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© 2009 Plant Management Network.
Accepted for publication 19 August 2009. Published 14 October 2009.

Soil and Effluent Irrigation Nutrient Monitoring of an Alabama Golf Course

E. A. Guertal, Professor, Agronomy and Soils, M. Dougherty, Assistant Professor, Biosystems Engineering, and E. van Santen, Professor, Agronomy and Soils, 201 Funchess Hall, Auburn University, AL 36849

Corresponding author: E. A. Guertal. eguertal@acesag.auburn.edu

Guertal, E. A., Dougherty, M., and van Santen, E. 2009. Soil and effluent irrigation nutrient monitoring of an Alabama golf course. Online. Applied Turfgrass Science doi:10.1094/ATS-2009-1014-01-RS.

Abstract

Although wastewater (effluent) application to golf courses is a practice of interest across the USA, research has largely centered on effluent use in the arid southwest. The objective of this research project was to sample effluent used to irrigate a southeastern golf course, and to also sample soil receiving effluent application. From October 2006 to October 2008 soil and effluent samples were taken monthly from three replicate fairways, the sewage lagoon itself, and a “no effluent” (control) area. Both soil and effluent samples were analyzed for nitrate (NO₃-N), ammonium (NH₄-N), phosphate (PO₄-P), and electrical conductivity (EC). Average EC of effluent was low (0.23 dS/m), and average EC in effluent treated soil was 0.26 dS/m, as compared to 0.21 dS/m in soil not receiving effluent. Extractable soil PO₄-P ranged from a low of 1.6 to a high of 62.2 ug/g, and always remained within the “medium” range for a P soil test, indicating that P was not accumulating in the upper 7.6 cm of soil. Highest and lowest effluent NO₃-N was 7.24 and 0.12 ug/mL, respectively, with a 2-year average of 1.88 and 2.11 ug/mL measured in fairway irrigation and lagoon effluent, respectively. In this 2-year period, continuous irrigation with effluent water posed no observed environmental or agronomic hazards to the sampled 7.6-cm deep soil layer nor to the hybrid bermudagrass [Cynodon dactylon (L.) Pers. X Cynodon transvaalensis Burtt-Davy] on the golf course fairways.

Introduction

Application of sewage effluent to golf course turf first received attention in the southwestern USA, where limited water supplies and an arid climate created interest in the suitability of effluent as an irrigation source. Twenty-five years ago the effect of effluent application on bermudagrass (Cynodon dactylon L. Pers.) in the arid southwestern USA was evaluated, and it was found that: (i) year-round use of effluent was possible in the arid climate; (ii) as effluent application rate increased, water use by the bermudagrass also increased; and (iii) turfgrass nutrient uptake made effective use of nitrate and phosphate contained in the effluent (2,24,17). A decade later, another series of papers evaluated the impact of effluent water irrigation on soil, turf, and leachate quality, collecting data from the first time that effluent was applied. After 16 mo of irrigation (either effluent or potable water), both soil and leachate electrical conductivity (EC) was greater in plots irrigated with effluent. Soil NO₃-N, NH₃-N, PO₄-P, and exchangeable sodium percentage (ESP) were always higher in effluent treated plots (13). For the turfgrass itself, application of the effluent reduced seedling emergence (Cynodon dactylon L. Pers. and Lolium perenne L.) and decreased the need for supplemental N and P fertilization (14). After 3.3 years of effluent irrigation soil salinity, Na, K, P, and pH all increased, but not to the extent that the quality of the sandy loam soil was negatively affected (20). The conclusion was that 3.3 years of irrigation with secondary wastewater effluent had no serious negative effects on the soil (20).

One area of concern with wastewater irrigation is the presence of byproducts from the process of water softening with sodium chloride (NaCl) or chlorination [N-nitrosodimethylamine (NDMA)]. When simulated water softener regenerated wastewater was applied to various turfgrasses there was higher tissue chloride in wastewater-treated plants, but no evidence of chloride toxicity or growth reduction was observed (34). In another study, when soil that had been irrigated with treated wastewater was leached, NDMA was detected in the leachate of 9 of 400 samples, and those 9 samples had concentrations close to the detection limit of NDMA. Thus, despite relatively high NDMA levels in the wastewater itself, there was little evidence of NDMA leaching (9). Later mass balance work found that the gaseous diffusion and volatilization were the likely loss pathways for most NDMA in treated wastewater (5).

Although wastewater application is an issue of concern across the entire USA, published research has largely centered on effluent use in the southwest (9,13,14,20,25,31,34). Recent work continued this trend, monitoring soil and turf indices over a 4.5-year period on nine golf courses in Nevada (6,7,19). Although courses that had a long-term history of irrigation with treated sewage effluent had greater soil salinity, measured plant responses (leaf xylem water potential, color) did not differ from that measured in the fresh-water irrigated courses (19). Successful irrigation with treated sewage effluent in the arid southwest required adequate leaching fractions, with minimal periods of deficit irrigations (7). Proper leaching fractions were deemed essential to control salinity, which, it was hypothesized, could increase from continued deficit irrigation using treated effluent water (6,7).

There is a southwestern regionalism to the published body of work about effluent irrigation, and research that examines effluent application to golf courses in other regions of the USA is somewhat scarce. Concerns with effluent application on southeast soils centered around the need to store effluent when not needed by the turfgrasses, and low infiltration rates of applied effluent into fine-textured soils (27). When effluent ponds from three North Carolina golf courses were sampled effluent conductivity in all ponds was low (~0.5 dS/m) (28). This despite the fact that many southeastern golf courses do use treated waste water, when available, to partly or completely irrigate their golf course (8). Thus, the objective of this research project was to examine the impact of treated sewage effluent used as the sole irrigation source on southeastern hybrid bermudagrass [Cynodon dactylon (L.) Pers. X Cynodon transvaalensis Burtt-Davy] golf course fairways, examining both water and soil quality indices.

Sampling Effluent and Soil in a Southeastern Golf Course

The two-year study was initiated in October 2006 at a 20-year-old central Alabama (USA) golf course located at latitude 32°49'52"N and longitude 85°45'49"W. All sampled areas in the study consisted of ‘Tifway’ hybrid bermudagrass. Soil types for the sampled fairways and areas were in the Gwinnett-Lloyd and Gwinnett-Agricola complexes (fine, kaolinitic, thermic Rhodic Kanhapludults), with textural surface horizons of loam for the Lloyd and Agricola series and sandy loam for the Gwinnett series.

The course had been irrigated with effluent for at least 5 years, with all irrigation applied to the course from the treated effluent from the surrounding lake/resort community sewage plant. The sewage plant from which effluent was obtained was an activated sludge plant with extended aeration, treated to secondary standards. Average discharge from the facility was 94,500 liter/day, with effluent stored in a 0.71-ha lagoon with a 15.3-million-liter storage capacity. Effluent water used for irrigation was chlorinated. The only section of the golf course that was not irrigated with effluent was an unused area at the side of the course clubhouse, which received little to no supplemental irrigation. This area was also in Tifway hybrid bermudagrass, and it served as our untreated (no effluent application) control plot for the length of the study. Fertilizers were applied to the course and control areas routinely in September, February, and May of each year at the rates shown in Table 1.

Table 1. Fertilization schedule for the golf course fairways and area
not receiving effluent for September 2006 to September 2008.

The study was conducted as a monthly survey of soil and effluent water quality sampling, with three fairways as replicates. Water samples were collected from: (i) the sewage lagoon which provided the effluent, (ii) irrigation heads on replicated fairways, and (iii) the “dump” zone where excess effluent was pumped if it was not needed for fairway irrigation. Soil samples were collected from the fairways, the dump zone and the control zone. The control zone was the rarely-irrigated area at the side of the clubhouse, which never received effluent application, and thus served as the “no effluent” control. For the two-year study period “rarely irrigated” refers to the four times that a home-type oscillating sprinkler was used to prevent death of the turf due to excessive drought. In those four instances potable water was used for irrigation, and water samples were not collected. The dump zone was a border (~0.2 ha in size) in the out-of-bounds area next to the number 2 fairway. This area was where excess effluent was piped and dumped when irrigation was not needed on the golf course. It was our hypothesis that this dump area would represent the worst-case surface accumulation of excess nutrients. In each of the specified areas soil (fairways, dump, and control) and water (fairways, dump, and lagoon) samples were collected as described below.

Selected replicate fairways were numbers 1, 2, and 12, with samples collected monthly and randomly from each fairway. For each fairway the following was done: (i) irrigation was run briefly (around 5 min) to clear the irrigation line and sprinkler heads of standing water; (ii) three randomly selected irrigation heads were removed, a sample (30 mL minimum) of water pulled from the pipe, and the three samples were then combined into one sample; and (iii) ten to 15 soil samples (0 to 7.6 cm sampling depth, 2.5 cm diameter) were removed from each fairway and combined into one soil sample. Soil samples from the control and dump zones were collected using this same sampling technique.

Water samples were also collected from the sewage lagoon. To do this water samples were removed directly from the upper 30 cm of the storage lagoon in which effluent water was stored. To collect these samples, a 250-mL catch beaker on a 1 m sampling rod was inserted into the lagoon (30 cm deep) and the water around the sampling area was mixed for around 30 sec. A sample of at least 50 mL in size was collected. This process was repeated three times randomly around the lagoon perimeter, and all samples were combined into one monthly sample. In some months of the study the lagoon was not accessible for research, and samples were not collected in those months. Water samples from the dump zone were collected by opening the valve on the transfer pipe that shunted water to the dump zone, allowing the water to run for a few moments, and collecting a sample of at least 50 mL.

All water and soil samples were stored on ice immediately after collection, and then frozen until analysis. For all samples (both water and soil) NO₃-N, NH₄-N, and PO₄-P were determined. Soil nitrate and ammonium samples were first extracted with 2M KCl, and then colorimetrically analyzed via microtiter plate (16,29). Soil phosphorus (PO₄-P) was determined by Mehlich-1 extraction and colorimetric analysis via microtiter plate reader (22,21). Water samples were analyzed using the same colorimetric techniques as used for the soil extracts. Soil samples and samples from the sewage lagoon were also analyzed for soluble salts (32) and for electrical conductivity (EC) (26).

Mixed models methodology as implemented in SAS PROC GLIMMIX was used for data analysis, where treatment, sample collection date, and their interaction were fixed effects, and replicate (fairways) within treatment the sole random effect. The residual covariance structure was modeled because of heterogeneity of variance issues. Starting with an unstructured variance model (each sampling date having its own variance) we combined the dates into homogeneous variance groups, and created the best fitting structure based on the AICC criterion. Treatments were compared within application date using the slicediff option of the LSMEANS statement of the abovementioned PROC. The simulation option was used to adjust the calculated P-values for multiple comparisons.

Observed Environmental or Agronomic Effects

For the two years of the study the southeastern USA was in a severe drought, and precipitation was well below typical amounts (Fig. 1). In the two-year study period there were only four months in which rainfall in a given month exceeded the 30-year average. These months were: October 2006 (the month in which the study was initiated), November 2006, August 2008, and October 2008. The only month in which rainfall significantly exceeded the 30-year average was in August 2008, when Tropical Storm Fay moved through, and 96 mm (3.8 inches) of rain fell on 24 August 2008, resulting in a total of 198 mm of rainfall for that month. Because of this prolonged drought, the excess effluent dump zone sampled in this study was never used throughout the two years of sampling, and all effluent water was used for course irrigation. Thus, for this two-year period the effluent dump zone could not be viewed as a worst case scenario of nutrient accumulation in the upper soil horizon.

Fig. 1. Monthly precipitation (mm) recorded for the Dadeville, AL, region for the 2 years of the experiment period, and for the 30-year average (1971-2000). Total precipitation for the study and 30-year period was 199 and 321 cm, respectively.

Although accumulation of salts is not typically an issue with irrigated turfgrass in Alabama, the fact that this study was an exploration of effluent irrigation meant that effluent salinity could be of concern. Effluent samples collected directly from the lagoon were analyzed for electrical conductivity and soluble salts, and those results are shown in Table 2. Electrical conductivity was low (average of 0.23 dS/m), indicating that the effluent would not pose a salinity hazard. Electrical conductivity in water below 0.7 dS/m is generally considered safe for irrigation water, while values that exceed 3.0 dS/m are considered potentially hazardous for crops that are not tolerant to salinity (11,18). Bermudagrass is considered relatively tolerant of salinity, and will tolerate soil salinity levels greater than 10 dS/m (11). In another study, in over 16 mo of sampling EC values of 0.65 to 0.91 dS/m were found in wastewater from a Tucson, AZ, treatment facility (13). A 4.5-year study found EC of up to 2.1 dS/m when reuse water was sampled directly from main treatment plants in southern Nevada (19). When data from five golf courses that had been exclusively irrigated with recycled wastewater in the Denver and Fort Collins, CO, area were surveyed, average EC of the wastewater was 0.84 dS/m, while surface water used to irrigate other golf courses had an average EC of 0.23 dS/m (25). In a published study from the southeastern USA, effluent samples from three different golf course effluent irrigation ponds had measured conductivity of 0.45 to 0.58 dS/m (28).

Table 2. Electrical conductivity^x and soluble salts^y measured
in sewage lagoon effluent used to irrigate hybrid bermudagrass
fairways, 2007-2008.

 ^x Electrical conductivity determined using the methods outlined
in Rhoades (26).

 ^y Soluble salts determined using the method outlined in
Reference Soil test Methods for the Southern Region of the
United States (26).

Measured soluble salts (Table 2) were also low, and were similar to those measured in other work. Water samples from a Colorado wastewater treatment plant had total dissolved salts of 614 and 126 mg/liter in recycled waste water and surface water, respectively (25). For this study, soluble salts in the effluent ranged from a low of 122 to a high of 191 mg/liter.

Unlike courses situated in arid environments, the development of surface soil layers with salinity issues would be less likely in the humid southeast. In fact, previous work in arid regions largely found that detrimental levels of salinity were not an issue, especially when irrigation was provided in a manner that minimized periods of deficit irrigation (6,7). In the humid southeast typical annual precipitation is 1422 mm/year, an average of 119 mm/month. Even in the drought-affected years of this study precipitation was sufficient that soil salinity did not become an issue. Over the entire study period the highest soil salinity observed was 0.33 dS/m, measured in the fairways in August 2007. Average soil salinity over two years was 0.26 dS/m and 0.21 dS/m in the effluent irrigated fairways and in the control area, respectively. Over a 4-year study, 1800 soil samples (0 to 15 cm) were taken from nine golf courses in southern Nevada. In that sampling period, the lowest and highest average EC measured in golf course fairways receiving 100% effluent irrigation were 3.08 and 15.21 dS/m, while the low and high EC from fairways irrigated with fresh water was 2.22 and 3.17 dS/m, respectively (7). Use of recycled water from the San Antonio Water System increased soil EC from 0.25 (potable) to 0.32 dS/m (31). Thus, in our humid southeastern environment, measured soil EC e after two years of 100% effluent irrigation were low and were observed to be well below the level (> 10 dS/m) that could damage turf or soil (11).

Of greater concern was the potential accumulation in the soil surface of nutrients (especially N and/or P) contained in the effluent. Table 3 provides water data for the 2 years of the study, while Table 4 provides results from the 2M KCl extraction for NO₃-N and NH₄-N, and Mehlich-1 extraction for PO₄-P concentration. Highest and lowest effluent NO₃-N was 7.24 (dump zone, April 2007) and 0.12 (lagoon, June 2008) ug/mL, respectively, with a 2-year average of 1.88, 2.11, and 1.68 ug/mL measured in the fairways, lagoon, and dump zone, respectively (Table 3). In comparison, an irrigation pond in southern Nevada receiving reuse wastewater from a wastewater treatment facility had NO₃-N concentrations that typically fell in the 8 to 16 mg/liter range, with a low of 1 and a high of 27 mg/liter (6). When the NO₃-N content of effluent sampled directly from the lagoon was compared to that from the fairways there were no consistent statistical differences due to sampling location. Out of the 14 sampling dates in which both lagoon and fairway samples were collected there were three dates in which the lagoon had a significantly higher effluent NO₃-N content than that measured in the fairway samples.

Table 3. Mean nitrate-N, ammonium-N and phosphate-P content in effluent from three sampling areas (fairways, dump, and lagoon) as affected by sampling date.

There are fewer directly attributed human health concerns with ammonium in effluent water, although risks to aquatic species from ammonia (NH₃-N is the toxic form, and not NH₄-N) have been well documented (3,4). The method used to measure NH₄-N in this study actually measured NH₃-N + NH₄-N, with the relative proportion of the two affected by water pH and water temperature. At the effluent pHs (< 8.0) found in these samples less than 10% of the ammonium would be in the toxic ammonia form (10). Typical concentrations of ammonia in untreated domestic wastewater range from 10 to 50 mg/liter (33). In our study effluent NH₃-N + NH₄-N ranged from 0.07 (October 2006, dump zone) to 19.92 (October 2007, fairways) mg/liter (Table 3). Concentration of ammonium in the fairway samples rarely differed significantly from that measured in the lagoon samples (Table 3).

Orthophosphate concentration in effluent ranged from a low of 0.19 to a high of 7.20 mg/liter. Typical concentrations of inorganic PO₄-P in municipal wastewaters range from 3 to 10 mg/liter (23). Wide ranges in PO₄-P have been found in other work, with values of 6.4 to 26.9 mg/liter measured in secondary treated municipal effluent (13). Other studies found PO₄-P ranges of 0 to 4.2 mg/liter, with concentrations reduced during summer months to meet state regulations on P discharge from treatment plants (6). On three sampling dates there was greater PO₄-P measured in the fairways than in the lagoon samples (October 2006, and June and July 2008) (Table 3).

Concerns about any environmental impact of surface accumulation from effluent-applied P were not evident in the soil data (Table 4). Extractable soil PO₄-P in surface soil samples ranged from a low of 1.6 (January 2007, dump zone) to a high of 62.2 (fairways, November 2006) ug/g. Average 2-year values for soil PO₄-P were 19.9, 17.9, and 10.6 ug/g for the fairways, control, and the dump zone, respectively. For a hybrid bermudagrass fairway this corresponded to soil-test rankings of “medium” for the first two values, and a “low” ranking for the dump zone (1). Soil test P values exceeding 113 kg/ha would place the soil in a “very high” soil-test rating, at which point no additional P fertilizer would be recommended. Thus, for the two years in which the soils were sampled, effluent and fertilizer P (Table 1) did not result in surface P accumulation that would pose an environmental concern, or a need to curtail regular P applications (according to current AL soil test recommendations). It should be noted, however, that soil-test P concentrations may not always predict dissolved P concentrations in runoff. In one study in New York state soil P levels that ranged from 0 to 658 mg/kg accounted for only half of the variation in runoff P from those samples (30). Even if not well-correlated with a particular soil-test, P losses (runoff or leaching) from turfgrass systems tended to occur during construction or immediately after cultivation, and such losses typically decline rapidly as the turfgrass becomes a uniform system (12,15).

Table 4. Mean nitrate-N, ammonium-N and phosphate-P content in soil samples (0 to 15 cm sampling depth) from three sampling areas (fairways, no effluent area, and dump) as affected by sampling date.

Soil NO₃-N and NH₄-N also did not show signs of surface nutrient accumulation (Table 4). Additionally, the May applications of N fertilizer (Table 1) did not affect extractable soil NH₄-N or NO₃-N (Table 4). There were two sampling dates in which soil NO₃-N concentrations in the control was significantly higher than that measured in the effluent-treated fairways, but at all other sampling dates there was no significant difference in soil NO₃-N. When NO₃-N concentrations in the fairway were compared to those measured in the dump zone there were also few significant differences due to sampling site. If significant differences were present (3 times in 22 sampling events) it was because soil NO₃-N was lower in the dump zone than that measured in the fairways. Over the long-term, NO₃-N could be prone to leaching from the possibly wetter dump zone, although that was not likely in the drought affected two years of this study. Leaching of nutrients applied via long-term effluent was not the focus of this study, but the question does deserve further study. Soil NO₃-N concentrations ranged from a low of 0.1 (January 2008, dump zone) to a high of 37.9 (March 2008, control) ug/g, with average values of 10.9, 12.7, and 3.1 ug/g for the fairways, control, and dump zone, respectively. Since the dump zone rarely received excess effluent irrigation during the 2-year period, and was not fertilized, an increase in soil NO₃-N was not expected in that sampled region. Values measured in this study were similar to those found in other work. After 16 mo of irrigation with effluent, soil NO₃-N was 22.3 mg/kg, as compared to 14.5 mg/kg in soils irrigated with potable water (13). In two studies increased NO₃-N was found in leachate, with values below 10 ug/mL in one study (13), but well above (49 to 53 mg/liter) in another (31).

Conclusions

Two years of soil and effluent water sampling revealed that, for these particular southeastern golf course fairways, there were no surface (0 to 7.6-cm layer) accumulations in soil NO₃-N, NH₄-N, PO₄-P, or EC. Effluent water measured both at the fairway and lagoon never had NO₃-N levels that exceeded EPA drinking water standards. Although PO₄-P in effluent samples were relatively high at times, this did not create increases in soil PO₄-P, as soil P in surface soils was consistently low enough that fertilizer P was still recommended. In this 2-year period (which was during a severe drought) irrigation with effluent water posed no observed environmental or agronomic hazards to the hybrid bermudagrass and the 0 to 7.6-cm soil layer on the golf course fairways.

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