Agriculture Reference
In-Depth Information
Capillary rise here
Figure 4.9
Capillary rise of water. The dyed water is less than 1 mm deep in the glass dish and
has risen approximately 10 mm into the sponge in a uniform front.
Hydraulic head (kPa)
−
20
−
10
0
10
20
30
40
50
60
70
80
0
Gravitational
suction
line
Water table
depth
Soil depth (cm)
120
Figure 4.10
The curved plot shows how the hydraulic head of water in a drying profile changes
withthematricandgravitationalsuctionsaboveandbelowawatertableat90cm.he
gravitationalsuctioniszeroatthesoilsurface;thematricsuctioniszeroatthewatertable.
This simple picture of soil water must be modified when there are dis-
solvedsalts,asoccurinsalinesoils.Saltysoilwaterhasanosmoticsuction,
with the result that the combination of matric and osmotic suction forces is
greaterthanforpure,freewateratthesamelocation.Consequently,atthe
surface of a saline soil, the total force pulling water upward is greater than
