Sprinkler Application Rates & Soil Considerations Bruce Sandoval, P.E. Irrigation Engineer...
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Transcript of Sprinkler Application Rates & Soil Considerations Bruce Sandoval, P.E. Irrigation Engineer...
Sprinkler Sprinkler Application Rates Application Rates
& Soil & Soil ConsiderationsConsiderations
Bruce Sandoval, P.E.Irrigation Engineer
USDA-NRCS
Sprinkler Application Rates & Soil Sprinkler Application Rates & Soil ConsiderationsConsiderations
• Sprinkler Application Rates
• Soil Infiltration Rates
• Application vs. Infiltration = Runoff ?
• Management to Eliminate/Reduce Runoff
Application Rates & ApplicationApplication Rates & Application– Instantaneous
– Average
– Total Application
RATES
Impact Sprinkler Pattern
InstantaneousInstantaneousApplication RateApplication Rate
where water is hittingwhere water is hittingthe groundthe ground
Area being Area being watered:watered:AverageAverage
Application RateApplication Rate
Impact Sprinkler:Impact Sprinkler:Pattern Profile of Average Application RatePattern Profile of Average Application Rate
0
0.05
0.1
0.15
0.2
0.25
Distance from Nozzle (ft)
Ap
plic
atio
n R
ate
(inch
es/h
ou
r)
Total Application for a Single Impact SprinklerTotal 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 RateInstantaneous Application Rate
Serrated Deflection PlateSerrated Deflection Plate
Depends onDepends onWhere TheWhere TheEvaluationEvaluationPoint isPoint is
Instantaneous Application RateInstantaneous Application RateFlat Deflection PlateFlat Deflection Plate
NozzleNozzle
Water hitting ground in most of outside part of area
Application Devices with Distinct Streams
Exaggerated Rotator-style Pattern w/ 4 individual streams
InstantaneousInstantaneousApplication RateApplication RateWhere water isWhere water is
Hitting the groundHitting the ground
Area of AverageArea of AverageApplication RateApplication Rate
Pattern Profile IllustrationsPattern Profile Illustrations
Total Application for a Single ApplicatorTotal 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:Reality Check:Consider Overlap & Sprinkler MovementConsider 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/linear-move 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
WettedDiameter
Soil
One point in the field
Instantaneous Application Rate Varies as Instantaneous Application Rate Varies as Machine Moves over the fieldMachine Moves over the field
App
lica
tion
Rat
e A
ppli
cati
on R
ate
Instantaneous Application Rates under a pivot or linear-move
Instantaneous Application Rates under a pivot or linear-move
Low Pressure SprayLow Pressure Spray
Moving ApplicatorMoving Applicator
High Pressure ImpactHigh Pressure Impact
Water ApplicationApplication Time (min)Water ApplicationApplication Time (min)
App
lica
tion
Rat
e (i
n/hr
)A
ppli
cati
on R
ate
(in/
hr) 8.08.0
7.07.0
3.03.0
6.06.0
5.05.04.04.0
2.02.01.01.0
0.00.000 1212 2424 3636 4848 6060 7272
Low Pressure ImpactLow Pressure Impact
Shapes also represent overlapped pattern
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 RatesSoil 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
0 12 24 36 48 60
5.0
4.0
3.0
2.0
1.0
0.0
INFILTRATION TIME, (minutes)
INF
ILT
RA
TIO
N R
AT
E, (
in/h
r)
Initial Rate is high
Rate Drops Rapidly
Silty soil
Sandy soil
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 SealingConditions 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 SealingConditions 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
0 12 24 36 48 60
5.0
4.0
3.0
2.0
1.0
0.0
INFILTRATION TIME, (minutes)
INF
ILT
RA
TIO
N R
AT
E, (
in/h
r)
Soil before sealing
Soil after sealing
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.
0 12 24 36 48 60
5.0
4.0
3.0
2.0
1.0
0.0
WATER APPLICATION TIME, (minutes)
APP
LIC
AT
ION
RA
TE
, (in
/hr)
55 foot Wetted Diameter
Water Application = 1.0 inchSystem Flow Rate = 800 gpm
5.0
4.0
3.0
2.0
1.0
0.0 INFI
LTR
AT
ION
RA
TE
, (in
/hr)
0.3 NRCS Intake Family Curve
System Length = 1340 feet
27% Potential Runoff
Peak Water Application Rate = 2.7 inches/hour
Instantaneous App rate “seen” by soil
Surface Storage
Potential Runoff
Runoff PotentialRunoff Potential
0 12 24 36 48 60
5.0
4.0
3.0
2.0
1.0
0.0
INFILTRATION TIME, (minutes)
INF
ILT
RA
TIO
N R
AT
E, (
in/h
r)0.3 Intake Family Curve
Infiltration vs. Application RatesInfiltration vs. Application Rates
Low Pressure SprayLow Pressure Spray
Rotating SprayRotating Spray
High Pressure ImpactHigh Pressure Impact
Water ApplicationApplication Time (min)Water ApplicationApplication Time (min)
Wat
er A
ppli
cati
on R
ate
(in/
hr)
Wat
er A
ppli
cati
on R
ate
(in/
hr)
8.08.07.07.0
3.03.0
6.06.0
5.05.04.04.0
2.02.01.01.0
0.00.000 1212 2424 3636 4848 6060 7272
Low Pressure ImpactLow Pressure Impact
SandSand
SiltSilt
Questions - Comments ?
What can we do to eliminate/minimize runoff?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 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 deviceBased on data from King & Kincaid
Instantaneous App rate “seen” by soil
Surface Storage
Potential Runoff
Runoff PotentialRunoff Potential
0 12 24 36 48 60
5.0
4.0
3.0
2.0
1.0
0.0
INFILTRATION TIME, (minutes)
INF
ILT
RA
TIO
N R
AT
E, (
in/h
r)0.3 Intake Family Curve
•Water time is increased•Total Application is same•Application rate “seen” by soil is decreased
Potential Runoff`
Reducing Application RateReducing Application Rate
0 12 24 36 48 60
5.0
4.0
3.0
2.0
1.0
0.0
INFILTRATION TIME, (minutes)
INF
ILT
RA
TIO
N R
AT
E, (
in/h
r)0.3 Intake Family Curve
Reduce Application Rates: Booms
What can we do to minimize/eliminate runoff?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
0 12 24 36
5.0
4.0
3.0
2.0
1.0
0.0
WATER APPLICATION TIME, (minutes)
AP
PL
ICA
TIO
N R
AT
E,
(in
/hr)
System Flow Rate = 800 gpm
5.0
4.0
3.0
2.0
1.0
0.0
INF
ILT
RA
TIO
N R
AT
E,
(in
/hr)
0.3 NRCS Intake Curve
System Length = 1340 feetApplication = 0.5 inchesRunoff = 11%
Application = 1.0 inchRunoff = 30%
Soil Surface Storage = 0.0 inches
What can we do to minimize/eliminate runoff?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?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 EliminatedRunoff Potential Eliminated
Surface Storage
0 12 24 36 48 60
5.0
4.0
3.0
2.0
1.0
0.0
INFILTRATION TIME, (minutes)
INF
ILT
RA
TIO
N R
AT
E, (
in/h
r)
No Runoff
Avoid a Wreck! Choose & Manage Wisely