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Physical Properties Of Soil Revision Questions: (To Determine The Texture…
Physical Properties Of Soil Revision Questions:
The Mineral Particles From Largest To Smallest:
Fine Sand
Silt
Course Sand
Clay
Gravel
The Five Physical Properties Of Soil:
Porosity & Density
Colour
Structure
Temperature
Texture
Soil texture
is a
measure of the proportion of different-sized mineral particles (sand, silt, clay) that are found in a sample of soil.
Loam soil
is
soil that contains equal amounts of sand, silt and clay.
To Determine The Texture Of A Soil Sample:
Place a stopper on the cylinder and shake it to mix the soil and water thoroughly.
Leave to settle for a few hours or overnight.
Pour the mixture of soil and water into the graduated cylinder, rinsing all soil from the beaker into the cylinder. add enough water to cover the soil completely.
Observe the layers that have settled in the graduated cylinder.
Add a sample of sieved soil to a beaker of water and stir it with the stirring rod.
Sand settlers at the bottom, silt above the sand layer and clay on top of the silt.
Using the graduation marks on the cylinder, record the amount of sand, silt and clay in the soil sample as a percentage of the total soils.
To Determine The Texture Of A Soil Sample:
Place crushed soil sample in the largest soil sieve. Place cover on sieve and shake it.
Remove the cover from the sieve and separate out each sieve. Weight the empty weighing boats.
Weight an empty weighing boat; place the crushed sample into the boat and reweigh. subtract the mass of the empty boat to calculate mass of the soil.
Pour the contents of each sieve into separate pre-weighed boats. Weight each sample in turn.
When soil is dry, crush it with a pestle and mortar.
Calculate each separate sample of sand, silt and clay as a percentage of the total soil mass.
Place soil sample in an oven to dry it out completely.
Why Good Soil Structure Is Important:
Air movement within the soil
Root penetration
Drainage of excess water
Impacts Of Soil Compaction:
Gaseous exchange is reduced in compacted soils as there are insufficient large pore spaces for diffusion of carbon dioxide back to the atmosphere and oxygen into the soil for plant root respiration. This will stun plant growth.
Plant roots cannot remove water from small capillary pores. This reduces water availability to growing plants even if the soil contains large amounts of water.
A compacted soil has a reduced rate of water infiltration and drainage. Large pores are necessary to drain water efficiently. This cannot happen is a compacted soil.
Repeated tillage operations can cause a plough plan. This can also cause the soil to form a crust after rainfall, which further affects drainage and infiltration rates.
Hygroscopic Water (Absorbed Water):
Water that forms a thin film around a soil particle and is held on the surface of the particle by force of attraction. It cannot be removed from the soil and is unavailable to plants.
Capillary Water:
Capillary water is held in the pores within the soil aggregates and in the pores between the soil aggregates. Capillary water that is held in small pores within the soil aggregates is unavailable to plants. Capillary water that is held in large pores between the soil aggregates in available for plant uptake.
Gravitational Water:
Gravitational water is moved through the soil by gravity. It is found in cracks in the soil and large soil pores. It is normally only available on a temporary basis to plants (E.g. After heavy rainfall) as it is drained away quickly. Air fills the pores when the gravitational water has drained away.
Field Capacity:
The amount of water in a soil after the gravitational water has drained away.
Permanent Wilting Point:
The point at which no more capillary water can be removed from a soil (by plant roots). Plants will die from drought if the soil in which they are growing reaches its permanent wilting point.
Available Water Capacity:
The amount of water between the field capacity and permanent wilting point that is available for absorption by plants. Available water capacity - field capacity - permanent wilting point.
Infiltration:
The rate at which water will pass or filter through soil.