Irrigation Methods
Furrow Irrigation Method
 Furrow
irrigation can be a very effective irrigation method. One of the biggest
requirements for furrow irrigation is that the field must have a positive and
continuous row grade. This usually requires precision land grading which can
be rather expensive. However, the grading results in positive field drainage
that greatly enhances production. The row grade should be a minimum of 0.1
percent and no more than 0.5 percent; row grades between 0.15 and 0.3 percent
are especially desirable.
The row length to be furrow irrigated is another key
consideration. Row lengths of 1/4 mile or less generally water more effectively
than longer rows. Row lengths less than 1/4 mile are usually required if sandy
soils are to be irrigated effectively.
When row lengths cannot be altered, it may be necessary to
control the furrow stream flow by adjusting the number of rows that are
irrigated at one time. Experience shows that in most situations it is desirable
to get the water to the end of the row in 10 hours or less. Watering much longer
than this can cause overwatering at the top of the row and cause problems,
especially if it rains and stays cloudy soon after the irrigation. This has
become more of a concern with the expanded use of irrigation tubing with punched
holes for furrow irrigation. The tendency with the tubing is to punch holes as
long as water still comes out of them without much concern for how long it will
take to water out the row. This is desirable from the standpoint of not having
to plug and open holes and operate the tubing in sets. However, the caution is
to water according to what is more effective for the field and crop rather than
what is easiest.
Furrow irrigation requires a water supply of at least 10 gpm per
irrigated acre, and more capacity is desirable if available. At 10 gpm/acre,
about five to six days should be expected to complete an irrigation. Practices
like waiting until morning to change sets when rows water out at night can add
significantly to the time, making it difficult to finish the field much before
it is time to begin the next irrigation. A well-defined furrow is needed to
carry the irrigation water. Planting on a good bed is the most desirable option
for having a good water furrow. If a bed is not used, then it is necessary to
cultivate with a furrow plow that moves enough soil from the middle of the rows
so that a good furrow is created. Plowing out a furrow is probably not an option
on rows less than 19 inches wide, so the border method may be a better option on
those fields.
Some producers prefer to water alternate middles under certain
conditions. This is especially true on row spacing of 20 to 30 inches. Watering
alternate middles can result in getting across the field quicker and not leaving
the soil as saturated as it might be if every middle were irrigated. Then, if
rain comes soon after the irrigation, it is possible for it to soak into the
soil rather than run off or collect and stand in low spots. However, with
alternate middles on narrow rows and/or cracking soils, the skipped middle is
sometimes saturated.
Producer preference and experience, along with the crop and
field condition, will determine whether it is best to water every middle or
alternate middles. Alternate middle irrigation will result in having to come
back with the next irrigation somewhat sooner than when every middle is watered
if the water doesn’t soak across the dry rows.
Furrow irrigation by necessity requires that there be some
amount of tail water runoff from the end of the rows. All the middles will not
water out at the same rate, especially those that are wheel middles. Also,
cracking soils can make furrow irrigation management more challenging. However,
irrigating on the appropriate schedule will reduce the problems associated with
too much cracking.
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