Single Fall Applications of Coated Urea Fertilizers Produce a High Quality Kentucky bluegrass Turf

Single Fall Applications of Coated Urea Fertilizers Produce a High Quality Kentucky Bluegrass Turf

Cale A. Bigelow, Kristina S. Walker, and Glenn A. Hardebeck, Agronomy Department, Purdue University, West Lafayette, IN 47907

Corresponding author: Cale A. Bigelow. cbigelow@purdue.edu

Abstract

Kentucky bluegrass (Poa pratensis L.) lawns generally require N fertilizer at 98 to 196 kg/ha/year to maximize appearance and growth. Most homeowners do not regularly fertilize, resulting in weed- and disease-prone lawns due to insufficient N. This two-year field study evaluated three urea-based N sources: urea, sulfur-coated urea (SCU), and polymer-coated urea (PCU) at N rates of 0, 49, or 147 kg/ha/year applied in early September only or 49 kg/ha/month from September through November. Mean turfgrass quality, canopy greenness, and total dry matter yield all increased with annual N rate. All fertilizer treatments, except the September-only SCU treatment at 49 kg of N per ha, produced more dry matter yield than the unfertilized control. The highest mean quality and greenest turf resulted from three consecutive applications of urea at the N rate of 49 kg/ha/month and single September-only PCU or SCU applications at the 147-kg/ha/year N rate. There was no advantage to monthly urea, PCU, or SCU applications when compared to September-only SCU or PCU applications of N at 147 kg/ha. These results demonstrate that homeowners can produce a high quality bluegrass turf with less effort by applying SCU or PCU in September only at N rates of 147 kg/ha.

Introduction

Nitrogen is the nutrient required in the greatest abundance for healthy turf growth and is an essential component of chlorophyll which confers the green color to plant leaves (22). The most widely planted turfgrass species for lawns throughout the cool-humid region is Kentucky bluegrass (2). To sustain a dark-green turf and vigor, turfgrass specialists throughout the cool-humid region have routinely recommend N at 98 to 196 kg/ha/year split into multiple fall applications (7,26,29). The agronomic and physiological benefits of fall-applied N fertilizers to cool-season turfgrasses are well documented (11,16,17,19,25,31,32,33,34).

Fertilizer N is generally not applied to maximize yield, which would result in increased mowing, but to sustain density and greenness. Thus, most N programs are specifically designed to moderate the N supply either with multiple N applications or changing N sources so that turf growth remains at submaximal levels (1). Many factors affect N-source selection including cost, availability, desired turf response, and potential for turf injury. Urea is the most widely used N source for lawn fertilization because it is water soluble, results in rapid greening and growth, and is relatively inexpensive. To minimize turf injury, growth flushes, and environmental loss, urea applications rarely exceed 49 kg of N per ha. Therefore, several urea-N applications are required to maintain greenness and sustain moderate growth. This frequent fertilization increases the time, effort, and dedication required to maintain a high quality lawn. Thus, controlled-release N sources, like SCU that do not rely on microbial degradation for N release, have been evaluated for their ability to produce a high quality turf (4,14,15,18,30). The newest group of controlled-release N sources is PCU but response data is limited and direct comparisons to SCU or urea in the same study is generally lacking.

Throughout the North Central region of the United States, turfgrass specialists have historically suggested an ideal timing for single annual N applications to be early September using predominantly controlled-release N source like SCU (26,29). Where improved appearance is desired an additional urea application of 49 kg of N per ha is suggested in early November. Other specialists have suggested three consecutive N applications spanning September through November (7). These late-season water soluble N applications have received increasing scrutiny for their potential to negatively affect water quality due to N leaching (4,5,6,8,9,10,21,23,24,27). Compared to commercial lawn care services, most homeowners are not committed to regular fertilization, resulting in malnourished, low density, weed- and disease-prone lawns primarily due to insufficient N. An additional challenge that homeowners encounter is product availability during mid to late fall because many large warehouse-type garden centers replace fertilizers with holiday decorations starting in early October.

Since it is accepted that a high quality turf requires N applications of approximately 98 to 147 kg/ha/year and homeowners are unlikely to commit extra effort to multiple N applications and the fact that N fertilizers are increasingly less available after early October, and if the current goal for lawn fertilization is to recommend programs that maximize turf performance with reduced management inputs, information regarding programs that limit fertilizer, labor, or both would be valuable. One alternative strategy to multiple fall N applications is a single relatively large, 147 kg of N per ha, September-only dose of a controlled-release N source like SCU or PCU. This strategy would provide sufficient N during a period of active growth, September-November, thus reducing leaching potential and minimize the labor required to produce a high quality turf.

Therefore, the objective of this study was to compare Kentucky bluegrass responses to three commercially available urea-based fertilizers applied either in three monthly low, 49 kg of N per ha, rate applications, a single heavy, 147 kg of N per ha, September-only dose of PCU or SCU fertilizer or a single low, 49 kg of N per ha, September-only application.

Comparing Kentucky Bluegrass Response to Urea-Based Fertilizer

This field study was conducted at the W. H. Daniel Turfgrass Research and Diagnostic Center at Purdue University, West Lafayette IN, from September 2003 through April 2006. Three commercially available "mini-sized" granular urea sources: urea (46-0-0), SCU (32-0-0, Knox Fertilizer Knox, IN) and PCU (Polyon, 41-0-0: Pursell Technologies, Sylacauga, AL) were applied to a one-year-old KBG ‘Premium Sod Blend’ containing equal portions of ‘Absolute,’ ‘Rugby II,’ ‘Bluemoon,’ and ‘Nuglade’ cultivars by weight. The turf was grown on a Starks-Fincastle silt-loam (fine-silty, mixed, mesic Aeric Ochraqualf) with pH of 7.2 and 1.6% organic matter. Additionally, the levels of magnesium, manganese, sulfur, and iron were sufficient with 400, 42, 21, and 52 ppm respectively. All fertilizers were initially applied on 12 September 2003 by hand using shaker bottles to 1.2 × 1.2-m plots separated by 0.5 m borders, and reapplied on 12 October and 12 November if specified by the treatments. These same treatment dates were followed in 2004 and 2005. Within 12 h of fertilizer application the entire plot area was irrigated with approximately 8 mm water via an overhead irrigation system. Throughout the growing season (April-November) irrigation was used to supplement rainfall and promote growth. In the absence of a significant (≥ 13-mm) rainfall event, irrigation was applied at approximately 5 mm nightly to achieve 35 mm/week. Pesticides were applied to control broadleaf weeds (dimethylamine salt of 2, 4-dichlorophenoxyacetic acid) in October and annual grassy weeds [dithiopr:S, S dimethyl ester 2-(difluoromethyl) -4-(2-methylpropyl)-6-(trifluoromethyl)-3,5-pyridinedicarbothioate] each April.

Clippings were harvested weekly throughout the growing season from each plot to a height of 6.35 cm using a rotary bagging mower (JS60, John Deere Inc. Moline, IL) then oven-dried at 82°C in a forced-draft oven for 72 h to determine dry matter yield. Initially, an attempt was made to replace the remaining clippings on each plot but this proved impractical because the dried tissue remnants contaminated the freshly-harvested tissue. Plots were visually assessed for turf quality at least twice monthly during the growing season (April-November) on a 0 to 10 scale with 0 = brown, dead turf; 10 = optimum color, density, and uniformity; and ≥ 6 = acceptable lawn turf. Only mean study and individual study year quality means are presented in Table 1, whereas the first and last yearly rating for 2004 and 2005 are presented in Table 2 as they are significant snapshots in time when dramatic differences in turf appearance were evident. Canopy greenness was determined twice monthly using a hand-held reflectance meter (FieldScout CM-1000, Spectrum Technologies Inc.). Five measurements were recorded per plot using a systematic grid pattern which measured the four corners and center of each plot. These measurements were averaged to produce a single plot rating and reported as a unitless color index. Dollar spot (Sclerotinia homoeocarpa F.T. Bennett) periodically affected quality and disease severity was rated as percentage blight on a linear 0 to 100% scale, where 0 = no damage and 100 = complete plot blight.

Table 1. Kentucky bluegrass turfgrass quality as affected by various urea N sources, application rates and timings.

Urea source^x	N rate (kg/ha)	Timing^y (month)	Turfgrass quality^w (visual rating, 0 to 10 scale)
Urea source^x	N rate (kg/ha)	Timing^y (month)	Fall 2003	2004	2005	Study mean
SCU	49	Sep only	6.7 a^z	5.7 c	5.9 c	6.0 c
Urea	49	Sep only	7.0 a	6.7 ab	6.5 bc	6.5 b
SCU	147	Sep only	7.0 a	6.8 ab	7.1 ab	7.2 a
Urea	49+49+49	Sep, Oct, Nov	6.8 a	6.5 b	7.1 ab	7.0 ab
SCU	49+49+49	Sep, Oct, Nov	6.7 a	6.6 ab	7.0 ab	7.0 ab
PCU	147	Sep only	7.0 a	7.1 a	7.6 a	7.4 a
PCU	49+49+49	Sep, Oct, Nov	6.8 a	6.8 ab	7.1 ab	7.0 ab
None	—	—	6.8 a	5.3 c	4.7 d	4.9 d

^w Turfgrass quality was visually rated twice monthly during the growing season on a 0 to 10 scale where 0 equals brown, dead turf and 10 equals optimum greenness, density and uniformity, ≥ 6 acceptable lawn turf.

^x Nitrogen fertilizer was applied either as urea (46-0-0), sulfur-coated urea (SCU), or polymer-coated-urea (PCU).

^y Fertilizers were initially applied on 12 September 2003 and reapplied, if specified, on 12 October and 12 November. These same application dates were used in 2004 and 2005.

^z Means in the same column followed by the same letter are not significantly different according to Fisher’s protected LSD t-test (P = 0.05).

Statistical analysis. Each treatment was replicated three times arranged in a randomized complete block design. Due to the large number of quality ratings and greenness measurements, data for each month were pooled into a single monthly value used for statistical analysis. All data was subjected to analysis of variance using the SAS system (SAS Institute Inc., Cary, NC) general linear model procedure and treatment means separated using Fisher’s protected least significant difference (LSD) test at the (P = 0.05) level (28).

Nitrogen Source and Timing Affects Visual Appearance

The overall mean turf quality values ranged from 4.9 to 7.4 and increased with increasing N rate with the worst quality occurring in the unfertilized control (4.9), and 49 kg of N per ha per year SCU (6.0) treatment, followed by 49 kg of N per ha per year urea (6.5) September only (Table 1). The biggest factor affecting quality was annual N rate with the highest quality resulting from the 147 kg of N per ha per year September-only SCU or PCU applications, (7.2 and 7.4, respectively). These treatments, however, were not different from the other 147 kg of N per ha per year treatments. The three monthly 49 kg of N per ha urea, SCU or PCU applied were not different from the single 49 kg of N per ha urea September-only application. Among treatments, only the unfertilized control had a mean quality value that would be considered commercially unacceptable, < 6.0. The overall annual quality values increased, ≥ 0.3, numerically from 2004 to 2005 for all fertilizer treatments except the 49 kg of N per ha per year urea and SCU treatments. Only the 49 kg of N per ha per year SCU and unfertilized control had unacceptable mean annual quality values for each study year, ranging from 4.7 to 5.9.

The agronomic benefits of a well-fertilized turf were visually evident as improved early spring and late-fall quality values and faster spring green-up (Table 2, Fig. 1). For the first quality rating of 2004, on 18 April, quality values ranged from 2.7 to 5.3 with all quality values below the acceptable threshold value of 6.0. There was no difference among the 147 kg of N per ha per year treatments (4.5 to 5.3) and both urea treatments were similar. The September-only SCU 49 kg of N per ha per year treatment (3.5) was similar to the unfertilized control (2.7). On 15 November 2004 all quality values were acceptable, ≥ 6.0, except for 49 kg of N per ha per year SCU (5.8) and the unfertilized control (4.5). It is important to mention that the 49 kg of N per ha per year SCU treatment was not different than any other fertilizer treatment except the 147 kg of N per ha per year PCU, September-only (7.7) treatment.

Table 2. Kentucky bluegrass spring and fall turfgrass quality and spring green-up as affected by various urea N sources, application rates, and timings.

Urea source^x	N rate (kg/ha)	Timing^y (month)	Turfgrass quality^v (visual rating, 0 to 10 scale)				Spring green -up^w
			2004		2005		2006
			18 Apr	15 Nov	16 Apr	12 Nov	17 Apr
SCU	49	Sep	3.5 cd^z	5.8 bc	3.0 de	7.5 c		5.3 b
Urea	49	Sep	3.7 bc	6.8 ab	3.3 d	7.5 c		4.3 b
SCU	147	Sep	4.7 a	7.5 ab	4.0 c	8.4 a		7.0 a
Urea	49+49+49	Sep, Oct, Nov	4.5 ab	6.8 ab	4.2 bc	8.0 abc		7.3 a
SCU	49+49+49	Sep, Oct, Nov	4.7 a	6.8 ab	4.3 bc	7.8 abc		7.3 a
PCU	147	Sep only	5.3 a	7.7 a	5.2 a	8.2 ab		7.7 a
PCU	49+49+49	Sep, Oct, Nov	4.8 a	6.8 ab	4.7 ab	7.7 bc		7.0 a
None	—	—	2.7 d	4.5 c	2.7 e	6.5 d		3.0 c

^v Turfgrass quality was visually rated on a 0 to 10 scale where 0 equals brown, dead turf and 10 equals optimum greenness, density and uniformity, ≥ 6 acceptable lawn turf. The quality ratings presented in this table represent the first and final ratings for 2004 and 2005 where substantial treatment differences were evident.

^w Spring green-up was visually rated on a 0 to 10 scale where 0 completely brown turf and 10 fully green.

^x Nitrogen fertilizer was applied either as urea (46-0-0), sulfur-coated urea (SCU), or polymer-coated-urea (PCU).

^y Fertilizers were initially applied on 12 September 2003 and reapplied, if specified, on 12 October and 12 November. These same application dates were used in 2004 and 2005.

^z Means in the same column followed by the same letter are not significantly different according to Fisher’s protected LSD t-test (P = 0.05).

Fig. 1. Enhanced Kentucky bluegrass spring green-up from to three consecutive years of fall fertilization using various controlled-release and traditional urea sources, an unfertilized control plot is located in the foreground (photo taken 18 April 2006).

In year two, quality values on 16 April 2005 were similar to 2004; however, the effects of annual N rate became apparent with the highest quality in the PCU fertilized turf (5.2). The three monthly 49 kg of N per ha/month PCU treatment was not different from the three consecutive urea or SCU treatments (4.3 to 4.7). Again, the 49 kg of N per ha per year SCU treatment (3.0) was similar to the unfertilized control (2.7). On 12 November 2005, quality values were substantially higher than in November 2004 with all treatments ≥ 6.5. These higher values could be attributed to several factors including extended, unusually warm weather combined with the repeated effects of two consecutive years of fall fertilization. All fertilized turf was superior to the unfertilized control with SCU or PCU 147 kg of N per ha per year September only, and three consecutive urea or SCU 49 kg of N per ha having the highest quality values (7.8 to 8.4). Although quality was not recorded in 2006, faster spring green-up and distinct separation between annual N rates was observed on 17 April. These observations of higher spring and fall quality and improved green-up from fall-applied N are all consistent with previous studies (13,16,21,25,32,33) The differences in overall quality were also related to treatment effects on canopy greenness and dollar spot severity.

Available Nitrogen Affects Dollar Spot Severity

Treatment differences for dollar spot were evident in the summer of both study years and ranged from 0 to 6% plot area blighted depending upon rating date and N treatment (Table 3). The disease was worst in the unfertilized control (2.3 to 6.0%) probably due to N deficiency and a lack of turf vigor. On 9 August 2004, however, the unfertilized control was not different from the 49 kg/ha SCU or urea September-only treatments. By 13 September, the unfertilized control (6.0%) was similar to both SCU treatments (2.7 to 4.2%). In 2005, all N treatments had less dollar spot than the unfertilized control. These results agree with what is commonly reported regarding dollar spot incidence and low annual N levels (3).

Table 3. Dollar spot severity in Kentucky bluegrass as affected by various urea N sources, application rates and timings.

Urea source^x	N rate (kg/ha)	Timing^y (month)	Dollar spot severity^w (percentage blight, %)
			2004		2005
			9 Aug	13 Sept	27 July	10 Aug
SCU	49	Sep	1.7 ab^z	4.2 ab	0.7 b	0.7 b
Urea	49	Sep	0.9 ab	1.3 b	0.1 b	0.4 b
SCU	147	Sep	0.2 b	0.4 b	0.1 b	0.2 b
Urea	49+49+49	Sep, Oct, Nov	0.1 b	2.3 b	0.0 b	0.0 b
SCU	49+49+49	Sep, Oct, Nov	0.1 b	2.7 ab	0.1 b	0.2 b
PCU	147	Sep	0.1 b	1.0 b	0.0 b	0.0 b
PCU	49+49+49	Sep, Oct, Nov	0.1 b	1.7 b	0.1 b	0.2 b
None	—	—	2.3 a	6.0 a	2.3 a	3.7 a

^w Dollar spot severity was rated as percentage plot area blighted on a 0 to 100% linear scale where 0 = no damage and 100 = plot completely blighted.

^x Nitrogen fertilizer was applied either as urea (46-0-0), sulfur-coated urea (SCU), or polymer-coated urea (PCU).

^y Fertilizers were initially applied on 12 September 2003 and reapplied, if specified, on 12 October and 12 November. These same application dates were used in 2004 and 2005.

^z Means in the same column followed by the same letter are not significantly different according to Fisher’s protected LSD t-test (P = 0.05).

Nitrogen Availability Increases Canopy Greenness

Greenness measurements ranged from 190 to 561 with higher values associated with increasing N rates (Table 4). Study means were highest for 147 kg of N per ha SCU (441) and PCU (456) applied September only, and 49 kg of N per ha/month urea (429) applied September to November. These aforementioned treatments also resulted in the highest greenness measurements during the first fall of N applications, probably due to more N availability. The lowest values resulted from SCU 49 kg of N per ha September only (381) and the three monthly 49 kg of N per ha SCU (387) or PCU (383) treatments which were not different from the unfertilized control (340). Interestingly, canopy greenness did not appear to greatly influence quality during the first fall (Table 1). By the end of 2004, greater treatment separation was apparent with the 147 kg of N per ha per year PCU and SCU September-only treatments having the highest greenness measurements (≥ 422) and the 49 kg of N per ha SCU (372) and unfertilized control (338) the lowest. In 2005 all 147 kg of N per ha per year treatments were greenest (447 to 467) and the monthly 49 kg of N per ha from urea, SCU, or PCU being not different from the 49 kg of N per ha per year September-only treatment (372). Additionally, the visual differences recorded for spring green-up on 17 April 2006 and separation by annual N rate (Table 2) were mirrored in the greenness measurements for that same date.

Table 4. Kentucky bluegrass canopy greenness as affected by various urea N sources, application rates and timings.

Urea source^x	N rate (kg/ha)	Timing^y (month)	Canopy greenness^w (spectrum units)
Urea source^x	N rate (kg/ha)	Timing^y (month)	Fall 2003	2004	2005	17 Apr 2006	Study mean
SCU	49	Sep	381 cd^z	372 cd	415 b	318 b	391 d
Urea	49	Sep	401 bc	392 bc	422 b	283 b	400 cd
SCU	147	Sep	444 ab	422 ab	467 a	511 a	441 ab
Urea	49+49+49	Sep, Oct, Nov	421 abc	394 bc	462 a	553 a	429 abc
SCU	49+49+49	Sep, Oct, Nov	387 cd	389 bc	448 ab	561 a	416 bcd
PCU	147	S only	474 a	450 a	463 a	522 a	456 a
PCU	49+49+49	Sep, Oct, Nov	383 cd	400 bc	447 ab	516 a	423 bc
None	—	—	340 d	338 d	334 c	190 c	331 e

^w Canopy greenness was measured with a hand-held reflectance meter (Field Scout CM-1000) using five measurements per plot at least twice monthly during the growing season.

^x Nitrogen fertilizer was applied either as urea (46-0-0), sulfur-coated urea (SCU), or polymer-coated urea (PCU).

^y Fertilizers were initially applied on 12 September 2003 and reapplied, if specified, on 12 October and 12 November. These same application dates were used in 2004 and 2005.

^z Means in the same column followed by the same letter are not significantly different according to Fisher’s protected LSD t-test (P = 0.05).

Annual Nitrogen Rate and Source Affects Dry Matter Yield

In addition to appearance, dry matter yield is an important consideration when developing N fertilizer programs, since excess yield results in more mowing. Total dry matter yields for the study ranged from 2926 to 7957 kg/ha and varied by study year and N treatment (Table 5). Similar to overall quality and greenness, there was distinct dry matter yield treatment separation by annual N rate with the unfertilized control having the least dry matter yield (2926 kg/ha) which was similar to the SCU 49 kg of N per ha per year September-only treatment (3938 kg/ha). In the first year DMYs ranged from 1739 to 4017 kg/ha with lowest dry matter yield for the unfertilized (1739 kg/ha), and SCU or urea 49 kg of N per ha per year September-only treatments. The highest dry matter yields occurred where 147 kg of N per ha per year was applied (3314 to 4017 kg/ha). In year two, dry matter yields ranged 1187 to 4128 kg/ha with more distinct treatment separation observed. For the unfertilized control dry matter yield fell dramatically from 1739 to 1187 kg/ha and this treatment was different from all N treatments. The highest dry matter yields resulted from both PCU treatments and the SCU, 147 kg of N per ha per year September-only treatment (3534 to 4128 kg/ha). The dry matter yields measured in this study were comparable to other reported values for similar N rates (5,12,20,31)

Table 5. Kentucky bluegrass dry matter yield as affected by various urea N sources, application rates and timings.

Urea source^x	N rate (kg/ha)	Timing^y (month)	Dry matter yield^w (kg/ha)
Urea source^x	N rate (kg/ha)	Timing^y (month)	Fall, Year 1	Year 1	Fall, Year 2	Year 2	Study Total
SCU	49	Sep only	341 d^z	1963 c	255 cd	1975 d	3938 bc
Urea	49	Sep only	588 ab	2526 bc	480 ab	2132 d	4658 b
SCU	147	Sep only	696 a	3488 a	622 a	3534 abc	7022 a
Urea	49+49+49	Sep, Oct, Nov	646 a	3586 a	555 ab	3028 c	6614 a
SCU	49+49+49	Sep, Oct, Nov	403 cd	3314 ab	367 bc	3347 bc	6661 a
PCU	147	Sep only	473 bc	4017 a	506 ab	3940 ab	7957 a
PCU	49+49+49	Sep, Oct, Nov	385 cd	3813 a	375 bc	4128 a	7941 a
None	—	—	373 cd	1739 c	170 d	1187 e	2926 c
Number of harvests			26		24		50

^w Dry matter yield was determined by harvesting all clippings at a 6.3-cm mowing height each week throughout the growing season.

^x Nitrogen fertilizer was applied either as urea (46-0-0), sulfur-coated urea (SCU), or polymer-coated urea (PCU).

^y Fertilizers were initially applied on 12 September 2003 and reapplied, if specified, on 12 October and 12 November. These same application dates were used in 2004 and 2005.

^z Means in the same column followed by the same letter are not significantly different according to Fisher’s protected LSD t-test (P = 0.05).

Summary and Recommendations

The highest quality and greenness occurred where 147 kg of N per ha per year from SCU or PCU was applied in September only or urea was applied at 49 kg of N per ha/month from September through November. These aforementioned treatments also resulted in the highest dry matter yields which were not different from any other 147 kg of N per ha per year treatment. These data suggest that homeowners could apply single 147 kg of N per ha in a single application using SCU or PCU in early September. This practice would ensure sufficient N availability across the fall months to produce a high quality bluegrass lawn with less effort than traditional programs that require two or three N applications. There was no apparent benefit to three consecutive 49 kg of N per ha monthly applications, of urea, SCU or PCU, when compared to the single 147 kg of N per ha September-only SCU or PCU applications. This is consistent with previous research reporting no long-term benefit of smaller N applications versus larger N applications a cool-season turf (1). Where reduced N inputs are desired, a moderately acceptable bluegrass lawn can be achieved by applying 49 kg of N per ha urea in September only which appears superior to a single SCU application since the SCU treatment was rarely different from the unfertilized control. It is important to note that these N recommendations are based on only two years of data where clippings were removed to determine dry matter yield, a practice not normally recommended. Where regular fertilization occurs and clippings are returned, annual N rates can sometimes be reduced by ≤ 50% (13,16). Additionally, for this particular study area a N-only fertilizer program could possibly be sustainable for several years until a soil test indicated nutrient deficiencies since the study area had high, 156 ppm, potassium and very high, 61 ppm Bray-1, phosphorus levels. This practice would minimize the potential for unwanted nutrient losses. Future studies providing additional information regarding the potential effects of these fertilizer recommendations on N leaching would be useful.

Acknowledgments

This research was made possible by the generous support of the Midwest Regional Turf Foundation and The College of Agriculture, Purdue University. Grateful appreciation is expressed to Ms. Christi Craven, Mr. Jim Newman, and Ms. Angela Carter for their technical assistance throughout this experiment.

Literature Cited

1. Bowman, D. C. 2003. Daily vs. periodic N addition affects growth and tissue nitrogen in perennial ryegrass turf. Crop Sci. 43:631-638.

2. Christians, N. 2004. Fundamentals of Turfgrass Management. John Wiley and Sons, Inc., Hoboken, NJ.

3. Couch, H. B. 1995. Diseases of turfgrasses. Krieger Publ. Co., Malabar, FL.

4. Engelsjord, M. E., and Singh, B. R. 1997. Effects of slow-release fertilizers on growth and on uptake and leaching of nutrients in Kentucky bluegrass turfs established on sand-based root zones. Can. J. Plant Sci. 77:443-444.

5. Frank, K. W., O’Reilly, K. M., Crum, J. R., and Calhoun, R. N. 2006. The fate of nitrogen applied to a mature Kentucky bluegrass turf. Crop.Sci. 46:209-215.

6. Geron, C. A., Danneberger, T. K., Traina, S. J., Logan, T. L., and Street, J. R. 1993. The effects of establishment methods and fertilization practices on nitrate leaching from turfgrass. J. Environ. Qual. 22:119-125.

7. Goatley, J. M., Jr., Chalmers, D. R., Hall, J. R., III, and Schmidt, R. E. 2004. Lawn fertilization in Virginia. Virginia Coop. Ext. Bull. No. 430-011.

8. Gold, A. J., DeRagon, W. R., Sullivan, W. M., and Lemunyon, J. L. 1990. Nitrate-nitrogen losses to groundwater from rural and suburban land uses. J. Soil Water Conserv. 45:305-310.

9. Guillard, K., and Kopp, K. L. 2004. Nitrogen fertilizer form and associated nitrate leaching from cool-season turfgrass. J. Environ. Qual. 33:1822-1827.

10. Hall, M. H., Beegle, D. B., Bowersox, R. S., and Stout, R. J. 2003. Optimum nitrogen fertilization of cool-season grasses in the northeast USA. Agron. J. 95:1023-1027.

11. Hanson, A. A., and Juska, F. V. 1961. Winter root activity in Kentucky bluegrass (Poa pratensis. L.). Agron. J. 53:372-374.

12. Harivandi, M. A., Hagan, W. L., and Elmore, C. L. 2001. Recycling mower effects on biomass, nitrogen recycling, weed invasion, turf quality, and thatch. Inter. Turf. Soc. Res. J. 9:882-885.

13. Heckman, J. R., Liu, H., Hill, W., DeMilia, M., and Anastasia, W. L. 2000. Kentucky bluegrass responses to mowing practice and nitrogen fertility management. J. Sustain. Agric. 4:25-33.

14. Hummel, N. W., Jr., and Waddington, D. V. 1981. Evaluation of slow-release nitrogen sources on Baron Kentucky bluegrass. Soil Sci. Soc. Am. J. 45:966-970.

15. Hummel, N. W., and Waddington, D. V. 1984. Sulfur-coated urea for turfgrass fertilization. Soil Sci. Soc. Am. J. 48:191-195.

16. Koop, K. L., and Guillard, K. 2002. Clipping management and nitrogen fertilization of turfgrass growth, nitrogen utilization, and quality. Crop Sci. 42:1225-1231.

17. Koski, A. J., and Street, J. R. 1985. Root growth and carbohydrates status of ‘Baron’ Kentucky bluegrass as affected by timing of nitrogen application. Page 118 in: Agronomy abstracts. ASA, Madison, WI.

18. Landschoot, P. J., and Waddington, D. V. 1987. Response to turfgrass to various nitrogen sources. Soil Sci. Soc. Am. J. 51:225-230.

19. Ledeboer, F. B., and Skogley, C. R. 1973. Effects of various nitrogen sources, timing, and rates on quality and growth rate of cool-season turfgrasses. Agron. J. 65:243-246.

20. Liu, H., and Hull, R. J. 2006. Comparing cultivars of three cool-season turfgrasses for nitrogen recovery in clippings. HortSci 41:827-831.

21. Mangiafico, S. S., and Guillard, K. 2006. Fall fertilization timing effects on nitrate leaching and turfgrass color and growth. J. Environ. Qual. 35:163-171.

22. Marschner, H. 1995. Mineral Nutrition of Higher Plants. Academic Press Inc., San Diego, CA.

23. Miltner, E. D., Branham, B. E., Paul, E. A., and Rieke, P. E. 1996. Leaching and mass balance of ¹⁵N-labeled urea applied to Kentucky bluegrass turf. Crop.Sci. 36:1427-1433.

24. Miltner, E. D., Stahnke, G. K., Johnston, W. J., and Golob, C. T. 2004. Late fall and winter nitrogen fertilization and turfgrass in two pacific northwest climates. HortScience 39:1745-1749.

25. Powell, A. J., Blaser, R. E., and Schmidt, R. E. 1967. Effect of nitrogen on winter root growth of bentgrass. Agron. J. 59:529-530.

26. Reicher, Z., and Throssell, C. 1998. Fertilizing established lawns. Purdue Agron. Ext. Stat. Bull. AY-22.

27. Starr, J. L., and DeRoo, H. C. 1981. The fate of nitrogen applied to turfgrass. Crop. Sci. 21:531-536.

28. Steel, R. G. D., Torrie, J. H., and Dickey, D. A. 1997. Principles and Procedures of Statistics: A Biometrical Approach, 3rd Ed. McGraw-Hill, Inc. New York.

29. Voigt, T., Fermanian, T., and Wehner D. 1998. Turfgrass fertilization. Ext. outreach, Turfgrass Program, Dept. of Natural Resources and Environ. Sci. Univ. of Ill., Urbana-Champaign.

30. Waddington, D. V., and Turner, T. R. 1980. Evaluation of sulfur-coated urea fertilizers on Merion Kentucky bluegrass. Soil. Sci. Soc. Am. J. 44:413-417.

31. Walker, K. S., Bigelow, C. A., Smith, D. R., VanScoyoc, G. E., and Reicher, Z. J. Above ground responses of three cool-season lawn species to varying annual nitrogen rates and application timings. Crop Sci. (In Press)

32. Wehner, D. L., and Haley, J. E. 1993. Effects of late fall fertilization on turfgrass as influenced by application timing and N source. Int. Turfgrass Soc. Res. J. 7:580-586.

33. Wehner, D. J., Haley, J. E., and Martin, D. L. 1988. Late fall fertilization of Kentucky bluegrass. Agron. J. 80:466-471.

34. Wilkinson, J. F., and Duff, D. T. 1972. Effects of fall fertilization on cold resistance, color, and growth of Kentucky bluegrass. Agron. J. 64:345-348.