Soil and Water Management
Rice Irrigation - Well Operation
The basic approach to rice irrigation is to flush if necessary to obtain an
acceptable rice stand and establish the initial flood at beginning tillering (6
to 10 inches tall). A shallow flood depth of 2 to 4 inches should be maintained
until about two weeks prior to harvest unless there is a reason for draining
such as for straighthead control. If blast develops, the flood depth may be
increased to help suppress the disease.
Research indicates that it may be possible to stop pumping as early as 14
days after heading if the field will retain a flood for 7 to 10 days after
pumping is ceased. If the weather forecast at 10 to 14 days after heading
predicts temperatures above 95°F and no rain, then the flood should be
maintained.
If the well continues operating until the last levee is flooded, a
significant amount of water can be wasted as runoff. Determining when to stop a
well so that the water in transit will fill the remaining levee area requires
experience. This depends on field size, soil type and well capacity.
Table 1 can be used as a guide. If the pumping rate is near the recommended
minimum, the water should be 90 percent down the field before the well is turned
off. When the pumping rate is near the desired value, you can typically turn the
well off when the water is 70 to 80 percent down the field. Some growers find
that they can better establish the initial flood by filling up the bottom levee
pad first and then stair-stepping the flood back up the field by raising the
levee spills (gates).
Electric companies offer a variety of rate structures that are suited to
particular situations. Visiting with your electric company representative to
determine the best rate structure is worthwhile. Significant energy savings (20
to 30 percent) are usually possible when the electric company is allowed to turn
off an electric well for two to four hours during the daily peak load periods.
Table 1 can be used as a guide to determine if enough pumping capacity
exists to take advantage of this option. If the pumping rate is closer to the
desired value than the minimum value, a two- to four-hour shutdown should be
allowable.
Power units operate over a wide range of speeds (1,500 to 2,400 RPM). The
best fuel consumption performance is usually obtained over a much narrower range
of speeds (1,600 to 1,900 RPM). It is best to determine the most economical
operating speed and run the unit at this setting whenever possible. Other
factors, such as desired pump speed and load on the power unit, must be
considered. This information can be determined from pump and power unit
performance specifications available through irrigation equipment dealers.
Reviewing this information with a dealer can be helpful, particularly when
operating a new well installation or a power unit that you are not familiar
with. It is also important to make sure the gear-head ratio is correct to assure
that the pump is turning the desired speed. A portable tachometer is a good tool
for verifying both engine and pump speed.
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