Soil Processes Week 2 Flashcards
water horizons in soil with distance from gw table
gw zone, saturated zone, capillary fringe, vadose zone = soil moisture zone, unsaturated zone, intermediate zone, rainfed rootzone
what does the term moisture imply?
water does not flow out spontaneously when a soil sample is taken - it is retained in the soil.
by which forces is the energy state of water determined?
gravity, adhesion, cohesion, osmotic forces
matrix forces
adhesion, cohesion, osmotic.
interactions between solid and liquid phase
what causes capillary force?
adhesion forces betweeen solid phase and water
+
cohesion forces between water molecules
what is static equilibrium
gravity pulling down and adhesion and cohesion pulling up are in equilibrium.
osmotic forces
cations are attracted to clay and OM. so there is a large conc. gradient so the water flows towards the clay/ OM.
clay and water retention
high bc negative surface, lots of small pores. Energy required to take up water is high so clay retains more water.
sand and water retention.
small bc large pores so small capillary rise, soil composition means not much osmotically bound water.
saline soils and water retention
salt conc. in soil solution is v. high adn can become higher than in root cells. osmosis happens out of the plant so plants have to work super hard against this, and this requires extra energy
the pressure under the phreatic plane is ________ than at hte water table
larger
air content in saturated soil is ___ than in unsaturated soil
smaller
height of ascent in a narrower capillary is _____ than in a wider one
larger
for gravitational potential, what is important to consider
your plane of reference - is it the earth’s surface or is it the top of the groundwater table?
what is z
gravitational head/ elevation head.
potential energy per unit weight of water at a height z above chosereference level.
what is h
pressure head - a relative potential due to the matrix forces. The energy state of the water as a result of the matrix forces. The reference level is a free water surface at atm. pressure. It is 0 at the water table.
when can matrix forces moisten the soil above the groundwater level?
when pressure head is lower than at the groundwater level.
what is H
hydraulic head
H = h + z
how does water flow in relation to H
water flows from high H to low H
can be horizontal - gw flow
vertical - capillary rise or percolation
when is pressure head positive
below gw level
when is pressure head negative
above gw level
when do you have static hydrological equilibrium
when H is constant, there is no flow
soil moisture retention curve
relation between h and moisture content theta.
what is a pF curve?
moisture content is plotted as a function of the log of absolute pressure head.
