Creatures that spend all of their lives in the soil environment
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Macrofauna
moles, mice, ants,beetles,termites,grubs,millipedes and earthworms
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Mesofauna
springtails and mites
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Microfauna
nematodes and single celled protozoans
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Flora
plant roots, algae and diatoms
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Microorganism
fungi, bacteria and actinomycetes
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Species Diversity
the mix of species present
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Functional Diversity
the capacity to use a wide variety of substrate and provide a range of ecosystem services.
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Functional Redundancy
several organisms can carry out each ecosystem service: Leads to ecosystem stability and resilience
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Keystone species
a species that is unique in filling an ecological niche and is therefore integral to the functioning of that system
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Global Biodiversity
great genetic resource of soil organisms
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Stability
the ability of soil, even in the face of wide variations in the environmental conditions and inputs, to continue to perform such functions of: cycling of nutrients; assimilation of organic waste; maintenance of soil structure.
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Resilience
the ability of soil to bounce back to functional health after severe disturbance has disrupted normal processes
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Soil Food Web
The community of organism living all/part of their lives in the soil
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Autotrophs
organism that can feed themselves by harnessing light energy to make organic molecules such as carbohydrates; proteins, lipid and nucleic acid out of inorganic raw materials
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Heterotrophs
organism capable of deriving energy for the life processes only from decomposition of organic compound and incapable of using inorganic compound such as sole sources of energy
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Photosynthesizers
First trophic level - algae Ø Role: capture solar energy to fix carbon dioxide
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Decomposers
Second trophic level - bacteria, fungi, protozoa Ø Role: breakdown residue, immobilizes nutrient in their biomass, create new organic compound, bind soil aggregates
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Mutualist
Second trophic level; Two organisms living in beneficial association -bacteria, fungi- Ø Role: enhance plant growth, fix N
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Symbiosis with mycorrhiza
Facilitates the uptake of P, other nutrients and water uptake Ø Glomus spp. P.tinctorious etc
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Biological Nitrogen Fixation (BNF)
Process by which microorganism in the soil fix atmospheric N and make it available for assimilation by plants. Ø Rhizobium, Azospirillum etc.
Second trophic level - nematodes, arthropods Ø Role: consume plant roots, crop yield loss
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Shredders
Third trophic level - earthworm, arthropods Ø Role: breakdown residue, enhance soil structure and provide habitat for bacteria in gut
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Organism abundance
Soil organism number are influenced primarily by amount and quality of food available and management practices
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physical factor
moisture temperature
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biotic factor
predation and competition
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chemical characteristics of soil
acidity, alkalinity and salinity
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Earthworm
Digest organic and mineral matter passing their bodies-30t/ha/year
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Earthworm
Excrete cast that has high amount of nutrients;
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Earthworm
Facilitate aeration and drainage- through channels created
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Earthworm
Increase size and stability of soil aggregates
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Nematodes
Help decomposition of OM -they invade plant roots and cause the death of roots
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Protozoa
They ingest other soil organism particularly bacteria -help hasten the release of some nutrient that have been immobilized by bacteria
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Bacteria
Involved in OM decomposition as well as in various transformation of nutrients such as: ammonification, nitrification, denitrification, immobilization, biological N fixation etc.
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Fungi
The most adaptable and versatile of soil organism
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Fungi
Able to thrive in extreme acidity and alkalinity
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Fungi
Able to decompose even the resistant organic compound such as lignin,cellulose.
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Mycorrhizae
help plants in solubilization of P an its absorption
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Actinomycetes
These organisms also attack and simplify complex and resistant organic compound such as cellulose, chitin and phospholipids
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Autotrophic
use carbon dioxide as their source of C and derived energy for their metabolism from the oxidation of simple inorganic compound
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Heterotrophic
oxidize organic matter to get C and energy
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Chemoautotrophic
use inorganic chemical compound
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Photoautotrophic
use sunlight as their source of energy
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Aerobic
requires oxygen to survive
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Anaerobic
not requires oxygen to survive
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Facultative
organism that makes ATP by aerobic respiration if oxygen is present but capable of switching to fermentation
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Microaerophiles
need low concentration of oxygen
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Aerotolerant
does not need oxygen but is not poisoned by oxygen
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Mesophilic
(20-45 0C)
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Thermophilic
(45- 80 0C)
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Psychrophillic or cryophilic
( -20 -10 0C)
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Hyperthermophilic
(\> 115 0C)
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Acidophiles
grow best in acidic condition
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Neutrophiles
grow best at neutral pH
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Alkaliphiles
grow best in alkaline condition
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Halophiles
requires some NaCl for growth
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Mild
requires 1-6% salt
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Moderate
requires 6-15% salt
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Extreme
requires 15-30% salt
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Halotolerant
grow best in the absence of NaCl
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Osmophiles
organisms able to live in environment high in sugar
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Xerophiles
organisms which live in dry environment
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Carbon Cycle
All organic matter eventually is oxidized (burned) and convert back to carbon dioxide and water
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Decomposition of Organic Compounds in Aerobic Soils
1. Carbon compound are enzymatically oxidized to produce CO2, H2O, energy and decomposer biomass.
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Decomposition of Organic Compounds in Aerobic Soils
2. The essential nutrient element such as: N, P and S are release and/or immobilized by series of specific reaction that are relatively unique each element.
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Decomposition of Organic Compounds in Aerobic Soils
3. Compound resistant to microbial action are formed, either: through modification of compounds in the original tissue or by microbial synthesis
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Decomposition in Anaerobic Soils
The product of anaerobic decomposition include a wide variety o partially oxidized organic compound such as: organic acids, alcohols, methane gas.
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Decomposition in Anaerobic Soils
Anaerobic decomposition releases relatively little energy for organism involved.
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Decomposition in Anaerobic Soils
Issues related to the product of anaerobic decomposition; they produce foul odor/ inhibit plant growth; the methane gas produce in wet soils is a major contributor to greenhouse effect
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Nitrogen Cycle
Form of N in the soil
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Organic N
amino acid
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Organic N
amino sugar
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Inorganic N
NH4+(ammonium)
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Inorganic N
N2O (nitrous oxide)
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Inorganic N
NO3-(nitrate) N
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Inorganic N
O2 (nitrogen dioxide)
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Inorganic N
NO2-(nitrite)
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Inorganic N
NO (nitric oxide)
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Inorganic N
N2(nitrogen gas)
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Inorganic N
NH3 (ammonia)
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Mineralization
conversion of organic N into inorganic forms
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Immobilization
the conversion of inorganic N back to organic N; Available N is used by soil microorganism and assimilated into their bodies
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Biological Nitrogen Fixation
Conversion/ reduction of nitrogen gas into ammonia
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Biological Nitrogen Fixation
Can only be done biologically by high specialized group of micro organism in the presence of the enzyme nitrogenase which catalyzes the reduction of nitrogen gas into ammonia
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Biological Nitrogen Fixation
N2 + 6e-+ 8H+ 2NH3 + H2
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Symbiotic Nitrogen Fixation
Association between higher plant (macrosymbiont) and a microorganism (microsymbiont) to acquire N from atmosphere Example: Rhizobium
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Symbiotic Nitrogen Fixation
The irritation causes nodules to form in roots. The bacteria in the roots trap atmospheric N which transform into NH3. NH3 combines with organic compound to form amino acids and proteins. In turn, the plant supplies the carbohydrates and energy for their metabolism.
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Non- Symbiotic Nitrogen Fixation
Conversion of atmospheric N by microorganism without associated plant host
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Nitrification
Biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of nitrite to nitrate
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Denitrification
Biochemical reduction of nitrate to gaseous N by anaerobic soil organism
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Ammonification
Result of the breakdown of organic matter such as dead animals and plants or waste material like excrement
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Ammonification
Microorganism produce ammonia and related compounds as a by-product of their metabolisms
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Sulfur Cycle
Like N, sulfur also undergoes mineralization, immobilization, oxidation-reduction through microbial activities.
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Sulfur Cycle
S become available to plant through decomposition of S- containing compound like: cysteine and methionine.
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Sulfur Cycle
Under aerobic environment, S may be oxidized by Thiobacillus thioxidans to SO42-with release of energy.
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Sulfur Cycle
Under anaerobic conditions as in paddy soils, sulfate may be reduced by the bacteria Desulfovibrio desulfuricans.
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Sulfur Cycle
They use the oxygen in sulfate to oxidize organic compound; The end product is H2S; The characteristic offensive odor of flooded soils is primarily emanating from H2S
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Pesticide Degradation
Biochemical degradation by soil organisms is the single most important method by which pesticide are removed from the soil.
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Pesticide Degradation
Certain polar groups on the pesticide molecules, such as –OH, -COO and NH2 provide points of the attack for the organisms