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Strategies for Reducing Irrigation Water Use
EM 8783
July 2001
L. Jensen and C.C. Shock
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Contents
General strategies
Strategies specific to furrow irrigation
When water is plentiful, growers usually schedule
irrigation practices around other farming activities. For example,
most growers change furrow irrigation sets at 12- or 24-hour
intervals because this timing is convenient and uses labor efficiently.
When water is in short supply, you need to rethink some practices
to obtain maximum benefit from available water. After all, next
to the land itself, water is a grower's second most important
resource. It makes sense to exchange management and labor for
water.
Not everyone faces serious water shortages now, but problems
might spread if Oregon has another dry winter. Also, power crises
will lead to growing pressure to save water for power generation
or endangered species such as salmon and bull trout. The issues
affecting the Klamath Basin or similar ones such as Total Maximum
Daily Load (TMDL) might be only a few years away from affecting
many parts of Oregon.
The ideas below are only suggestions. Hopefully, one or more
of them will work on your farm. They are not prioritized, but
some will save more water than others. The first group of strategies
can apply to any type of irrigation. The second group applies
specifically to furrow irrigation.
- Leave some ground idle and apply the saved water to high-value
crops. Because irrigation districts must keep their system charged
with water, this strategy will have a greater impact if everyone
in the district cuts back on irrigated acres.
- Do not over-irrigate. This sounds simple, but isn't. Most
growers err on the side of excess. Too much water has less visual
impact than too little, but it wastes soil and fertilizer as
well as water.
- Use "ET" (evapotranspiration) charts from the Bureau
of Reclamation AgriMet
system. The charts show fairly accurate estimates of crop
water use and can help you decide when and how much to irrigate.
(See the example below for more
information about how to use these charts.) Some typical annual water use estimates for Malheur
County also are shown below.
- Use soil-moisture monitoring equipment to measure how much
moisture is in the soil. There are several types of sensors available.
The most commonly used in Oregon are Watermark sensors, the Diviner,
and tensiometers. These instruments, when used with ET charts,
provide a fairly accurate estimate of irrigation needs. For more
information on measuring soil moisture, see Instrumentation
for Soil Moisture Monitoring.
- Graph soil moisture readings. The most important aspect of
soil-moisture monitoring is graphing the readings in order to
improve your irrigation accuracy. Even if you measure soil moisture
with a shovel and your fingers, you can graph the readings. The
following portion of a graph used for Watermark sensors is one
example.
Download complete graph
(requires Microsoft Excel)
- Know each crop's tolerance of drought stress and irrigate
accordingly. Some plants handle drought stress better than others.
Barley uses less water than wheat. Sugar beets can extract moisture
from a greater depth than most crops. Russet Burbank potatoes
suffer greatly in quality when drought stressed--losing tuber
grade and fry color. Shepody potatoes suffer less quality reduction
than Russet Burbank, but still more than other crops. Total yield
is reduced when Shepody and Umatilla Russet varieties are drought
stressed. Potatoes can be stressed very early, but not after
setting tubers. Water stress on onions affects yield and grade
and reduces the percentage of single centers. Wheat and corn
lose test weight and yield. For most crops, water stress at the
flowering stage is most damaging.
- Know the water-holding capacity of your soils. A sandy loam
soil will not hold as much water as a silt loam; thus it must
be irrigated more frequently, but apply less water with each
irrigation. Any extra water is lost to leaching.
- Know the water-use requirements of the crops you intend to
grow, and make sure you have enough water to get an economic
yield.
Top
How
To Use The AgriMet Crop Water Use Chart
Example
|
(1)
ESTIMATED CROP WATER USE - JULY 16, 2000 ONTO
|
(2)
CROP |
(3)
START |
(4)
DAILY
CROP WATER USE- (IN)
PENMAN ET - JULY |
(5)
Daily
Forecast
|
(6)
COVER DATE
|
(7)
TERM DATE
|
(8)
SUM
ET
|
(9)
7 DAY
USE
|
(10)
14 DAY
USE
|
| |
|
12 |
13 |
14 |
15 |
|
|
|
|
|
|
| ONYN |
401 |
0.32 |
0.3 |
0.29 |
0.31 |
0.32 |
710 |
820 |
20.6 |
2.16 |
4.3 |
| POTS |
501 |
0.33 |
0.32 |
0.3 |
0.32 |
0.34 |
610 |
820 |
19.7 |
2.3 |
4.28 |
(1) = Location of weather station: ONTO = Ontario, Malheur
Experiment Station
(2) = Crop: ONYN = Onions; POTS = Shepody Potatoes
(3) = Start Date: Crop emergence date
(4) = Amount of water used by the crop each day for the past
4 days
(5) = Estimated water use for the date on the chart, i.e., July
16
(6) = Cover date: Date the crop reached full canopy
(7) = Term date: Date irrigation stops or crop is harvested
(8) = Sum ET: Total estimated water use from the beginning of
the growing season to the current date
(9) = 7 day use: Prediction of water needed by crop for the next
7 days
(10) = 14 day use: Prediction of water needed by crop for the
next 14 days
Top
Estimated
annual water use of selected Malheur County Crops
|
Crop |
Water use (inches/year) |
| Alfalfa |
45 |
| Pasture |
36 |
| Winter wheat |
26 |
| Spring wheat |
26 |
| Sugarbeets |
38 |
| Onions |
32 |
| Potatoes |
30 |
| Beans |
24 |
| Field corn |
30 |
| Peppermint |
28 |
| *From ET values at the Malheur Experiment
Station for the 2000 crop year. Depending on the irrigation efficiency
of your farming operation, actual water use might be more or
less than these values. However, they are a good, relative guide. |
Top
Strategies specific to furrow
irrigation
|
- Consider surge irrigation or at least use a modified surge
program on the first irrigation. The wetting-drying cycle of
surge irrigation reduces water loss to deep percolation, which
is particularly important on the first irrigation when the soil
is friable and takes a lot of water. For a modified surge irrigation
program, alternate siphon tubes between rows every couple of
hours on the first irrigation. This method can save water and
reduce nitrogen loss through leaching.
- Use alternate-row irrigation; irrigate one side of a bed
on one irrigation, the other row or side on the next. This practice
works well with crops that are less sensitive to moisture stress.
- Irrigate only the wheel row. Since its infiltration rate
usually is much lower than that of the soft row, water is less
likely to move below the root zone.
- Compact the soft, non-traffic rows in furrow-irrigated fields
so that their infiltration rate is similar to that of the wheel-traffic
rows.
- Switch to sprinkler irrigation, which allows you to manage
water more efficiently and apply it to the depth needed. Remember
that some crops might have more disease problems under sprinklers
because the foliage stays wet. Also, with increased power costs,
this might not be a good option unless the water intake is high
enough above the rest of your farm to allow you to set up a gravity
flow system.
- Drip irrigation can save a lot of water, in many cases more
than half of the amount used for furrow irrigation. It often
increases yields as well. A drip system is costly to set up,
but is practical for onions and promising for seed alfalfa. The
Malheur Experiment Station is investigating ways to leave the
tape in the ground through several cropping cycles. See Drip
Irrigation: An Introduction for more information.
- Change irrigation sets when water reaches the end of the
furrow rather than at a specified time of day.
- Use PAM (polyacrylamide) or straw mulch to improve water
infiltration in tight soils (those with a low water infiltration
rate).
- Eliminate deep watering of shallow-rooted crops such as onions
and beans. Frequent, light irrigations help keep water in the
root zone where plants can use it.
- Avoid over-watering the top of the field by cutting the water
as soon as it reaches the end of the field. Most people over-water
the top of the field, which stresses plants and causes nitrogen
deficiency as nitrogen leaches below the root zone. Slightly
drought stressing the bottom of the field should cause production
losses similar to those caused by over-watering the top of the
field. Straw the bottom of the field so that the water that gets
there soaks in.
- Use catch basins to collect runoff and reuse it. Sometimes
this involves pumping water to the top of the field or to the
next field. Analyze the cost of pumping to see whether this strategy
is cost-effective.
Top
Prepared by Lynn Jensen, Extension agent (crops), Malheur County; and Clinton C. Shock, Superintendent, Malheur Experiment Station, Oregon State University.
July 2001.
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