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Published online 31 May 2007
Published in Crop Sci 47:1225-1236 (2007)
© 2007 Crop Science Society of America
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TURFGRASS SCIENCE

Aboveground Responses of Cool-Season Lawn Species to Nitrogen Rates and Application Timings

Kristina S. Walkera,*, Cale A. Bigelowa, Douglas R. Smithb, George E. Van Scoyoca and Zachary J. Reichera

a Dep. of Agronomy, Purdue Univ., West Lafayette, IN 47907-2054
b USDA-ARS, 275 S. Russell St., West Lafayette, IN 47907-2054

* Corresponding author (kswalker{at}purdue.edu).


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Lawns are the largest managed turf acreage in the USA. This large acreage of fertilized turf has generated public concern regarding nitrogen (N) fertilizer misuse. This 2-yr field study evaluated the effects of eight N programs that varied by N amount, 0 to 196 kg N ha–1 yr–1, and seasonal application timing on the aboveground plant responses of three cool-season lawn species: Kentucky bluegrass (Poa pratensis L.; KBG), perennial ryegrass (Lolium perenne L.; PRG), and turf-type tall fescue (Festuca arundinacea Schreb.; TTTF). Significant cumulative species dry matter yield differences were measured for the study, with 9426, 7750, and 7011 kg ha–1 for TTTF, KBG, and PRG, respectively. Kentucky bluegrass generally possessed the greenest canopy when averaged across all N programs, followed by TTTF and PRG. Annual turfgrass quality (TQ) was highest and most seasonally consistent for TTTF, followed by KBG and PRG. Although, KBG overall TQ was lower than TTTF, primarily due to slow spring green-up, KBG was superior to TTTF on many ratings during active growth. Perennial ryegrass produced the lowest TQ compared with TTTF and KBG. This was due to summer disease in both years and substantial turf cover losses, 24 to 81% in 2005. If the goal in lawn management is to maximize turfgrass response with the fewest N inputs, the species that met this goal was TTTF, which provided acceptable TQ and color, and had less disease at relatively low, 73 to 123 kg ha–1 yr–1, N levels.

Abbreviations: DMY, dry matter yield • KBG, Kentucky bluegrass • LSNF, late-season nitrogen fertilization • N, nitrogen • PRG, perennial ryegrass • TQ, turfgrass quality • TTTF, turf-type tall fescue.


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
LAWNS PROVIDE numerous benefits and comprise the largest managed turf acreage in the USA (Beard and Green, 1994; National Turfgrass Federation, 2003). As urban and suburban development continues, lawns are rapidly replacing cropland as the principal managed land cover. To maintain a dense, persistent, visually attractive lawn capable of recovery from environmental stress and pest damage requires regular fertilization (Christians, 2004). Of all the necessary plant nutrients, N is required in the greatest amount and is a component of many biochemical constituents such as chlorophyll, which confers the green color to plant leaves (Marschner, 1995). The public generally associates dark green, dense lawns with exceptional turfgrass appearance and quality. Therefore, to sustain greenness and promote growth, N is applied at 50 to 200 kg ha–1 yr–1 based on the owner's desired appearance and management intensity. Due to the large acreage occupied by lawns and the perception that most lawns are heavily fertilized (>150 kg N ha–1 yr–1), there is continued public concern regarding N fertilizer misuse.

Previous N-fertility research has focused on turfgrass responses to specific N application rates, sources, or effects on water quality (Ledeboer and Skogley, 1973; Petrovic et al., 1986; Landschoot and Waddington, 1987; Gold et al., 1990; Guillard and Kopp, 2004). While N application rate, source, and timing are important considerations for single applications, an annual N program should be based on the amount of N required to consistently meet plant demands. Nitrogen is generally not applied to maximize turfgrass dry matter yield (DMY), which would increase mowing frequency, but to sustain a dense, healthy turf. Thus, most programs should be designed specifically to moderate the N supply so that turf shoot growth remains at submaximal levels (Bowman, 2003). Rarely will a single annual N application meet the growth needs or quality expectations for most lawns.

Specific N programs are influenced by growing environment, climatic zone, individual turfgrass species or mixtures, desired appearance, and management intensity. Throughout the cool-humid region and upper transition zone of the USA, cool-season turfgrass species like Kentucky bluegrass (KBG) are preferred because they generally do not go dormant and turn brown during winter months. Although KBG may be the most widely planted lawn species, it is notoriously slow to germinate and establish from seed. Landscape contractors typically mix KBG with perennial ryegrass (PRG) during seeding because PRG germinates and establishes quickly, which stabilizes the soil (Christians, 2004). Perennial ryegrass alone is undesirable as a lawn species because it is extremely susceptible to numerous diseases that are difficult to control and manage without fungicides (Couch, 1995). In many establishment situations, however, seedling PRG crowds out KBG, resulting in a predominately PRG lawn that must then be managed. In recent years, turf-type tall fescue (TTTF) has gained popularity and become widely planted following the introduction of darker green, more narrow leaved TTTF cultivars. Compared with KBG, TTTF germinates quickly and stabilizes the soil. The species is also comparatively deep rooted, which may necessitate less irrigation and presumably less fertilizer to sustain quality.

Early N programs for cool-season lawn species were designed to match the cool-season seasonal shoot growth pattern. This involved the majority of N being applied during the spring, which coincided with the period of most active shoot growth, and moderate autumn N applications during slower shoot growth (Christians, 2004). This approach often resulted in midseason turf deterioration due to summer diseases or severe drought stress due to shallow rooting because succulent shoot growth was stimulated at the expense of the root growth. The amount and timing of N-fertilizer applications is also important, because heavy late-spring N application to cool-season grasses often results in turf decline and encourages the incidence of spring and summer diseases like rhizoctonia blight (Rhizoctonia solani Kuhns), and pythium blight (Pythium spp.) (Couch, 1995). By contrast, insufficient N fertilizer can increase the incidence of spring and summer diseases such as dollar spot (Sclerotinia homoeocarpa F.T. Bennett), red thread (Laetisaria fuciformis (McAlpine) Burdsall), and rust [Puccinia spp. and Uromyces (Link) Unger] (Couch, 1995).

Initially, it was thought that substantial autumn N applications to cool-season grasses resulted in poor winter hardiness (Beard, 1973). Researchers began studying the effects of this practice and reported the benefits, which include increased carbohydrate reserves, reduced disease incidence, improved late-season color retention, increased root growth, and earlier spring green-up, which ultimately reduced the need for early-spring N applications (Powell et al., 1967; Wilkinson and Duff, 1972; Koski and Street, 1985; Wehner et al., 1988; Wehner and Haley, 1993). Most of these studies included a late-season N fertilization (LSNF) with a water-soluble N source like urea applied sometime from mid-October to mid-December after active shoot growth had ceased. Powell et al. (1967) reported that soluble N fertilizer applied in late fall or winter improved turfgrass color retention, whereas an October application was not as efficient for color retention. Wehner and Haley (1993) reported that soluble N applications in either December or January in Illinois provided better turf color and yields than a November or October application, and that a November application produced better color the following spring than an October application. The exact timing of the LSNF appears dependent on climate and geographic location. For example, along the northeast coast of the USA, LSNF recommendations specify mid-October. In the Midwest, LSNF has historically been applied in early to mid-November to minimize pink snow mold (Microdochium nivale) severity.

Based on these studies, turfgrass specialists in the cool-humid region have recommended that the majority (>50%) of cool-season grass N be applied during late summer through late autumn split into two or three N applications, with an essential N timing being September at 49 kg N ha–1 (Reicher and Throssell, 1998).

The published research regarding the relative effectiveness of different N fertilization schedules is limited. The individual species and cultivar being grown affects the amount of N required to sustain growth and quality. It is generally believed that KBG requires more N to sustain quality than PRG or TTTF (Christians, 2004). Since KBG is the most widely planted lawn species, the majority of research has been conducted using this species (Hanson and Juska, 1961; Hummel and Waddington, 1981; Starr and DeRoo, 1981; Jiang and Hull, 1998; Heckman et al., 2000) or KBG species mixtures (Kopp and Guillard, 2002). Much less information exists for PRG (Watson, 1987; Liu et al., 1993; Miltner et al., 2001; Engelsjord et al., 2004), or TTTF (Liu et al., 1993; Hall et al., 2003; Bigelow et al., 2005; Liu and Hull, 2006), which comprises a large portion of the lawns planted in the last decade.

Although the agronomic and physiological benefits of autumn N applications to cool-season turfgrass has been well documented, the ability of consumers to acquire appropriate N sources from large commercial warehouse-type garden centers during the autumn months has become increasingly difficult. Often the fertilizers are replaced with holiday decorations starting in early October. Therefore, consumers are forced to purchase and apply N during the spring months simply due to product availability. With the exception of evaluating autumn and LSNF practices, information regarding the relative effectiveness of alternative N application timings, rates, or various N programs for lawns is lacking. Additionally, very few studies have directly compared the growth responses of the major cool-season turfgrass species to N programs under identical field conditions (Liu et al., 1997; Liu and Hull, 2006). By carefully evaluating the effects of various annual N programs, application rates, and timings on the aboveground plant responses (e.g., DMY, duration of greenness, and disease incidence and severity), the minimum N requirements that produce moderate DMYs and a turf that remains moderately green and attractive can be determined. These data will assist turfgrass specialists in their efforts to recommend judiciously based N-fertility programs and annual N rates for lawns that maximize turfgrass quality while minimizing mowing needs and disease incidence. Therefore, the objective of this study was to evaluate the aboveground responses of the three primary cool-season lawn species to various annual N programs, which varied by N application timing and rate.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
A field experiment was conducted from September 2003 through December 2005 at the Purdue University, W.H. Daniel Turfgrass Research and Diagnostic Center, West Lafayette, IN, on a Stark silt loam (fine-silty, mixed, mesic Aeric Ochraqualf) with a pH of 7.4, 67 kg ha–1 P, 147 kg ha–1 K, and 47 g kg–1 organic matter. Before planting, the entire study area was fumigated with methyl bromide to minimize existing weed competition. Cultivar blends (by weight) of TTTF, KBG, and PRG were established by seed at rates of 391, 98, and 292 kg ha–1, respectively, in May 2003. Seed was supplied by Jacklin Seed Co. and the cultivar blends consisted of the following; Triple A TTTF (‘Quest’ [33%], ‘Pixie’ [33%], and ‘Arid III’ [33%]), Premium Sod Blend KBG (‘Absolute’ [25%], ‘Rugby II’ [25%], ‘Bluemoon’ [25%], and ‘Nuglade’ [25%]), and Medalist Gold PRG (‘Monterey II’ [33%], ‘Caddieshack’ [33%], and ‘Goalkeeper’ [33%]). After seeding, the entire study area received an application of 73 kg ha–1 P as 6–24–24 (N–P–K) and was covered with an Agrofabric Pro17 germination blanket (American Agrifabrics, Alpharetta, GA) for 2 wks to conserve moisture, promote germination, and prevent species contamination from adjacent plots. The study area was frequently irrigated via an overhead sprinkler system to keep the upper 2 cm moist to promote germination and seedling establishment.

The N fertilizer programs were initiated on 10 Sept. 2003. Eight N-fertility programs were evaluated, which varied by annual N, ranging from 0, 49, 73, 123, and 196 kg N ha–1 yr–1, and application timing (Table 1). These programs were classified as "low" (49 kg N ha–1 yr–1 in September or 73 kg N ha–1 yr–1 in November), medium (123 kg N ha–1 yr–1, applied either April, May, and July [AMJ]; September and November [SN]; or September, October, and May [SOM]), and high (196 kg N ha–1 yr–1, applied September, October, November, April, and May [SONAM] or September, November, May, and July [SNMJ]). Nitrogen was supplied either as S-coated urea (controlled release, 31–0–0), urea (water soluble, 46–0–0), or a 50:50 (w/w) mixture depending on the season of application. The specific N application dates and N -sources are footnoted in the data tables.


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  		Table 1. Experimental N programs for three cool-season turfgrass species.

 
Dry Matter Yield and Leaf Nitrogen Content
Turf response to the N programs was measured through DMY, clipping N concentration, and visual ratings. Dry matter yield was determined by harvesting fresh clippings from the entire plot to a height of 6.35 cm using a rotary bagging mower (JS60, John Deere) weekly throughout the growing season. Fresh clippings were oven dried at 82°C in a forced-draft oven for 72 h and weighed. Initially, an attempt was made to replace the remaining clippings on each plot but this proved impractical because the dried tissue remnants contaminated the newly harvested fresh tissue. A subsample (approximately 10 g) of dried leaf tissue was ground in a UDY mill (UDY Corp., Ft. Collins, CO) to pass through a 0.5-mm screen. Approximately 0.05 g from each plot was analyzed for tissue N content using a LECO CHN-2000 analyzer (LECO Corp., St. Joseph, MI). There were 8, 26, and 23 clipping harvests for 2003, 2004, and 2005, respectively.

Turf Appearance
Turfgrass appearance was evaluated using visual ratings and quantifying canopy greenness. Turfgrass quality (TQ) was visually rated weekly throughout the growing season using a 1 to 9 scale, where 1 = completely brown, dead turf; 6 = minimally acceptable lawn turf; and 9 = optimum uniformity, density, and greenness. Canopy greenness was quantified using a handheld reflectance meter (FieldScout CM-1000, Spectrum Technologies, Plainfield, IL). Five measurements were taken per plot using a systematic grid pattern, which measured the four corners and center portions. These five measurements were averaged to produce a single plot measurement and are reported as a color index. Periodically, TQ was impacted by diseases such as dollar spot, Rhizoctonia blight, and red thread. When a disease outbreak occurred, the plots were rated for blight percentage on a linear 0 to 100% scale, where 0 = no damage and 100 = completely blighted turf.

General Plot Maintenance
The study site was located in full sun with no surrounding obstructions, which was conducive to rapid drying of the canopy in the early morning hours. Irrigation was used to supplement rainfall and promote plant growth. In the absence of a significant (≥13-mm) rainfall event, overhead irrigation was applied throughout the growing season (April–November), approximately 5 mm nightly to achieve 35 mm wk–1. Pesticides were periodically applied for broadleaf weeds each October [2,4-D: dimethylamine salt of (2, 4-dichlorophenoxy)acetic acid], annual grassy weeds each April [dithiopyr: S,S'-dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-3,5-pyridinedicarbothioate], and a single curative fungicide application (chlorothalonil: tetrachloroisophthalonitrile) was applied in July of each year to limit disease damage. Weather data was collected from the Purdue University Airport, West Lafayette, IN, located 3 km from the experiment site.

Experimental Design and Statistical Analysis
Individual plots were 1.5 x 1.5 m surrounded by 0.3-m borders of hard fescue [Festuca tryachyphylla (Hackel) Krujina] to avoid nutrient contamination from adjacent plots. Plots were arranged in a randomized, complete block design and each treatment was replicated three times. Data was pooled into four seasonal growth periods per year: early spring (April–12 May), early summer (17 May–July), summer (July–August), and fall (September–November). All data were subjected to ANOVA using the general linear model procedure in SAS (SAS Institute, 1999) and individual species treatment means separated using Fisher's protected LSD. Percentage data were arcsine transformed where necessary (Steel et al., 1997).


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Weather Conditions
Environmental conditions, precipitation measured as rainfall, air temperature, and soil temperature, varied dramatically between the two study years (Fig. 1). Rainfall totaled 951 and 577 mm yr–1 for 2004 and 2005, respectively. Rainfall was greater in the spring months of 2004 (584 mm) than 2005 (176 mm). Additionally, rainfall during the autumn months (October–November) 2004 (97 mm) was greater than in 2005 (43 mm). Average air temperatures were slightly higher during summer 2005 than 2004, averaging 23 and 21°C, respectively. Furthermore, the higher air temperatures persisted longer into the autumn (September) in 2005 (20°C) than in 2004 (19°C).


Figure 1
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  		Figure 1. Rainfall, air, and soil (grass cover, 10 cm) temperatures from September 2003 to December 2005.

 
Species responses to N programs measured as DMY, canopy greenness, leaf tissue N percentage, visual disease severity and incidence ratings, and TQ were strongly affected by individual turfgrass species and N program (Table 2).


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  		Table 2. Cumulative mean study totals for dry matter yield, canopy greenness, leaf tissue N, disease severity, and turfgrass quality of three turfgrass species averaged across eight N programs and ANOVA for species and N program.

 
Dry Matter Yield
When totaled across the entire study and averaged across N program, TTTF had greater DMY than KBG, followed by PRG, producing 9426, 7750, and 7011 kg ha–1, respectively (Tables 2 and 3). For the individual years, averaged across N program, TTTF produced higher DMYs than both KBG and PRG in 2004 (Table 3). In 2005, however, the TTTF DMY was higher than KBG, which was higher than PRG. The higher DMY for KBG in 2005 compared with PRG was probably due to substantial, >50%, losses in PRG stand density due to disease, which was reflected in the July to November harvests. For each species, DMY increased with increasing annual N rate. There were, however, some notable exceptions such as the similar DMYs between the low September-only N program and the unfertilized turf. Although TTTF generally produced the highest DMY values, as a species it had the least variation among N programs.


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  		Table 3. Dry matter yield of Kentucky bluegrass, (KBG), perennial ryegrass (PRG), and turf-type tall fescue (TTTF) as affected by eight nitrogen (N) programs.

 
When evaluating the data for each individual study year, 2004 and 2005, and each species, some unique seasonal growth trends emerge. For KBG, DMY ranged from 1785 to 5099 kg ha–1 and DMY averaged across N programs increased from 3187 to 3441 kg ha–1 for 2004 and 2005, respectively. This is somewhat surprising, since there were fewer harvests in 2005. For PRG, DMYs ranged from 1232 to 3721 kg ha–1 and, when DMY was averaged across all N programs, a slight 3022 to 2775 kg ha–1 decline was measured between years, probably due to the fewer harvests. For the unfertilized PRG turf, however, a substantial decline, 1641 kg ha–1 in 2004 to 1232 kg ha–1 in 2005, was measured and primarily attributed to disease damage. For TTTF, DMYs ranged from 1872 to 5443 kg ha–1 and, like PRG, the average annual DMY between years declined slightly from 4333 to 4003 kg ha–1. The unfertilized TTTF DMY declined from 2615 to 1872 kg ha–1 and since disease levels were low for TTTF, this drop in DMY can only be attributed to the fewer harvests or possibly the slight effects of soil nutrient depletion associated with the weekly clipping removal.

While no species x N program interactions were observed during the first year of N fertilization, during the middle portion (May–August) of 2005, a species x N program interaction was measured that persisted for the remainder of the study. This interaction was due to the lack of N-program response for PRG that was attributed to disease. Therefore, each species was analyzed separately and significant but variable differences in N programs are evident. For KBG, the two high-N programs (SONAM and SNMJ) produced the greatest total DMYs for the study, which ranged from 10100 to 11200 kg ha–1, followed by the medium-N treatments, which ranged from 7842 to 8463 kg ha–1 (Table 3). Two of the medium-N programs, the SOM (8463 kg ha–1) and the SN (8333 kg ha–1), were also similar to the high-N programs. Additionally, some minor seasonal differences are evident when evaluating the individual yearly growth periods. For KBG in 2004, the period of most active growth occurred from May to July, whereas this period occurred during July to August in 2005. The repeated effect of each N program is most clear when evaluating the cumulative DMY data for the entire year in 2005, the second full year of N applications. The high-, medium-, and low-N programs separate into distinct statistical groups, with the low-N programs frequently being similar to the unfertilized turf. These data indicate that following two consecutive years of N fertilization, a single annual N application to KBG is not effective to maintain turf growth as measured by DMY.

For PRG, there were fewer differences among N programs than for KBG. Furthermore, during the last two growth periods in 2005, N program was not significant, probably due to disease and a substantial loss in stand density (Table 3). When totaled across the entire study, the two high-N programs again resulted in the highest DMY, ranging from 8235 to 8861 kg ha–1 for the SNMJ and SONAM programs, respectively. The high-N programs were not different than the medium SN (7107 kg ha–1) or the SOM (8830 kg ha–1), but were different than the medium AMJ (7643 kg ha–1). The low November-only program (6513 kg ha–1) was similar to the low September-only program (5082 kg ha–1), but not the unfertilized (3820 kg ha–1) program.

For TTTF, study DMY totals ranged from 5460 to 11700 kg ha–1 and there were fewer differences among the high-, medium-, and the low-N programs. Similar to KBG and PRG, the low September-only N program produced DMY similar to the unfertilized turf: 5780 and 5460 kg ha–1, respectively. For the individual years in 2004, all N programs were similar except for the low September-only and unfertilized N programs. In 2005, there were slightly more differences between N programs. The high-N programs, ranging from 4877 to 4986 kg ha–1, were similar to the medium AMJ and SN programs but not the medium SOM (3958 kg ha–1) program. For the low-N programs, the low September-only (2170 kg ha–1) N program was similar to the unfertilized (1872 kg ha–1) program but not the low November-only (3602 kg ha–1) N program. The November-only N program was similar to both the SN and SOM medium-N programs.

The DMYs measured in this study were generally comparable to other reported values with some small exceptions. Liu and Hull (2006) reported total annual DMYs of 5152, 4600, and 3680 kg ha–1 for TTTF, KBG, and PRG fertilized with 147 kg N ha–1 grown in Rhode Island. Frank et al. (2006) reported DMYs of 2091 and 3531 kg ha–1 for KBG fertilized with low (98 kg N ha–1 yr–1) and high (245 kg N ha–1 yr–1) N programs, respectively. In our study, DMYs for KBG were higher at slightly lower N rates. It is possible that slightly more N mineralization could be occurring due to the higher soil temperatures and longer growing season in Indiana compared with Michigan. For a KBG–PRG mixture located in California and fertilized with 195 kg N ha–1 yr–1, Harivandi et al. (2001) measured a DMY of 4724 kg ha–1. At a much higher annual N rate (293 kg N ha–1) than evaluated in our study, Engelsjord et al. (2004) reported DMYs of 7680 and 7850 kg ha–1 for KBG and PRG, respectively, with no difference between KBG and PRG. In our study, KBG and PRG were significantly different, with the highest KBG DMY of 5099 kg ha–1 at 196 kg N ha–1 yr–1 (Table 3). Slightly lower TTTF DMY values were reported for a previously neglected TTTF that was fertilized solely with N supplied from a well-fertilized (250 kg N ha–1 yr–1) TTTF clipping donor area (Bigelow et al., 2005). In that study, TTTF produced DMYs of 340, 1874, and 4742 kg ha–1 during the April through October growing season when fertilized at N rates of 0, 200, and 400 kg N ha–1 yr–1, respectively. The slightly lower DMYs in that study compared with this study are probably due to the fact that the N source, turfgrass clippings, was slowly available and that the N was applied weekly in small doses rather than the larger, ≥49 kg N ha–1 doses. A N program that produces a high DMY is not necessarily desirable when managing a lawn because this would probably result in more frequent mowing needs. Therefore, before drawing conclusions regarding the best lawn N program, additional data such as appearance and disease incidence should be taken into account.

Canopy Greenness
Canopy greenness varied by species and when averaged across the entire study and N programs, KBG was the greenest followed by TTTF and PRG, with color indices of 454, 401, and 355, respectively (Table 2). For each individual species, canopy greenness generally increased with increasing annual N rate, with the high-N programs resulting in the highest values (Table 4). There were, however, several exceptions such as for KBG, where the medium SOM N program was similar to the high-N programs, ranging from 496 to 527, and for PRG, where the medium SOM and AMJ N programs were similar to the high-N programs, ranging from 372 to 402. Lastly, for TTTF, all three medium-N programs were similar to the SNMJ high-N program with indices ranging from 407 to 433.


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  		Table 4. Canopy greenness as measured by reflectance for Kentucky bluegrass (KBG), perennial ryegrass (PRG), and turf-type tall fescue (TTTF) fertilized with eight N programs.

 
The aforementioned greenness trends were also generally displayed for each individual species in each calendar study year. For KBG in 2004, the two high-N programs and the medium SOM N program were greenest, with values ranging from 504 to 578. In 2005, the two high-N programs and the medium AMJ N programs were greenest, with values ranging from 503 to 556. For PRG in 2004, the high SNMJ N program and medium AMJ N program were greenest, with values ranging from 408 to 448; however, the high-N programs were not different from the medium SOM N program. In 2005, the high and medium AMJ and SOM N programs were similar, but the medium SOM N program was not different from the low November-only N program. For TTTF in 2004, all the high- and medium-N programs were similar, but the medium SOM and SN N programs were not different from the low November-only N program, 405. In 2005, the high and medium AMJ N programs produced the greenest turf, with values ranging from 453 to 476.

One of the most desirable attributes of an N program for a cool-season lawn species is the ability to provide sufficient greenness for as long a period as possible during the growing season. An ideal N program will encourage rapid spring green-up and retain the green color late into the autumn months. When evaluating the data for each individual species, some of the differences among N programs are apparent. For example, with KBG during mid-April of both years, the N programs slowest to green up were the unfertilized and low September-only programs, with values ranging from 221 to 318, compared with the faster greening high-N programs, which produced values >452. Additionally, the medium AMJ N program, which received spring-only N, was slower to green up in both years. This is interesting because the turf had recently received 49 kg N ha–1 in April but the greening effects were dramatic. The slow spring green-up was not as severe for PRG or TTTF. As for KBG, the low September-only N program and unfertilized plots for each species were slowest to green up. By contrast, the low November-only N program and the April N application in the medium AMJ N program provided rapid greening. The autumn, October, greenness measurements for each species matched very closely to N-program averages for the individual study year averages discussed above. In general, among the high-N programs, KBG was the greenest (>567) species compared with PRG (>396) or TTTF (>417). It is important to mention that the late-season (e.g., December) effects of the November N applications are not evident in this data set because field measurements concluded in mid-November. In general, greenness was also related to leaf tissue N content, which averaged 33.9, 35.2, and 31.5 g kg–1 for KBG, PRG, and TTTF, respectively, for the entire study period across N programs (Table 2).

Our results compare favorably with the well-established response and previously reported data regarding the benefits of autumn N applications (Powell et al., 1967; Wilkinson and Duff, 1972; Wehner et al., 1988; Wehner and Haley, 1993; Mangiafico and Guillard, 2006). Wilkinson and Duff (1972) reported higher mid-April chlorophyll values for KBG turf fertilized in November or December compared with KBG fertilized in October. Our study generated similar results, especially among the medium-N programs, where the SN N program often provided superior spring green-up compared with the SOM N program, which last received N in October. In a similar study with KBG, increasing the autumn N rate from 49 to 98 kg N ha–1 and applying urea in November resulted in higher color ratings than when N was applied in October (Wehner and Haley, 1993). Additionally, Mangiafico and Guillard (2006) reported that applying water-soluble N at 49 kg N ha–1 from 15 October to 15 December improved turf color and density better than a September-only N application. They cautioned, however, that applying N after 15 September to soils in coastal Connecticut may have a serious negative effect on water quality.

One of the most interesting observations during this study was the stark contrast between KBG and PRG or TTTF for spring green-up. The overall slow greening of KBG at lower, ≤73 kg N ha–1, annual N levels is primarily attributed to the cultivar blend used in this study, which contained some traditionally slower greening ‘Midnight’-type cultivars. This is important because these cultivars are widely used in many sod blends planted in lawns. Our data supports the requirement for middle and late-autumn N applications to KBG where fast spring green-up and duration of greenness is important. Regardless of species, the public generally associates a healthy lawn with one that possesses a consistent, dark-green color and, therefore, greenness is a major consideration when suggesting N programs for lawns.

Disease Incidence and Severity
Significant differences among species and, to a lesser extent, N programs for disease incidence and severity were recorded in both study years (Tables 2, 5, and 6). Turf damage assessed as stand blight was attributed primarily to dollar spot (Sclerotinia homoeocarpa F.T. Bennett); however, traces of red thread [Laetisaria fuciformis (McAlpine) Burdsall] and rhizoctonia blight (Rhizoctonia solani Kuhns) were also apparent but not independently rated because they were visually difficult to discern. In the summer of 2004, disease levels when averaged across all N programs were relatively low, ≤6.7% (Table 5). Among species, TTTF had slightly more blight than KBG, 1 to 7%, on three rating dates but was similar to PRG on 12 June and 16 June. Although there were significant species differences, at these low disease levels the differences are probably not practically important. In 2005, significant species differences were again recorded and TTTF and KBG again had relatively low blight levels, 1.0 to 2.3%. Perennial ryegrass, however, sustained substantially more (42–81%) blight compared with 2004, when disease levels were rather low, <11% (Table 6). Although not statistically significant, on 12 June 2004, a trend toward increased (>3%) disease was recorded associated with the low to medium annual N levels or where little spring N had been applied. By 16 June 2004, some of these trends became significant, and the medium SN (10.7%) N program had the highest blight followed by the medium SOM (7.2%) and the low September-only (5.2%) N programs (Table 6). On 23 June 2004, the SN N program had the highest (4.1%) blight, followed by the low September (4.0%) and the low November (0.9%) N-programs, which were similar to the unfertilized (2.0%) turf. In 2005, N program was not significant, probably because blight levels were extremely high, ranging from 32 to 82%, depending on rating date. It is likely that N effects were not apparent because disease simply overwhelmed the PRG regardless of N program. The trend for increased dollar spot where low annual N levels were applied was also generally consistent for KBG and TTTF but disease levels were generally low (Walker, 2006). Of all the N programs, the unfertilized and low September-only N program consistently resulted in more blight than the others. These results are in agreement with what is commonly reported regarding dollar spot and turf N requirements to minimize this disease (Couch, 1995). It is also important to note that, throughout this study, no increase in disease incidence due to a high, 196 kg N ha–1 yr–1, N program or spring-applied N was observed. This is partially attributed to the study location, which was in full sun with minimal periods of extended leaf wetness. Results under shaded conditions may be different.


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  		Table 5. Mean disease ratings for three cool-season turfgrasses averaged across eight N programs.

 

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  		Table 6. Disease severity of perennial ryegrass as affected by eight nitrogen (N) programs.

 
Turfgrass Quality
When averaged across the entire study and N programs, TQ ranked TTTF > KBG > PRG, with mean values of 7.0, 6.7, and 6.3, respectively (Table 2). Yearly TQ ratings for each species generally followed the seasonal growth pattern for cool-season turfgrass, with higher TQ values in the spring, lower values during summer, and an improvement in the fall (Walker, 2006). The superior performance of TTTF over KBG and PRG was primarily due to the more consistent annual appearance during each growing period. Of all three species, KBG was the slowest to green up, resulting in low (2.8–6.0) TQ ratings, which would be deemed unacceptable (<6.0) when rating lawn TQ (Walker, 2006). In 2005, TTTF resisted summer disease more than PRG, resulting in higher TQ ratings.

For each species, TQ generally increased compared with the unfertilized plots as annual N >49 kg N ha–1 yr–1 (Table 7). For all species on many rating dates, the low September-only N program produced TQ ratings similar to the unfertilized plots. The highest TQ values were generally associated with the high-N programs, which resulted in the greenest turf (Table 4). Some of the medium-N programs, however, also resulted in TQ ratings equivalent to the high-N programs. Examples of these programs include the SOM N program in 2004 for KBG, the AMJ N program for PRG in 2004, and the AMJ and SN N programs for TTTF. For PRG, mean annual TQ values for each N program decreased numerically from 2004 to 2005. This annual decline is attributed to the significant losses in stand density described above, and therefore lower TQ values, which negatively affected TQ ratings well into the autumn months. By contrast for KBG and TTTF, mean annual TQ ratings improved for all N programs in 2005, except for the unfertilized and low September-only N programs. While the mean annual TQ values for KBG were sometimes lower than TTTF, on many rating dates during active growth the well-fertilized, ≥123 kg N ha–1 yr–1, KBG had the highest TQ values of all three species, frequently >8.0 (Walker, 2006). These high TQ values may be one reason why KBG remains a preferred species throughout much of the cool-humid region for intensively managed, high-quality lawns.


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  		Table 7. Visual turfgrass quality ratings for three cool-season lawn species as affected by eight N programs.

 
To effectively recommend N programs for cool-season lawns, DMY, greenness, and overall appearance must be considered. Of these factors, greenness and DMY are most important. When DMY and greenness are compared directly for each individual species (Fig. 2–4GoGo), potential lawn N fertilizer recommendations can be made that maximize greenness without excessive DMY. For example, with KBG, there is no difference between the two high and medium SOM N programs for canopy greenness (Fig. 2). There is a difference, however, between the high SONAM and medium SOM N programs for DMY, which means that these N programs result in the same greenness but the medium SOM N program produces less DMY, which may be more desirable where decreased mowing or less annual N is desired. For PRG, the medium AMJ and SOM N programs are not different from the high-N programs for greenness and DMY, showing that there appears to be no advantage in applying ≥123 kg N ha–1 (Fig. 3). This species, however, was severely damaged by disease in 2005 regardless of N program and these two factors alone may not be enough to make recommendations for planting PRG. The same trend for DMY and greenness is also true for TTTF; however, it is the medium AMJ and SN and the high-N programs that are not different (Fig. 4). For all three species, these figures show that there appears to be no advantage to single annual N applications of 49 kg N ha–1 yr–1 in September compared with the unfertilized control for both canopy greenness and DMY. There is a significant advantage, however, to applying a single annual N application, 73 kg N ha–1 yr–1, in November, especially for TTTF.


Figure 2
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  		Figure 2. Kentucky bluegrass mean study dry matter yield and canopy greenness as affected by eight N programs that varied by annual N rate and application timing. Months of application: September (S), October (O) November (N), April (A), May (M), and July (J); annual N rate is in kilograms per hectare.

 

Figure 3
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  		Figure 3. Perennial ryegrass mean study dry matter yield and canopy greenness as affected by eight N programs that varied by annual N rate and application timing. Months of application: September (S), October (O) November (N), April (A), May (M), and July (J); annual N rate is in kilograms per hectare.

 

Figure 4
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  		Figure 4. Turf-type tall fescue mean study dry matter yield and canopy greenness as affected by eight N programs that varied by annual N rate and application timing. Months of application: September (S), October (O) November (N), April (A), May (M), and July (J); annual N rate is in kilograms per hectare.

 

   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Turfgrass specialists throughout the cool-humid region have routinely recommended that ≥49 kg N ha–1 yr–1 should be applied to a cool-season lawn to maximize appearance and growth, with an optimum N application, where only a single application is desired, being late summer (e.g., 1–15 September) (Reicher and Throssell, 1998). If the current goal in lawn management is to be sustainable or maintain lawn turf systems that produce the highest visual appearance with only moderate growth using the fewest N inputs, the results of this study demonstrate that this goal can be achieved by planting an improved TTTF blend and fertilizing with relatively low, 74 to 123 kg N ha–1 yr–1, N levels. Compared with KBG, however, some additional mowing, particularly during the spring months should be expected if TTTF receives ≥123 kg N ha–1 yr–1. This, in turn, may increase maintenance costs due to the increased demand for labor and fuel. While KBG appearance often exceeded TTTF on many rating dates, consistent seasonal performance was limited by slow spring green-up relative to both TTTF and PRG and therefore KBG may necessitate higher (≥123 kg N ha–1 yr–1) annual N levels to optimize TQ. Among species, PRG was the worst performing species, with very few differences between N programs. Although PRG greened up faster in the spring than KBG, it was severely blighted by dollar spot regardless of N program and therefore PRG monoculture stands for moderate to low management intensity lawns in the middle to lower cool-humid region should be avoided. Last, if a turf manager desires to apply N only once during the year, a single N application in mid-November appears to be more beneficial than the traditionally recommended September-only application in central Indiana, especially for TTTF. It is important to mention that these N recommendations for KBG, PRG, and TTTF are based on two consecutive years of data in which clippings were removed for the purpose of accurately determining DMY, a practice not normally recommended for most lawns. In many mature lawns where clippings are returned, annual N rates can sometimes be reduced by 50% without decreasing TQ (Kopp and Guillard, 2002).


   ACKNOWLEDGMENTS
 
We extend grateful appreciation to the Midwest Regional Turf Foundation and the College of Agriculture, Purdue University, for their financial support of this study. Additionally, we would like to offer special thanks to Glenn and Jonathan Hardebeck, James Bergdoll, Jared Nemitz, Jake Metz, and Eddie Walker for their technical assistance during the establishment of this experiment and assistance with sample collection and processing.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

Received for publication September 20, 2006.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 





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