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Nitrogen Affects the Summer Density of Creeping Bentgrass
December 1, 2008 By: Adam C. Moeller, Cale A. Bigelow TurfGrass TrendsThe SD values for HSD cultivars in this study were generally similar to some previously reported values (Ervin et al., 2000; Bruneau et al., 200) but lower than others (Beard et al., 2001; Sifers et al., 2001; Jordan et al., 2003). Sweeney et al. (2001) reported similar shoots dm2 . They did not, however, report significant density reductions and in some instances measured an increase in SD from spring through summer. Some possible reasons for our lower values may be the slightly higher cutting height and the more intensive/abrasive light frequent sand topdressing program employed to reflect contemporary management practices.
In general, annual N regime did not significantly affect SD (Figure 1). In August of each year, however, when overall SD was lowest, the high N regime resulted in significantly more shoots than low N plots when averaged across cultivars, 1,170 versus 1,330 and 1,220 versus 1,310 shoots dm2 for the low and high N regimes in the 2006 and 2007 study years, respectively. For example, SD reductions for A-4, L-93 and Penncross from June to August of each year averaged 23 percent, 23 percent and 37 percent at 2.3 lbs N/1,000 ft2 yr-1 , respectively. By comparison, at the 4 lbs N/1,000 ft2 yr-1 N rate, reductions were 17 percent, 15 percent and 23 percent, respectively.
Summary and recommendations
As superintendents continue to strive to produce smooth, firm, consistent, putting green conditions, it is clear that several important factors affect bentgrass appearance and overall health. Of utmost importance is cultivar selection and N fertility level, particularly with respect to summer performance. The HSD cultivars are more reliable than Penncross because they maintain a dense turf canopy even with SD losses during the summer. Consider the following: When Penncross was most dense, during May or June, its SD was nearly equivalent to A-4 and L-93 at their lowest SD.
In response to golfers' desires for fast green speeds, many superintendents are applying low annual N, often < 2.5 lbs N/1,000 ft2 yr-1 . This management approach is risky, and may compromise bentgrass health, especially on heavily trafficked greens grown in poor growing environments. These ultra-low N regimes result in malnourished turf, which is more prone to environmental stress, pest damage and Poa annua invasion. An alternative approach might be to apply 3 lbs to 4 lbs N/1,000 ft2 yr-1 and manipulate other inputs such as applying plant growth regulators and using lightweight rollers to achieve a desired green speed.
In this field study, increasing the annual N level from 2.3 to 4 lbs N/1,000 square feet per hear had little effect on the overall seasonal SD of each cultivar. The exception, however, occurred in August when a beneficial response of the higher N level for SD was observed for both Penncross and A-4. Additionally, although increased N did not significantly enhance SD, it dramatically improved bentgrass visual appearance (data not shown). These data support the recommendation that moderate summer N (0.4 to 0.5 lbs N/1,000 square feet per month) should be applied to minimize stand loss and ensure rapid recovery at the onset of favorable growing weather.
Due to the increased SD and organic matter accumulation associated with HSD cultivars, many golf course managers are on an aggressive sand topdressing program to maintain a firm, smooth surface. This normally involves the light application of sand topdressing every seven days to 10 days throughout the growing season. Although not directly evaluated in this study, we suggest that care should be exercised when attempting this management strategy for older bentgrass cultivars like Penncross, especially when maintained using a low N fertility program. Sand topdressing is a mechanically abrasive practice and may cause deleterious effects and, if improperly timed, further reduce Penncross SD and negatively affect overall putting green quality.
Where the densest, most aesthetically pleasing and persistent putting greens are desired, modern bentgrass cultivars should be planted and ample annual N should be applied. In the cool-humid region this will be about 3 to 4 lbs N/1,000 square feet per year for mature sand-based putting greens. In addition, a large proportion of the annual N should be supplied during the summer months using light, frequent liquid applications in order to promote recovery during the heavy-use seasons.
Adam Moeller is a United States Golf Association Northeast regional agronomist located in Easton, Pa. He can be contacted at amoeller@usga.org. Cale Bigelow is an assistant professor of agronomy/turfgrass science at Purdue University in West Lafayette, Ind. He can be reached at cbigelow@purdue.edu.
REFERENCE
Beard, J.B., P. Croce, M. Mocioni, A. DeLuca, and M. Volterrani. 2001. The comparative competitive ability of thirteen Agrostis stolonifera cultivars to Poa annua. Intl. Turfgrass Soc. Res. J. 9:828-831.
Beard, J.B. 2002. Turf management for golf courses. 2nd ed. Ann Arbor Press, Chelsea, MI.
Bruneau, A.H., C.A. Bigelow, R.J. Cooper, and D.C. Bowman. 2001. Performance of creeping bentgrass cultivars maintained at two mowing heights and under two fungicide regimes in North Carolina. Intl. Turfgrass Soc. Res. J. 9:835-842.
Ervin, Erik H.; Frame, Scott; Smith, Adam; Zelko, Alan. 2000. Turfgrass: 2000 Research & Information Report [Missouri]. p. 13-14. [Online]. http://agebb.missouri.edu/pdc/turf/report00.pdf (verified 13 Nov. 2007).
Jordan, J.E., R.H. White, D.M. Vietor, T.C. Hale, J.C. Thomas, and M.C. Engelke. 2003. Effect of irrigation frequency on turf quality, shoot density, and root length density of five bentgrass cultivars. Crop Sci. 43:282-287.
Landry, G., and M. Schlossberg. 2001. Bentgrass (Agrostis spp.) cultivar performance on a golf course putting green. Intl. Turfgrass Soc. Res. J. 9:886-897.
Schlossberg, M.J., and K.J. Karnok. 2001. Root and shoot performance of three creeping bentgrass cultivars as affected by nitrogen fertility. J. Plant Nutr. 24:535-548.
Sifers, S.I., J.B. Beard, and M.L. Fraser. 2001. Botanical comparisons of twelve Agrostis cultivars in a warm-humid climate. Intl. Turfgrass Soc. Res. J. 9:213-217.
Sweeney, P., K. Danneberger, and D. Wang. 2001. Root weight, nonstructural carbohydrate content, and shoot density of high-density creeping bentgrass cultivars. HortSci. 36(2):368-370.
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