Nutrient Runoff From Bermudagrass Golf Course Fairways After Aerification

Justin Q. Moss, Department of Plant Sciences, University of Wyoming, Laramie 82071; Gregory E. Bell and Dennis L. Martin, Department of Horticulture and Landscape Architecture, and Mark E. Payton, Department of Statistics, Oklahoma State University, Stillwater 74078

Corresponding author: Justin Q. Moss. jmoss@uwyo.edu

Abstract

Aerification is a common turf management practice, but little is known about its influence on nutrient runoff. The objective of this study was to investigate the influence of hollow-tine aerification on nutrient runoff from a bermudagrass [Cynodon dactylon L. (Pers.)] golf course fairway under natural rainfall conditions. Collection troughs and automated samplers were positioned at the bottom of six 12.3- × 24.4-m plots (5% slope) for surface runoff collection. Three plots received hollow-tine aerification and three plots served as control in a randomized complete block design. Aerification and fertilizer (N at 49 kg/ha/month and P₂O₅ at 24 kg/ha/month) were applied at the beginning of each month during the study. Runoff samples were collected and tested for NO₃-N, NH₄-N, and dissolved reactive phosphorus (DRP) after seven natural rainfall events. Aerification delayed runoff by 4 min but did not significantly reduce runoff volume or nutrient losses when compared to control plots. For both treatments, the total amount of applied fertilizer lost to surface runoff was extremely low (<1%). Nutrient concentrations were not statistically different between treatments and had an average concentration of 0.54 mg/liter NO₃-N, 0.44 mg/liter NH₄-N, and 1.20 mg/liter DRP. The practice of hollow-tine aerification neither reduced nor contributed to a loss of nutrients to natural rainfall runoff.

Introduction

Golf course fairways often border lakes, streams, and other water features. Nitrogen and phosphorus are two of the most important nutrients used for the establishment and maintenance of golf course turf (1). Bermudagrass (Cynodon spp.) is a commonly used turfgrass for golf course fairways and may be fertilized at rates as high as 49 kg of N per ha/month and 24 kg of P₂O₅ per ha/month during the growing season. Both N and P have the potential for off-site movement in surface runoff.

High nitrate and phosphate nutrient concentration levels in surface water enable an undesirable growth of algae and aquatic plants that can deplete oxygen and affect plants and animals in the area. This process is called eutrophication and can be accelerated by an overabundance of P and N in surface waters. Nitrogen is transported in water runoff from turfgrass areas primarily as nitrate-N (NO₃-N) and ammonium-N (NH₄-N) and may contribute to eutrophication at concentrations as low as 1 mg/liter (10). Phosphorus in surface runoff from golf course turf areas is primarily transported as HPO₄^2- and H₂PO₄^- which may also be called dissolved reactive phosphorus (DRP) and can contribute to eutrophication at concentrations as low as 25 μg/liter (10). Many blue-green algae can assimilate atmospheric N₂, and therefore P, as opposed to N, is typically the more important contributing factor for eutrophication of surface water (8).

Turfgrass is effective at reducing nutrient runoff (4,5), especially if the fertilizer is lightly irrigated after application. This light irrigation following fertilization is often referred to in the industry as being "watered-in" (9). However, nutrient concentrations in runoff from turf were high enough to contribute to eutrophication in previous studies (3). Research has demonstrated that vegetative filter strips, commonly called buffers, may reduce nutrient runoff from golf course fairways (2,6), but in both studies nutrient concentrations were high enough to contribute to the degradation of surface-water quality. Additional research is required to determine management practices that further reduce nutrient runoff from turf.

Aerification is the process of drilling, spiking, or punching holes in turf and its underlying soil to alleviate soil compaction. Golf course superintendents often aerate bermudagrass fairways one or more times during the growing season. Cole et al. (2) found that aerification of golf course buffer strips (roughs) did not affect nutrient runoff from simulated golf course fairways, but little is known about the effects of aerifying the fairway itself. Hollow-tine aerification transfers soil from beneath to above the turfgrass surface. After the soil cores are transferred to the turfgrass surface, they are typically broken into smaller pieces and transferred back into the core holes with a mat or rake pulled behind a tractor. Another possible management practice is to pull the soil cores from below the turfgrass surface and then leave them on top of the turfgrass surface. Whether the soil cores are dragged back into the core holes, or left on the turfgrass surface, portions of the soil located on the turfgrass surface could potentially contribute to nutrient runoff. Alternatively, the aerification holes could increase water infiltration and decrease potential nutrient runoff.

The objective of this study was to investigate the influence of hollow-tine aerification on nutrient runoff from bermudagrass golf course fairways under natural rainfall conditions. It was hypothesized that aerification would reduce nutrient runoff from bermudagrass golf course fairways under natural rainfall conditions by increasing water infiltration into the soil profile.

Site Description

This research was conducted on the Oklahoma State University Turfgrass Runoff Research Site, Stillwater, OK. The soil at the site was Norge silt loam (fine-silty, mixed, active, thermic Udic Paleustolls) with a bulk density of 1.50 g/cm³. The runoff site was divided into three large blocks. Each block consisted of two experimental units that measured 12.3 m wide with a uniform 5% slope that measured 24.4 m long. The site was graded and sodded with ‘U-3’ bermudagrass [Cynodon dactylon L. (Pers.)] in the summer of 1998. Plots were mowed three times a week at 1.3 cm during the growing season. Prior to this study, plots were fertilized with N at 49 kg ha/month and P₂O₅ 24 kg/ha/month during the growing seasons of 2000, 2001, and 2002. Earthen berms that confined runoff to the area under investigation separated experimental units and blocks. Covered troughs collected runoff water from each experimental unit and channeled it through calibrated Parshall flumes by gravity flow. The collection troughs were made of polyvinylchloride pipe (15 cm diameter) cut in half length-wise and were mounted on wooden support posts. The posts (10 by 10 by 60 cm long) were buried in concrete below the soil frost line to stabilize the troughs. A galvanized shingle-type attachment was fixed to an aluminum angle along the bottom edge of each plot to channel runoff water into the corresponding collection trough (2). The shingle-type attachment was sealed to the soil with paraffin wax to prevent water from running beneath the trough. Stainless steel bolts supported a galvanized cover 7.6 cm above the shingle to allow runoff collection while eliminating the entry of unwanted irrigation or rainfall into the trough.

Isco 6700 portable samplers (Isco, Lincoln, NE) were secured to concrete platforms located between each experimental block. Ultrasonic Modules (Isco 710) mounted over each Parshall flume used ultrasonic reflection to measure water level (6). The sampler was programmed to determine water flow rate from these water level measurements based on a pre-determined calibration of each Parshall flume. A pump in each sampler provided runoff sample collection through vinyl suction line tubing (0.95 cm) fitted with a screen strainer and secured to the Parshall flume. A Rapid Transfer Device (Isco 581) enabled information transfer from samplers to a computer.

Time-domain-reflex probes were permanently buried along the slope in each experimental unit to assess soil moisture content and to help maintain antecedent soil moisture at uniform conditions prior to natural rainfall. These probes were centered within each experimental unit at 2.1, 10.2, and 18.3 m from the top of the fall line and buried 15.2 cm deep. An in-ground sprinkler-type irrigation system that delivered 51 mm/h was located along the edges of each block. The experimental units were irrigated three times per week to field capacity determined by volumetric water content 24 h after saturation. The runoff site was at or very near field capacity (0.22 m² of water per m³ soil) immediately before all natural rainfall events.

Runoff Sampling Methodology

Treatments consisted of three plots (one plot per block) that were aerated with hollow tines and three plots that received no aerification. Data was collected for two months in 2003 and for two months in 2004. The aerated treatments were applied at the beginning of each of the four months during the study. Aerification treatments were applied in a single direction using a 9100 Greens Aerator (Toro, Bloomington, MN) with 1.6-cm diameter tines that were 7.6 cm long. Spacing between tines and aeration holes was 6.4 cm in all directions. After aerification, cores were dragged within each plot with a wire rake pulled behind a utility vehicle and the remaining soil core pieces were further broken down by mowing each plot with a reel mower. Following aerification treatments, fertilizer was applied to all plots as urea at 49 kg of N per ha/month and as triple superphosphate at 24 kg of P₂O₅ per ha/month. Plots were irrigated lightly for 7 min at the rate of 51 mm/h after fertilization to "water-in" the nutrient application. Time from the beginning of rainfall to the initiation of runoff was recorded for each event and runoff water samples were collected in 5-min intervals for 60 min.

Analytical Procedures

Water samples were analyzed for NO₃-N and NH₄-N using colorimetric methods by automated flow injection analysis and DRP using the phosphomolybdate colorimetric procedure employed by Murphy and Riley (7). The detection limit was 0.01 mg/liter for each nutrient in the runoff water samples. The average background levels of nutrients in the natural rainfall samples were 0.58 mg/liter for NO₃-N, 0.29 mg/liter for NH₄-N, and 0.09 mg/liter for DRP. The nutrient mass and concentrations reported in this paper are the background nutrient levels plus fertilizer losses. The background nutrient levels were subtracted from the measured concentrations in collected runoff samples when the proportion of fertilizer loss from plots was determined. Seven natural rainfall events that produced measurable runoff were recorded on 14 May (15 mm), 16 May (41 mm), 10 June (19 mm), 25 June (55 mm), and 30 August in 2003 (17 mm), and on 4 March (64 mm), and 10 April in 2004 (33 mm). Runoff water nutrient samples were collected following the first significant rainfall event after aerification each month. Therefore, no water nutrient samples were collected on 16 May and 25 June 2003. Flow data was recorded for all events.

Nutrient losses following runoff initiation were calculated by multiplying the average nutrient concentration during each sampling interval [(concentration at time 1 + concentration at time 2) / 2] by the total amount of runoff that passed through the Parshall flume during each specific 5-min sample period. The total nutrient loss for each treatment following runoff initiation was computed by adding the total amount of NO₃-N, NH₄-N, or DRP that were calculated for each 5-min sample period.

Statistical analyses were performed using SAS version 8.1 (SAS Institute Inc., Cary, NC). Analysis of variance procedures were used to determine nutrient runoff as a function of precipitation duration for a randomized complete block design. Repeated measures analysis was performed using PROC MIXED with time as the repeated measure treatment. A model for intra-plot variance was determined using an auto regressive variance model. All results were tested at α = 0.05.

Rainfall and Runoff Response

There was no collection date × treatment interaction so data are presented after averaging over all collection dates. The minimum rainfall amount required to produce runoff from fairway plots during the course of this study was 15 mm. Aerification had no significant effect on flow rate or nutrient concentration during 60 min of runoff (Figs. 1, 2, and 3). There was no significant difference in peak runoff rate between aerated and control plots. Runoff from all plots reached an average maximum flow rate of 61.1 liter/min at 25 min after runoff began. There was no significant difference in nutrient concentrations in runoff samples between aerated and control plots. The average nutrient concentrations in the runoff samples (n = 360) were NO₃-N at 0.54 mg/liter, NH₄-N at 0.44 mg/liter, and DRP at 1.20 mg/liter. Less than 1% of the urea and triple superphosphate applied were lost to runoff. This was probably due to the fact that the fertilizer was lightly irrigated immediately after application and that rainfall did not occur for an average of 13 days following treatment. These results concur with the findings of Shuman (9) who demonstrated that nutrient losses from bermudagrass fertilization were lowered after being lightly irrigated immediately after application and reduced as time between application and runoff increased. Aerification significantly delayed runoff initiation by an average of 4.1 min (Table 1) when compared to the control plots. The average time to initiation of runoff was 47.9 min for control plots and 52.0 min for aerated plots. This delay may be attributed to an increase in water infiltration due to aerification.

Fig. 1. Flow rate during 60 min of runoff from bermudagrass fairway plots. The results are an average of seven natural rainfall events that occurred from May 2003 to April 2004. The bars indicate the standard error interval at each collection period.

Fig. 2. Concentration of N (NO₃-N + NH₄-N) in natural rainfall runoff from bermudagrass fairways for 60 min after runoff began. The results are an average of seven natural rainfall events that occurred from May 2003 to April 2004. The bars indicate the standard error interval at each collection period.

Fig. 3. Concentration of dissolved reactive phosphorus (DRP) in natural rainfall runoff from bermudagrass fairway plots for 60 min after runoff began. The results are an average of seven natural rainfall events that occurred from May 2003 to April 2004. The bars indicate the standard error interval at each collection period.

Table 1. Average time from initiation of precipitation to the
beginning of runoff for control and aerated bermudagrass
fairways during seven natural rainfall events.

Treatment	n	Time (minutes)
Treatment	n	mean	S.E.
Control	21	47.9	1.3
Aerated	21	52.0*	1.3

* Significant at α = 0.05 level.

Table 2. Cumulative volume of natural rainfall runoff from bermudagrass fairway plots for 60 min after runoff began and total mass of N (NO₃-N + NH₄-N) and dissolved reactive phosphorus (DRP) in natural rainfall runoff from bermudagrass fairway plots for 60 min after runoff began. The results are an average of seven natural rainfall events.

Treatment	n	Cumulative volume (liter/ha)		N (g/ha)		DRP (g/ha)
		mean	S.E.	mean	S.E.	mean	S.E.
Control	21	96034	33032	16.8	4.1	22.8	6.4
Aerated	21	60951 NS†	16583	23.6 NS	7.2	27.9 NS	8.7
Source of variation	df	P value
Treatments	1	0.1522		0.1532		0.4733
Blocks	2	—		—		—
Error	2	—		—		—
Total	5	—		—		—

* NS = not significant at the 0.05 level.

Aerification did not result in a statistically significant reduction in total nutrient loss or in a statistically significant reduction in runoff volume (Table 2). Average N and DRP loss from plots were 20.2 and 25.4 g/ha, respectively, and average cumulative runoff volume from plots was 78493 liter/ha. The maximum average nutrient concentrations for N and DRP occurred at 5 min after runoff initiation and were 1.7 and 1.5 mg/liter respectively (Figs. 2 and 3). There was no significant difference in nutrient concentrations at any sample time during this study. While these nutrient concentrations were relatively low, they were above the minimum that are capable of enhancing eutrophication of surface waters (10). It should be noted that although treatment effects were not significant at the α = 0.05 significance level, it is apparent that surface runoff from the aerated plots was consistently lower than surface runoff from the control plots (Fig. 1). In addition, N and DRP nutrient concentrations were consistently higher for during the first 5 min of runoff from the aerated plots when compared to the control plots. With the high variability of natural precipitation and the use of only 3 replications for each treatment in this study, the large standard error values for surface runoff and nutrient concentrations could be expected. The construction of a larger turfgrass surface runoff study area than the one utilized in this study could be beneficial for future research by providing more replications and degrees of freedom.

Conclusions

Aeration is a common turf management practice that serves to alleviate compaction, promote new growth, and increase soil oxygen content. According to the results of this study, aerification will neither increase or decrease surface water runoff and nutrient loss from bermudagrass golf course fairways under natural rainfall conditions. While aerated plots consistently produced less runoff volume under the parameters of this study, it was not statistically significant when compared to control plots. Using management practices similar to this study, golf course managers may aerate their fairways one or more times during the growing season without affecting nutrient losses to surface runoff.

Introduction

1. Beard, J. B. 2002. Turf management for golf courses. 2nd ed. Ann Arbor Press, Chelsea, MI.

2. Cole, J. T., Baird, J. H., Basta, N. T., Huhnke, R. L., Storm, D. E., Johnson, G. V., Payton, M. E., Smolen, M. D., Martin, D. L., and Cole J. C. 1997. Influence of buffers on pesticide and nutrient runoff from bermudagrass turf. J. Environ. Qual. 26:1589-1598.

3. Harrison, S. A., Watschke, T. L., Mumma, R. O., Jarrett, A. R., and Hamilton, G. W., Jr. 1993. Nutrient and pesticide concentrations in water from chemically treated turfgrass. Pages 191-207 in: Pesticides in Urban Environments: Fate and Significance. K. D. Racke and A. R. Leslie, ed. Amer. Chem. Soc. Symp. Series No. 522. ACS, Washington, DC.

4. Krenitsky, E. C., Carroll, M. J., Hill, R. L., and Krouse, J. M. 1998. Runoff and sediment losses from natural and man-made erosion control materials. Crop Sci. 38:1042-1046.

5. Linde, D. T., Watschke, T. L., Jarrett, A. R., and Borger, J. A. 1995. Surface runoff assessment from creeping bentgrass and perennial ryegrass turf. Agron. J. 87:176-182.

6. Moss, J. Q., Bell, G. E., Kizer, M. A., Payton, M. E., Zhang, H., and Martin D. L. 2006. Reducing nutrient runoff from golf course fairways using grass buffers of multiple height. Crop Sci. 46:72-80.

7. Murphy, J., and Riley, J. P. 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta 27:31-36.

8. Sharpley, A., Foy, B., and Withers, P. 2000. Practical and innovative measures for the control of agricultural phosphorus losses to water: An overview. J. Environ. Qual. 29:1-9.

9. Shuman, L. M. 2004. Runoff of nitrate nitrogen and phosphorus from turfgrass after watering-in. Commun. Soil. Sci. Plant Anal. 35:9-24.

10. Walker, W. J., and Branham, B. 1992. Environmental impacts of turfgrass fertilization. Pages 105-219 in: Golf Course Management and Construction: Environmental Issues. J. C. Balogh and W. J. Walker, ed. Lewis Publ., Chelsea, MI.