Effective Use of SeawaterIrrigation on TurfgrassThis article is the second in a three-part series on water quality,the first of which appeared in the November/December 1999 issue.

by R. R. DUNCAN, R. N. CARRO~ and MIKE HUCK

Water is available in many different forms. The ability to irrigate a golf course withseawater has long been a dream. This dream will soon become a reality as turfgrass-quality ecotypes of seashore paspalum tolerant to ocean-level salt concentrationsbecome commercially available.

TIE PROBLEM: Availability ofadequate water in terms of qualityand quantity will be the number-

one issue affecting turfgrass manage-ment in the 21st century.

Global demand for fresh potablewater is doubling every 20 years. Irri-gated areas have increased about 1%per year worldwide during the 1990s.During the past 30 years, the popula-tion of the United States has increased52% while total water use has in-creased 300%. Renewable water re-sources per person decreased 50%between 1960 and 1998 in the UnitedStates. Another 50% reduction is pro-jected by 2025. By 2000, 20% of allU.S. communities will experience watershortages in the form of water rationingor short-term cutoffs. Competition forpotable water will force turfgrass man-agers to search for alternative waterresources - from recycled wastewaterto seawater.

Water is available in many differentforms. Seawater (34,486 ppm salt) en-compasses 96.5% of the total globalwater supply (Gleick, 1993). Freshwater reserves total 2.5%. Ground-water, which makes up 1.7% of thetotal global water supply, includes 55%saline and 45 % fresh water. A total of30.1 % of fresh water comes from thegroundwater.

Lake water reserves (0.013% of totalwater resources) include 0.006% oftotal saline and 0.007% of fresh water.Swamp water (0.0008% of total waterreserves), river flows (0.0002%), gla-ciers plus permanent snow cover(1.74%), and ground ice/permafrost(0.022%) account for the remainingglobal water reserves.

Crop plants normally utilize 40-45 %of the water applied through irrigation,with the remaining 55-60% lost asrunoff, deep percolation, or evapora-tion/evapotranspiration. Turfgrassesare probably slightly more efficient inwater use than most crop plants due togreater canopy coverage of the soil andtheir perennial nature.

The DilemmaWater quality and availability have

a dramatic influence on site-specificturfgrass management strategies, re-gardless of whether salt-laden effluent(recycled water), ocean water, or blendsof the two sources are used as the watersource. Saltwater intrusion is a majorconcern in coastal areas (Newport,1997; Todd, 1997). Water withdrawalfrom coastal groundwater can con-tribute to degradation of water and soilquality. Renewal time for groundwaterresources is estimated at 300 years(Gleick, 1993).

Salinization of irrigated land occurswhen dissolved salts accumulate in theupper soil layers on naturally salinelands, on lands with poor drainage, inarid/semi-arid regions, or on landsutilizing salt-laden effluent (recycled '"water). The percentage of irrigatedlands affected by salinization includes20-25% in the United States, 13% inIsrael, 30-40% in Egypt, 15% in China,and 15-20% in Australia (Gleick, 1993).The use of highly saline irrigation watergreatly enhances the potential to de-grade soil by salinization unless definiteconstruction and management prac-

JANUARY/FEBRUARY 2000 11

tices are followed. Accumulation ofexcess total salts (salinization) andsodium (sodic soil formation) in thesoil is more rapid as irrigation waterquality declines. The dilemma con-fronting turfgrass managers is how toeffectively use water of poor qualitywithout causing excessive salt prob-lems that will result in substantialdecline in turfgrass quality andperformance.

Potential climatic changes will com-plicate water and salt management.Possible climatic changes projectedglobally from increasing CO2 atmo-spheric levels include:

• 2-5°C increase in temperature;• 0- to 32-inch increase in sea level;• Precipitation increase of 7-15%;• Direct solar radiation change -10%

to +10%; 5-10% evapotranspirationincrease (Woodward, 1992).

These climatic changes will signifi-cantly affect turfgrass management inthe 21st century. Because of thesechanges, most recreational turf willpossibly be mandated to be irrigatedwith nonpotable resources (CaliforniaAssembly Bill 174,Oct. 1991).Desalini-zation is one option as an alternativewater resource, but cost comparisonsand the volume of water produced arekey considerations (California CoastalCommission, 1999).

Irrigating with SeawaterWith the availability of ocean-level,

salt-tolerant turf species, using seawaterfor irrigation becomes a viable optionin turfgrass management. The focus ofthis article is to emphasize those criticalis-sues that arise when this worst-casewater option (i.e. seawater) is selectedas the irrigation source. The basic prin-ciples are applicable to sites using salt-laden effluent.

Irrigating food crops, as well asturfgrass, with seawater requires that anumber of basic guidelines be con-sidered (Glenn et al., 1998):

1. Halophyte turfgrasses (salt-toler-ant species such as seashore paspalum,saltgrass, or alkaligrass) and landscapeplants should be planted.

2. Golf courses should be con-structed on sandy, well-drained coastalsites for long-term sustainability.

3. Water should be available at suffi-cient volumes to leach salts, minimiz-ing the concentration of salts in therootzone and preventing dry down ofthe surface caused by evaporation andpercolation. High leaching events arecritical, and proper irrigation schedul-ing is essential to success. All irrigated

12 USGA GREEN SECTION RECORD

areas on the golf course, includingroughs, surrounds, and mounds mustbe managed as primary areas.

4. Salts must be removed by drainagesystems and be properly disposed of toprevent contamination of any potablegroundwater under the site and toprevent soil salinization.

5.The cost of pumping from wellsnear the ocean is increased due toincreasing irrigation demands (forproper leaching). Minimal water liftingis required, which offsets some of thosecosts.

6. Coastal aquatic sites are impacted(especially saltwater intrusion) andshould be carefully monitored.

7.Maintenance costs may be 50%higher than in non-salt affected areasbecause of continuous application ofamendments to minimize salt buildupand corrosion damage to maintenance,irrigation, and other equipment, requir-ing more frequent replacement.

8. Highly trained turfgrass managersare necessary because of the site-specific complexity of the salt-relatedproblems.

9. Unnecessary traffic on turf shouldbe reduced or eliminated to (a) offsetthe lack of wear recovery caused bygrowth reduction resulting from saltstress and (b) avoid compacting satu-rated soils that are frequently irrigatedto field capacity in order to promoteleaching.

Pre-Construction ConsiderationsGrass Selection

As we enter the new millennium andpotable water becomes a more scarceresource, continued development ofsalt-tolerant species (turfgrass, trees,ornamentals, and other landscape~plants) will become increasingly impor-tant for all recreational landscapes, in-cluding golf courses. Research fundedby the USGA has resulted in thedevelopment of high-quality, environ-mentally friendly and ocean level salt-tolerant seashore paspalum turfgrassesfor use on greens, tees, fairways, androughs. This grass currently provides aunique opportunity in temperate andtropical climates to utilize alternativewater resources for irrigation. Addi-tional research and breeding efforts toimprove salt tolerance of cool-seasonspecies (some private companies havemade this a priority) will extend alter-native water use to northern climates.

Irrigation with ocean water (34,486ppm salt), brackish water (at salt con-centrations < 34,000 ppm), seawater

blended with other nonpotable waterresources, or salt-laden effluent is nowfeasible (Duncan and Carrow, 2000).The problem of saltwater intrusioninto coastal aquifers that results inunintentional application of seawateronto golf courses, and coastal or low-land saltwater inundation from stormsurges/salt deposition now can beaddressed with the most salt-tolerantturfgrass (Carrow and Duncan, 1998).These extreme cases of the ultimatepoor water quality require serious anddiligent pre-construction, establish-ment, grow-in/post establishment con-siderations for successful turfgrassmanagement. The site-specific natureof salinity-challenged environmentscauses the most complex and, often,most confusing situations involved inturfgrass management. Mistakes oromissions become readily apparentand amplified once the grass is plantedand the turf responds to its environ-ment.

Growth rates of all turfgrasses, in-cluding seashore paspalum, are re-duced when exposed to increasinglevels of salinity. Older bermudagrass(Tifway) and creeping bentgrass culti-vars (Seaside, Seaside II, SR1020, andMariner are better choices) will tolerateonly about one-third ocean level salt,and therefore may be suitable for usewith some effluent and/or brackishsources, depending on water quality.However, selected ecotypes of sea-shore paspalum can tolerate straightocean water (TDS = 34,486 ppm salt,ECw = 54 dSm-1

, SAR = 57.4 meq L-l,Na = 10,556 ppm, CI = 18,980 ppm,Mg = 1,304 ppm, Ca = 420 ppm, K =390 ppm, S04 = 2,690 ppm, HC03 =146 ppm). Landscape plants also mustbe able to tolerate high total salts andtoxic CI and Na levels. Careful planningand proper managment are the keys tosuccess when using seawater for irri-gation on turfgrass.

Water Quality AssessmentMonitor water quality by location

and over time, especially if the sourceis brackish or the water is obtainedfrom a well subjected to saltwaterintrusion where the salt water retreatsduring wet periods or encroaches dur-ing dry periods. Intrusion of salt waterinto a well head can occur abruptlyand, consequently, regularly scheduledwater quality testing will be necessary.If salt-laden effluent is used directlyor blended with seawater, qualityshould be monitored over time. Rela-tively inexpensive electrical conduc-

Commercially available, putting green quality seashore paspalum tolerates lowmowing heights and ocean-level salt concentrations in the irrigation water.

tivity meters can be easily used by turfmanagers for on-site monitoring oftotal salinity. Seawater drawn fromwells may be influenced by local soilconditions, such as those exhibitinghigher bicarbonates (HC03t or fromexcessive levels of other components,such as heavy metals or boron orextremely low pH «5.0) conditionswhere Al or Mn levels might beextremely high. Knowledge of waterconstituents and their fluctuation overtime is essential for making manage-ment decisions.

The Irrigation SystemIrrigation system design efficiency

includes sprinkler head spacing foruniform coverage, nozzle size tailoredto soil texture (percolation rate, e.g.,fine-textured soils may require low ap-plication rates), and individual sprin-kler head control to ensure flexiblescheduling. Pulse irrigation is essentialon soils with low infiltration and per-colation or with poor or slow drainagecharacteristics since it can be difficultto effectively manage and match pre-cipitation rates of large turf sprinklersto the infiltration rates in these salt-challenged soils. Pulse irrigation pro-vides water to the turf at a rate up torunoff and then stops to allow forinfiltration/percolation, followed byrepeated cycles. The intermittent appli-cation of water throughout a daily irri-gation cycle via pulse irrigation pro-vides for:

1. Maximum leaching of excess salts.2. Minimal buildup of excess Na,

which causes soil structural breakdown(sodic soil conditions).

3. Minimal bicarbonate precipitationand sealing at the surface of sandysoil profiles caused by light, frequentirrigation.

The number-one management re-quirement of all salt-affected turfgrasssites is leaching to remove excess saltsor to prevent sodium and chlorideaccumulation. The leaching require-ment (LR) is the quantity of water re-quired to maintain a moist soil profilewith consistent net downward move-ment of salts below the turfgrass root-zone that is over and above turf evapo-transpiration (ET). Turfgrass ET can behigh due to coastal winds or hightemperatures, especially during estab-lishment when soil evaporation isexcessive. Total saltwater needs includeLR + ET + correction for irrigationdesign inefficiency. Total water usecould average 30-50% higher using

ocean water compared to non-saltaffected situations.

The additional volumes of waterneeded to leach salts delivered by sea-water or other poor-quality recycledor brackish water can require specialconsideration when designing thehydraulic capacity of the irrigationsystem. Pipe sizes need to be increasedto avoid excessive flow velocities thatcause subsequent water hammer andfatiguing damage to PVC components.Inadequate pipe sizing will result in alonger window for total operating time,resulting in sprinklers operating beforedusk and after dawn, interfering withboth maintenance operations and golfplay. A general rule of thumb whendesigning the irrigation system is thatno greater than an 8-hour window ofoperation should be needed to irrigatethe golf course at maximum ET whileincluding the proper leaching fraction.

A "dual" mainline irrigation systemto allow irrigation of salt -sensitive areas(cool-season grass putting greens, club-house landscape areas) with a better-quality water also is an option. Anotheralternative is a system of multiplestorage lakes that allow blending ofalternative water sources for leaching.Under either ofthese scenarios, reverseosmosis could be incorporated into thesystem to supply water for occasionalleaching, blending, or management ofsalt -sensitive areas. Any of these op-tions should be included in the designphase on a cost-effective basis.

A dual irrigation system would provebeneficial for:

1. Blending seawater with waste-water to dilute the total salts and highNa+levels (improve overall quality).

2. Irrigation of golf greens withreduced salt-laden sources (such asreverse-osmosis water).

3. Use of alternative water resourcesduring periods of high volume leaching.

4. Application of fertilizer or otheramendments through the irrigationsystem.

Desalinization is one option as analternative water resource, but costcomparisons and volume of water pro-duced are key considerations (Cali-fornia Coastal Commission, 1999).

Corrosion of irrigation hardwareand other equipment exposed to oceanwater also is a major concern andshould be addressed within the designspecifications. Plastic pipe and sprin-klers are naturally preferred wherefeasible. Where steel components are"normally specified, epoxy coating,high-grade stainless steel (Austenitic)or ductile iron fittings on PVC mainsshould be investigated for improvedlongevity and economic feasibility.Custom manufacturing using seawater-resistant nonferrous metal blends andmarine or reclaimed water grade equip-ment and paint also may be options forconsideration. Components exposed tosalty sprinkler spray (wetting and dry-ing cycles) will deteriorate more rapidlythan those that are always submerged.Items such as controller cabinetsshould be manufactured from stainlesssteel or plastic and be maintained ina relatively watertight condition toinhibit corrosion of internal electricalcomponents and connections. It also isimperative that all buried wiring splicesare made with the highest-qualitywaterproof-type connections. Anotheroption would be to install a radio-operated control system (such asOSMAC from Toro and FREEDOMfrom Rainbird) that eliminates the needfor hard wiring of a low-voltage signalloop between the computer centralcontrol and the satellites. This type ofsystem would eliminate a number ofadditional and potentially troublesomeelectrical connections that are prone tofailure under highly saline conditions.

JANUARY IFEBRUARY 2000 13

Highly sandy soils are very desirablesince leaching is much easier on sandscompared to fine-textured soils thathave lower infiltration/percolation/drainage rates. Additionally, sandy soilsthat drain more rapidly will return toplayable conditions in less time follow-ing leaching and will resist compactionfrom maintenance equipment andother traffic when wet. Continuouspaved cart paths and cart restrictionson the turf also are recommended tominimize traffic damage from stressesdue to:

1. The reduction of turf growth andrecovery from wear caused by saltaccumulation.

2. Excess compaction when trafficoccurs on saturated soils followingregular leaching events.

Salt DisposalThe golf course design must include

plans for environmentally sound dis-posal of leached salts (and/or brine ifreverse osmosis is used) when seawateris to be used for irrigation. The primaryconsiderations involve:

1. Avoidance of salt accumulationbelow the turfgrass rootzone in anincreasingly concentrated form. Even-tually, this zone of salt accumulationwill rise to the soil surface and causecatastrophic injury to all plants andtheir root systems.

2. Prevention of leachate or saltseepage into a potable water source orfreshwater off-site area, or contami-nation by saltwater intrusion due toexcessive removal from the good watersource.

Both considerations involve properland surface contouring and adequatedeep-tile drainage lines (3-5 feet) withoutlets either directly into the oceanor into a carefully constructed andimpervious well or holding pond. The34,486 ppm of total salts in seawater isequivalent to 2, 153lbs. of salt per 1,000square feet per foot of seawater applied.Deep coarse sands (>0.50 mm) withhigh percolation rates (>10 inches perhour) are strongly preferred when sea-water is used for irrigation.

Long-Term Maintenance CostsSeawater irrigation requires pro-

active management to minimize theconstant threat of saline-sodic soilconditions and their resulting impacton turfgrass performance. Increasedbudgeting needs include:

1. Extra chemicals (gypsum, acids,lime, micronutrient fertilizers, highly

14 USGA GREEN SECTION RECORD

soluble fertilizers) that will be neededcontinuously and periodically at highrates. Some of these added costs areoffset by reduced needs for herbicidesand other pesticides and a less expen-sive water source.

2. Cultivation equipment (both sur-face and subsurface types) to maintainwater movement for efficient leachingof salts through soils. Fine-texturedsoils will require much more aggressivecultivation programs than sandy soils.The effectiveness of a cultivationoperation is typically reduced by one-half on high-Na sites and cultivationfrequency must be increased. Bothdeep (10-12 inches) and shallow (3-5inches) aeration practices are essentialfor proper salt leaching. Deep-tinecultivators include Verti-drain, SoilReliever, Aerway Slicer, and Deep-drill.The Yeager-Twose Turf Conditioner isless effective for deep cultivation (i.e. >7 inches), but has excellent chemicalinjection capabilities (capable of apply-ing 80-90 lbs. gypsum per 1,000 squarefeet at a 7-to 8-inch depth). The Hydro-ject units also can be used to enhanceseawater irrigation percolation into thesoil profile.

3. Extra irrigation equipment. Thecorrosive nature of the high salts inocean water will require constantmonitoring and more frequent replace-ment of certain components likesprinkler heads and irrigation pumps.Injector systems can occasionally beused to treat seawater. Acidification(H2S04, N-phuric acid, or urea sulfuricacid, sulfur dioxide generator) to aid inthe formation of gypsum (CaS04) in thesoil by reaction with surface-appliedlime (CaC03) is one method of supply-ing considerable Ca2+to replace Na+onsoil cation exchange sites (CEC). Theexcess Na combines with the availableS04 from the acids to form Na2S04,

which then can be leached.Another method of supplying high

levels of Ca2+ ions to counter high Na+levels in seawater is a gypsum injectorlinked with the irrigation system. CaClz,Ca(N03)2, or other highly solubleamendments can be added with thisunit. Although seawater contains rela-tively low HC03- (146 ppm), water thatis pumped from ground wells near theocean can occasionally contain levelsexceeding 550 ppm, which wouldbenefit from acidification to remove theexcess bicarbonates. This removalreleases the Ca and Mg in the water tocounteract the excessive Na in theseawater. Additional lakes, pumps, andpiping for blending, dual irrigation

systems, and desalinization/reverseosmosis equipment will raise ongoinglong-term maintenance costs.

4. Accelerated equipment replace-ment schedules for maintenance equip-ment and course accessories are com-monly required on sites with salineirrigation sources. Daily exposure tosalt-laden irrigation spray, exudationwater, and runoff deteriorates metalcomponents on mowing equipment,utility vehicles, and course accessoriessuch as signs, benches, and ball-wash-ers (much like the corrosion on auto-mobiles in northern climates causedfrom salting and deicing highways).Undercoating and rustproofing treat-ment of undercarriages on all equip-ment is recommended. A potable watersource also should be used when wash-ing equipment after every use to slowthe corrosion process.

5. The turf manager must be welltrained in order to maintain high-quality turf. Salt-related problems aresite-specific and very complex becauseof multiple environment/turf inter-actions.

Sand Capping and DrainageIf saline-sodic soil is dredged from

an ocean bay and added as the top-soil for the turfgrass rootzone, severalpractices are suggested to alleviatethe high total salts and excess Nathat cause considerable soil structuraldeterioration:

1. Deep-tine (10-14 inches) aerateand apply 200-600 lbs. gypsum per1,000 square feet to the soil surface andrototill into the top six inches. Higherrates may be needed for heavier claysoils.

2. Apply an additional 200 lbs.gypsum per 1,000 square feet to thesurface and cap with two inches ofcoarse sand. Till into the top 1 or 2inches of soil.

3. Cap with an additional six inchesof coarse sand. The more coarse thesand (especially 0.5 to 1.0 mm rangeand none exceeding 2.0 mm), the betterthe rate of percolation and the faster theleaching with less volume of seawaterirrigation. Coarse sand in the 1.0 to 2.0mm range should probably not exceed10-20% (by volume) of the total coarsesand to minimize damage to golf clubsand maintenance equipment.

If fine-textured soils that are highin silt and clay content have low infil-tration and percolation rates, appli-cation of a 6- to 12-inch coarse sandlayer (cap) over the existing soil will

As we enter the new millennium and fresh water becomes increasingly more scarce,alternative water supplies and salt-tolerant turfgrasses for golf become a much betteroption than the "other" alternative.

enhance the leaching effectiveness inthe rootzone and help maintain waterinfiltration by reducing surface soilcompaction. Incorporating 4-5 % or-ganic matter into the coarse sand priorto capping will (a) provide improvedwater-holding capacity, (b) help main-tain a moist soil profile for a longer timeframe compared to straight sand withno organic matter, and (c) minimize orslow down upward movement of saltsconcentrated below the rootzone whensurface evaporation demands exceedseawater application rates.

Wind + high temperatures + exposedsandy surfaces during establishmentand early grow-in can place very highevaporative demands on the overallturfgrass system. Heavy leaching atnight to keep the salts moving down-ward followed by periodic seawaterapplications during the heat of the dayin an effort to maintain uniform soilmoisture and prevent upward move-ment of concentrated salts are the keyirrigation maintenance practices forsuccessful establishment and grow-inof turf with seawater irrigation.

One additional alternative - a fair-way system with full drainage - couldbe considered. The concept involvescreating the world's largest USGAgreen by letting the subsoil seal withexcess Na+(creating a lake bottom) andinstalling a subsurface drainage systembelow the sand cap. The drainagesystem allows collection and disposalof the salt -laden drainage water, ifengineered correctly, and also protectsany potable groundwater or aquifersin the immediate area. Constructioncosts are initially higher, but savings indeep aeration, gypsum applications,and associated labor to perform thesemaintenance operations could. con-ceivably pay for the drainage systemover a six-year period.

For example, approximately 2,378lbs. gypsum (23% Ca) per 1,000 squarefeet must be applied for every 12 inchesof seawater irrigation to counter thehigh Na+concentration. In deep sandswith < 2-3 % silt and clay, the gypsumrate can be reduced by 50-70%. How-ever, sand-capped sites still require thehigher gypsum rates to maintain non-sodic conditions in the subsoil. Forpractical purposes, assume the golfcourse covers 100acres and the gypsumcosts $100 per ton, or about $2,178 permonth (at 100 lbs. per 1,000 square feetper month, or about $5,180 per acre-foot of seawater). Assuming a 7,000-yard course and $6.00 per linear footfor solid perforated pipe including

main drains and occasional drainbasins, 30-foot lateral spacing wouldcost about $997,000 and 20-foot lateralspacing would cost about $1,432,800initially for the fairway drainage. If thegypsum rates could be reduced to 50%for treating the sand cap (instead ofkeeping the subsoil draining) and utili-zing subsurface drainage, the systemcould pay for itself relatively quickly.With heavy rains from monsoons, hur-ricanes, or tropical storms, this drain-age system would be extremely bene-ficial for rapid removal of excess water.

EstablishmentAll turfgrass and landscape plants are

more sensitive to high-salt problemsduring initial root formation and earlyestablishment. Besides the high -saltimpact on the root system, the turfgrass

growth rate will be reduced, prolongingthe grow-in period. Additionally, saltaccumulation on the soil surface occursvery rapidly when seawater is used forirrigation unless appropriate manage-ment practices are used. Proper man-agement techniques can minimize theneed for an expensive replanting. Fac-tors to consider~nclude:

1. Reduction of total salts for estab-lishment. Seawater has a total salinitylevel of ECw = 54 dSm-1• Total salts willonly be reduced below 54 dSm-1 (a)after a heavy rainfall or prolongedrainy period, (b) by use of better-qualitywater sources (effluent, brackish,reverse-osmosis water), or (c) by blend-ing with lower salt-containing watersources.

2. Alleviation of Na-induced soilphysical problems in the surface zone.

JANUARY/FEBRUARY 2000 15

As the bermudagrass succumbs to high salt levels, seashore paspalum (lighter color)fills in the putting green.

Aggressive deep and shallow aeration,gypsum application, cultivation, top-dressing, and leaching are key manage-ment options. Gypsum applicationsshould always be made immediatelyfollowing aeration to avoid creating aNa+-affected layer deeper in the soilprofile.

3. Maintenance of a uniformly moistsoil profile. Preventing the soil surfaceECe from rising above 54 dSm-1 whenseawater is the sole source of irrigationwater will require:

(a) Keeping the salts moving - acontinuous program of supplying suf-ficient water volume is necessary tomaintain net downward movement ofsalts away from the rootzone and soilsurface, and to prevent them fromrising back up by capillary/absorptivewater movement.

(b) Maintaining moist soil profileconditions between irrigation eventsso that salts do not concentrate in thesoil solution or rise by capillary actionfrom below the surface zone. If thesalts move down at ECe = 54 dSm-1

and concentrate, high evaporation insandy soils can bring the salts back tothe surface at ECe > 54 dSm-1 and killthe young turf seedlings.

Light, frequent seawater irrigation atestablishment or on mature turf with-out adequate leaching will result inrapid surface resalinization and subse-quently lead to turfgrass failure evenwith the most tolerant turfgrass culti-vars. Scheduling high leaching eventsat night will minimize competitionfrom wind and the high evaporative

daytime demands when using seawater.On sands, the nighttime leaching eventshould be sufficient to move surfacesalts (i.e. the wetting front in the soilprofile) to at least 12 inches and onfine-textured soils to at least 16-20inches depth. This will minimize capil-lary rise of more concentrated saltsback to the surface and into the turf-grass rhizosphere. This heavy leachingevent may be done over two nights onfine-textured soils if percolation ratesare low. Seawater irrigation schedul-ing during the day should be frequentenough to maintain a continuous anduniformly moist soil profile with mini-mal surface drying. A monthly gypsumapplication of 100-200 lbs. per 1,000square feet can be surface-applied as asodic-soil preventative strategy whenusing seawater for irrigation.

4. Adequate initial fertilization andcareful monitoring of micronutrientswith continuous leaching events. Aspoon-feeding approach (frequentapplications, 110 to 12rates) is necessaryon seawater-irrigated sites, with totalannual fertilizer nutrients applied at1.5 to 2.0 times that used on areas irri-gated with non-salt-Iaden water. Whilehigher annual rates of fertilizer arerequired, the rates per application aresimilar to non -salt-affected sites, but thefrequency is greater. Use of highlysoluble fertilizers and fertigationthrough a well-designed irrigationsystem is very beneficial.

Adequate phosphorus (2-3 lbs. P20S

per 1,000 square feet) should be appliedto the surface at planting to promote

establishment. Soil test analysis willreveal the need for additional nutrientsin conjunction with nutrients suppliedby the seawater. High leaching eventscan deplete micronutrient (Fe, Mn)levels, and careful monitoring is neces-sary on a continuous basis. Potassium,Ca, and Mg also are subject to leachinglosses and should be monitored closely.

Post- Establishment/Mature TurfThe use of seawater for turfgrass

irrigation produces two very importantresults that significantly impact man-agement strategies:

1. Seawater supplies additionalnutrients that require adjustment infertilization protocols, and chemicalsthat are applied to replace excess Na+on soil CEC sites necessitate additionalnutritional adjustments (Table 1).

• All ions in Table 1 contribute tooverall high total salts, with Na+ andCI- ions contributing the most saltsbecause of total quantity. As long asadequate irrigation water is applied,chloride is easily leached. Excesschloride can detrimentally affect nitrateuptake.

• Excess Na+ will rapidly cause asevere sodic-soil condition (soil struc-tural deterioration) unless high quan-tities of Ca+2ions are added to replaceNa+ on the CEC sites and sufficientwater is added to leach the ion awayfrom the turfgrass root system. A sodic-soil situation is much more serious onfine-textured soils than on sands. Atleast 547 lbs. elemental Ca+2per 1,000square feet or 2,378 lbs. gypsum (23%Ca) per 1,000 square feet must beapplied for every 12 inches of seawaterirrigation to counter the high Na+ con-centration. In deep sands with < 2-3 %silt and clay, the gypsum rate can bereduced by 50-70%. Sand-capped siteswill still require the higher gypsum ratesto maintain non-sodic conditions inthe underlying soil, unless a completesubsurface drainage system has beenincluded (discussed in sand-cappingsection) .

• Additional highly soluble Casources could include CaCl2 orCa(N03h, which could be appliedthrough injector systems. Lime (CaC03)

can be applied to the soil to react withS04-2in the seawater to form gypsum.Approximately 170 lbs. lime per 1,000square feet per 12 inches seawaterirrigation is needed to react with 168lbs. SO/ in the seawater.

• A 3:1 to 8:1 ratio of Ca:Mg is pre-ferred in irrigation water. Ca deficiencymay occur below 3:1 and Mg deficiency

16 USGA GREEN SECTION RECORD

Table 1Quantity of nutrients applied with typical seawater irrigation

Ibs.ll,OOO sq. ft. perIon 12 inches seawater meq VI ppm 0/0 of CationsCa+2 26.2 21.0 420 3.5Mg+2 81.4 106.8 1,304 17.9K+ 24.3 9.9 310 0.8Na+ 659 458.8 10,556 76.9S04.2 168 56.0 2,690CI' 1,185 534.6 18,980HC03' 9 2.4 146C03 <1N 11.5P 0.06Mo 0.01Fe 0.002Mn 0.0002

above 8:1. The 1:5 ratio of these twoelements in seawater is usually not aproblem since large quantities of Ca areapplied as an amendment to replaceNa+when using seawater for irrigation.If extra Mg is needed, dolomitic limecan be used as a slow-release Mgsource, or a soluble Mg source can beapplied by fertilization.

• Even though 24.3 lbs. K is appliedper 1,000 square feet per 12 inches sea-water irrigation, high N a+suppressesK+ uptake. A routine spoon-feedingprogram with KN03 or K2S04is recom-mended. On sand-capped areas orwell-drained deep sands, adding 5%by weight of medium to coarse zeolite(0.25-1.00 mm diameter) will enhanceselective retention of K+ions.

2. High leaching requirements willenhance the leaching of all nutrients.

• N-P-K fertilizers should be appliedin a spoon-feeding approach at 1.5 to2.0 times annual rates (compared tosites with good-quality water).

• Slow-release fertilizers applied fre-quently in ~o to lIb. per 1,000 squarefeet per application increments can beused as the base fertilization with ferti-gation of water-soluble sources usedto supplement turfgrass nutrition. Spotfertilization of wear/traffic areas withgranular, quick-release, soluble fertil-izers may be necessary.

• The micro nutrients Fe and Mnmay require extra foliar applications at0.025 Fe and 0.013 lbs. Mn per 1,000square feet every two to three weeks.Additional granular applications maybe needed several times per year. Agood micronutrient fertilizer should be

applied at the recommended rate, but1.5-2.0 times more frequently.Summary

Seawater irrigation on turfgrass isfeasible with:

• Highly salt-tolerant turf species.• Coarse, sandy soil profiles.• Irrigation strategies that keep salts

moving with regular leaching eventsand keep the soil profile uniformlymoist to minimize concentrated saltsfrom rising into the rootzone.

• Good surface and subsurface drain-age design.

• Environmentally safe disposal ofexcess salts.

• Careful nutrient management andcontinuous monitoring.

• The entire course must receivehigh-level management.Pros for Using Seawater Irrigation

• Non-interruptible supply of irriga-tion water during shortages/ droughts/rationing.

• Reduced water costs when com-pared to "purchased" potable or re-cycled water.

• Reduced pumping costs comparedto similar quality brackish wells.

Cons for Using Seawater Irrigation• Higher ongoing maintenance costs:

cultivation (labor, replacement tines,equipment repairs), amendments, equip-ment replacement (undercoatings),salt/brine/ drainage disposal.

• Higher construction costs: sandcapping, additional drainage, enhancedirrigation systems, reverse-osmosisequipment.

ReferencesCalifornia Assembly Bill 174 (October)1991.Water resources - reclaimed water-nonpotable use. In Statutes of 1991-1992Regular Session. State of California Legis-lative Counsel's Digest. Chapter 553, p.2321-2322.California Coastal Commission. 1999. Sea-water desalinization in California. Website:www.ceres.ca.gov Icoastalcomml desalrptIdkeyfact. html.Carrow, R. N., and R. R. Duncan. 1998.Salt-affected tur/grass sites: assessmentand management. Ann Arbor Press.Chelsea, Mich.Duncan, R. R., and R. N. Carrow. 2000.Seashore paspalum: the environmentalturfgrass. Ann Arbor Press. Chelsea, Mich.(Projected publication by January 2000).Gleick, P. H., ed. 1993. Water in Crisis: aguide to the world's freshwater resources.Oxford Univ. Press, Oxford, UK.Glenn, E. P., J. J. Brown, and J. W O'Leary.1998. Irrigating crops with seawater. Scien-tific American 279(2):76-81.Herbert, F. 1999. Principles of water move-ment. Sports Turf 15(2):24-28.Iyengar, E.R.R., and M. P. Ready. 1994. Cropresponse to salt stress: seawater applica-tion and prospects, p. 183-201. In M.Pessaraki (ed.) Handbook of Plant andCrop Stress. Marcel Deklar Inc. New York,N.Y.Newport, B. P. 1997.Saltwater intrusion inthe United States. EPA-600/8-77-011.Todd, D. K. 1997.Salt water and its control.Water Works Assoc. 66(3).Woodward, F. I. (ed.). 1992. Globalclimatic change; the ecological conse-quences. Academic Press. London, UK.

RONNY R. DUNCAN, Ph.D., is professorof tUrfgrass breeding and stress physiology,Crop &> Soil Sciences Department, Univer-sity of Georgia, Griffin. Research empha-sis is on developing tUrfgrasses with mul-tiple environmental, soil, and man-madestress tolerance, as well as developmentof environmentally sound managementpractices.ROBERT N. CARROW; Ph.D., is professorof tur/grass stress physiology and soilstresses, Crop &> Soil Sciences Department,University of Georgia, Griffin. Researchemphasis is on turfgrasses as affected byenvironmental, traffic, and soil physical!chemical stresses.MIKE HUCK is an agronomist with theUSGA Green Section, Southwest Region,where everyday water shortages makealternative water supplies a current issue. )He resides in the coastal community ofDana Point, California, near what he nowviews as potentially one of the largestirrigation reservoirs in the world - thePacific Ocean!

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