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Microirrigation. 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

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Microirrigation1
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


Water application characteristics
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



Advantages
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


Disadvantages
Disadvantages

  • 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 downward by successive water applications

Salt accumulation leached radially outward from drip tubing


Types of systems
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



Types of systems contd
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


Types of systems contd1
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


Types of systems contd2
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"


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
System Components

  • Pump

  •  Control head

    • Filters

    • Chemical injection equipment (tanks, injectors, backflow prevention, etc.)

    • Flow measurement devices

    • Valves

    • Controllers

    • Pressure regulators


System components contd
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
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)



Emitter hydraulics

Emitter Type

Coefficient, K - Exponent, X

Emitter Discharge, gpm

Operating Pressure

8 psi

12 psi

16 psi

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

Emitter Hydraulics


Estimating emitter exponent coefficient
Estimating Emitter Exponent & Coefficient

Requires discharges qe1, qe2 at two pressures h1, h2

  • Emitter Exponent

  • Emitter Coefficient

    or


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 water)

    • 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
    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


    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



    • 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


    Subsurface drip irrigation advantages
    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


    Subsurface drip irrigation disadvantages
    Subsurface Drip Irrigation Disadvantages

    • 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 section field et 0 25 in day
    Subsurface Drip-Center Pivot Comparison(¼-Section Field; ET = 0.25 in/day)



    Schematic of Subsurface Drip Irrigation (SDI) System

    Filtration System

    Backflow

    Prevention

    Device

    Flowmeter

    Pump Station

    Chemical

    Injection

    System

    Submain

    X

    X

    X

    X

    Air & Vacuum

    Release Valve

    Zones

    1 and 2

    Dripline

    Laterals

    Pressure Gage

    Flush Valve

    x

    X

    Zone Valve

    X

    X

    Flushline

    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
    SDI System Maintenance

    • Lateral flushing schedule (sediment)

    • 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 downward by successive water applications

    Salt accumulation leached radially outward from drip tubing






    Components for Drip Lateral-Submain Connection installation

    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


    Typical Drip Tubing Connection to Submain installation

    (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


    Flush Risers on Distal End of Research Plots installation

    Air Vent to Release Trapped Air from Laterals

    Ball Valve for Manual Flushing of Drip Laterals


    Sdi water application rates inches hour 60 inch tubing spacing
    SDI Water Application Rates installation(inches/hour)(60-inch tubing spacing)

    Emitter Spacing

    Emitter Discharge


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