Irrigation Methods
Levee Irrigation Method
 Flood
irrigation with levees should really be thought of as flush irrigation. The
challenge is to get the water across the field as quickly as possible. It is
also important that irrigation is started before the crop experiences drought.
If plants are drought stressed and then subjected to an extended wet soil
condition, plant development can be delayed and some plants may die.
Levees should be marked early to strengthen the commitment to
pull levees and irrigate when needed. The levee spacing depends on the slope,
but spacing on a vertical difference of 0.3 to 0.4 feet is common. A narrower
spacing on a 0.2- to 0.3-foot vertical difference may be necessary on very flat
fields or when trying to irrigate small crops (less than 8 inches tall). Levees
are often broken in several places or completely knocked down to get the water
into the next bay. Rebuilding the levee in time for the next irrigation is often
difficult because the levee area tends to stay wet. Some growers install gates
or spills in the levees to avoid irrigation delays due to rebuilding the levees
between irrigations. When possible, it is recommended that gates or spills are
also installed in the outside levee. This provides better drainage of a field in
a situation where a rain occurs during or soon after the irrigation.
It is recommended that water not be allowed to stand on any area
for longer than two days. This can be difficult on big, flat fields. Some
growers are able to divide these type fields into two smaller fields when they
start irrigating so they can better manage the water. If this isn’t practical,
then providing multiple water inlets to the field can be helpful. Multiple
inlets help avoid running water too long at the top of the field in order to get
water to the bottom of the field. One multiple inlet method is to water the
upper half of the field from the pump discharge or riser and then run irrigation
pipe or tubing from the discharge down the field to water the lower half. A
canal or flume ditch alongside the field can also be used for multiple inlets.
The water can be directed from the ditch through cuts or spills into individual
bays down the length of the field.
Another possibility is to run tubing the full length of the
field and install several of the 2 1/2-inch plastic gates in each bay. These
slide gates are adjustable from completely closed to fully open, where they
deliver 65 to 75 gpm and they are reusable from year to year. This method is
well suited to fields that have a permanent outside levee or road that the
tubing can be laid on. However, the heavier tubing (9 to 10 mil) has been run up
and over levees successfully as long as it is going down slope. The 9- to 10-mil
tubing is better suited for these multiple inlet-type applications than the 6-
to 7-mil tubing.
If the soil cracks readily, then levee irrigation becomes even
more of a challenge. Multiple inlets can help, but it is still important to
irrigate on time. Planting on a raised bed can also provide extra drainage and
help avoid some of the water management challenges of levee irrigation.
A minimum irrigation capacity of 15 gpm per irrigated acre is
recommended for levee irrigation. At that rate, about four days would be
required to complete an irrigation. Starting late would increase the time
required, resulting in severe drought stresses in the last portion to get water.
The more pumping capacity available for levee irrigation, the better.
Opportunities for getting more pumping capacity to a field should be explored
and developed whenever possible so the pumping time required to irrigate a field
can be reduced. Although levee irrigation presents a challenge, it can be done
successfully. There are many producers who consistently produce high yields by
paying close attention to the precautions and recommendations that have been
presented.
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Methods
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