Micro irrigation

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• Delivery of water at low flow rates through
  various types of water applicators by a
  distribution system located on the soil
  surface, beneath the surface, or suspended
  above the ground
• Water is applied as drops, tiny streams, or
  spray, through emitters, sprayers, or porous
Water Application Characteristics
  •   Low rates
  •   Over long periods of time
  •   At frequent intervals
  •   Near or directly into the root zone
  •   At low pressure
  •   Usually maintain relatively high water content
  •   Used on higher value agricultural/horticultural
      crops and in landscapes and nurseries
Schematic of a Typical Microirrigation System
• High application efficiency
• High yield/quality
• Decreased energy requirements
• Reduced salinity hazard
• Adaptable for chemigation
• Reduced weed growth and disease
• Can be highly automated
• High initial cost
• Maintenance requirements (emitter
  clogging, etc.)
• Restricted plant root development
• Salt accumulation near plants (along the
  edges of the wetted zone)
Salt Movement Under Irrigation with Saline Water
      Subsurface Drip               Sprinkler/Flood

                             Salt accumulation leached
Salt accumulation leached    downward by successive water
radially outward from drip   applications
        Types of Systems
• Surface trickle (drip)
  – Water applied through small emitter
    openings to the soil surface (normally less
    than 3 gal/hr per emitter)
  – Most prevalent type of microirrigation
  – Can inspect, check wetting patterns, and
    measure emitter discharges
Point Source Emitters in a New Orchard
  Types of Systems Contd…
• Spray
  – Water applied (spray, jet, fog, mist) to the soil
    surface at low pressure (normally less than
    about 1 gal/min per spray applicator)
  – Aerial distribution of water as opposed to soil
  – Reduced filtration and maintenance
    requirements because of higher flow rate
  Types of Systems Contd…
• Bubbler
  – Water applied as a small stream to flood the
    soil surface in localized areas (normally less
    than about 1 gal/min per discharge point)
  – Application rate usually greater than the soil's
    infiltration rate (because of small wetted
  – Minimal filtration and maintenance
 Types of Systems Contd…
• Subsurface trickle
  – Water applied through small emitter
    openings below the soil surface
  – Basically a surface system that's been
    buried (few inches to a couple feet)
  – Permanent installation that is "out of the
 Typical Subsurface Drip Tubing Installation for Row Crops

                                                    30 in
        Non Wheel-
        Track Row

                             12 – 14 in

                            Drip Tubing

                          Wetting Pattern
                                60 in

60-inch dripline spacing is satisfactory on silt loam & clay loam soils
       System Components
• Pump
• Control head
  – Filters
  – Chemical injection equipment (tanks, injectors,
    backflow prevention, etc.)
  – Flow measurement devices
  – Valves
  – Controllers
  – Pressure regulators
System Components, Contd…
• Mainlines and Submains (manifolds)
  – Often buried and nearly always plastic (PVC)
• Laterals
  – Plastic (PE)
  – Supply water to emitters (sometimes
    "emitters" are part of the lateral itself)
    Applicator Hydraulics
• General
  – Need pressure in pipelines to distribute
    water through the system, but the
    applicator needs to dissipate that pressure
  q  KH x
  – qe = emitter discharge
  – K = emitter discharge coefficient
  – H = pressure head at the emitter
  – X = emitter discharge exponent
                 (varies with emitter type)
Characteristics of Various Types of Emitters
           Emitter Hydraulics
                                            Emitter Discharge, gpm

                                                Operating Pressure
Emitter Type

                                        8 psi          12 psi        16 psi
         Coefficient, K - Exponent, X

Porous Pipe -    0.112          1.00    2.07            3.1          4.14

Tortuous Path     0.112         0.65    0.75            0.97         1.17

Vortex/Orifice   0.112          0.42    0.38            0.45         0.51

Compensating     0.112          0.20    0.20            0.22         0.23
Estimating Emitter Exponent & Coefficient
  Requires discharges qe1, qe2 at two pressures h1, h2
  • Emitter Exponent

          log( qe1 / qe 2)
           log( h1 / h 2)
  • Emitter Coefficient
        q1                  q2
      K x         or     K x
        h1                  h2
Applicator Hydraulics Contd…
• Emitters (Point Source)
  –   Long-path
  –   Orifice
  –   Vortex
  –   Pressure compensating (x < 0.5)
  –   Flushing
• Line-source tubing
  – Porous-wall tubing (pores of capillary size that ooze
  – Single-chamber tubing (orifices in the tubing or pre-
    inserted emitters)
  – Double-chamber tubing (main and auxiliary passages)
  – Sprayers
     • Foggers, spitters, misters, etc
     • Relatively uniform application over the wetted area
• Lateral hydraulics
  – Very much like sprinkler hydraulics, but on a
    smaller scale
  – Since there is usually a large number of emitters,
    multiple outlet factor (F)  0.35
Other Design and Management Issues
 • Clogging
   – Physical (mineral particles)
   – Chemical (precipitation)
   – Biological (slimes, algae, etc.)
 • Filtration
   – Settling basins
   – Sand separators (centrifugal or cyclone
   – Media (sand) filters
   – Screen filters
There are many different types
of filtration systems.

The type is dictated by
the water source and
also by emitter size.
Filtration Requirements for Drip Emitters

            Filter openings should be
            1/7th – 1/10th the size of
            the emitter orifice

                                         0.020-inch orifice
Plugging Potential of Irrigation Water for
• Chemical treatment
  – Acid: prevent calcium precipitation
  – Chlorine
     • control biological activity: algae and bacterial slime
     • deliberately precipitate iron
• Flushing
  – after installation or repairs, and as part of routine
  – valves or other openings at the end of all pipes,
    including laterals
• Application uniformity
  – manufacturing variation
  – pressure variations in the mainlines and laterals
  – pressure-discharge relationships of the applicators
     Subsurface Drip Irrigation
•   High water application efficiency
•   Uniform water application
•   Lower pressure & power requirements
•   Adaptable to any field shape
•   No dry corners (vs. center pivot)
•   Adaptable to automation
   Subsurface Drip Irrigation
• High initial cost
• Water filtration required
• Complex maintenance requirements
  – Flushing, Chlorination, Acid injection
• Susceptible to gopher damage
• Salt leaching limitations
 Subsurface Drip-Center Pivot Comparison
             (¼-Section Field; ET = 0.25 in/day)

                                    Subsurface Drip     Center Pivot
Area Irrigated                         160 acres          125 acres
Initial Cost                        $800-1000/acre      $280-360/acre
Irrigation Efficiency                   90-95%             70-85%
Water Requirement                   5.0-5.3 gpm/acre   5.5-6.8 gpm/acre
Operating Pressure                     10-20 psi          25-35 psi
Energy Requirement                   36 hp-hr/ac-in     48 hp-hr/ac-in
(250-ft lift, ¼ mile supply line)
Gopher Damage on Subsurface Drip Tubing
Schematic of Subsurface Drip Irrigation (SDI) System

            System                          Flowmeter Backflow
                                                      Prevention Pump
                                                        Device   Station

                        X   X                     X
                                                               Air & Vacuum
                                                               Release Valve
Dripline            Zones
                                                               Pressure Gage
Laterals           1 and 2
                                                               Flush Valve

 X                                                X        X   Zone Valve
                                    Diagram courtesy of Kansas State University
 Netafim Typhoon® Drip Irrigation Tubing
                  (Clear Demo Tubing)
  16-mm diameter, seamless, 13-mil thick extruded PE tubing

                                            Emitter outlet

Turbulent flow PVC emitter welded inside tubing
Netafim Typhoon® Drip Irrigation Tubing

           Flap over emitter outlet:
                  - prevents root intrusion
                  - prevents blockage by mineral scale
  Typical Drip Tubing Installation for Row Crops

                                                    30 in
        Non Wheel-
        Track Row

                             12 – 14 in

                            Drip Tubing

                          Wetting Pattern
                                60 in

60-inch dripline spacing is satisfactory on silt loam & clay loam soils
Wetting Pattern of a Subsurface Drip Lateral

Photo Courtesy of Kansas State University
Wider dripline spacings may not work.

                   Photo Courtesy of Kansas State University
    SDI System Maintenance
• Lateral flushing schedule
• Chlorine injection schedule
     (biological growths)
• Acid injection schedule
     (chemical precipitates & scaling)
Salt Movement Under Irrigation with Saline Water
     Subsurface Drip                Sprinkler/Flood

Salt accumulation leached    Salt accumulation leached
radially outward from drip   downward by successive water
tubing                       applications
Small research plots during supply line installation
Plowing in drip tubing
Trenching across the drip tubing ends for PVC manifold installation
Drip tubing end after being sheared by the trencher
Components for Drip Lateral-Submain Connection
 21/32” Hole in Submain        Stainless Steel Wire Twist Tie

            Neoprene Grommet

                          5/8” Polyethylene
        Polyethylene      Supply Tube
        Barb Adapter      (Usually 2-3 ft long)

                                  5/8” Drip Irrigation Tubing
Typical Drip Tubing Connection to Submain
              (1 ½ -inch Submains and Larger)
     Supply Submain or Flushing Manifold
                                                Stainless Steel
            Neoprene Grommet Inserted           Wire Twist Tie
            in 21/32” hole in manifold

                5/8” Polyethylene
                Supply Tubing               5/8” Drip
                                            Irrigation Tubing
    Polyethylene Barb Adapter
    Inserted in Grommet

Identical connection on distal end for flushing manifold connection
Flush Risers on Distal End of Research Plots
                             Air Vent to Release Trapped
                             Air from Laterals

 Ball Valve for Manual
 Flushing of Drip Laterals
        SDI Water Application Rates
                        (60-inch tubing spacing)

      Emitter Spacing
                        12 inches      18 inches   24 inches
Emitter Discharge

   0.16 gph               0.043          0.034      0.026

   0.21 gph               0.056          0.045      0.034

   0.33 gph               0.088          0.071      0.053

   0.53 gph               0.142           0.113     0.085

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