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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
[9marks]
(b) What are the forces associated with the potential of water in the soil
and when is each important?
[6marks]
(c )
Write short notes on:
i)
the soil moisture characteristic curve
[5marks]
ii)
The capillary fringe
[5marks]
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
[15marks]
(b) How could problems associated with bottom land farming be
ameliorated?
[10 marks]
Individual Assignment
Assignment I
1) Define soil water potential
2) Water in soils can be expressed:
i)
Quantitatively
ii)
Energy status
[3marks]
Explain clearly how each is achieved. Of the two methods which one
has an advantage over the other?
[10marks]
3) Discuss the potential or combination of potentials that are responsible for
water movement under the following conditions:
a) Soil to plant roots
[3marks]
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
[25marks]
5) a) Prove that ᴪ = 0.15/r
[5marks]
b) Calculate the radius of the largest water filled pores at field capacity and
wilting point.
[6marks]
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.
[10marks]
d) How much water does this soil contain in m3/ha of land.
[6marks]
6.
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.
i)
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.
[8marks]
ii)
Using this equation find the wetness value corresponding to a count
rate of 30 000cpm.
[2marks]
Iii)
Prove the following relationship between porosity, particle density
and bulk density.
𝜚𝑏
F = 𝜚𝑠
[5marks]