Bentgrass Shoot Density Affects Organic Matter Content and Moss Incidence on Golf Greens.

Creeping bentgrass (Agrostis stolonifera var. palustris Huds. Farw.) is the preferred turfgrass species for golf greens.  During summer months, however, shoot density (SD) often declines, resulting in poor stand quality.  High shoot density bentgrass cultivars have been reported to better resist weed invasion than more laterally growing cultivars, such as ‘Penncross’ but, they also have been reported to be more prone accumulate more organic matter (OM).  The objective of this field study was to measure how seasonal SD affects OM content and moss (Bryum argentum Hedw.) incidence of three creeping bentgrass ('A-4', 'L-93', Penncross) cultivars when maintained under two annual nitrogen (N) regimes (112 vs. 196 kg N ha^-1 yr^-1).  Among cultivars, Penncross at both N-regimes had more moss (2.6 and 1.8 % moss plot ^-1, respectively) than both A-4 (0.1 % moss plot^-1) which had the least, and L-93 (0.3 and 0.1 % moss plot^-1 respectively) at either N-regime in 2006.  When comparing moss incidence and SD, a weak correlation was measured (R² = 0.533) suggesting that as SD increases, moss incidence is less of a problem.  Significant seasonal SD differences were measured and cultivars ranked A-4 (1400-2130 shoots dm^-2) > L-93 (1320-1680 shoots dm^-2) > Penncross (760-1330 shoots dm^-2).  A correlation between SD and OM (R² = 0.731) supports the general observation that high shoot density bentgrass cultivars are more prone to OM accumulation with A-4 and L-93 having more OM then Penncross.  In summary, for a high quality golf green, where the densest, most aesthetically pleasing and persistent turf is desired, modern bentgrass cultivars should be planted and OM must be properly managed.  Additionally, ample (146-196 kg N ha^-1 yr^-1) annual N should be regularly applied, particularly during the summer months for lower SD cultivars.