December 2022 - 26

IRRIGATION & WATER MANAGEMENT
Improve uniformity in your irrigation system
By Younsuk Dong,
Lyndon Kelley and
Ben Werling
Michigan State University
Irrigation systems - whether pivots,
solid-set, or trickle - pump water
from a source and distribute to a
larger area of vegetables. Multiple
nozzles, sprinkler heads, and emitters
help wet the soil over this broader
area. Ideally, just the right amount
of irrigation water is applied by all
sprinklers and emitters.
The reality is, however, that every
sprinkler and emitter may have a
slightly different output. Put another
way, the output is non-uniform. A
little non-uniformity is not a problem,
but excessive levels can lead to overand
under-watering of plants, along
with wasted fuel or electricity and
water, non-uniform fertigation or
leached nutrients.
Evaluating center pivot
irrigation systems
For center pivot systems, nonuniformity
can have several causes,
including how old the system is: As
center pivot irrigation systems age,
joints may leak, sprinklers can get
clogged or sprinkler heads may be
missing. The " catch can method " is a
simple way to evaluate the uniformity
of a center pivot and determine if
action needs to be taken (www.egr.
msu.edu/bae/water/irrigation). The
procedure includes placing 32-ounce
disposable soda cups (catch cans) 10
feet apart in a straight line outward
from the pivot elbow. Once the catch
cans are installed in the field, start
irrigating and record the water level
in each of the cans using a graduated
Figure 1: Catch can test demonstration. White cups in the photo are catch cans to evaluate the distribution uniformity of the
center pivot irrigation system.
cylinder after the pivot passes. Figure 1
shows a demonstration of the catch can
test in Three Rivers, Michigan.
To illustrate the benefits of this
process, the Michigan State University
(MSU) Irrigation group collaborated
with two irrigators to evaluate the
uniformity before and after replacing
sprinkler packages in 2022. We used
the catch can test data to calculate the
Scheduling Coefficient (SC), which is
a run time multiplier that shows the
amount of extra water that needs to
be applied to get the dry areas of the
field wet. After the sprinkler package
was replaced, we found the SC was
reduced from 1.3 to 1.2 in Field A
and from 1.6 to 1.2 in Field B. In
other words, replacing the sprinklers
improved uniformity.
Here is an example of the potential
economic impact of this upgrade
for field crops (also relevant for
vegetables):
* Water savings for each inch
applied due to improved
uniformity: 0.2 inches.
* Annual average irrigation
applications in corn and soybean
production: 6 inches.
* Total irrigation saving per year:
A x B = 1.2 inches.
* Range of irrigation power costs
in Michigan: $3.16-$7.50 /acre/
inch.
* Annual total energy saved for a
100-acre field (with an energy
cost of $5.33/acre/inch): $5.33/
acre/inch x 100 acres x 1.2
inches = $640.
* Total sprinkler package cost
(parts only): $3,000.
* Payback period: 4.7 years.
Evaluating micro- and drip
irrigation systems
Irrigation distribution uniformity
evaluation is also important in a
micro/drip irrigation system. To
check the distribution uniformity,
at least 24 emitters in the irrigation
zone can be tested. Figure 2 shows
the MSU Irrigation Lab conducting a
uniformity test for trickle irrigation
in 2022. The distribution of
uniformity was found to be 0.8 (or
80%). Distribution uniformity can be
calculated by dividing the average of
the lowest quarter irrigation volume
(lowest volumes from 6 emitters) by
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2022
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December 2022

Table of Contents for the Digital Edition of December 2022