...Using Science to Benefit Golf

Turfgrass and EnvironmentalResearch Online

Volume 8, Number 13July 1, 2009

Precision Turfgrass Management (PTM) is a developing information-based approach tomanaging turfgrass sites. PTM integrates the use of various sensors, mobile sensor plat-forms, and GPS and GIS technology to more accurately assess the need to apply water andother materials to turfgrass sites and provides information to assess the need for other man-agement operations (i.e. cultivation), as well. Shown above is the Toro Mobile Monitoringdevice (TMM) mapping soil volumetric water content (VWV) in the surface 4-inch zone, pen-etrometer resistance, and normalized difference gegetative index (NDVI, a measure of planthealth) at Old Colliers Golf Club, Naples, FL.

PURPOSE

The purpose of USGA Turfgrass and Environmental Research Online is to effectively communicate the results ofresearch projects funded under USGA’s Turfgrass and Environmental Research Program to all who can benefitfrom such knowledge. Since 1983, the USGA has funded more than 350 projects at a cost of $29 million. The pri-vate, non-profit research program provides funding opportunities to university faculty interested in working on envi-ronmental and turf management problems affecting golf courses. The outstanding playing conditions of today’sgolf courses are a direct result of using science to benefit golf.

Editor

Jeff Nus, Ph.D.1032 Rogers PlaceLawrence, KS 66049jnus@usga.org(785) 832-2300(785) 832-9265 (fax)

Research Director

Michael P. Kenna, Ph.D.P.O. Box 2227Stillwater, OK 74076mkenna@usga.org(405) 743-3900(405) 743-3910 (fax)

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USGA Turfgrass and Environmental Research Committee

Steve Smyers, Co-chairmanGene McClure, Co-chairman

Julie Dionne, Ph.D.Ron Dodson

Kimberly Erusha, Ph.D.Pete Grass, CGCSAli Harivandi, Ph.D.

Michael P. Kenna, Ph.D.Jeff Krans, Ph.D.

James MooreJeff Nus, Ph.D.

Paul Rieke, Ph.D.James T. Snow

Clark Throssell, Ph.D.Ned Tisserat, Ph.D.Scott Warnke, Ph.D.

James Watson, Ph.D.Chris Williamson, Ph.D.

"Where, when, and how much" arequestions golf superintendents ask about theinputs used on golf courses. A dramatic transfor-mation in traditional agriculture has occurred overthe past two decades based on technologicaladvancements that allow a greater degree of site-

specific management, and precise and efficientinput. This practice of site-specific managementis referred to as Precision Agriculture (PA), and itsadoption has had positive repercussions involvingcosts, labor, and environmental impact (1, 5, 7, 18,20). More recently, the Precision TurfgrassManagement (PTM) concept has evolved in theturfgrass industry, based on the PA principle oflimiting input application to a site's spatial, tem-poral, and rate requirements - i.e. application ofinputs, such as irrigation water, only where need-ed, when needed, and at the rate required (15, 16,22, 23).

Both PA and PTM rely on advanced sensortechnology, mobile sensor platforms, use of GPS(global positioning systems), and application ofGIS (geographic information systems) to analyzeand display the intensive data. The focus of thispaper is to define the PTM concept and discusspotential applications for the golf industry, partic-ularly related to efficient application of inputs.

Driving Forces

Several factors have recently converged tofocus attention on the concept of PTM as a meansto improve input efficiencies. Driving forces fos-tering PTM as a means of improving input effi-ciency are economic, environmental, and social innature, and these are likely to continue in thefuture. These factors include: a) potential for site-specific application to save cost of inputs, labor,and equipment wear related to maintainingacceptable turfgrass quality; b) demand for moreprecise and efficient irrigation as a key water con-servation strategy on turfgrass sites; c) societalpressure for natural resource and energy sustain-ability; and d) recognition by many businessesthat a "green company image" that entails the pre-vious aspects is good business and a necessaryfactor to be a leader in the industry.

Precision Turfgrass Management: A New Concept for Efficient Application of Inputs

Robert N. Carrow, Joseph Krum, and Chris Hartwiger

SUMMARY

Precision Turfgrass Management (PTM) is a developinginformation-based approach to managing turfgrass sites.PTM integrates the use of various sensors, mobile sensorplatforms, and GPS and GIS technology to more accurate-ly assess the need to apply water and other materials to turf-grass sites and provides information to assess the need forother management operations (i.e. cultivation). The focusof this paper is to define the PTM concept and discusspotential applications for the golf industry.

Site-specific management requires site-specific infor-mation. Detailed knowledge of the spatial nature of plantand soil properties is necessary. This requires site data to beacquired on a close-spaced grid - i.e., intensive mapping.

PTM is based on 1)advanced sensor technology, 2)mobile sensor platforms for site mapping, 3) GPS to definethe exact site for each data point, and 4) application GIStechnologies to analyze and display spatial data.

Determining areas that are characterized by similarinput requirements is essential for efficient input allocationand are the basis of PTM. Site-specific Management Units(SSMUs) are areas of similar water-holding capacity, soiltexture, topography, and microclimate properties that havethe same management requirements.

Software programs with extensive geospatial mappingand analytical capabilities can illustrate spatial variabilityusing the spatial mapping information and help determinehow management practices can be modified to increaseefficiency and conservation.

ROBERT N. CARROW, Ph.D., Professor of Turfgrass Science,Dept. of Crop and Soil Sciences, Georgia Experiment Station,University of Georgia, Griffin, GA; JOSEPH KRUM, GraduateStudent, Dept. of Crop and Soil Sciences, University of Georgia,Athens, GA; and CHRIS HARTWIGER, Senior Agronomist,USGA Green Section, Birmingham, AL.

1USGA Turfgrass and Environmental Research Online 8(13):1-12.TGIF Record Number: 151939

Several of these driving forces are broaderenvironmental issues and not just turfgrass man-agement related, which reflects a similar trend intraditional agriculture. In PA, the primary focushas been on improved efficiency of inputs relatedto crop yield via site-specific management, whereintensive site mapping was conducted to providethe information to make good decisions. However,the same site mapping information has increasing-ly been used to foster Precision Conservation(PC), which is the use of spatial mapping of sur-face conditions to manage for soil and water sus-tainability (9). For turfgrass sites, use of PTM toenhance irrigation efficiency while achievingacceptable quality turfgrass also has a water con-servation goal, illustrating the convergence ofPTM and PC.

Another essential driving force has beenthe limitation hindering progress of PTM forlarge, complex sites, such as golf courses, namelythe development of mobile soil sensor platforms

specifically designed for turfgrass situations thatare capable of intensive site mapping. A recentreview of optical sensing applications in turfgrassmanagement demonstrated that considerableresearch has been conducted on spatial mappingof turfgrass sites using optical sensors, such asspectral reflectance and infrared canopy tempera-tures (2). But, the review also revealed theabsence of mobile platforms with soil sensors tomeasure key soil attributes that would relate toturfgrass performance.

Rhoades (18), in the early 1990s, recog-nized this as a critical limitation in PA, and hedeveloped mobile platforms to spatially determineimportant soil characteristics, which could then berelated to crop data such as end-of-year yield orplant performance indices from satellite spectralinformation or ground-level optical sensing data.It was the coupling of key soil and plant attributesthat has allowed PA to better understand and spa-tially determine factors that influence plant per-

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Experimental Salinity Monitoring Device (SMD) conducting salinity mapping of surface salinity, subsurface salinity, and plantNDVI at Old Colliers Golf Club, Naples, FL in May 2009. Data are GPS-labeled and mapping grid is 5 by 10 feet.

formance, and this need is also critical for PTM(6, 7, 8, 15, 18, 19, 20, 21). The specific devicesdeveloped for turf situations are discussed in thenext section.

Key Principles

Knowledge of the key principles of PTMis important in understanding the potential appli-cations for this concept. Although PTM is basedon PA, it is beyond the scope of this article toaddress the current state of PA, but this is dis-cussed in several of the references (1, 3, 5, 8, 9,18, 20). Both PA and PTM are dependent on thefollowing premises.

Intensive, Site-specific Information

Site-specific management requires site-specific information. To apply inputs more pre-cisely, such as on sub-areas of a fairway, detailedknowledge of the spatial nature of plant and soilproperties is necessary. This requires site data tobe acquired on a close-spaced grid - i.e., intensivemapping.

Integrated Technology

Acquisition of spatial data required theappropriate technological developments in bothPA and PTM; thus both are based on 1) advancedsensor technology, 2) mobile sensor platforms forsite mapping, 3) GPS to define the exact site foreach data point, and 4) application GIS technolo-gies to analyze and display spatial data. Due tothe large quantities of information, these systemsmust be highly integrated for efficiency.

Spatial Mapping Via Mobile Devices

Development and application of mobilesensing equipment can overcome the inherenttime and cost barriers associated with hand-helddevices, as well as penetration difficulties for soilsensors. Also, as noted, extensive adoption of PAoccurred only after instrumentation was devel-oped that could measure both plant status and soil

attributes relating to plant performance. In 2005,the Toro Company developed the Turf MobileMulti-Sensor (TMM) mapping experimental unitas the first device capable of monitoring key plantand soil attributes on turfgrass landscapes. TheTMM allowed intensive and rapid GPS-refer-enced surface zone (0 to 4 inch) volumetric watercontent (VWC), turfgrass performance by normal-ized difference vegetative index (NDVI), and pen-etrometer resistance (PR) mapping. Spectralreflectance is utilized to determine NDVI, whiletime-domain reflectrometry is used for VWC dataacquisition.

In the absence of topographic maps, theTMM GPS also provides an estimate of topogra-phy. With the TMM it was now possible to spa-tially map a fairway in 30 to 45 minutes with 600to 1,100 individual VWC measurements on a gridof approximately 10 feet. Consequently, the spa-tial variability of a site could be characterized andassessed relatively quickly, and it was possible toconduct the necessary research studies to establishPTM on a sound science foundation.

Site-specific Management Units (SSMUs)

Determining areas that are characterizedby similar input requirements is essential for effi-cient input allocation and are the basis of PA aswell as PTM (7, 8, 10, 14, 24). SSMUs are areasof similar water-holding capacity (VWC), soiltexture, topography, and microclimate propertiesthat have the same management requirements. InPA, SSMUs are sub-field areas, while PTMSSMUs are sub-fairway (golf courses), sub-athlet-ic field, sub-field (sod farms), or sub-areas of gen-eral landscapes. Other names for SSMUs aremanagement zones, site-specific managementzones, or management classes. Once SSMUs aredelineated, additional information on the soilchemical and characteristics within SSMUs canbe obtained over time to supplement the initialspatial mapping information.

SSMUs are best defined using stable soilcharacteristics that relate to plant performance.The use of VWC measurements taken at fieldcapacity is a decided advantage for turfgrass sites

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compared to the most common means of deter-mining SSMUs in PA, since VWC is directlyrelated to stable soil properties such as texture,organic matter content, and structure (20, 21).

Topography, another stable landscape fea-ture, is also included when defining SSMUboundaries since it influences rain and irrigationdistribution. However, in PA the most commonmeans to estimate soil properties has been appar-ent soil electrical conductivity (ECa) measure-ments by electromagnetic (EM) devices on amobile sensor platform, while yield mapping orspectral reflectance via ground level or remotedevices provide crop performance information (6,7, 8, 19, 24).

The EM readings are indirect estimates ofthe combined effects of soil moisture, structure,and bulk density in non-saline soil, and separation

of which factor is most important is not alwaysclear. Also, the normal soil depth zone of determi-nation by EM is approximately 30 cm comparedto the 10 cm (4 inch) zone of VWC by TMM.Volumetric water content as determined by TDR,while greatly desired in PA, has not been widelyused since a deeper soil zone is required for meas-urements than for turfgrass, and this precludes anon-the-go system for data acquisition.

Visualizing, Characterizing, and AnalyzingSpatial Mapping Results

In the field, important differences in soiland plant attributes that could determine inputallocation are oftentimes difficult to distinguish.One area of a landscape could have water, fertiliz-er, and/or cultivation requirements that are sub-

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Figure 1. Spatial mapping of soil volumetric water content (left, dark blue = highest VWC) with SSMU boundaries along withtopographic map and clay content (determined by soil sampling within SSMU areas.

stantially different from another location withinclose proximity. ArcGIS or similar software pro-grams with extensive geospatial mapping and ana-lytical capabilities can illustrate spatial variabilityusing the spatial mapping information and helpdetermine how management practices can bemodified to increase efficiency and conservation.Furthermore, GIS is a powerful tool that can beused by turf managers to demonstrate to decision-makers the need for particular resources by visu-ally illustrating the nature, degree, and implica-tions of spatial differences so that budget priori-ties can be adjusted accordingly.

Field Applications

Since there may be several reasons to con-duct spatial mapping, it is important to a) initiallydetermine the specific purposes for mapping, andb) to ensure that the mapping protocols or condi-tions are appropriate to achieving the stated pur-poses (6, 7, 15). Inattention in these areas canresult in nice-looking spatial maps where theresults cannot be explained and are, therefore, oflittle practical use. For PA, site mapping ofsoil parameters is conducted before planting andoften without regard to soil moisture status.However, for turfgrass sites, access is more flexi-ble and soil moisture status can be altered to max-imize results for each mapping purpose. Our pur-pose in this article is to outline field applicationsthat are achievable based on the current level ofknowledge and technology, and note some basicprotocols.

Emphasis on environmental stewardshiphas intensified in recent years. In times of watershortages, golf courses are among the first entitiescriticized for wasteful water management prac-tices. Moreover, under current economic circum-stances, cost-cutting measures are being exploredmore extensively throughout the turfgrass indus-try, involving water and pumping/energy expendi-tures. For these reasons, a focus on practices tar-geted toward increasing irrigation efficiency andother water conservation strategies is gaining pop-ularity and recognition.

The precision of site-specific irrigation is

dependent upon the degree of control offered bythe irrigation system. In older irrigation systemsthat are associated with zoned irrigation heads(multiple irrigation heads per zone), the ability toallocate variable irrigation rates to specified areasis severely limited. However, the versatilityoffered by newer irrigation systems capable ofsingle-head irrigation control is much greater.Therefore, as irrigation system versatility/controlincreases, a higher degree of site-specific irriga-tion becomes possible. As advances in the irriga-tion head itself come to fruition, water-use effi-ciency and irrigation precision will increaseaccording.

Water-use efficiency/conservation, includ-ing the energy associated with water movement,can be enhanced through at least three differenttypes of mapping. First is to define SSMUs bymapping at field capacity to determine the spatialpatterns of soil VWC, which is a good estimate ofsoil texture and organic matter content patterns(20, 21). Initial SSMU areas based on soil VWCmay be refined to consider topography, such asdegree of slope, where strongly sloped areas mayrequire different irrigation programs (e.g. pulseirrigation cycles) to allow water to infiltrate.

Also, if VWC is mapped during dry-downfrom field capacity, conditions within an initialSSMU that would influence spatial plant wateruse in the SSMU may be identified. For example,a strongly sloped area facing the southwest mayexhibit more rapid dry-down than other locationswithin the SSMU, even though the initial fieldcapacity VWC is similar; or there may be shadepatterns that influence ETc. Thus, in terms ofwater relationships, it is important to identifySSMU boundaries based on the stable landscapefactors of soil texture and organic matter content(both reflected in VWC field capacity measure-ments) and topography. It may also be useful toidentify transient factors within a SSMU, such asshifting shade patterns that may require some sea-sonal adjustment of irrigation scheduling.

The emphasis on soil VWC is key, sincesoil water characteristics are primary causes forspatial variation in crops and turfgrass (14, 20,21). As Sadler et al (20) noted, "no prime candi-

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date other than water" exists for explaining thespatial variability of crops in a field, and that"ensuring the success of irrigated farming enter-prises will require the development of reliable andmore timely information on field and plant statusto support the decision-making process."

Appropriate statistics provide a quantita-tive means to describe spatial data within a SSMU

compared to the whole area or other SSMUs - e.g.,measures of central tendency (mean); measuresof dispersion (range, standard deviation, coeffi-cient of variation); indications of data set shape orrelative position (skewness, kurtosis) (6, 7).

A potentially useful means to characteriz-ing spatial variability of VWC at field capacityacross a whole fairway or within a SSMU is adap-

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Figure 2. Spatial variability of soil VWC. Note the wind effects from right to left on spatial VWC patterns.

tation of the distribution uniformity (DU)approach used for assessing irrigation water appli-cation uniformity, but using soil VWC rather thanthe traditional catch-can values (10). The value ofthis approach is:

Whole fairways or greens can be evaluated ver-sus more limited areas, typical of the traditionalcatch-can method.

The DU analysis based on VWC at field capac-ity would not only reflect the influence of irriga-tion system distribution, but would also determinethe natural variation in VWC when at field capac-ity. The lower quartile distribution uniformity(DUlq) can be calculated to quantify the variabil-ity within a SSMU with a high DUlq indicatinggood uniformity of VWC within an SSMU.Calculation of the DUlh (lower half distributionuniformity) is commonly used as a run time mod-ifier for irrigation scheduling, and this could beapplied to a SSMU for irrigation scheduling on amore site-specific basis (10, 13).

The 50 to 60 % of field capacity (FC) VWCvalue (or a value selected by the turf manager torepresent the degree of surface drying allowableon their site) is a good estimate for lower VWClimit within each SSMU. The difference betweenthe FC VWC and 50 % FC is an estimate forreplacement ET within the SSMU. The actualreplacement water needs may be greater if dry-down is sufficient to remove water from below the0 to 4-inch zone, but the surface values providesan initial ball-park value on a spatial basis acrossthe landscape.

Spatial mapping at field capacity allows notonly variability to be determined and definedwithin a fairway, but also across a whole golfcourse. Normally, a golf course may have 6 to 8distinct SSMUs that are located across differentfairways with each distinct SSMU exhibiting sim-ilar irrigation needs regardless of location.

Once SSMUs are characterized within fairwaysand across a golf course, this information is a

good guide for placement of in-ground soil sen-sors. This is a very important aspect, since whereto place soil sensors in complex landscapes hasbeen a major question - along with how to deter-mine the fewest sensors necessary.

The second field application related towater conservation is assessing spatial soil mois-ture distribution by mapping under drier condi-tions from a "typical" irrigation cycle used on thesite. This mapping would essentially be an alter-native water audit method compared to the tradi-tional catch-can method. It is essential that theirrigation system be evaluated for maximum per-formance before conducting the audit -- all com-ponents are operating and adjusted properly, prop-er pressure to the heads, appropriate scheduling,etc. With these adjustments, the irrigation systemdistribution capabilities can then be assessed on awall-to-wall basis with the results reflecting truesystem capabilities or deficiencies (such asimproper head spacing) as well as any other factorthat alters spatial distribution of VWC - wind,slope, etc.

The third potential mapping that couldassist in irrigation decisions would be to use rou-tine NDVI monitoring on a site by mounting thespectral units on mobile equipment to rapidly goover a site periodically for the purpose of identi-fying problem areas. Usually, these may be rela-tively small, representing for example, a mis-aligned head, malfunctioning head, under/overirrigation on an area, or localized dry spot. Spatialmapping under good irrigation conditions can aidestablishing benchmark NDVI values with inSSMUs. Routine NDVI maps can highlight prob-lem areas which the turf manager can thenobserve for the cause.

With water-use efficiency/conservationbecoming a necessity on golf courses, new con-cepts and approaches are needed to progresstoward true site-specific management. Whilethese PTM concepts may seem rather futuristic, inreality the technology already exists. An interest-ing question is "what alternatives are there interms of actually improving irrigation systemdesign and operation for water-use efficiency?"

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Site-specific Cultivation

Soil hardness is a function of soil moisturecontent, percent of clay, type of clay, and soilstructure (i.e. degree of soil compaction). Whensites are mapped at field capacity for penetrome-ter resistance, the soil moisture aspect is eliminat-ed as a factor contributing to spatial patterns. Theresulting penetrometer resistance maps becomeuseful to determine areas with the highest degreeof penetrometer resistance, often due to trafficpatterns. The potential then exists for site-specif-ic cultivation rather than cultivation of wholeareas as means to save labor, energy, and equip-ment wear. Benchmarking of penetrometer data

for acceptable levels is another possibility fordetermining when to cultivate.

Site-specific Fertilizer and Soil AmendmentApplications

The cost of fertilizers and soil amend-ments continue to increase, but cost-effectivemeans of identifying spatial areas for site-specificapplication of these products have not been devel-oped separate from intensive and costly grid sam-pling. Delineating SSMUs based on soil VWC atfield capacity does offer ability to make more site-specific decisions for these products since theSSMUs reflect soil texture and organic matter dif-

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Figure 3. This is a map of soil VWC on two athletic fields but similar results could occur on golf course areas. Irrigation distri-bution pattern of soil VWC was mapped under drier conditions when the irrigation system uniformity could be expressed. Theunderlying pink areas denote the the drier sites (dark pink = driest) and are located on the edges and near sprinklers indicat-ing poor overlap of sprinkler areas. However, this system was actually well designed but the operating pressure was too lowfor the design and resulted in poor overlap. This illustrates the necessity of conducting a good system evaluation to insure opti-mum performance of a system before assessing spatial soil VWC or the traditional catch-can water distribution uniformity eval-uation. System design was for 67 feet head spacing, but the irrigation water only covered 47 feet.

ferences - both which directly relate to soil cationexchange capacity (ability of soil to retain nutri-ents). Considerable activity in PA has been direct-ed to the issue of efficient soil and plant sampling(3, 4, 7, 11, 14, 17, 18).

A basic tenant of soil testing is to samplesimilar areas together, not combining samplesfrom unlike areas. On golf courses, this tenant isnot followed; for example, golf course fairwaysare tested as a whole area rather than sub-areas(SSMUs) within a fairway. Simply by usingSSMUs as soil sampling units offers severaloptions for site-specific application of fertilizersand amendments. Recently, NuTec Soil, Inc.(http://www.nutecsoil.com/) applied PA principlesto golf courses in the Carolinas for this very pur-pose. They used grid sampling (about 70 soil sam-ples per fairway on a 50-60 ft grid); put data intoArcGIS maps for display; and used GPS guidancefrom the GPS tagged ArcGIS maps for site-spe-cific fertilization. NuTec then used GPS-capablefertilizer applicators to make site-specific nutrientapplications. This would be costly if there is aanalysis charge for each soil sample However, thesame thing can be done using the SSMUs conceptwith several options, such as:

A typical fairway may have 2 to 3 SSMUs.Taking about 10 samples per SSMU zone (30 totalfor fairway) would give as much or more accuratedata than the NuTec grid sample approach, pro-vided the soil sample locations were selectedusing appropriate spatial sampling protocols.Statistical programs are available to indicate theleast number of soil samples and their location inorder to provide the best estimate for assessing thewhole SSMU soil chemical and physical proper-ties. Any soil physical or chemical determinationsthat correlate to the mapping data (especiallyVWC) can be spatially displayed as ArcGIS mapsand used in the same fashion as the grid-based soilsampling procedure on NuTec.

Collecting 8-10 subsamples per SSMU andcombining them within an SSMU (i.e., 3 total soilsamples per fairway for the example of a fairwaywith 3 SSMU) would give data sufficient for site-

specific fertilization that would be almost as accu-rate as either the NuTec or the previous option.This approach would be consistent with goodsampling protocols and would result in approxi-mately 54 soil samples from an 18-hole course.

Another version would be to obtain soil sam-ples from all the same type of SSMU units acrossdifferent fairways. Thus, if there were 8 distinctSSMU units located across fairways, only 8 soilsamples would be taken from the course. Thisoption would allow site-specific fertilizationbased on SSMU soil test results and would bemore sound in terms of soil sampling than the cur-rent practice of combining all soil samples withina fairway when there may be major SSMU differ-ences in a fairway.

All methods are versions of PTM, but theapproach taken obviously makes a big differenceon cost of sampling. Options exist for more site-specific fertilization based on the selected soilsampling scheme, but the critical component isdetermination of the SSMUs. These optionswould allow site-specific recommendations to beformulated for site-specific application, with sav-ings possible from reduce product need, energyfor application, and labor.

A recent example of considering soil spa-tial variability for soil nutrients is the paper byGardner et al. (12), which reported on spatial vari-ability of the Illinois soil N test on golf coursefairways. They did not determine SSMUs to useas sampling units, but sampled on a 30-ft gridsample pattern. In this study, the amino sugar Nconcentrations were not highly variable and sam-pling by traditional means would be sufficient.

Site-Specific Management of Soil Salinity

Currently, within the turfgrass industry,mobile salinity mapping devices are under devel-opment and testing. All would map total solublesalts on a salt-affected site, but spectral devicescan map plant performance, and the TDR devicemay be able to map VWC at the same time.Although salt retention is affected by soil type, in

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turfgrass situations, the most common source ofsalts is irrigation water. But, any factor affectingwater distribution and the quantity of waterapplied (i.e. degree of leaching occurring at a spe-cific location) are more dominant factors than soiltype on spatial salinity patterns. Thus, "salinitySSMUs" often differ from the VWC at fieldcapacity-based SSMUs discussed above. Definingspatial salinity patterns offer several managementoptions for PTM, namely:

Identification of spatial distribution of salinitylevels is an essential requirement to do site-spe-cific leaching, thereby conserving water com-pared to using the same leaching requirement overa whole site. Instead of using an estimated leach-

ing requirement over a whole area, irrigation canbe targeted to the 'hot spots.'

With appropriate mobile salinity monitoringdevices, as well as hand-held units that coulddetermine soil salinity by soil depth, it would bepossible to evaluate whether the selected leachingprogram was effective on a salt SMMU.

Locations that consistently exhibit the mostrapid accumulation of soluble salts would be idealsites for soil salinity sensor placement to providereal-time data on salt accumulation and leaching.

Sites highest in soluble salts are also those mostlikely to be highest in Na, which could allow for

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Figure 4. Salinity mapping results from March 30 and May 4 for fairway 1 at Old Collier Golf Club using experimnetal SaltMonitoring Device. ECe saturated past extract salinity is the standard means of reporting soil salinity. Seawater has a salini-ty level of 45 dS./m or 34,000 ppm salts. The bright red areas are approximately the same salinity as ocean water. Site is irri-gated with saline water from 4,000 to 7,000 ppm during winter and spring. Soil VWC data (smal insert map) was mapped byTMM and reflets VWC in the surface 1-inch zone.

site-specific application of gypsum rather thanwhole-area applications.

Additionally, sites high in soluble salts will bethose receiving or retaining most of the variouschemical constituents that may influence spatialfertility requirements.

Other PTM Application on Golf Courses

The field applications previouslyaddressed were based on soil mapping, except forthe NDVI routine monitoring example. Thereview paper by Bell and Xiong (2) present thehistory and current applications for optical sens-ing, including pest mapping. When golf courseshave basic GPS delineated features, and possiblytheir own GPS units to define areas that exhibit ahistory of nematode, disease, or insect activity,this becomes another application for PTM princi-ples.

Conclusion

Precision Turfgrass Management, basedon the concepts evolved in PA over the past 25years but with refinements specific to turfgrasssituations, offers another management tool to turf-grass managers seeking a greater understanding ofspatial variability of their site and the implicationsfor resource needs. The PTM area will developover time, with new technologies incorporated;however, there is considerable potential for thisconcept at the current state-of-the-science toaddress efficiency questions related to inputs of"where, when, and how much" on a more site-spe-cific basis than the current practices.

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