Sprinkler
Application Rates
& Soil
Considerations
Bruce Sandoval, P.E.
Irrigation Engineer
USDA-NRCS
Sprinkler Application Rates & Soil
Considerations
•
•
•
•
Sprinkler Application Rates
Soil Infiltration Rates
Application vs. Infiltration = Runoff ?
Management to Eliminate/Reduce Runoff
Application Rates & Application
– Instantaneous
– Average
– Total Application
RATES
Impact Sprinkler Pattern
Instantaneous
Application Rate
where water is hitting
the ground
Area being
watered:
Average
Application Rate
0.25
0.2
0.15
0.1
0.05
Distance from Nozzle (ft)
51
48
44
41
38
34
31
28
25
21
18
15
11
8
5
0
2
Application Rate (inches/hour)
Impact Sprinkler:
Pattern Profile of Average Application Rate
Total Application for a Single Impact Sprinkler
Total Application = Average Rate x Run Time
• IF
– Nozzle q = 5 gpm
– Nozzle throw = 45 ft
• THEN
– The average application rate over the area to which
water is applied (the green circle) is 0.076 inches/hour
(if all the water makes it to the ground)
• AND SO
– If the sprinkler is run for 10 hours TOTAL APPLICATION
is 0.76 inches
Pivot & Linear-move Application Devices
Instantaneous Application Rate
Depends on
Where The
Evaluation
Point is
Serrated Deflection Plate
Instantaneous Application Rate
Flat Deflection Plate
Nozzle
Water hitting ground in most of outside part of area
Application Devices with Distinct Streams
Exaggerated Rotator-style Pattern w/ 4 individual
streams
Instantaneous
Application Rate
Where water is
Hitting the ground
Area of Average
Application Rate
Pattern Profile Illustrations
Total Application for a Single Applicator
Total Application = Average Rate x Run Time
• IF
– Nozzle q = 5 gpm
– Nozzle throw = 25 ft
• THEN
– The average application rate is 0.245 inches/hour
• AND SO
– If the sprinkler is run for 10 hours TOTAL APPLICATION
is 2.45 inches (if all the water makes it to the ground)
Reality Check:
Consider Overlap & Sprinkler Movement
• Individual Patterns are Overlapped for Uniformity
– Typical hand/wheel line spacing of 40’ (& 50’ or 60’ in solid
sets)
– Adjacent applicators on a pivot/linear-move
• Consider the movement of the pattern as the pivot/linearmove advances
– the instantaneous application rate the soil “sees” will change
because the overlapped pattern is not perfectly uniform
– Initially the soil “sees” a small rate, gradually getting more
intense until it peaks, then gradually decreases again as the
machine moves away
Instantaneous Application Rate Varies as
Machine Moves over the field
Wetted
Diameter
Soil
One point in the field
Instantaneous Application Rates
under
a
pivot
or
linear-move
8.0
Shapes also represent
7.0
overlapped pattern
6.0
Low Pressure Spray
5.0
4.0
Moving Applicator
3.0
Low Pressure Impact
2.0
1.0
0.0
High Pressure Impact
0
12
24
36
48
60
Water Application Time (min)
72
Application Rate Summary
• Instantaneous Application Rate is the rate “seen” by
the soil at one point in the field at one point in time –
NOT influenced by speed of machine
• Average Application Rate is the average rate “seen” by
the soil at one point in the field over the time it receives
water– NOT influenced by speed of machine
• Total Application is total “depth” of water received by
the soil in the field. Equal average rate x time watered
Questions - Comments ?
Soil Infiltration Rates
• Vary with Soil Texture
• Vary with Soil Structure
• Vary with time
– Short term
– Long term
• Vary with other factors
Soil texture defined by relative percentages of sand, silt, & clay
Infiltration Rate Varies With Time
5.0
INFILTRATION RATE, (in/hr)
Initial Rate is high
4.0
3.0
Sandy soil
Rate Drops Rapidly
2.0
Silty soil
1.0
0.0
0
12
24
36
INFILTRATION TIME, (minutes)
48
60
Soil Structure: arrangement &
grouping of soil particles
• Good structure in finer grained soils provides small
cracks, or macropores, that provide infiltration capacity
• Other things related to structure:
– Compaction degrades structure
– Organic Matter aids structure; residue at surface aids infiltration
capacity
– Soil and Water Chemistry can affect structure
Conditions that May Produce Surface Sealing
Salts
– Sodium tends to break down structure and produce
“dispersed” conditions which lead to reduced
infiltration rates
– Calcium tends to bind particles together, improving soil
structure and, thus, infiltration rates
– These impacts typically seen in soils with large
percentages of clay particles
Conditions that May Produce Surface Sealing
Compaction/Sealing
• By Equipment
• By impact of water particles with soil
– Intense rainstorm
– Application Rate & Energy of Sprinkler Droplet; energy is
basically a function of size of droplet
– Silty soils more susceptible; aggregates broken down and the silt
particles “float” on top, producing a seal
– Effect is progressive, getting worse throughout the irrigation
season
• Organic or other material added to soil surface
Sealing Effect on Infiltration Rate
INFILTRATION RATE, (in/hr)
5.0
4.0
3.0
2.0
Soil before sealing
1.0
Soil after sealing
0.0
0
12
24
36
INFILTRATION TIME, (minutes)
48
60
Questions - Comments ?
Application vs. Infiltration = Runoff ?
• There is potential for runoff when Application
Rate exceeds Infiltration Rate.
• Runoff will occur if “surface storage” cannot
temporarily hold the water not being infiltrated.
P
e
a
k
W
a
t
e
r
A
p
p
l
i
c
a
t
i
o
n
R
a
t
e
=
2
.
7
i
n
c
h
e
s
/
h
o
u
r
5
.
0
W
a
t
e
r
A
p
p
l
i
c
a
t
i
o
n
=
1
.
0
i
n
c
h
S
y
s
t
e
m
F
l
o
w
R
a
t
e
=
8
0
0
g
p
m
S
y
s
t
e
m
L
e
n
g
t
h
=
1
3
4
0
f
e
e
t
4
.
0
5
5
f
o
o
tW
e
t
t
e
d
D
i
a
m
e
t
e
r
3
.
0
4
.
0
3
.
0
2
7
%
P
o
t
e
n
t
i
a
l
R
u
n
o
f
f
2
.
0
5
.
0
2
.
0
1
.
0
1
.
0
INFLTRAIONRATE,(in/hr)
APLICATIONRATE,(in/hr)
0
.
3
N
R
C
S
I
n
t
a
k
e
F
a
m
i
l
y
C
u
r
v
e
0
.
0
0
0
.
0
1
2
2
4
3
6
4
8
W
A
T
E
R
A
P
P
L
I
C
A
T
I
O
N
T
I
M
E
,
(
m
i
n
u
t
e
s
)
6
0
Runoff Potential
0.3 Intake Family Curve
INFILTRATION RATE, (in/hr)
5.0
4.0
3.0
Instantaneous App
rate “seen” by soil
2.0
Potential
Runoff
1.0
Surface Storage
0.0
0
12
24
36
48
INFILTRATION TIME, (minutes)
60
Infiltration vs. Application Rates
8.0
7.0
6.0
5.0
4.0
3.0
Low Pressure Spray
Rotating Spray
Sand
2.0
1.0
0.0
Low Pressure Impact
Silt
High Pressure Impact
0
12
24
36
48
60
Water Application Time (min)
72
Questions - Comments ?
What can we do to eliminate/minimize runoff?
Reduce Application Rates
• Choose application device with lower average rate
– but be careful to consider droplet size and its
effect, as well as pressure & energy costs
• Utilize booms to one degree or another
– Zig-zag offsets
– splitters
– Mega-booms (structural issues to consider)
Reduce Application Rates: Booms
Booms: Reduction of Peak Application Rate
Boom Offset from Pipe
Zig-Zag Configuration
Reduction*
(%)
10 ft
5 – 15%
15 ft
15 – 30%
20 ft
30 – 40%
*Varies with application device
Based on data from King & Kincaid
Runoff Potential
0.3 Intake Family Curve
INFILTRATION RATE, (in/hr)
5.0
4.0
3.0
Instantaneous App
rate “seen” by soil
2.0
Potential
Runoff
1.0
Surface Storage
0.0
0
12
24
36
48
INFILTRATION TIME, (minutes)
60
Reducing Application Rate
0.3 Intake Family Curve
INFILTRATION RATE, (in/hr)
5.0
•Water time is increased
•Total Application is same
•Application rate “seen” by
soil is decreased
4.0
3.0
2.0
Potential
Runoff`
1.0
0.0
0
12
24
36
48
INFILTRATION TIME, (minutes)
60
Reduce Application Rates: Booms
What can we do to minimize/eliminate runoff?
Reduce Total Application per Irrigation
• Less Total Application takes advantage of initially
high, then decreasing, infiltration rates
• Be careful!
– Applying less per irrigation will actually require more
seasonal water because of increased evaporation from
the frequently wet soil surface.
– Irrigating the entire root zone of the crop – getting
water to the bottom of the root zone – is good practice.
Lesser Total Applications may wet only the upper part
of the root zone.
Water Application Depth Increases Runoff
5
.
0
S
o
i
lS
u
r
f
a
c
e
S
t
o
r
a
g
e
=
0
.
0
i
n
c
h
e
s
S
y
s
t
e
m
F
l
o
w
R
a
t
e
=
8
0
0
g
p
m
y
s
t
e
m
L
e
n
g
t
h
=
1
3
4
0
f
e
e
t
A
p
p
l
i
c
a
t
i
o
n
=
0
.
5
i
n
c
h
e
sS
R
u
n
o
f
f=
1
1
%
A
p
p
l
i
c
a
t
i
o
n
=
1
.
0
i
n
c
h
R
u
n
o
f
f=
3
0
%
4
.
0
3
.
0
0
.
3
N
R
C
S
I
n
t
a
k
e
C
u
r
v
e
4
.
0
3
.
0
2
.
0
INFILTRATIONRATE,(in/hr)
APLICATIONRATE,(in/hr)
2
.
0
5
.
0
1
.
0
1
.
0
0
.
0
0
.
0
0
1
2
2
4
W
A
T
E
R
A
P
P
L
I
C
A
T
I
O
N
T
I
M
E
,(
m
i
n
u
t
e
s
)
3
6
What can we do to minimize/eliminate runoff?
Increase & Maintain Infiltration Rates
• Choose application package that minimizes
surface sealing: small droplets & low application
rates
• PAM…& other soil/water amendments?
• Leave crop residue on & near soil surface
• Deep tillage
• If required, irrigate bare soil w/ small droplet and
low application rate package
What can we do to minimize/eliminate runoff?
Increase Surface Storage
• Reservoir Tillage
– more effective on flat fields than sloping
(0-2%, ¾; 2-5%, ½”; >5%,1/4”)
“Mini ponds” tend to break down as the season progresses
• Choose application package that minimizes
surface sealing; small depressions hold ponded
water at soil surface; usually < 0.25”
• Maximize surface residue - intercepts and
temporarily holds water
Runoff Potential Eliminated
INFILTRATION RATE, (in/hr)
5.0
4.0
3.0
2.0
No Runoff
1.0
Surface Storage
0.0
0
12
24
36
48
INFILTRATION TIME, (minutes)
60
Avoid a Wreck! Choose & Manage
Wisely