Tuesday, November 14, 2006
168-20

Evaluation of Cool-Season Turfgrasses Quality with Multispectral Radiometry.

Hyeonju Lee and Dale Bremer. Kansas State University, 2021 Throckmorton Plant Sciences Center, Manhattan, KS 66506

Turfgrass quality is typically evaluated by visual observations of color, uniformity, density, and texture. Multi-spectral radiometry (MSR) may provide quantitative, objective evaluations of turfgrass quality and its responses to various stresses. Significant relationships between MSR reflectance data and visual quality have been observed in warm-season turfgrasses. Objectives of this study were to examine (ⅰ) correlations between canopy reflectances and visual ratings in four cool-season grasses and (ⅱ) effects of two irrigation and two mowing height treatments on canopy reflectances. Research was conducted under a rainout shelter at the Rocky Ford Turfgrass Research Center in Manhattan, KS. The rainout shelter shields turf plots from rainfall and allows for precise of irrigation application. Two irrigation treatments (60% or 100% evapotranspiration [ET]) were applied to Kentucky bluegrass (Poa pratensis L., ‘Apollo’), tall fescue (Festuca arundinacea Schreb., ‘Dynasty’) and 2 hybrid bluegrasses, genetic crosses between Poa arachnifera Torr. and Kentucky bluegrass (‘Thermal Blue’ and ‘Reveille’), mowed at 7.6 cm. A lower mowing treatment (3.8 cm) was applied to Apollo and Thermal blue only. Plots were mowed and irrigated twice weekly, and reflectance measurements were collected weekly from mid June through late September in 2005 and 2006. Visual quality was rated on a scale from 1 (dead, brown turf) to 9 (optimum uniformity, density, and color). Reflectances at 8 wavelengths, and the calculated ratios of normalized difference vegetation index (NDVI, [R935 - R661] / [R935 + R661]), IR/R (LAI, R935 / R661), Stress1 (R706 / R760) and Stress2 (R706 / R813), were compared with visual ratings. Results indicated that visual quality was highly correlated with NDVI (r = 0.88), IR/R (r = 0.83), Stress1 (r = -0.84), and R661 (r = -0.80), which suggests that MSR may be useful in providing objective ratings of turf quality in cool-season turfgrasses.