Natural Organic Fertilizers and Bentgrass Cultivar Effects On Rootzone Organic Matter Content.

High quality putting greens are commonly established with creeping bentgrass [Agrostis stolonifera L. var palustris (Huds.) Farw.] cultivars on sand-based rootzones.  Excessive organic matter (OM) accumulation can degrade the optimum soil physical properties like rapid drainage and aeration pore space of sand-based rootzones.  Currently there are concerns regarding the frequent use of natural organic (NO) fertilizers which may have adverse affects on sand-based rootzone physical properties due to the presence of fine mineral and organic components which may occlude aeration pore space.  High shoot density bentgrass cultivars are commonly planted because they persist under ultra-low (< 3 mm) cutting heights and have a more uniform and upright leaf architecture compared to traditional cultivars.  These cultivars, however, have been reported to accumulate more OM than older cultivars which produce less canopy biomass.  This field study examined the effect of five commercially available fertilizers applied to three creeping bentgrass cultivars (‘Penn A-4’, ‘L-93’, ‘Penncross’) on rootzone surface OM content after four years of multiple annual applications.  The products included synthetic, water-soluble fertilizers as well as slow release NO fertilizers.  The total OM content lost on ignition of the NO fertilizers ranged from 499-663 g kg^-1 while synthetic fertilizers ranged from 980-996 g kg^-1.  Synthetic and NO fertilizers had no effect on surface OM content in the rootzone despite significant differences in OM content of each fertilizer.  Among cultivars, ‘Penn A-4’ and ‘L-93’ had more (324 and 316 g kg^-1) OM compared to ‘Penncross’ (279 g kg^-1).  These data suggest that cultivar is a greater factor regarding increases in rootzone OM accumulation and compromised physical properties, not the use of NO fertilizers.  Therefore, where newer cultivars are grown turf managers should pay close attention to rootzone OM levels and ensure management practices are conducted to minimize excess OM accumulation.