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6. Install only one block in each hole and fasten the leads to a stake so that they
can be kept clean and are easily located for reading. Identify the lead wire
according to the depth of the blocks. This can be accomplished by a colored tag
or by making a knot on the shallow block, 2 knots on the deep one (3 knots on
the next, if three blocks are used in the same station).
NOTE: It is recommended that the blocks be soaked in water for 1 hour and
allowed to dry as soon as received. This additional wetting-drying cycle will
improve their uniformity. Before “planting the blocks, they should be soaked
again for 2 to 3 minutes to improve contact with the soil.
WHERE TO PLACE BLOCKS
It is not possible to give precise instructions, which apply to all cases. The
location and depth of the blocks depends on the nature of the crops, its potential
root zone, the type of soil with regard to texture and subsurface formation, and
the profile of the field. However, there are some guidelines to be followed: (A
“string” of blocks 2, 3, or 4, depending on the depth to be reached, is called
“station”).
Locate the stations in the representative areas of the field. Don’t place the
blocks in low or high spots or near changes in slope of the irrigation run unless
you wish to measure variability in water penetration caused by such differences.
Select a station location where the plant population is representative of the field.
Keep the soil around the stations from becoming compacted when taking
readings especially where blocks are planted near the surface. Don’t walk in
furrows in which soil moisture readings are being measured. Walk in the next
furrow. Mark each “walk” furrow when installing the blocks.
When using sprinkler systems, make sure the blocks are set so they will not be
damaged when the sprinkler is moved. Inaccurate readings can also result if the
blocks are placed too close to the sprinkler head.
The blocks should not be shielded by any low hanging branches nor in an area
that may be flooded by run-off. In the case of row crops, the blocks should be
located directly in the row. As for orchards, the blocks are located at the drip line
of a tree.
It is also suggested that a second “string” of a few blocks be placed in the ground
not far from the first – 10” to 20” apart. This will serve as a control on the blocks
and on other factors. If the readings of tw2o adjacent blocks at the same depth
show a significant discrepancy, the cause should be determined. It may be poor
distribution of water from the sprinkler system, or difference in sprinkler
distribution caused by wind, differences in root concentration surrounding the
block installations, or difference in the soil.
