Irrigation FundamentalsIrrigation FundamentalsIrrigation FundamentalsIrrigation FundamentalsR. Troy Peters, Ph.D.R. Troy Peters, Ph.D.

WSU Extension Irrigation EngineerWSU Extension Irrigation EngineerWSU Extension Irrigation EngineerWSU Extension Irrigation Engineer

DemonstrationDemonstrationDemonstrationDemonstration

Composition of SoilComposition of SoilComposition of SoilComposition of Soil

Water

Air

Minerals

Water

Minerals(rocks)

Soil WaterSoil WaterSoil WaterSoil WaterSaturation

Excess WaterField Capacity (FC)

Available Soil Moisture

P t Wilti

Total porespacePermanent Wilting

Point (PWP)

p

Unavailable Water

O DOven Dry

Field Capacity (FC)Field Capacity (FC): Maximum amount of : Maximum amount of water that a soil can hold indefinitely against water that a soil can hold indefinitely against gravity (% of volume)gravity (% of volume)gravity (% of volume)gravity (% of volume)

Permanent Wilting Point (PWP)Permanent Wilting Point (PWP): The amount : The amount f t i i i th il ft l tf t i i i th il ft l tof water remaining in the soil after plants can no of water remaining in the soil after plants can no

longer pull water from the soil (wilt & die)longer pull water from the soil (wilt & die)

Available Water (AW)Available Water (AW) = FC = FC –– PWPPWP

Management Allowable Deficit (MAD)Management Allowable Deficit (MAD): percent : percent deficit of Available Water (AW) that management deficit of Available Water (AW) that management will acceptwill acceptwill acceptwill accept

Soil Texture and Available WaterSoil Texture and Available WaterSoil Texture and Available WaterSoil Texture and Available Water

Soil Texture Available Water (AW) Soil Texture ( )in/ft

Coarse Sand 0.2 - 0.8Fine Sand 0 7 1 0Fine Sand 0.7 - 1.0

Loamy Sandy 0.8 - 1.3Sandy Loam 1.1 - 1.6

Fine Sandy Loam 1.2 - 2.0Silt Loam 1.8 - 2.8

Silty Clay Loam 1.6 - 1.9y ySilty Clay 1.5 - 2.0

Clay 1.3 - 1.8Peat Mucks 1 9 2 9Peat Mucks 1.9 - 2.9

Production Reduction FunctionProduction Reduction Function

100%

110%

70%

80%

90%

oduc

tion

40%

50%

60%

Max

imum

Pro

FC

PW

P

MA

D10%

20%

30%

% o

f M

0%

0%10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

% of Available Water% of Available Water

Effective Effective Rooting ZoneRooting Zone

Water BalanceWater Balance

RunoffDeepPercETCapillaryIrrigRainSWSW .12

Variation in Crop Water Use

Average Crop Water Use

Variation in Crop Water Usefrom growing season

to growing season

eW

ater

Use

Cro

p W

Germinationand

Emergence

VegetativeGrowth

Reproduction(seed set)

Maturityand

Senascence

Growing Season

ET and WeatherET and WeatherET and WeatherET and Weather

0 400.40

0.35

0 300.30

0.25

0.20ay)

0.15

0.10(inch

es/d

a

4/10 5/10 6/09 7/09 8/08 9/07 10/07

0.05

0.00

ET (

4/10 5/10 6/09 7/09 8/08 9/07 10/07

Date

Avg. Crop Water NeedsAvg. Crop Water Needs

12

14

Walla Walla, WA

10

12

(in)

Effective PrecipApples/CherriesGrapesP

,

8

per M

onth Peas

4

6

Wat

er U

se p

2

W

0Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Washington Ag Weather Network

http://weather.wsu.edu/

AWN Models

Select Station and Dates

Water Use

Select Crop

ET R tET Report

Example Soil Water BudgetExample Soil Water BudgetExample Soil Water BudgetExample Soil Water Budget

Silt loam: AW = 2 in/ftSilt loam: AW = 2 in/ft Eff ti ti d th 2 5 ftEff ti ti d th 2 5 ft Effective rooting depth: 2.5 ftEffective rooting depth: 2.5 ft Total water holding capacity: 2Total water holding capacity: 2inin//ft ft x 2.5ft=5inx 2.5ft=5inMAD: 30%MAD: 30% Irrigation Efficiency: 75%Irrigation Efficiency: 75% Irrigation Efficiency: 75%Irrigation Efficiency: 75% Soil water deficit at MAD: 5 in * 30% = 1.5 inSoil water deficit at MAD: 5 in * 30% = 1.5 in

Example Soil Water Budget contExample Soil Water Budget contExample Soil Water Budget cont..Example Soil Water Budget cont..

Daily ET rate: 0.25 in/day (or use actuals Daily ET rate: 0.25 in/day (or use actuals from web site)from web site)))

Time to dewater full profile to MAD:Time to dewater full profile to MAD:1 5 in / 0 25 in/day =1 5 in / 0 25 in/day = 6 days6 days1.5 in / 0.25 in/day = 1.5 in / 0.25 in/day = 6 days6 days

Irrigation Efficiency: 75%Irrigation Efficiency: 75% Irrigation Amount: 1.5 in / 75% = Irrigation Amount: 1.5 in / 75% = 2 in2 inHow long does it take to put on 2 in?How long does it take to put on 2 in?g pg p

Good Irrigation ManagementGood Irrigation ManagementGood Irrigation ManagementGood Irrigation Management20

Field Capacity

15

Field Capacity

MAD

10

es o

f wat

er

Wilting Point

5 inch

e

Irrigation + Rain

-5

0

Neutron Probe Reading Deep Percolation

5 104 112 120 128 136 144 152 160 168 176 184 192 200 208 216 224 232 240 248 256 264 272 280

day of year

Poor Irrigation ManagementPoor Irrigation ManagementPoor Irrigation ManagementPoor Irrigation Management20

FC

15

MAD

10

hes

of w

ater

WP

0

5 inch

Irrigation + Rain

-5

0

104 112 120 128 136 144 152 160 168 176 184 192 200 208 216 224 232 240 248 256 264 272 280

Neutron Probe Reading Deep Percolation

104 112 120 128 136 144 152 160 168 176 184 192 200 208 216 224 232 240 248 256 264 272 280day of year

Methods Used in Washington to Methods Used in Washington to Determine When to IrrigateDetermine When to Irrigate

10000

6000

8000

arm

s

4000

6000

Num

ber o

f Fa

0

2000

p il ar t. s r s nt er or s

N

ition

of C

rop

Feel

of S

oi

nal C

alen

da

by Ir

rig. D

ist.

yET

Rep

orts

stur

e Se

nsor

h N

eigh

bors

Con

sulta

n

Oth

e

stur

e Se

nso

pute

r Mod

els

Con

di

Pers

on

Dec

ided

b

Dai

ly

Soil

Moi

s

Wat

ch

Plan

t Moi

s

Com

p

Levels of Irrigation SchedulingLevels of Irrigation SchedulingLevels of Irrigation SchedulingLevels of Irrigation SchedulingWorst

fitab

le

Same schedule all season / GuessingSame schedule all season / Guessing Kicking the dirt / Looking at the plantsKicking the dirt / Looking at the plants Le

ss P

rof

g g pg g p

Look and feel method using shovel or soil Look and feel method using shovel or soil probeprobe ow

ers

probeprobe Checkbook method / ET (AgWeatherNet)Checkbook method / ET (AgWeatherNet) Soil moisture monitoringSoil moisture monitoring fit

able

Gro

Soil moisture monitoringSoil moisture monitoring Neutron probe + checkbookNeutron probe + checkbook

Mor

e P

rof

Best

IrrigationIrrigationU if it d Effi iU if it d Effi iUniformity and EfficiencyUniformity and Efficiency

Courtesy Michael Dukes Univ. Florida

Courtesy Michael Dukes Univ. Florida

Courtesy Michael Dukes Univ. Florida

Courtesy Michael Dukes Univ. Florida

Courtesy Michael Dukes Univ. Florida

Irrigation Efficiency DefinedIrrigation Efficiency Defined

Effi iWaterBenficiallyUsed

Efficiencyf y

WaterFlowingOntoField

Forms of Water LossForms of Water LossForms of Water LossForms of Water Loss

Wind DriftWind DriftWind DriftWind DriftDroplet EvaporationDroplet Evaporation Evaporation from FoliageEvaporation from Foliage Evaporation from Soil SurfaceEvaporation from Soil SurfaceppRunoffRunoffDeep PercolationDeep PercolationDeep PercolationDeep Percolation

OverwateringOverwateringN U if itN U if it Non UniformityNon Uniformity

I i ti Effi i iI i ti Effi i iIrrigation EfficienciesIrrigation Efficiencies

Highly dependant on:Highly dependant on:g y pg y p System DesignSystem Design ManagementManagement ManagementManagement MaintenanceMaintenance WeatherWeather Operating ConditionsOperating Conditions

Irrigation EfficienciesIrrigation EfficienciesIrrigation EfficienciesIrrigation Efficiencies

Borders: Well graded and managed 60-80%Surface Irrigation

g gBorders: Poorly graded and managed 30-60%Furrow: Well graded and managed 50-70%F P l d d d d 30 50%Furrow: Poorly graded and managed 30-50%Furrow: Surge-flow with tail water recovery 60-90%Level Basins 75-95%Level Basins 75 95%

Drip/Trickle 70 95%Drip/Trickle 70-95%

Irrigation EfficienciesIrrigation EfficienciesIrrigation EfficienciesIrrigation Efficiencies

Sprinkler Type Range AverageSprinklers

p yp g gHand-move 50-70% 65Side-roll 50-70% 65Solid Set 60-75% 70Center Pivot 70-85% 75Li 6 8 %Linear move 65-85% 75Big Gun 55-65% 60

Improve Efficiencies By:Improve Efficiencies By:Improve Efficiencies By:Improve Efficiencies By:

Get a good designGet a good designGet a good designGet a good designMaintain your systemMaintain your system

Replace worn nozzlesReplace worn nozzles Replace worn nozzlesReplace worn nozzles Fix leaky pipesFix leaky pipes

Improve managementImprove management Improve managementImprove management Irrigation SchedulingIrrigation Scheduling Operate at designed pressure and flowOperate at designed pressure and flow Operate at designed pressure and flowOperate at designed pressure and flow Irrigate on calm cool daysIrrigate on calm cool days Increase Application RateIncrease Application Rate Increase Application RateIncrease Application Rate

Why Should I Care?Why Should I Care?Why Should I Care?Why Should I Care?

Y C ’t Aff d t D it WY C ’t Aff d t D it WYou Can’t Afford to Do it WrongYou Can’t Afford to Do it Wrong

Even if the water is free, poor irrigation Even if the water is free, poor irrigation t h l tt h l tmanagement has very real costsmanagement has very real costs

Yields and quality are Yields and quality are very stronglyvery stronglycorrelated with irrigation water managementcorrelated with irrigation water management

Expensive fertilizers washed outExpensive fertilizers washed outpp Environmental damageEnvironmental damage

Water CostsWater CostsWater CostsWater Costs

Assumptions:Assumptions: Assumptions: Assumptions: 50 acres50 acres

150 ft deep well150 ft deep well 150 ft deep well150 ft deep well sprinkler irrigating (80 psi required at pump)sprinkler irrigating (80 psi required at pump)

50% irrigation efficiency (poor management)50% irrigation efficiency (poor management) 50% irrigation efficiency (poor management)50% irrigation efficiency (poor management) Growing corn (seasonal water req’d: 36 in)Growing corn (seasonal water req’d: 36 in)

$3 600$3 600Unnecessary energy costs paid Unnecessary energy costs paid $3,600$3,600(compared to 80% efficiency)(compared to 80% efficiency)

Decrease your Irrigation CostsDecrease your Irrigation CostsDecrease your Irrigation CostsDecrease your Irrigation Costs

Lower the pumping pressureLower the pumping pressure Lower flow rate (quantity of water pumped)Lower flow rate (quantity of water pumped)(q y p p )(q y p p )

Better uniformityBetter uniformity Better efficiencyBetter efficiency Better efficiencyBetter efficiency Irrigation scheduling saves water and Irrigation scheduling saves water and

increases yieldincreases yieldincreases yieldincreases yield

Decrease your Irrigation CostsDecrease your Irrigation CostsDecrease your Irrigation CostsDecrease your Irrigation Costs

L t ti d l bL t ti d l b Lower management time and labor Lower management time and labor requirements by upgrading your systemrequirements by upgrading your system

Irrigate to take advantage of offIrrigate to take advantage of off--peak peak power ratespower rates

Update or upgrade your pump (inefficient Update or upgrade your pump (inefficient pumps cost $)pumps cost $)p p $)p p $) Pumps most efficient at designed flow and Pumps most efficient at designed flow and

pressurepressurepp

BenefitsBenefits Most things that decrease your irrigation costs alsoMost things that decrease your irrigation costs also

BenefitsBenefits Most things that decrease your irrigation costs also Most things that decrease your irrigation costs also

benefit the environmentbenefit the environment More flow for fish, less dirty water returning to riversMore flow for fish, less dirty water returning to rivers Less consumption of energyLess consumption of energy Less fertilizer, pesticides in streams and groundwaterLess fertilizer, pesticides in streams and groundwater

M b t ti (t k COM b t ti (t k CO t f th i )t f th i ) More carbon sequestration (takes COMore carbon sequestration (takes CO22 out of the air)out of the air)

EQUIP (NRCS) mone a ailableEQUIP (NRCS) mone a ailable especiallespeciall EQUIP (NRCS) money available EQUIP (NRCS) money available –– especially especially converting from surface to sprinkle or dripconverting from surface to sprinkle or drip

But Make Some Real Money!But Make Some Real Money!But Make Some Real Money!But Make Some Real Money!

Saving money small compared to the yieldSaving money small compared to the yield Saving money small compared to the yield Saving money small compared to the yield increases and crop quality improvements increases and crop quality improvements common from improved irrigation watercommon from improved irrigation watercommon from improved irrigation water common from improved irrigation water management.management.

Soil Moisture SensorsSoil Moisture SensorsSoil Moisture SensorsSoil Moisture Sensors

Soil Moisture SensorsSoil Moisture SensorsTensiometersTensiometers

StrengthsStrengths StrengthsStrengths Soil water tension Soil water tension

(same as plant sees)(same as plant sees) Less expensiveLess expensive Widely used, studied Widely used, studied

and acceptedand acceptedand acceptedand accepted Not affected by salinityNot affected by salinity

WeaknessesWeaknesses WeaknessesWeaknesses Small sample areaSmall sample area Indicates “when” toIndicates “when” toIndicates when to Indicates when to

irrigate, not “how much”irrigate, not “how much”

Soil Moisture SensorsSoil Moisture SensorsNeutron ProbeNeutron Probe

StrengthsStrengthsgg AccurateAccurate Gives soil water contentGives soil water content

Large soil sample areaLarge soil sample area Large soil sample areaLarge soil sample area Unaffected by salinity or Unaffected by salinity or

temperaturetemperatureR t blR t bl RepeatableRepeatable

Easy to sample at different Easy to sample at different depthsdepths

WeaknessesWeaknesses Highly regulated (nuclear Highly regulated (nuclear

device)device))) Can’t leave in the fieldCan’t leave in the field ExpensiveExpensive

Soil Moisture SensorsSoil Moisture SensorsResistance typeResistance type

StrengthsStrengthsgg InexpensiveInexpensive Usable trendsUsable trends Give soil water Give soil water

potential (same as potential (same as plant sees)plant sees)

Easy to log dataEasy to log data WeaknessesWeaknesses

Aff t d b li itAff t d b li it Affected by salinityAffected by salinity Imperfect accuracyImperfect accuracy Samples small areaSamples small area Samples small areaSamples small area

Soil Moisture SensorsSoil Moisture SensorsDielectric constant/CapacitanceDielectric constant/Capacitance

StrengthsStrengthsgg Usable trendsUsable trends Gives soil water contentGives soil water content

Easy to log data (realEasy to log data (real time)time) Easy to log data (realEasy to log data (real--time)time)

WeaknessesWeaknesses Imperfect accuracyImperfect accuracy Inconsistent (high variability)Inconsistent (high variability) Small sample areaSmall sample area Can be expensiveCan be expensive Can be expensiveCan be expensive Proper installation is critical, Proper installation is critical,

and difficult to doand difficult to doAffected by salinity andAffected by salinity and Affected by salinity and Affected by salinity and temperaturetemperature

Soil Moisture SensorsSoil Moisture SensorsTi D i R flTi D i R flTime Domain ReflectometryTime Domain Reflectometry

StrengthsStrengths StrengthsStrengths AccurateAccurate Not sensitive to Not sensitive to

temperaturetemperature Soil independentSoil independent

WeaknessesWeaknesses Complicated to useComplicated to use

Si l l iSi l l i Signal analysis Signal analysis equipment is expensiveequipment is expensive

Soil Moisture SensorsSoil Moisture SensorsThe “Look and Feel Method”The “Look and Feel Method”

AdvantagesAdvantages CheapCheap

EE EasyEasy Forces you to get Forces you to get

out in the fieldout in the fieldou e e dou e e d WeaknessesWeaknesses

SubjectiveSubjectivejj

Soil Moisture SensorsSoil Moisture SensorsSummarySummary

Neutron Probe is still the bestNeutron Probe is still the bestNeutron Probe is still the best.Neutron Probe is still the best. All others are not as accurate, and are not All others are not as accurate, and are not

as repeatable to varying degreesas repeatable to varying degreesas repeatable to varying degreesas repeatable to varying degreesMost sensors will give a trend that is Most sensors will give a trend that is

bl f i i ti h d libl f i i ti h d liusable for irrigation scheduling.usable for irrigation scheduling. Proper installation of sensors is critical and Proper installation of sensors is critical and

must be done right or data is worthlessmust be done right or data is worthlessNot all sensors are suitable to all soil typesNot all sensors are suitable to all soil typesypyp

Washington Irrigation GuideWashington Irrigation Guide http://www.wa.nrcs.usda.gov/technical/ENG/irrigathttp://www.wa.nrcs.usda.gov/technical/ENG/irrigat

ion_guide/index.htmlion_guide/index.html

Extension Irrigation PublicationsExtension Irrigation Publications http://pubs.wsu.edu/cgihttp://pubs.wsu.edu/cgi--bin/pubs/index.htmlbin/pubs/index.html

Web Soil SurveyWeb Soil Survey http://websoilsurvey.nrcs.usda.govhttp://websoilsurvey.nrcs.usda.govp y gp y g