Overseeding Cool-Season Grasses on Zoysia japonica Steud. in Korea.

     Research was initiated to investigate several growth characteristics in Korean lawngrass overseeded by cool-season grasses. A total of 8 overseeding treatments were used in the study. Cool-season grasses were applied at seeding rate of 50 to 150 g/m² early October in 2007. Treatments were comprised of Kentucky bluegrass(KB), perennial ryegrass(PR), tall fescue(TF) and their mixtures. Such growth characteristics as turf coverage, visual density, uniformity, visual color, leaf color retention and summer performance etc. were measured in overseeded Korean lawngrass.

     Significant differences were observed among the treatments. Turf coverage and density in almost a year after overseeding was highest in KB, followed by Mixture I (KB33+PR33+TF33), and lowest in PR. Greatest uniformity was associated with KB and Mixture II (KB25+PR50+TF25) and poorest with PR. The overseeded Korean lawngrass showed greater color retention of approximately 3.5 to 5 months longer than the non-overseeded control. Visual color ratings and leaf color retention, however, differed depending on cool-season grass composition and their mixing rates. Summer drought injury was variable with turfgrass species in cool-season grass mixtures. In a overseeding practice here in Korea, the higher the PR, the greater the injury. However, the higher the KB or TF, the less the injury.

     From this study, a variety of treatments could be widely applied in a overseeding practice, depending on lawn types, cultural intensity, the turf quality expectation, and so on. As for gardens, parks, school playgrounds and golf courses with Korean lawngrass of a medium quality level, but requiring sustainable quality of cool-season grass after the overseeding, it would be the best choice to apply with the equal combination of KB, PR and TF by 1/3 in mixtures.