441 - 1
NATURAL RESOURCES CONSERVATION SERVICE
CONSERVATION PRACTICE STANDARD
IRRIGATION SYSTEM, MICROIRRIGATION
DEFINITION design discharge less than 60 gal/hr at each
individual lateral discharge point.
An irrigation system for frequent application of
small quantities of water on or below the soil NRCS Conservation Practice Standard,
surface: as drops, tiny streams or miniature Irrigation System, Sprinkler (442), applies to
spray through emitters or applicators placed systems with design discharge of 60 gal/hr or
along a water delivery line. greater at each individual lateral discharge
This practice may be applied as part of a
conservation management system to achieve General Criteria Applicable to All Purposes
one or more of the following purposes:
The system shall be designed to uniformly
Efficiently and uniformly apply irrigation apply water and/or chemicals while
water and maintain soil moisture for plant maintaining soil moisture within a range for
growth. good plant growth without excessive water
loss, erosion, reduction in water quality, or salt
Prevent contamination of ground and accumulation.
surface water by efficiently and uniformly
applying chemicals. Microirrigation systems consist of point-source
emitter (drip, trickle, and bubbler), surface or
Establish desired vegetation. subsurface line-source emitter, basin bubbler,
Reduce energy use. and spray or mini sprinkler systems.
The system shall include all irrigation
CONDITIONS WHERE PRACTICE APPLIES appurtenances necessary for proper operation.
On sites where soils and topography are Appurtenances shall be sized and positioned
suitable for irrigation of proposed crops and an in accordance with sound engineering
adequate supply of suitable quality water is principles and site-specific features.
available for the intended purpose(s). Appurtenances include but are not limited to
Microirrigation is suited to vineyards, orchards, totalizing flow measurement devices, water
field crops, windbreaks, gardens, greenhouse filtration, air vent valves, vacuum relief valves,
crops, and residential and commercial pressure relief valve(s), water control valve(s),
landscape systems. Microirrigation is also pressure gauges, pressure regulators, and
suited to steep slopes where other methods pressure reducers.
would cause excessive erosion, and areas Water Quality. The irrigation water supply
where other application devices interfere with shall be tested and assessed for physical,
cultural operations. chemical and biological constituents to
Microirrigation is suited for use in providing determine suitability and treatment
irrigation water in limited amounts to establish requirements for use in a microirrigation
desired vegetation such as windbreaks, living system.
snow fences, riparian forest buffers, and Emitter discharge rate. The design
wildlife plantings. discharge rate of applicators shall be
This practice standard applies to systems with determined based on manufacturer’s data for
expected operating conditions. The discharge
Conservation practice standards are reviewed periodically and updated if needed. To obtain NRCS, NHCP
the current version of this standard, contact your Natural Resources Conservation Service
State Office or visit the Field Office Technical Guide. May 2011
441 - 2
rate shall not create runoff within the adequately protect the pipe network against
immediate application area. surge.
For bubbler irrigation, a basin beneath the Main and submain lines shall be designed and
plant canopy shall be required for water installed to meet the applicable criteria in
control, and applications shall be confined to NRCS Conservation Practice Standard,
the basin area. Irrigation Pipeline (430).
Number and spacing of emitters. The Emission Uniformity. Pipe sizes for mains,
number and spacing of emitters along a lateral submains, and laterals shall maintain subunit
line shall be adequate to provide water (zone) emission uniformity (EU) within
distribution to the plant root zone and percent recommended limits as determined by
plant wetted area (Pw). Procedures found in procedures contained in NEH, Part 623,
NRCS National Engineering Handbook (NEH), Chapter 7, Trickle Irrigation.
Part 623, Chapter 7, Trickle Irrigation, shall be
Filters. A filtration system (filter element,
used to calculate Pw.
screen, strainer, or filtration) shall be provided
Operating pressure. The design operating at the system inlet. Under clean conditions,
pressure shall be in accordance with published filters shall be designed for maximum head
manufacturer recommendations. The system loss of 5 psi. Maximum design head loss
operating pressure must compensate for across a filter before cleaning shall be based
pressure losses through system components on manufacturer recommendations. In the
and field elevation effects. absence of manufacturer data the maximum
permissible design head loss across a filter is
Emitter manufacturing variability. The
10 psi before filter cleaning is required.
manufacturer’s coefficient of variation (Cv)
shall be obtained and used to assess the The filter shall be sized to prevent the passage
acceptability of a particular product for a given of solids in sizes or quantities that might
application. obstruct the emitter openings. Filtration
systems shall be designed to remove solids
The CV shall be less than 0.07 for point source
based on emitter manufacturer
emitters and less than 0.20 for line source
recommendations. In the absence of
manufacturer data or recommendations,
Allowable pressure variations. filtration systems shall be designed to remove
solids equal to or larger than one-tenth the
Manifold and lateral lines. Manifold and lateral
emitter opening diameter.
lines, operating at the design pressure, shall
be designed to provide discharge to any The filter system shall provide sufficient
applicator in an irrigation subunit or zone filtering capacity so that backwash time does
operated simultaneously such that they will not not exceed 10% of the system operation time.
exceed a total variation of 20 percent of the Within this 10% time period, the pressure loss
design discharge rate. Internal pressure shall across the filter shall remain within the
not exceed manufacturer recommendations manufacturer's specification and not cause
during any phase of operation. unacceptable EU.
Main and submain lines. Main and submain Filter/strainer systems designed for continuous
lines shall be designed to supply water to all flushing shall not have backwash rates
manifold and lateral lines at a flow rate and exceeding 1.0% of the system flow rate or
pressure not less than the minimum design exceeding the manufacturer's specified
requirements of each subunit. Adequate operational head loss across the filter.
pressure shall be provided to overcome all
Air/Vacuum relief valves. Vacuum relief shall
friction losses in the pipelines and
be designed and installed to prevent ingestion
appurtenances (valves, filters, etc.). Mains
of soil particles if there are summits in system
and submains shall maintain flow velocities
less than 5 ft/sec during all phases of
operation, unless special consideration is Air/vacuum relief valves shall be installed on
given to flow conditions and measures taken to both sides of all block or manifold water supply
441 - 3
Pressure regulators. Pressure regulators of operation per day.
shall be used where topography and the type
Subsurface Drip Irrigation (SDI). Tubing
of applicator dictate their use. Pressure
depth and spacing are soil and crop
regulators shall not be planned to compensate
dependent. Emitter line depth shall consider
for improperly designed pipelines.
the auxiliary irrigation methods used for
System flushing. Appropriate fittings shall be leaching, germination, and initial development.
installed above ground at the ends of all Maximum lateral line distance from the crop
mains, submains, and laterals to facilitate row shall be 24 inches for annual row crops
flushing. The system shall be designed and and 48 inches for vineyard and orchard crops.
installed to provide a minimum flow velocity of EU shall be designed for a minimum of 85
1 ft/sec during flushing. During flushing percent.
submain and manifold (pipelines located
Additional Criteria Applicable to Preventing
downstream from a control valve) velocities
Contamination of Ground and Surface
shall not exceed 7 ft/sec velocity. Each
flushing discharge outlet shall include a
pressure gauge and/or Schrader valve tap. Chemigation and Chemical Water
Treatment. System EU shall not be less than
Water Management Plan. An Irrigation Water
85 percent where fertilizer or pesticides, or
Management Plan meeting the requirements of
treatment chemicals are applied through the
NRCS Conservation Practice Standard,
Irrigation Water Management (449), shall be
developed for use with this practice. Backflow prevention devices shall be provided
on all microirrigation systems equipped for
Additional Criteria Applicable to Efficiently
and Uniformly Apply Irrigation Water
Injectors (chemical, fertilizer or pesticides) and
Depth of application. Net depth of application
other automatic operating equipment shall be
shall be sufficient to replace the water used by
located and installed in accordance with
the plant during the plant peak use period or
manufacturer’s recommendations and include
critical growth stage. Gross depth of
integrated back flow prevention protection.
application shall be determined by using field
application efficiencies consistent with the type Chemigation shall be accomplished in the
of microirrigation system planned. minimum length of time needed to deliver the
Applications shall include adequate water for chemicals and flush the pipelines. Application
leaching to maintain a steady state salt amounts shall be limited to minimum amount
balance. necessary, and rate shall not exceed
maximum rate recommended by chemical
System capacity. The system shall have
either (1) a design capacity adequate to meet
peak water demands of all crops to be irrigated Proper maintenance and water treatment shall
in the design area, or (2) enough capacity to be followed to prevent clogging based upon
meet water application requirements during dripper and water quality characteristics.
critical crop growth periods when less than full
irrigation is planned. The rationale for using a Irrigation water supply tests shall be used to
plan for addressing or avoiding chemical
design capacity less than peak daily irrigation
reactions with injected chemicals to prevent
water requirement shall be fully explained and
precipitate or biological plugging.
agreed upon by the end user. Design capacity
shall include an allowance for reasonable Additional Criteria Applicable to
water losses (evaporation, runoff, and deep Establishing Desired Vegetation
percolation) during application periods.
System capacity. The system shall have
design capacity adequate to provide
The system shall have the capacity to apply a supplemental water at a rate that will insure
specified amount of water to the design area survival and establishment of planned
within the net operation period. Minimum vegetation for a period of at least 3 years. The
system design capacity shall be sufficient to system shall have the capacity to apply the
deliver the specified amount of water in 90% of specified amount of water to the design area
the time available, but not to exceed 22 hours
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within the net operation period. germination. Special provisions should be
made for germination (i.e. portable sprinklers),
Gross application volume per plant shall be
or the microirrigation system should apply
determined using field application efficiency
water at a rate sufficient to adequately wet the
consistent with the type of microirrigation
soil to germinate seeds or establish
system planned. If a need is indicated by
transplants. The depth of subsurface systems
water test results, applications shall include
on annual crops should be limited by the ability
adequate water for leaching to maintain a
of the system to germinate seeds, unless other
steady state salt balance.
provisions are made for this function.
Microirrigation systems installed solely to
Potential rodent damage should be considered
deliver supplemental water for establishment
when selecting materials and deciding on
of windbreaks or riparian vegetation shall be
above or below ground system installation.
designed to deliver a minimum of eight gallons
per tree or shrub per week to assist in the Chemigation may or may not be required at
establishment process. Design net application the same time the plant requires irrigation,
volumes per plant are dependent on the which may affect the economics of
species of tree or shrub and the age (first, chemigation. Weather conditions should be
second, or third year). considered before applying chemicals. Pest or
nutrient management planning should address
Drip lateral lines installed on the ground
the timing and rate of chemical applications.
surface shall be placed along the plant row(s)
in a serpentine pattern to allow for expansion Field shape and slope often dictate the most
and contraction of the line while keeping the economical lateral direction. Laying laterals
emitter close to the tree or shrub. Above down slope can allow for longer lateral run
ground drip line shall be pinned or anchored to lengths and/or lateral size reduction. Uneven
prevent the line from being dislodged or moved topography may require use of pressure
away from the trees or shrubs. compensating emitters.
Windbreaks shall be planned, designed, and For terrain slopes steeper than 5%, lateral
installed according to the requirements of lines should be laid along the field contour and
NRCS Conservation Practice Standard, pressure-compensating emitters specified or
Windbreak-Shelterbelt Establishment (380). pressure control devices used along
downslope submains at lateral inlets.
When lateral emitter spacing or capacities vary
with each row, the laterals must be designed Economic assessments of alternative designs
separately. should include equipment and installation as
well as operating costs.
Operation and maintenance items specific to
vegetation establishment are included in NEH, Longer, less frequent irrigations of windbreaks
Part 652, National Irrigation Guide, Chapter 6. during establishment are recommended to
encourage deeper root development that
Additional Criteria Applicable to Reduce
increases drought tolerance.
Media filters should be followed by secondary
Provide analysis to demonstrate reduction of
screen filters or a rinse cycle valve to prevent
energy use from practice implementation.
carryover of contaminants following the
Reduction of energy use is calculated as backwashing process.
average annual or seasonal energy reduction
Chemicals should not be applied if rainfall is
compared to previous operating conditions.
CONSIDERATIONS Installation and operation of microirrigation
systems have the potential to save energy as a
In the absence of local experience field
result of reduced seasonal irrigation
application efficiency (E) of 90% should used
application, and in some situations reduced
to estimate system capacity.
In arid climates with subsurface systems
natural precipitation and/or stored soil water is
sometimes inadequate to provide crop
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PLANS AND SPECIFICATIONS Check applicator discharge often; replace
applicators as necessary.
Plans and specifications for the microirrigation
system shall be in keeping with this standard Check operating pressures often; a
and shall describe the requirements for pressure drop (or rise) may indicate
properly installing the practice to achieve its problems.
Check pressure gauges to ensure proper
OPERATION AND MAINTENANCE operation; repair/replace damaged
A site specific operation and maintenance
(O&M) plan shall be developed and reviewed Inject chemicals as required to prevent
with the landowner/operator. The O&M plan precipitate buildup and algae growth.
shall provide specific instructions for operating Check chemical injection equipment
and maintaining the system to ensure that it regularly to ensure it is operating properly.
functions properly, including reference to
periodic inspections and the prompt repair or Check and assure proper operation of
replacement of damaged components. backflow protection devices.
Operation and Maintenance Plan should
include but is not limited to: REFERENCES
Install flow meter and monitor water USDA-NRCS, National Engineering
application. Handbook, Part 623, Chapter 7, Trickle
Clean or backflush filters when needed.
USDA-NRCS, National Engineering
Flush lateral lines at least annually. Handbook, Part 652, National Irrigation Guide.