scholarly journals 510 PB 260 COMPARISON OF FIELD AND SHADEHOUSE MICROCLIMATE FACTORS RELATED TO EVAPORATION AND CROP TRANSPIRATION

HortScience ◽  
1994 ◽  
Vol 29 (5) ◽  
pp. 504e-504
Author(s):  
Robert H. Stamps
Keyword(s):  
Photon Flux ◽  
Pressure Gradients ◽  
Crop Canopy ◽  
Photosynthetic Photon Flux ◽  
Water Losses ◽  
Air Temperatures ◽  
Plant Water Use ◽  
Adjacent Field ◽  
Rumohra Adiantiformis ◽  
Incoming Light

Microenvironmental conditions in a shadehouse covered with shade fabric designed to exclude 70% of incoming light were monitored and compared to those in an adjacent field to quantify differences related to plant water use. Radiant flux density and photosynthetic, photon flux inside the shadehouse varied seasonally between about 18% to 28% of outside values. During the day, leaf and air temperatures around the crop canopy were generally lower and relative humidities higher inside the shadehouse than outside. Leaf-to-air vapor pressure gradients inside the shadehouse averaged about half those outside. Wind run inside was <10% of wind run outside. Differences between reference ET (ETo) values, calculated using Penman's equation), inside and outside the shadehouse were greatest during summer months. Outside evaporatory pan (Epan) water losses ranged from 205 mm in July to 95 mm in Nov. For the same months, Epan losses inside were about 80% lower. Monthly ETactual, as determined for Rumohra adiantiformis growing in lysimeters in the shadehouse, ranged from around 40% to 80% of inside Eo.

scholarly journals Effects of Air Temperature Regimes on Physiological Disorders and Floral Development of Tomato Seedlings Grown under Continuous Light

HortScience ◽  
2005 ◽  
Vol 40 (5) ◽  
pp. 1304-1306 ◽  
Author(s):  
Katsumi Ohyama ◽  
Yoshitaka Omura ◽  
Toyoki Kozai
Keyword(s):  
Air Temperature ◽  
Floral Development ◽  
Continuous Light ◽  
Photon Flux ◽  
Photosynthetic Photon Flux ◽  
Tomato Seedlings ◽  
Physiological Disorders ◽  
Air Temperatures ◽  
Temperature Regimes ◽  
Leaf Chlorosis

Providing continuous light (24-h photoperiod) at a relatively low photosynthetic photon flux (PPF) is one possible way to reduce both initial and operational costs for lighting and cooling during transplant production with an artificial light. However, physiological disorders (i.e., chlorosis and necrosis) are often observed in several species under continuous light with a constant temperature. The objective of this study was to find an effective air-temperature regime under the continuous light to avoid such physiological disorders, and simultaneously enhance floral development, using tomato [Lycopersicon esculentum Mill.] as a model. The seedlings with fully expanded cotyledons were grown for 15 d at a PPF of 150 μmol·m–2·s–1, a relative humidity of 70%, and a CO2 concentration of about 380 μmol·mol–1 (atmospheric standard). Leaf chlorosis was observed when the air temperature was constant regardless of average air temperature (16, 22,or 28 °C). Neither leaf chlorosis nor necrosis was observed when the air temperatures were alternated [periods of high (28 °C) and low (16 °C) air temperatures of 16/8, 12/12, and 8/16 h·d–1]. Faster floral development was observed in the seedlings grown at lower average air temperatures. These results indicated that physiological disorders of tomato seedlings grown under continuous light could be avoided, and at the same time floral development could be enhanced, by lowering the average air temperature through modification of the periods of high and low air temperatures.

scholarly journals Effects of Three Hotcap Designs on Temperature and Tomato Transplant Development

HortScience ◽  
1993 ◽  
Vol 28 (9) ◽  
pp. 878-881
Author(s):  
G.E. Welbaum
Keyword(s):  
Solar Energy ◽  
Lycopersicon Esculentum ◽  
Growth Chamber ◽  
Photon Flux ◽  
Photosynthetic Photon Flux ◽  
Ripe Fruit ◽  
Air Temperatures ◽  
Cloudy Weather ◽  
Soil Temperatures ◽  
Opaque Plastic

Hotcaps are covers used to protect individual plants from suboptimal temperatures. Temperature, solar energy, photosynthetic photon flux (PPF), and tomato (Lycopersicon esculentum Mill.) transplant development were compared for three hotcap designs: 3.8-liter, opaque plastic jugs (PJs); 24-cm-tall wax paper (WP); and Wall-O-Water water-filled plastic teepees (PTs). The average solar energy inside the hotcaps was 57.3%, 67.6%, and 28.9% of full sun at midday and PPF was 44.7%, 49.7%, and 43.8% of full sun at midday for WP, PJs, and PTs, respectively. The rate of temperature decline in a growth chamber was fastest for PJs and slowest for PTs. In the field, air and soil temperatures inside hotcaps were higher than ambient during sunny periods and essentially the same during cloudy weather. The overall mean and mean maximum daily soil and air temperatures for all hotcaps were higher than ambient. PTs had the highest minimum daily soil and air temperatures—2.0 and 1.9C above ambient, respectively. The meantime to first ripe fruit was reduced by 10.7 days for PTs, 6.7 days for WP, and increased by 5 days for PJs compared to noncovered plants. Plants grown under hotcaps weighed less and produced fewer fruit on the first cluster. PJs could not maintain night air temperatures above ambient and were not effective hotcaps.

scholarly journals Estimation of Global and Diffuse Photosynthetic Photon Flux Density under Various Sky Conditions Using Ground-Based Whole-Sky Images

2019 ◽  
Vol 11 (8) ◽  
pp. 932
Author(s):  
Megumi Yamashita ◽  
Mitsunori Yoshimura
Keyword(s):  
Flux Density ◽  
Photosynthetic Photon Flux Density ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Diffuse Component ◽  
Photosynthetic Photon Flux ◽  
Physiological Processes ◽  
Sky Conditions ◽  
Mean Square Errors ◽  
Relative Root

A knowledge of photosynthetic photon flux density (PPFD: μmol m−2 s−1) is crucial for understanding plant physiological processes in photosynthesis. The diffuse component of the global PPFD on a short timescale is required for the accurate modeling of photosynthesis. However, because the PPFD is difficult to determine, it is generally estimated from incident solar radiation (SR: W m−2), which is routinely observed worldwide. To estimate the PPFD from the SR, photosynthetically active radiation (PAR: W m−2) is separated from the SR using the PAR fraction (PF; PAR/SR: unitless), and the PAR is then converted into the PPFD using the quanta-to-energy ratio (Q/E: μmol J−1). In this procedure, PF and Q/E are considered constant values; however, it was reported recently that PF and Q/E vary under different sky conditions. Moreover, the diffuse ratio (DR) is needed to distinguish the diffuse component in the global PAR, and it is known that the DR varies depending on sky conditions. Ground-based whole-sky images can be used for sky-condition monitoring, instead of human-eye interpretation. This study developed a methodology for estimating the global and diffuse PPFD using whole-sky images. Sky-condition factors were derived through whole-sky image processing, and the effects of these factors on the PF, the Q/E of global and diffuse PAR, and the DR were examined. We estimated the global and diffuse PPFD with instantaneous values using the sky-condition factors under various sky conditions, based on which the detailed effects of the sky-condition factors on PF, Q/E, and DR were clarified. The results of the PPFD estimations had small bias errors of approximately +0.3% and +3.8% and relative root mean square errors of approximately 27% and 20% for the global and diffuse PPFD, respectively.

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