IrrigationandWater UseDr. James R. WatsonVice President, TORO Corp.

Water is essential for plant growthand plant activity. It is involved

either directly or indirectly in all phases ofthe care and management of turfgrass andlandscape areas. Water transpired byleaves and evaporated from the surfaceserves as a temperature regulator. Syring-ing of the golf greens during periods ofexcessive evapotranspiration is based onthis phenomena. The amount of waterwithin the cells of grass leaves plays animportant role in combating the effect oftraffic.

When the plant cells are filled withwater, they are said to be turgid, a condi-tion that helps the leaves resist pressurefrom traffic (foot or vehicular) and avoidthe damage, or even death, that might'otherwise occur. Wilt is a condition thatexists when the cells do not containenough water and are said to be flaccid. Aten percent loss of water from the plantbody will usually cause permanent wiltingand death.

To understand the complexity of factorsinvolved in water management and irriga-tion of turfgrass, one must recognize thefundamental role water plays in plantgrowth; understand the effects climateand weather have on growth rates andhow they influence water-use rates andchoice of grass. Further, effective and ef-ficient satisfaction of water requirementsof turfgrasses demands a knowledge of thebasic physical and chemical soil propertiesand how these relate to water absorption,storage and drainage as well as the fre-quency, rate and manner in which watermust be applied. All such basic informa-

tion must be correlated with the require-ments for colour, play or use adjusted tofit the existing or planned irrigation facili-ties, and modified to suit or to be adjustedto the level or standard of maintenance atwhich the turfgrass facility is being kept ormaintained.

EvapotranspirationEvapotranspiration (ET) refers to thewater lost by surface evaporation (grassand soil) and from transpiration by theplant ~lItgrass areas. Transpiration ac-counts for most (80 to 85%) of the waterlost by plants. ET is a solar driven "pump-ing" phenomenon. Plants literally pumpwater taken in by the roots through theplant body and pass it off to the atmos-phere as water vapour. Only a small por-tion (5 to 10%) is retained for growth anddevelopment.

Transpiration rates vary almost hourlywithin any given season, They are greaterin summer and lower in fall and spring. Asimilar phenomena, desiccation, occursduring the winter months and is oftenresponsible for the loss of turfgrasss onhigh, exposed sites. Light intensity andduration, temperature, wind, rainfall andphysiological factors all influence the rateof transpiration. Of these sunlight is themost critical. Thus, a measure of solarenergy can be used to develop ET datawhich serves as the key to meeting irriga-tion needs of turfgrass.Let me give you some very basic princi-ples which may guide and direct your irri-gation programs.1. Determine texture and degree of com-

paction of your soil - controls infiltra-tion rate.

2. Determine water holding capacity ofyour soil.

3. Determine depth of the root system

Then, if the need for moisture as indi-cated by ET is 0.25 inches daily - as thecase may be during the heat of summer inmany locations - the soil must supply tothe plant 0.25 inches of water betweenirrigations. Soils that are otherwise verygood for putting greens may hold only 0.5to 0.75 inches per cubic foot. This wouldbe an adequate amount of water for oneto two days if all of it were available tothe plant. For this is not the case, the rootsmust extend through (permeate) the entirevolume of soil and the soil must have thecapability to supply the needed amount ofwater at a rate rapidly enough to permituptake by the roots. The root system ofmany turfgrass areas, especially golf andbowling greens and often sports fields fre-quently do not extend to a one-foot depth(especially in the summer). When theygrow only to a depth of three or fourinches, the volume of potentially availablewater is reduced by one-third to one-fourth.Water management under these condi-tions calls for the reservoir (soil) insuffi-ciency to be replenished by irrigation.Thus, the advice to water deeply and in-frequently is not valid for many puttinggreens; or for that manner, for many tur-fgrass areas. To water in this manner maynot be cost effective. Water cost, energyand equipment wear are higher since a

large portion of the applied water leachesbelow the root zone or runs off.

Poor aeration, whether from poor drain-age, compaction or an inherent soil condi-tion, further complicates the watermanagement practices needed to meetwater requirements of turfgrass on shal-low soils of low water-holding capacityand poor drainage characteristics. To sus-tain growth and keep turfgrass green dur-ing the growing season requires uniformprecipitation throughout the season; oth-erwise supplemental water (irrigation) willhave to be applied in varying amounts.

The problem is uniformity of precipita-tion not amount, put another way "loca-tion" of rainfall and amount on your turffacility - not Joe's which lies across town.The most effective, most efficient, mostconvenient and most economical way towater golf courses, parks, lawns, sport turfplaying fields and other landscaped turfand recreational facilities is by automaticunderground sprinklers. Solid state con-trolled systems, when properly pro-grammed, are flexible and constant -always on duty and available on demand.They are cost effective and a practicalmeans of preventing waste, conservingwater and of assuring good watering tech-niques.

Practical Water ManagementOnce the physiological requirements ofthe grass and the influence of climate andsoil properties are understood, irrigationmanagement or the proper use of water,relates to the frequency of application, theamount to apply and the manner in whichthe water is applied.

Actual watering practices become a mat-ter of judgement - judgement based onknowledge and understanding of the par-ticular set of conditions existing on eachturfgrass area. The limitations imposed byfrequency and amount of play, the capac-ity of a given irrigation system, the avail-ability of personnel and the prevailingweather conditions, all have importantbearing on specific watering practices.

FrequencyThe frequency of irrigation is governedby the water-holding capacity of the soiland the rate at which the available water

Actual watering practicesbecome a matter of

judgement - based onknowledge and understanding

of the cond itionson each turfgrass area.

is depleted. Depletion rate is a function ofevapotranspiration and drainage. For themost vigorous and healthy growth, water-ing should begin when approximately 50percent of the available water has beendepleted. Most plants show a markedgrowth response when soil moisture ismaintained between this level and fieldcapacity. Theoretically, maximum growthoccurs at field capacity because minimumstress - zero tension exists at this mois-ture level. Assuming equal depth of root-ing, sandy-type soils will have to bewatered more frequently than will loamsor clays.Some climatic conditions as high windmovement, intense sunlight, low humidityand high temperature contribute to highwater use rates. When the transpirationrate (discharge rate) exceeds the rate ofintake (by the roots) or flow (by the con-ducting tissue - xylem) the plant will wilt.Itmay wilt even through there is adequatesoil moisture available. At such times"syringing" to reduce temperature is im-perative. This will initiate translocation ofaccumulated photosynthesis and re-initi-ate photosynthesis.

Frequent watering (too often and toomuch) on poorly drained or compactedsoils (inadequate amount of large pores)tends to keep the upper layers of the rootzone near the saturation point most of thetime. This condition will encourage shal-low rooting and will promote weak turfwhich is suscep~ble to weed invasion (es-pecially Poa annua) and insect attacks aswell as further damage from traffic, sincesoil compacts more severely when wet.Frequent and excess watering of well-drained soils may not, in itself, be tooserious but such practices, unless control-led, may not be economical. They cause

excessive leaching of nutrients, requiremore manpower, use more water thannecessary and produce more wear and tearon equipment and facilities. In short, poorirrigation practices are expensive andshould not be tolerated.

Amount to ApplyThe amount of water to apply at anyonetime will depend upon how much water ispresent in the soil when irrigation isstarted, the water holding capacity, rootdepth and drainage characteristics of thesoil. T!Ie amount to apply also will dependto a certain extent upon the kind of grassand toa large extend, on local weatherconditions. For good irrigation manage-ment that amount which is used by theplant should be replenished. Computercontrolled systems connected to localweather stations have the capability tocalculate daily water use and direct thecontroller to supply the needed water.

The amount of water actually needed isa function of the difference between eva-potranspiration (use) and rainfall. This as-sumes excess water has drained. Whenevapotranspiration exceeds rainfall, thedeficit must be supplied by supplementalirrigation. Water deficit tables will serveas a guide in determining the amount.

Enough water should be applied to in-sure that the entire root zone will be wet-ted. Too, on natural soils (as opposed tothose modified for intensive use) sufficientwater should be applied to bring aboutcontact with subsoil moisture. Continu-ous contact between the upper and lowerlevels of moisture will avoid a dry layerthrough which roots cannot penetrate.Application of too much water at one timeis serious only if the soil is poorly drainedand the excess cannot be removed withina reasonable period of time.

Manner of Water ApplicationWater should never be applied at a ratefaster than it can be absorbed by the soil.Irrigation systems that do not adequatelydisperse water; or those equipped withsprinklers that deliver a large volume ofwater within a concentrated area, causesurface runoff. Whenever water is appliedat a rate faster than it can be absorbed bya given soil, the water is being waste and

Irrigation & Water Usecontinued from page 7

costs increase. The sound irrigation pro-gram, then, would call for sprinklers thatapply moisture slowly enough to permitready absorption. When compaction ex-ists, it should be corrected by aeration(cultivation) or spiking. This will materi-ally improve the infiltration rate of water.Likewise, lowering of the precipitationrate and recycling after a period of timemay be necessary for efficient wateringpractices.At any rate, once surface runoff is evi-dent, the sprinklers should be turned off.If the soil has not been watered to thedesired depth - this may be determinedby probing and examining the depth ofpenetration - then the system may beturned on again at the end of thirty min-utes to an hour, depending upon the per-meability of the soil. This type of recyclingshould be a routine part of programmingan automatic system.

SUMMARYTo irrigate properly and conserve waterrequires an understanding of the funda-mental role water plays in plant growth,and of the effects climate and weatherhave on growth rates; how they influencewater use rates and choice of grass. Goodirrigation management demands a knowl-edge of the basic physical and chemicalsoil properties, how they affect water ab-sorption, storage and drainage as well asthe frequency, rate and manner in whichwater must be applied.Further, proper use of water means cor-relating such basic information with re-quirements for play, for mowing andother management practices and pro-gramming a cost effective watering sched-ule to fit the existing irrigation facilities soas to make the most efficient and costeffective use of them and the availablelabour force.

[Reproduced by permission from a pres~n-tation made by Dr. Watson at the OntarioTurf Symposium, Toronto, Jan. 2 - 5, 1996J

TUrfgrass Specialistsin Establishing and Maintaining Turf for all Purposes

Norman Rothwell, President

~"'-/E3 IDISTRIBUTION

Vanden IUS5cheIrrigation & Equipment UmitedR.R.#4, MiltonOntario L9T 2X8

Metro Toronto: (416) 798-4745®:'::i:'\Milton: (905) 875-4545 T1-800-263-41 12 ..~.,."."Fax: (905) 878-4501 C"NAOIANIR~:::~~SSOCl"TION

~ TOM RSCHERT~F CARE Commercial Sales Manager

UBC plansTurfgrass Centre

At the 1995 Western CanadaTurfgrass Conference, an an-nouncement was made of plansfor a turfgrass centre to be estab-lished at the University of BritishColumbia. Dr. Bryan Holl of thePlant Science Department ofUBC says the function of thecentre would be to researchproblems of direct and long-term significance to the turf in-dustry and to provide ecologicalservices which relate to soundmanagement alternatives, dis-ease monitoring, identificationand prevention.

Box 171Harriston, OntarioNOG lZ0Phone (519) 338-3840Fax (519) 338-2510

J. Robert Dippel

TORO® - new and used turf equipment & irrigationproducts

PAR EX® - fertilizersE-Z-GO® - new & used golf cars & utility vehicles

Turf Care Products Canada Ltd.200 Pony Drive

Newmarket, Ontario L3Y 786Phone: (905) 836-0988