LE3 Flashcards
Soil microorganisms play a very important role in the ff
- Soil health
- Ecosystem functions
- Plant nutrition and growth promotion
Activities of Soil Microorganisms
- Decomposition of organic compounds
- Transformation of nutrients such as Nitrogen and Sulfur
- Pesticide degradation
The compound that is resistant to microbial action
Humus
TRUE OR FALSE
Anaerobic decomposition is very -fast- and may result in the accumulation of organic matter
FALSE
very slow
Factors affecting SOM decomposition
- Aeration
- Soil temperature
- Soil moisture
- Soil pH
- Soil texture
- C/N ratio of organic material
TRUE OR FALSE
Fungi is -unaffected- by pH level
TRUE
At what soil pH are bacteria and actinomycetes inhibited?
pH 5.5
It is a convenient tool for predicting the rate of decomposition
Carbon/Nitrogen ratio
It is the optimum C/N ratio of organic materials for faster decomposition
20:1
It is the reduction of atmospheric nitrogen gas to ammonia
Nitrogen Fixation
Process that makes N available for assimilation by plants
Nitrogen Fixation
What is the nitrogen-fixing bacteria that can convert atmospheric nitrogen into useable form of ammonium?
Rhizobium
In mineralization/ammonification/decay, what are the fates of NH4+?
- fixed by clay minerals
- lost by soil erosion
- used by plants
- volatilization
What are the factors that influence the rates of mineralization?
- temperature
- moisture
- aeration
It is the process in which nitrate and ammonium are taken up by soil organisms and therefore become unavailable to crops
Immobilization
TRUE OR FALSE
Incorporation of materials with a high carbon to nitrogen ratio will -increase- biological activity and cause a greater demand for N, and thus result in N immobilization
TRUE
It is the process by which microorganisms convert ammonium to nitrate to obtain energy
Nitrification
TRUE OR FALSE
Nitrification is most rapid when soil is warm and moist and well-aerated, but is virtually halted below 5 degrees celsius and above 50 degrees celsius
TRUE
TRUE OR FALSE
The nitrifying bacteria are -anaerobic-
FALSE
Aerobic
Soil microbial activity that can significantly increase soil acidity due to the production of H+ ions
Nitrification
A process where N is lost through the conversion of nitrate to gaseous forms of N such as nitric oxide, nitrous oxide and dinitrogen gas
Denitrifiction
It is common in poorly-drained soils and occurs when the soil is saturated, and the bacteria uses nitrate as an oxygen source
Denitrification
Bacteria responsible for denitrification belong to the ff genera
- Pseudomonas
- Clostridium
- Bacillus
- Paraccoccus
Under aerobic environment, sulfur may be oxidized by ___________ to SO4 with a release of energy
Thiobacillus thiooxidans
Under anaerobic conditions, sulfate may be reduced by what bacteria?
Desulfovibrio desulfuricans
It is the end product of sulfur transformations and emanates the characteristic offensive odor of flooded soils
H2S
Hydrogen sulfide
Processes involved in the inactivation of pesticides in the soil
- Detoxification
- Conjugation
- Degradation
It is the conversion of the pesticide molecule to a non-toxic compound
Detoxification
A process by which an organism make the substrate more complex by combining the pesticide with cell metabolites; addition of amino acid, organic acid or methyl crown to the substrate
Conjugation
It is the breaking down/transformation of a complex substrate into simpler products leading finally to mineralization
Degradation
It is the single most important method by which pesticides are completely removed from soils
Biochemical degradation of pesticides by microorganism
TRUE OR FALSE
The organophosphate insecticides, such as parathion, are degraded quite -rapidly- in soils by a variety of organisms
TRUE
Creatures that spend all part of their lives in the soil environment
Soil organisms
Roles of soil organisms
- maintaining fertility, structure, drainage and aeration of soil
- decomposition
- conversion of nutrients into plant-available forms
It is the mix of species present
Species diversity
It is the capacity to use a wide variety of substrates and provide a range of ecosystem services of function
Functional diversity
The species diversity and functional diversity of the soil are influenced primarily by the ______________________
amount and quality of available food
What are the classifications of soil organisms?
- based on size
- based on metabolism
- based on ecological function
- based on hierarchy of organisms in the soil food web
Classification of soil organism based on size with a range of 20mm upward
megafauna
Classification of soil organisms based on size with a range of 2 to 20mm
macrofauna
Classification based on size with a range of 100 micrometers to 2mm
mesofauna
Classification of soil organisms based on size with a range of 1 to 100 micrometers
microfauna and microflora
These are the primary producers and organisms that obtain their C mainly from CO2
autotrophs
Autotrophs that obtain energy from sunlight
Photoautotrophs
Autotrophs that obtain energy from or oxidation of various elements
chemautotrophs
Organisms that are incapable of making their own food from light or organic compounds that’s why they feed on organisms or remains of other organisms to get their necessary energy to survive
Heterotrophs
Organisms that subsist on living plants
herbivores
Organisms that subsist on dead plant debris
detritivores
Organisms that consume animals
predators
Organisms that live off but do not consume other organisms
parasites
These are known as the “cows” of the soil and these tackle easy to decompose materials like green yard waste and manure
soil bacteria
These are known as the “goats” of the soil that consumes the tougher, hard to decompose materials like straw, pine needles, bark and wood
fungi
In the third level of the soil food web, these are highly mobile organisms that feed on bacteria and on each other
Protozoa
In the third level of the soil food web, these organisms feed on fungi and plant-feeding nematodes; they chew fresh organic material into smaller pieces for easier decomposition
microarthropods
These are the ingested soil expelled by earthworms
globular casts
What are the major groups of soil microorganisms?
- bacteria
- fungi
- actinomycetes
- algae
These are prokaryotic, single-celled, microscopic oganisms that is considered the most important in terms of their effect on soil properties
bacteria
Classifications of bacteria
- based on morphology
- based on nutritional requirements
Groupings of bacteria based on oxygen requirement
- aerobic
- anaerobic
- facultative
- microaerophiles
- aerotolerant
Bacteria group that prefers aerobic respiration but is capable of switching to anaerobic if oxygen is absent
facultative
Bacteria group that needs low concentration of oxygen
microaerophiles
Bacteria group that doesnt need oxygen but is not poisoned by oxygen
aerotolerant
Bacteria groupings based on pH for optimum growth
- acidophiles (below neutral)
- neutrophiles (neutral)
- alkaliphiles (alkaline)
Bacteria grouping based on temperature for optimum activity
- mesophilic (20-45C)
- thermophilic (45-85C)
- psychrophilic/cryophilic (-20-10C)
- hyperthermophilic (115C)
Functional groups of bacteria in the soil
- decomposers
- mutualists
- pathogens
- lithotrophs/chemautotrophs
Microscopic cells that usually grow as long threads or strands called hyphae
fungi
Fungi are __________
aerobic and heterotrophic
It is a symbiotic association composed of a fungus and roots of a vascular plant
mycorrhiza
TRUE OR FALSE
Mycorrhizal plants are often more resistant to diseases
TRUE
It is an intermediate between bacteria and fungi; unicellular and do not have distinct cell wall like bacteria
actinomycetes
It is important in the degradation of organic materials in the soil including lignin
actinomycetes
It is present in most of the soils where moisture and sunlight are available; aerobic and photoautotrophic
algae
Four main classes of algae
- cyanophyta (blue-green)
- chlorophyta (grass-green)
- xanthophyta (yellow-green)
- bacillariophyta (golden-brown)
Specialized cells that are possesed by some blue green algae which is the site of nitrogen fixation
heterocyst
It is the capacity of a soil to provide essential chemical elements in adequate quantities and proportions for the growth of specified plants
soil fertility
It is the capacity of a soil for producing a specified plant or sequence of plants under a specified system of management
soil productivity
Other factors that make a soil productive
- moisture
- aeration
- absence of pests and diseases
- presence of micro-organisms that support plant growth
- management practices
- large amount of topsoil
How many nutrient elements are considered essential for plant growth
18
The essential nutrient elements are derived from :
- organic matter
- minerals
- air
- water
What is the major source of N?
organic matter
What are the major sources of P?
- acid soluble P
- calcium phosphate
- aluminum phosphate
- iron phosphate
Nutrient element that are found in minerals like feldspars and micas
potassium
Nutrient element that are found in minerals like gypsum and pyrite
sulfur
It is among the most abundant of micronutrients
iron
TRUE OR FALSE
Kaolinite clays exchange Ca2+ more readily at a much lower %BS
TRUE
What are the mechanisms of nutrient uptake?
- root interception
- mass flow
- diffusion
What are the most active points of nutrient uptake?
root hairs
A concept that states plant growth is constrained by the essential element that is most limiting
Justus von Liebig’s Law of Minimum
Any organic or inorganic material or compound which can supply one or more of the essential nutrients needed by plants for normal growth
fertilizers
It is the guaranteed minimum analysis of the plant nutrient in terms of N, P, K percentage
fertilizer grade
It is the relative proportion of each of the primary nutrients in a fertilizer material
fertilizer ratio
Any substance added to fertilizer materials to provide bulk, prevent caking or serve some purpose other than providing essential plant nutrients
filler
Classification of fertilizers
- organic
- inorganic
Common approaches used to determine fertilizer needs
- nutrient hunger signs on growing crops
- plant analysis
- soil tests
- fertilizer trials
The Rs in the proper use of fertilizers
right type, right time, right place, right amount, right method
It is the loss of soil through the action of water, wind, or gravity
soil erosion
TRUE OR FALSE
75% of the Philippines’ croplands are vulnerable to erosion
TRUE
On-site impacts of soil erosion
- reduction in soil depth
- structure deterioration
- nutrient loss
- decline in soil fertility
- loss of production
- decline in soil biota
What are the general types of soil erosion?
- geological erosion
- accelerated erosion
A type of soil erosion that is described as wearing away of the earth’s surface by water or other natural agents under natural environmental conditions of climate, vegetation and so on; undisturbed by man
geological erosion
A type of soil erosion that is much more rapid than normal, natural, geological erosion; primarily a result of the activities of humans or, in some cases, animals
accelerated erosion
The process of soil erosion
detachment, transport, deposition
It is the most important detachment agent
rainfall
It is a step in the soil erosion process that occurs when sufficient energy is no longer available to transport the particles
deposition
Three important effects of raindrop impact
- it detaches the soil
- it destroys granulation
- its splash, under certain conditions, causes an appreciable transportation of soil
Kinds of soil erosion by water
- sheet erosion
- rill erosion
- gully erosion
It is the removal of a fairly uniform layer of soil from the land surface by runoff water
sheet erosion
It occurs mainly on cultivated soils wherein numerous small channels of only several centimeters in depth are formed
rill erosion
It is a kind of soil erosion wherein water accumulates in narrow channels and, over short periods, removes the soil from this narrow area to considerable depths
gully erosion
For rainfall, it is a function of intensity, duration, mass of raindrop, diameter of raindrop, and velocity of raindrop
erosivity
TRUE OR FALSE
Fine particles are resistant to detachment because of their cohesiveness
TRUE
It is the function of slope length and slope steepness
slope
TRUE OR FALSE
As slope steepness increases, soil loss rate also rises at an increasing rate
TRUE
It is the greatest deterrent to soil erosion
plant cover
It reduces vegatation cover due to tillage, burning, overgrazing, mining, logging and road construction
human activities
It is the most widely-used to tool to estimate soil erosion
Universal Soil Loss Equation (USLE)
The soil erodibility factor K can be approximated from a ____________
nomograph
What are the methods of soil conservation?
- control of soil erosion
- maintenance of soil fertility and productivity
- avoidance of soil toxicities
It is the single most effective measure in reducing erosion
surface covers
These are temporary vegetative cover of fast growing annuals
cover crops
These are perennials or regenerating annuals specifically established to protect soil from erosive agents
ground cover
It is the practice of spreading plant residues/other organic materials on the ground between crop rows or round tree trunks to protect the bare soil
mulching
It is the use of coconets to protect the slopes
geotextiles
These are constructed along the contour of the land at defined intervals, to intercept and/or divert runoff
physical barriers
It is a method where slope is converted into series of level to nearly level steps running across the slope supported by steep risers with horizontal cultivated area on the step
bench terracing
These are fence-like structures made up of rocks and/or stones piled along the contour of sloping lands
contour rockwalls
These are embankments of stones, grasses, or compacted soil which are constructed along the contour to slow down surface runoff and trap eroded soil
contour bounds
These are ipil-ipil stems bundled into rows across the slope and staked to form low barriers
pole barriers/contour fences
These are hedges of leguminous trees or shrubs or grasses grown on the contour at a defined interval
contour hedgerows
These are naturally occurring vegetation like grasses and herbs that are left in narrow strips to serve as barriers
natural vegetative strips
These are banks or barrier trashes and/or earth that are constructed across the slope of the land to check surface runoff and soil erosion
contour composting
These are natural/artificial drainage channel along the steepest slope, in the valley or along the boundaries of the upland farm used to accomodate runoff
diversion canals
These are holes that are dug immediately along water channels
contour canals
These are channels constructed across the slope to catch upslope runoff and divert it safely to a nearby gully, waterway/river
grassed waterways
These are obstruction walls across the bottom of a gully which reduce the velocity of the runoff and prevent the deepening or widening of the gullies
check dams
These are small canals dug along the contour line
soil traps
It is the practice of sowing crops directly into the residue of the previous crop without cultivation
zero tillage
It is the practice of sowing crops on lightly cultivated soil
minimum tillage
It is the practice of plowing, harrowing, and furrowing along the contour of the land
contour plowing
It is a method that forms multi-layered canopy that reduces rainfall velocity
multi-storey agroforestry system
The soil classification system used by the Philippines
USDA Soil Taxonomy
Soil order with formative element alf
Afisols
Soil order with formative element and
Andisols
Soil order with formative element id
Aridisols
Soil order with formative element ent
Entisols
Soil order with formative element el
Gelisols
Soil order with formative element ist
Histosols
Soil order with formative element ept
Inceptisols
Soil order with formative element oll
Mollisols
Soil order with formative element ox
Oxisols
Soil order with formative element od
Spodosols
Soil order with formative element ult
Ultisols
Soil order with formative element ert
Vertisols
How many soil orders are there?
12
Three soil orders that are not found in the Philippines
Gelisols, aridisols and spodosols
