Biological Soil Properties : Soil Organisms

Biological Soil Properties

by Dr. Sumihar Hutapea, MS/

Indah Apriliya, SP, M.Si 6^th Meeting

Biological Soil Properties : Soil Organisms

• The organisms that live in the soil are called soil organism

• Micro organisms are numerous in number with monopolized biological activity in soil (60-80% of total biological activity). The study of living organisms in soil is called soil biology.

• The organisms in the soil not only help development of soils but also carryout a number of transformations facilitating the

availibility of nutrients to the plants.

• The soil organisms are classified into two broad group, viz. soil flora and soil fauna.

Soil Fauna (Animal Kingdom) Soil Flora (Plant Kingdom)

01

02

• Macro-flora : Plant roots, Macro-algae

• Micro-flora : Bacteria, Actinomycetes, Fungi, Algae

•

Micro-fauna : Protozoa, Nematodes

•

Macro-fauna : Earthworms, Termites, Ants, Grubs

Classification of

soil organisms

Soil Macroflora : Plant Roots

Function in soil :

• The dead plant contribute to the formation of the soil organic matter which provides food, energy, and nutrients to microorganisms.

• Decay of plant roots, thereby changing soil properties. Eg : Soil aggregation, Water and nutrients retention, etc

Soil Microflora : Bacteria

• Bacteria are unicellular organism, have flagella, and motile.

• Size varies from 0.5 to 1 micron (length)

• They are most abundant in soil

• Shape : coccus, bacill, spiral.

• Bacterial population vary from few billion to three trilion in each kg of soil

• Types on the basis of temperature :

- Psychrophiles  <10 C

- Mesophiles  20-40 C

- Thermophiles  >40C

Genera :

- Pseudomonas

- Azotobacter

- Bacillus

- Agrobacterium

- Arthrobacter

- Etc

Soil Microflora : Bacteria

Function :

• Biological fixation of N

• Symbiotic and non-symbiotic N-fixation

• Decomposition of carbohydrates and lignins

• Decomposition of protein with the

liberation of ammonia or ammonification, nitrification, and denitrification

• Transformation of C, N, P, S, Fe, Mn

Soil Microflora : Fungi

• They are longer than bacteria, aerobic and heterotropic in nature

• Fungi are broadly grouped into yeast, molds and mushrooms.

• Prefer acid medium (4.5 to 6.5). Some Fungi can tolerate even pH 9.0

• Important molds in soil are Penicillium, Mucor, Fusarium and Aspergillus

Soil Microflora : Fungi

Functions :

• A mutually beneficial (symbiotic) aasociation between numerous fungi and the roots of higher plants is called ‘Mycorrhizae’. Eg : VAM-fungi

• Fungi decomposes almost anything in organic that cannot tackle by bacteria. They decompose

carbohydrate, celluloses, lignins, etc.

Soil Microflora : Actinomycetes

• Thread/filamentous bacteria

• A common genus is streptomyces

• Actinomycetes have transitional

characteristics between bacteria and fungi, sometimes called fungi-like bacteria.

Soil Microflora : Actinomycetes

Function :

• Actinomycetes can degrade all sorts of organic substances as celluloses,

polysaccgarides, protein, fats, etc.

• Slower activity than bacteria and fungi

• It produce very little mycelium, so less contribute humus.

Soil Microflora : Algae

• Chlorophyll containing organism, Aerobic, Photoautotrophic

• Blue green algae (BGA) also called cynobacteria are free living N- fixer

• Soil algae have been devided mainly into four classes, there are:

- Blue green algae/ Cynophyta (Anabaena, nostoc, etc)

- Chlorophyta (Grass green algae)

- Xanthophyta (Yellow green algae)

- Bacillariophyta )Golden-brown algae)

Soil Macrofauna : Earthworms

• These having slender cylindrical bodies with varing diameters

• There feed on dead organic tissues and soil materials

• Mineral soil constituents are digested and decomposed in digestive system

• Their excreta are richer in bacteria and available mineral nutrients

• They are more common in fine texture soil

Soil Macrofauna : Ants

• Ants are the most widespread species of insect in soil, and consume plant residues

• But are more active in humifying insect than plants

Soil Microfauna : Soil Protozoa

• Soil protozoa-are unicellular but larger than bacteria, size varing from few microns to few cm, found in all arable soils.

Functions

• The role of protozoa in soil is not definitely known

• As they feed on bacteria and actinomycetes, they probably help to maintain a favorable balance of the microflora in soil

https://www.nrcs.usda.gov/

Soil Microfauna : Nematodes

• Also called eelworms, thread worms or round worms

• There are various types of nematodes :

- Saprophytic (feed on decaying OM)

- Predatory (feed on earthworm)

- Parasitic (feed on roots of higher plants)

https://www.nrcs.usda.gov/

Soil Microfauna : Viruses

• These are ultramicroscopic obligate parasite (have head-tail stucture, with diameter 0.05 to 0.1 micron) always requiring a living host for their multiplication

• They are much smaller than bacteria, only visible through electron microscope

• The viruses in soil is known as bacteriophases

• When they parasitize and destroy a

bacterium of agricultural importance like

Rhizobium, they attain economic importance.

https://msystems.asm.org/

Interaction among soil organisms

• The association existing between one organism and another whether of symbiotic or antagonistoc influences the population and activity of soil

microbes

• The predatory habit of protozoa and some

mycobacteria which feed bacteria may suppress or eliminate certain bacteria

• Activities of some of the microorganisms are beneficial to each other.

Role of Organism in Soil Fertility

Soil microbes breakdown organic matter

Breakdown organic matter

Recycle nutriens

Create humus Create soil

structure

Fix nitrogen Promote plant

growth

Control pests

and diseases

“There can be nolife without soil and no soil without life, they have evolved

together”

- Charles E Kellogg

THANK YOU

Stay Safe and Healthy everyone..!!