Questions Flashcards
A sticky, putty-like feed indicates a high % of which soil separate
Clay
For which substance would the particle density equal the bulk density
quartz
Soil colours are scientifically described by____ colour designations such as 10YR3/4
Munsell
Brown and red colours in subsurface horizons are caused by ___ in the soil
iron oxides
Due to greater surface area per unit of soil mass, silt loam generally have a greater capacity than loamy sand to __
Absorb water, absorb gas, Release nutrients by weathering
Which soil has more pore space: clay vs sand
Clay - micropores + macropores (clay aggregates)
Soil organic matter consist of
organisms, dead tissues, polymerized and non-minerals
What is material deposited in lakes called
Lacustrine
Which of the following is not a characteristic of soil colloids
low water holding capacity
A well-drained soil under a rain forest in brazil contains significant amounts of a clay, which is likely
Kaolinite
Which of the silicate clays would likely have the highest of potassium in the crystal structure
Fine Grained Mica
Drainage of wetlands can result in extreme soil acidity. Which process, is occurring when the soil is drained
Oxidation of sulfur-bearing minerals that produces sulfuric acid
Phosphorous availability in acid soils is constrained by the presence of significant quantities of reactive___
Iron
The very high pH levels found in some arid region soils are most likely due to high levels of exchangeable
Na+
In various parts of the world, soil phosphorous is associated with which of the following health/environmental problems
eutrophication of lakes because of a build-up of soil P in the water sheds
In most soils, mineralization of SOM is an important source of plant available
both P + K
You would be most likely to find P deficient plant in which location
Sub-Saharan Africa
In what range of soil pH is phosphorous generally most available to plants
6-7
The total phosphorous lost from various watersheds is most closely correlated with high soil erosion (T/F)
true
The principal form of sulfur taken up by plants is by sulphate ion (T/F)
true
Oxidation of sulfides to sulphuric acid in soils developed in marine marshes can become extremely acidic if drained (TF)
true
The water contents are different in these soils, but the water potential is the same (TF)
True (the width of the film around the soil particles) Water film thickness is the same, so water potential is the same
The great majority of nitrogen in soils can be found in the form of dissolved anions
false Nitrogen is in an organic form, only a small amount is available as dissolved ions
Denitrification is NO3- (nitrate) becomes N2(gas) and goes into the atmosphere TF
true
What process is this? Biological oxidation of ammonia to NO2 (nitrite) then NO3 (nitrate), usable by plants
nitrification
Sodic soils are commonly formed by leaching saline-sodic soils TF
true
The mineral nitrogen is required for which part of a plant
DNA, enzymes, chlorophyll
The great majority of nitrogen in soils can be found in the form of
organic compounds
Secondary minerals are more prominent in the ____ fraction of soils
clay
Opposite of mineralization
immobolization
what is mineralization
process by which chemicals present in organic matter are decomposed or oxidized into easily available forms to plants
all but a few nematodes are pests TF
false
the osmotic potential is dependent on the presence of salts and other solutes in the soil
true
CEC of the soil is determined primarily by the amount and type of colloids in the soil, and by the pH
true
Natural causes of salt in soils
Weathering of minerals such as magnesium, calcium, sulphates etc.
Lack of drainage - Arid and semi arid environments have a lack of drainage and this causes low precipitation and minimal leaching
Sea water intrusion - Mediterranean regions
Man-made sources of salt in soil
Excessive fertilization
Soil amendments such as compost, manure, etc.
Deicer from roads
Management techniques for salty soils
Grow salt tolerant crops - doesn’t solve the problem
Use high quality irrigation water that is not saline
Keep soil moist because water dilutes salt
Avoid over fertilization
Mulching to prevent evapotranspiration (water from leaving soil and plants)
Monitor soil so you prevent soils from becoming too saline
Three general rules to reclaiming salty soils
Establish internal drainage - add drain tiles
Replace excess exchangeable salt - removable by leaching of excess soluble salts without bringing in further Na+
Leach out most of the soluble salts
6 ways roots add organic compounds to rhizosphere
getting rid of root cap cells
excretion of mucigel
spilling of cell contents with when epidermal cells are lysed
releasing of specific compounds produced by root hairs
releasing of various compounds by cortical cells
export of symbiotic compounds to fungi
What is carbon sequestration
Plants take in CO2 from the atmosphere through the process of photosynthesis in order to make glucose to feed themselves. Carbon sequestration is the process of the plants holding on to this CO2 in their roots.
3 functional groups of soil fungi
Decomposers: breakdown dead tissues and convert it to organic matter
Mutualists: mycorrhizal fungi colonize plant roots and have a symbiotic relationship where they provide a larger surface area for the plants in order to absorb
Pathogens or parasites: colonize roots and other organisms causing them death or reduced production
Describe an important role of protozoa
Contribution to Mineralization
Protozoa have a low amount of N in their cells in comparison to the bacteria that they eat
When they eat the bacteria they want to get rid of the excess N so they release it in the form of ammonium (NH4)
Bacteria and other organisms rapidly take up the ammonium but some is left for the plant as available nutrients
4 important roles of earthworms
Increase infiltration: when they move for soil they increase porosity.
This helps with the flow of soil air and water
Provide channels for root growth
Increase water holding capacity
Mix and aggregate soil - their waste helps create aggregates
What are the four chemical processes in soil weathering?
Hydrolysis
Hydration
Carbonation
Oxidation
Define Hydrolysis
the chemical process where water is added to a material
Define Hydration
absorption of water by materials causing swelling
Define Carbonation
CO2 dissolves causing carbonic acid which acidifies water and increases solvent action
Define Oxidation
inclusion of oxygen into a mineral
4 fates of nitrates in the soil
Immobilization by microorganisms:
Ammonium and nitrates are taken up by microorganisms and therefore become unavailable to crops
Removal by plant uptake
Leaching to groundwater:
Nitrates are very volatile and leach easily
Volatilization/Denitrification:
Nitrates to nitrogen gas or ammonia gas which is released into the atmosphere
Ammonification:
Dead OM & waste turns into ammonium in the soil
What are 4 of the main functions of SOM?
Water storage
Nutrient Storage
Soil aggregation
Carbon sequestration
How does OM improve mineral, sandy, and clay soils? (6)
Sandy soils - increase water and nutrients content
Clay soils - loosens and improves tilth
Stores organic and inorganic nutrients used by plants and other organisms
Soil aggregates
Improves soil structure
Improves water and air filtration
How much water can SOM store?
Both humus (stabilized OM) and SOM absorb water like a sponge, humus can store 6 times its own weight
Why/how does SOM provide and hold nutrients?
Colloids hold water and nutrients
Aggregates help prevent soil erosion which washes away nutrients
Makes several nutrients more available for plant use
Describe soil aggregates as a function of SOM
Aggregate formation increases water/O2 flow while also preventing erosion and leaching
Describe carbon sequestration as a function of SOM
Keeps carbon out of the atmosphere
Carbon comes from the atmosphere into the plant and then the plant residues become part of the SOM and the carbon is retained
List and describe the groups of nematodes
4 groups of free-living nematodes based on their diet
Bacteria feeders
Fungal feeders
Predatory nematodes: eat all types of nematodes and protozoa
Omnivores: eat a variety of organisms or different organisms at different points of their life cycle
Root-feeding nematodes - not free-living
What are nematodes functions?
Nutrient cycling:
release nutrients in plant available forms
Grazing:
at low nematode densities they stimulate the growth of their prey such as bacteria, plants, and fungus
Dispersal of microbes:
distribute these by carrying them in their digestive systems and then pooping them out
Food source:
nematodes are food for higher predators - including nematode feeding nematodes
Disease suppression and development:
some nematodes consume disease-causing organisms
Where are nematodes located in the soil?
Nematodes are located near their prey groups
They are more common in larger grained soils because of their size
How many nematodes are in a tablespoon of soil in the following locations: agricultural soils, grasslands, forests
Agricultural soils usually have less than 100 nematodes in each teaspoon
Grasslands have around 50 to 500 nematodes in their soil
Forests have several hundreds of nematodes in their soils
What are nematodes useful indicators of? and why?
Nematodes are useful indicators of soil quality because of their tremendous diversity and participation in many functions of the soil food web
Changes in nematode populations reflect changes in ___ __________
soil microenvironments
What type of soil will you find nematodes in?
Undisturbed & high SOM
What are actinomycetes?
Type of bacteria
Major factors that effect/influence the amount of soil OM present (7)
· Vegetation · Climate · Soil texture · Drainage · Tillage · Rotations/residues · Policy
How to manage SOM and keep it around (7)
Conservation tillage
Conserve crop residues
Practice yard recycling
Grow CC, incorporate green manure
Crop rotation
Mulches to manage soil moisture
Cover crops always used – no bare soil
Good management of SOM increases: (8)
· Soil stability · Air filtration · Water and nutrient holding capacity · Infiltration · Aggregation · Structure · Humus · CEC
define wilting point
there is so little water in the soil that the plant cannot overcome adhesion in order to absorb the water
What is soil respiration?
the amount of CO2 released from the soil
What are 3 sources of CO2 in the soil?
Respiration of plants through their roots - during the day most plants take in CO2 to perform photosynthesis (create food for themselves in the form of glucose) then during the night they release CO2 (less than they take in during photosynthesis).
Faunal respiration - nematodes, earthworms, protozoa, etc. all breath in oxygen and release CO2
Microbial respiration - aerobic decomposition of SOM to obtain energy for their growth
Why does clay have 30% water in it and sand is very well drained?
Soils ability to retain water is strongly related to particle size, clay has a larger surface area than sand which means that it has more potential sites for water to attach to (this relationship between water and soil particles is called adhesion).
Clay soils have micropores inside of them as well as macropores on the outside. Sandy soils have very few micro pores compared to clay soils.
CEC
Micro vs macropores
SA
Why do clay and sandy soils have a different field capacity and wilting point?
What is the cation exchange capacity (CEC)?
The total number of cations that a soil can hold.
How does CEC affect soil fertility?
a soil with a high CEC is able to hold more cations - meaning they can hold more nutrients
Describe the rhizosphere: where it is, and 3 benefits/purposes of it (4)
1-2mm from plant roots
site of nutrient cycling
can act as a significant carbon sink
mineralization: break down nutrient to be part of inorganic pool
What are causes of acidity? (6)
Industrial fertilizers
Accumulation of OM can produce a lot of Humic acids
Removing crops from land
Soil water - creation of carbonic water
Rain - usually is around 5.5-6.5 when it hits the ground
Nitrification - H+ is released which increased pH
Does fungi like more acidic soils than bacteria and actinomycetes?
Yes
What are colloids? (1) What are some properties of colloids? (5)
Groupings of soil (clay and OM) that are the seat for most of the chemical, physical, and biological properties of the soil.
VERY small (less than 2 micro m) MASSIVE surface area Can have negative and positive charges Absorb lots of ions and water molecules Absorb ions that often are exchanged with plant roots
The lower the CEC, the faster the pH will lower over time?
yes
What are some factors that effect soil fertility? (bad and good) (10)
positive vs negative
clay vs sand humus vs loss of OM good structure vs compaction warm vs cold or hot soil depth - deep vs shallow moist soil vs dry or wet soil good drainage vs no drainage fertilization vs erosion desirable microbes vs root damaging pests neutral pH vs pH that is too alkaline or acidic
