Research Topic: Over-Seeded Rough Bluegrass (Poa trivialis) Response to Selected N Sources (2007), J. Sartain, University of Florida

Cool-season turfgrasses respond differentially to N sources depending on their release characteristics, soil texture, and organic matter composition. A field study was established on dormant tifdwarf bermudagrass over-seeded with rough bluegrass with the objective to evaluate the visual quality, growth and N uptake response of different N sources including a new technology meal and soy protein, soluble, traditional and synthetic slow release, traditional organic.

Five N sources (Green Spec® 16-4-8 and 7-7-7, ammonium sulfate (AS), 60% IBDU & 40% AS, and Milorganite) were applied at 1.0 lbs N/1000 sq ft/45 days to dormant tifdwarf bermudagrass over-seeded with rough bluegrass. Plots (6 by 9 ft) were arranged in a randomized complete block design and replicated four times. Visual ratings and chlorophyll meter readings were taken weekly. Clippings were collected every 30 days for growth rate and N uptake estimates. The study was run for two 45 day evaluation periods.

Statistically significant differences in visual quality were observed during the second 45 day evaluation cycle relative to N source applied. The Green Spec 16-4-8 and Seven Iron™ 7-7-7 began the cycle rating approximately 7 in visual quality and ended the cycle at around 6.5, thus these two materials maintained above acceptable quality turfgrass during the entire 45 day cycle. The 60% IBDU and 40% AS mixture began the cycle as an intermediately rated N source but ended the cycle as the top rated mixture. In general, the control plots declined over the evaluation period and completed the evaluation period with a below acceptable level of turfgrass quality. The 7-7-7 material produced superior quality turfgrass and milorganite produced the lowest quality turfgrass of the N sources applied.

When averaged over the entire 90 day period, the Green Spec 7-7-7, AS and IBDU/AS N sources produced equivalent superior chlorophyll meter readings, whereas the Green Spec 16-4-8 and Milorganite produced somewhat lower meter readings. The Green Spec 7-7-7 mixture supplied the largest quantity of N to the turfgrass over the entire 90 day evaluation period. The Green Spec 16-4-8, AS and IBDU/AS mixtures supplied an intermediate level of N and the Milorganite the lowest quantity of N. When averaged over the entire 90 day evaluation period, the Green Spec 7-7-7 and AS produced the highest mean growth, the Green Spec 16-4-8 and IBDU/AS mixtures produced intermediate growth and Milorganite the least growth.

Based on the visual quality ratings, chlorophyll meter readings, growth rate estimates and total N uptake it appears that the Green Spec 7-7-7 N source was superior to the other N sources in supplying N and promoting the growth of quality cool-season turfgrass during this 90 day evaluation period. This was a relatively short term study and these results should not be used to draw major long term conclusions but the initial results do appear promising and warrant addition study.