Distribution Uniformity in
Surface Irrigation Systems and
Soil Moisture Monitoring
Daniel Munk
University of California Cooperative Extension
Access to groundwater
• Less Surface water
• Increased
pumping
• Depth
• Well yield
• Reduced volume
to irrigate
What is Irrigation Efficiency?
How do we measure it?
Irrigation Efficiency =
Beneficial Use
Applied water



Water used by the crop (ET)
Water needed to leach salts
Water used for frost protection
What is irrigation efficiency?
How do we measure it?
Irrigation Efficiency =
Beneficial Use
Applied water


Goal is to make all applied water a
beneficial use.
Limiting losses to runoff an deep
percolation
Irrigation System Performance
• Irrigation efficiency greatly influenced by
the uniformity of applied water.
• Crop ET uniform throughout the field
• Water replacement needs to be uniform
Complications in achieving
uniform applications
• Surface irrigation issues are completely
different from pressurized systems
• Governed in part by soil infiltration
rates
• Variable surface intake rates
Complications in achieving
uniform applications:
Infiltration rates vary throughout the
season

Soil properties in fall & winter leave soils open w/
high infiltration rates.
Complications in achieving
uniform application:
Infiltration amounts depend on
opportunity time
• Amount of time allowed for infiltration.
• Recession time - Advance time
Infiltration and Uniformity
6
5
Advance Time in Hours
• Furrow advance
time reflects rate of
infiltration
• High infiltration
rates correspond
to low DU, esp. in
surface systems.
Hanford Sandy Loam - Conventional Tillage
4
14-May
9-Jun
3
6-Aug
2
1
0
0
200
400
Distance (feet)
600
Estimating DU
Advance ratio = Total Irrigation time
time to reach field end
AR= 12 hrs. = 2.0
6 hrs.
AR > 2.0 is generally an indicator of good
uniformity (> 80 percent).
•
Applies best when low quarter receives less water than head of field.
Dealing with low DU fields
• Reduce the time required to advance to
the end of the field.
– Increase flow to check
– Narrow check
• Shorten run length
Improving DU’s and limiting
deep percolation losses?
 Reduce field length.
 Often the most effective option
 Also often the least popular option
Irrigation
Amount
1250’
1250’ Field
600’ Field
9.1”
5.4”
1250’
Distribution Uniformity = The “eveness”
of water infiltration
low ¼ average applied 2.0”
X 100 = 67%
average applied water 3.0”
Uniformity depends on system design
and maintenance!
Infiltration and Management
• Management influences
water infiltration in soils
– Tillage
– OM content
– Additions of organic
amendments
– Additions of salts
(gypsum)
– Method of irrigation
(crusting)
Cumulative Infiltration (inches)
7
Hanford sandy loam - Late Season
Brome Cover Crop
Gypsum Applied
Conventional Till
6
5
4
3
2
1
0
0
1
2
3 4 5 6
Time in Hours
7
8
9
Soil Water Storage
and Nutrient Leaching
• Include stored soil
water into irrigation
planning decisions
10
Volumetric Water (%)
20
30
40
50
0
1
Field
Capacity
Depth (ft.)
2
3
4
Saturation
5
6
7
8
9
Alfalfa
Soil Water Storage
and Nutrient Leaching
– Soil water deficit at time
of irrigation is known
– Good estimate of water
applied for irrigation
– Match application with
water deficit
10
Volumetric Water (%)
20
30
40
50
0
1
Field
Capacity
2
Depth (ft.)
• Include stored soil
water into irrigation
planning decisions
• Leaching potential is
minimized when:
3
4
Saturation
5
6
7
8
9
Cotton
Insanity: doing the same thing over and
over again and expecting different
results… Albert Einstein
Complex field conditions that include rapid
infiltration rates, high soil variability and limited
options to deal with poor irrigation system
performance do exist.
Consider an irrigation system change
Summer 2009: Overhead is more efficient than furrow
100
Ea = 87%
Ea = 95%
80
Water (cm)
60
40
20
0
Furrow 1
2
Overhead
-20
-40
AP
ET
DP
Catch-Can Captured Depths - August 21, 2009
Captured Depth per unit length (in/yrd)
2.5
2
1.5
1
0.5
0
1
2
CU = 93.27
Row 9
3
4
5
Row 7
6
7
8
9
Row 5
10
11
12
Row 3
13
Catch-can Number (North to South)
14
15
16
Row 1
17