Transcript Micro irrigation - Oklahoma State University–Stillwater

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
• Water is applied as drops, tiny streams, or
spray, through emitters, sprayers, or porous
tubing
Water Application Characteristics
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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
Advantages
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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
• 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
Salt accumulation leached
radially outward from drip
tubing
Sprinkler/Flood
Salt accumulation leached
downward by successive water
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
distribution
– 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
diameter)
– Minimal filtration and maintenance
requirements
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 WheelTrack 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
x
q  KH
e
– 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
Coefficient, K - Exponent, X
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
Estimating Emitter Exponent & Coefficient
Requires discharges qe1, qe2 at two pressures h1, h2
• Emitter Exponent
log( qe1 / qe 2)
x
log( h1 / h 2)
• Emitter Coefficient
q1
K x
h1
or
q2
K x
h2
Applicator Hydraulics Contd…
• Emitters (Point Source)
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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 preinserted 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
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
Plugging Potential of Irrigation Water for
Microirrigation
• 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
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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
• 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
160 acres
125 acres
$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
36 hp-hr/ac-in
48 hp-hr/ac-in
Area Irrigated
Initial Cost
Energy Requirement
(250-ft lift, ¼ mile supply line)
Gopher Damage on Subsurface Drip Tubing
Schematic of Subsurface Drip Irrigation (SDI) System
Filtration
System
Chemical
Injection
System
Flowmeter Backflow
Prevention Pump
Station
Device
Submain
X
X
Dripline
Laterals
X
X
X
Air & Vacuum
Release Valve
Zones
1 and 2
Pressure Gage
X
x
Flush Valve
X
Zone Valve
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 WheelTrack 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
(sediment)
• Chlorine injection schedule
(biological growths)
• Acid injection schedule
(chemical precipitates & scaling)
Salt Movement Under Irrigation with Saline Water
Subsurface Drip
Salt accumulation leached
radially outward from drip
tubing
Sprinkler/Flood
Salt accumulation leached
downward by successive water
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
Stainless Steel Wire Twist Tie
21/32” Hole in Submain
Neoprene Grommet
Polyethylene
Barb Adapter
5/8” Polyethylene
Supply Tube
(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
Neoprene Grommet Inserted
in 21/32” hole in manifold
5/8” Polyethylene
Supply Tubing
Stainless Steel
Wire Twist Tie
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
(inches/hour)
(60-inch tubing spacing)
Emitter 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 Discharge