irrigation principles ert 349 soil and water engineering

IRRIGATION PRINCIPLESIRRIGATION PRINCIPLES

ERT 349 SOIL AND WATER ENGINEERINGERT 349 SOIL AND WATER ENGINEERING

IntroductionIntroduction

Importance of IrrigationImportance of IrrigationDefinitionDefinition– ““the supply of water to crops and landscaping the supply of water to crops and landscaping

plants by artificial means”plants by artificial means”

Estimates of magnitudeEstimates of magnitude– world-wide: 544 million acres world-wide: 544 million acres

(17% of land (17% of land 1/3 of food production) 1/3 of food production)

PurposePurpose

Raise a crop where nothing would grow Raise a crop where nothing would grow otherwise (e.g., desert areas)otherwise (e.g., desert areas)– Supply water to root zone Supply water to root zone

Grow a more profitable crop (e.g., alfalfa Grow a more profitable crop (e.g., alfalfa vs. wheat)vs. wheat)

Increase the yield and/or quality of a given Increase the yield and/or quality of a given crop (e.g., fruit)crop (e.g., fruit)

Increase the aesthetic value of a Increase the aesthetic value of a landscape (e.g., turf, ornamentals)landscape (e.g., turf, ornamentals)

Reasons for yield/quality increaseReasons for yield/quality increase

Reduced water stressReduced water stress

Better germination and standsBetter germination and stands

Higher plant populationsHigher plant populations

More efficient use of fertilizerMore efficient use of fertilizer

Improved varietiesImproved varieties

Other Benefits of IrrigationOther Benefits of IrrigationLeach toxic elements from soils.Leach toxic elements from soils.

– All water contains salts so irrigation adds salts to All water contains salts so irrigation adds salts to soil. soil.

– Evaporation of water from soil surface carries salts Evaporation of water from soil surface carries salts to through soil to surface. to through soil to surface.

– Allow extra irrigation water just for leaching Allow extra irrigation water just for leaching purposes to dissolve soil salts and flush them away purposes to dissolve soil salts and flush them away in drainage water.in drainage water.

saline soils = contain Ca2+ and Mg2+ salts. These reduce saline soils = contain Ca2+ and Mg2+ salts. These reduce available water to plants causing plants to wilt and burn. available water to plants causing plants to wilt and burn. May show up as white crust on soil surface. May show up as white crust on soil surface. sodic soils = contain Na+ salts. Sodium damages soil tilth sodic soils = contain Na+ salts. Sodium damages soil tilth and structure, can lead to formation of hardpans that resist and structure, can lead to formation of hardpans that resist penetration of water and plants roots so get poor plant penetration of water and plants roots so get poor plant growth, stunted. growth, stunted.

Frost protectionFrost protection– When water freezes it releases latent heat to the air. When water freezes it releases latent heat to the air.

Other Benefits of IrrigationOther Benefits of Irrigation

Plant/soil coolingPlant/soil cooling– Misting increases relative humidity around Misting increases relative humidity around

upper portion of plant thereby reducing plant upper portion of plant thereby reducing plant stress, evapotranspiration, temperature. stress, evapotranspiration, temperature.

Chemical applicationChemical application– Supply pesticides (chemigation); fertilizers Supply pesticides (chemigation); fertilizers

and liquid animal manure (fertigation) more and liquid animal manure (fertigation) more efficiently since control timing of release, efficiently since control timing of release, amount, and to some degree, placement. amount, and to some degree, placement.

Wind erosion controlWind erosion control

An Historical PerspectiveAn Historical Perspective

Nile River Basin (Egypt) - 6000 B.C.Nile River Basin (Egypt) - 6000 B.C.Tigris-Euphrates River Basin (Iraq, Iran, Syria) - Tigris-Euphrates River Basin (Iraq, Iran, Syria) - 4000 B.C.4000 B.C.Yellow River Basin (China) - 3000 B.C.Yellow River Basin (China) - 3000 B.C.Indus River Basin (India) - 2500 B.C.Indus River Basin (India) - 2500 B.C.Maya and Inca civilizations (Mexico, South Maya and Inca civilizations (Mexico, South America) - 500 B.C.America) - 500 B.C.Salt River Basin (Arizona) - 100 B.C.Salt River Basin (Arizona) - 100 B.C.Western U. S. - 1800’sWestern U. S. - 1800’sInvolvement of federal government - 1900 (only Involvement of federal government - 1900 (only about 3 million acres then)about 3 million acres then)

Types of SystemsTypes of SystemsSprinklerSprinkler– pressurized irrigation through devices called pressurized irrigation through devices called

sprinklers (water is discharged into the air and sprinklers (water is discharged into the air and hopefully infiltrates near where it lands)hopefully infiltrates near where it lands)

– used on agricultural and horticultural crops, turf, used on agricultural and horticultural crops, turf, landscape plantslandscape plants

– Many types including:Many types including:- single sprinkler systems - single sprinkler systems - boom sprinkler systems: single boom (arm) has - boom sprinkler systems: single boom (arm) has many nozzles) many nozzles) - multiple sprinkler systems: side roll, center pivot etc. - multiple sprinkler systems: side roll, center pivot etc. - permanent systems, ex. orchard - permanent systems, ex. orchard - movement may be via hand, tractor or self-propelled- movement may be via hand, tractor or self-propelled

Types of SystemsTypes of SystemsSurfaceSurface– Irrigation water flows across the field to the point of Irrigation water flows across the field to the point of

infiltrationinfiltrationmost common method of irrigation world-wide, esp. in most common method of irrigation world-wide, esp. in developing nations developing nations

– primarily used on agricultural crops and orchardsprimarily used on agricultural crops and orchards– Types:Types:

- flood = total immersion for long period of time, ex. rice field- - flood = total immersion for long period of time, ex. rice field- - border irrigation. Water - -introduced at one end of field and - border irrigation. Water - -introduced at one end of field and allowed to disperse and travel down to other end. allowed to disperse and travel down to other end. - furrow irrigation. Water introduced through tubes from canal - furrow irrigation. Water introduced through tubes from canal directly into individual furrows.directly into individual furrows.

MicroMicro (drip, trickle) (drip, trickle)– frequent, slow application of irrigation water using frequent, slow application of irrigation water using

pressurized systemspressurized systems– used in landscape and nursery applications, and on high-used in landscape and nursery applications, and on high-

value agricultural and horticultural cropsvalue agricultural and horticultural crops

Types of SystemsTypes of Systems

SubirrigationSubirrigation– water is applied below ground surface via drain water is applied below ground surface via drain

tile/tubes or through deep surface ditches tile/tubes or through deep surface ditches – goal is to increase the height of the watertablegoal is to increase the height of the watertable– Requirements:Requirements:

- very permeable soil so that water can move upwards - very permeable soil so that water can move upwards

- impermeable layer or natural water table near root - impermeable layer or natural water table near root zone zone

- low hazard due to salt accumulation since no leach - low hazard due to salt accumulation since no leach provided by this irrigation methodprovided by this irrigation method

AssignmentAssignment

From your reading on textbook and other From your reading on textbook and other references:references:

1.1. List and describe the factor affecting you List and describe the factor affecting you to choose the irrigation method for your to choose the irrigation method for your farm.farm.

2.2. With the chosen crops, consider the best With the chosen crops, consider the best economical method with high crops economical method with high crops production.production.

Irrigation Water Irrigation Water RequirementRequirement

EvapotranspirationEvapotranspirationTerminologyTerminology– EvaporationEvaporation

Process of water movement, in the vapor form, into Process of water movement, in the vapor form, into the atmosphere from soil, water, or plant surfacesthe atmosphere from soil, water, or plant surfaces

– TranspirationTranspirationEvaporation of water from plant stomata into the Evaporation of water from plant stomata into the atmosphereatmosphere

– EvapotranspirationEvapotranspirationSum of evaporation and transpiration (abbreviated Sum of evaporation and transpiration (abbreviated “ET”)“ET”)

– Consumptive useConsumptive useSum of ET and the water taken up the plant and Sum of ET and the water taken up the plant and retained in the plant tissue (magnitude approximately retained in the plant tissue (magnitude approximately equal to ET, and often used interchangeably)equal to ET, and often used interchangeably)

Magnitude of ETMagnitude of ET

Generally tenths of an inch per day, or tens of Generally tenths of an inch per day, or tens of inches per growing seasoninches per growing season

Varies with type of plant, growth stage, Varies with type of plant, growth stage, weather, soil water content, etc.weather, soil water content, etc.

Transpiration ratioTranspiration ratio– Ratio of the mass of water transpired to the mass Ratio of the mass of water transpired to the mass

of plant dry matter produced (g Hof plant dry matter produced (g H22O/g dry matter)O/g dry matter)

Typical values:Typical values: 500 for wheat 500 for wheat

900 for alfalfa 900 for alfalfa

Plant Water Use PatternsPlant Water Use PatternsDaily Water Use:Daily Water Use: peaks late in afternoon; very little water use at nightpeaks late in afternoon; very little water use at night

DAILY CROP WATER USE PATTERN

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 400 800 1200 1600 2000 2400

TIME OF DAY, (hour)

ET

RA

TE

, (m

m/h

r)

Alfalfa: Ft. Cobb, OK

June 26, 1986

Plant Water Use PatternsPlant Water Use PatternsSeasonal Use Pattern:Seasonal Use Pattern: Peak period affects designPeak period affects design

Corn Water Use PatternCorn Water Use PatternIrrigation system must be Irrigation system must be able to meet peak water use able to meet peak water use rate or the crop may be lostrate or the crop may be lost.

Evaporation Rate and Time Since IrrigationEvaporation Rate and Time Since Irrigation

Energy or Water Availability as the Limiting Factor in ET RateEnergy or Water Availability as the Limiting Factor in ET Rate

Estimation based on:Estimation based on:– climateclimate– cropcrop– soil factorssoil factors

ETc = Kc EToETc = Kc EToETc = actual crop evapotranspiration rateETc = actual crop evapotranspiration rate

ETo = the evapotranspiration rate for a reference cropETo = the evapotranspiration rate for a reference crop

Kc = the crop coefficientKc = the crop coefficient

Evapotranspiration ModelingEvapotranspiration Modeling

Reference Crop ET (ETReference Crop ET (EToo))– ET rate of actively growing, well-watered, “reference” cropET rate of actively growing, well-watered, “reference” crop– Grass or alfalfa used as the reference crop (alfalfa is higher) Grass or alfalfa used as the reference crop (alfalfa is higher) – A measure of the amount of energy available for ET A measure of the amount of energy available for ET – Many weather-based methods available for estimating EToMany weather-based methods available for estimating ETo

(FAO Blaney-Criddle; Jensen-Haise; Modified Penman; Penman-Montieth)(FAO Blaney-Criddle; Jensen-Haise; Modified Penman; Penman-Montieth)

Crop Coefficient (Kc)Crop Coefficient (Kc)– Empirical coefficient which incorporates type of crop & stage Empirical coefficient which incorporates type of crop & stage

of growth (Kcb); and soil water status-- a dry soil (Ka) can of growth (Kcb); and soil water status-- a dry soil (Ka) can limit ET; a wet soil surface (Ks) can increase soil evaporationlimit ET; a wet soil surface (Ks) can increase soil evaporation

– Kc = (Kcb x Ka) + Ks Kc = (Kcb x Ka) + Ks – Kc values generally less than 1.0, but not always Kc values generally less than 1.0, but not always

Evapotranspiration ModelingEvapotranspiration Modeling

http://agweather.mesonet.orghttp://agweather.mesonet.org

Using the ET Table to Schedule Lawn IrrigationUsing the ET Table to Schedule Lawn Irrigation

Effective RainfallEffective Rainfall

Effective RainfallEffective Rainfall = portion of rainfall that contributes to = portion of rainfall that contributes to ET (some does not wet soil deep enough / goes to ET (some does not wet soil deep enough / goes to runoff / lost to deep percolation) runoff / lost to deep percolation)

– Pe = estimated effective rainfall for a soil depth of 75 mm (mm) Pe = estimated effective rainfall for a soil depth of 75 mm (mm) – Pm = mean monthly rainfall (mm) Pm = mean monthly rainfall (mm) – ET = average monthly evapotranspiration (mm) ET = average monthly evapotranspiration (mm) – D = soil water deficit = net irrigation depth (mm) D = soil water deficit = net irrigation depth (mm) – f(D) adjustment factor f(D) adjustment factor

Note: Pe <= lowest of ET and Pm Note: Pe <= lowest of ET and Pm

3725

000955.0824.0

103221094801160530

]10][93.225.1)[(

D x .D x .D..f(D)

PDfPe ETm

Moisture AccountingMoisture AccountingSoil Water ReservoirSoil Water Reservoir

AW = (FCAW = (FCvv-PWP-PWPvv)D)Drr

Where Where – AW = Available waterAW = Available water– FC = volumetric field capacityFC = volumetric field capacity– PWP = volumetric wilting pointPWP = volumetric wilting point– Dr = depth of root zone or depth of layer of soil Dr = depth of root zone or depth of layer of soil

within the root zonewithin the root zone– Refer to Table 15-2 pg. 337.Refer to Table 15-2 pg. 337.

Soil Water ReservoirSoil Water Reservoir

RAW = MAD x AWRAW = MAD x AW

RAW = readily available water RAW = readily available water

From Table 15-4From Table 15-4

MAD = management allowed depletionMAD = management allowed depletion

System PlanningSystem Planning

Because irrigation is a major water user, it is Because irrigation is a major water user, it is essential that irrigation system be planned, essential that irrigation system be planned, designed, and operate efficiently.designed, and operate efficiently.

Determine need - estimate crop use vs. rainfall Determine need - estimate crop use vs. rainfall

Examine site Examine site – topography (slope, changes in elevations) topography (slope, changes in elevations) – soil characteristics (root zone depth, water holding soil characteristics (root zone depth, water holding

capacity, infiltration rate) capacity, infiltration rate)


Availability of water - quantity & quality. Availability of water - quantity & quality. Generally groundwater is better quality than Generally groundwater is better quality than surface water. Need well with sufficient pumping surface water. Need well with sufficient pumping capacity if bringing in water through an irrigation capacity if bringing in water through an irrigation canal. canal.

Economic analysis - compare cost of installing Economic analysis - compare cost of installing and operating irrigation system vs. expected and operating irrigation system vs. expected increase in yields. In Indiana, generally need an increase in yields. In Indiana, generally need an increase of the magnitude of 50 bushels of corn increase of the magnitude of 50 bushels of corn per acre per year to justify expense. per acre per year to justify expense.


Available Water: Available Water:

– AW = (FC - PWP)Dr / 100 AW = (FC - PWP)Dr / 100 – AW = available water (mm, in) AW = available water (mm, in) – FC = volumetric field capacity (decimal) FC = volumetric field capacity (decimal) – PWP = volumetric permanent wilting point PWP = volumetric permanent wilting point

(decimal) (decimal) – Dr = depth of root zone or depth of soil layer Dr = depth of root zone or depth of soil layer

of interest (mm, in)of interest (mm, in)


Leaching RequirementLeaching Requirement (LR) = extra water (LR) = extra water applied to dissolve and carry away salts in the applied to dissolve and carry away salts in the soil. soil.

– value will be given if needed value will be given if needed – expressed as a portion of the total irrigation water expressed as a portion of the total irrigation water

applied applied – ex. LR = 0.2 and total applied = (1+LR) x soil water ex. LR = 0.2 and total applied = (1+LR) x soil water

deficit deficit

*From Figure 15-3 (pg 344) textbook*From Figure 15-3 (pg 344) textbook


Irrigation Requirement:Irrigation Requirement:

IR = [(ET - Pe)(1 + LR)] / Ea IR = [(ET - Pe)(1 + LR)] / Ea – Pe = effective rainfall Pe = effective rainfall – Ea = application efficiency Ea = application efficiency – ET = u from Blaney-Criddle ET = u from Blaney-Criddle

evapotranspiration equation evapotranspiration equation

Efficiencies and UniformitiesEfficiencies and Uniformities

Efficiency:Efficiency:– Output divided by an input an usually expressed as a Output divided by an input an usually expressed as a

percentage.percentage.– There are 3 basic efficiency concept:There are 3 basic efficiency concept:

1. Water Conveyance Efficiency:1. Water Conveyance Efficiency:– Can be applied along any reach of a distribution Can be applied along any reach of a distribution

systemsystem– Example: A water conveyance efficiency could be Example: A water conveyance efficiency could be

calculated from a pump discharge to a given field or calculated from a pump discharge to a given field or from a major diversion work to a farm turnoutfrom a major diversion work to a farm turnout


Water Conveyance Efficiency, EcWater Conveyance Efficiency, Ec

Where Where

WWdd= water delivered by a distribution system= water delivered by a distribution system

WWi i = water introduced into the distribution = water introduced into the distribution

systemsystem

i

dc W

WE 100


2. Water Application Efficiency, Ea2. Water Application Efficiency, Ea– The efficiency may be calculated for an The efficiency may be calculated for an

individual furrow or border strip, for an entire individual furrow or border strip, for an entire field or entire farm/project.field or entire farm/project.

– When applied to areas larger than a field, it When applied to areas larger than a field, it overlaps the definition of conveyance overlaps the definition of conveyance efficiency.efficiency.

Efficiencies and UniformitiesEfficiencies and UniformitiesApplication efficiency (EApplication efficiency (Eaa))

– WWss = water stored in the root zone by irrigation = water stored in the root zone by irrigation

– WWd d = water delivered to the area being = water delivered to the area being

irrigatedirrigated– fraction or percentagefraction or percentage

d

sa WWE


3. Water Use Efficiency, Eu3. Water Use Efficiency, Eu

WhereWhere

WWuu = water benefecially used = water benefecially used

WWdd = water delivered to the area being = water delivered to the area being

irrigatedirrigated

d

uu W

WE 100

ExampleExample

Refer textbook:Refer textbook:– Pg. 345Pg. 345– Example 15-5Example 15-5

Application UniformityApplication Uniformity

Coefficient of Uniformity (UC)Coefficient of Uniformity (UC)

– n = number of observations (each representing the n = number of observations (each representing the same size area)same size area)

– d = average depth for all observationsd = average depth for all observations– yyii = depth for observation i = depth for observation i

Popular parameter for sprinkler and Popular parameter for sprinkler and microirrigation systems in particularmicroirrigation systems in particularFor relatively high uniformities (CU > 70%), For relatively high uniformities (CU > 70%),

Eq. 5.4 and 5.5 relate CU to DUEq. 5.4 and 5.5 relate CU to DU

n

i

i

nd

dyUC

1

1

Turf Sprinkler Uniformity TestTurf Sprinkler Uniformity Test (catch cans placed on a 5 ft x 5 ft grid)(catch cans placed on a 5 ft x 5 ft grid)

AdequacyAdequacy

Because of nonuniformity, there is a tradeoff Because of nonuniformity, there is a tradeoff between excessive deep percolation and plant between excessive deep percolation and plant water stresswater stressAdequacy: the percent of the irrigated area that Adequacy: the percent of the irrigated area that receives the desired depth of water or morereceives the desired depth of water or more

Water LossesWater Losses

Water lossesWater losses– EvaporationEvaporation– DriftDrift– RunoffRunoff– Deep percolationDeep percolation

Water LossesWater Losses

Irrigation SchedulingIrrigation Scheduling

Irrigation SchedulingIrrigation Scheduling

If water is available, schedule so as to If water is available, schedule so as to achieve maximum yields achieve maximum yields

If water is limited / expensive then If water is limited / expensive then schedule so as to maximize economic schedule so as to maximize economic return return

Typically start irrigation when available Typically start irrigation when available water = 55% maximum water = 55% maximum

General ApproachesGeneral Approaches

Maintain soil moisture within desired limitsMaintain soil moisture within desired limits – direct measurementdirect measurement– moisture accountingmoisture accounting

Use plant status indicators to trigger Use plant status indicators to trigger irrigationirrigation– wilting, leaf rolling, leaf colorwilting, leaf rolling, leaf color– canopy-air temperature differencecanopy-air temperature difference

Irrigate according to calendar or fixed Irrigate according to calendar or fixed schedule schedule – Irrigation district delivery scheduleIrrigation district delivery schedule– Watching the neighborsWatching the neighbors

Irrigation Timing/PeriodIrrigation Timing/Period

Actual irrigation interval, (days)Actual irrigation interval, (days)

ddee = effective depth of irrigation, (in. or mm) = effective depth of irrigation, (in. or mm)

c

e

ETdT

Irrigation PeriodIrrigation Period

# days over which irrigation cycle must be # days over which irrigation cycle must be complete. Equals the time it take for field at FC complete. Equals the time it take for field at FC to reach 55% AW without rainfall occurringto reach 55% AW without rainfall occurring

Example:Example:

Root zone depth = 1 m, allowable depletion = Root zone depth = 1 m, allowable depletion = 40% AW, AW = 150 mm/ m depth, ave. ET = 8 40% AW, AW = 150 mm/ m depth, ave. ET = 8 mm. daymm. day– IP = [150 mm/m (1m) (0.4)] / 8 mm/day = 7.5 days IP = [150 mm/m (1m) (0.4)] / 8 mm/day = 7.5 days – So can divide up entire area to be irrigated such that So can divide up entire area to be irrigated such that

repeat irrigation at same site every 7.5 days.repeat irrigation at same site every 7.5 days.

Possible Irrigation Scheduling Possible Irrigation Scheduling Management ObjectivesManagement Objectives

Maximum yield/biomass productionMaximum yield/biomass production

Maximum economic returnMaximum economic return

Functional value of plants (e.g., athletic Functional value of plants (e.g., athletic fields)fields)

Aesthetic value of plants (e.g., landscapes)Aesthetic value of plants (e.g., landscapes)

Keeping plants aliveKeeping plants alive

Plant Root ZonesPlant Root Zones

Depth used for scheduling vs. Depth used for scheduling vs. maximum depth where roots are maximum depth where roots are foundfound

Influenced by soil characteristicsInfluenced by soil characteristics– Soil textureSoil texture– HardpanHardpan– BedrockBedrock

Perennial vs. annual plantsPerennial vs. annual plants

Components of Crop Root Zone Water BalanceComponents of Crop Root Zone Water Balance

Other Irrigation Scheduling MethodsOther Irrigation Scheduling Methods

Soil Water MeasurementSoil Water Measurement– Need measurements at several locationsNeed measurements at several locations– Need measurements throughout root zone Need measurements throughout root zone

depthdepth– Doesn’t indicate how much water to applyDoesn’t indicate how much water to apply

Other Irrigation Scheduling MethodsOther Irrigation Scheduling MethodsPlant Status IndicatorsPlant Status Indicators– Leaf water potential (energy status of leaf water)Leaf water potential (energy status of leaf water)

Use pressure chamber or thermocouple Use pressure chamber or thermocouple psychrometerpsychrometer

Measured at mid-day; many samples neededMeasured at mid-day; many samples needed– Foliage/Air temperature differenceFoliage/Air temperature difference

Well-watered plants cooler than airWell-watered plants cooler than air

Use infrared thermometerUse infrared thermometer– Leaf appearanceLeaf appearance

Color, wilting, etc.Color, wilting, etc.

Indicators show up too lateIndicators show up too late– Irrigate at critical growth stages (e.g.: flowering)Irrigate at critical growth stages (e.g.: flowering)

irrigation principles ert 349 soil and water engineering

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