Effects of Seeding Rates on Top Growth and Root Development in Establishing Kentucky Bluegrass under the USGA Soil System

This research was initiated to investigate the effects of seeding rates on top and root growth characteristics in Kentucky bluegrass (KB, Poa pratensis L.) under the USGA (United States Golf Association) soil system and to provide practical information on proper KB seeding rates. Treatments were comprised of the following five seeding rates: VLS (6 g·m-2), LS (9 g·m-2), MS (12 g·m-2), HS (15 g·m-2) and VHS (18 g·m-2). Each treatment was replicated four times in a randomized complete block design. Visual turfgrass color, turf quality and root growth were measured from May to December in 2009. Thesse growth characteristics varied with seeding rate and increased with month after seeding (MAS). Evaluation in the establishment phase indicated that the best color was associated with VHS until 3 MAS, but with HS after that. The turf quality rating score was greatest with VHS until 5 MAS, but with HS after that. Data on root growth, however, showed opposite responses as compared with those of top growth characteristics. During the study, the lower the seeding rate, the longer the root length. Therefore, the best root growth performances were associated with LS and VLS, while HS and VHS, in which the seeding rate was over 15 g·m-2, showed poor performances. In the first-year establishment phase, optimum seeding rates in KB are between 15 and 18 g·m-2 in regards to turfgrass color and quality. However, in terms of root growth, they are in the range of 6 to 9 g·m-2. Further data analysis in a mature-phase will be a practical necessity for the best turfgrass quality and sustainable performance on high-quality sports turf design, construction and management.