Relationship of multispectral radiometry data to qualitative data in turfgrass research

Multispectral radiometry provides a method for assessing plant light reflectance in the visible and near-infrared ranges. Reflectance of narrow wavelength ranges as well as ratios of different ranges have been highly correlated with absorbency of photosynthetically active radiation, leaf area index (LAI), and plant response to stresses. The objectives of this research were to determine if data obtained by multispectral radiometry might accurately correlate with qualitative data (used as rapid estimates of color, density, and uniformity) typically used in turfgrass research. Furthermore, it was our objective to determine whether multispectral radiometry could discriminate between stressed and nonstressed turfgrass plots. This research was conducted in two consecutive trials during 1997 on seven seashore paspalum (Paspalum vaginatum Swartz) ecotypes and three hybrid bermudagrass (Cynodon dactylon L. x C. transvaalensis Burtt-Davy) cultivars established on a native Appling (clayey, kaolinitic, thermic Typic Kanhapludult) soil at the University of Georgia Experiment Station in Griffin, GA. Reflectance at 661 and 813 nn, as well as the ratios normalized difference vegetation index (NDVI, computed as R-935 - R-661/R-935 + R-661), infrared/red (IR/R) (LAI, computed as R-935/R-661), Stress1 (R-706/R-760), and Stress2 (R-706/R-813) were highly correlated with visual turf quality, shoot density, and shoot tissue injury (STI) ratings, but not with shoot clipping growth. Regression analysis also indicated very strong associations with each of these qualitative variables, but not with shoot growth data. Additionally, spectral measurements at all wavelengths except 559 and 706 nm were able to consistently distinguish between wear-treated and untreated plots; This methodology may have applications in both turfgrass research and management to provide quantitative measures with physiological significance to traditional visual qualitative estimates of shoot aspects.