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                          NATURAL RESOURCES CONSERVATION SERVICE
                                  CONSERVATION PRACTICE STANDARD

                         IRRIGATION SYSTEM, MICROIRRIGATION
                                                            (Ac.)

                                                         CODE 441

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
                                                                    point.
PURPOSE
                                                                    CRITERIA
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
emitters.
                                                    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
                                                    laterals.
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
                                                    control valves.

NRCS, NHCP
May 2011
                                                                                               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
                                                    Water
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,
                                                    system.
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
                                                    chemical injection.
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
                                                    label.
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

                                                                                    NRCS, NHCP
                                                                                         May 2011
441 - 4


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.
Energy Use
                                                    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.
                                                    imminent.
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.
                                                    operating pressures.
In arid climates with subsurface systems
natural precipitation and/or stored soil water is
sometimes inadequate to provide crop

NRCS, NHCP
May 2011
                                                                                               441 - 5


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.
intended purpose.
                                                       Check pressure gauges to ensure proper
OPERATION AND MAINTENANCE                               operation; repair/replace damaged
                                                        gauges.
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
                                                    Irrigation.
   Clean or backflush filters when needed.
                                                    USDA-NRCS, National Engineering
   Flush lateral lines at least annually.          Handbook, Part 652, National Irrigation Guide.




                                                                                    NRCS, NHCP
                                                                                         May 2011

				
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