Em4885 irrigation management practices to protect ground water

4 CHAPTER
Soil variability may be something that the grower just has to live with. On the other hand,
depending on the patterns of variability it may be possible to change set management as the
irrigation progresses. For example, given that a sandy streak in a field is generally in the
direction of the furrow, shorter sets with larger furrow flows may be used as the irrigation
progresses through the sandy area.
Another type of soil and topography variability are high and low spots in the field.
Laser-controlled land leveling (IP 2.02.08) is in common use and can be used periodically
to “touch up” a field.
Border strips
The above discussion of down-row, cross-row, and soil variability was directed primarily
at furrow/rill irrigation systems. These are all concerns with border strips also. Cross-
”strip” uniformity is not affected as much by differences in infiltration rates due to the
width of the strips. However, it is still imperative that the same flow be set into each strip.
It is important to note that irrigation management of border strips is different from furrows
for one important reason. When water is turned off in a furrow, it recedes relatively
quickly. That is, water runs off the furrow relatively quickly. With a border strip, however,
the hydraulics of the wide flow path and friction due to a crop create a large volume of
water on the surface of the strip. This requires a significant “recession” time to run off or
infiltrate after the inflow is shut off. The recession time in border strips can be very useful
for equalizing the opportunity time from the top of the strip to the bottom.
Advance ratios are not used for recommendations concerning flows into a border strip.
Also, surface runoff should normally be much less with a border strip than with a furrow.
Down-row uniformity with a border strip is a matter of equalizing the effects of the
advance rate of the water during irrigation and the recession time after the water is turned
off. System evaluations of border strips will identify the balance between the advance rate
and the recession rate and are very helpful in improving performance.
IP 2.02.01 - Increase Furrow Flows to Maximum Non-Erosive Streamsize
if Water Advance is Too Slow
Objective
Achieve an appropriate advance time for water during the initial wetting phase of a furrow
irrigation. This will give good down-row uniformity.
Description
As previously explained, a good down-row uniformity is the result of sufficiently fast water
advance during the initial wetting of the furrow. Depending on the length of run, type
of soil, condition of furrow, and land slope, this may or may not require the maximum
non-erosive stream size. The smallest stream size necessary to achieve good advance
speed should be used.
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