Micro Irrigation
Is it the right choice and design
considerations
Natural Resources Conservation Service
First of all, micro irrigation
is….
…the broad classification of frequent, low
volume, low pressure application of water on
or beneath the soil surface by drippers, drip
emitters, spaghetti tube, subsurface or surface
drip tube, basin bubblers, and spray or mini
sprinkler systems. It is also referred to as
drip or trickle irrigation. (NEH Part 652,
Irrigation Guide, ‘97)
…an irrigation system for distribution of water
directly to the plant root zone by means of
surface or subsurface applicators. (Draft PS
441,Natural
‘00)Resources Conservation Service
Why would I use micro?
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high uniformity with good design (90+ % achievable)
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less wetted surface area   evaporation &  weed problems
good in windy conditions (Uniformity &  evaporation)
good in undulating or steep areas (Uniformity)
excellent system control with automation
system flexibility
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MAY result in excellent efficiency   inputs of water, power, and
chemicals
 growth/production
odd “field” shapes
supply nutrients to a specific point so spacing/variety of plant is
not limiting
soils with low water holding capacity (frequent, low volume
applications)
Natural Resources Conservation Service
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Why would I use micro?
(cont.)
low operating cost
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odor control for waste water applications (esp. subsurface)
climate control
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 or  temperature
 or  humidity
“disease” control
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high efficiency with low pressures & flow rates  energy savings
less labor
eliminate wetting of tree trunks
eliminate wetting of leaf/fruit
easily adapted to automation
……any others?…...
Natural Resources Conservation Service
Why wouldn’t I use micro?
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Issues associated with “dirty” water
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potential clogging of emitters
cost of filtration
High Level of O&M Required
High Pest Damage Potential
High Initial Cost
Most, if not all, of these issues can be overcome but at
some point it becomes a matter of economics
Natural Resources Conservation Service
So, if micro is right for the
situation…..
Micro Design
Considerations
Natural Resources Conservation Service
Information Needed for Micro
Design
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Soil Characteristics (Water Holding Capacity, pH, etc.)
Tree/Shrub/Crop Characteristics
 Layout (spacing, numbers, etc.)
 Tree/Shrub/Crop Water Requirements over time
 Root Zone over time
 Sensitivity to Available Moisture (MAD)
 Sensitivity to Water/Soil Quality
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Good topographic survey - at least 2 foot intervals.
Water & Power Source
 Location
 Quantity
 Quality
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Owner/Operator Characteristics & Desires
Natural Resources Conservation Service
Micro Design Considerations
NRCS Standards, Specifications & References
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PS and GS 380 Windbreak/Shelterbelt Establishment
 “…supplemental or permanent watering of the planting will be
evaluated in areas with less than 20 inches average annual
precipitation……”
 “… Use Idaho Forestry TN 14 (12/93) for water requirements.”
 “soak soil to 3 to 5 ft depth”
 MAD of 50 to 60%
 if poly fabric mulch used, supplemental water use may be
reduced by up to 50%
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PS 441 Irrigation System, Trickle (‘82)
 design application efficiency not to exceed 90%
 for individual laterals, individual emitter q ± 15% of average q
 main and submains must meet PS 430
 “A filtration system shall be provided…..”
Natural Resources Conservation Service
Micro Design Considerations
NRCS Standards, Specifications & References
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Draft PS 441 Irrigation System, Microirrigation (‘00)
 max time of operation for design is 22 hr/day
 design application efficiency not to exceed 90%
 # & spacing of emitters (Pw) based on NEH 623, Ch. 7
 manufacturer’s coefficient of variation
 for individual subunits (blocks), individual emitter q ± 10% of
average q (total variation of 20% allowed)
 main and submains must meet PS 430
 “A filtration system shall be provided…..” with constraints
 other: pressure regulators, chemical treatment, flushing,
subsurface installation, chemigation, germination, water
quality, salinity issues
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NEH Part 623, Irrigation, Chapter 7, Trickle Irrigation
Natural Resources Conservation Service
Micro Design Considerations
NRCS Standards, Specifications & References
NEH Part 652, Irrigation Guide, Chapter 6, Irrigation System
Design (9/97) - Windbreaks
 if designing to irrigate throughout lifespan, use NEH 623, Ch.
7
 if designing just for establishment
 design to last at least first 5 years
 after initial establishment of trees/shrubs water applications
should be greater in volume and less frequent to encourage root
zone development
 suggests augering and backfilling a deep, small diameter hole
near each tree/shrub to allow deeper penetration of water and,
hence, deeper rooting
 for arid & semiarid climates, apply water early in spring after
soil thaws to fill soil profile
 discontinue watering in the fall before freezing to encourage
“hardening” (perhaps should irrigate after “hardening,”
however)
Service
Natural
do notResources
provideConservation
full irrigation
Micro Design Considerations
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System reliability/management is important
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Flushing ability
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frequent applications  typically “wetter” soils  
infiltration capacity during storm events
effects of weed barrier fabric
point sources
Saline/Sodic conditions
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individual laterals
connect ends with flushing main (also gives system
resiliency)
required velocity at end of lateral > than operating velocity
Runoff - Infiltration Rate vs. Application Rate
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 soil volume wetted   WHC  “dry” quicker
frequent applications  continuous dilution of salty water
but, “salt profile” can be moved back into root zone with
precip
System Drainage
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frequent
cycling  overapplication in drainage areas
Natural Resources Conservation Service
Micro Design Procedure (Irrigation
Guide)
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NOT a linear procedure since these steps are
interrelated
Step 1: Determine net amount of water required
Step 2: Emitter design
Step 3: Subunit/block design
Step 4: Size laterals, submains, & mains
Step 5: Pump selection
Step 6: Filtration design
Steps 7 & 8: Fertilizer & chemical injection design
Step 9: Pressure gauge, valves, drains, measuring
devices
Step 10: Irrigation scheduling plan
Step 11: O&M plan
Natural Resources Conservation Service