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Dana Sullivan, Jing Zhang, Alexander R. Kowalewski, Jason B. Peake, William F. Anderson, F. Clint Waltz Jr. and Brian M. Schwartz

assessing turfgrasses, which are widely used and recognized by turf researchers ( Morris and Shearman, 1998 ). In recent years, more quantitative methods (i.e., digital image analysis and spectral reflectance) have been developed to supplement visual ratings

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Soumaila Sanogo, Osama I. El-Sebai and Robert Sanderson

-flooding conditions on severity of Verticillium wilt, plant growth, and spectral reflectance-based physiological indices of chile pepper. Materials and Methods Inoculum preparation and plant production. An isolate of V. dahliae , recovered from a field

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J.R. Davenport, R.G. Stevens, E.M. Perry and N.S. Lang

The ability to monitor plant nutrient status of high value horticultural crops and to adjust seasonal nutrient supply via fertilizer application has economic and environmental benefits. Recent technological advances may enable growers and field consultants to conduct this type of monitoring nondestructively in the future. Using the perennial crop apple (Malus domestica) and the annual crop potato (Solanum tuberosum), a hand-held leaf reflectance meter was used to evaluate leaf nitrogen (N) status throughout the growing season. In potato, this meter showed good correlation with leaf blade N content. Both time of day and time of season influenced leaf meter measurement, but leaf position did not. In apple, three different leaf meters were compared: the leaf spectral reflectance meter and two leaf greenness meters. Correlation with both N rate and leaf N content were strongest for the leaf reflectance meter early in the season but nonsignificant late in the season, whereas the leaf greenness meters gave weak but significant correlations throughout the growing season. The tapering off of leaf reflectance values found with the hand-held meter is consistent with normalized difference vegetation index (NDVI) values calculated from satellite images from the same plots. Overall, the use of leaf spectral reflectance shows promise as a tool for nondestructive monitoring of plant leaf status and would enable multiple georeferenced measurements throughout a field for differential N management.

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Pinghai Ding, Leslie H. Fuchigami and Carolyn F. Scagel

Kazantsev, 2007 ). However, derivative changes the original peak form and may eliminate some important peaks. Different wavelengths have different levels of spectral (reflectance and/or transmission) sensitivity and accuracy for measuring Chl. Reflectance

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C.H. Blazquez, H.N. Nigg, L.E. Hedley, L.E. Ramos and S.E. Simpson

Spectral reflectance measurements were taken from immature and mature leaves of `Rio Red' grapefruit `McCarty' grapefruit `Minneola' tangelo, `Satsuma' mandarin, `Dancy' tangerine, `Nagami' oval kumquat, and `Valencia' orange from 1330 to 1530 hr 1 day at the Florida Citrus Arboretum, Division of Plant Industry, Winter Haven, Fla. A PS-1000 spectrometer was used with fiber optic cables and a lens source (visible range of the spectrum 400-800 sun) coupled with a tungsten halogen light source. A data acquisition card was connected to a notebook computer with a SpectraScope computer program for processing and data storage. Immature and mature leaves of `Minneola' tangelo had greater percentage reflectance in the 500-800 sun range than the other cultivars and leaf ages measured. More detailed information was obtained with the PS-1000 than with conventional spectrometers. The slope of the citrus spectral curves in the 800 nm range was not as sharp as conventional spectrometers, but had a much higher reflectance value than those obtained with a different spectrometer. The system used here was convenient to transport and use in the field and produced clear, interpretable data.

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R. Savé, J. Peñuelas, I. Filella and C. Olivella

One-year-old gerbera plants subjected to 1 night at 5C had reduced leaf water losses and chlorophyll content and increased root hydraulic resistance, but stomatal conductance and leaf water potential did not change. After 3 nights, leaf water potential had decreased and leaf reflectance in the visible and the near-infrared had increased. Similarly, abscisic acid (ABA) in leaves had increased and cytokinins (CK) in leaves and roots had decreased, but ABA levels in roots did not change. After 4 days at 20C, root hydraulic resistance, reflectance and leaf water loss returned to their initial values, but leaf water potential and chlorophyll content remained lower. Leaf ABA levels reached values lower than the initial, while root ABA and leaf CK levels retained the initial values. These data suggest that in the gerbera plants studied, 3 nights at 5C produced a reversible strain but otherwise plants remained uninjured, so this gerbera variety could be cultured with low energetic inputs under Mediterranean conditions. The results may indicate that ABA and CK were acting as synergistic signals of the chilling stress. Spectral reflectance signals seemed to be useful as plant chilling injury indicators at ground level.

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Yiwei Jiang and Robert N. Carrow

Canopy reflectance has the potential to determine turfgrass shoot status under drought stress conditions. The objective of this study was to describe the relationship of turf quality and leaf firing versus narrow-band canopy spectral reflectance within 400 to 1100 nm for different turfgrass species and cultivars under drought stress. Sods of four bermudagrasses (Cynodon dactylon L. × C. transvaalensis), three seashore paspalums (Paspalum vaginatum Swartz), zoysiagrass (Zoysia japonica), and st. augustinegrass (Stenotaphrum secundatum), and three seeded tall fescues (Festuca arundinacea) were used. Turf quality decreased 12% to 27% and leaf firing increased 12% to 55% in 12 grasses in response to drought stress imposed over three dry-down cycles. The peak correlations occurred at 673 to 693 nm and 667 to 687 nm for turf quality and leaf firing in bermudagrasses, respectively. All three tall fescues had the strongest correlation at 671 nm for both turf quality and leaf firing. The highest correlations in the near-infrared at 750, 775, or 870 nm were found in three seashore paspalums, while at 687 to 693 nm in Zoysiagrass and st. augustinegrass. Although all grasses exhibited some correlations between canopy reflectance and turf quality or leaf firing, significant correlation coefficients (r) were only observed in five grasses. Multiple linear regression models based on selected wavelengths for turf quality and leaf firing were observed for 7 (turf quality) and 9 (leaf firing) grasses. Wavelengths in the photosynthetic region at 658 to 700 nm or/and near-infrared from 700 to 800 nm predominated in models of most grasses. Turf quality and leaf firing could be well predicted in tall fescue by using models, evidenced by a coefficient of determination (R 2) above 0.50. The results indicated that correlations of canopy reflectance versus turf quality and leaf firing varied with turfgrass species and cultivars, and the photosynthetic regions specifically from 664 to 687 nm were relatively important in determining turf quality and leaf firing in selected bermudagrass, tall fescue, zoysiagrass and st. augustinegrass under drought stress.

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Yiwei Jiang, Robert N. Carrow and Ronny R. Duncan

Traffic stresses often cause a decline in turfgrass quality. Analysis of spectral reflectance is valuable for assessing turfgrass canopy status. The objectives of this study were to determine correlations of narrow band canopy reflectance and selected reflectance indices with canopy temperature and turf quality for seashore paspalum exposed to wear and wear plus soil compaction traffic stresses, and to evaluate the effects of the first derivative of reflectance and degree of data smoothing (spectral manipulations) on such correlations. `Sea Isle 1' seashore paspalum (Paspalum vaginatum Swartz) was established on a simulated sports field during 1999 and used for this study. Compared to original reflectance, the first derivative of reflectance increased the correlation coefficient (r) of certain wavelengths with canopy temperature and turf quality under both traffic stresses. Among 217 wavelengths tested between 400 and 1100 nm, the peak correlations of the first derivative of reflectance occurred at 661 nm and 664 nm for both canopy temperature and turf quality under wear stress, respectively, while the highest correlations were found at 667 nm and 820 to 869 nm for both variables under wear plus soil compaction. Collectively, the first derivative of reflectance at 667 nm was the optimum position to determine correlation with canopy temperature (r > 0.62) and turf quality (r < -0.72) under both traffic stresses. All correlations were not sensitive to degrees of smoothing of reflectance from 400 to 1100 nm. A ratio of R936/R661 (IR/R, Infrared/red) and R693/759 (stress index) had the strongest correlations with canopy temperature for wear (r = -0.63) and wear plus soil compaction (r = 0.66), respectively; and a ratio of R693/R759 had the strongest correlation with turf quality for both wear (r = -0.89) and wear plus soil compaction (r = -0.82). The results suggested that the first derivative of reflectance could be used to estimate any single wavelength simultaneously correlated with multiple turf canopy variables such as turf quality and canopy temperature, and that the stress index (R693/R759) was also a good indicator of canopy stress status.

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Yun-wen Wang, Bruce L. Dunn and Daryl B. Arnall

calculated over six replications of four N rates (n = 24) for each cultivar. The coefficient of determination R 2 was used to indicate the explained variance. Discriminant analysis of the canopy spectral reflectance data was done using PROC DISCRIM in SAS

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Yiwei Jiang, Huifen Liu and Van Cline

reflectance without destructive sampling because spectral reflectance in the visible and infrared regions is closely associated with leaf pigment content ( Bell et al., 2004 ; Cater and Spiering, 2002 ; Stiegler et al., 2005 ) and water content ( Penuelas et