PSC104 Study Guide - Final Guide: Feldspar, Parent Material, Vermiculite
Topic 1:Soils influences on plant growth
Physical medium for plant growth:
- Root depth
- Erosion (wind and water)
- Subsurface erosion (tunnel erosion)
- Access to water and nutrients (cations and anions)
- Supply of water:
- Infiltration (getting water in): need large pores to move water (eg. sand)
- Water storage: clay soils hold more water than sandy soils
- Water drainage: large pores for good drainage, waterlogging = no oxygen as
pores are filled with water - bad drainage.
- Oxygen supply:
- Plants require oxygen for normal respiration
- Soil must be able to allow air to diffuse to roots
- grey/blue soil = low/no oxygen supply
- red/brown soil = oxygen rich soil
Chemical environment:
- Essential elements needed for growth
- No chemical problems (eg. pH to high or low)
- Salinity
Biological environment:
- Soil is a home for living organisms
- Some organisms are good and some are bad (pathogens)
- Pesticides can kill both good and bad organisms
- Living organisms break down organic matter
Summary:
1. Physical: roots, water, aeration
2. Chemical: nutrients, pH, salinity
3. Biological: function, limitation
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Soil influences on animal production:
- Quantity of pasture
- Quality of pasture:
- A soil with low nitrogen concentration = low pasture nitrogen = low protein =
lower growth rates in animals.
- Disease and animal health:
- Liver fluke, lives in waterlogged soils. Can be controlled with well draining soils.
- Sandy soils, increases wear on animals teeth particularly sheep and goats.
- Essential elements for animals only found in soils, cobalt (Co), selenium (Se),
iodine (I), florine (F).
Soil influences on the environment:
- Soil erosion (wind) (dust storms), air quality
- Soil erosion (water) (runoff into rivers), water quality
- Soil pollution (algal blooms)
Composition of soil:
- Determines suitability for plant growth
- 25% gas
- 25% liquid
- 50% solid
Soil solids:
- Inorganic: don’t contain carbon , residual minerals from rocks , minerals formed when
rock break down.
- Organic: has carbon in structure (some stage was alive), humus (resistant), organic
material fresh and/or decomposing, living (worms and other microbes) only makes up
1-5% of soil mass
Soil liquids:
- Water that is held in the soil pores
- Dissolved materials (cation and anion = nutrients)
Soil gas:
- Nitrogen gas (N2)
- Oxygen (O2)
- Carbon Dioxide (CO2), concentration of CO2 is higher in the soil than in the atmosphere
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Properties of soils:
Bulk density: (pb)
-ensity d=volume
weight =total volume of soil
mass of oven dry soil =m3
Mg
- Bulk density is a measure of compaction
- Average bulk density = 1-1.2 Mg/m3
- Compacted soil bulk density = > 1.7 Mg/m3
- Soil rich with organic material bulk density = 0.3 Mg/m3 (organic material weight less
than soil)
Particle density or absolute density: (pp)
- The ratio of mass of solids to the volume of solids (*doesn’t include pore space)
-bsolute densityA =volume
weight =mass of solids
volume of solids =m3
Mg
- Average pp = 2.65mg/m3 (this is constant)
- Organic soils may have pp = <1.3mg/m3
Total porosity:
- The proportion of the soil volume occupied by pores- including those containing air and
water
- As the soil becomes more compacted = porosity decreases
-otal porosity 1 ) 00T= ( − bulk density
particle density (2.65mg/m)× 1
Pore size distribution:
- Pores are spaces in the soil
- Small pores hold water
- Texture is the influencing factor
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Document Summary
Access to water and nutrients (cations and anions) Infiltration (getting water in): need large pores to move water (eg. sand) Water storage: clay soils hold more water than sandy soils. Water drainage: large pores for good drainage, waterlogging = no oxygen as pores are filled with water - bad drainage. Soil must be able to allow air to diffuse to roots grey/blue soil = low/no oxygen supply red/brown soil = oxygen rich soil. No chemical problems (eg. ph to high or low) Soil is a home for living organisms. Some organisms are good and some are bad (pathogens) Pesticides can kill both good and bad organisms. Summary: physical: roots, water, aeration, chemical: nutrients, ph, salinity, biological: function, limitation. A soil with low nitrogen concentration = low pasture nitrogen = low protein = lower growth rates in animals. Sandy soils, increases wear on animals teeth particularly sheep and goats.
