DRIP IRRIGATION OF CITRUS-PANEL

DRIP IRRIGATION OF CITRUS IN CALIFORNIA

Don Gustafson 1

Oranges and lemons were introduced into Californiawith the founding of the first Spanish mission in SanDiego in 1769. Soon, each mission along EI Camino Realhad orange trees in their gardens, but the only orchard ofany size was at San Gabriel Mission near Los Angeles.The industry had its beginning in 1841 when WilliamWolfskill planted an orange grove in what is now downtownLos Angeles. He later added lemons. Navel oranges wereintroduced in 1873 and by 1900, the winter orangebusiness was booming. Today, the citrus industry inCalifornia consists of approximately 336,700 acres(136,300 hal, divided by variety as follows:

Citrus is grown from the Pacific coast to the desert.The climate of warm sunny days, mild breezes and coolnights make it possible to grow many colorful and flavor-rich varieties that are picked and shipped year-round.Citrus can be found growing on many kinds of soil. fromalmost pure sand to decomposed granite to loams to claysoils. Terrain ranges from flat desert to sloping or relativelysteep hillsides.

California citrus must be irrigated as total rainfall isnever adequate. but distribution is more important. Rainusually occurs from November to March or April. withmost rain falling in December to February. Occasionally.good rainfall occurs between April and June. but in mostyears irrigation must be done from February-March toNovember.

~ ..&.

110,000133,00062,00015,00016,000

700

44,50053,80025,1006,1006,500

-1§Q.

DRIP IRRIGATION

Valencia orangesNavel orangeslemons

GrapefruitMandarins. TangerinesLimes

336,700 136,280

The center of the citrus industry was located inSouthern California until about 1957 when a great influx ofpeople caused a great demand for land on which to puthouses, commercial developments and industrial complexes.Growers sold ranches for high prices to developers andre-invested in citrus in the desert, Arizona and the greatCentral Valley of California, as new irrigation projectsopened up thousands of acres.

Conventional irrigation consists mainly of sprinklerirrigation, with some desert areas using flood or basinirrigation where water is inexpensive. The high costs ofwater, upwards of $50 to $100 per acre-foot (12 ha-cm), inmany citrus districts has forced growers into cost-cuttingoperations and improved cultural practices. Drip irrigationwas introduced into California in 1969-70 on a commercialscale and it appeared at that time that this new methodof irrigation could result in cost savings while stillmaintaining tree health and production.

New installations went in allover California asgrowers became acquainted with drip irrigation. Between50,000 and 60,000 acres (20,200 and 24,300 ha) have beeninstalled on all crops, including thousands of acres oncitrus, a gigantic increase from only 100 acres (40 ha) in1970. Growers quickly realized the potential of this newirrigation technology. The experience of the lsarelis,

1 Farm Advisor, California Agriculturel EXter*on Service, San

Diego County, San Diego.

81

irrigation. Much of the surface soil never becomes wet, thusorchard operations are not interrupted. Weed growth isreduced so control efforts are reduced. Frequent irrigationsmaintain a soil moisture condition that does not fluctuatebetween wet and dry extremes and keeps most of the soilwell aerated. Avoidance of intermittent drying permitsthe use of more saline water than can be used with otherirrigation methods.

62

Australians and Mexicans showed that there were manyadvantages in the drip system, such as 1) water saving,2) increased yields, 3) labor saving, 4) simultaneousfertilizer application, 5) less weeds and 6) better youngplant vigor. There are also possible problems such as 1) or-ifice blocking, 2) filtration, 3) salinity, 4) disease factorsand 5) engineering design.

Drip irrigation has created a wide interest in a shorttime in spite of a relatively small amount of experience,information and development. The main factor behind thisinterest is the potential of drip irrigation to reduceoperating costs. Experience has shown that trees can beirrigated with 50% less water. Increased yields have beenreported. Labor cost for irrigation is cut, since waterapplied by drip irrigation usually needs no tending, but isregulated by turning on valves. Growers are also faced withscarcity and high prices for labor and water.

Drip irrigation is the frequent, slow application ofwater to soil through mechanical devices called emitterslocated at selected points along water delivery lines. Theapplication rate must be slow enough so that the flow ofwater across the soil surface is limited, and runoff in theusual sense does not occur. Most of the lateral movementof water to wet the soil between emitters occurs bycapillarity beneath the soil surface. The volume of soilwetted in 8n orchard depends on soil characteristics andnumber of emitters but is usually much less than thatwetted by other methods of irrigation, varying from 10%for newly planted orchards to as much as 50% for maturecrops.

Some ProblemsThe emitter outlets through which water must flow

are very small, they can become plugged by particles ofmineral or organic matter carried in the water. Dissolvedsalts can also crystallize around the external perimeter ofthe orifices, reducing the size of opening. These restrictionsmay reduce the emission rate, upset the uniformity ofdistribution of irrigation water, and cause plant damagebefore plugging is detected.

Most emitters operate at 3 to 20 psi. Nozzle pressureand discharge during the irrigation period may differ up to50% from that intended if the field slopes steeply, and thelines drain through lower emitters after the water is shutoff. Some plants would receive too much, others too little.

Some soils may not have sufficient infiltrationcapacity to absorb water at the usual discharge rate withoutrunoff or undesirable ponding. The soil must have aninfiltration capacity of 0.5 inch (1.25 cm) per hour to keepthe pool of free water around the emitter from exceeding2 feet (61 cm) in diameter when the discharge rate is 1 gph.Sandy soils are probably best adapted to drip irrigation,especially those with slight horizontal stratification. Sua,stratification is beneficial for drip irrigation because itpromotes lateral water movement and wets a greatervolume of soil. Experience has shown that the systemusually performs well in medium-textured soils, but theremay be problems with sorne fine-textured soils.

Salts tend to concentrate at the soil surface and alsoat the perimeter of the soil volume wetted by each emitter.Light rains will leach surface-accumulated salts into theroot zone, thus irrigations should continue on scheduleuntil substantial rain has fallen. Drying of the soil betweenirrigations may cause a reverse movement of soil water,resulting in the transfer of salt from the perimeter towardsthe emitter. Water movement must always be away fromthe emitter to avoid salt damage. The foraging ability of theroots for nutrients and water is limited to the small volumeof soil wetted. Damage to the crop could occur ratherquickly should uncontrolled events cause suspension ofwater and fertilizer supplies.

The number of emitters used ranges from 1 or 2emitters for newly planted trees to 8 or more for largetrees. Each emitter provides the slow water-flow needed.Most emitters are manufactured to provide a fixed rate ofoutput with a specified water pressure. A few haveadjustable rates. Rates available usually range from 0.5 to2 gallons per hour (gph), 1 gph being most common. Mostemitters prov,ide a point source of water, usually placeddirectly on the soil surface or buried at a shallow depth.Others provide a line source of water from a tube havingperforated or porous walls, which is usually ooried.

The emitters are connected t%r are part of a smalldiameter (3/8 to 3/4 inch or 9.5 to 19 mm) plastic lateralline. The laterals generally lie on the soil surface oot may beburied at shallow depth for protection. They connect to aburied plastic main line that receives water from a head.The head is the control station for the system, where wateris measured, filtered, treated with fertilizer in solution andregulated as to pressure and timing of application.

OPBrBtion of SystemClean water is essential. Most failures observed are

caused by inadequate filtering. Multiple screen~ as fine as

Some AdvBn~$Drip rates are low, hence main line and lateral line

sizes can be smaller than those for sprinkler or surface

63

of water comes out of the emitter at the bottom of theorchard as at the top. Also, the fill-up time of the system,as well as the drain-out time, should be fitted into thecalculations so one set of trees does not get more waterthan another portion of the orchard.

There are many emitters on the market today. Theyfall into 3 main categories: the moving parts type, theadjustable type and the fixed discharge type.

SUMMARY

It may be interesting in summary to note the cropsusing drip irrigation, either commercially or in experimentalunits.

200 mesh or sand filters should be used.Irrigations must be frequent and lifj\t. The duration

of each irrigation must not be too lengthy, helping aloidlocal excessive wetness in soils lacking rapid permeabilityand minimizing algae growth in laterals. The amount ofwater applied should be based on measured or carefullyobserved soil-water conditions.

Lateral lines must be designed with adequate capacityto carry the maximum expected flow rate with little or noloss of pressure, although water emission rates are low.Lateral lines are generally of uniformly small diameter buttheir length should not exceed 300 to 400 feet (91 to 122m). Additional main lines are preferable to excessive laterallengths.

Lateral lines must be designed to carry the largerinitial flow rate needed for flushing if flushing-type emittersare used.

Pressure regulators are necessary on sloping land.Laterals should be laid as level as possible.

Phosphate fertilizers should not be applied through adrip irrigation system. Phosphates react with calcium inirrigation water, forming a precipitate that can clogemitters.

The fruit crops include: avocados, grapes (table andwine), strawberries, grapefruit, lemons, limes, navel oranges,'Valencia' oranges, tangerines, tangelos, macadamia nuts,papaya, peaches, pears, persimmons,. walnuts, apples,boysenberries, melons, avocado nurseries, citrus nurseries,apricots, pistad1io, plums, cherries, almonds, pecans,pineapple, coffee, bananas, mangoes, olives, figs, passionfruit and others.

Ornamentats, vegetables, and agronomic crops knownto be using drip irrigation include: tomatoes, cucumbers,celery, potatoes, peppers, com, asparagus, egg plant, peas,lettuce, ornamental trees and shrubs, bedding plants, cactusand succulents, bulbs, carnations, gladioli, poinsettias,chrysanthemums, ground covers on highway road cuts,street medians, turf (both home yards and golf courses),Christmas trees, forestry trees, radishes, sugar cane, cotton,sorghun:t. alfalfa, pasture, wheat and many others.

A preliminary report on the 1975 Worldwide DripI rrigation Survey shows the following data for acreageunder drip irrigation for the countries responding to date:

1974 Est.

Acres

(He)

1975 Est.

Acres

tHe)

1979 Est

Acr.

1H8)

,~ EstAcrelIHe)

U.S.A. 72,(XX)

129,150)

74,000

(29,950)

217.(0)

187.800)

362,cm

1146,5001

Other 65.IXXJ

(26,3001123,000C49,~)

90,000

(36,4001

24 1 .(XX)

(97.5601

Australia, Brazil, Canada, Costa Rica, Honduras, India,Iran, Israel, Japan, Mexico, New Zealand, Panama, PuertoRico, South Africa, United Kingdom and West Africa arethe only countries responding to date.

The 1974 and 1979 acreage figures were submitted atthe time the 1974 survey was conducted. The 1975 and1980 figures were derived from the 1975 questionaire.There are many other countries where drip irrigation is .being used, but for some reason, the questionaire has notbeen received from them. However, it is safe to state thatdrip irrigation continues to create interest throughout theUnited States and in many other countries.

Equipment ~d InstallationTwo types of irrigation systems are installed in

orchards, the conventional spitter system that can beconverted to sprinklers and the drip system. There aredifferent ways the drip irrigation system can be installed.The conventional type is buried PVC rigid pipe with a riserto each tree, and a plastic hose with emitters attached tothe riser. Another method is to lay the hose on the groundin one continuous line near the trunk of the tree with3 or 4 emitters placed at each tree site.

Equipment used in drip irrigation systems is veryimportant. There are many pieces of equipment required.They include plastic hose or pipe, spaghetti hose, emitters,pressure regulators, pressure gauges, valves, fertilizer tanks,filters (both sand and screen), time clocks, tensiometers,evaporative pans, meters and fertilizer injectors. The mostimportant item in the hardware for drip irrigation systemsis the filter. Filtration is a must and extra money put intogood filtration will give the required performance fromemitters.

Increasing numbers of installations are going in withcomplete automation. Automation is accomplished withthe use of a timer that can be set for daily operation at acertain hour of the day, or with the more sophisticated unitthat is controlled by electrified tensiometers under thetrees and coupled with the timer for operation.

Pressure regulation is very important. The differenceof discharge of water from one emitter to the other mustbe kept to a minimum. This becomes extremely importantand critical on hillside plantings. Engineers must make

allowances in designing systems for differences in elevationeither by pipe size difference or the installation ofnumerous pressure regulating devices so the same amount