Search Results

You are looking at 1 - 10 of 551 items for :

  • "photosynthetically active radiation" x
Clear All
Full access

Bruce D. Lampinen, Vasu Udompetaikul, Gregory T. Browne, Samuel G. Metcalf, William L. Stewart, Loreto Contador, Claudia Negrón and Shrini K. Upadhyaya

( Fig. 1 ). Fig. 1. Mobile platform measurement system retrofitted on a utility vehicle (model 610 Mule; Kawasaki Heavy Industries, Tokyo) for measurement of photosynthetically active radiation ( PAR) interception in orchards; IRT = IR thermometers, GPS

Free access

E.A. Guertal and C.B. Elkins

Photosynthetically active radiation (PAR) was measured at two times of day (8:00 am and noon Central Standard Time) in a 915 × 915-cm area of a 1006 × 915-cm gable roof greenhouse. PAR measurements were taken across a grid at 40-cm intervals, a total of 529 data points. Spatial variation of PAR in the greenhouse was evaluated through contour plots and the geostatistical technique of semivariogram construction. Semivariograms provide a visual guide to the degree of spatial correlation of a variable, allowing a quantification of the distance at which variables cease to be spatially correlated (the range) Measured PAR contained distinct zones of lowered values, a function of overhead greenhouse structures, wall-hung electrical boxes, and tall plants in adjacent greenhouses. Although the amount of PAR changed over time, zones of high and low PAR remained relatively constant, except at the sides of the greenhouse. Constructed semivariograms revealed that PAR contained strong spatial correlation (up to a 350-cm separation) as measured in the north-south direction, moving parallel to greenhouse bench placement. When PAR measurements perpendicular to benches (east-west) were used in directional semivariograms PAR was found to be completely random, plotting as a horizontal line called a nugget effect. Thus, plants placed perpendicular to the greenhouse benches (east-west) would not be affected by the spatial correlation of PAR.

Free access

William L. Bauerle and Joseph D. Bowden

This report describes a system for integrating photosynthetically active radiation (PAR) using fiberoptics. Many photoelectric sensors or 1-m-long line sensors that integrate individual interception points for spatial averaging were replaced with fiberoptics, which integrate interception points. Depending on the positioning of optical fibers and the amount of fibers terminated at a PAR sensor, whole-plant, canopy layer, and individual leaf light interception can be determined. The use of fiberoptics has the added advantage of being very small in comparison to the bulk of a typical quantum sensor. The fiberoptic-based system potentially is a more accurate, less expensive method to integrate PAR throughout plant canopies than PAR sensors.

Free access

J.H. Lieth and C.C. Pasian

A mathematical description for the relationship between the rate of rose (Rosa hybrida L.) leaf net photosynthesis and photosynthetically active radiation, leaf temperature, and leaf age is developed. The model provides a tool for the prediction of these rates for leaves growing in a rose crop canopy.

Free access

C. Campillo, M.H. Prieto, C. Daza, M.J. Moñino and M.I. García

, is the most important type from an ecophysiological viewpoint because it relates to photosynthetically active radiation ( PAR ). A direct method for determining the percentage of intercepted radiation (LI) is to measure PAR both above and below the

Free access

Ajay Nair and Mathieu Ngouajio

quantum light sensors (PAR Light Sensor; Spectrum Technologies) were installed one per treatment, both inside and outside the rowcovers, to record ambient temperature and photosynthetically active radiation ( PAR ). In 2009, temperature sensors were also

Free access

David M. Glenn

et al. (2007) modeled light absorption and distribution within walnut and almond trees with and without a kaolin PF to understand the paradox and demonstrated that although there is an ≈20% reduction of photosynthetically active radiation ( PAR) to

Free access

D. Michael Glenn

productivity, contrary to the assertion of Blum (2005) . Environmental effects on WUE include the response to the abiotic environmental effects of vapor pressure deficits (VPD), photosynthetically active radiation ( PAR ), and water deficits in addition to

Full access

Pamela C. Korczynski, Joanne Logan and James E. Faust

The daily light integral (DLI) is a measurement of the total amount of photosynthetically active radiation delivered over a 24-hour period and is an important factor influencing plant growth over weeks and months. Contour maps were developed to demonstrate the mean DLI for each month of the year across the contiguous United States. The maps are based on 30 years of solar radiation data for 216 sites compiled and reported by the National Renewable Energy Lab in radiometric units (watt-hours per m-2·d-1, from 300 to 3,000 nm) that we converted to quantum units (mol·m-2·d-1, 400 to 700 nm). The mean DLI ranges from 5 to 10 mol·m-2·d-1 across the northern U.S. in December to 55 to 60 mol·m-2·d-1 in the southwestern U.S. in May through July. From October through February, the differences in DLI primarily occur between the northern and southern U.S., while from May through August the differences in DLI primarily occur between the eastern and western U.S. The DLI changes rapidly during the months before and after the vernal and autumnal equinoxes, e.g., increasing by more than 60% from February to April in many locations. The contour maps provide a means of estimating the typical DLI received across the U.S. throughout the year.

Free access

D. Michael Glenn

Kaolin-based particle films have use in reducing insect, heat, photosynthetically active radiation (PAR), and ultraviolet radiation stress in plants resulting from the reflective nature of the particles. Particle films with a residue density of 1 to 4 g·m−2 have been evaluated in a range of crops and agricultural environments. The particle film is a general insect repellant resulting from the change in the plant’s leaf/fruit texture but also because it changes the reflected light signature of the plant causing insect avoidance for many pests. The alteration of reflected light is the result of the ability of the particle film to reflect infrared (IR), PAR, and ultraviolet radiation. Reflection of IR can reduce canopy temperature as much as 5 °C, which will reduce potential transpiration. The reduction of PAR by the film at the leaf level is compensated in varying degrees by diffusion of PAR into the interior of the canopy. Whole canopy photosynthesis can be increased by the combined particle film effects of reduced canopy temperature and increased diffusion of PAR into the interior of the canopy. In apple, reducing fruit surface temperature, PAR, and ultraviolet is an effective means of reducing sunburn damage. The use of a reflective particle film is effective in mitigating environmental stress and has significant economic benefits in agricultural crops.