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Journal of Environmental Quality 31:1710-1715 (2002)
© 2002 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America

TECHNICAL REPORTS
Surface Water Quality

Phosphorus and Nitrate Nitrogen in Runoff Following Fertilizer Application to Turfgrass

L. M. Shuman*

Department of Crop and Soil Sciences, Univ. of Georgia, Griffin Campus, 1109 Experiment Street, Griffin, GA 30223-1797

* Corresponding author (lshuman{at}gaes.griffin.peachnet.edu)

Received for publication July 31, 2001.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY
 REFERENCES
 
Intensively managed golf courses are perceived by the public as possibly adding nutrients to surface waters via surface transport. An experiment was designed to determine the transport of nitrate N and phosphate P from simulated golf course fairways of ‘Tifway’ bermudagrass [Cynodon dactylon (L.) Pers.]. Fertilizer treatments were 10–10–10 granular at three rates and rainfall events were simulated at four intervals after treatment (hours after treatment, HAT). Runoff volume was directly related to simulated rainfall amounts and soil moisture at the time of the event and varied from 24.3 to 43.5% of that added for the 50-mm events and 3.1 to 27.4% for the 25-mm events. The highest concentration and mass of phosphorus in runoff was during the first simulated rainfall event at 4 HAT with a dramatic decrease at 24 HAT and subsequent events. Nitrate N concentrations were low in the runoff water (approximately 0.5 mg L-1) for the first three runoff events and highest (approximately 1–1.5 mg L-1) at 168 HAT due to the time elapsed for conversion of ammonia to nitrate. Nitrate N mass was highest at the 4 and 24 HAT events and step-wise increases with rate were evident at 24 HAT. Total P transported for all events was 15.6 and 13.8% of that added for the two non-zero rates, respectively. Total nitrate N transported was 1.5 and 0.9% of that added for the two rates, respectively. Results indicate that turfgrass management should include applying minimum amounts of irrigation after fertilizer application and avoiding application before intense rain or when soil is very moist.

Abbreviations: HAT, hours after treatment


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY
 REFERENCES
 
MANY TURFGRASS AREAS are intensively managed with high inputs of fertilizers, herbicides, and pesticides. Golf courses and commercial landscapes are especially highly managed, leading to environmental concerns about transport of nutrients to surface waters. These inputs may lead to eutrophication (Carpenter et al., 1998), which is often persistent, and the water is slow to recover. Research on the fate of fertilizer nutrients from turfgrass areas has been somewhat limited (Petrovic, 1990). Research results from studies performed mostly in pasture situations have shown that P does not leach to a great extent, but is readily carried to surface waters in drains and through macropores (Gachter et al., 1998; Hooda et al., 1999; Sims et al., 1998). It has been found that for grassed areas, the loss mechanism in runoff water is by dissolved phosphorus, whereas for cropland it is more by movement with soil particles in the adsorbed state (Sharpley et al., 1994). Since grass greatly ameliorates soil erosion, grassed buffer strips can reduce nitrogen and phosphorus loss by runoff from cropland by "catching" the particulate forms (Heathwaite et al., 1998).

Nutrient transport is highly dependent on the runoff volume, which in turn depends on several factors. One is rainfall intensity. Chichester (1977) found the greatest nitrogen runoff during summer months when rainfall intensities were highest. A second determinant of runoff volume is soil moisture at the time of the rainfall event. Using a portable rainfall simulator, Cole et al. (1997) found that seven days after a natural rainfall of 165 mm, the nutrient loss to surface runoff for a simulated event was 10 to 15% of that applied, whereas for dry soil the loss was only 2% of applied. Likewise, Pote et al. (1999) found that soluble phosphorus in runoff water in August when the soil was moist was nearly twice that in May when the soil was dry. Thus, runoff volume depends to a great extent on rainfall intensity and the soil moisture at the time of the rainfall event.

There is a dearth of information about nitrogen and phosphorus transport by runoff water from turfgrass. The information that is available is not definitive. It has been shown that phosphorus loss from perennial pasture in Australia where application of up to 1000 kg ha-1 (1.8 lb P per 1000 ft2) resulted in transport of soluble phosphorus, and not particulate phosphorus (Austin et al., 1996). Significant losses of nitrogen and phosphorus above control were reported for turfgrass fertilized with 220 kg N ha-1 (4.5 lb per 1000 ft2), but losses were small compared with losses from agronomic row crops (Gross et al., 1990). Nitrate in runoff from soluble fertilizer sources was related to rates of nitrogen and water volume applied (Brown et al., 1977). In this study, where irrigation was kept near the evapotranspiration rate, the loss of nitrate was low.

Because information on nutrient transport from turfgrass areas is limited, and nutrient transport to surface waters is a current environmental concern, we conducted runoff trials using field runoff plots.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 SUMMARY
 REFERENCES
 
Twelve individual plots (7.0 x 3.6 m) separated by landscape timbers were built in a grid with a 5% slope from the back to the front. The topsoil was a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludult) that has a mixed surface horizon (70.2, 18.1, and 11.8% sand, silt, and clay, respectively; pH 5.8; Mehlich 1–extractable phosphorus 6.15 mg kg-1; total carbon 12 mg kg-1; cation exchange capacity 5.43 cmolc kg-1; water holding capacity 85 g kg-1). The soil is typical of the Piedmont area of the U.S. Southeast. The slope was developed by removing the topsoil, grading the subsoil, and returning the topsoil over the area. The plots were sprigged with ‘Tifway’ bermudagrass, and all plots had complete ground cover. A trough was installed in a ditch at the front of each plot to collect the runoff water in a tipping bucket sample collection apparatus. The tipping bucket tips each time that 2 L of runoff water is collected, tripping a microswitch attached to a data collecting device that counts the tips. With each tip a slot between the buckets collects a subsample of the runoff water in a stainless steel container. Collected water was analyzed after each simulated rainfall event. Wobbler off-center rotary action sprinkler heads (Senninger Irrigation, Orlando, FL) were mounted 7.4 m apart and 3.1 m above the sod surface. Operated at 138 kPa, the measured simulated rainfall intensity was 27 mm h-1 (about 1 inch h-1), which is lower than reported by Smith and Bridges (1996) for this same facility. Simulated rainfall water had an electrical conductance of 0.116 S m-1, nitrate N concentration of 0.14 mg L-1, and a phosphate P concentration of 0.06 mg L-1.

Fertilizer treatments were 10–10–10 granular at rates to give 0, 12, and 24 kg N ha-1 (0, 0.25, and 0.5 lb N per 1000 ft2) and rates of 0, 5, and 11 kg P ha-1 (0, 0.11, and 0.22 lb P per 1000 ft2). The major nitrogen and phosphorus source was monoammonium phosphate. This fertilizer source was used because balanced agricultural-grade fertilizers are often applied to fairways. Treatments were made through the summer months from April to September each of two years. The fertilizer was spread with a calibrated drop spreader for the first year and weighed and spread by hand the second year. Each rate was added to every plot so that each rate was replicated 12 times. Rainfall events were simulated at 24 h (25 mm) before treatment and at 4 (50 mm), 24 (50 mm), 72 (25 mm), and 168 (25 mm) hours after treatment (HAT). Samples were collected after each simulated rainfall event and also for any natural rainfall events during the course of the experiment. Treatments were spaced to allow natural runoff and incorporation into the soil to lower the potential carryover from one treatment to the next. Soil moisture was determined before each simulated rainfall event by oven-drying a 7.5-cm-deep soil core.

Subsamples collected from each rainfall event were stored at 4°C prior to analysis. Nitrate N and phosphate P were determined for samples filtered through 0.45-µm filters, which is considered to be the soluble form (Sharpley et al., 1992). Nitrate N was analyzed colorimetrically with a Lachat (Milwaukee, WI) flow analyzer. The instrument first reduces nitrate to nitrite with a copper–cadmium column and the nitrite color is developed with a sulfanilamide and N-(1-naphthyl) EDTA reagent. The magenta color is read at 520 nm. Phosphate was also determined colorimetrically (Murphy and Riley, 1962). The first year the samples were analyzed without the aid of the flow analyzer. We developed the color in 50-mL volumetrics and measured absorbance with a spectrophotometer at a wavelength of 880 nm. The second year they were analyzed with the Lachat flow system.

Means of nitrate N and phosphorus concentration and mass were separated with analysis of variance with an LSD at the 5% level of significance. A General Linear Model was used to test years to determine if there were interactions. The Year x Rate interactions were tested with Rep x Year as the error term. If the interaction was significant, then the data are presented for each year. If it was nonsignificant, then the data are presented as an average of the two years.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
SUMMARY
 REFERENCES
 
The volumes of runoff water for the various experimental runs were enough alike for the two years statistically that they could be averaged (Fig. 1) . Ideally, all the volumes for 4 and 24 HAT (50-mm simulated rainfalls) and 72 and 168 HAT (25-mm simulated rainfalls) would be the same. However, as can be seen, there was some variation for the three treatments within a time period and the time periods were also different (statistics not shown for the time periods). The 4 HAT volumes were lower than for 24 HAT, probably due to the soil being more saturated at 24 HAT. The soil was brought to field capacity the day before treatment, so after 24 HAT the soil had 50 mm simulated rain for three days in a row. The volumes for 72 and 168 HAT simulated rainfalls were lower for two reasons. Only 25 mm of simulated rain was applied, and there was time for the soil to dry out. The volumes for the 168 HAT simulated rainfall were lower than the volumes for the 72 HAT simulated rainfall because of the four-day time period to dry out. Some of the variation in volumes came from weather conditions affecting the rate of soil drying. The soil would naturally dry out more on hot, sunny days than on cool, cloudy days. The experiments were performed during a time span of April to September, so drying would be different in the spring and fall as compared with summer. These simulated rainfall intensities and amounts were lower than those used by Cole et al. (1997), who used 51 to 64 mm h-1 for 75 to 140 min within 24 HAT.



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  		Fig. 1. Runoff volumes for three rates of fertilizer as averages of two years. Bars with the same letters within a time interval are not different according to an LSD at the 5% level.

 
Since soil moisture has an effect on runoff volume, soil moisture was sampled just before each runoff event. Regression analyses were performed on the averages of the 12 replications for each event for each year (not averages of years). The data are presented for the 50- and 25-mm simulated rainfall events separately (Fig. 2) . Some of the soil moisture data sets are missing, which accounts for the number of points presented. Most of the data are from the second year. For the 50-mm simulated rainfalls there is a good linear relationship with only one outlier. The R2 value is significant. For the 25-mm simulated rainfall events, there is a linear pattern, but the points are more scattered. This scatter, and the fact that there are only six points, led to a nonsignificant R2 value. The longer times between rainfall events allowed more variation in soil drying than for the first two rainfall events. Cole et al. (1997) likewise found that the higher the antecedent soil moisture, the higher the runoff volumes from simulated rainfall.



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  		Fig. 2. Runoff volume versus soil moisture for 25- and 50-mm simulated rainfall events.

 
The amount of water that ran off the plots is expressed as a percent of that added in Table 1. These data are essentially the same as for Fig. 1, but are calculated with the amounts that were theoretically added with each simulated rainfall event. These data were not statistically different for the two years and are presented as averages of the years. For the 50-mm simulated rainfall events, there was a high of 43.5% and a low of 24.3% on soil that was near field capacity. For the 25-mm simulated rainfall events, the range was from 17.7 to 27.4%. These variations had much to do with the moisture status of the soil at the time of the rainfall event. In a simulated rainfall experiment with bermudagrass, when the soil was relatively dry, runoff was 4 to 16% of that applied, whereas when the soil was moist, the runoff was 49 to 80% of that added (Cole et al., 1997). These authors used a rainfall intensity of 51 or 64 mm h-1, adding from 63 to 149 mm total within 24 h of adding nutrients. As shown in Fig. 2 there was a direct relation between soil moisture and amount of runoff. Also, the time of year, the temperature, cloud cover, and humidity all play a part in how moist the soil is at the time of the rainfall event. In some cases we received natural rain during the course of an experiment, which caused the later runoff volumes at 72 and 168 HAT to be higher than normal. At the 168 HAT simulated rainfall event, the soil was usually dry and the runoff volume from the 25-mm rainfall was very low. These data indicate that dry soil conditions when applying fertilizer are beneficial for reducing runoff volume, and thus nutrient transport from turf areas.


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  		Table 1. Percent of applied water in runoff averaged over two years.

 
The phosphorus concentrations in the runoff water for the first two runoff events are presented in Fig. 3 . The individual years gave slightly different data resulting in a significant interaction, so the years are presented separately. Nonetheless, the general patterns were similar for the two years. At the zero control rate the phosphorus concentrations were about 0.5 to 1 mg L-1 in the runoff water. Even this concentration, if undiluted, could lead to eutrophication, since the threshold is usually given at less than 0.1 mg L-1 (USEPA, 1976; Schindler, 1977). There were step-wise increases in phosphorus concentrations for both 4 and 24 HAT, but concentrations were much higher in the water from the first runoff event than the second. Austin et al. (1996) found a similar linear relationship between soluble phosphorus concentration in runoff from flood-irrigated pastures and phosphorus rates as superphosphate. Phosphorus concentrations in the water from the second runoff event were still above the zero control level. The second runoff event at 24 HAT produced the highest runoff volumes (Fig. 1).



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  		Fig. 3. Phosphorus concentrations in runoff water for three fertilizer rates at 4 hours after treatment (HAT) and 24 HAT for each of two years. Bars with the same letters within a time interval are not different according to an LSD at the 5% level.

 
The second two runoff events resulted in much lower phosphorus concentrations in the runoff water (Fig. 4) . Note that to aid comparisons, the y axis is the same scale as for Fig. 3. The concentrations for treated plots were generally not significantly different from the zero control plots with the exception of the second year for the 72 HAT simulated rainfall event, where the highest phosphorus rate resulted in a concentration level higher than the zero rate. However, it still was not higher than the control and middle rate for the first year for the 168 HAT runoff event. Thus, the significance is not believed to be consequential. These results show that the major flush of fertilizer phosphorus would be with initial rainfall events, and very little treatment fertilizer phosphorus would be transported in later rainfall events. A similar exponential decrease in soluble phosphorus concentrations with successive irrigation events was reported by Austin et al. (1996).



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  		Fig. 4. Phosphorus concentrations in runoff water for three fertilizer rates at 72 hours after treatment (HAT) and 168 HAT for each of two years. Bars with the same letters within a time interval are not different according to an LSD at the 5% level.

 
As for phosphorus concentrations, the nitrate N concentrations in the runoff water were different for the two years. Nitrate N concentrations were very low for the first two runoff events, and treatments caused values only slightly above the zero rate control plots (Fig. 5) . The y axis is higher than the data may seem to warrant, so that comparisons with the nitrate N concentrations for the second two simulated rainfall events are possible. The treatments did produce high enough nitrate N levels to be significantly different, but did show some step-wise increase for all but the 4 HAT simulated rainfall event for the first year. Nitrate N concentrations in the runoff water were a bit higher for the 24 HAT than the 4 HAT runoff event. This is most likely because the ammonia form had 20 h to be transformed to the nitrate form. These data show that when the ammonia form of nitrogen is added, the nitrate concentrations in the runoff water are very low, and much below the 10 mg L-1 drinking water standard (USEPA, 1976). Runoff of nitrate N from Kentucky bluegrass (Poa pratensis L.) fertilized with urea was lower than for agricultural crops (Gross et al., 1990). In that study, the nitrogen would have to have been converted to the nitrate form.



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  		Fig. 5. Nitrate N concentrations in runoff water for three fertilizer rates at 4 hours after treatment (HAT) and 24 HAT for each of two years. Bars with the same letters within a time interval are not different according to an LSD at the 5% level.

 
Contrary to the results for phosphorus concentrations, the nitrate N concentrations were higher in the runoff water for the 72 and 168 HAT runoff events than the earlier events (Fig. 6) . At the 72 HAT runoff events, the treated plots had nitrate N concentration values just slightly above the zero control plots, but were statistically significant. At the 168 HAT runoff event, the ammonia form added in the 10–10–10 fertilizer had seven days to revert to the nitrate form and was thus elevated. The highest rate did not give the highest nitrate N concentrations. There was some variability in this data that may have led to this unusual result, which was consistent across the two years. Again, the nitrate N concentrations were well below the 10 mg L-1 drinking water standard (USEPA, 1976).



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  		Fig. 6. Nitrate N concentrations in runoff water for three fertilizer rates at 72 hours after treatment (HAT) and 168 HAT for each of two years. Bars with the same letters within a time interval are not different according to an LSD at the 5% level.

 
Another way to look at amounts of nutrients in runoff water is to calculate the mass of nutrient by multiplying the concentrations by the runoff volumes. The phosphorus mass data are not shown, because they are almost the same as the concentration data as far as the pattern of transport. The mass of nitrate N, however, had a different pattern than the concentration (Fig. 7) . These data were produced by using data in Fig. 1, 5, and 6. The mass data were not statistically different for the two years, so the two years were averaged. In these data we see increases in nitrate N mass for treatments over control at each simulated rainfall event with the exception of 168 HAT, where concentration was the highest. There were obvious step-wise increases in nitrate N mass with treatment, especially at 24 HAT. Since volumes were not significantly different (Fig. 1) at 24 HAT, these differences were caused by nitrate N. Differences in nitrate N mass were low among treatments for the simulated rainfalls at 72 and 168 HAT. This result may have been due to the conversion of ammonia to nitrate. The conversion rate may not be the same for each rate of ammonia nitrogen.



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  		Fig. 7. Mass of nitrate N in runoff water for three fertilizer rates at four times after treatment as averages of two years. Bars with the same letters within a time interval are not different according to an LSD at the 5% level.

 
The amounts of nitrate N and phosphorus that were transported from the runoff plots are expressed as percentages of that applied in Table 2. For phosphorus, the most came at the 4 HAT rainfall event. The amounts as percentages were very similar for the two fertilizer rates, indicating that the amounts in the runoff will be proportional to that added. The total phosphorus transported was 13.8 and 15.6% for the two rates. The percentages of nitrate N were, of course, much lower at around 1 to 1.5% for the totals. These data reflect the fact that the ammonia form was added, which had to be converted before any nitrate N would appear. The percent nitrate N recovered in the runoff was lower for the higher rate for the 4 and 24 HAT runoff events. In a similar runoff experiment where phosphorus and nitrogen each was added at 49 kg ha-1 (1 lb per 1000 ft2) as urea or sulfur-coated urea and superphosphate, the highest percent phosphorus of added recovered in runoff was 10% and for nitrogen it was 4% (Cole et al., 1997). These authors also found that buffer strips, buffer mowing height, and length of buffer did not affect amounts of nutrient transport.


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  		Table 2. Percent of applied phosphorus and nitrate N in runoff averaged over two years.

 

   SUMMARY
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY
REFERENCES
 
Although these experiments were performed under somewhat severe conditions where runoff was forced, the results yield some interesting observations about nutrient runoff from turfgrass, and some recommendations can be made. The runoff volume is related to rainfall amounts and soil moisture. Thus, irrigation after fertilization should be held to a minimum and certainly low enough to prevent runoff. Fertilizer should not be applied when soil moisture is near or above field capacity and not applied when intense rainfall is expected. Phosphorus concentrations and mass in the runoff water varied directly with fertilizer rate. Therefore, several small applications of phosphorus throughout the year are preferable to one large application once a year from an environmental standpoint. The percent of phosphorus of that added was near 14% for the conditions of these experiments for both rates applied. Nitrate N will initially be low in runoff water when the ammonia form is applied. This amount increases with time as the ammonia is converted to nitrate. However, the concentration of nitrate N in the runoff water for this experiment never exceeded the 10 mg L-1 drinking water standard. As for phosphorus, it is always a good practice to apply low amounts of nitrogen of any form to prevent nitrogen loading of surface waters through transport.


   ACKNOWLEDGMENTS
 
The author gratefully acknowledges Ray Pitts, Kathy Evans, and Garland Layton for technical assistance. This research as supported by the United States Golf Association, the Georgia Turfgrass Foundation Trust, and by State and HATCH funds allocated to the Georgia Experiment Stations.


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




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