Drip Irrigation for Veggies - Kansas State University Cooperative Extension

8/9/2019 Drip Irrigation for Veggies - Kansas State University Cooperative Extension

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DRIP IRRIGATIONFOR VEGETABLES

Drip (trickle) irrigation was pioneered in the

1940s in England, but not until the advent of poly-ethylene plastics in the 1960s did field applicationof this efficient watering method become wide-spread. Drip irrigation is a method of applyingsmall amounts of water, often on a daily basis, to theplants root zone.

A drip irrigation system has four major compo-nents and two options.

Major Components

Delivery system: emitters or line source driptubing

Filters: sand, disk, or screen

Pressure regulators: spring or valve

Valves: hand-operated, hydraulic, or electrical

Options

Controller: simple electric clock or computer

Fertigation system: electric pumps, hydraulicpumps, venturi systems, etc.

How you put these components together, and

which options you choose, will depend on the sizeof the system, the water source, the crop, and thedegree of sophistication you desire.

ADVANTAGES AND DISADVANTAGES

Although many advantages favor installationof a drip system, there are some limitations as well.

Advantages

1. Smaller water sources can be used, as trickleirrigation may require less than half of the waterneeded for sprinkler irrigation.

2. Lower pressures mean reduced energy forpumping.

3. High levels of water management are achievedbecause plants can be supplied with preciseamounts of water.

4. Diseases may be lessened because foliage re-mains dry.

5. Labor and operating costs are generally less,and extensive automation is possible.

6. Water applications are precisely targeted. Noapplications are made between rows or othernon-productive areas.

7. Field operations can continue during irrigationbecause the areas between rows remain dry,resulting in better weed control and lower pro-duction costs.

8. Fertilizers can be applied efficiently to rootsthrough the drip system.

9. Watering can be done on varied terrains and invaried soil conditions.

10. Soil erosion and nutrient leaching can bereduced.

ByCharles W. MarrDanny Rogers

KANSAS STATE UNIVERSITYAGRICULTURAL EXPERIMENT STATION

AND COOPERATIVE EXTENSION SERVICE

COMMERCIAL VEGETABLE PRODUCTION


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a drip system. Municipal sources generally providedocumentation of water quality tests, making iteasier to spot potential problems. Surface water such

as streams, ponds, pits or rivers will contain bacte-ria, algae or other aquatic life, and sand filters are anabsolute necessity. Sand filters are generally moreexpensive.

MAJOR COMPONENTS OF A DRIP SYSTEM

1. Delivery system

Mainline distribution to field

Sub-mainline (header line)

Feeder tubes

Drip tube

2. Filters

3. Pressure regulators

4. Valves or gauges

Delivery System

Mainline distribution to field: Underground plasticor PVC pipe or above-ground aluminum pipecan be used to deliver water from its source(pump, filtering system, etc.) to sub-mainline

(header line). Sub-mainline (header): It is common to use vinyl

lay flat hose as the sub-mainline (header line).The hose is durable, long-lasting, and lays flatwhen not in use so equipment can be drivenover it. The lay flat hose and feeder tubes areretrieved after each growing season and storeduntil the following year.

Feeder tubes: Water flows to the drip tubingthrough small plastic tubes called feeder tubesconnecting the sub-mainline (header line) andeach drip tube. Feeder tubes can be inserted

directly into the vinyl hose.

Drip tube: The design of most drip tubing con-sists of an inner and outer chamber that allowsfor even water distribution over a wide rangeof conditions. Most tubing is polyethylene blackplastic, 4 to 8 mil thick, with holes at intervalsof 8 to 24 inches. In general, the sandier the soil,the closer the spacing needed. A 12-inch spacing

Disadvantages or problems

1. Initial investment costs may be more on a peracre basis than other irrigation options.

2. Management requirements are high. A criticaldelay in operation decisions may cause irrevers-ible damage to crops.

3. Frost protection that can be achieved by sprin-kler systems is not possible with drip systems.

4. Rodent, insect, or human damage to drip tubesmay cause leaks.

5. Filtration of water for trickle irrigation is neces-sary to prevent clogging of the small openingsin the trickle line.

6. Water distribution in the soil is restricted.

SPECIFIC ADAPTATIONS TO VEGETABLES

Drip irrigation can be used in orchard, nursery,windbreaks, landscape, and other crop applications.This publication will concentrate only on applica-tions for vegetable crops.

Because vegetables are usually planted in rows,a drip tubing with prepunched emitter holes, calleda line source emitter, is used to wet a continuousstrip along the row. Also, because most vegetables

are considered annuals and are grown for only oneseason, a thin-walled disposable tubing (4 or 8 milthick) generally is used for only one season. Lessemphasis is usually placed on buried mainlines andsub-mainlines to allow the system to be dismantledand moved from season to season. Costs may behigh, so a goal should be to develop an inexpensiveyet functional system that allows maximum produc-tion with minimal costs. You may purchase an entiresystem from an irrigation dealer or adapt your owncomponents. Assistance in design from an irrigationdealer or professional can be very helpful in avoid-ing problems later on.

WATER SOURCES

The water supply may come from wells, ponds,lakes, municipal lines, or pits. Well water sourcesgenerally are fairly clean and require only a screenfilter to remove particles. However, precipitates orother contaminants in the water should be deter-mined by a water quality test prior to considering


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Valves or Gauges

Watering several fields or sections of fields fromone water source can be accomplished by a zone

system using valves to open and close various lines.A backflow/anti-siphon valve is a necessity on awell or municipal source where fertilizers or chemi-cals are to be injected into the line. Hand-operatedgate or ball valves or electric solenoid valves canbe used to automate the system using a time clock,water need sensor (discussed later), or automaticcontroller box (computer controller).

Optional Additions

Fertigation or chemigation: Soluble fertilizers canbe added to the drip irrigation water to provideuniform crop fertilization. A simple hozon venturiinjector siphons soluble fertilizer from a bucket orjug into the line at a pre-set ratio (usually 1:16 or1 gallon for every 16 gallons of water flowingthrough the line). The hozon injection system,however, is only suitable for 12 acre plantings or less.Other venturi units are available in sizes upto 2 inches in diameter. More expensive injectorswith greater capacity and accuracy, use electric orhydraulic pumps to inject fertilizer solutions froma stock tank into the line. A hydraulic device, calleda Dosatron, can be set at various dilution rates and

operates with water flowing directly through thedevice which is placed in the mainline. Use onlyhigh quality, soluble fertilizers that completely dis-solve. All fertilizer injections should be made ahead ofthe main filters in the line so that any contaminants are

filtered out.

Fertigation is most commonly used to supplynitrogen since it is highly soluble and moves eas-ily through soils to roots. Phosphate and potashare best applied before planting and not injectedthrough the irrigation system. Other chemigationapplications may include pest control measures,but check label restrictions on use in chemigation applica-tions. If fertilizer or chemicals are applied throughthe system a check valve to ensure no contaminationof the water source is a necessity. For regulations onwater use, well and valve requirements, and waterpermits contact the Division of Water Resources ofthe Kansas Department of Agriculture, Topeka.

is common. The tubing is shipped flattened on aroll and is often called drip tape. Most drip tapesemit water at about 25 gallons per 100 feet per

hour when operated at l0 psi pressure. Standardrolls of tape contain enough tubing tape for1 acre of crop on 5-foot row centers.

Filters

Filters are essential to the operation of a dripsystem and may be viewed as the most importantcomponent of a drip system. For wells or municipalwater a screen filter or disc filter can be used. Screenfilters (150 to 200 mesh screen) are available in sizesfrom 34 inch (used only for 12 acre) to 6-inch (usedwith several acres). Some filters have a valve to open

and flush the filter. Disc filters operate witha series of discs stacked vertically to separate outsmall particles. Although more expensive to pur-chase, they are reliable and easy to clean.

For any open or surface water sources, sandfilters are an absolute necessity. They are installedas pairs of sand-filled canisters and can be back-flushed to accomplish cleaning. Canisters from14 inches (enough for 2 acres) to 48 inches in diam-eter are used, depending on the size of the system.

The need to clean or flush filters can be deter-mined by the loss of pressure through the filter. You

can install pressure gauges on either side of the filterto indicate the need to flush when pressure lossexceeds 5 to 7 psi. With only one pressure gauge be-hind the filter, watch for reduced operating pressurein normal operation. When stream or river water isused, a sand separator is usually neededto remove suspended sand from the water beforeit enters the sand filter.

Pressure Regulators

Most drip tubing is designed to operate at 8 to15 psi pressure, with 10 psi being standard operat-ing pressure. A spring-type (used on smaller sys-tems) or diaphragm-type pressure regulator canbe purchased to hold pressure steady. These areinexpensive and reliable. Both adjustable and pre-settypes are available.


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growth increases. Thus, as the season progresses,more water needs to be applied and, obviously, un-der hot, dry conditions, more water is neededto replace evaporative losses (crop water use).

As an example, the operation time needed fora young crop in cool weather on a typical Kansasvegetable crop may be one to two hours every twoor three days. As the crop grows, two or three hoursper day may be required. In extreme stresses, threeor more hours may be required. The exact water re-quirement, however, will depend on crop, weather,soil and system capacity.

Water lost by evapotranspiration can be estimat-ed by an open pan and is usually quoted by agricul-tural weather reports as pan evaporation.A crop in full vegetative growth usually needs tobe replenished at about 80 percent of the pan evapo-ration level.

Calculations are made using the formula:

Gallons/100 ft/day = 50 80% pan evaporation Row spacing in feet

Example: If .25 inch of water is lost per day frompan evaporation on a crop of melons on 5-foot rowcenters, how much water should be supplied?

MULCHES

Drip systems operate most effectively whenused in conjunction with plastic mulches. Mulchesreduce evaporation of water from soils and im-prove economy of drip water application. Vegetableoperators typically use 4-foot-wide rolls of black orwhite-on-black polyethylene plastic mulch on 5-footrow centers with drip tape buried 1 to 3 inches deepbelow the plastic and either 3 to 5 inches to the sideof the row or in the center, depending upon whethera single- or double-row crop is being grown. Usecare in laying tubing straight so it will not be dam-aged when transplanting. Plastic laying machinescan lay drip tape and plastic mulch inone operation.

WATER MANAGEMENT AND OPERATION

Drip irrigation is, in many ways, a different wayof irrigating. A small supply of water is appliedas the plant needs it, usually on a daily or morefrequent basis. The goal should be to achieve a highlevel of efficiency to get maximum production ofproduce from minimal amounts of water. As theplant grows, larger quantities of water are neededas root systems become more extensive and foliage

Layout of a TypicalTrickle Irrigation System

PressureGauge Feeder

Well Fertilizer Injector Primary Pressure Tube(optional) Filter Regulator

Mainline Drip TubeDistributionto field

Sub-Mainline(headerline)

Additional valves may be added to controlseveral rows or zones in the field.


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Vinyl lay flat hose with feeder tube attached (left), Feeder tubeinserted into drip tape (center), and plastic drip tape (right).

Bacteria, algae and slime in lines can beremoved by injections of chlorine or commercialbacterial control agents applied through the fertiga-tion system. Use a 2 ppm chlorine daily rinse atthe end of the irrigation cycle or a 30 ppm shocktreatment if slime becomes a problem in the sys-tem. Consult with a drip system representative fordilution rates for commercial cleaning products.

Periodic flushing of the mainline, sub-mainlineand drip tape is an excellent maintenance practice.Adapters are available for the ends of each drip tapeto automatically flush lines at the end of each irriga-tion cycle, or they can be manually opened to allowa few gallons of water to flush from the end. Thiswill prevent any build-up of particles or slime at theend of the drip line.

Regulator and FiltrationAdustable pressure regulator (upper left), Preset pressureregulator, pressure gauge and filter (center), Y filters (lower left

and upper right).


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About the authors: Charles W. Marr is an extension horticulturist, vegetable crops; Danny Rogers is anextension engineer, irrigation

Brand names appearing in this publication are for product identification purposes only. No endorsement is intended,

nor is criticism implied of similar products not mentioned.

Publications from Kansas State University are available on the World Wide Web at: http://www.oznet.ksu.edu

Contents of this publication may be freely reproduced for educational purposes. All other rights reserved. In each case, credit Chuck Marr,

Drip Irrigation for Vegetables, Kansas State University, October 1993.

Kansas State University Agricultural Experiment Station and Cooperative Extension Service

MF-1090 October 1993

It is the policy of Kansas State University Agricultural Experiment Station and Cooperative Extension Service that all persons shall have equal opportunity and

access to its educational programs, services, activities, and materials without regard to race, color, religion, national origin, sex, age or disability. Kansas State

University is an equal opportunity organization. Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June 30, 1914, as amended. Kansas

State University, County Extension Councils, Extension Districts, and United States Department of Agriculture Cooperating, Marc A. Johnson, Director.

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Drip Irrigation for Veggies - Kansas State University Cooperative Extension