lec 10 soils Flashcards
why learn about soil?
-allows to make better decisions on plant materials
– “ of soil has been created since the glaciation
8-10 “
what is soil/ earth
-material that constitutes the outermost solid layer of the planet
what is def’n of soil?
naturally occurring mixture of inorganic and organic ingredients with a definite form, structure and composition
what is average soil ingredients?
45% mineral matter
25% water
25% air
5% organic matter or humus
why are compacted soil bad?
removes air space which removes air space giving less ability for organic matter to live
how is soil formed
by interaction of the earth’s crust with atm and biological influences through combination of 5 factors
what are 5 soil forming factors
- parent material
- regional climate
- topography
- biotic potential
- time
what is parent material
earth material; both mineral and organic
describe role of regional climate in soil formation
parent material is broken down into finer particles via weathering- controlled by climate of location
-temp and water major climatic forces
describe topography
-hilliness, flatness or amount of slope of the land
describe biotic potential/ organisms in formation of soil
-plants and animals help create soil via decomposition and disturbance via digging
t or f; true soil is a mass of mineral particles
false; influenced, modified, and supplemented by living organisms
what is humus
- semi- soluble chemical (biochemical) substance
- produced via decomposition of organic matter into by fungi and bacteria
what do soil organisms such as earthworms, beetles and termites do for soil ?
vertically redistribute humus within the mineral matter found beneath surface of soil
what are 3 benefits of humus
- enhances a soils ability to hold and store moisture
- primary source of carbon and nitrogen req’d by plants
- improves soil structure
what are the layers of soil called . why are they formed
- horizons
- integrated effects of climate and biosphere change
- becomes less pronounced with depth
what is a soil profile?
-vertical cross- section view of soil
what 4 horizons are noted in soil profile ?
- o= organic
- a= topsoil
- b= subsoil
- c= parent material
what does the organic layer consist of
-fragments of leaf litter, twigs, roots, and other organic material lying on surface of soil at various levels of decomposition and humus
t or f; organic layer is not present in cultivated fields
true
what is found in the topsoil layer ?
- humus and other organic material mixed with mineral particles
- zone of translocation which illluviation has removed finer particles and soluble substances to a lower layer
- dark in colour, light texture and porous
what is the most productive soil layer?
top soil
what are characteristics of subsoil?
- light coloured, dense and low organic matter
- strongly influenced by illuviation ; receives materials from A
- may be coloured by oxides of irons and aluminum or by calcium carbonate
describe the parent material layer
unconsolidated organic and mineral in which soil forms
-largely uninfluenced
what layer would you find bedrock? what is bedrock?
c= parent material
-solid rock underlies soil and other unconsolidated material
what is the easiest way to characterize soil?
-physical characteristics : colour and texture
what are 3 categories of colour in soil
dark, mod dark and light
how is soil texture characterized?
-expressed in terms of % sand, silt and clay
how many textural classes are there?
12
describe texture characteristics of sand
- 3D, round, gritty
- large particles= more drainage
- dif to retain water
describe texture characteristics of silt
- 3d, round floury texture
- smaller particle
- increased retention, less drainage
describe texture characteristics of clay
- small flat particle form impenetrable plates
- min drainage, dif aeration
what does texture of soil refer to
- size distribution of mineral particles found in sample
what is the most important mineral particle found in soil? and why?
clay ; highly reactive, ability to attract and hold positively charged nutrient ions
what are aggregates
grouping of soil particles into porous compounds
t ir f; soil structure is stable
false; aggregates can be destroyed by tiliage, compaction and depletion
how can aggregates be destroyed
tillage, compaction, depletion of sol organic matter
t or f, poor soil structure in creases total porosity
false; good structure increase porosity because large pours b/ween aggregates= better root penetration and air and water movement
what pH is considered acidic? alkaline ?
6-1; 8-12
t or f; soil pH can influence plant growth, quantity activity and types of microorganisms
true
t or f soil ph does not impact nutrient transformations and solubility of essential nutrients available to plants
false
what essential micronutrient is available in slightly acidic- slightly alkaline soil?
phosphorus
essential micronutrients become more available with ___ ph
decreasing ( more acidic)
at what pH level can essential micronutrient become available to a point of toxicity in plants? what essential micronutrients do these include?
<5.5; Al, Mn, Fe
what are important mediators on nutrient exchange systems? where are they most active?
bacteria, slightly acidic- slightly alkaline
what are On soils mostly containing?
- calcareous; limestone parents rock material
- higher Ca= higher pH
what is the main problem with ‘designer soils’
- contain too much organic matter
- can’t be sustained naturally over time decomposes an d settles
what are mycorrhiza?
symbiotic relationship b/ween fungus and root
t or f; soil fumigants, excess fertilizer, excessive irrigation, poorly drained soil inhibit mycorrhizae activity
true
name 7 things that encourage mycorrhizal activity
- coarse woody mulch
- consv. additions of N fertilizer
- warm temp
- mild drought/ nutrient deficiency
- reduced pesticide
- reduced aoil disruption
- increase plant diversity
what are the top 3 ways to improve soil conditions
- cover cropping
- muching
- composting
__% of landfill waste is food waste
20
what happens when food decomposes? why is this an issue?
-release of methane gas, heat up earth 20 times faster than CO2
what is vermicomposting?
- ’ cold composting’
- lower carbon to nitrogen ratio
- uses worms to compost
