Microirrigation

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Microirrigation
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Microirrigation

• 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
  tubing

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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

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Schematic of a Typical Microirrigation System
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Advantages

• High application efficiency
• High yield/quality
• Decreased energy requirements
• Reduced salinity hazard
• Adaptable for chemigation
• Reduced weed growth and disease problems
• Can be highly automated

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Disadvantages

• High initial cost
• Maintenance requirements (emitter clogging, etc.)
• Restricted plant root development
• Salt accumulation near plants (along the edges of
  the wetted zone) 

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Salt Movement Under Irrigation with Saline Water
Subsurface Drip
Sprinkler/Flood
Salt accumulation leached downward by successive
water applications
Salt accumulation leached radially outward from
drip tubing
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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

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Point Source Emitters in a New Orchard
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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
  distribution
• Reduced filtration and maintenance requirements
  because of higher flow rate

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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
  diameter)
• Minimal filtration and maintenance requirements

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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 way"

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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
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System Components

•  Pump
•  Control head
• Filters
• Chemical injection equipment (tanks, injectors,
  backflow prevention, etc.)
• Flow measurement devices
• Valves
• Controllers
• Pressure regulators

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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)

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Applicator Hydraulics

• General
• Need pressure in pipelines to distribute water
  through the system, but the applicator needs to
  dissipate that pressure
• qe emitter discharge
• K emitter discharge coefficient
• H pressure head at the emitter
• X emitter discharge exponent (varies with
  emitter type)

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Characteristics of Various Types of Emitters
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Emitter Hydraulics
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Estimating Emitter Exponent Coefficient

• Requires discharges qe1, qe2 at two pressures h1,
  h2
• Emitter Exponent
• Emitter Coefficient
• or

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Applicator Hydraulics Contd

• Emitters (Point Source)
• Long-path
• Orifice
• Vortex
• Pressure compensating (x lt 0.5)
• Flushing
• Line-source tubing
• Porous-wall tubing (pores of capillary size that
  ooze water)
• Single-chamber tubing (orifices in the tubing or
  pre-inserted emitters)
• Double-chamber tubing (main and auxiliary
  passages)

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• 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

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Other Design and Management Issues

•  Clogging
• Physical (mineral particles)
• Chemical (precipitation)
• Biological (slimes, algae, etc.)
• Filtration
• Settling basins
• Sand separators (centrifugal or cyclone
  separators)
• Media (sand) filters
• Screen filters

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There are many different types of filtration
systems.
The type is dictated by the water source and also
by emitter size.
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Filtration Requirements for Drip Emitters
Filter openings should be 1/7th 1/10th the size
of the emitter orifice
0.020-inch orifice
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Plugging Potential of Irrigation Water for
Microirrigation
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• 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 maintenance
• 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

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Subsurface Drip Irrigation Advantages

• 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

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Subsurface Drip Irrigation Disadvantages

• High initial cost
• Water filtration required
• Complex maintenance requirements
• Flushing, Chlorination, Acid injection
• Susceptible to gopher damage
• Salt leaching limitations

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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 (250-ft lift, ¼ mile supply line) 36 hp-hr/ac-in 48 hp-hr/ac-in
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Gopher Damage on Subsurface Drip Tubing
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Diagram courtesy of Kansas State University
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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
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Netafim Typhoon Drip Irrigation Tubing
Flap over emitter outlet - prevents root
intrusion - prevents blockage by mineral scale
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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
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Wetting Pattern of a Subsurface Drip Lateral
Photo Courtesy of Kansas State University
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Wider dripline spacings may not work.
Photo Courtesy of Kansas State University
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SDI System Maintenance

• Lateral flushing schedule (sediment)
• Chlorine injection schedule (biological
  growths)
• Acid injection schedule (chemical precipitates
  scaling)

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Salt Movement Under Irrigation with Saline Water
Subsurface Drip
Sprinkler/Flood
Salt accumulation leached downward by successive
water applications
Salt accumulation leached radially outward from
drip tubing
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Small research plots during supply line
installation
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Plowing in drip tubing
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Trenching across the drip tubing ends for PVC
manifold installation
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Drip tubing end after being sheared by the
trencher
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Components for Drip Lateral-Submain Connection
Stainless Steel Wire Twist Tie
21/32 Hole in Submain
Neoprene Grommet
5/8 Polyethylene Supply Tube (Usually 2-3 ft
long)
Polyethylene Barb Adapter
5/8 Drip Irrigation Tubing
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Typical Drip Tubing Connection to Submain (1 ½
-inch Submains and Larger)
Supply Submain or Flushing Manifold
Stainless Steel Wire Twist Tie
Neoprene Grommet Inserted 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
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Flush Risers on Distal End of Research Plots
Air Vent to Release Trapped Air from Laterals
Ball Valve for Manual Flushing of Drip Laterals
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SDI Water Application Rates(inches/hour)(60-inch
tubing spacing)
12 inches 18 inches 24 inches
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
Emitter Spacing
Emitter Discharge