Em4885 irrigation management practices to protect ground water

41
CHAPTER 4
Advance ratios in fine-textured soils should be in the range of 1/2. That is, the initial water
advance over the full length of the furrow should occur in about 1/2 the time of the total set.
The recommended advance ratio for coarse-textured soils is about 1/4 to 1/3. For medium
soils the advance ratio can be in the range of 1/3 to 1/2.
IP 2.02.02 - Use Torpedoes to Form a Firm, Obstruction
Free Channel for Furrow Flow
Objective
Improve down-row uniformity by increasing speed of water advance during the
initial wetting phase.
Description
Depending on the soil type, newly listed or cultivated furrows may have a cloddy,
hydraulically rough surface. This Practice consists of using some type of implement to
form a slicked or unobstructed channel in furrows. Although in some soils there may be
significant sub-surface compaction, the intention is to reduce surface obstructions.
The results of this practice can be either an increase in advance rate for a given furrow flow,
or an equalizing of soil infiltration rates between adjacent furrows, or both. The smoothing
of the furrow surface, along with some decrease in water infiltration rates due to surface
compaction, will allow faster advance rates. This in turn will result in better
distribution uniformity.
An inherent problem in furrow irrigation systems is the different compactions in furrows
due to the presence of tractor traffic. Normally, tractor traffic is confined to the same
furrows for each field pass so as to maintain bed alignment. The weight of the tractor will
result in high compaction in some furrows. This results in different infiltration rates
between the compacted and uncompacted furrows. Using a furrow slicker or press may
modify the infiltration rates so as to make them more uniform among the furrows. This
modification of rates could result in higher distribution uniformities.
Excessive soil compaction is to be avoided. In those soils where compaction is a problem,
lighter weight implements can be used so as to only reduce the surface roughness of the
furrows. Also, soil water content during cultivations is a critical factor in determining
resulting compaction. Cultivations on soil at or near field capacity are to be avoided
whenever possible.
The local Cooperative Extension agent or SCS office can show growers how to make
torpedoes out of scrap pipe, old compressed gas bottles, or some other suitable material.