5.10 Soil Water Facts
Field Capacity
Field capacity is the amount of water a soil continues to
hold a few days after rain
This will be higher for soils with greater clay content.
But clay holds soil water so strongly that about half of the water cannot
be extracted by plants.
The result is that most soils (sandy loams to clays) hold
about the same amount of plant available water.
Plant Available Water
This is the amount of soil water that can be extracted by
roots and used for growth
Most plant available water is held in pores which range in
size between 0.02mm and 0.005mm. Sands don't have many pores of this size
Wilting Point
When all available soil water has been used, the plant's
wilting point is reached
In clay soils where approximately 50 percent of soil water
is unavailable, moisture may still be recorded even when the soil is at
wilting point.
Soil Structure
The water holding, release and infiltration properties of
soil are determined by its clay content and can be changed if soil
structure can be improved
The best soil structure for storage of available water and
root growth will have a high number of water stable aggregates 1 - 2mm in
size.
Between these aggregates will be stable pore spaces which
hold available water and oxygen
Stable aggregates are formed when the basic soil particles
i.e. sand, silt and clay, are bound together by 'organic glues' and
'fungal ropes'.
Conclusion
-
More organic residues = more food for soil biota and
more soil biota
-
More soil biota = more 'organic glue' and 'fungal
ropes'
-
More 'glue' and 'ropes' = more stable aggregates
-
More stable aggregates = more pore spaces = more
available water storage
-
More water = more plant growth
The effects of water on different
soil particles.
5.10 Soil Water Facts
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