Activity IX
1. A 200g sample of wet soil looses 50g of water by oven drying. Find the
percent moisture in the wet sample.
2. The volume water percent (%Mv) is used to determine the reservoir of water in a soil
volume or,
from an irrigator's point of view, the depth of water per depth of soil needed to recharge
the soil pores.
Using the symbols on the previous page simplify the following equation to find the
definition for volume
water percent (%Mv) in soil. (NOTE: To divide fractions you must first invert
and multiply.)
%Mv = weight of water/density of water
weight of dry soil/soil bulk density
3. Using the same process, substitute the above symbols for the terms in the equation
below, simplify, and
restate the definition of %Mv in words. (Hint: note, 1 gram water = 1cm water = 1ml
water)
%Mv = % moisture by weight x soil bulk
density
4. If the above soil has a BD value of 1.35g/cm3, are the values for %Mv and %Mw the
same?
5. A sample of undisturbed saturated soil was taken from the Bend clay loam
series A horizon using a
cylindrical core sampler.
The core is 7 cm tall with an inside diameter of 7 cm. After the sample
of soil was carefully collected,
the core was placed in a special vacuum chamber to remove the water from the
soil and to study the soil's
ability to retain water. Draw a diagram of the core.
The following data were obtained:
1. Weight of empty
core
42.0 g
2. Weight of saturated soil and
core
527.2 g
3. Weight of soil and core at Field Capacity
474.8 g
4. Weight of soil and core at Wilting
Point
415.1 g
5. Weight of soil and core when Air
Dry
399.8 g
6. Weight of Oven Dry soil and
core
392.3 g
Find the values for A through K below:
A. Soil bulk density
B. Soil particle density
C. Calculated porosity using the porosity formula.
D. Porosity by direct measurement from water data
E. The total percent water in the soil
F. The percent available water in the sample
G. The cm of available water in 60cm of the soil
H. The weight of a cubic meter of the soil when dry (kg)
I. The weight of a cubic meter of the soil when saturated (kg)
J. The volume of gravitational water in the core sample
K. The days between irrigations if allowable depletion is
45% and rate of use is 0.76 cm/day