellulose, lignin, and chitin

Actinomycetes and Fungi

This group of actinomycetes can produce antibiotics such as: Streptomycin and Chloramphenicol

Streptomyces

These microflora are achlorophyllous and are heterotrophic with some being multicellular and some not

Fungi

In what pH do molds dominate the soil?

Low pH

Unicellular fungi

Yeast

What makes up the largest biomass of any microbe in soils?

Fungi

These are symbiotic associations between specialized soil fungi and plant roots where the fungus provides enhanced nutrient and water absorption in exchange for carbohydrates produced by the plant.

Mycorrhiza

This is known as the fungus-root symbiotic association

Mycorrhiza

These are complex symbiotic organisms consisting of a mutualistic partnership between a fungus and a photosynthetic partner

Lichen

This is known as the fungus-algae symbiotic association

Lichen

These microflora are photosynthetic and are found in moist to wet soils or at a neutral pH

Algae

Why do algae live near soil surfaces?

They are photosynthetic and require direct access to sunlight

At what depth are most microorganisms found?

3-8 cm

This refers to microscopic soil animals, such as protozoa and nematodes, that primarily function as consumers within the soil food web.

Microfauna

This consists of microscopic plants and organisms like bacteria, fungi, and algae that act as the primary decomposers and nutrient cyclers in the ecosystem.

Microflora

True/False

There is an inverse relationship between the size of organisms and their total population

True

Moisture content of soils best for microorganisms

Field Capacity

This is known as the threshold temperature

Biological Zero

What is the value of the biological zero?

5°C

These microorganisms have an adequate temperature range of -5 to 25 °C

Psychrophiles

These microorganisms have an adequate temperature range of 15 to 40 °C

Mesophiles

These microorganisms have an adequate temperature range of 40 to 70 °C

Thermophiles

These microorganisms have an adequate temperature range of at least above 60°C, usually at 80 to 100 °C

Hyperthermophiles

Food source for microorganisms

Organic Matter

True/False

Bacteria thrive in acidic conditions

False

True/False

Fungi are more resistant to acidic conditions than bacteria

True

True/False

Microbial enzymes can be denatured by pH changes

True

True/False

pH may affect the solubility of chemicals which may become toxic to microbes at high concentrations and limiting at low concentrations

True

These microbes require oxygen to survive

Aerobes

These microbe do not require oxygen to survive

Anaerobes

This is a microbially-mediated process whereby complex organic matter are reduced to simpler ones

Decomposition

This is the rapid breakdown of organic matter by oxygen-requiring microorganisms that produces carbon dioxide, water, and heat as byproducts.

Aerobic Decomposition

This is the slower breakdown of organic materials by specialized microbes in the absence of oxygen, resulting in the production of methane, organic acids, and often foul-smelling gases.

Anaerobic Decomposition

What factors affect the rate of decomposition?

Substrate, Environment, and The Microbes

This is the specific surface or material upon which an organism lives or the particular organic compound that a soil enzyme acts upon during decomposition.

Substrate

In this process, atmospheric nitrogen is converted into ammonia

Nitrogen Fixation

What microbe performs nitrogen fixation?

Rhizobium sp.

These are known as pioneer organisms in soil for their dual roles in acquiring carbon and nitrogen from the atmosphere

Cyanobacteria, Algae, and Lichen

These are two essential elements that are lacking in the soil parent material

Carbon and Nitrogen

These are bacteria that convert soil nitrates into gaseous nitrogen or nitrous oxide under anaerobic conditions, completing the nitrogen cycle but potentially reducing soil fertility for crops.

Denitrifying Organisms

What denitrifies nitrate from septic systems?

Denitrifying Organisms

These fungal structures may wrap soil particles which encourage the formation of aggregates

Fungal Hyphae

__________ of some bacteria may serve as glue in aggregate formation

Mucilaginous exudates

These refer to microbes that use light as their primary source of energy

Phototrophic

These are microbes that use chemical compounds and reactions as their source of energy

Chemotrophic

These are microbes that obtain carbon from organic compounds and are the most numerous in number

Heterotrophs

These microbes obtain carbon for fixation of carbon dioxide

Autotrophs

This refers to the organic fraction of the soil

Soil Organic Matter

This is the stable fraction of organic matter in the soil

Humus

This refers to the complex organic materials that are resistant to further decomposition

Humus

In soil organic matter composition, this is composed of 85 to 90% water and 10 to 15% dry matter

Green Tissue

C, H, and O composes how much of soil organic matter?

90%

This contains all nutrients but is an important reservoir of N, P, K, and S

Soil Organic Matter

Cellulose, starches, sugars, amino acids, and proteins are what type of materials when it comes to decomposition?

Rapidly Decomposing Materials

Fats, oils, resins, and lignin are what type of materials when it comes to decomposition?

Slowly Decomposing Materials

This refers to the ratio of C to N in the plant residue

C/N Ratio

In this ratio, the material is low in N so microbes lack N and decomposition is slow

Wide Ratio

In this ratio, the material contains excess N and decomposition of residues is fact

Narrow Ratio

This is the major source of nitrogen in most soil systems

Organic Matter

The amount and type of nutrients in organic materials depend on the type of what?

Organic Residues

This is the source of C and energy in most microorganisms

Substrate

These refer to materials from previously living organisms and are sources of carbon

Organic Matter

This provides the distinct black color of soils

Organic Matter

True/False

The dark color of soil improves its ability to absorb the sun’s heat

True

This is a good cementing agent that contributes to structure development via aggregate formation and stabilization

Organic Matter

Functions of organic matter in soil

Source of essential elements, Substrate of most soil organisms, provides the distinct black color of soils, Improves soil physical properties, contributes to CEC, and Good buffer against pH change

The branch of soil science which focuses on the occurrence, classification, distribution, and the activity of living organisms in the soil.

Soil Biology

The study of the interactions of soil organisms and the soil environment

Soil Ecology

This is a subfield of soil biology focusing on microorganisms

Soil Microbiology

These are soil organisms that require a microscope to observe and study

Soil Microorganisms

This refers to the need for presence or absence of oxygen

Aeration

This is a microbially facilitated process where nitrate is reduced to nitrogen gas through a series of intermediate gaseous nitrogen oxide products, typically occurring in anaerobic or waterlogged soil conditions.

Denitrification