Lecture 4: Soil Water- Characteristics and Behavior Flashcards
Capillarity
cohesion and adhesion result in the formation of a capillary fringe around regions of moist soil
Difference in the distance of capillary flow in coarse vs fine textured soils
capillary rise is greater in soils with smaller pores, but the convoluted and discontinuous pore space of soils results in a shorter rise than expected from the pore radius alone
What is soil water potential?
Water will always move from a zone of higher soil water potential to a zone of lower soil water potential (Ws)
Components of soil water potential
Gravimetric, matric, osmotic, and hydrostatic
Gravimetric
(Wg)
-In saturated/wet soils, water moves downwards/down slope from high Wg to low Wg
Matric
(-Wm)
Adhesion of water to surfaces reduces the potential energy of water molecules
Osmotic
(-Wo)
-Dissolved inorganic and organic substances REDUCE the potential energy of water molecules
-little influence on water movement in soils
-only really relevant in dry soils
pure water Wo= 0 kPa salty water Wo= -4000kPa
Hydrostatic
(Wh)
-only relevant in fully saturated soils like aquaphor
Effects of soil compaction on bulk density and water content/ soil moisture
Compaction increases bulk density and volumetric soil content
Shape of water release curve/ water potential curve
Backwards s shape (flat on higher top then steep decline and tapers off flat at the bottom)
Difference of curve shapes for soils with different textures
Shortest to tallest (Sand, Loam, Clay, Peat)
Sand and peat both have drastic declines but loam and clay have more of a gradual decrease (almost like a backwards c with a tapered end)
Soil water potential equation
Ws= Wg + (-)Wm + (-)Wo + Wh
fully saturated, water travels down
gravimetric (Wg)
drier, water travels any direction
matric (Wm)
What does water potential of 0 mean?
HIGH water potential; fully saturated
