Microirrigation David Midmore Central Queensland University, Australia Presented at the drip irrigation workshop held in Bogor Agricultural University, Bogor, Indonesia, May 2007

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 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 is applied as drops, tiny streams, or spray, through emitters, sprayers, or porous tubing

Water Application Characteristics Low rates Low rates Over long periods of time Over long periods of time At frequent intervals At frequent intervals Near or directly into the root zone Near or directly into the root zone At low pressure At low pressure Usually maintain relatively high soil water content Usually maintain relatively high soil water content Used on higher value agricultural/horticultural crops and in landscapes and nurseries Used on higher value agricultural/horticultural crops and in landscapes and nurseries

Schematic of a Typical Microirrigation System

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

Water losses with other irrigation methods

Disadvantages High initial cost High initial cost Maintenance requirements (e.g., emitter clogging, filter cleaning) Maintenance requirements (e.g., emitter clogging, filter cleaning) Restricted plant root development Restricted plant root development Salt accumulation near plants (along the edges of the wetted zone) Salt accumulation near plants (along the edges of the wetted zone)

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

Types of Systems Surface trickle (drip) – Water applied through small emitter openings to the soil surface (normally less than 9 L/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 Types of Systems Contd… Spray Spray – Water applied (spray, jet, fog, mist) to the soil surface at low pressure (normally less than about 3 l/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 Bubbler – Water applied as a small stream to flood the soil surface in localized areas (normally less than about 3 l/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 Types of Systems Contd… Subsurface trickle Subsurface trickle – Water applied through small emitter openings below the soil surface – Basically a surface system that's been buried (few cm to 30/40 cm) – Permanent installation that is "out of the way"

75 cm 1.5 m Typical Subsurface Drip Tubing Installation for Row Crops cm Non Wheel- Track Row Wetting Pattern Drip Tubing 1.5 m dripline spacing is satisfactory on silt loam & clay loam soils

System Components Pump, or pressure head Control head 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) Mainlines and Submains (manifolds) – Often buried and nearly always plastic (PVC) Laterals Laterals – Plastic (PE) – Supply water to emitters (sometimes "emitters" are part of the lateral itself)

Characteristics of Various Types of Emitters

Emitter Hydraulics Emitter Type Coefficient, K - Exponent, X Coefficient, K - Exponent, X Emitter Discharge, gallons per minute Operating Pressure 8 psi 12 psi 16 psi Porous Pipe Tortuous Path Vortex/Orifice Compensating

Other Design and Management Issues Clogging – Physical (mineral particles) – Chemical (precipitation) – Biological (slimes, algae, etc.) Filtration 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.

Chemical treatment Chemical treatment – Acid: prevent calcium precipitation – Chlorine control biological activity: algae and bacterial slime control biological activity: algae and bacterial slime deliberately precipitate iron deliberately precipitate iron Flushing 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 Application uniformity – manufacturing variation – pressure variations in the mainlines and laterals – pressure-discharge relationships of the applicators

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

Mammal Damage on Subsurface Drip Tubing

Turbulent flow PVC emitter welded inside tubing Netafim Typhoon ® Drip Irrigation Tubing (Clear Demo Tubing) 16-mm diameter, seamless, 13-mil thick extruded PE tubing Emitter outlet

Netafim Typhoon ® Drip Irrigation Tubing Flap over emitter outlet: - prevents root intrusion - prevents blockage by mineral scale

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

Small research plots during supply line installation

Ploughing in drip tubing

SDI Water Application Rates (inches/hour) (60-inch tubing spacing * gallons per hour) 12 inches 18 inches 24 inches 0.16 gph* gph gph gph Emitter Spacing Emitter Discharge

Amore (CLSU, Philippines)

MMSU, Michengel Ganda

A screen filter A 200 mesh screen is used often in trickle irrigation. Water filtered with a 200 mesh screen will contain only particles of very fine sand or particles of even smaller sizes). CREDITS: RETURN

Some advantages of low-head drip Slow release from bigger emitters, less clogging at low pressure Water saving for crops (increase WUE) Round the clock irrigation Labour saving Fewer diseases Low cost Simple to install Easy to adapt to shape of land Profitable after or during first season

Some disadvantages of low-head drip Breakage of filter Less flexibility in terms of emitter spacing and lateral lengths Punctured easily Non-uniformity if land not level or head height varies Spares and service Leakages especially at bucket connector Theft Pests eat tubing

Setting up considerations Slope has more effect on uniformity than head height or lateral length Plant species with differing water reqts along lateral length If holes, then reduce orifice size as go along the lateral, to equalise pressure Higher head if long lateral (>10/15 m)

Some calculations for water reqts Flow rates vs. Pressure:  Pressure Flow rate 10 m x 10 m 30 emitters 0.07 bar 0.26 lph 7.8 l/hr 23.4 l/3h 0.10 bar 0.33 lph 9.9 l/hr 29.7 l/3h 0.20 bar 0.43 lph 12.0 l/hr 38.7 l/3h At 10 m x 10 m for 5 mm/d (0.5 cm) need 500 l/d. Reduce area to 7 m x 10 m need 350 l/d

Some calculations for water storage If with 10 m x 10 m plot, need to store 30 m 3 if 3.3 mm/d average ET for three months If with 10 m x 10 m plot, need to store 50 m 3 if 5.5 mm/d average ET for three months Important consideration if no running water supply

Conclusions Low cost drip with considerable advantages Shown to work, and mimic costly systems How to satisfy demand by crops for water Need to harvest/conserve rainy season water Economics of water harvesting Attempt to integrate drip into agroforestry, cover crop systems to maximise advantages of each ‘technology’