IRRIGATION GUIDANCE
FOR PLANNERS
Rick Schlegel
Irrigation Engineer
USDA - NRCS
FIRST STEP - DO AN IRRIGATION
SYSTEM INVENTORY
 System
capacity or flow available
 Conveyance system & condition
 Irrigation system types
 Crops to be irrigated
 Predominate soil types being irrigated
 Irrigation water management being
practiced by producer
AFTER COMPLETING
INVENTORY
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After the inventory is done, decide if the existing
system is adequate or if the irrigator needs to:
Install a new irrigation system
Install flowmeters or chemigation valves
Install a new pipeline or delivery system
Change his cropping system to be more efficient
Manage or schedule irrigation applications
Decommission inadequate wells
Let’s break down the inventory and
talk about each item
SYSTEM CAPACITY
 Needs
to be large enough to meet crop
water needs in a timely manner
 RULE OF THUMB FOR PLANNERS:
 High water use crops such as corn or
peanuts - 7.0 gpm/acre needed
 Medium water use crops such as cotton,
milo, soybeans – 5.0 gpm/acre needed
 Minimum to meet standard – 3.0 gpm/acre
PUMP CURVES
Conveyance System
 Generally
use underground PVC
 Replace leaky or undersized lines
 RULE OF THUMB FOR PLANNERS:
Below 400 gpm – 6” PVC
400 – 750 gpm – 8” PVC
750 – 1200 gpm – 10” PVC
1200 – 1700 gpm – 12” PVC
 Plan High Pressure Line when delivery
system is long length or large elevation
increases are encountered
COMMON IRRIGATION SYSTEMS
UNDER EQIP
 LEPA –
Low Energy Precision Application
 LESA – Low Elevation Spray Application
 LPIC – Low Pressure In Canopy
 MESA – Mid Elevation Spray Application
 Drip System or Microirrigation
LEPA SYSTEM
LEPA SYSTEM
LESA
SYSTEM
LPIC
SYSTEM
MESA
MESA
SYSTEM
CROPS AND SOILS
 Determine
crops to be irrigated
 Determine predominate soils to be
irrigated
 Use Oklahoma Irrigation Guide to gather
information for IWM plan
 Teach producer how to do Irrigation
Scheduling
UNDERSTANDING
SOIL – WATER – PLANT
RELATIONSHIPS
TYPICAL
CROP
ROOT
ZONE
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V
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P
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ET
EVAPOTRANSPIRATION
DEEP PERCOLATION
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AVAILABLE WATER CAPACITY
(AWC)
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THE ROOT ZONE CAN ONLY HOLD SO MUCH
WATER ( FIELD CAPACITY ). THE REST IS
LOST TO DEEP PERCOLATION.
 “AWC” IS THE AMOUNT OF WATER HELD IN
THE ROOT ZONE OF THE CROP THAT IS
AVAILABLE TO THE CROP.
AVAILABLE
WATER
CAPACITY
A
W
C
CLAY, CLAY
LOAM & SILTY
CLAY LOAM
2.0 IN/FOOT
SANDY CLAY
LOAM, LOAM,
& SILT LOAM
1.8 IN/FOOT
SANDY LOAM
& FINE
SANDY LOAM
1.5 IN/FOOT
FINE SAND
AND LOAMY
FINE SAND
0.9 IN/FOOT
MANAGING THE
AVAILABLE WATER
Using
Management Allowable Depletion
MAD
MAD
WATER
BALANCE
A
W
C
M
A
D
S
T
I
N
G
Y
TWO METHODS PLANNED
 1.
Manage the available moisture at
50% AWC
 2. Manage the available moisture to let it
drop to the level of a typical producer
irrigation plus leaving a one to two inch
depletion for rainfall. (1.5” + 1.0” = 2.5”)
“MAD” EXAMPLES AT 50%
 CROP
WITH FOUR FOOT ROOT ZONE:
 CLAY, CLAY LOAM, OR SILTY CLAY
LOAM
AWC = 8.0” MAD WB= 4.0”
 SANDY CLAY LOAM, LOAM, OR SILT
LOAM
AWC = 7.2” MAD WB= 3.6”
 SANDY LOAM OR FINE SANDY LOAM
AWC = 6.0” MAD WB=
3.0”
 FINE SAND OR LOAMY FINE SAND
AWC = 3.6” MAD WB= 1.8”
AVAILABLE WATER CAPACITY
CAN ALSO BE LIMITED BY:
AWC
PLOW PAN
DEVELOPING AN
IRRIGATION WATER
MANAGEMENT PLAN
SCHEDULING
IRRIGATION
USING EVAPOTRANSPIRATION
METHODS
Evapotranspiration Methods
 Using
the Atmometer
 Using the Agweather Site on the Mesonet
EVAPOTRANSPIRATION USING
THE OKLAHOMA MESONET
USING MESONET “ET” DATA
USING EXCEL SPREADSHEET
EQIP Incentive Payment ($10/acre)
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Eight basic requirements:
1. Irrigation system meets standards
2. IWM plan is followed
3. Report flow twice during season
4. Install two rain guages and record rain
5. Determine daily ET to use in scheduler
6. Spot check soil moisture monthly
7. Record irrigation amounts and durations
8. Keep scheduler & records & submit to NRCS
9. USE SCHEDULER TO MAKE DECISIONS