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Group assignments
1. (a) Describe how gravimetric and volumetric content are related and in
turn, how they are related to matric potential
(b) What are the forces associated with the potential of water in the soil
and when is each important?
(c )
Write short notes on:
the soil moisture characteristic curve
The capillary fringe
2. (a) A substantial area of land in Zimbabwe is low land (dambo). Discuss
the advantages and disadvantages associated with bottom land farming in
these regions
(b) How could problems associated with bottom land farming be
[10 marks]
Individual Assignment
Assignment I
1) Define soil water potential
2) Water in soils can be expressed:
Energy status
Explain clearly how each is achieved. Of the two methods which one
has an advantage over the other?
3) Discuss the potential or combination of potentials that are responsible for
water movement under the following conditions:
a) Soil to plant roots
b) In biological materials
[3 marks]
c) Under unsaturated soil conditions
[3 marks]
d) Under saturated soil conditions
[3 marks]
4) Write short notes on each of the following terms :
a) Osmotic potential
b) Gravitational head
c) Darcy’s law
d) Hysteresis
e) Hygroscopic coefficient
f) Void ratio
g) Air filled porosity
5) a) Prove that ᴪ = 0.15/r
b) Calculate the radius of the largest water filled pores at field capacity and
wilting point.
c) How many centimeters equivalent depth of water are contained in a soil
profile 1metre deep if the mass wetness of the upper 40cm is 15% and that
of the lower 60cm is 25%. The bulk density is 1.2g/cm3 in the upper layer
and 1.4g/cm3 in the deeper layer.
d) How much water does this soil contain in m3/ha of land.
From calibration of a neutron probe we know that when a soil’s volumetric
wetness is 15% we gwt a reading of 24000cpm (counts per minute) and at a
wetness of 40% we get 44000cpm.
Find the equation of the straight line defining the calibration curve in
the form Y = aX + b, where Y is cpm, X is volume wetness, a’ is slope and b is the
intercept on the Y-axis.
Using this equation find the wetness value corresponding to a count
rate of 30 000cpm.
Prove the following relationship between porosity, particle density
and bulk density.
F = 𝜚𝑠