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