Optimizing soil pH and nutrient levels are the primary objectives of soil management for turf areas. The various inorganic and organic nitrogen sources are described

Deputy, James

Hensley, David

Tavares, James

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Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June30, 1914, in cooperation with the U.S. Department of Agriculture. Charles W. Laughlin, Director and Dean, Cooperative Extension Service, CTAHR, Universityof Hawaii at Manoa, Honolulu, Hawaii 96822. An Equal Opportunity / Affirmative Action Institution providing programs and services to the people of Hawaii withoutregard to race, sex, age, religion, color, national origin, ancestry, disability, marital status, arrest and court record, sexual orientation, or veteran status.Cooperative Extension Service Turf ManagementMay 1999TM-7Water applied to supplement rainfall is essential tomaintain attractive lawns in most parts of Hawaii.Much development in Hawaii occurs in areas that are con-sidered true deserts—they receive less than 10 inches ofrainfall per year. Even in areas receiving abundant naturalrainfall, its seasonal distribution is sometimes uneven andnot adequate to maintain uniformly green grass with goodvigor throughout the year. Supplemental irrigation in theproper amount is necessary to prevent lawns from turningbrown or dying from moisture stress.Watering is one of the most often abused and leastunderstood aspects of turfgrass culture. Improper water-ing is wasteful, costly, and damaging to the grass and land-scape. As Hawaii continues to grow and develop, wateruse for turf and landscape plantings will become more andmore restricted. Our water use must be more efficient andfollow the principles of good water management. In thefollowing, we describe three basic steps to an efficientwatering program.1. Determine when water is neededThe worst possible irrigation program is to water turf dailyfor 5–10 minutes. Unfortunately, this is the most commonmethod used by homeowners and many professionals.Light, daily irrigations encourage shallow rooting, therebyreducing the amount of soil the turf has available for waterstorage. The grass depends on the daily drink and wilts orbrowns very quickly if it does not receive it. Brief dailyirrigation encourages disease problems, weed invasion,accumulation of thatch, and soil compaction. Shallowrooted turf is also more prone to traffic injury.A newly seeded or planted lawn is the exception to therule of deep watering. For the first few weeks after plant-ing, water frequently and lightly to encourage seed germi-nation or good growth of stolons or sprigs. As the lawnbecomes established, water less frequently and for longerperiods.There is no single irrigation schedule that will meetthe need of every landscape. Timing of waterings dependson the site, soil type, management practices (mowing andfertilizer application), season of year, and type of turf. Anefficient and economical way to irrigate a lawn is to applywater at the first signs of water stress. Research has shownWatering Lawns1Department of Horticulture,2Cooperative Extension Service, Kahuluithat turf watered at the first signs of visual wilt used 33percent less water. Waiting too long, however, can causebrowning or permanent damage. The initial signs of stressmay include the following:• Color changes, and bluish-gray areas can be seen in thelawn.• Footprints or tire tracks remain in the grass for severalhours after they are made.• Many leaf blades are rolled or folded in half.• A soil sample from the root zone feels dry.Soil moisture sensors can be used to determine water stress.A tensiometer measures the soil moisture tension (howstrongly the soil holds water against plant uptake) and canbe used to determine when to irrigate. By monitoring theturf and the tensiometer, the soil moisture tension level atwhich wilting and drought stress symptoms appear can bedetermined. This will be relatively constant, regardless ofseason. By irrigating just before the symptoms would havebecome evident, water is applied only when it is needed.Research has shown that tensiometer-scheduled irrigationused half as much water as a rigid schedule.An easy method to calibrate an automatic irrigationsystem is simply to turn off the irrigation system and notethe number of days required for stress signs to show in theturf. Adjust the timer to irrigate one day before stress symp-toms appear. For example, if wilting and stress are evidentafter four days without water, set the system to water ev-ery three days. The time for stress symptoms to appearwill vary with exposure to wind and sun. Evaluate and setthe timer for different irrigation zones individually, andallow for seasonal variations.The best time of day to water a lawn is early morning,when the wind is less likely to alter distribution patterns,evaporation is minimal, disease development is minimized,and water pressure is usually greater. Watering during theheat of the day wastes water because evaporation rates arevery high. Watering in the evening results in water stayingon the grass all night, encouraging the spread of fungaldiseases. Avoid watering in the evening.David Hensley1, Jay Deputy1, and James Tavares2TM-7 Watering Lawns CTAHR — May 199922. Determine how much water should be appliedThe amount of water absorbed at any one time varies withthe amount of water present in the soil, the water-holdingcapacity of the soil, and the soil’s drainage characteristics.An efficient irrigation wets only the root zone, does notsaturate the soil, and does not allow water to run off.Water enters a dry soil more rapidly than a wet soil.This is particularly true of heavy clay soils, where 1 inch ofwater may take less than an hour to soak in when the soil isvery dry, but as much as 5 hours when it is wet. Once thesurface soil is saturated, water movement into the soil (per-colation) depends on soil texture. Soils vary in texture fromsandy to loamy to clayey. Soil texture determines both therate at which water moves into the soil and how the water isheld in the soil. Water moves rapidly into sandy soils, buttheir ability to store plant-available water is limited com-pared to loams and clays. Therefore, sandy soils need to beirrigated more frequently. Clayey soils, in general, absorbwater slowly and hold relatively large amounts of water,although much of that water is held so tightly that plantscannot absorb it. Some of Hawaii’s clay soils, particularlyin the rainier areas, are an exception to the general rule:they are well aggregated, and water moves through themrapidly. The soil type and location will therefore greatly in-fluence when and how much water should be applied dur-ing an irrigation.Information on soil characteristics can be obtainedfrom soil survey reports of the islands, but much of whatyou need to know about your soil can be determined by asimple experiment. Push a can with both ends removedinto the soil and observe the time it takes for water pouredinto the can to enter the soil. Observe this both when thesoil is dry and when it is wet. Percolation through a moistsandy soil can be as rapid as 2 inches per hour, 10 timesfaster than through a heavy clay soil. One inch of waterapplied to a moist sandy soil may be absorbed in a halfhour, compared to 2–3 hours for a moist loam or clay-loamand 5 hours for a moist heavy clay that is not of the free-draining type.Plant roots generally grow in the upper 12–24 inchesof soil. This area, called the root zone, is the plant’s onlysource of available water. Sandy soils hold about 1 inch ofplant-available water in the top 12 inches of soil. Loamswill hold about 2–21⁄2 inches of plant-available water in theupper 12 inches. The percolation rate of a soil is the rate atwhich water drains through it. Overwatering can saturatethe root zone, leading to deep percolation, where waterdrains below the root zone and is lost. Deep percolationcan leach fertilizers and other chemicals from the root zoneinto the groundwater. Most of the water losses in landscapeirrigation occur through deep percolation, which cannot beseen and is not easily measured. Many landscape managersmistakenly attempt to overcome poor uniformity of waterinfiltration by applying more water than is necessary, sothat an adequate amount is received at the driest location.This practice is the leading cause of deep percolation.Generally, Hawaii turfgrasses require no more than 3⁄10inch of water per day in mid-summer and about 1⁄5 inch orless in the cool winter months. Plant water use is also higherin hot, dry areas than in cool, high-elevation areas. Underextreme conditions, water use can be as high as 2⁄5 inch ofwater per day. One inch of water is equivalent to 620 gal-lons of water for each 1000 square feet of lawn. The aver-age lawn will therefore require 5000–7000 gallons of wa-ter per 1000 square feet per month. Grasses use much lesswater during seasons when they are not actively growing.A simple irrigation schedule would be to apply 3⁄4–1inch of water at the first visual signs of wilt. Typically, thiswill require two or three waterings per week during sum-mer and fall. Watering too much reduces root growth andincreases disease problems for turf and landscape plants.To determine the application rate of the irrigation sys-tem, measure the amount of water applied by placing sev-eral straight-sided cans in the sprinkler pattern. Run thesystem for 15 minutes and measure the depth of the waterin each can. Calculate the amount of water the system ap-plied in one hour by multiplying the measurement by 4.The uniformity of the coverage can also be determined inthis manner.Many sprinklers and irrigation systems apply waterfaster than the soil can absorb it. Water is wasted throughsurface runoff when the amount of water applied exceedsthe amount entering the soil. Runoff from home and com-mercial landscapes also carries away nitrogen and pesti-cides, making it a potential contributor to non-point waterpollution.Infiltration (absorption of water into the soil) and run-off potential can be determined by running the irrigationsystem or sprinkler and observing how long it takes forrunoff to occur. Irrigating longer than that time will bewasteful. Runoff can be controlled by changing the size ofthe sprinkler heads or the application method to reduce therate of application, or by reducing the length of time thatthe system operates. It may be necessary to irrigate a lawnor a zone for several short periods during the day to allowsufficient time for the desired amount of water to infiltrateinto the soil without runoff. Core-aerating the turf with amachine that removes small plugs of soil greatly improvesthe water infiltration rate into compacted or clay soils andturf with thatch.Irrigation with brackish water requires some special-ized watering techniques. Consult an expert if you are us-ing brackish, non-potable, or reclaimed water to irrigateyour lawn.3TM-7 Watering Lawns CTAHR — May 1999The impact or impulse head shoots water out in a pulsating action. Some have anadjustable screw or paddle that breaks up the water jet stream and disperses thewater pattern. The head can be set to water a full or partial circle. This type ofsprinkler is best for large areas and accurately distributes water when placed in anoverlapping triangular pattern.The traveling sprinkler usually has a whirling-type head and the travelingaction can cover a large area without assistance. The path is guided by hose place-ment, which can easily be manipulated for large, irregular lawn shapes. Levelground and an overlapping pattern are required for even water distribution. Thistype is not suited for newly seeded lawns or other situations where soft soil con-ditions can lead to a stuck sprinkler.The whirling head is good for watering tight locations. It deposits largeamounts of water in a short period of time and must be moved often. Use a 50percent overlapping pattern, because most of the water is deposited close to thesprayer head.The stationary or fixed-spray head is usually a circular or square pattern.Water is applied in irregular patterns even with overlapping moves, making itdifficult to water large areas uniformly. It is best for spot watering in tight loca-tions. It deposits large amounts of water in a short period of time and must bemoved frequently.Oscillating sprinklers deliver water in a rectangular pattern and deposit muchof the water in the middle of the pattern near the sprinkler head. It is difficult toachieve even distribution on large areas with this type. The pattern can be ad-justed to cover smaller rectangular areas and other tight locations.The perforated-hose sprinkler is a flat, pin-holed hose that sprays fine streamsof water and may require several moves to uniformly cover a medium-sized area.Water delivery is slow, which is good for hard-to-wet locations. The hose can bemanipulated to water irregular areas and long, tight areas along a house or walk-way. It can be placed under and around dense shrubs to reach hard-to-water areas.Types of hose-end sprinklers3. Determine how water is to be appliedThe most common way of watering lawns is by overheadirrigation. The least expensive way to apply overhead irri-gation is a sprinkler on the end of a hose. Impact, oscillat-ing, and some fixed-type sprayers can be adjusted to vari-ous spray patterns. Rotary, fixed,and perforated-hose sprayers haveonly one pattern, which can beadjusted in size by varying thewater pressure. Overhead sprin-klers can be connected in tandemor series to expand the area ofcoverage from a single water out-let. Some degree of automationcan be obtained by attaching abattery-operated timer at the water outlet (at left, below).If overhead hose-end sprinklers are the primary sourceof water in hot, dry areas, the irrigation system often re-quires considerable time and attention to maintain a qual-ity lawn. Also, with the exception of the perforated-hosetypes, hose-end sprinklers often apply water much fasterthan most soils in Hawaii can absorb it, and there is poten-tial for run-off and waste of water.In-ground, automatic systems are expensive to install,but if they are properly installed and programmed they canmaintain a higher quality lawn with less work and less wasteof water than overhead, hose-end systems. In-ground sys-tems require regular maintenance and close attention totheir settings. Most problems, including wasted water, thatoccur with automated systems are due to the operatorsIllustrations courtesy of L.R. Nelson CorporationTM-7 Watering Lawns CTAHR — May 19994rather than the systems. For example, an attempt to pro-duce a showcase lawn can lead to over-irrigation. Incor-rect timer settings lead to water being applied at the wrongtime of day. Failure to modify settings to compensate forchanging water needs and precipitation can under-applyor waste water. Operators usually set each zone to run forthe same length of time, although adjusting the run-timefor individual zones will often solve some watering prob-lems. Automatic systems that are carelessly set and moni-tored are conspicuous to observers, leading them to a badimpression of the level of management skill and social re-sponsibility not just of the system’s operator but, by exten-sion, of the household, business, or agency occupying thegrounds. To ensure proper functioning of an automatic, in-ground sprinkler system, inspect the following aspects ofthe system frequently.• Check sprinkler heads for even spray pattern, over-throwonto paved areas, and direction of spray.• Check for damaged sprinkler heads and replace leakingones. Check them after mowing and other operationsthat can result in damage.• Check the time and settings on the clock-controller andadjust them for seasonal differences.• Do not mix sprinkler head types within the same zone.• Make sure the system irrigates uniformly.Tips on water conservationMuch of the water used around the house is for outsideuses. An efficient watering program for turfgrass combinesproper mowing height and moderate levels of fertilizationto produce a superior lawn. Turf that is allowed to growtoo tall before mowing will have an increased water re-quirement. For effective water conservation, adjust mow-ers to the higher end of the optimum mowing height rangefor your turf, and keep the blades sharp. Mow frequentlyso that not more than one-third of the leaf blade is removedin a mowing. To increase water and air movement into thesoil, core-aerify compacted soils and de-thatch heavilythatched turf. This is best done in the cooler seasons; inmid-summer, coring may cause excessive drying of the soil.Maintain proper fertilization. Adequate levels of po-tassium apparently reduce the tendency of turfgrasses towilt. By using slow-release fertilizers, nitrogen will not washaway as quickly as it may with soluble fertilizers. Applyonly enough nitrogen to support the desired level of growth.Operate automatic irrigation systems for maximumefficiency. Use a “rain-out” to shut the system off auto-matically if it is raining. These devices are inexpensiveand can be adapted to almost any automatic irrigation sys-tem. Set the duration of irrigation for different sprinklerzones to reflect real water needs and soil conditions, ratherthan setting all zones for the same amount of time. Avoidwatering during the hottest part of the day or late in theevening. Move portable sprinklers frequently enough toavoid puddles and run-off.Turf’s resistance to droughtMany people believe that a drought-tolerant grass requiresless water. Drought tolerance is a plant’s ability to surviveextended periods of moisture stress. If a grass with thisability is to be maintained in an attractive condition, it willneed about as much water as a grass that is not considereddrought tolerant. Water use rates of the various grassescommon to Hawaii lawns do not differ greatly. Droughttolerance does become important, however, during peri-ods of water use restrictions. On Oahu, Maui, and some-times elsewhere in Hawaii, water use restrictions are be-coming more of a reality.Mention or display of a trademark, company, or proprietary namedoes not constitute an endorsement, guarantee, or warranty bythe University of Hawaii Cooperative Extension Service or its em-ployees and does not imply recommendation to the exclusion ofother suitable products or companies.See also CTAHR publication L-10, Using tensiometers for mea-suring soil water and scheduling irrigation.Relative drought tolerance of common Hawaii turfgrassesHIGHEST bermudagrasseszoysiagrassesSt. Augustinegrassseashore paspalumcentipedegrasscarpetgrassLOWEST hilograssThe last wordApplication of irrigation water requires more judgementon the part of the homeowner or turf manager than anyother aspect of lawn management. Common mistakes madeby the average homeowner include watering too often forshort periods of time and applying water faster than thesoil can absorb. Soils and local environments vary widelyover short distances in Hawaii, and environmental condi-tions affecting turfgrasses change throughout the year.Therefore, watering schedules should be carefully plannedand, when necessary, adjusted. Whenever possible, irrigateproblem areas by hand and postpone the need to water theentire lawn. Problem areas, or “hot spots,” may be causedby compacted soil that absorbs water slowly, slopes fromwhich water runs off, southern or western exposure, andwarming from being next to driveways or walkways (es-pecially the narrow strips of lawn between sidewalks andstreets). Perforated-hose sprinklers that supply water slowlyand have a narrow water distribution pattern may be use-ful in these areas.

Watering Lawns

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Watering Lawns

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