The spectral quality of solar radiance affects plant growth and development. The purpose of this study was to assess the spectral quality of deciduous shade, coniferous shade, building shade, and full sun in a natural environment common to turfgrass growth throughout a day and throughout a growing season. A spectroradiometer was used to acquire solar spectra in these four environments. Acquisitions were made on an hourly basis from 0730 to 1930 h, biweekly, from vernal equinox to autumnal equinox at The Ohio Turfgrass Foundation Research and Educational Center and from 10 April to 1 July 1997 at The Ohio State University campus. Data were tested for variation in spectral quality between morning hours and afternoon hours in full sun and among full sun and deciduous, coniferous, and building shade. Results indicated that changes in spectral quality occurred between morning and afternoon periods in full sun, but total (red + blue) photosynthetically active irradiance was not affected. Measurements indicated that a deciduous tree and a conifer tree filtered significantly more high activity (red + blue) quanta than a building. Blue irradiance relative to total irradiance increased and red irradiance decreased with increasing shade density. Significant differences were detected between full sun, tree shade, and building shade for blue photoreceptor potential (blue photon flux/far‐red photon flux) and phytochrome potential (red photon flux/far‐red photon flux). Results indicated that relationships among blue, red, and far‐red irradiance that influence many plant responses were affected by both shade source and shade density.

Visual evaluation of turfgrass quality is a subjective process that requires experienced personnel. Optical sensing of plant reflectance provides objective, quantitative turf quality evaluation and requires no turf experience. This study was conducted to assess the accuracy of optical sensing for evaluating turf quality, to compare the rating consistency among human evaluators and optical sensing, and to develop a model that describes a relationship between optically sensed measurements and visual turf quality. Visual evaluations for turf color, texture, percent live cover (PLC), and optically sensed measurements were collected on the National Turfgrass Evaluation Program (NTEP) tall fescue (Festuca arundinacea Schreb) and creeping bentgrass (Agrostis palustris Huds.) trials at Stillwater, OK. Measurements were made monthly for 12 consecutive months from June 1999 through May 2000. Red (R) and near infrared (NIR) reflectance were collected with sensors and converted to normalized difference vegetative indices (NDVI). The NDVI were closely correlated with visual evaluations for turf color, moderately correlated with percent live cover (PLC), and independent of texture. Measurements of turf color and PLC were evaluated more consistently with optical sensors than by visual ratings. Normalized difference vegetation index (Y) could be reliably predicted by the following generalized model for turf color (X) and PLC (Z): Y = B(0) + B(1)log10X + B(2)Z(3). Optical sensing provided fast, reliable turf assessment and deserves consideration as a supplemental or replacement technique for evaluating turf quality.

The objective of this study was to evaluate seasonal differences in bermudagrass response to N fertilization and irrigation by using optical sensing. A second objective was to determine if optical sensing could measure N status when the turf response to N was confounded by differences in moisture status. Bermudagrasses (Cynodon dactylon L.) ‘Rivera’ and ‘Yukon’ were managed under three irrigation treatments and six N treatments during the growing seasons in 2003 and 2004. Turf quality, normalized difference vegetation index (NDVI), green normalized difference vegetation index (GNDVI), red light reflectance in relation to near infrared reflectance (R/NIR), and green light reflectance in relation to near infrared reflectance (G/NIR) were measured. Bermudagrass demonstrated a noticeable third‐order polynomial seasonal trend in response to N and irrigation treatment, and this trend was characterized as early‐, peak‐, mid‐ and late‐season responses. Normalized difference vegetation index and GNDVI demonstrated a better relationship with turf quality and N status than R/NIR and G/NIR. A comparison among the four indices showed NDVI to be more closely correlated with irrigation, N fertilization, and turf quality. Minimum acceptable and target NDVI were developed by seasonal period based on visual turf quality assessment. It was also found that NDVI response to N fertilization was not strongly affected by irrigation treatment and could be used as an indicator of N status and need regardless of irrigation treatment.

Creeping bentgrass (Agrostis palustris Huds.) turf exposed to shade during morning hours may decline more readily than similar turf exposed to afternoon shade. This study compared the quality and physiological responses of creeping bentgrass turf exposed to morning shade with turf exposed to afternoon shade and evaluated responses of the same species exposed to varying shade densities during the same period. Semipermanent shade structures were placed on a creeping bentgrass range maintained at a 6.4-mm height. Structures provided 6 h of morning shade or 6 h of afternoon shade during the summer solstice. Each structure was covered with either 80 or 100% shade cloth and replicated three times. Control treatments of full sun and perpetual shade were also included. Treated turf was evaluated monthly for color, density, root mass, pigment concentrations, and total nonstructurai carbohydrates (TNC). Regardless of response tested, no significant variation was found between plots receiving morning shade and afternoon shade or between plots in 80 and 100% shade. Canopy temperature, in comparison with air temperature, was 7% greater in morning shade than in afternoon shade, but the relationship between canopy temperatures in full sun and shade did not change during the day. Perpetual shade caused a 38% decrease in color and a 33% decline in density but treatments receiving 6 h of shade did not vary from the full sun treatment. Concentrations of chlorophyll a (46%) and b (50%), neoxanthin (31%), violaxanthin (44%), lutein (34%) declined in perpetual shade compared with full sun. Violaxanthin concentration was influenced by photosynthetic photon flux, suggesting its potential use as a shade stress indicator. S HADE is considered detrimental to turfgrass growth and development. Reduced levels of photosynthetic irradiance result in thinner, more delicate leaf blades (Dudeck and Peacock, 1992) prone to mechanical injury and disease infection. Under shaded conditions, carbohydrate availability is limited due to decreased photosynthetic production and results in reduced stem and root growth, reduced tillering, and poor shoot density. Trees, smaller plants, and structures providing shade also reduce air circulation and increase relative humidity, causing leaf surfaces to remain wet with dew for many hours. These wet leaf surfaces combined with reduced evapotranspiration create a microclimate conducive to disease development. Physiological turfgrass features such as pigment concentrations (Possingham, 1980; Wilkinson and Beard, 1975) and carbohydrate reserve (Voskresenskaya, 1972; Burton et al., 1959) may be affected by shade stress. A reduction in the ratio of

Cynodon transvaalensis Burtt-Davy (African bermudagrass) is used as a turfgrass and in interspecific hybridization to produce turfgrass cultivars. Information is lacking on the magnitude of intraspecific genetic variation for traits related to turfgrass performance. A Design II mating population comprised of 320 F 1 plants (4 parental sets, 16 crosses set 21 , 5 F 1 hybrids cross 21 ) was used to estimate genetic parameters for 21 traits. The F 1 plants were evaluated in replicated field (13 traits) and greenhouse (8 traits) experiments in Stillwater, OK during 2002-2003. Genetic variation was detected for 17 of the 21 traits as indicated by significant (P , 0.05) differences among families within sets. Both additive and dominance genetic effects were detected for most of the 17 traits, but dominance effects usually prevailed over additive effects. Broad sense heritability estimates varied from 0.42 to 0.96. Population improvement via recurrent selection techniques would be possible but difficult as indicated by low levels of additive genetic variation for genetic color, raceme number, seed number, and percent seed set. Dominance effects might be exploited to select clonally propagated F 1 hybrid cultivars with enhanced sensor-rated color, density, turf quality, spring greenup, fall dormancy, percent living cover, raceme number, raceme length, number of florets per inflorescence, plant height, stolon length, number of internodes, internode length, and leaf length.