Abstract
Turf grasses entering the Nordic winter must be healthy and have sufficient reserves. The objective of this research was to investigate the effects of autumn mowing height and late autumn fertilization (LAF) on golf greens. Eighteen experiments were carried out on golf courses in Finland (3), Sweden (3) and Norway (7), nine in 2008/2010 and nine in 2009/2010. Starting in late August or early September, the greens were cut for about one month at 100% or 150% of the height practiced during summer. Within each mowing height, 2 g N/m2 was applied in a complete, mineral fertilizer when the turf had stopped growing. Unfertilized control plots were established using tarpaulin covers, three within each mowing height. The grass species were creeping bent grass (Agrostis stolonifera L.: 6 expt.), red fescue (Festuca rubra: 4 expt.), velvet bent grass (Agrostis canina: 3 expt.), and annual meadow grass (Poa annua: 5 expt). Overall winter damage, turf coverage and overall turf impression were assessed in spring. The results showed different responses among species: (1) Red fescue-dominated greens had significantly better turf grass coverage and overall impression after LAF. Higher mowing tended to improve spring performance. (2) LAF improved coverage and overall impression, but did not reduce winter damage or winter diseases on creeping bent grass greens. There was no effect of mowing height. (3) Velvet bent grass greens showed no significant effect of either mowing height or LAF. On annual meadow grass greens higher mowing improved spring performance more than LAF.
Since there were no negative effects of LAF, we conclude that LAF is beneficial for golf greens under Nordic conditions. The effect of higher mowing in autumn differed among species, but can be recommended for annual meadow grass and red fescue. Further research is needed to find optimal time and fertilizer rate.
Introduction
Long, dark and cold winters are typical for continental parts of Norway, Sweden and Finland. At 60 °N, the latitude of the three capitals Oslo, Stockholm and Helsinki, temperature fluctuations around 0 °C often result in ice build-up on putting greens and anoxic conditions. The snow moulds Microcochium nivale and Typhula incarnata are the most severe turf grass diseases. Under these conditions, it is critical that turf grasses enter the winter as healthy as possible and with sufficient reserves. Two of the most important management practices affecting turf grass health before the winter are autumn mowing height and autumn fertilization.
It is often recommended to raise the mowing height in autumn in order to reduce winter damage (e.g. Happ Citation2004, Charbonneau Citation2010, Gilhuly Citation2010). The rationale behind this recommendation is that a higher leaf area index will stimulate photosynthesis and thus carbohydrate storage. However, unlike the well-documented effect of mowing height on the tolerance of cool-season turf grasses to summer stress (e.g. Huang and Fry Citation2000, Fagerness and Yelverton Citation2001, Liu and Huang Citation2002), we have not been able to find experimental evidence documenting the effect of mowing height on winter survival on golf greens.
Extremely high mowing, like 5 cm, has been proven to reduce cold tolerance of creeping bent grass (White and Smithberg Citation1980). These authors also reported the same cold tolerance for smooth-stalked meadow grass (Poa pratensis) and red fescue mowed at 1.5 and 5 cm height. Beard (Citation1969), on the other hand, mentions low cut as a factor which increases the risk of frost injury on smooth-stalked meadow grass. But none of these experiments were conducted under green conditions. A compromise advocated by Stier and co-workers in Wisconsin is that mowing height should be increased in autumn only if the turf has been struggling due to shade, too low mowing, or other stresses during summer (Stier Citation2006, Stier and Koeritz Citation2008, Stier and Fei Citation2008). Stier and Fei (Citation2008) also suggested that too high mowing in autumn could increase the risk for snow mould.
While late autumn fertilization (LAF) has become common practice amongst greenkeepers in the northern part of USA (Rieke Citation1998, Lloyd Citation2009), this practice has, so far, not been recommended for golf greens in the Nordic countries. As with mowing heights, most experimental evidence on the effect of LAF comes from latitudes further south and from turf grass species not used on golf greens. Furthermore, studies have often focused on other aspects than winter survival. For example, it is well documented that LAF will result in better winter colour, earlier spring green-up and improved spring performance of smooth-stalked meadow grass (Poa pratensis) (Hanson and Juska Citation1961, Wilkinson and Duff Citation1972, Kussow Citation1988, Hummel Citation1990, Wehner and Haley Citation1993). This species has, however, better winter tolerance and deeper winter dormancy than most other turf grasses, and results are therefore not necessarily transferable to golf greens. This also holds for Webster and Ebdon's (Citation2005) findings that LAF did not increase the potential for winter injury in perennial ryegrass, and for Culleton et al.'s (Citation1991) report that LAF had some effect on turf grasses in France but not in Ireland. More relevant for golf courses are the studies by Powell et al. (Citation1967a, Citation1967b) who reported better winter colour, increased winter root growth and higher carbohydrate content in spring after LAF of bent grass putting greens in Virginia, and those by Lloyd (Citation2009) who found nitrogen application on 15 October to be more efficient than application on 15 September or 15 November in enhancing autumn colour and spring growth of putting greens in Minnesota and Wisconsin.
Perhaps the weightiest argument against LAF is that it may increase nutrient leakage through drainage water (Mangiafico and Guillard Citation2006, Lloyd Citation2009). In unstable winters, this risk is probably even higher on sand-based golf greens than on ordinary soils. Many turf grass managers are also concerned about snow mould, although it has not, to our knowledge, been documented that moderate LAF will increase this problem on golf greens.
A review of the effects of autumn-applied nitrogen on cold season grasses (Bauer et al. Citation2012) underlines the need for more experiments, especially under more northern climatic conditions.
The objective of this research was to investigate the effects of autumn mowing height and LAF on winter survival and spring performance of various turf grass species on Nordic golf greens. Our hypothesis was that increased mowing height and one application of 2 g N m−2 as a balanced mineral fertilizer in late autumn would reduce winter injuries and improve turf coverage and overall impression in spring.
Materials and methods
Experimental sites and set-up
Experiments were set up on golf greens where winter injuries occur regularly. Golf clubs volunteered to participate and offered a green in play for the experiment and their head greenkeeper to do the technical work and to collect data. Three experimental greens at Bioforsk Turfgrass Research Centres Landvik and Apelsvoll were also included.
The experiments started in 2008 on 15 golf courses in Finland, Sweden and Norway. The project was scheduled to go on for 2 years, but some experiments were not followed up during the project period. For those golf courses having experiments in both years, observation plots were usually not the same in the 2 years. Thus, the present paper is based on 18 individual experiments, nine in 2008/09 and nine in 2009/10 ().
Table I. Overview of experiments included in project.
The experiment was set up with two factors, mowing height and late autumn fertilization. Mowing heights were either the normal height practiced on the golf course during summer and early autumn or increased 50% during the last month of the growing season. Different mowing heights were established by dividing the experimental green into two, and mowing continued until the turf had stopped growing in October. Actual mowing heights are given in . Late autumn fertilization was either no LAF (control), or 2 g N m−2 applied when leaf elongation had stopped, but before permanent soil frost or snow cover. As a guideline, soil temperature in the afternoons should be beneath 6 °C as an average for some days. The exact dates were decided by the greenkeepers.
The fertilizer used in autumn 2008 was a granular, easily soluble, complete fertilizer (Arena Start 10-1-10 + 1% Fe). In autumn 2009, greenkeepers used comparable products from local dealers. The whole green was fertilized. Covers made of tarpaulin (1.5×1.5 = 2.25 m2) defined the unfertilized plots, half of them on the high- and half on the low- cut part of the green. The number of unfertilized plots within each half of the green (mowing height) was usually three.
Registrations
Registrations were made by the greenkeepers and reported as per cent winter damage and overall impression of the turf in spring on a scale from 1 to 9, where 9 is the best. The evaluation was done just after snow melt and when the course opened for play. Some greenkeepers also did a final evaluation 2 weeks after opening. The observations of winter damage included both abiotic and biotic damages, which were not always easy to separate. Some greenkeepers did, however, specify per cent of plot area with obvious snow mould damage.
General weather conditions
Weather conditions during the 2 experimental years were different. The winter 2008/2009 was unstable and the main injury was caused by ice encasement and anoxia. The next winter was stable with a permanent snow on most of the greens from the beginning of December until the middle of March. Snow moulds were the most common reason for winter damage in the second year of the project.
Statistical analyses
Mean values for the four combinations of mowing height and LAF in each trial were entered into four datasets for greens dominated by red fescue, creeping bent grass, velvet bent grass and annual meadow grass, respectively. When analysing these datasets, each trial was considered one block, with the main effects of mowing height, LAF and mowing height×LAF being tested against their pooled interaction with block (trial) number.
Significant results refer to p < 0.05, tendencies to p < 0.15.
Results
Red fescue
Red fescue dominated greens had significantly better turf grass coverage and overall impression in the spring after LAF (). LAF also tended to reduce winter damage. The effects of mowing heights were less evident than those of LAF, but higher mowing tended to give better overall impression despite slightly more disease just after snow melt. This positive effect of higher mowing occurred both at Vestfold GC and Bioforsk Landvik in 2008/2009, but results in 2009/10 were inconsistent (data not shown). On average for four experiments, the best overall impression in spring was found on plots with high mowing and LAF (a).
Figure 1. Main effects of late autumn fertilization (LAF) (2 g m−2), and increased mowing height (+50%), on greens dominated by (a) red fescue, (b) creeping bent grass, (c) velvet bent grass and (d) annual meadow grass. The average of 4, 6, 3 and 5 experiments respectively.
Table II. Main effects of mowing height in the autumn and late autumn fertilization on red fescue greens. Results from 2 experimental years.
Creeping bent grass
On average for six experiments, LAF improved coverage and overall impression, but not overall winter damage or winter diseases in creeping bent grass. Effects of mowing were negligible. There were no significant interactions (). As for red fescue, b shows that the highest overall impression scores were given to plots with high mowing and LAF.
Table III. Main effects of mowing height in the autumn and late autumn fertilization on creeping bent grass greens. Results from 2 experimental years.
Velvet bent grass
The overall analyses of three experiments revealed no significant effect of either mowing height or LAF on spring performance of velvet bent grass (). There were tendencies to less winter damage and better overall impression in spring on plots that had received LAF. As in red fescue and creeping bent grass, the best overall impression was recorded on plot with increased mowing height and LAF, but the difference from the other combinations was far from significant (c).
Table IV. Main effects of mowing height in the autumn and late autumn fertilization on velvet bent grass greens. Results from 2 experimental years.
Annual meadow grass
Unlike in red fescue, creeping bent grass and velvet bent grass, spring performance of annual meadow grass was influenced more by autumn mowing height than by LAF. Overall winter damage or winter diseases were not influenced by either mowing height or LAF, but increased mowing height led to significant improvements in turf grass coverage in spring and tended to have a similar effect on turf grass overall impression (). Winter damage was severe regardless of treatment, but the least damage, 45%, was found on a plot with elevated mowing height and no fertilization in late autumn (not shown). This combination also produced the highest turf grass overall impression in spring (d).
Table V. Main effects of mowing height in the autumn and late autumn fertilization on annual meadow grass greens. Results from 2 experimental years.
Discussion
Late autumn fertilization (LAF)
The most significant finding in this project was the positive effect of LAF in creeping bent grass and red fescue, the species most commonly seeded on golf greens in the Nordic countries. Firstly, it is noteworthy that LAF did not increase winter damage in these species; in fact, it tended to reduce it in red fescue. Secondly, the late fertilizer input enhanced turf grass coverage and overall impression in spring in a manner similar to that earlier reported for smooth-stalked meadow grass (Hanson and Juska Citation1961, Wilkinson and Duff Citation1972, Kussow Citation1988, Hummel Citation1990). Our results indicate that root uptake was still active when the fertilizer was applied in late October, November or even early December. Most probably, the fertilizer increased the content of nitrogen in turf grass apical regions, thus preparing the turf for a more rapid green-up and recovery from winter damage in spring (Lloyd Citation2009). The fact that the positive effects of LAF were seen on golf courses throughout Finland, Sweden and Norway in 2 years with contrasting winter conditions gives confidence to our conclusion that LAF is beneficial for red fescue or creeping bent grass putting greens in the Nordic countries.
Both creeping bent grass and red fescue are winter-hardy turf grass species that were probably in the midst of their winter-hardening phase at the time of LAF. New knowledge about the photosynthetic activity under low temperatures (Höglind et al. Citation2011) emphasizes the importance of keeping plants vigorous during cold adaptation in autumn. Turf grass managers are often reluctant to apply nitrogen in autumn as they believe it will promote growth and reduce the storage pool of carbohydrates before winter. However, with correct timing and at moderate rates, it is likely fertilization in the autumn will increase rather than reduce turf grass reserves before winter. Plants’ adaptation to cold includes a comprehensive reorganizing of the cell structure and metabolic pathways (Lütz Citation2010). The specific leaf weight increases as do the amount of chlorophyll per unit leaf area and the content of sugar in cytosol (Ensminger et al. Citation2006). Instead of giving a relatively large application shortly before frost, the fertilizer input in autumn should be spilt into several small applications throughout October and November. This aspect warrants further research as it also would reduce the risk for nutrient runoff and leaching.
Even though the significance levels were not as convincing as in red fescue and creeping bent grass, our recommendation for LAF also holds for velvet bent grass. This species is used on only a few courses in Norway and Sweden, but Finland has almost 250 velvet bent grass greens (K. Laukkanen, Finnish Golf Union, pers. comm.). Possible explanations why velvet bent grass showed less response to LAF than creeping bent grass and red fescue might be that velvet bent grass has a lower metabolic rate and a better colour retention in autumn and therefore needs less nitrogen to maintain its photosynthetic capacity during cold acclimation (Aamlid et al. Citation2012).
Contrary to the three perennial and persistent species, annual meadow grass did not benefit from LAF in this study. Although the effect of LAF on winter damage was not significant, the most likely explanation for this is that annual meadow grass utilized the late fertilizer input for growth rather than for storage. Even though the annual meadow grass on old golf courses such as Saltsjöbaden and Royal Drottningholm may well belong to the perennial subspecies Poa annua ssp. reptans, winter dormancy was probably not as profound as in fescue and the bent grasses. This explanation is in agreement with Lloyd (Citation2009) who found N application on 15 October to enhance shoot growth of annual meadow grass (ssp. reptans) but not of creeping bent grass in Wisconsin, and with Aamlid et al. (Citation2009) who documented higher metabolic activity in annual meadow grass than in creeping bent grass at temperatures close to 0 °C. On the other hand, our results do not support Vargas and Turgeon (Citation2004) who, under Michigan conditions, recommended to apply 4.9 g N m−2 as dormant fertilization to annual meadow grass greens around 1 November.
One common argument against increased mowing height of turf grass in autumn is that it will result in more damage from snow mould during winter (e.g. Rieke Citation1998, Stier and Fei Citation2008). In our material there tended to be such an effect in red fescue and velvet bent grass but, surprisingly, not in creeping bent grass and annual meadow grass. We have no good explanation for this difference among species other than that there was more variation among the individual trials in creeping bent grass and annual bluegrass than in the other species.
Snow mould attacks in red fescue, creeping bent grass and velvet bent grass are often not lethal as the turf will be able to recover from apices that are not affected. How fast this recovery occurs depends on turf grass reserves, which is why we had hypothesized a positive effect of increased mowing height in autumn. For red fescue, which has lower tiller density and more upright growth than the bent grasses, our hypothesis tended to be confirmed by the results from the unstable winter 2008/2009, but not from the winter 2009/2010 during which the turf was covered by snow for 3–4 months with no possibility for photosynthesis. It is also understandable that higher mowing had no positive effect in velvet bent grass as carbohydrate accumulation in this very dense species was hardly limited by lack of green leaf area. The inconsistent effects of autumn mowing height in creeping bent grass are more difficult to explain, in particular because there were a couple of experiments in 2009/2010 (Bioforsk Landvik, Mørk GC) in which higher mowing in autumn led to better overall impression in spring in spite of the long-lasting snow cover.
The most clear-cut effects of increase mowing height in autumn on turf grass spring performance were found in annual meadow grass. This might reflect that the generally lower storage pool of fructans (e.g. Hull Citation1992) makes photosynthesis, and thus leaf area, more critical in this species than in the more perennial grasses. Annual meadow grass is susceptible to anthracnose (causal fungus Colletotrichum graminicola), including the basal form which, at least in North America, is active even in late autumn and during winter (Smiley et al. Citation2005). Higher mowing has been reported to reduce anthracnose levels and result in more robust annual meadow grass greens in summer (Inguagiato et al. Citation2009), and our results suggest that this may be the case even before the winter period. Still another reason why increased mowing height may be advantageous in annual meadow grass is that seeds will be shed and contribute to new plants in spring rather than being collected with the turf grass clippings. Combined with little or no benefit of raising mowing heights of creeping bent grass in autumn, these results may have interesting implications for autumn management of mixed bent grass/meadow grass greens, which are common both in North America and in the Nordic countries. As the experimental quality of our on-course trials in annual meadow grass were mostly not as good as for the other species, we will, however, not draw any definite conclusion for annual meadow grass at this stage. Even for the other species, the rather broad on-site approach taken in this project ought to be followed up with more detailed studies at turf grass research centres.
Acknowledgements
The authors thank the Scandinavian Turfgrass and Environment Research Foundation for funding this project and the contributing golf clubs and greenkeepers for their support.
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