Turfgrass Color, as Influenced by Pigment Composition and Measurement Methods.

Turfgrass color rankings have been a numbers based system defined on a subjective 1-9 scale. Recently color measurements have involved using digital photography or hand held colorimeters. These measurements use color scales including CIE (Commission Internationale de l'Eclairage) L*a*b* scales. There is variation in the results, which is thought to be due primarily to tissue nitrogen, chlorophyll and canopy density. The objectives of this study were to investigate which pigment is most responsible for turfgrass color and find a correlation between pigments and a range of methods for determining color rankings. Six cultivars of colonial bentgrass (Agrostis capillaris), and nine cultivars of creeping bentgrass (Agrostis stolonifera), tall fescue (Schedenorus phoenix), fine fescue (Festuca spp.) perennial ryegrass (Lolium perenne) and kentucky bluegrass (Poa pratensis) were selected based on dark / intermediate and light green color ratings using National Turfgrass Evaluation Program trial results. Each cultivar was sown at standard seeding rates, germinated in greenhouse conditions and matured for 10 weeks. Turfgrass color was then measured by a handheld colorimeter, extract color measurement and analysis of leaf tissue nitrogen and chlorophyll. Human subjects (42) ranked the darker tall fescue and fine fescues significantly higher (P=0.05) on a 1-9 scale, in agreement with NTEP results.  Chlorophylls (CHL) A, B and total chlorophyll varied by grass and cultivar when measured by volume but only CHL A and CHL total varied when measured across area. Tissue nitrogen (N) levels were significantly different across all grasses which impacts human assessment, but N had little impact on lab color analysis. The three tested methods of color analysis had benefits and weaknesses, but none of them offered a comprehensive color analysis linked to the plant’s pigmentation breakdown.