Unit 4, 5 Flashcards
What is nitrification?
the process performed by soil bacteria that turns ammonium into nitrate
Why is the symbiotic relationship between rhyzobia bacteria and root beneficial?
nitrogen fixation - nitrogen is converted to ammonia by the rhyzobia bacteria, then the nitrifying bacteria turns the ammonia into nitrate
What is the soil organism associated with roots of some plants that has been effective at cleaning up pipeline spills?
mycorrhizal
What component (fraction) of SOM promotes formation of large aggregates that show water aggregate stability?
active
What is the best description of humus?
- dark in color very resistant to microbial decomposition
Properties of humus that are similar to clay?
- negative charges
- form aggregates
- colloidal nature
- high specific surface area
- large water holding capacity
What is a benefit of clay and humus forming a strong interaction?
- helps form aggregates
- humus is protected from decomposition
Which combination of climate and soil aeration results in highest accumulation of SOM?
- cold temps
- waterlogged conditions
What is the difference between active and stable SOM?
- active: non-humic, most important food source for microbes, quickly decomposed
- stable: humus, dark colour, strongly attached to soil mineral particles, does NOT decompose easily
What is more affected by management practices, active or stable SOM?
active
What is SOM?
- complex and diverse mixture of organic substances
- all organic substances contain organic carbon (from photosynthesis)
The 3 major components of SOM?
- living biomass
- active
- stable
What are the main groups of soil microorganisms?
- bacteria and fungi
What is the topsoil (0-15cm) biological activity dominated by?
- earthworms & microorganisms
How many microorganisms can be found in a teaspoon of healthy soil?
15 million to 4 billion
What are benefits of soil microorganisms?
SOM decomposition
- mineralization: nutrients change from organic to mineral ionic form
- production of organic glue
- formation of by-products used for humus synthesis
- nitrification
- nitrogen fixation
- phosphorus plant uptake
- mycoremediation
- plant growth enhancement
- phytoremediation
- humus synthesis
What is mineralization?
SOM decomp
nutrients changing from organic to mineral ionic form
How is organic glue formed and how is it helpful?
- produced by soil microorganisms decomposing the SOM. as they eat the SOM it produces glue
-sugar like product that binds soil particles into larger water stable aggregates - promotes aggregate formation and stability
What is nitrification?
Nitrosomonas and nitrobacter
bacteria oxidizes ammonium to nitrate
NH4+ + 2O2 → H2O + 2H+ + NO3
What is nitrogen fixation?
- rhizobia bacteria associated with legume roots are the most important nitrogen fixing microorganisms
What is a symbiotic relationship?
mutually beneficial
What is phosphorus uptake?
Mycorrhizae (fungus)-root
symbiotic association increases plant P uptake
What is mycoremediation?
Mycorrihizae fungi from dandelion roots are inoculated into straw mats and rolled out into crude oil contaminated sites to break down the hydrocarbons
What is humus synthesis?
- microbes link decomposed by-products into complex compounds called humus making them resistant to further decomp
What is carbon to nitrogen ratio?
The higher the C/N ratio of a plant residue the slower its decomposition - not enough nitrogen
to satisfy microorganisms’ growth
What are aerobic microbes?
need oxygen for metabolism
What are anaerobic microbes?
use powerful compounds such as NO3 and may produce N2O (greenhouse gas)
What is the ideal temp for microbe growth?
20-40C
What is the most important food source for microbes?
active SOM (non-humic)
Does hummus decompose easily?
no, can stay in soil for centuries or even millennia
Which type of SOM is colloidal in nature?
stable (Humus)
Is SOM the only factor that forms water stable aggregates?
yes
Soil property benefits of SOM?
- improves consistence
- increase porosity
- improve drainage (fine soils)
- improve water holding capacity (medium soils)
- decrease bulk density
- reduces / prevents erosion
- ## improve fertility
Environmental benefits of SOM?
- less water needed
- less fertilizer
- reduced water pollution
- greater plant production
- carbon sink / storage
Which factors result in high SOM accumulation?
- low temp
- low aeration
Which texture of soil has the highest accumulation of SOM?
clayey soils
Why does more SOM stay in chernozemic cultivated soils vs luvisolic forested cultivated soils?
- forested soils are more acidic so the OM doesn’t decay as quickly
Which practices reduce loss / increase SOM?
- no till
- no summer fallow
- varied crop rotation
- addition of animal manure
- cover crops
What is the importance of cation exchange process in soils?
- allows soil to both store and supply nutrients
- reduce leaching losses
Why are forested soils more acidic than grassland soils, in general?
forested vegetation is more acidic
Which of the following ions are non-acidic (base cations)?
Ca, Mg, K, Na
Is every alkaline soil saline?
no
What is the main cause of poor plant growth in saline soils?
difficulty of water uptake
What is the main cause of soil salinity in the prairies?
movement of excess saline groundwater to the soil surface
What is capillary rise?
salinized groundwater to come to the surface
What are common salt tolerant weeds in southern AB?
koshia, foxtail barley
Solonetzic is the name for which types of soil in canada?
saline-sodic
What is active acidity?
- concentration of H+ in soil solution
- a pH test will only measure active acidity
What is reserve acidity?
- -H+ adsorbed on clay and humus colloids
- much larger than active acidity
What is an exchange of cations?
when one adsorbed cation diffuses into the soil another moves into its place, adsorbed cations are held by weak forces
What is CEC?
cation exchange capacity
total sum of exchangeable cations adsorbed or loosely held by soil colloids
Is CEC an indicator for soil fertility?
yes
What is percent base saturation?
a formula used in diagnosing chernozemic A horizon
How are CEC units expressed?
cmol(+)/kg (centimol of positive charges per kg of soil)
What is a common type of clay in semi-arid climates?
smectites (80-120 cmol/kg)
Which soil textures have higher CEC?
clay, humus
What is buffering capacity?
the soils capacity to maintain a relatively stable pH despite the presence of acidifying or alkalizing factors
Would soils with high CEC need more lime or less lime to correct pH?
more lime to correct pH
Does sand have a high or low buffering capacity?
low
Acids produce which ion when dissolved in water?
hydrogen H+
Bases produce which ion when dissolved in water?
hydroxide OH-
What is pH?
- measurement of the concentration of H+ ions in a solution
- measures the soil reaction
In pure water OH- is equal to H+, which means a pH of?
7
An increase in H+ ions would mean that the solution pH increases or decreases?
decreases. it becomes more acidic with more H+ ions
More hydrogen = more acidic
What is the pH range for luvisolic soils?
about 4-6
contains pyrite
What is the pH range for productive agricultural soils?
5.5 - 8
What is considered a neutral pH in soil terms?
6.5 - 7.5
Why are soils with a pH below 5.5 a concern?
- increase in Mn, Fe, Al
- reduces nitrogen, Ca, Mg, K, P
- reduces soil bacteria
What happens to phosphorus when soil is too acidic?
P bonds tightly to Al, Mn and Fe and is removed from soil solution
Which ion is highly toxic to plants?
aluminum
Which metal micronutrients are essential to plants but too much becomes toxic?
Mn, Fe
How is aluminum (pg 24)
What is hydrolysis?
when H and O split from H2O
