Natural Resources Conservation Service s26

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NATURAL RESOURCES CONSERVATION SERVICE CONSERVATION PRACTICE STANDARD

IRRIGATION SYSTEM, MICROIRRIGATION (No. and Ac.)

CODE 441

DEFINITION snow fences, riparian forest buffers, and wildlife plantings. An irrigation system for frequent application of This practice standard applies to systems with small quantities of water on or below the soil design discharge less than 60 gal/hr at each surface: as drops, tiny streams or miniature individual lateral discharge point. spray through emitters or applicators placed along a water delivery line. Conservation Practice Standard 442, Irrigation System, Sprinkler applies to systems with PURPOSE design discharge of 60 gal/hr or greater at each individual lateral discharge point. This practice may be applied as part of a conservation management system to support CRITERIA one or more of the following purposes. General Criteria Applicable to All  To efficiently and uniformly apply irrigation Purposes water and maintain soil moisture for plant growth. The system shall be designed to uniformly apply water and/or chemicals while  To prevent contamination of ground and maintaining soil moisture within a range for surface water by efficiently and uniformly good plant growth without excessive water applying chemicals. loss, erosion, reduction in water quality, or salt accumulation.  To establish desired vegetation Microirrigation systems consist of point-source emitter (drip, trickle, and bubbler), surface or CONDITIONS WHERE PRACTICE subsurface line-source emitter, basin bubbler, APPLIES and spray or mini sprinkler systems. The system shall include all irrigation On sites where soils and topography are appurtenances necessary for proper operation. suitable for irrigation of proposed crops and an Appurtenances shall be sized and positioned adequate supply of suitable quality water is in accordance with sound engineering available for the intended purpose(s). principles and site-specific features. Microirrigation is suited to vineyards, orchards, Appurtenances include but are not limited to field crops, windbreaks, gardens, greenhouse totalizing flow measurement devices, water crops, and residential and commercial filtration, air vent valves, vacuum relief valves, landscape systems. Microirrigation is also pressure relief valve(s), water control valve(s), suited to steep slopes where other methods pressure gauges, pressure regulators, and would cause excessive erosion, and areas pressure reducers. where other application devices interfere with cultural operations. Water Quality. The irrigation water supply shall be tested and assessed for physical, Microirrigation is suited for use in providing chemical and biological constituents to irrigation water in limited amounts to establish determine suitability and treatment desired vegetation such as windbreaks, living requirements for use in a microirrigation

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 electronic Field Office Technical Guide. August 2006 441 - 2 system. operation, unless special consideration is Emitter discharge rate. The design given to flow conditions and measures taken to discharge rate of applicators shall be adequately protect the pipe network against determined based on manufacturer’s data for surge. expected operating conditions. The discharge rate shall not create runoff within the Main and submain lines shall be designed and immediate application area. installed according to criteria in reference 3.

For bubbler irrigation, a basin beneath the Emission Uniformity. Pipe sizes for mains, plant canopy shall be required for water submains, and laterals shall maintain subunit control, and applications shall be confined to (zone) emission uniformity (EU) within the basin area. recommended limits as determined by Number and spacing of emitters. The procedures contained in Reference 4. number and spacing of emitters along a lateral Filters. A filtration system (filter element, line shall be adequate to provide water screen, strainer, or filtration) shall be provided distribution to the plant root zone and percent at the system inlet. Under clean conditions, plant wetted area (P ). Procedures found in w filters shall be designed for maximum head Reference 4 shall be used to calculate Pw. loss of 5 psi. Maximum design head loss Operating pressure. The design operating across a filter before cleaning shall be based pressure shall be in accordance with published on manufacturer recommendations. In the manufacturer recommendations. The system absence of manufacturer data maximum operating pressure must compensate for permissible design head loss across a filter is pressure losses through system components 7 psi before filter cleaning is required. and field elevation effects. The filter shall be sized to prevent the passage Emitter manufacturing variability. The of solids in sizes or quantities that might manufacturer’s coefficient of variation (Cv) obstruct the emitter openings. Filtration shall be obtained and used to assess the systems shall be designed to remove solids acceptability of a particular product for a given based on emitter manufacturer application. recommendations. In the absence of manufacturer data or recommendations, The C shall be less than 0.07 for point source V filtration systems shall be designed to remove emitters and less than 0.20 for line source solids equal to or larger than one-tenth the emitters. emitter opening diameter. Allowable pressure variations. The filter system shall provide sufficient Manifold and lateral lines. Manifold and lateral filtering capacity so that backwash time does lines, operating at the design pressure, shall not exceed 10% of the system operation time. be designed to provide discharge to any Within this 10% time period, the pressure loss applicator in an irrigation subunit or zone across the filter shall remain within the operated simultaneously such that they will not manufacturer's specification and not cause exceed a total variation of 20 percent of the unacceptable EU. design discharge rate. Internal pressure shall Filter/strainer systems designed for continuous not exceed manufacturer recommendations flushing shall not have backwash rates during any phase of operation. exceeding 1.0% of the system flow rate or Main and submain lines. Main and submain exceeding the manufacturer's specified lines shall be designed to supply water to all operational head loss across the filter. manifold and lateral lines at a flow rate and Air/Vacuum relief valves. Vacuum relief shall pressure not less than the minimum design be designed and installed to prevent ingestion requirements of each subunit. Adequate of soil particles if there are summits in system pressure shall be provided to overcome all laterals. friction losses in the pipelines and appurtenances (valves, filters, etc.). Mains Air/vacuum relief valves shall be installed on and submains shall maintain flow velocities both sides of all block or manifold water supply less than 5 ft/sec during all phases of control valves.

NRCS, NHCP, December 1998

Pressure regulators. Pressure regulators leaching, germination, and initial development. shall be used where topography and the type Maximum lateral line distance from the crop of applicator dictate their use. Pressure row shall be 24 inches for annual row crops regulators shall not be planned to compensate and 48 inches for vineyard and orchard crops. for improperly designed pipelines. EU shall be designed for a minimum of 85 percent. System flushing. Appropriate fittings shall be installed above ground at the ends of all Criteria Applicable to Preventing mains, submains, and laterals to facilitate Contamination of Ground and flushing. The system shall be designed and Surface Water installed to provide a minimum flow velocity of 1 ft/sec during flushing. During flushing Chemigation and Chemical Water submain and manifold (pipelines located Treatment. System EU shall not be less than downstream from a control valve) velocities 85 percent where fertilizer or pesticides, or shall not exceed 7 ft/sec velocity. Each treatment chemicals are applied through the flushing discharge outlet shall include a system. pressure gauge and/or Schrader valve tap. Backflow prevention devices shall be provided Criteria Applicable to Efficiently and on all microirrigation systems equipped for Uniformly Apply Irrigation Water chemical injection.

Depth of application. Net depth of application Injectors (chemical, fertilizer or pesticides) and shall be sufficient to replace the water used by other automatic operating equipment shall be the plant during the plant peak use period or located and installed in accordance with critical growth stage. Gross depth of manufacturer’s recommendations and include application shall be determined by using field integrated back flow prevention protection. 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 System capacity. The system shall have maximum rate recommended by chemical either (1) a design capacity adequate to meet label. 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 design capacity less than peak daily irrigation plan for addressing or avoiding chemical water requirement shall be fully explained and reactions with injected chemicals to prevent agreed upon by the end user. Design capacity precipitate or biological plugging. shall include an allowance for reasonable Criteria Applicable to Establishing water losses (evaporation, runoff, and deep Desired Vegetation percolation) during application periods. The system shall have the capacity to apply a System capacity. The system shall have specified amount of water to the design area design capacity adequate to provide within the net operation period. Minimum supplemental water at a rate that will insure system design capacity shall be sufficient to survival and establishment of planned deliver the specified amount of water in 90% of vegetation for a period of at least 3 years. The the time available, but not to exceed 22 hours system shall have the capacity to apply the of operation per day. specified amount of water to the design area within the net operation period. Subsurface Drip Irrigation (SDI). Tubing depth and spacing are soil and crop Gross application volume per plant shall be dependent. Emitter line depth shall consider determined using field application efficiency the auxiliary irrigation methods used for consistent with the type of microirrigation system planned. If a need is indicated by

NRCS, NHCP, December 1998 441 - 4 water test results, applications shall include the same time the plant requires irrigation, adequate water for leaching to maintain a which may affect the economics of steady state salt balance. chemigation. Weather conditions should be considered before applying chemicals. Pest or Microirrigation systems installed solely to nutrient management planning should address deliver supplemental water for establishment the timing and rate of chemical applications. of windbreaks or riparian vegetation shall be designed to deliver a minimum of eight gallons Field shape and slope often dictate the most per tree or shrub per week to assist in the economical lateral direction. Laying laterals establishment process. Design net application down slope can allow for longer lateral run volumes per plant are dependent on the lengths and/or lateral size reduction. Uneven species of tree or shrub and the age (first, topography may require use of pressure second, or third year). compensating emitters. Drip lateral lines installed on the ground For terrain slopes steeper than 5%, lateral surface shall be placed along the plant row(s) lines should be laid along the field contour and in a serpentine pattern to allow for expansion pressure-compensating emitters specified or and contraction of the line while keeping the pressure control devices used along emitter close to the tree or shrub. Above downslope submains at lateral inlets. ground drip line shall be pinned or anchored to Economic assessments of alternative designs prevent the line from being dislodged or moved should include equipment and installation as away from the trees or shrubs. well as operating costs. Windbreaks shall be planned, designed, and Longer, less frequent irrigations of windbreaks installed according to NRCS, Conservation during establishment are recommended to Practice Standard, Windbreak-Shelterbelt encourage deeper root development that Establishment, Code 380. increases drought tolerance. When lateral emitter spacing or capacities vary Chemicals should not be applied if rainfall is with each row, the laterals must be designed imminent. separately. Installation and operation of microirrigation Operation and maintenance items specific to systems have the potential to save energy as a vegetation establishment are included in result of reduced seasonal irrigation Chapter 6 of reference. application, and in some situations reduced operating pressures. CONSIDERATIONS PLANS AND SPECIFICATIONS In the absence of local experience field application efficiency (E) of 90% should used Plans and specifications for the microirrigation to estimate system capacity. system shall be in keeping with this standard In arid climates with subsurface systems and shall describe the requirements for natural precipitation and/or stored soil water is properly installing the practice to achieve its sometimes inadequate to provide crop intended purpose. germination. Special provisions should be made for germination (i.e. portable sprinklers), OPERATION AND MAINTENANCE or the microirrigation system should apply water at a rate sufficient to adequately wet the A site specific operation and maintenance soil to germinate seeds or establish (O&M) plan shall be developed and reviewed transplants. The depth of subsurface systems with the landowner/operator. The O&M plan on annual crops should be limited by the ability shall provide specific instructions for operating of the system to germinate seeds, unless other and maintaining the system to ensure that it provisions are made for this function. functions properly, including reference to Potential rodent damage should be considered periodic inspections and the prompt repair or when selecting materials and deciding on replacement of damaged components. above or below ground system installation. Operation and Maintenance Plan should include but is not limited to: Chemigation may or may not be required at

 Install flow meter and monitor water  Check and assure proper operation of application. backflow protection devices.  Clean or backflush filters when needed. REFERENCES  Flush lateral lines at least annually. 1. Design and Installation of Microirrigation  Check applicator discharge often; replace Systems, American Society of applicators as necessary. Agricultural Engineers (ASAE), ASAE EP405.1, February 2003.  Check operating pressures often; a pressure drop (or rise) may indicate 2. National Engineering Handbook, Part problems. 652, Irrigation Guide, 1996.

 Check pressure gauges to ensure proper 3. NRCS, Conservation Practice Standard operation; repair/replace damaged Irrigation Water Conveyance, Pipeline, gauges. High Pressure Plastic, Code 430DD, 1988.  Inject chemicals as required to prevent precipitate buildup and algae growth. 4. National Engineering Handbook, Part 623, Chapter 7, Trickle Irrigation, 1984.  Check chemical injection equipment regularly to ensure it is operating properly. 5. National Engineering Handbook, Part 623, Chapter 2, Irrigation Water Requirements, 1993