Leaching for Salinity Managementon Turfgrass SitesWhere salts are a problem, leaching is the answer.by R. N. CARRO~ M. HUCK, and R. R. DUNCAN

Well water can vary greatly and change over time. Regular monitoring of well water is necessary to prevent undesirablecontamination. Here brine has entered the water supply through a damaged well casing.

"SALINITY MANAGEMENT" issynonymous with leaching ofsalts. Leaching is the single most

important management practice foralleviating or preventing salt stresses onturfgrass sites. Especially when the irri-gation water contains appreciable salts,turfgrass managers must operate froma mindset of "keep the salts movingdownward!"

Although the principle is simple,achieving an effective leaching programthat keeps salts moving past the root-zone is complex. Salinity managementis influenced by: salt type, soil factors,water quality/quantity, rainfall, turf-grass species and varieties, and time of

year.l,4,9The approach in this article isto discuss each of these factors, usingtypical field situations as practicalexamples.

Which Salt Problem?1. High total salinity is the most

common and injurious salt problem(i.e., saline or saline-sodic soil). It ismeasured as electrical conductivity(EC) of irrigation water (ECw)or withinsoils (ECe, from a saturated pasteextract)1,3,4.When the total soluble saltlevel in the rootzone becomes exces-sive, turfgrass water uptake is reduced,a situation often referred to as physio-logical drought. This salt-induced

drought stress causes typical droughtsymptoms, including wilting and re-duced growth rate, even though soilmoisture may appear to be adequate.As the stress continues, grasses oftenstart to exhibit chlorosis and decline inquality.l,9 These symptoms are oftenmistaken for disease injury.9

Leaching of excessive soluble salts isthe easiest of the various salt problemsto alleviate. Since the salts are solubleand the majority are in solution whenthe soil is well irrigated, removal ofthese salts requires the least quantity ofwater and time. Only sufficient waterapplications are needed; amendmentswill not improve salt movement unless

NOVEMBER/DECEMBER 2000 15

other specific problems exist with thesoil or water. With sufficient watermoving through the soil, leaching mayrequire 1 to 4 weeks for reclamationpurposes. However, accumulation ofexcessive soluble salts can rapidlyreappear due to high salt additions fromirrigation water not followed by ampleleaching, as well as from soluble saltsmoving by capillary rise from below therootzone up into the root area.

2. Excessive sodium (Na) levels with-in the soil can lead to specific ion toxi-city to root tissues and to deteriorationof soil structural (i.e., sodic or saline-sodic soil).1 The latter condition isevaluated by the soil SAR (sodiumadsorption ratio), the SARw (SAR ofirrigation water), and RSC (residualsodium carbonate) value of irrigationwater.3

The effects of sodium ion toxicity onroot tissues of grasses and high totalsalinity result in greater expression ofdrought stress symptoms. Soil structuredeterioration from excess Na+ on soilcolloid (clays, colloidal organic matter)exchange sites causes: a decline in

water infiltration/percolation/ drainage;low soil O2, which further limits root-ing; waterlogged and poorly drainedsoil; and, sometimes, black layersymptoms.

Leaching of Na+requires addition ofa relatively soluble Ca+2 source todisplace the Na+ from the soil cationexchange sites. When this happens, theNa+ goes into solution and can beleached.1 It is important that a solubleCa+2source be added whenever leach-ing with a Na-Iaden irrigation watersource is conducted. If not, the Naproblem can be compounded by theleaching of all remaining Ca+2,allow-ing replacement with Na supplied byNa-Iaden leaching water, and causinga complete sealing at the soil surface.

Compared with the removal of hightotal salts, a much longer time period isrequired and more water must movethrough the soil profile. Generally, forthe reclamation of a Na-affected site,a year or more may be required toalleviate the Na-induced structuralproblem, though only 1to 4 weeks areneeded to alleviate the specific ion

toxicity threat. Obviously, preventing asodic condition from forming is veryimportant and is much easier than re-claiming a sodic soil.

3. Toxic soil levels of the salt boron(B) is another salt-related problem thatrequires leaching. Since B is adsorbedto soil particles, two to three times theleaching water volume is necessarycompared to the quantity needed forremoval of total soluble salts. In con-junction with leaching, collection andoff-site disposal of clippings can assistin reducing B since it is accumulatedin turfgrass leaf tips. This strategy canalso be used with total salt and sodiumproblems as a supplemental method ofsalt reduction.

Salt FactorsA number of soil characteristics in-

fluence salt and water movement!retention and, therefore, leaching prac-tices. Major differences in soil proper-ties are especially apparent when com-paring sandy soils (i.e., sands, sandyloams, loamy sands) to fine-texturedtypes (Le., containing appreciable

A distinct layer in the profile is inhibiting water movement, resulting in black layer development near the surface.Frequent core cultivation is needed to keep water and salts moving down through the profile.

16 USGA GREEN SECTION RECORD

*The actual ET varies with grass species/cultivar, wind speed, management level,etc., but these values provide "ballpark" estimates. Also, as soil moisture leveldeclines, ET decreases dramatically.

tact, which creates many macroporesand gives the soil good resistance tocompaction. If excessive fines areadded to the soil or excessive organicmatter fills most of the macropores,infiltration rates can decline, butgenerally, sands have high infiltrationrates conducive to leaching of salts.Although high Na+ content does notcause "structural breakdown" of singlegrain sand particles, it does cause anycolloidal particles (clay or organicmatter in nature) to be dispersed andbecome susceptible to particle migra-tion. Pond, lake, or river water withhigh turbidity can contribute fines dur-ing irrigation. Often, these fine particlesaccumulate at the normal depth ofirrigation water penetration and cancause a layer and eventually mayinduce black layer formation. Thissequence of events would then inhibitsalt leaching.

As noted previously, high levels ofNa+ cause structural deterioration offine-textured soils. This is especiallyserious on 2:1 clays, since they oftenexhibit poor drainage even under lowNa+ due to their swelling/sealing na-ture. High Na+ content further de-creases water movement throughoutthe whole soil profile.

5. Capillary rise of the soil solutionand any dissolved salts in the solutionoccurs in the micropores (pores of <0.12mm diameter) and can result inmajor redistribution of salts withinthe soil profile. When ample water isapplied to cause net downward leach-ing of salts, salinity near the surface issimilar to the initial irrigation watersalinity level, but salinity then increaseswith depth. Under high evapotranspi-ration (ET) conditions, salts may start

Table 1Evapotranspiration averages by environment for turfgrasses

under well-irrigated conditions for different climate conditions

Aver~eEvapotranspiration *

(inches per day)

0.10 to 0.150.15 to 0.250.15 to 0.200.20 to 0.250.20 to 0.250.25 to 0.35

ClimateSituations

Cool humidCool dryWarm humidWarm dryHot humidHot dry

to soil compaction than 2: 1 clays.Because 1:1 clays evolve in humid,high-rainfall areas, they often exhibit aB horizon where clay content is higherdue to downward movement of par-ticles over many years. For example,many Piedmont red clays (1:1 types)contain 40% to 50% clay in the Bhorizon versus 15% to 25% in the sur-face A horizon, and water movement isslower across the B horizon.

In arid and semi-arid climates, wheresalt problems occur most often, 2:1clays predominate. Nevertheless, theycan be present in most climatic zones.When drying, 2:1 types are "self-culti-vating" because cracks form. Unfor-tunately, under well-watered to satu-rated moisture conditions, these claysswell and most macropores are lost.When total salinity problems developon these soils, deep cultivation andfilling the cultivation holes with sandor sand plus gypsum (sodic sites) isnecessary to maintain a sufficientnumber of macropores to at least thedepth of cultivation. In contrast, deepcultivation operations are effective forlonger time periods on 1:1 clays evenwithout filling holes with sand.

4. Good soil structure on fine-tex-tured soils is important for maintainingmacropores. As aggregates are formed,macropores are developed betweenaggregates or structural units. Soilcompaction from recreational trafficdestroys many of the macropores in thesurface 3-inch zone, but a well-struc-tured soil will usually have somemacropores deeper in the profile. The2:1 clays are much more prone to soilcompaction than the 1:1 types.

Sandy soils with> 85% sand contentexhibit sand particle-to-particle con-

amounts of silt and clay). Sandy soilsare typical of high -sand -content greens,while fine-textured types are represen-tative of pushup greens (native soilgreens), fairways, and many tees.

1. Cation exchange capacity (CEC),the ability of a soil to retain cations, ismuch higher for fine-textured soilsthan with sands. As a result, less totalsoluble salts, Na+, or B are requiredbefore CEC sites of sands are adverselyaffected compared to fine-textured soilCEC sites, and these salts start toaccumulate in the soil solution wherethey are more active. Although saltsreach adverse levels more rapidly insands, removal by leaching is also morerapid.

2. Macropores, soil pores with adiameter> 0.12mm, are much moreprevalent in sands than fine-texturedsoils. Macropores are critical for rapidwater movement into the soil surface(infiltration), through the rootzone(percolation), and beyond the root-zone (drainage). Effective leachingcannot be accomplished withoutmacropores, and macropores must bepresent throughout the soil profile.

Even a thin zone or layer with fewmacropores within a soil profile willboth limit water movement and resultin salt accumulation above this layer.Any soil layer or horizon that inhibitswater movement will be a major hin-drance to effective leaching - whetherit is at the surface (surface compaction)or subsurface (e.g., B horizon, cultiva-tion pan, buried layer from flood depo-sition of fines, etc.). Cultivation opera-tions that enhance infiltration andpercolation (deep cultivation tech-niques) are done essentially to createtemporary macropores. If the cultiva-tion holes are filled with sand, themacropores remain for a longer periodof time. Thus, turfgrass managers mustbe familiar with the entire soil profileand should "visualize" whether macro-pores exist for effective leaching downto the deep subsoil or to drain lines.

3. Clay type has a significant influ-ence on water movement. Non-shrink/swell clays (kaolinite, Fe/Al oxides) arecalled 1:1 clay types, and these do notcrack when dry or seal by swellingwhen wet. The benefits of cultivationgenerally last longer on 1:1 clays thanthe 2:1 types discussed below. Also, ahigher level of Na+ is required on 1:1CEC sites before soil structure beginsto deteriorate, usually at > 24% Nasaturation compared to > 9% Na formany 2:1 types (montmorillonite, illite).Generally, 1:1 clays are more resistant

NOVEMBER/DECEMBER 2000 17

Figure 1. Examples of salt levels throughout the soil profile. Top: Represents goodleaching conditions with adequate leaching requirement (LR) applied. Bottom:Represents what happens when insufficient water is applied in midsummer withhigh evapotranspiration (ET) conditions.

to rise by capillary action and by planttranspiration if the leaching fractionis less than ET (Table 1). Salts thenwill move back into the rootzone andstart to accumulate near the surface(Figure 1).

Capillary rise of salts will be morerapid on fine-textured soils than sandsbecause fine-textured soils containmore micropores. Other factors thatincrease capillary rise of salts are lowleaching rates, high ET conditions, anda high water table.

6. Water table location is anothersoil factor that influences salinity con-trol. Turfgrass soils often contain a layerin the profile that inhibits water perco-lation or drainage. This can create atemporary perched water table as

18 USGA GREEN SECTION RECORD

water flow is slowed or stopped whenthe wetting front reaches this layer.Salts then will accumulate above thelayer and can rise to the surface when-ever low leaching rates and/or high EToccurs. The quantity of water needed tocause net salt leaching in low-ET con-ditions may not be adequate for leach-ing under hot, dry situations (Table 1).

Subsurface layers that are 1 to 3 feetbelow the surface are often overlookedin arid or semi-arid regions whereheavy rainfall events that are sufficientto pond water up to the soil surface arerare. But, these hidden layers cancontribute to major salt accumulationso that when conditions favor capillaryrise, the resulting water has very highsalinity.

In many turfgrass soils, the layer thatlimits water percolation/drainage hasfew macropores. Cultivation depthmust penetrate completely through thelayer to be very useful for maintainingwater flow when excess water applica-tion occurs by irrigation or rainfall.

Another type of perched water tableis found in many high sand contentconstructed profiles, such as those builtwith the USGA green constructionmethod. In this case, ample macro-pores are present but sufficient water isrequired to break the perched watertension and to initiate rapid drainage orflushing of the rootzone. During sum-mer months when ET is high, saltsabove the perched water table zonemay start to rise toward the roots andsoil surface if thorough leaching is notpracticed. Prolonged drought, hightemperatures, and dry, windy condi-tions can escalate this capillary rise ofconcentrated salts.

In addition to perched water tables,sometimes the natural water tablelevel is near the surface. The capillaryfringe of semi-saturated water condi-tions above a free water table is usually2 to 8 inches for sands and 8 to 12inches for fine-textured soils. However,high ET conditions and limited leach-ing can cause salts to rise well abovethese distances over time. Capillary riseon fine-textured soils is still stronglycontrolled by climatic conditions (Le.,ET) at a depth of 2.5 to 3.0 feet andpossibly down to about 5.0 feet.

Another problem with a water tablerelatively near the surface occurs whenpoor irrigation water quality requires ahigh leaching fraction. Over time, thewater table may rise even higher andcause massive salinization of the root-zone. On sites where shallow watertables may rise, the turf manager shouldinvestigate means to lower the watertable.

7. Total pore space (pore volume,PV) of a soil also influences salt leach-ing. Soils with higher PV require morewater to leach the same quantity ofsalts.7 The PV range of sands, loams,and clays is about 35% t040%, 40% to50%, and 45% to 55%, respectively.For a soil depth of 12 inches, 1 PV ofapplied water would represent 4.6 to4.8 (sands), 4.8 to 6.0 (loams), and 5.4to 6.6 (clays) inches of irrigation. Thus,more water is required to leach fine-textured soils than sands.

Water and Irrigation Factors1. Irrigation water quality strongly

influences the quantity of water needed

pletely purged is to locate the outflowdrain line exiting the green cavity andinstall an inspection port. Drainageflow can be observed, and samplescollected and tested with the portable(EC) meter. Once the EC of the drain-age water is at or near the EC of theirrigation water, then leaching has beencompleted. Although native soils mayrequire 1 to 4 weeks to reclaim, well-drained sand constructed putting greenrootzones with perched water tablescan often be reclaimed in 1 to 3 days.

Between leaching events, additionalirrigation may be needed on a light,frequent basis until turf roots regen-erate, which may not occur on bent-grass/ Poa annua greens until coolerweather arrives.

2. Reclamation leaching differsfrom the previous maintenance LRconcept, which focused on maintain-ing salinity levels at an existing accept-able level. In reclamation, a higherquantity of water is required to decreaserootzone salinity to acceptable levels.Once this acceptable level is achieved,the LR irrigation approach (mainte-nance leaching) can be used, since itrequires less extra water. The reclama-tion approach occurs in two primarysituations in turfgrass management:a) when a seriously salt-affected soil(e.g., highly saline and/or sodic condi-tion) must be leached of excess saltsbefore grass can be established, andb) when a turf manager has not main-

= 0.0714LR= (2)5(6) - 2

which means that the LR is 7.1% more irrigation water volume than that neededto meet ET needs. Thus, if irrigation of 0.50 inches of water is required to replacesoil moisture lost by ET, an additional 7.1% or (0.50 x 0.07) = 0~035 inches ofwater would be required for a total of 0.535 inches to maintain a particularsalinity level. Itshould be noted that a more saline irrigation water with higherECwor a less-saU-tolerant grass would increase the LR.

Table 2Determination of the Maintenance Leaching Requirement (LR)

(after Rhoades6)

Concept: Once the soil salinity level in the turfgrass rootzone is at an acceptableor desirable level, the leaching requirement (LR) approach is used to maintainthis level. The "leaching requirement" (LR) is the minimum amount of waterthat passes through the rootzone to control salts within an acceptable range.A good formula to determine LR is:

LR= ECw5ECe-ECw

where ECw= irrigation water salinity (dSm-1)

ECe = threshold soil salinity at which growth starts to decline for the turfgrasson the site. Carrow and DuncanI has an extensive listing.Example: For turfgrass with a threshold ECeof 6 dSm-1and irrigation water thathas an ECw= 2 dSm-1•

water for leaching. The process depictedin Figure 1 (bottom) is initiated.

Light, frequent irrigation increasessalt accumulation in the surface zone,where most of the roots are located.Also, salts rise by capillary action intothe rootzone from: a) a high salt zonecommon in pushup greens, or b) theperched water of a USGA green that isnot adequately flushed. Injury normallyappears on the most elevated, open,and exposed greens where high ETconditions prevail due to high solarradiation and wind movement. Sincethe bentgrass/ Poa annua is now underhigh temperature stress, the salt-in-duced drought is a serious additionalstress.

By being aware of this sequence ofevents, the turf manager can apply anextra leaching irrigation every 1 to 4weeks to avoid salt accumulation. Thefrequency between leaching events willvary depending upon water quality,rootzone depth, and the threshold ECof individual turfgrass varieties. Theleaching frequency and threshold ECcan be accurately determined by use ofan inexpensive portable EC meter.10 ECat the soil surface and throughout theprofile can be monitored regularly(daily if necessary) and, as thethreshold EC is reached, leaching canbe initiated to purge the perchedwater table.

A practical method to assure thatthe perched water table has been com-

Assuming the initial rootzone salinitylevel is acceptable, when the LR isnot sufficient to maintain salt leach-ing, two adverse salt responses occur:a) first, salts applied in the irrigationwater start to accumulate within thesurface few inches, and b) capillary riseof salts from deeper in the soil andbeyond the rootzone starts to bringsalts back into the rootzone (Figure 1).Oftentimes, this zone of accumulatedsalts has a very high ECe and uponreaching the lower rootzone can in-duce rapid salinity stress. When thishappens, alleviating salinity stress(physiological drought with reducedwater uptake for transpirational cool-ing) now requires much more appliedwater than the LR amount because itis a reclamation problem (as well as aserious threat to job security).

This scenario is most often observedon high sand bentgrass/ Poa annuagolf greens irrigated with water ofmedium to high salinity. In addition,turf managers who apply water withrelatively low total salt levels (500 to600 ppm) may experience this situationunder extreme environmental condi-tions. The turf manager may be achiev-ing adequate leaching in the spring andearly summer using ample irrigation orrainfall. However, by midsummer, threeevents can impede leaching: a) hot, dryweather increases the ET and increasesthe quantity of irrigation needed just tomaintain soil moisture (Table 1);b) turfroots start to die back; and c) turf man-agers shift to light, more frequent irriga-tion which does not supply sufficient

to leach salts, with more water requiredas water salinity level increases. Theleaching requirement (LR) is theminimum amount of water that mustpass through the rootzone to keepsalts (i.e., keep salts moving) withinan acceptable range. Thus, LR is usedfor maintenance leaching where suf-ficient water is applied to maintain soilsalinity at an acceptable level.

Several methods are used to deter-mine the LRI. The method of Rhoades6

provides a good approximation and isbased on the irrigation water salinitylevel (ECw, dSm-1) and grass salinitytolerance using the threshold ECe (thesoil salinity, ECe, at which growthdeclines compared to growth undernon-saline conditions), where (seeTable 2):

LR = ECw = percent extra5ECe - ECw water above ET

to leach salts

NOVEMBER/DECEMBER 2000 19

r--~,,,------;,-----------------------'Table 3

Determining Reclamation Leaching Needs(adapted after Rhoades and Loveday7)*

The following equation is used:Dw= k x Ds x ECeo- ECw

ECe-ECwwhere: Dw = depth of water to apply for leaching (feet)

Ds = depth of soil to be reclaimed or leached (feet)ECe = final soil salinity desired. This value is usually the

threshold ECe for the turfgrass being used or somewhatless than the threshold ECe

ECeo = initial or original soil salinityECw = salinity of irrigation water used for leachingk = factor that varies with soil type and water application

method (efficiency of irrigation system)For sprinkler irrigation applied by pulse irrigation to allow drainage rangingfrom 1 to 2 hours (sands) to 2 to 8 hours (fine-textured soils) between a pulseirrigation event until the total quantity of water is applied:k = 0.05 for high sand content each with> 950/0sand content

(Le., < 5% silt + clay content)k = 0.10 for all other soilsFor continuous ponding or continuous sprinkler irrigation applied to keepthe soils saturated during leaching:k = 0.45 for organic soilsk = 0.30 for fine-textured soilsk = 0.10 for sandy soilsExample: A high-sand-content golf green with an initial soil EC = 8.0 dSm-1

(Le., ECeo)and the turf manager desires a final soil EC = 2.0 dSm-1 (i.e., ECe).The irrigation water used for leaching has an ECwof 1.50 dSm-1and the desiredleaching depth (Ds) is 16 in. to reach the drain tile, where 16 in. = 1.33 ft.

D = k x D x ECeo- ECww s ECe_ ECw

= 0.86 ft. of leaching water= IDA inches of water

• If the leaching water quality was better (for example, ECw= 1.0 dSmC1),

then: Dw = 5.6 inches of water.• If the final salinity level (ECe) was higher because of a more salt-tolerant

grass (for example, ECe = 4.0 dSm-1), then: Dw = 2.6 inches of water.• If the green was a pushup green with < 95% sand where k == 0.10, then:

D,w = 20.7 inches of water.

*Adjustments in the k value for high-sand-content greens are based on experience ofCarrow, Huck, and Duncan.

tained an adequate LR and the root-zone has increased in salinity to severelevels. This latter situation is mostlikely to occur during hot, dry summerswhen ET rates have increased, but thetotal water applied for ET + LR has notbeen adjusted to keep up with actualET. Cool-season turfgrasses subjectedto this sudden and intense salinityshock (a combination of drought, hightemperature, and greater wear stressesfrom slower growth, all induced bysalts) often do not survive. The take-home lesson for this type of stress isprevention by adequate, continualapplication of sufficient LR water tokeep salts moving downward and awayfrom the turf root system.

Reclamation leaching needs can beestimated by the procedure presentedby Rhoades and Lovedai (Table 3).This procedure takes into considera-tion: depth of leaching, desired ECe,current or initial ECe leaching waterquality, and soil type.

Once the depth of water (Dw) re-quired for leaching is determined interms of "inches of water to apply,"then the influence of rainfall canbe factored into the situation. Forexample, in Table 3, the situation indi-cates that IDA inches of water would berequired for reclamation where theleaching water has an ECw= 1.5 dSm-1•

If an ECw of 0.10 dSm-1 is used forrainfall, then the Dw = 3.32 inches ofrain to achieve the same degree ofleaching as IDA inches of ECw = 1.5dSm-1 irrigation water.

When comparing the Dw leachingneeds using an irrigation water withECw= 1.5 dSm-1 quality versus rainfall(Table 3), it is clear that water qualityhas a similar important influence onreclamation leaching and on mainte-nance LR. A second implication is thatturfgrass managers should use theirrainfall periods to maximize leaching.For example, following a good rainfallperiod when substantial salt leachinghas occurred and has adequatelyleached salts below the rootzone, donot stop a maintenance LR program toconserve water. Instead, the LR frac-tion should be continued to preventsalts from rising back into the rootzone.If resalinization of the rootzone isallowed to occur, a reclamation leach-ing with substantially more water isrequired to achieve what the rainfallevent had accomplished.

In the previous discussions on main-tenance LR and reclamation leachingneeds, the emphasis has been on totalsoluble salts and their removal. Nor-

20 USGA GREEN SECTION RECORD

mally, a site contains an array of solublesalts. However, if the water quality testand soil tests indicate that CI is thedominant salt ion, the amount of waterrequired for leaching this ion is lessthan for other total soluble salts due tothe high mobility of Cl. As an approxi-mation, leaching needs could be re-duced by about one-third for a trialperiod and then readjusted based onthe results. Reduced leaf tip burnsymptoms on landscape plants wouldbe a good indication of your leachingsuccess.

A second means of estimating recla-mation leaching is noted in Table 4.This method considers soil type, per-cent of total salts to be leached, anddepth of leaching. It does not, how-ever, take into account leaching waterquality.

3. Irrigation scheduling for effectiveleaching. A highly efficient, well-zonedirrigation system is a priority for effec-tive leaching of salts. The method ofwater application, even with a well-designed system, though, influences thequantity of water required for effective

until the desired quantity of water isapplied. Runoff from the soil surface isminimized. Generally, the time intervalbetween pulses is ~ to 1 hour (sands),1 to 2 hours (loamy sands, sandyloams), 2 to 4 hours (loams), and 3 to6 hours (clays). A good surface culti-vation program, to maintain adequatewater infiltration without runoff, willreduce the time required between irri-gation pulses.

With this type of irrigation, waterflow within the soil is primarily unsatu-rated flow, which moves as a moreuniform wetting front downwardthrough the soil profile. Water move-ment occurs more in the micro poresthan in the macropores; therefore,leaching is more effective. Wettingagents often aid in maintaining a moreuniform wetting front for leaching. Infact, one-third to one-half the water isrequired for pulse irrigation versusheavy continuous irrigation. A light,continuous rainfall can simulate pulseirrigation as long as the rainfall rate isless than the saturated water hydraulicconductivity of the soil (i.e., the infil-tration rate when the soil is saturated).

On high sand content greens, thesurface 1- to 2-inch zone is where thewater movement rate generally is thelowest. If a good maintenance LR pro-gram is followed, such that salts havenot been allowed to accumulate in thesurface, periodic surface cultivation tokeep vertical "macropores" or holesopen across this zone is beneficial toallow rapid water infiltration duringheavier rains. Also, maintaining highinfiltration rates across the surfacezone makes irrigation programmingeasier, and a pulse approach may not benecessary under these conditions.

If salts are allowed to accumulate atthe surface, however, due to insufficientLR, then a pulse approach is necessary.Attempting to implement a heavyleaching event will result in most ofthe water flowing through the cultiva-tion holes that penetrate through thesalt-troubled surface zone. A pulseapproach is better because it allowsleaching between holes where salt hasaccumulated.

4. Irrigation scheduling to avoidsoggy soils is a challenge, especiallyfor fine-textured soils. When saltsaccumulate in the surface zone and/or deeper in the rootzone to a pointwhere reclamation leaching is required:a) a good surface cultivation program isnecessary to allow rapid infiltration; b)deep cultivation is needed to allowwater percolation. Also, this will allow

(.35)(12) = 4.204.565.045.406.00

Inches of Water Per12 Inches Soil to Fill PV ~

flow or near-saturated conditions,water flow is primarily through thelarger macropores, and water does noteffectively leach between the macro-pores, i.e., within soil aggregates ormicropore areas. On high sand contentsoils, which do not form aggregates butare more single grain sand in structure,saturated flow works better than onfine-textured soils.

• Pulse irrigation occurs when wateris applied in increments of 0.20 to 0.33inches, with a time interval before thenext pulse, and this cycle is repeated

PV(%)

3538424550

Table 4Estimated Reclamation Leaching Needs Based on SoillYPe*An alternative to determining "Reclamation Leaching Needs"by the methods of Rhoades and Loveday7 presented in Table 1

is based on the soil total pore space or pore volume (PV)

Basic Relationships:

SoillYPe

Sand « 95% sand content)Loamy sandSandy loamLoamsClays

PV Equivalent of Water Required to Leach 70% of Total Soluble Salts:Sand « 95% sand content) = 0.70Loamy sand = 1.00Sandy loam = 1.00-1.25**Loams = 1.50-2.50**Clays = 2.50-4.00**

Example: A high-sand-content golf green with leaching desired to a depth of16 in. to reach the tile lines. PV = 35% = 4.20 in. of water per 12 in. of soildepth, thus for 16 in.:

(4.20 in. of water) x ~~ = 5.60 in. of water to fill the PV to 16 in.

For a high-sand-content green (> 95% sand), a PV equivalent of 0.70 is usedto achieve approximately 70% leaching of total soluble salts, therefore:(5.60 in. of water)(O.70) = 3.92 in. of water should be applied to achieve

70% leaching of salts across the 16 in. soil depthIf only 50% salt leaching is required, adjust the PV equivalent, for example:

(5.60 in. of water)(O. 70 x ~g~)=2.80 in. of water

If a pushup green is present, then PV equivalent becomes 1.25 (assuming asandy loam, 2:1 clay) and the inches of water per 12 in. soil depth is 5.04 in.Then, for 70% leaching of salts:

(5.04 in. of water) x ~~ = 6.72 in. of water to fill the PV to 16 in.

(6.72 in. ofwater)(1.25) = 8.4 in. of water applied

*Rhoades and Loveday7. PV equivalent values are adjusted by Carrow, Huck, andDuncan based on experience.

**For 2:1 shrink/swell cracking clays, use the higher value, and for 1:1 non-crackingclays, use the lower value.

leaching.4,7 Potential means to applywater for reclamation or maintenanceLR needs are:

• Heavy continuous water applica-tion by sprinklers where the soil isessentially saturated or near saturationthroughout the leaching period. Thiswould be similar to soil conditions thatcould occur from heavy rainfall orcontinuous ponding of water abovethe soil surface. Water application byany of these methods requires the mostwater to achieve leaching, especially onfine-textured soils. Under saturated

NOVEMBER/DECEMBER 2000 21

better water penetration during heavyrains, and c) additional drainage, suchas tile lines, may be needed to keep thesalts moving away from the rootzone.

Reclamation leaching will normallyresult in temporary soggy conditionsfor fine-textured soils due to the inten-sive nature of leaching. Thus, the bestway to avoid soggy soils is to avoidbeing in a reclamation condition. Thisis achieved by a good routine mainte-nance LR program that continuouslykeeps salts leached out of the rootzone.Maintenance LR programs requiremuch less water than reclamationsituations and therefore are less likelyto create waterlogged or soggy soils.

Following are guidelines for sched-uling routine irrigation events on fine-textured soils that include the LR aswell as ET replacement components.

• When the irrigation water is mod-erate to high in salinity, schedule irri-gation so that the bottom one-thirdof the rootzone is subjected to onlymoderate moisture stress. Grassesextract water primarily from the surfacetwo-thirds of their rootzone until themoisture in this zone becomes limited.Since salts concentrate in the soil solu-tion with soil drying, sites irrigated withsaline water should be irrigated morefrequently (i.e., with less dry-down toinduce moisture stress) than non-salinesites. Thus, if a non-saline area wouldreceive irrigation every 7 days withwater to replace the 7-day ET loss, thena saline site may need to be irrigatedon day 5, with the 5-day ET replace-ment water plus the additional LR.

• When irrigation is applied, pulsescheduling is preferred to achievebetter leaching and avoid soggy soils.The interval between irrigation pulseswas noted previously as 2 to 4 hours(loams) and 3 to 6 hours (clays), withthe longer interval required on com-paced sites or Na+-affected soils (i.e.,sodie soils or soils starting to becomesodie). Such intervals may only allow2 to 3 pulse applications per evening at0.20 to 0.33 inches per application.Thus, it may require two or more con-secutive evenings to apply sufficienttotal water (i.e., ET + LR). Anotherpossibility is to schedule pulses duringthe daytime when the golf course isclosed (often Mondays) as well asduring the evenings. For example, fromSunday evening through early Tuesdaymorning would provide a 32-hourperiod for pulse irrigation. Considera-tion for traffic restrictions (golf cars andmaintenance equipment) in fine-tex-tured soil areas (fairways and roughs)

22 USGA GREEN SECTION RECORD

may be necessary for 1 to 3 days fol-lowing a heavy leaching.

• The use of the LR fraction as partof normal irrigation should be a con-tinuous, routine practice, especially:a) when the irrigation water quality ishigh in total soluble salts or Na, b) onfine-textured soils but particularly 2:1clay types, and c) on any sodie or pre-sodie soil. A common reason for re-salinization of rootzones or ineffectiveleaching of total salts/Na is the elimi-nation of the LR application after arainfall period, followed by redistribu-tion of salts.

• Application of the LR should startearly in the growing season, if soilsalinity is at an acceptable level,9Ifnot,then reclamation leaching should beinstituted until the soil salinity levelbecomes acceptable. Thereafter, theLR application should be initiatedand maintained. This will prevent theadvent of salts accumulating to harmfullevels during high-ET summer monthswhen reclamation leaching is verydiffieult.

5. Irrigation water quantity obvi-ously influences leaching effectiveness.Up to this point, we have noted that theIrrigation Quantity (IQ) for routineirrigation consists of replacement ofsoil moisture lost by evapotranspiration(ET) plus LR. However, a third factorinfluences total irrigation needs. Thisfactor is nonuniformity (efficiency) ofthe irrigation system. Water applicationrate must be increased by a SchedulingCoefficient (SC) to account for non-uniform water application. Thus, totalirrigation quantity required includes:

IQ = SC(ET + LR) = inches ofirrigation waterto apply

where the SC may be a factor such as1.1 to adjust for non uniformity of theirrigation system.

On turfgrass sites receiving salineirrigation water, identifying a correct IQand adjusting the value as the weatherchanges is essential for good salinitymanagement and high turfgrass per-formance. Once an acceptable soilsalinity has been achieved, the pri-mary cause of resalinization is in-adequate water application (i.e., IQ).Turfgrass managers are strongly en-couraged to think in terms of quantityof water applied rather than minutesof irrigation time. Salt leaching re-quires an adequate quantity of waterand only by monitoring the quantity ofapplied water can there be confidence

of achieving long-term maintenanceleaching.

HuckS presents an excellent discus-sion on irrigation system efficiencyand design considerations. Nonuni-formity of water application may resultfrom several factors, including: a) im-proper sprinkler head spacing forwind and water pressure conditions,including hydraulic losses from frictionand elevation differences; b) incorrectsprinkler or nozzle selection; and c)poor system maintenance such asleakage, sprinkler/nozzle wear, andmixing of nozzles. Adjustments in thesefactors during design and, if necessary,after installation can improve deliveryefficiency and enhance leaching ofsalts.

Where irrigation uniformity is lack-ing and cannot be improved due to apoor irrigation system, the use of port-able hose-end sprinklers can be aneffective method to apply additionalwater in areas lacking coverage. Ultra-low precipitation rate models are mosteffective. They are normally placed inthe problem area and allowed tooperate from dusk until dawn.

Site-specific water management isimportant for salinity managementand to avoid waterlogged areas. Someexamples are: a) dual irrigation systemsfor greens and the surrounds. The idealsystem would include the ability toirrigate greens with a different, higher-quality water source, but dual systems,even with the same water source, allowfor better scheduling. b) Mounds,berms, bunker tongues, and steepslopes present a problem. West- andsouth-facing exposures in the northernhemisphere are especially vulnerable tohigh-ET losses and salt accumulation.On facilities with highly saline irriga-tion water, irrigation designers shouldconsider how to effectivelyirrigate wateron these peripheral areas. c) On fair-ways with south-facing slopes whereET is normally greater, zones should bedesigned to accommodate this need.Portable sprinklers can also be usedeffectively to specifieally leach puttinggreen surfaces and avoid floodingbunkers or saturating green surroundsduring the leaching process.ll

6. Infiltration, percolation, anddrainage of applied water is essentialfor salt leaching. The soil profile oneach site on a golf course should beassessed in terms of any barriers towater movement, starting with infiltra-tion. Carrow and Duncan 1 present themost common soil physical problemson sandy and fine-textured soils that

The effects of high salt levels in the irrigation water are obvious on this pine tree.

impede water movement downwardthrough the whole profile. Appropri-ate cultivation, soil modification, anddrainage operations should be con-ducted to ensure that water (and salts)are able to move downward. Drainageand salt disposal options should also beconsidered as part of an overall watermanagement plan. 1

7. Water and soil amendments needto be considered to ensure good waterinfiltration and to facilitate alleviationof sodic conditions on sodic sites. Thevarious situations requiring irrigationwater treatment have been discussed byCarrow et aF and Carrow and Duncan 1.

Proper amendment selection (for waterand soil), application method, andrates are all very important, especiallywhen sodic conditions might occur orare already present. Due to the detailednature of these subjects, they are be-yond the scope of this article. However,treatment of irrigation water or the soilwith amendments will be ineffective foralleviating salt problems unless a goodleaching program is followed.

Grass TypeSalinity management is influenced

by the type of grass, salt types present,soil factors, and water/irrigation factors.

1. Salinity tolerance of the grass isthe most important influence of grassspecies/cultivar in salinity manage-ment. As demonstrated in the examplein Table 1, the LR is influenced by thesalinity level the grass can tolerate. Thethreshold ECe is used as a guide and isdefined as the soil salinity at whichgrowth starts to decline compared to anonsaline condition.1 Grasses withmoderate to very high salinity tolerancecan be irrigated to maintain the soilsalinity at greater than the thresholdECe, perhaps at ECe of 25% or 500/0growth reduction. The grass vigor andability to withstand wear from trafficshould be considered in selecting theappropriate maintenance ECe.

2. Turfgrass rooting depth impactssalinity management. Provided thatadequate soil moisture is present in thelower one-third of the root system toavoid salt concentration (i.e., soilmoisture is about field capacity in thiszone), turfgrass growth is related toaverage rootzone ECe,regardless of thesalt distribution with in the rootzone.Thus, when monitoring soil ECe bydepth within the rootzone, the averageECe is the value used to compare withthe turfgrass salinity tolerance levelselected, such as ECe for 25 % growthreduction.

Especially with high-saline irrigationwater, irrigation events should bescheduled to avoid depletion of soilmoisture within the lower one-third ofthe rootzone. Otherwise, serious saltstress will occur. Irrigation events needto be scheduled more often than on asimilar nonsaline site, with the IQdependent on ET losses since the lastirrigation plus the LR. Also, a deep-rooted turfgrass will allow for moredays between irrigation events than ashallow-rooted grass.

Rooting depth determines the root-zone that must be leached by the LR.

This is the Ds (depth of soil) to be re-claimed or leached in Table 2 and theleaching depth in Table 3.

Monitoring Soil SalinityMonitoring soil salinity by soil depth

is critical for assessing the success of asalinity management program.1,4 Thesoil depth for monitoring is determinedby the rootzone depth. Soil ECevalueswithin the surface one-third and bot-tom one-third of the rootzone are themost important. Soil sampling proce-dures and methods for monitoring fieldsalinity are given by Carrow and

NOVEMBER/DECEMBER 2000 23

A combination of poor water quality and poor irrigation system distributionhas caused severe salt stress injury on this green and surrounds.

Duncan1 and Hanson et a1.4 On siteswith an ongoing salinity problem, ob-taining instruments to determine soilsalinity in-situ should be considered.J. D. Rhoades of the u.s. SalinityLaboratory has developed two proce-dures4: a) the four-electrode salinityprobe, which can be used to measuresalt levels at different depths, and b) theelectromagnetic conductivity meterfor rapid surface measurement, includ-ing down to a depth of 3 to 4 feet.VermeulenlO also discusses an inexpen-sive conductivity meter useful for bothmonitoring drainage water and soilsalinity in the field.

Summary

Development of a salinity manage-ment program requires the considera-tion of a number of soil, water, andgrass factors. Leaching of salts is the

24 USGA GREEN SECTION RECORD

most important component of anysalinity management program. Unlesssalts are consistently leached from therootzone, resalinization will occur fromirrigation salt additions and capillarymovement from below the rootzone.The peak time of year for massive re-salinization and the accompanyingdecline of turf performance is oftenmid- to late summer. This is the leastfavorable time to experience salinitystress and the most difficult time toinstitute reclamation leaching. The bestoption for managing salinity is a con-tinuous, routine maintenance leach-ing program using an adequate LR.The most common reason for notapplying sufficient irrigation watervolume for leaching of salts is under-estimating the daily ET requirement forreplacement of soil moisture lost by ET,rather than underestimating the LRfraction of total irrigation needed.

Also, understand that many of thescientific principles outlined in this textwere first researched and developed foragricultural crop production situations,where daily equipment and pedestriantraffic, as well as maintaining a playingsurface, can be controlled or are not ofconcern! Therefore, golfers need tounderstand that in implementing asalinity control program, playing con-ditions will need to be compromisedfrom time to time.

ReferenceslCarrow, R. N., and R. R. Duncan. 1998.Salt-affected turfgrass sites: assessment andmanagement. Ann Arbor Press, Chelsea,Mich.2Carrow, R N., R R Duncan, and M. Huck.1999. Treating the cause, not the symptoms:irrigation water treatment for better infil-tration. USGA Green Section Record.37(6): 11-15.3Duncan, R R, R N. Carrow, and M. Huck.2000. Understanding water quality andguidelines to management. USGA GreenSection Record. Vol. 38(5):14-24.4Hanson, B., S. R Grattan, and A. Fulton.1999. Agricultural salinity and drainage.Div. of Agric. and Nat. Res. Pub. 3375. Univ.of Calif., Davis, Calif.SHuck, M. 1997. Irrigation design, rocketscience, and the SPACE program. USGAGreen Section Record. 35(1):1-7.6Rhoades, J. 0. 1974. Drainage for salinitycontrol. In J. van Schilfgaarde (ed.). Drain-age for Agriculture. Agronomy MonographNo. 17. Amer. Soc. of Agron., Madison, Wis.7Rhoades, J. D., and J. Loveday. 1990.Salinity in irrigated agriculture. In B. A.Stewart and 0. R Nielson (eds.). Irrigationof Agricultural Crops. Agronomy No. 30.Amer. Soc. of Agron., Madison, Wis.8Skaggs,R. W, and J. van Schilfgaarde (eds.).1999. Agricultural Drainage. Agronomy No.38. Amer. Soc. of Agron., Madison, Wis.9Yenny, Reed. 1994. Salinity management.USGA Green Section Record, Vol. 32(6):7-10.lOVermeulen,P. H. 1997. Knowing when toover-irrigate. USGA Green Section Record.Vol. 35(5):16.llGross, P. 1999. Flood your greens - notyour bunkers. USGA Green Section Record.Vol. 37(3):26.

DR. RON R DUNCAN (turfgrass genetiCs/breeding, stress physiology) and DR.ROBERI' N. CARROW (turfgrass stressphysiology and soil physical and chemicalstresses) are research scientists in the Cropand Soil Science Department, University ofGeorgia, Georgia Experimental Station atGriffin. MIKE HUCK is an agronomist withthe USGA Green Section Southwest Region.