Phosphorus and Nitrate Nitrogen in Runoff Following Fertilizer Application to Turfgrass L. M. Shuman* ABSTRACT volume, which in turn depends on several factors. One Intensively managed golf courses are perceived by the public as is rainfall intensity. Chichester (1977) found the greatest possibly adding nutrients to surface waters via surface transport. An nitrogen runoff during summer months when rainfall experiment was designed to determine the transport of nitrate N intensities were highest. A second determinant of runoff and phosphate P from simulated golf course fairways of ‘Tifway’ volume is soil moisture at the time of the rainfall event. bermudagrass [Cynodon dactylon (L.) Pers.]. Fertilizer treatments Using a portable rainfall simulator, Cole et al. (1997) were 10–10–10 granular at three rates and rainfall events were simu- found that seven days after a natural rainfall of 165 mm, lated at four intervals after treatment (hours after treatment, HAT). Runoff volume was directly related to simulated rainfall amounts and the nutrient loss to surface runoff for a simulated event soil moisture at the time of the event and varied from 24.3 to 43.5% was 10 to 15% of that applied, whereas for dry soil the of that added for the 50-mm events and 3.1 to 27.4% for the 25-mm loss was only 2% of applied. Likewise, Pote et al. (1999) events. The highest concentration and mass of phosphorus in runoff found that soluble phosphorus in runoff water in August was during the first simulated rainfall event at 4 HAT with a dramatic when the soil was moist was nearly twice that in May decrease at 24 HAT and subsequent events. Nitrate N concentrations when the soil was dry. Thus, runoff volume depends to were low in the runoff water (approximately 0.5 mg L 1) for the first a great extent on rainfall intensity and the soil moisture three runoff events and highest (approximately 1–1.5 mg L 1) at 168 at the time of the rainfall event. 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- There is a dearth of information about nitrogen and wise increases with rate were evident at 24 HAT. Total P transported phosphorus transport by runoff water from turfgrass. for all events was 15.6 and 13.8% of that added for the two non-zero The information that is available is not definitive. It has rates, respectively. Total nitrate N transported was 1.5 and 0.9% of that been shown that phosphorus loss from perennial pasture added for the two rates, respectively. Results indicate that turfgrass in Australia where application of up to 1000 kg ha 1 management should include applying minimum amounts of irrigation (1.8 lb P per 1000 ft2) resulted in transport of soluble after fertilizer application and avoiding application before intense phosphorus, and not particulate phosphorus (Austin et rain or when soil is very moist. 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 M any turfgrass areas are intensively managed with high inputs of fertilizers, herbicides, and pesticides. Golf courses and commercial landscapes are 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 vol- especially highly managed, leading to environmental ume applied (Brown et al., 1977). In this study, where concerns about transport of nutrients to surface waters. irrigation was kept near the evapotranspiration rate, the These inputs may lead to eutrophication (Carpenter et loss of nitrate was low. al., 1998), which is often persistent, and the water is Because information on nutrient transport from turf- slow to recover. Research on the fate of fertilizer nutri- grass areas is limited, and nutrient transport to surface ents from turfgrass areas has been somewhat limited waters is a current environmental concern, we con- (Petrovic, 1990). Research results from studies per- ducted runoff trials using field runoff plots. formed mostly in pasture situations have shown that P does not leach to a great extent, but is readily carried MATERIALS AND METHODS to surface waters in drains and through macropores (Gachter et al., 1998; Hooda et al., 1999; Sims et al., Twelve individual plots (7.0 3.6 m) separated by land- scape timbers were built in a grid with a 5% slope from the 1998). It has been found that for grassed areas, the loss back to the front. The topsoil was a Cecil sandy loam (fine, mechanism in runoff water is by dissolved phosphorus, kaolinitic, thermic Typic Kanhapludult) that has a mixed sur- whereas for cropland it is more by movement with soil face horizon (70.2, 18.1, and 11.8% sand, silt, and clay, respec- particles in the adsorbed state (Sharpley et al., 1994). tively; pH 5.8; Mehlich 1–extractable phosphorus 6.15 mg kg 1; Since grass greatly ameliorates soil erosion, grassed total carbon 12 mg kg 1; cation exchange capacity 5.43 cmolc buffer strips can reduce nitrogen and phosphorus loss kg 1; water holding capacity 85 g kg 1). The soil is typical by runoff from cropland by “catching” the particulate of the Piedmont area of the U.S. Southeast. The slope was forms (Heathwaite et al., 1998). developed by removing the topsoil, grading the subsoil, and Nutrient transport is highly dependent on the runoff 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 Department of Crop and Soil Sciences, Univ. of Georgia, Griffin Cam- plot to collect the runoff water in a tipping bucket sample pus, 1109 Experiment Street, Griffin, GA 30223-1797. Received 31 July collection apparatus. The tipping bucket tips each time that 2001. *Corresponding author (email@example.com). Published in J. Environ. Qual. 31:1710–1715 (2002). Abbreviations: HAT, hours after treatment. 1710 SHUMAN: PHOSPHORUS AND NITRATE NITROGEN IN TURF RUNOFF 1711 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 ana- lyzed 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 Fig. 1. Runoff volumes for three rates of fertilizer as averages of two monoammonium phosphate. This fertilizer source was used years. Bars with the same letters within a time interval are not because balanced agricultural-grade fertilizers are often ap- different according to an LSD at the 5% level. plied to fairways. Treatments were made through the summer months from April to September each of two years. The fertil- izer was spread with a calibrated drop spreader for the first would be the same. However, as can be seen, there was year and weighed and spread by hand the second year. Each some variation for the three treatments within a time rate was added to every plot so that each rate was replicated period and the time periods were also different (statis- 12 times. Rainfall events were simulated at 24 h (25 mm) before treatment and at 4 (50 mm), 24 (50 mm), 72 (25 mm), tics not shown for the time periods). The 4 HAT vol- and 168 (25 mm) hours after treatment (HAT). Samples were umes were lower than for 24 HAT, probably due to collected after each simulated rainfall event and also for any the soil being more saturated at 24 HAT. The soil was natural rainfall events during the course of the experiment. brought to field capacity the day before treatment, so Treatments were spaced to allow natural runoff and incorpora- after 24 HAT the soil had 50 mm simulated rain for tion into the soil to lower the potential carryover from one three days in a row. The volumes for 72 and 168 HAT treatment to the next. Soil moisture was determined before simulated rainfalls were lower for two reasons. Only each simulated rainfall event by oven-drying a 7.5-cm-deep 25 mm of simulated rain was applied, and there was soil core. time for the soil to dry out. The volumes for the 168 Subsamples collected from each rainfall event were stored HAT simulated rainfall were lower than the volumes at 4 C prior to analysis. Nitrate N and phosphate P were for the 72 HAT simulated rainfall because of the four- determined for samples filtered through 0.45- m filters, which day time period to dry out. Some of the variation in is considered to be the soluble form (Sharpley et al., 1992). Nitrate N was analyzed colorimetrically with a Lachat (Mil- volumes came from weather conditions affecting the waukee, WI) flow analyzer. The instrument first reduces ni- rate of soil drying. The soil would naturally dry out trate to nitrite with a copper–cadmium column and the nitrite more on hot, sunny days than on cool, cloudy days. The color is developed with a sulfanilamide and N-(1-naphthyl) experiments were performed during a time span of April EDTA reagent. The magenta color is read at 520 nm. Phos- to September, so drying would be different in the spring phate was also determined colorimetrically (Murphy and and fall as compared with summer. These simulated Riley, 1962). The first year the samples were analyzed without rainfall intensities and amounts were lower than those the aid of the flow analyzer. We developed the color in 50-mL used by Cole et al. (1997), who used 51 to 64 mm h 1 volumetrics and measured absorbance with a spectrophotome- for 75 to 140 min within 24 HAT. ter at a wavelength of 880 nm. The second year they were Since soil moisture has an effect on runoff volume, analyzed with the Lachat flow system. soil moisture was sampled just before each runoff event. Means of nitrate N and phosphorus concentration and mass were separated with analysis of variance with an LSD at the Regression analyses were performed on the averages 5% level of significance. A General Linear Model was used of the 12 replications for each event for each year (not to test years to determine if there were interactions. The averages of years). The data are presented for the 50- Year Rate interactions were tested with Rep Year as and 25-mm simulated rainfall events separately (Fig. 2). the error term. If the interaction was significant, then the data Some of the soil moisture data sets are missing, which are presented for each year. If it was nonsignificant, then the accounts for the number of points presented. Most of the data are presented as an average of the two years. 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 RESULTS AND DISCUSSION simulated rainfall events, there is a linear pattern, but The volumes of runoff water for the various experi- the points are more scattered. This scatter, and the fact mental runs were enough alike for the two years statisti- that there are only six points, led to a nonsignificant R2 cally that they could be averaged (Fig. 1). Ideally, all value. The longer times between rainfall events allowed the volumes for 4 and 24 HAT (50-mm simulated rain- more variation in soil drying than for the first two rain- falls) and 72 and 168 HAT (25-mm simulated rainfalls) fall events. Cole et al. (1997) likewise found that the 1712 J. ENVIRON. QUAL., VOL. 31, SEPTEMBER–OCTOBER 2002 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. 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 Fig. 2. Runoff volume versus soil moisture for 25- and 50-mm simu- event, the soil was usually dry and the runoff volume lated rainfall events. from the 25-mm rainfall was very low. These data indi- cate that dry soil conditions when applying fertilizer are higher the antecedent soil moisture, the higher the run- beneficial for reducing runoff volume, and thus nutrient off volumes from simulated rainfall. transport from turf areas. The amount of water that ran off the plots is expressed The phosphorus concentrations in the runoff water as a percent of that added in Table 1. These data are for the first two runoff events are presented in Fig. 3. The essentially the same as for Fig. 1, but are calculated with individual years gave slightly different data resulting the amounts that were theoretically added with each in a significant interaction, so the years are presented simulated rainfall event. These data were not statisti- separately. Nonetheless, the general patterns were simi- cally different for the two years and are presented as lar for the two years. At the zero control rate the phos- averages of the years. For the 50-mm simulated rainfall phorus concentrations were about 0.5 to 1 mg L 1 in the events, there was a high of 43.5% and a low of 24.3% runoff water. Even this concentration, if undiluted, could on soil that was near field capacity. For the 25-mm lead to eutrophication, since the threshold is usually given simulated rainfall events, the range was from 17.7 to at less than 0.1 mg L 1 (USEPA, 1976; Schindler, 1977). 27.4%. These variations had much to do with the mois- There were step-wise increases in phosphorus concen- ture status of the soil at the time of the rainfall event. trations for both 4 and 24 HAT, but concentrations were In a simulated rainfall experiment with bermudagrass, much higher in the water from the first runoff event when the soil was relatively dry, runoff was 4 to 16% than the second. Austin et al. (1996) found a similar of that applied, whereas when the soil was moist, the linear relationship between soluble phosphorus concen- runoff was 49 to 80% of that added (Cole et al., 1997). tration in runoff from flood-irrigated pastures and phos- phorus rates as superphosphate. Phosphorus concentra- Table 1. Percent of applied water in runoff averaged over two tions in the water from the second runoff event were years. still above the zero control level. The second runoff Rate (N, P) 4 HAT† 24 HAT 72 HAT 168 HAT event at 24 HAT produced the highest runoff volumes kg ha 1 % (Fig. 1). 0.00, 0.00 24.3b‡ 38.2a 17.7b 15.3a The second two runoff events resulted in much lower 0.25, 0.11 31.5b 36.6a 23.6a 3.1b 0.50, 0.22 35.3a 43.5a 27.4a 5.5b phosphorus concentrations in the runoff water (Fig. 4). Note that to aid comparisons, the y axis is the same † HAT, hours after treatment. ‡ Values followed by the same letter within a column are not different scale as for Fig. 3. The concentrations for treated plots according to the LSD at the 5% level. were generally not significantly different from the zero SHUMAN: PHOSPHORUS AND NITRATE NITROGEN IN TURF RUNOFF 1713 Fig. 4. Phosphorus concentrations in runoff water for three fertilizer Fig. 5. Nitrate N concentrations in runoff water for three fertilizer rates at 72 hours after treatment (HAT) and 168 HAT for each rates at 4 hours after treatment (HAT) and 24 HAT for each of of two years. Bars with the same letters within a time interval are two years. Bars with the same letters within a time interval are not different according to an LSD at the 5% level. not different according to an LSD at the 5% level. slightly above the zero control plots, but were statisti- control plots with the exception of the second year for cally significant. At the 168 HAT runoff event, the am- the 72 HAT simulated rainfall event, where the highest monia form added in the 10–10–10 fertilizer had seven phosphorus rate resulted in a concentration level higher days to revert to the nitrate form and was thus elevated. than the zero rate. However, it still was not higher than The highest rate did not give the highest nitrate N con- the control and middle rate for the first year for the 168 centrations. There was some variability in this data that HAT runoff event. Thus, the significance is not believed may have led to this unusual result, which was consistent to be consequential. These results show that the major across the two years. Again, the nitrate N concentrations flush of fertilizer phosphorus would be with initial rain- were well below the 10 mg L 1 drinking water standard fall events, and very little treatment fertilizer phos- (USEPA, 1976). phorus would be transported in later rainfall events. Another way to look at amounts of nutrients in runoff A similar exponential decrease in soluble phosphorus water is to calculate the mass of nutrient by multiplying concentrations with successive irrigation events was re- the concentrations by the runoff volumes. The phospho- ported by Austin et al. (1996). rus mass data are not shown, because they are almost As for phosphorus concentrations, the nitrate N con- the same as the concentration data as far as the pattern centrations in the runoff water were different for the of transport. The mass of nitrate N, however, had a two years. Nitrate N concentrations were very low for different pattern than the concentration (Fig. 7). These the first two runoff events, and treatments caused values data were produced by using data in Fig. 1, 5, and 6. only slightly above the zero rate control plots (Fig. 5). The mass data were not statistically different for the The y axis is higher than the data may seem to warrant, two years, so the two years were averaged. In these data so that comparisons with the nitrate N concentrations we see increases in nitrate N mass for treatments over for the second two simulated rainfall events are possible. control at each simulated rainfall event with the excep- The treatments did produce high enough nitrate N levels tion of 168 HAT, where concentration was the highest. 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 run- off 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. Contrary to the results for phosphorus concentra- tions, the nitrate N concentrations were higher in the Fig. 6. Nitrate N concentrations in runoff water for three fertilizer runoff water for the 72 and 168 HAT runoff events than rates at 72 hours after treatment (HAT) and 168 HAT for each the earlier events (Fig. 6). At the 72 HAT runoff events, of two years. Bars with the same letters within a time interval are the treated plots had nitrate N concentration values just not different according to an LSD at the 5% level. 1714 J. ENVIRON. QUAL., VOL. 31, SEPTEMBER–OCTOBER 2002 1997). These authors also found that buffer strips, buffer mowing height, and length of buffer did not affect amounts of nutrient transport. SUMMARY 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 recommenda- tions 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 capac- Fig. 7. Mass of nitrate N in runoff water for three fertilizer rates at ity and not applied when intense rainfall is expected. four times after treatment as averages of two years. Bars with the Phosphorus concentrations and mass in the runoff water same letters within a time interval are not different according to an LSD at the 5% level. varied directly with fertilizer rate. Therefore, several small applications of phosphorus throughout the year are preferable to one large application once a year from There were obvious step-wise increases in nitrate N an environmental standpoint. The percent of phospho- mass with treatment, especially at 24 HAT. Since vol- rus of that added was near 14% for the conditions of umes were not significantly different (Fig. 1) at 24 HAT, these experiments for both rates applied. Nitrate N will these differences were caused by nitrate N. Differences initially be low in runoff water when the ammonia form in nitrate N mass were low among treatments for the is applied. This amount increases with time as the ammo- simulated rainfalls at 72 and 168 HAT. This result may nia is converted to nitrate. However, the concentration have been due to the conversion of ammonia to nitrate. of nitrate N in the runoff water for this experiment The conversion rate may not be the same for each rate never exceeded the 10 mg L 1 drinking water standard. of ammonia nitrogen. As for phosphorus, it is always a good practice to apply The amounts of nitrate N and phosphorus that were low amounts of nitrogen of any form to prevent nitrogen transported from the runoff plots are expressed as per- loading of surface waters through transport. centages of that applied in Table 2. For phosphorus, the most came at the 4 HAT rainfall event. The amounts ACKNOWLEDGMENTS as percentages were very similar for the two fertilizer The author gratefully acknowledges Ray Pitts, Kathy Ev- rates, indicating that the amounts in the runoff will be ans, and Garland Layton for technical assistance. This research proportional to that added. The total phosphorus trans- as supported by the United States Golf Association, the Geor- ported was 13.8 and 15.6% for the two rates. The per- gia Turfgrass Foundation Trust, and by State and HATCH centages of nitrate N were, of course, much lower at funds allocated to the Georgia Experiment Stations. around 1 to 1.5% for the totals. These data reflect the fact that the ammonia form was added, which had to REFERENCES be converted before any nitrate N would appear. The Austin, N.R., J.B. Prendergast, and M.D. Collins. 1996. Phosphorus percent nitrate N recovered in the runoff was lower for losses in irrigation runoff from fertilized pasture. J. Environ. 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