decreased the anthocyanin content of wines, but sensory analysis yielded no corresponding differences in flavor or perceived aromas ( Morrison and Noble, 1990 ). Total phenolic content of ‘Shiraz’ fruit was correlated with the percentage of ambient PAR
Christina M. Bavougian, Paul E. Read, Vicki L. Schlegel, and Kathryn J. Hanford
Mark E. Uchanski, Dawn M. VanLeeuwen, Steven J. Guldan, Constance L. Falk, Manoj Shukla, and Juliette Enfield
water temperature inside the barrel for the month of January. PAR was measured each season within 1 month of the winter solstice, 21 Dec., at noon. Measurements were taken at six locations associated with each high tunnel: outside the high tunnel
A. Cutlan, G. Nordwig, R. Warner, and J.E. Erwin
Variation in red/far red leaf and photosynthetically active radiation (PAR) absorption by an individual leaf of various ornamental hanging basket species was measured. Red/far red ratios varied from 0.30 to 0.83 for Syngonium podophyllum Schott. and Chlorophytum comosum Thunb. `vittatum', respectively. Reduction in PAR varied from 86% to 61% for those same species, respectively. Estimated state of phytochrome photoequilibria for understory crops when grown under each species was calculated. Cucumis sativus L. seedling hypocotyl elongation was measured under different species to validate hypothesized differences in stem elongation associated with differences in red/far red filtering through individual leaves. Implications with respect to light quality effects on stem elongation and dry weight accumulation of plants grown under different species are discussed.
David Llewellyn, Youbin Zheng, and Mike Dixon
preferential absorption of red light by the upper plant canopy. It has been postulated, by various growers, that reductions in plant quality when grown below HB crops are due to a combination of insufficient PAR and reductions in the R:FR at the lower crop
Dave Llewellyn, Katherine Schiestel, and Youbin Zheng
systems falls in the green (G, 500 to 600 nm) region or outside of the PAR region altogether ( Bergstrand et al., 2016 ). Therefore, LED-generated PAR may be more efficiently used in many horticultural production scenarios. Most of the greenhouse
T.H. Morsil, A.D. Matthias, and J.L. Stroehlein
The effects of trellising on absorption of photosynthetically active radiation (PAR, 400- to 700-nm wavelength) by foliage and fruits, on fruit composition, and yield were studied in 1988 under semi-arid conditions using field-grown Vitis vinifera L. `Petite Sirah' grapevines in a mature vineyard. A vertical inclination was obtained by attaching shoots to a vertically arranged three-wire trellis; 60° shoot inclination from horizontal was obtained by attaching shoots to a “V-type” Tatura trellis; a standard two-wire trellis (control) was used in which shoots attached to the upper wire were permitted to orient downward to the vineyard floor. PAR absorption by foliage during mid-morning to mid-afternoon periods was highest in the standard trellis and lowest in the Tatura trellis. PAR available for absorption by fruits was lowest in the standard trellis and highest in the Tatura trellis. Analysis of fruit composition at harvest revealed that total dissolved solids (°Brix) was significantly higher for berries from the Tatura trellis than for the vertical trellis or the control. The Tatura trellis resulted in the highest alcohol content of wine. Per-vine yields did not differ significantly among the three trellis systems.
Juan Carlos Díaz-Pérez
10 min and store hourly averages for each plot. Air temperature data were obtained from a University of Georgia weather station located within 300 m of the plots. Incoming and reflected photosynthetically active radiation ( PAR ) was determined with
Chase Jones-Baumgardt, David Llewellyn, and Youbin Zheng
radiation ( PAR ) a crop received [i.e., total light integral (TLI); mol·m −2 ] in the literature, particularly in greenhouse environments, due to incomplete descriptions of the canopy-level PPFD from natural and/or supplemental sources. Although TLI [also
Mathieu Ngouajio and Jeremy Ernest
Weed control is one of the benefits associated with the use of plastic mulches used for vegetable production. The mulches decrease light transmission and prevent development of most weed species. Plastics chemistry has developed films varying in their ability to reflect, absorb, and transmit light. Laboratory and field experiments were conducted to 1) measure light transmitted through colored mulches, 2) evaluate weed populations under each mulch type, and 3) determine if light transmission could be used as an indicator for weed populations in the field. The polyethylene mulches were black, gray, infrared transmitting brown (IRT-brown), IRT-green, white, and white-on-black (co-extruded white/black). On average, 1%, 2%, 17%, 26%, 42%, and 45% light in the 400 to 1100 nm range was transmitted through the black, white/black, gray, IRT-brown, IRT-green, and white mulches, respectively. In field experiments, density and dry biomass of weeds growing under the mulches were evaluated. The white mulch had the highest weed density with an average of 39.6 and 155.9 plants/m2 in 2001 and 2002, respectively. This was followed by the gray mulch, with 10.4 and 44.1 weed seedlings/m2 in 2001 and 2002, respectively. Weed density was <25 plants/m2 with the other mulches in both years. Weed infestation was correlated with average light transmission for white, black, white/black, and gray mulches. However, both light quantity and quality were necessary to predict weed infestations with the IRT mulches. Weed infestation under the IRT mulches was better estimated when only wave lengths in the photosynthetically active radiation range (PAR; 400 to 700 nm) were considered. Low weed pressure and high light transmission with the IRT mulches would make them appropriate for use in areas where both weed control and soil warming are important factors.
Jerneja Jakopič, Franci Štampar, and Robert Veberič
of trees with a 1-m long sensor (LI-COR; μmol·m −2 ·s −1 ) for all treatments every week during ripening. On each tree, three fruit samples were marked, and the photosynthetically active radiation ( PAR ) was measured using the LI-COR quantum sensor