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Published online 5 June 2006
Published in Agron J 98:951-961 (2006)
DOI: 10.2134/agronj2005.0190
© 2006 American Society of Agronomy
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Turfgrass

Environmental Impact of Irrigating Turf with Type I Recycled Water

James C. Thomasa,*, Richard H. Whitea, Jonathan T. Vorheisb, Heather G. Harrisb and Kenneth Diehlc

a Soil and Crop Sciences Dep., Texas A&M Univ., College Station, TX 77843-2474
b CH2M HILL Inc., San Antonio and Austin, TX
c Resource Protection and Compliance Dep., San Antonio Water System, San Antonio, TX

* Corresponding author (jc-thomas{at}tamu.edu)

Received for publication June 23, 2005.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
As our water reserves diminish, recycled water is increasingly being used for irrigation of turfgrasses. This study was conducted to determine the fate of nutrients contained in Type I recycled water used to irrigate turf and its effect on turf quality. Eighteen plots were randomly assigned to three replications of three irrigation treatments and two grasses. Irrigation treatments included Edwards Aquifer water applied at the evapotranspiration (ET) rate (EA), recycled water applied at the evapotranspiration rate (1XRW), and recycled water applied at 1.1 times the evapotranspiration rate to provide a leaching fraction (LFRW). Grasses included ‘Tifway’ bermudagrass (Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt Davy) and ‘Jamur’ zoysiagrass (Zoysia japonica Steud.). Rain, runoff, leachate, and soil samples were collected and analyzed for total salts, Ca, Cu, Fe, Mg, Mn, N, K, Na, and Zn. The use of San Antonio Water System (SAWS) Type I recycled water had no adverse effect on turf quality but did result in a significant increase in soil electrical conductivity (EC) from 0.2518 dS m–1 in the EA treatment to 0.3132 and 0.3171 dS m–1 in the 1XRW and LFRW treatments, respectively. The Ca content increased from 134 108 and 135 467 mg L–1 in the EA and 1XRW treatments to 142 835 mg L–1 in the LFRW treatment. Na concentrations in the soil were not affected by the use of recycled water. The use of recycled water resulted in increased total salts (EC), Na and nitrate (NO3) concentrations in leachate passing below 76 cm. The EC increased from 0.425 dS m–1 for the EA treatment to 0.626 and 0.614 dS m–1 for the 1XRW and LFRW treatments, respectively. Na concentrations in leachate increased from 18.33 mg L–1 for the EA treatment to 49.10 and 52.91 mg L–1 for the 1XRW and LFRW treatments, respectively. Runoff water from treatments irrigated with recycled water exhibited a trend of increased EC, Ca, Mn, and Na.

Abbreviations: EA, replacement of ET with Edwards Aquifer water • EAA, Edwards Aquifer Authority • EARZ, Edwards Aquifer Recharge Zone • ET, evapotranspiration • 1XRW, replacement of ET with recycled water • LFRW, replacement of ET with recycled water plus 10% for leaching • SAWS, San Antonio Water System • TKN, total Kjeldahl nitrogen


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
AS OUR POPULATION INCREASES, so does the strain on our nation's potable water supply. The major sources of drinking water are surface water, for example, lakes and rivers, or underground aquifers. Every year, the rate of withdrawal of water from these sources increases, largely due to the constantly increasing demand for potable water supplies. The City of San Antonio is heavily dependent on the Edwards Aquifer as its major water source (Diehl, 2000), however, pumping from this aquifer has reached the estimated maximum rate of withdrawal without causing environmental damage due to reduced spring flows which in turn will threaten endangered species that are dependent on these springs for their habitat.

The Edwards Aquifer Authority (EAA) regulates the amount of water that can be withdrawn from the Edwards Aquifer by well owners. As part of this program, pumping limits have been established by the EAA for the wells operated by the SAWS. Reuse of treated municipal wastewater for irrigation is an essential element of the SAWS Conservation and Reuse Plan designed to reduce the use of potable groundwater for nonpotable applications. Two major goals of this plan are (i) to virtually eliminate the use of groundwater for irrigation and stream augmentation and (ii) to preserve the integrity of the Edwards Aquifer, which underlies much of south-central Texas. Therefore, it is in the best interest of the population to use the aquifer water primarily for potable needs and to use lower quality water sources for nonpotable applications, including irrigation of large turf areas.

To achieve this goal, the City of San Antonio, through SAWS, has constructed wastewater treatment facilities and a distribution pipeline capable of producing and distributing approximately 4305 ha-m yr–1 of Type I recycled water suitable for nonpotable uses (Note that the terms recycled, reclaimed, and reuse can be used interchangeably). Since large irrigators located on the Edwards Aquifer Recharge Zone (EARZ) have shown interest in the use of SAWS' recycled water, SAWS desired to obtain technical data on the fate of certain constituents found in recycled water before deciding whether or not to provide recycled water service to these potential customers. The overall concern is that chemical constituents of the recycled water may migrate into and, potentially, pollute the aquifer, thus damaging its usefulness as a long-term potable water source for this large population center.

Previous research on the use of recycled water for irrigation purposes has shown that the major constituents of concern within leachate include total salts, Ca, Cl, Mg, N (particularly the NO3 form), P, K, and Na (Pepper and Mancino, 1994). In particular, the high total salt content and high Na level may require special management, including the use of a leaching fraction and periodic gypsum applications to prevent the accumulation of excessive salt concentrations in the soil (Hayes et al., 1990a). Without the use of a leaching fraction, Wu et al. (1996) documented significant increases in total salts (EC) of soils irrigated with simulated wastewater. However, when a 20% leaching fraction was used, increases in soil EC were small and posed no threat to plant growth (Mancino and Pepper, 1992).

Because NO3 is a highly mobile anion, it is of major concern as a leachable contaminant that may impair groundwater quality. Mancino and Troll (1990) reported maximum NO3 concentrations of 41 mg L–1 and 69 mg L–1 in leachate samples following N application of 48.8 kg ha–1 as calcium nitrate and ammonium sulfate, respectively. However, Anderson et al. (1981) showed that a sand-textured soil with a mature bermudagrass turf cover could effectively remove large amounts of NO3 from up to 12.7 cm of effluent water per week and maintain an average NO3 concentration of 10 mg L–1 or less in the leachate. It should be noted that 12.7 cm of applied water was 3.4 times more than needed and resulted in 9 cm of leachate. Thus, soil-turf systems should be effective in reducing NO3 concentrations even when excess water in the form of a leaching fraction is applied as a means of maintaining acceptable amounts of total salts in the root zone (Anderson et al., 1981; Hayes et al., 1990b). Exact depths of water that can be treated at a given site will be primarily dependent on the initial N content of the reclaimed water, irrigation practices, the turf species being grown, and the associated soil texture and climatic conditions.

The present study was conducted to provide information regarding the environmental fate of nutrients contained in Type I recycled water used to irrigate turf areas and the effect of this recycled water on turf quality.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
A total of 18 plots, each 6.1 by 6.1 m, were established in 1998 at a site in southern Bexar County approximately 4.8 km south of San Antonio, TX. The experimental site was located on an area of Lewisville silty clay (fine-silty, mixed, thermic Udic Calciustolls). The plots were divided into three blocks of six plots with each block representing a different replication. Within each block, the plots were randomly assigned to three irrigation treatments and two grasses. Irrigation treatments included replacement of ET using Edwards Aquifer water, replacement of ET using recycled water, and replacement of ET plus 10% for a leaching fraction using recycled water. The chemical composition of the EA water, recycled water, and the rain water are presented in Table 1. Turfgrasses used were ‘Tifway’ bermudagrass and ‘Jamur’ zoysiagrass. These warm-season grasses are commonly used in the San Antonio area. The study site was equipped with a weather station (manufactured by Campbell Scientific and configured by Dynamax Corp., Houston, TX) for measurement of environmental conditions and calculation of ET based on the Penman–Monteith Equation (Monteith, 1965). Each plot was surrounded on all sides with a 1.52-m wide non-irrigated aisle. All plots were surrounded with plastic edging (10-cm tall, placed an average of 7 cm belowground and 3 cm aboveground) to separate the plot areas from the aisles. The experimental period was 2 yr, beginning March 2002 and ending February 2004. Because the site had not been regularly irrigated or maintained during the 1998–2002 period, the soil was very dry and cracked at the start of the experimental period. In addition, some time (March–May 2002) was required to initiate proper mowing, install runoff collection devices, ensure the proper functioning of all equipment, and perform all the necessary calibrations. By 15 June 2002, the study team determined that stable soil moisture conditions had been achieved, all equipment was functioning correctly, and data collection could proceed with confidence. Therefore, data collection was possible from 15 June 2002 to February 2004.


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  		Table 1. Chemical constituents in the rainwater, Edwards Aquifer (EA) water, and recycled water that was applied to the test plots.

 
Irrigation was accomplished by installing a pop-up sprinkler head (Rainbird T-Bird Series) with an output rate of 3.8 L min–1 at each corner of all plots. This provided head-to-head coverage with an average distribution uniformity of 82.2% (Fipps, 2004). Calibration of the irrigation system, including calibration of the individual sprinkler heads and determination of the precipitation rate and uniformity, was conducted at the beginning of the study and semi-annually thereafter. All piping was routed through the aisles and care was taken not to disturb the soil on the plot areas. The irrigation heads for the six randomly located plots receiving EA water were connected using a manifold and controlled by a single solenoid valve. Similar manifold and solenoid systems were used for the 1XRW and LFRW treatments. The water source for the EA treatment was a potable water supply from SAWS. The source for the 1XRW and LFRW treatments was Type 1 Recycled Water from the SAWS recycled water transmission trunk line.

Every 2 wk, the data were downloaded from the weather station and used to determine the ET using the Pennman–Monteith method. The overall irrigation controllers were then programmed every 2 wk to apply irrigation equal to the ET measured for the previous 2-wk period for all treatments plus an additional 10% leaching fraction for the LFRW treatment only. A totalizing water meter was installed on each manifold as a double check to ensure that programmed amounts of water were applied.

Each plot was equipped with three underground glass block lysimeters (Barbee and Brown, 1986; Brown, 1986) for leachate collection. Lysimeter installation followed the procedures of Barbee and Brown (1986), with three exceptions. First, a washed geotextile was substituted for the fiberglass sheet used to cover the upper surface of the glass block. Second, a sheet of 0.01-cm thick plastic was used to cover the entire side of the trench in which the lysimeters were installed before backfilling the trench. Third, the depths of placement were 15.2-, 45.7-, and 76.2-cm below the soil surface. All sampling tubes were run to the surface and coiled into a 15-cm diameter irrigation valve box. This protected the tubes from damage due to sunlight, animals, and maintenance activities such as mowing. The lysimeters at the 45.7- and 76.2-cm depths were installed into the side of the trench. However, the lysimeter at the 15.2-cm depth was installed by excavating a hole to the proper depth from the surface, leveling the bottom of the hole, installing the sampler, routing the collection tube underground to the valve box and backfilling the hole. Sampler installation was done before establishing turf cover. Lysimeters were off set so that overlying lysimeters would not interfere with water flow to lower instruments.

One replication of each irrigation treatment and grass combination was equipped with a runoff collection device which consisted of a 60-cm diameter, 15-cm tall metal ring. Each ring had a single outlet for 1.27-cm diameter pipe located midway up the side. Rings were oriented with the outlet on the down-slope side and hammered into the ground so that the outlet was at ground level. A 1.27-cm diameter pvc pipe was used to conduct the collected water to a 20-L glass runoff collection jar located belowground in the aisle.

Sample Collection
Leachate and runoff samples were collected monthly. In addition, unscheduled leachate and runoff samples were collected immediately after rainfall events that produced 3.8 cm or more precipitation within a 24-h period at the study site. Leachate samples were collected by connecting the lysimeter sample tube to a 2-L glass collection jar that was connected to a vacuum source. When the rate of water coming from the lysimeters approached zero, the vacuum and sample tubes were disconnected and the sample volume was measured and recorded. Samples greater than 50 mL were transferred to clean polyethylene containers, labeled, and stored on ice in a cooler until transported to the laboratory for analysis.

Soil samples were collected from the upper 15 cm of each plot quarterly using a 2.3-cm diameter Oakfield auger (ELE International, Lake Bluff, IL). Ten to 20 samples were collected from a given plot, placed in a clean plastic bucket, mixed, and subsampled. A single composite sample from each plot was submitted to the laboratory for analysis. All sampling holes were filled with clean soil from an undisturbed area of the field just beyond the experimental area.

Turf quality was assessed visually each month. Each plot was evaluated for turf density, color, and uniformity using a scale of 1 to 3 for each component. A density rating of 1 was indicative of few plant shoots per square inch and containing numerous areas of visable soil surface while a rating of 3 indicated a high plant density covering the entire plot area. A color rating of 1 indicated severely yellowed or straw colored turf while a rating of 3 indicated an aesthetically pleasing dark green color. A uniformity rating of 1 indicated turf that was highly variable in plant height, leaf texture, and plant species composition, while a rating of 3 indicated an even plant height, similar leaf texture throughout the plot and a nearly weed free stand of turf. The scores were then totaled to arrive at an overall score ranging from 3 to 9. A score of 9 represented turf with a high plant density, good color, and a very uniform appearance. Ratings below 5 would not be acceptable for typical fairway turf during the growing season.

Sample Analysis
Soil and water samples were analyzed at the SAWS' Dos Rios Laboratory, San Antionio, TX, using the methodology listed in Table 2. When there was adequate sample volume, all parameters were measured. When sample volume was limiting, measurement of ammonia-N, nitrate-N, and nitrite-N took priority, and other parameters were measured as sample size allowed.


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  		Table 2. Laboratory analytical methods employed for analysis of soil, water and tissue samples in this study.

 
Maintenance
To ensure that all plots contained adequate fertility, soil samples were collected from the upper 10- to 15-cm of soil every 3 mo and tested for macro- and micronutrients. The analysis consistently showed that all plant nutrients other than N remained in the adequate to high range. Based on these results and the alkaline pH of the soil, ammonium sulfate was chosen as the preferred N source.

Nitrogen fertilization of the experimental area was done using two methods. The target goal for N application during 2002 was to apply a total of 11 g m–2 to all plots in addition to that from the irrigation water. This was accomplished by making a single N application of 3.67 g m–2 using ammonium sulfate during the first week of May 2002, before the data collection period followed by two additional N applications of 3.67 g m–2 each using ammonium sulfate, one during the first week of August and one during the first week of October 2002. Quantities of N and other constituents supplied via the irrigation water were in addition to the ammonium sulfate applications. The total amounts of all nutrient applications (fertilizer plus irrigation water) are shown in Table 3.


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  		Table 3. Total nutrient applications (fertilizer plus that in the irrigation water) to the experimental plots during each year of the study. Irrigation treatments included the replacement of evapotranspiration (ET) using Edwards Aquifer water (EA), the replacement of ET using San Antonio Water System (SAWS) Type I recycled water (1XRW), and the replacement of ET plus 10% for leaching using SAWS Type I recycled water (LFRW).

 
In 2003, the N nutritional program was changed to more closely approximate best management practices for a facility using recycled water in which the target N goal includes the N from the water sources and thereby minimizes spikes in turf growth. Target N goals of 19.5 and 29.3 g m–2 were established for zoysiagrass and bermudagrass, respectively. These were divided into six equal applications and were reduced by the estimated amount of N from the irrigation water applied during that period. Applications were made in April, May, June, August, September and October 2003.

Plots were mowed weekly at a cutting height of 5 cm and clippings were returned to the plots. One fungicide application was made to all plots at a curative rate in early 2003 to control an outbreak of Take All Patch (Gaeumannomyces graminis var. graminis). No verticutting, aeration, or other cultural practices were employed.

Experimental Design and Statistical Analysis
A split-block design with three replications was used for this study. Factors included irrigation, grass, and date. In the case of leachate measurements, depth was also included as a factor in the design and analysis. Main blocks were grass type, subblocks were irrigation treatment and sub-subblocks were depth. The entire data set was subjected to analysis of variance (ANOVA) using the GLM model of the SAS program (Ver 8.2, SAS Institute, Cary, NC). In the absence of significant interactions, means were separated using Tukey's Studentized Range Test. Differences among treatments in the text are reported at P = 0.05. When significant interactions involving sample date were present, the data were pre-sorted by date and individually analyzed by date. Because runoff samples were collected from only one replication of each treatment, they could not be statistically evaluated. Therefore, runoff data are presented in this manuscript as only representing trends in the data.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Total monthly rainfall, potential ET, and irrigation depths are shown in Table 4. It should be noted that three major rainfall events, each in excess of 203 mm, occurred in July, September and October of 2002. Thus, during the summer of 2002, the site experienced an unusually high amount of rainfall, which occurred in the form of major rainfall events. In addition to generating a large amount of runoff, such intense storms likely caused leaching of salts and other soluble constituents deep into the soil profile.


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  		Table 4. Monthly evapotranspiration (ET), rainfall, and irrigation amounts for the research site in Southern Bexar County, TX. Irrigation treatments included the replacement of ET using Edwards Aquifer water (EA), the replacement of ET using San Antonio Water System (SAWS) Type I recycled water (1XRW), and the replacement of ET plus 10% for leaching using SAWS Type I recycled water (LFRW).

 
Rainfall during 2003 and 2004 was much more typical of an "average year" in the San Antonio area. However, even in 2003 there was in excess of 100 mm of rain in the months of June, July, and September.

Runoff Water
Because only one replicate of each treatment was equipped with a runoff collection device, the resulting data could not be statistically compared. However, the data were examined for the presence or absence of any trends. The electrical conductivity of the runoff from the zoysiagrass plots (Fig. 1a ) in the EA treatment began with a conductivity of 169 dS m–1 in July 2002 and showed a slight overall decrease throughout the study and ended with a conductivity of 97 dS m–1. The LFRW treatment was similar but remained 50 to 70 dS m–1 above the EA throughout the study. The 1XRW treatment was in between the EA and LFRW for most of the study except for a spike in EC during March 2003.


Figure 1
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  		Fig. 1. (a) Electrical conductivity, (b) Ca concentrations, (c) Na concentrations, (d) nitrate (NO3) concentrations, and (e) Mn concentrations measured in runoff samples from the zoysiagrass plots as affected by irrigation treatment. Irrigation treatments included EA, the replacement of evapotranspiration (ET) using Edwards Aquifer water; 1XRW, the replacement of ET using San Antonio Water System (SAWS) Type I recycled water; and LFRW, the replacement of ET plus 10% for leaching using SAWS Type I recycled water. Vertical bars indicate the standard error of the mean.

 
The Ca concentration in the runoff from the zoysiagrass plots (Fig. 1b) in the EA treatment began with a concentration of 36 mg L–1 in July 2002 and showed a slight overall decrease throughout the study and ended with a conductivity of 13 mg L–1. The LFRW treatment was similar but remained 10 to 15 mg L–1 above the EA throughout the study. The 1XRW treatment began with Ca concentrations that were similar to the EA treatment but had a large spike in concentration during March 2003. Following this spike, the concentration decreased to 23 mg L–1 which is between that of the EA and LFRW treatments.

The Na concentration in the runoff from the zoysiagrass plots (Fig. 1c) in the EA treatment began with a concentration of 3.5 mg L–1 in July 2002 and showed a slight overall decrease throughout the study and ended with a conductivity of 0.7 mg L–1. The LFRW treatment was similar but started with a higher concentration of 15.8 mg L–1 and ended with 4.1 mg L–1. The 1XRW treatment began with Na concentrations that were slightly above the LFRW treatment but had a large spike in concentration during March 2003. Following this spike, the concentration decreased to 4.7 mg L–1 which is similar to that of the LFRW treatment.

The NO3 concentration in the runoff from the zoysiagrass plots (Fig. 1d) in the EA treatment began with a concentration of 0.2 mg L–1 in July 2002 and remained in the range of 0.1 to 2.4 mg L–1 throughout the study period. The LFRW treatment was similar and began with a concentration of 2.1 mg L–1 and ended with a concentration of 1.0 mg L–1. The LFRW had a small spike in concentration in early October 2002 when the concentration reached 8.2 mg L–1 but otherwise remained below 3 mg L–1 throughout the study. The 1XRW treatment began with NO3 concentrations that were similar to the EA treatment but had a large spike in concentration in the March and June 2003 samples. Following this spike, the concentration decreased to 1 mg L–1 which is similar to that of the EA and LFRW treatments. It is notable that of all the runoff samples for this plot, only one exceeded the drinking water standard of 10 mg L–1.

The Mn concentration in the runoff from the zoysiagrass plots (Fig. 1e) in the EA treatment began with a concentration of 0.14 mg L–1 in July 2002 and showed a rapid decrease to 0.03 mg L–1 in September 2002 after which there was only a very slight overall decrease throughout the remainder of the study and ended with a concentration of 0.02 mg L–1. The LFRW treatment was similar and remained within 0.04 mg L–1 of the EA treatment throughout the study. The 1XRW treatment began with Mn concentrations that were similar to the EA treatment but had a small increase in concentration during March 2003. Following this spike, the concentration decreased to 0.04 mg L–1 which is between that of the EA and LFRW treatments.

Concentrations of all other elements measured in the runoff water showed no trends due to irrigation treatment.

Soil Samples
Grass species had no significant effect on the EC of the soil but, irrigation treatments did (Table 5). The soil from the EA treatment had significantly lower EC than either of the recycled water treatments. This is in general agreement with Qian and Mecham (2005) who also measured increased fairway soil EC measurements on golf courses that had been irrigated for many years with recycled wastewater. As expected, the grass species had no significant effect on the Ca content of the soil. Irrigation treatments did, however, impact soil Ca concentrations. The LFRW treatment contained significantly more Ca than either the EA or 1XRW treatments. Plots planted with bermudagrass had significantly lower soil concentrations of Fe, Mg, Mn, and K, which indicated that the bermudagrass was more efficient than zoysiagrass at removing these nutrients. Irrigation treatments produced no significant differences in soil concentrations of Fe, Mg, Mn, and K.


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  		Table 5. Mean concentration of 11 nutrients and electrical conductivity (EC) measured in soil samples from plots planted with two turfgrasses and subjected to three irrigation treatments. Irrigation treatments included the replacement of evapotranspiration (ET) using Edwards Aquifer water (EA); the replacement of ET using San Antonio Water System (SAWS) Type I recycled water (1XRW); and the replacement of ET plus 10% for leaching using SAWS Type I recycled water (LFRW).

 
Neither grass species nor irrigation treatment had a significant effect on concentrations of Cu, Na, Zn, NH4, or TKN in soil. The NO3 concentration in soil was significantly lower for zoysiagrass than for bermudagrass. This is most likely due to the lower N fertilizer amounts applied to the zoysiagrass.

Turf Quality
In June 2002, the turf quality for both bermudagrass and zoysiagrass was 7.0 or greater and increased to 8.0 or above in July (Fig. 2a and 2b). The turf quality for both grasses remained at 8 or above through August and increased to nearly 9 in September. Following September, turf quality declined as turf growth slowed and color waned because of suboptimal growth temperatures. By January 2003, both grasses had gone into winter dormancy. Although the color was poor, turf density and uniformity remained high. As green-up was reached in March 2003, the cycle of turf quality repeated itself. Except for one date (March 2003) during an outbreak of Take-All Patch, there were no significant differences in turf quality due to grass or irrigation treatments.


Figure 2
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  		Fig. 2. Turf quality ratings over the study period for (a) bermudagrass and (b) zoysiagrass subjected to three irrigation treatments. Irrigation treatments included EA, the replacement of evapotranspiration (ET) using Edwards Aquifer water; 1XRW, the replacement of ET using San Antonio Water System (SAWS) Type I recycled water; and LFRW, the replacement of ET plus 10% for leaching using SAWS Type I recycled water. Arrows denote fertilizer applications and vertical bars denote the standard error of the mean.

 
Leachate Samples
Analysis of the leachate data showed no significant interactions for EC, pH, K, Mg, Mn, Na, or Ca. Therefore, only main effects will be discussed for these parameters. Leachate from the bermudagrass treatment had a higher EC (Table 6), which indicated a higher concentration of total salts. Part or all of this difference may be due to the higher N fertilization requirement of the bermudagrass. Although the difference was significant, the EC of both grass treatments was well within the safe range for turf production. Turfgrass species had no effect on the pH of the leachate or in the concentrations of Mg, Mn, or Na. Leachate from bermudagrass contained higher concentrations of Ca and lower concentrations of K than did the leachate from zoysiagrass.


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  		Table 6. Mean electrical conductivity (EC), pH, K, Mg, Mn, Na, and Ca concentrations in leachate samples collected at three depths below two turfgrasses with three irrigation treatments over the entire study period. Irrigation treatments included the replacement of evapotranspiration (ET) using Edwards Aquifer water (EA), the replacement of ET using San Antonio Water System (SAWS) Type I recycled water (1XRW), and the replacement of ET plus 10% for leaching using SAWS Type I recycled water (LFRW).

 
When evaluated as a function of depth, the leachate from the 15-cm deep lysimeters had a greater EC and a greater pH than did leachate from greater depths. In addition, leachate samples from the 15-cm lysimeters had higher concentrations of K, Mg, and Na. This is likely a result of some of the water soluble nutrients being transported to this depth before being adsorbed to soil cation exchange sites. Under the conditions of this study, it appears that a depth of 45.7 cm was sufficient to lower the concentration of these elements to near background levels.

Leachate from the EA water treatment resulted in significantly lower EC and Na concentrations compared with leachate from either recycled water treatment. This is likely due to the greater concentration of total salts and Na in the recycled water. The use of a 10% leaching fraction did not increase or decrease the EC or Na in the leachate compared to the 1XRW treatment. Irrigation water source had no effect on the concentration of Mn and Ca in the leachate. The concentration of Mg in the leachate was greatest in the LFRW treatment and least in the 1XRW treatment. In contrast, K concentrations were greatest in the leachate from the 1XRW treatment.

Analysis of the leachate data showed that there were significant interactions involving date for NO3, NO2, NH3, and TKN. Therefore, it was necessary to evaluate these data on an individual sampling event basis for statistical significance among irrigation water sources. Over the entire course of the experiment, NO2 concentrations in the leachate (data not shown) ranged from 0.01 to 0.71 mg L–1 and were similar among irrigation water sources on all dates. Concentrations of NH3 ranged from 0.09 to 0.21 mg L–1 and, except for the 23 July 2002 sample, were similar among irrigation water sources.

Nitrate concentrations in the leachate varied over a fairly wide range, extending from 0.10 to 32.7 mg L–1 (Table 7). Only 11% (8 out of 71) of the measurements over the experimental period exceeded the drinking water standard of 10 mg L–1. Differences in leachate NO3 concentrations among irrigation water sources occurred on only 6 of 27 sampling dates (12 Dec. 2002; 27 Feb. 2003; 23 Sept. 2003; 22 Dec. 2003; 20 Jan. 2004; and 17 Feb. 2004). In all six cases, the treatment irrigated with EA water had the lowest NO3 concentrations. Except for the 23 Sept. 2003 sample, the differences occurred during the months of December, January, and February. Historically, these are the months when warm-season turfgrasses are dormant and have low irrigation and fertilization requirements. Therefore, it is likely that all the N applied as a component of the recycled water used for irrigation during these months could not be used and some was subject to leaching.


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  		Table 7. Concentrations of nitrate (NO3) and total Kjeldahl N (TKN) measured in leachate samples from lysimeters over the study period. Irrigation treatments included the replacement of evapotranspiration (ET) using Edwards Aquifer water (EA), the replacement of ET using the San Antonio Water System (SAWS) Type I recycled water (1XRW), and the replacement of ET plus 10% for leaching using SAWS Type I recycled water (LFRW).

 
Total Kjeldahl Nitrogen was measured in leachate collected on 26 dates over the course of this experiment. Significant differences only occurred on four dates (8 July 2002; 11 Sept. 2002; 9 June 2003; and 17 June 2003). However, in all cases the leachate from the EA treatment had the lowest TKN concentration. Since organic and NH4 forms of N commonly make up the majority of TKN in soil samples, the higher TKN of the 1XRW and LFRW treatments compared to the EA treatment may be primarily attributed to the N fraction added via the reclaimed water.

Iron concentrations in leachate collected on 25 dates over the course of this experiment ranged from 0.02 to 2.06 mg L–1 and showed no differences due to irrigation water source (data not shown). Copper concentrations in the leachate were also low throughout the study and ranged from 0.01 to 0.05 mg L–1 (data not shown). No differences due to irrigation water source were found except for the 25 Mar. 2003 sample.

Zinc concentrations in leachate collected on 25 dates over the course of this experiment ranged from 0.01 to 3.13 mg L–1 with significant differences due to irrigation water source occurring on the 12 Dec. 2002 and 25 Mar. 2003 sampling dates (Table 8). Overall, there were no trends in Zn concentrations in leachate due to irrigation water source.


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  		Table 8. Concentrations of Zn in leachate samples from lysimeters over the study period. Irrigation treatments included the replacement of evapotranspiration (ET) using Edwards Aquifer water (EA), the replacement of ET using the San Antonio Water System (SAWS) Type I recycled water (1XRW), and the replacement of ET plus 10% for leaching using SAWS Type I recycled water (LFRW).

 
Mass Balance
The mass balance calculated for Ca, Cu, Fe, Mg, Mn, K, Na, Zn, and total N in the bermudagrass for different irrigation regimes is shown in Table 9. For Ca, Fe, Mg, and K, the mass balance accounted for 90 to 110% of the nutrients. Mass balances for Cu, Zn, and total N were lower and ranged from 62 to 94% due to the small amounts of these nutrients present in the system. The Na concentration was more variable and resulted in recovery amounts of 54 to 125%. The data confirm an increased amount of stored Ca, Cu, Fe, Mg, Na, Zn, and total N in the soil at the end of the study as compared to that which was initially present. In contrast, amounts of Mn and K in the soil decreased during the study.


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  		Table 9. Mass balance of nine nutrients for bermudagrass plots under three irrigation treatments. Irrigation treatments included the replacement of evapotranspiration (ET) using Edwards Aquifer water (EA), the replacement of ET using the San Antonio Water System (SAWS) Type I recycled water (1XRW), and the replacement of ET plus 10% for leaching using SAWS Type I recycled water (LFRW).

 
The mass balance calculated for the same nine nutrients in the zoysiagrass is shown in Table 10. For Ca, Fe, Mg, and K, the mass balance accounted for 90 to 117% of the nutrients. Mass balances for Cu, Mn, and total N and were lower and ranged from 75 to 152% due to the small amounts of these nutrients present in the system. Na concentrations were more variable due to the high solubility of Na and resulted in recovery amounts of 57 to 123%. The data confirm increased amounts of stored Mg, Na, Zn and total N in the soil at the end of the study as compared to that which was initially present. In contrast, stored amounts of Mn and K in the soil decreased over the study period.


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  		Table 10. Mass balance of nine nutrients in zoysiagrass plots under three irrigation treatments. Irrigation treatments included the replacement of evapotranspiration (ET) using Edwards Aquifer water (EA), the replacement of ET using the San Antonio Water System (SAWS) Type I recycled water (1XRW), and the replacement of ET plus 10% for leaching using SAWS Type I recycled water (LFRW).

 

   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
The results of this study indicated that under the conditions of this study, the use of SAWS Type I recycled water for irrigation did not adversely affect the turf quality of bermudagrass and zoysiagrass. Using a leaching fraction of 10% did not improve turf quality or environmental parameters, given the environmental conditions and rainfall in this test. However, the use of recycled water did result in a significant increase in soil EC and Ca content compared with using EA water for irrigation which indicates the potential for a long-term problem of salt accumulation. In addition, the use of recycled water resulted in increased total salts (EC), Na, and NO3 concentrations of the leachate passing the 76-cm depth. However, NO3 concentrations in leachate from areas irrigated with recycled water exceeded the drinking water standard on only 6 of the 27 sampling dates and occurred primarily during periods of inactive turfgrass growth. Runoff water from plots irrigated with recycled water also exhibited a trend of increased EC, Ca, Mn, and Na compared with using EA water for irrigation. The results of this study indicated that Type I recycled water may be used for irrigation of actively growing warm-season turf with minimal environmental impact on groundwater quality provided that turf areas are irrigated responsibly using ET or a fraction thereof as the basis for irrigation and a judicious nutrient management program is employed.


   ACKNOWLEDGMENTS
 
We thank the San Antonio Water System for their financial support of this project.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 





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