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TURFGRASS SCIENCE

Blending Kentucky Bluegrass Cultivars of Different Quality Performance Levels

Simplot, West 5300 Riverbend Ave., Post Falls, ID 83854

^* Corresponding author (doug.brede{at}simplot.com).

By tradition, Kentucky bluegrass (Poa pratensis L.) turfgrass seed is sown in blends of two or more cultivars. The purpose of this study was to determine (i) the impact on turfgrass quality (TQ) of diluting a high-performing cultivar with a lower-performing one, (ii) whether the relationship between blend ratio and TQ is linear or nonlinear, and (iii) whether a certain quantity of diluent (lower-performing cultivar) can be tolerated without diminishing TQ. Three field trials were planted using an elite cultivar (‘Award’) blended with either a medium-(‘NuBlue’) or low- (‘Huntsville’) performance cultivar. Nonlinear regression was used to test for a segmented curve: TQ = intercept + slope x (blend ratio – pivot point), where the slope is zeroed at blend ratios < pivot point. Adding Huntsville decreased TQ of Award on 71% of rating dates, adding NuBlue decreased TQ on 60% of dates, while adding Huntsville or NuBlue increased TQ on 4% of dates, all related to establishment. Pivot points were significant on 14 of 52 monthly means for Huntsville and two for NuBlue, indicating that under certain circumstances the lower-performing cultivar could serve as a diluent (seed price mitigator) at up to a 50:50 seed ratio, with little detriment on TQ after the first year. Lowering the cutting height to 13 mm from 32 mm in one trial year resulted in a 55% change in slope for Huntsville and 63% for NuBlue; pivot points were unchanged. More field research is needed to verify the many popular theories for blending bluegrass.

Abbreviations: NTEP, National Turfgrass Evaluation Program • TQ, turfgrass quality