Soil Hydrology Flashcards
Bulk density
Low is better
Mass / Volume
Low: V pores > V solids; good soils
High: V solids > V pores; compaction
High = more energy to extend roots
Clays have lower threshold so worse
Aggregation and pores
Water storage in pores are inaccessable to plants - inside aggregates
Transmission pores: network of tubes between aggregates and transmit nutrients through soil - plants get nutrients from here
Mass flow
Movement of nutrients dissolved in soil soluton as water absorbed by plants for transpiration
Water storage
Gravitational: when pores are full (saturation of field capacity) so water drains out of root zone
Capillary: water held in micropores; interaction w soil particle surfaces and forms around aggregates; holds water against gravity and is absorbed by roots; larger pores drained first as lower resistance
Hygroscopic: water left around particles after some drained; hard to take up and adhered tightly to soil particles
Readily available: proportion of moisture extracted w/ being stressed
Available water capacity
Water availability impacted by: root zone size and restriction, soil material and texture, soil org matter content, rocks
Space between field capacity and wilting point is the available water
Plants in sandy soils have extensive roots to get water before it drains
Potential energy
Energy held by an object
Determines how water in soil moves w reference to flat surface
0 = no movement
+ve = energy released
-ve = energy expended to do work
Lower water content = more force required so -ve potential
Plant has to expend energy to remove water
Total water potential
Matric: interactions w soil particles; most important
Osmotic: water flows from salty to non salty
Grav: elevation above sea level
Pressure: pressure applied forces movement
Matric potential
Water stuck to itself and sucked to surfaces of particles
Van der Waals forces cause meniscus between pores due to surface tension; fluctuating charge as more e- on one side of atom; water is a fluctuating dipole
