Soil Water relations & Organic matter Flashcards
What does there need to be a balance of in the soil?
Air and Water
Need a balance for plant roots to function.
What are large pores called?
Macropores.
These pores can drain easily within hours after being saturated.
What are small pores called?
Micropores
These continue to contain water after saturation and drainage has occurred.
What are medium pores called?
Mesopores
These pores hold water or can drain freely. They hold water which is available to the plant.
What is the optimum pore size for plant growth?
A combination of pore sizes where macropores contain air, mesopores and micropores contain water.
What do all soil particles have around them?
A film of water.
What kind of pores do clay soils have?
Many micropores (very small pore spaces). Clay particles cling onto water molecules due to adhesion and cohesion and water stays in the small pore spaces due to capillarity rather than draining away. Sometimes clay soils has a lot of water clinging to the minerals, but the roots do not have enough force to overcome the cohesive forces of water molecules to absorb the water. Even though water is present in the soil it is unavailable to the plant roots.
What kind of pores do sandy soils have?
Many macropores. Large pore spaces. Water flows downwards with gravity and does not stick to soil particles. A thin film of water will adhere to sand particles.
What kind of pores do loam soils have?
A mix of micro, macro and mesopores.
This means they are moisture retentive but free draining.
Which pores join together to form narrow tubes?
Micropores
Which pores join together to form very wide tubes?
Macropores
Mesopores form what sized tubes between them?
Medium sized.
The soil water is held in pores with different strengths. Which pore has the strongest hold?
Micropores
The soil water is held in pores with different strengths. Which pore has the weakest hold?
Macropores
What is infiltration?
Water soaking into the soil with gravitational flow.
Describe surface run off?
Water running off the surface of the soil.
What are the 3 definitions for Water?
Saturation Point
Field Capacity
Permanent Wilting Point.
Describe Saturation Point?
When water occupies all the pore spaces in the soil.
All of the pores (macro, micro and meso) are filled with water.
Indicated by pooling on the surface.
Describe Field Capacity?
The maximum amount of water held by soil after it has been saturated and then allowed to drain freely.
The macropores are filled with air, as the water has drained away.
The micropores hold hygroscopic water which is not available to the plant roots.
The mesopores hold water which is available to the plant roots.
A soil at field capacity has the maximum water content for the optimal plant growth.
Good for most crops a plenty of water available but pore spaces for air.
Define ‘Water holding capacity’?
‘Water holding capacity’ is the total amount of water a soil can hold at field capacity.
Describe Permanent Wilting Point? PWP
At Permanent wilting point there is no more available water in the soil.
The macropores and the mesopores are filled with air.
The micropores has water present but it is tightly bound to soil particles so is not available to plant roots.
What does ‘Available water content’ mean?
This is the amount of water held in the soil between field capacity and permanent wilting point.
The amount of water that is available for plant uptake and is held in the mesopores.
For example:
At Full Capacity At Permanent Wilting P
Coarse sand 26mm 1mm
So Available Water Content is 26mm-1mm = 25mm
Give 4 examples of factors which can make a soil saturated?
Heavy rainfall Poor drainage Iron pan Heavy clay soil High water table.
Give 4 examples of factors which can make a soil dry out?
Sandy soil - soil type.
Over cultivation of sandy soil
Dry weather spell - no rain.
Raised beds dry out more quickly.
Give 4 situations where excess water can become an issue?
Lawn - compaction of clay soils.
Remedy - Aerate with hollow tines.
Veg garden - Soil cultivation pan caused by rotavator on clay soil.
Remedy - Cultivate when soil is dryer to varying depths. Add OM
High water table
Remedy - raised beds.
Newly planted herbaceous border - high rain water or over irrigation.
Remedy - better gardening practise. Hand water or mulch to conserve water instead of watering.