Irrigation Efficiency and
Uniformity
R. Troy Peters, PhD, PE
Average Annual Rainfall
USGS 1995 Consumptive Use Numbers
% Consumptive Use
of Renewable Supply
•
•
•
•
•
Entire Colorado River Basin
California – Nevada
Montana – Wyoming – Nebraska
Entire Mississippi River Basin
Washington – Oregon – Idaho
103%
35%
30%
9%
4%
• 80% of WA water withdrawals is for Agriculture
• Greater % of consumptive use is irrigation
Irrigated Acres
Market Value of Ag. Products Sold
Washington Irrigation
•
•
•
•
1.8 M irrigated acres
80% sprinkler, 15% surface (gravity), 5% drip
75% surface water, 25% groundwater
Today irrigators apply ¾ the amount of water
that they were in the early 1970’s and getting
much better yields
• Recently (2002) the total sprinkler irrigated acres
in the U.S. surpassed surface irrigated acres
2003 Census of Agriculture. Farm and Ranch Irrigation Survey
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
AvgLowQuarter
DU Calculation

of DU
Avg
4
3.5
Catch (inches)
3
2.5
2
1.5
1
Average
Low Quarter
0.5
Overall Average
0
1
4
7
10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55
Data Point
Christiansen Coefficient of
Uniformity
zm

CU  1 
z
where:
CU = coefficient of uniformity
z = individual catch (in)
m = average catch (in)
Catch in Inches
3.5
Catch in Inches
3
DU= 43.8%; CU=58.8%
2.5
2
1.5
1
0.5
0
0
200
400
600
800
1000
Distance from Pivot Center
1200
1400
1600
Catch in Inches
1.6
DU = 76.4%; CU = 84.3%
1.4
Catch in Inches
1.2
1
0.8
0.6
0.4
0.2
0
0
200
400
600
800
Distance from Pivot Center
1000
1200
1400
Catch in Inches
0.8
0.7
Catch in Inches
0.6
0.5
0.4
0.3
0.2
0.1
0
0
100
200
300
400
500
600
700
800
900
1000 1100 1200 1300 1400
Distance from Pivot Center
Uniformity
•
•
•
•
•
•
•
Better yields
Improved crop quality (more uniform)
Less water used = $$ savings
Less lost fertilizers
Less mess
Better for the environment
Chemigate or fertigate with confidence
Why Distribution Uniformity is Important $$$
120
% Additional Water Required to
Adequately Irrigate Whole Field
100
% N in Solution Lost per Application
1000
80
100
60
40
10
20
1
0
0
0.2
0.4
0.6
0.8
Distribution Uniformity of the Low Quarter
1
% of Nitrogen in Solution
Lost per Irrigation
Required % Addtional Water
Pumped
10000
Improve Uniformity
• Run at pressure and flow rate that the sprinkler
package was designed for.
• Keep correct nozzle sizes in correct position
– Keep your sprinkler chart. Double check it.
• More sprinkler overlap
– closer spacing
– larger wetted diameter (sprinkler throw distance)
• Replace nozzles every 3-5 years (inexpensive)
• Rotator/Wobblers are better, but must be rotating.
Fix leaks. Fix and unplug heads.
Center Pivot Uniformity
• Replace sprinklers about every 7 years.
• Use pressure regulators on sloping fields
(depends on operating pressure; > 10-15 ft
elevation difference).
• Run at the pressure and flow rate
specified in the nozzle package. If
pressure or flow rate changes, renozzle.
• End gun and cornering system uniformity
is typically poor.
Irrigating Potatoes
• Large yield & quality
losses caused by water
stress in all stages of
development
• Deficit irrigating is not
economically justified on
potatoes.
• Large differences in
profitability on potato
production due solely to
irrigation management
Irrigation Efficiency
Irrigation Efficiency Defined
WaterStoredInSoil
ApplicationEfficiency 
WaterApplied
WaterBenficiallyUsed
Efficiency 
WaterFlowingOntoField
Forms of Water Loss
•
•
•
•
•
•
Wind Drift
Droplet Evaporation
Evaporation from Foliage
Evaporation from Soil Surface
Runoff
Deep Percolation
– Overwatering
– Non Uniformity
Runoff
Irrigation Efficiencies
Highly dependant on:
– System Design
– Management
– Maintenance
– Weather
– Operating Conditions
Irrigation Efficiencies
Surface Irrigation
Borders: Well graded and managed
Borders: Poorly graded and managed
Furrow: Well graded and managed
Furrow: Poorly graded and managed
Furrow: Surge-flow with tail water recovery
Level Basins
Drip/Trickle
70-95%
60-80%
30-60%
50-70%
30-50%
60-90%
75-95%
Irrigation Efficiencies
Sprinklers
Sprinkler Type
Hand-move
Side-roll
Solid Set
Center Pivot
Linear move
Big Gun
Range Average
50-70%
65
50-70%
65
60-75%
70
70-85%
75
65-85%
75
55-65%
60
Improve Efficiencies By:
• Get a good design
• Maintain your system
– Replace worn nozzles
– Fix leaky pipes
• Improve management
– Irrigation Scheduling
– Operate at designed pressure and flow
– Irrigate on calm cool days
– Increase Application Rate
Why Should I Care?
• Even if the water is free, poor irrigation
management has very real costs
• Yields and quality are very strongly
correlated with irrigation water management
• Expensive fertilizers washed out
• Environmental damage
cabbage
Marketable
Yields
for
Various
Vegetable
Crops
rape
carrot
tomato
Imtiyaz, M., N.P. Mgadla, B. Chepete, and S.K.
Manase. 2000. Response of six vegetable crops to
irrigation schedules. Agricultural Water
Management. 45(3):331-342
spinach
onion
Over-Irrigating
• Increased incidence of plant diseases
– Blights, molds, rots, wilts
• Reduced storability
• Difficulty with harvesting and cultural
operations
• Less oxygen in root zone, yield loss
• Additional labor, pumping, fertilizer costs
Water Costs
• Assumptions:
–
–
–
–
130 acres
100 ft deep well
Center Pivot (40 psi required at pump)
56% irrigation efficiency (85% application
efficiency, 30% loss to deep percolation, additional
water for poor uniformity)
– Growing corn (seasonal water req’d: 36 in)
– $0.04/kW-hr
• Unnecessary electric power costs paid $3,200
(compared to 80% efficiency)
Pumping Costs
• $1.29/acre-in pumping costs
• At 80% irrigation efficiency and 85% uniformity
$1.90/acre-in of plant water requirements
• About $250 to apply 1 inch to a ¼ mile pivot.
Fertilizer Losses
• Assume:
–
–
–
–
silt loam soil (2 in/ft),
growing potatoes, 1.5 ft root zone
at field capacity
even concentration of fertilizer throughout profile and
leached water
• Over-irrigating 1 inch = about 14% of soluble
fertilizers percolated out of the root zone.
• Results in lost $, lower yield and potato quality
Benefits
• Most things that decrease your irrigation
costs also benefit the environment
– More flow for fish, less dirty water returning
to rivers
– Less consumption of energy
– Less fertilizer, pesticides in streams and
groundwater
– More carbon sequestration (takes CO2 out of
the air)
But Make Some Real Money!
• Saving money small
compared to the yield
increases and crop
quality improvements
common from
improved irrigation
water management.
Management
Good Irrigation Scheduling
20
Field Capacity
i n c h e s o f w a te r
15
MAD
10
W ilting Point
5
Irrigation + Rain
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
Moi s
ture
S
Com
r
dels
Sens
o
r Mo
isture
pute
Plan
t Mo
t
Othe
r
Cons
ultan
rs
enso
r
ET R
epor
ts
Watc
h Ne
i ghbo
Soi l
Cale
ndar
il
by I r
rig. D
ist.
Dai ly
Deci
ded
Per s
onal
of So
of Cr
op
Feel
Cond
i tion
Number of Farms
Methods Used in Washington to
Determine When to Irrigate
10000
8000
6000
4000
2000
0
Levels of Irrigation Scheduling
•
•
Guessing / Same schedule all season
Kicking the dirt / Looking at the plants
Less profitable
•
Look and feel method using shovel or soil
probe
Checkbook method / ET (AgWeatherNet)
Soil moisture monitoring
Neutron probe + checkbook (consultant)
Profitable growers
Worst
•
•
•
especially cost effective for high value vegetable crops
Best
Percent of total growers by where they get
their irrigation information
60%
50%
40%
30%
20%
10%
0%
Other
Electronic
Information
Services
Media
Reports
Federal or
State
Agencies
Consultants
Water
Supplier
Extension
Agents
Equipment Neighboring
Dealers
Farmers
2003 Census of Agriculture. Farm and Ranch Irrigation Survey
Questions?
Center Pivot
Sprinkler Packages
Pivot Sprinkler Packages:
The Goals
•
•
•
•
•
•
•
High uniformity
High efficiency
Maintain soil structure
No ponding or runoff – good infiltration
Low pressure (saves $$$)
Low initial costs
Long life
Sprinkler Packages
Droplet Size Distribution
• Large drops compared to small:
– Higher efficiency – less surface area
– Less wind distortion
• Large drops break up soil surface
structure (“don’t treat soil like dirt”)
– Especially in heavier textured soils (silts and
clays)
• Small droplets better for bare soil
• Large droplets better after full cover, hay
• Higher pressure = smaller droplet size
What sprinkler
package should I
specify?
(gpm/acre)
Simple Unit Conversion
1 in/day = 18.86 gpm/acre
(use 19 to get close)
• Multiply maximum water use requirement
in inches per day by 18.86 gpm/acre.
• Divide gpm/acre by 18.86 to get in/day.
Examples:
0.2 in/day = 3.8 gpm/acre
7.5 gpm/acre = 0.4 in/day
Dual Sprinkler Packages
• Low flow package (4-6 gpm/acre)
good in spring
– Gentler on the soil – maintains soil
structure, doesn’t cause surface
sealing (easier for small seeds to
break through surface crust
– Not an issue on sandy soils (no
need for dual packages)
• Higher flow packages (6-8.5
gpm/acre) needed in summer
– Required to keep up with higher
crop water use rates during hot
summer months
DUAL FLOW SPRINKLER PACKAGES
NELSON 3TN Dual Nozzle Clip
Dual Nozzle
Clip
Evapotranspiration (ET): net demand that must be replenished to maintain available supply of water for
crop production.
Height... The lower you go…
• Higher efficiency (more of pumped water gets to crop)
• Less uniformity distortion by wind
• Slightly poorer uniformity (less overlap) under low wind
conditions
• Smaller wetting pattern – possible infiltration problems
• Lower pressure required (save $$ on pumping energy)
• Poor uniformity when rotated into corn
• Requires more drops/span
Pressure Regulators
• Pressure changes = flow changes = poor uniformity
Senninger Irrigation
Pressure Regulators
• Needed for:
– Steeply sloped fields
– If delivery pressure is highly variable
– If end gun doesn’t have booster pump
• 5 psi > regulated pressure required
to work properly
• Regulators cost money ~$8-12/each
– Would like to not use them if possible: flat fields,
single source supply
Pressure Regulators
Maximum elevation difference that will cause
a 10% flow variation
Elevation
Operating
Pressure (PSI) Difference (ft)
7
15
11
25
15
35
20
45
24
55
29
65
33
75
37
85
Pumps and Energy
Water and Power
Flow  Pressure
Power 
Efficiency / 100
Pay for power (kW) over time (hrs) = kW-hr (KWH)
Centrifugal
Pumps
3 phase vs. Single phase
•
•
•
•
•
•
•
•
•
•
Power is generated in 3 phase
3 phase is ideal for electric induction motors
Higher starting torque
More efficient
Less expensive
Smaller motor
Simple and reliable (less vibration)
3 phase motors are more efficient at higher hp
Necessary for pumps > 10 hp
Not typically supplied to residences
Variable Frequency Drives
•
•
•
•
Changes motor spin speed. AC→DC→AC
Solid state. No moving parts. Cost ↓ Quality ↑
Works with existing motor and pump.
Can use a 3-phase motor on single phase
power source
www.joliettech.com
Variable Frequency Drives
• Power savings.
– No burning up pressure across valves.
– Soft starts – longer pump life
• Produce heat that must be vented.
• ~ $100/hp installed
• Possible cost share from power company.
(BPA)
• Cost effective if flows vary widely and for
long periods of time.
Cost Sharing
• EQUIP – USDA, NRCS
– Major efficiency upgrades, surface to sprinkler
• Conservation districts
• Bonneville Power Administration – For energy
saving projects.
– Through electric utility provider.
– SIS - $5/acre. Grower must get weekly report.
– $0.15/KWH saved or 70% of improvement, whichever
is less.
– Must verify energy savings
http://irrigation.wsu.edu
Chemigation
Chemigation
General term that includes:
• Fertigation
• Herbigation
• Insectigation
• Fungigation
• Nematigation
Advantages of Chemigation
•
•
•
•
Economics
Timeliness
Reduced soil compaction and crop damage
Operator safety
Disadvantages
• High management (need to know algebra)
• Additional equipment required
Calculating Injection Rates
1. Batch/Bulk Applications
– Drip, Hand-line, Wheel-lines, Solid set
2. Continuous Move Injections
– Center pivots, Linear Moves, Travelers,
Booms
3. Controlling water chemistry
– Drip (algae/bacteria growth control, root
intrusion)
Batch/Bulk Applications
Timing is Key
Batch Applications
– Herbicides and Insecticides
• Apply during the last few minutes (follow
the label)
– Fertilizers
• Time to put the chemical in the active root
zone, and so that the injection is finished
before irrigation is done. Rate is less
critical
Batch Injection Rates
Applied Early in the
Irrigation Cycle
Drip Tape
Soil
40%
30%
20%
10%
More danger of leaching.
Batch Injection Rates
Applied Late in the
Irrigation Cycle
Drip Tape
Soil
Don’t leave chemicals in the lines.
40%
30%
20%
10%
Less danger of leaching.
Batch Application
• Weight Method
– Mix desired amount of material in a
convenient amount of water.
– Inject until it is gone.
– Injection rate set to limit irrigation line
concentration and injection time.
• Volume Method
– Similar except applying a set volume.
Injection Rate
Vol
Ic 
T
Ic = Injection Rate (gpm)
Vol = Volume of Chemical to inject (gallons)
T = Injection Time (min)
Question
• Given:
– Need 50 lbs/acre N
– Mixture is 4.7 lbs N/gallon
– Wheel-move: 60 ft between sets, 40 ft between
sprinklers, 30 heads operating.
– 24 hour sets
•
•
•
•
How many gallons of liquid fertilizer needed?
What is a good injection time period?
What should we set the injection rate at?
When should we start injecting?
Checking Maximum Solution
Concentration in Lines
(Will it corrode my lines?)
Ic
Cs 
Qw
Cs = Solution Concentration in Irrigation Lines (%)
Ic = Chemical Injection Rate (gal/min)
Qw = Water Flow Rate (gal/min)
Question
• Given:
– Irrigation pipeline flow rate of 1000 gpm
– Injecting 3 gpm
– Maximum line concentration from the label is
2%
• Are we underneath the maximum line
concentration?
Continuous Move
Injection Rate is Critical
Calculate Injection Rate by Mass
(given lb/acre specs)
Qw  A
Ic 
C T
Ic
Qw
A
C
T
=
=
=
=
=
Chemical Injection Rate (gal/min)
Quantity of chemical to be applied (lb/acre)
Area (acres)
Concentration of injected solution (lb/gal)
Injection Time (min)
Question
• Given:
– 100 acre pivot
– Want to apply 20 lbs/acre N
– Fertilizer is UAN 32 which has 2.5 lb/gallon N
– Takes 2000 min for full rotation
• What is the injection rate (gpm)?
Calculate Injection Rate by Volume
(given pint/acre specs)
Qv  A
Ic 
T
Ic
Qv
A
T
=
=
=
=
Chemical Injection Rate (gal/min)
Quantity of chemical to be applied (gal/acre)
Area (acres)
Injection Time (min)
Question
• Given:
– 125 acre pivot
– 10 hour full rotation time
– Want to apply 1 gallon/acre fungicide
• What is the required injection rate?
(gallons/hour)
Water Chemistry Control
Goal is ppm water concentration
Water Chemistry Control
0.006  Fw  Cw
Ic 
P
Ic
Fw
Cw
P
=
=
=
=
Chemical Injection Rate (gal/hr)
Flow rate of the Irrigation water (gpm)
Desired chemical concentration (ppm)
Percentage of chemical in solution (%)
Question
• Given:
– Irrigation system flow rate of 1000 gpm
– Need 5 ppm chlorine in water to kill bugs
– Using household bleach (5.25% chlorine)
• What is the required injection rate?
(gallons/hour units on the pump settings)
Venturi Valves and other
proportional rate injectors
Tank mixture concentration is key
Question
Determining amount of solution for fixed
ratio injectors
Given:
IR = 0.571 gal/hr of bleach
1. Calculate total flow of irrigation system in one hour
100 gpm x 60 min/hr = 6000 gallons per hour
2. Calculate total gallons of solution to be injected
(divide Step 1 by ratio)
6000 gph ÷ 100 = 60 gallons of solution
3. Mix the 0.571 gallons of bleach with 60 gallons of water in the
injection tank
Mixing Dry Chemicals
Total Chemical to be Applied
(How much dry chemical to mix with water)
A  Rm
Wt 
Pcnt
Wt
A
Rm
Pcnt
=
=
=
=
Weight of chemical to be applied (lbs)
Area (acres)
Rate to apply by mass (lb/acre)
Percent concentration in mix (%)
Mixing Dry Chemicals
Minimum Volume for mixing dry
(Minimum amount of water to use)
Vmin
Wt

S
Vmin = Minimum volume (gallons)
Wt = Weight of chemical to be applied (lbs)
S = Solubility of chemical (lb/gal)
Mixing Dry Chemicals
Weight of dry to get ppm level
Ci
Wt 
1205
Wt = Raw chemical per 100 gallons of water (lbs)
Ci = Desired concentration (ppm)
Calibration of Equipment
•
Small differences in injection rates make
large differences in total amount of
chemical applied
- Insufficient or excessive ($$) application
•
•
Calibration involves injecting water and
checking the actual volume of water
injected
Set/check injector rate by injecting water
for 1 minute