• Journal of Bio-Environment Control
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• v.22 no.4
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• pp.349-354
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• 2013

This study examined a technique for cooling root zone aimed at lowering substrate temperature for sweet pepper (Capsicum annum L. 'Orange glory') cultivation in coir substrate hydroponics during hot season, from the $16^{th}$ of July to $15^{th}$ of October in 2012. The root zone cooling technique was applied by using an air duct (${\varnothing}12$ cm, hole size 0.1 mm) to blow cool air between two slabs during night (5p.m. to 3a.m.). Between the $23^{rd}$ of July and $31^{st}$ of August (hot temperature period), average daily substrate temperature was $24.7^{\circ}C$ under the root zone cooling, whereas it was $28.2^{\circ}C$ under condition of no cooling (control). In sunny day (600~700 W $m^{-2}{\cdot}s^{-1}$), average substrate temperatures during the day (6a.m. to 8p.m.) and night (8p.m. to 6a.m.) were lower about $1.7^{\circ}C$ and $3.3^{\circ}C$, respectively, under the cooling treatment, compared to that of control. The degree of temperature reduction in the substrate was averagely $0.5^{\circ}C$ per hour under the cooling treatment during 6p.m. to 8p.m.; however, there was no decrease in the temperature under the control. The temperature difference between the cooling and control treatments was $1.3^{\circ}C$ and $0.6^{\circ}C$ in the upper and lower part of the slab, respectively. During the hot temperature period, about 32.5% reduction in the substrate temperature was observed under the cooling treatment, compared to the control. Photosynthesis, transpiration rate, and leaf water potential of plants grown under the cooling treatment were significantly higher than those under the control. The first flowering date in the cooling was faster about 4 days than in the control. Also, the number of fruits was significantly higher than that in the control. No differences in plant height, stem thickness, number of internode, and leaf width were found between the plants grown under the cooling and control, except for the leaf length with a shorter length under the cooling treatment. However, root zone cooling influenced negligibly on eliminating delay in fruiting caused by excessively higher air temperature (> $28^{\circ}C$), although the substrate temperature was reduced by $3^{\circ}C$ to $5.6^{\circ}C$. These results suggest that the technique of lowering substrate temperature by using air-duct blow needs to be incorporated into the lowering growing temperature system for growth and fruit set of health paprika.

• Journal of Bio-Environment Control
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• v.24 no.3
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• pp.243-251
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• 2015

This study aimed to determine the effects of root zone cooling using air duct on air temperature distribution and root zone and leaf temperatures of sweet pepper (Capsicum annum L. 'Veyron') grown on coir substrate hydroponic system in a greenhouse. When the air duct was laid at the passage adjacent the slab, the direction of air blowing was upstream at $45^{\circ}$. The cooling temperature was set at $20^{\circ}C$ for day and $18^{\circ}C$ for night. For cooing timing treatments, the cooling air was applied at all day (All-day), only night time (5 p.m. to 1 a.m.; Night), or no cooling (Control). The air temperature inside the greenhouse at a height of 40 and 80cm above the floor, and substrate and leaf temperatures, fruit characteristics, and fruit ratio were measured. Under the All-day treatment, the air temperature was decreased about $4.4{\sim}5.1^{\circ}C$ at the height of 40cm and $2.1{\sim}3.1^{\circ}C$ at the height of 80cm. Under the Night treatment, the air temperature was decreased about $3.4{\sim}3.8^{\circ}C$ at the height of 40cm and $2.2{\sim}2.7^{\circ}C$ at the height of 80cm. The daily average temperature in the substrate was in the order of the Control ($27.7^{\circ}C$) > Night ($24.1^{\circ}C$) > All-day ($22.8^{\circ}C$) treatment. Cooling the passage with either upstream blowing at $45^{\circ}$ or horizontal blowing at $180^{\circ}$ was effective in lowering the air temperature at a height of 50cm; however, no difference at a height of 100cm. Cooling the passage with perpendicular direction at $90^{\circ}$ was effective in lowering the air temperature at the height between 100 and 200cm above the floor; however, no effect on the temperature at the height of 50cm. A greater decrease in leaf temperature was found at 7 p.m. than that at 9. a.m. under both All-day and Night treatments. Fresh weight partitioning of fruit was in the order of the All-day (48.6%) > Night (45.6%) > Control (24.4%) treatment. A higher fruit production was observed under the All-day treatment, in which the accumulated average temperature was the lowest, and it may have been led to a higher proportion of photosynthate distributed to fruit than other treatments.