PALISOC, LEOJHUN C.
BSABE 3-A
1. Why measurement of soil moisture important?
Knowing the condition of soil moisture enables highly efficient irrigation,
supplying water as needed and avoiding wasted water consumption when irrigation is
not needed.
2. List the methods of estimating soil moisture. Give the merits and limitations of
each method.

Gravimeter Method
This method is a classic procedure for checking all other methods. Soil is
sampled, placed in a container, weighed as a sampling (wet), dried in the oven
and reweighed after drying. Drying is carried out at 105 ° 110 ° C (221 ° F 230 °
F) to constant volume (2 hours for small samples, up to several days for bulky
clay soil samples and low kiln airflow).

Electrical Conductivity Method
This method is based upon the changes in electrical conductivity with the
variation in soil moisture. A gypsum block inside of which are two electrodes at a
definite distance apart are used. These gypsum blocks require calibration for
uniformity before use.
The blocks are buried in the soil at a desired depth and the conductivity is
measured with a modified Wheatstone bridge. Through this method, the
percentage of moisture from the field capacity to the wilting percentage can be
easily measured.
The limitation of this method is that it cannot be used on high salinity soils that
interfere with the measurement. This method is practiced in the laboratory.

Measurement by using Tensiometers
The tension gauge measures the matrix potential of soil moisture in-situ
(field) using a porous clay cup attached to a tube filled with water. The water in
the cup and tube is connected to a vacuum barometer or mercury barometer.
When the earth dries, water flows through a porous cup, creating a suction or
vacuum in the water column. These suction measurements are then calibrated
with a meter to the specific soil to interpret the moisture content.
The Tension Meter can be used to schedule irrigation by placing the
equipment at a depth with maximum root density and activity. The second device
can be located near the bottom of the active root zone. For example, watering
requirements can be indicated by reading or calculating 500 cm of water (0.5
bar) for an active root zone tension meter and 400 cm or less of water (0.4 bar)
for a depth tension meter.
The main limitation of the Tension Meter is that it does not measure soil
matrix potential values as low as normal wilt values. The actual effective
measurement range is 0 to 0.85 bar. Tension gauges are useful for measuring
the moisture content of sandy soils rather than clayey soils due to the high matrix
potential present in early soils.

Neutron Scattering Method
Neutron probes appear like flashlight cylinders with lengthy cords
attached.The probe consists of radioactive material (radium or beryllium that
emits hastily transferring neutrons).
As the neutrons emitted from the probe collide with hydrogen ions (of
which water is a chief source), they're slowed and deflected, and a number of the
slowed deflected neutrons are deflected lower back to the probe in which a
counter measures them. Only slowed neutrons are counted. The extra slowed
neutrons that return (indicating massive quantity of collisions), the extra the
water content material of the soil.
3. For what purposes would you consider feel and appearance of the soil sufficiently
accurate as an indicator of soil moisture content?
4. The volume of the soil wetted to field capacity by an irrigation depends on several
factors. List four of these factors
Temperature and moisture are the two main factors affecting its
development. , especially crop residue and decaying roots, promotes aggregation so
that larger soil pores develop, allowing water to infiltrate more readily. Determined by
the proportion of different soil separates--sand, silt and loam--in a soil.
5. Discuss some of the common symptoms which indicate that the permanent wilting
point have already been reached.
Wilting point is the minimum soil moisture required by a plant not to wilt. At
this point, any decrease in soil moisture will result in wilting. When a plant wilts, its
leaves dry out, droop, and wither.
6. Explain why bulk density and apparent specific gravity have unequal dimensions
but have equal numerical values?
Specific gravity (SG) and bulk density (BD) are physical tests for an object.
Specific gravity is the ratio of the weight of a volume of the substance to the weight of
an equal volume of the reference substance. Bulk density is weight of a unit volume
of a material to the same volume of water including voids.