Part 3

1. 1
Advanced Soil and Water
Engineering #3
Masahiro Tasumi
Dept. Forest & Env. Sci.
Class schedule
No. Date Contents
1 4/11 Course outline for Advanced Soil and Water Engineering
2 4/18 Physical characteristics of soil I
3 4/25 Physical characteristics of soil II (NO CLASS)
4 5/9 Physical characteristics of soil III
5 5/16 Physical characteristics of soil IV
6 5/23 Micrometeorology I
7 5/30 Micrometeorology II
8 6/6 Micrometeorology III
9 6/13 Micrometeorology IV
10 6/20 Soil water and Evapotranspiration I
11 6/27 Soil water and Evapotranspiration II
12 7/4 Soil water and Evapotranspiration III
13 7/11 Soil and water engineering in operation I
14 7/18 Soil and water engineering in operation II
15 7/25 Discussions
Today’s Topic
(1) Clay
(2) Soil water and
the “Potential”
-Physical Characteristics of Soil II
Homework Assignment 1
Assume that you teach “soil water potential” to
undergraduate students, using power-point, in 15-30
minutes. Please make a power-point file with
explanatory, because not the presentation but the file
is evaluated. Please do this homework by your own.
Assignment due date is May 9 (next class).
Total potential (ΨT), gravimetric potential (Ψz), solute
potential (Ψs), soil matric potential (Ψm), pressure
potential (Ψp)
The purpose of the assignment is to promote your
understanding of the concept of soil water potential.

2. 2
Particle size classification (from last week) Part 1. Clay
O
OまたはOH

3. 3
Question:
Does “Water flows (i.e. moves) from higher
location to lower location”?
Part 2. Soil water and the “Potential”
Intermolecular
force is
balancing in all
direction
Intermolecular
force is
unbalancing
Surface tension
Surface
tension
Takes a sphered
shape in air
(After, Prof. Inosako of Tottori University)
Surface tension
Contact angle: In order for a drop resting
on a solid surface to be in equilibrium with
that surface and with a gas phase, the
vector sum of the three forces arising from
the three types of surface tension present
must be zero.

4. 4
（cm）
α≒0°for very clean glass and pure water
T depends on temperature
（e.g. 0.0725 N/m at 20C）
Capillary rise
96.2=
0098.0×1.0
1×000725.0×4
=h （cm）
Capillary rise
Where T is surface tension (kN/cm)
α is contact angle
d is diameter of the tube
γw is the unit weight of the liquid (kN/cm3)
Capillary rise for d = 1mm grass tube
on 20C water surface is…
“Potential” Water moves from a higher total potential
point to a lower total potential point.
ΨT = Ψz+Ψs+Ψm+Ψp
There are some different definitions and
explanations available. In this class, let’s use:
Where ΨT is total potential
Ψz is the gravimetric potential
Ψs is solute potential
Ψm is soil matric potential
Ψp is the pressure potential

5. 5
Gravimetric potential, Ψz
… The driving force of river water flow.
Pressure potential, Ψp
… The driving force of tap (piped) water.
Soil matric potential, Ψm
… The “suction” of the water by soil,
combination of forces theoretically explained
such as capillary rises, electrical
characteristics of clay surface, etc.
Solute potential, Ψs
Semipermeable membrane

6. 6
Water Constants
Gravitational potential
equals to matric potential.
e.g. 2-3days after heavy
rain
Vegetation dies.
Reduce transpiration or
photosynthesis
Conceptual irrigation water
management using Matric Potential
as an index.
（Std. Atmos. Pressure ＝101.325kPa）
Volumetric water content (%)
Field Capacity
Wilting Point
Allowable soil water
Excess water (e.g. after rain)