Department of Environmental Horticulture, The University of Seoul1
Department of Green Technology Convergence, KonKuk University2
Protected Horticulture Experiment Station, National Institute of Horticultural & Herbal Science, Rural Development Administration3
This study aimed to determine an appropriate cooling timing in the root zone for lowering substrate temperature and its effect on physiological response of sweet pepper (Capsicum annum L. ‘Orange glory’) grown on coir substrate in summer, from the July 16 to October 15, 2012. Daily temperature of substrate, root activity, leaf water potential, first flowering date, and the number of fruits were measured by circulating cool water through a XL pipe in the root zone during either all day (all-day) or only night time (5 p.m. to 3 a.m.; night) from the July 23 to September 23, 2012. For comparison, no cooling (control) was also applied. Between the 23rd of July and 31st of August (hot temperature period), daily average temperatures in substrates were 25.6°C, 26.1°C, and 29.1°C for the all-day and night treatment, and control respectively. About 1.8 to 5°C lower substrate temperature was observed in both treatments compared to that of control. In sunny day (600-700 W･m-2･s-1), the highest temperature of substrate was measured between 4 p.m. and 5 p.m. under both the all-day and night treatments, whereas it was measured between 7 p.m. and 8 p.m. under the control. Substrate temperatures during the day (6 a.m. to 8 p.m.) and night (8 p.m. to 6 a.m.) differed depending on the treatments. During the day and night, averaged substrate temperature was lower about 3.3°C and 4.0°C for the all-day, and 2.1°C and 3.4° for the night treatment, compared to that of control. In the all-day and night treatment, the TD [TD = temperature of (control)] was greater in bottom than that of other regions of the substrate. Between the day and night, no different TD values were observed under the all-day treatment, whereas under the night treatment there was difference with the greatest degree in the bottom of the substrate. During the hot temperature period, total numbers of days when substrate temperature was over 25°C were 40, 23 and 27 days for the control, all-day, and night treatment, respectively, and the effect of lowering substrate temperature was therefore 42.5% and 32.5% for the all-day and night treatment, respectively, compared to that for the control. Root activity and leaf water potential of plants grown under the all-day treatment were significantly higher than those under the night treatment. The first flowering date in the all-day treatment was similar to that in the night treatment, but 4-5 day faster than in the control. Also, the number of fruits in both treatments was significantly higher than that in the control. However, there was no effect of root zone cooling on eliminating delay in fruiting caused by excessively higher air temperature (> 30°C), although the substrate temperature was reduced 1.8°C to 5°C. These results suggest that the method of cooling root zone temperature need to be incorporated into the lowering growing temperature for growth and fruit set of health paprika.
1. Bakker, J.C. 1989. The effects of temperature on flowering, fruit set and fruit development of glass sweet pepper. J. Hort. Sci. 64:313-320.
2. Behboudian, M.H., W.R. Graves, C.S. Walsh, and R.F. Korcak. 1994. Water relations, mineral nutrition, growth and C discrimination in two apple cultivars under daily episodes of high root-medium temperature. Plant Soil 162:125-133.
3. Gosselin, A. and M.J. Trudel. 1985. Influence of root zone temperature on growth, development and yield of cucumber plants cv. Toska. Plant Soil 85:327-336.
4. He, J., S.K. Lee, and I.C. Dodd. 2001. Limitations to photosynthesis of lettuce grown under tropical conditions: Alleviation by root-zone cooling. J. Expt. Bot. 52:1323-1330.
5. Hirata, K. 1990. Plant nutrition experiment method. Hakubunkansha Publishers, Ltd., Tokyo, Japan. p. 52-55.
6. Jang, Y.A., J.G. Lee, Y.C. Um, S.Y. Kim, S.S. Oh, and S.H. Cha. 2010. Effects of nutrient solution cooling on fruit setting and yield of paprika in summer hydroponics. Kor. J. Hort. Sci. Technol. 28:58-59. (Abstr.)
7. Khan, E.M. and H.C. Passam. 1992. Flowering, fruit set and development of the fruit and seed of sweet pepper cultivated under conditions of high ambient temperature. J. Hort. Sci. 67:251-258.
8. Kim, K.D, Y.S. Ha, K.M. Lee, D.H. Park, S. Kwon, J.M. Park, and S.W. Chung. 2010. Development of temperature control technology of root zone using evaporative cooling methods in the strawberry hydroponics. J. Bio-Env. Con. 19:184-188.
9. Kim, S.E., Y.S. Kim, and S.Y. Sim. 2011. Root-zone temperature control of tomato plant cultivated in perlite bag during summer season. Kor. J. Hort. Sci. Technol. 29:102-109.
10. Lee, H.W. and Y.S. Kim. 2011. Application of low pressure fogging system for commercial tomato greenhouse cooling. J. Bio-Env. Con. 20:1-7
11. Lee, J.H., K.J. Kwon, O.K. Kwon, Y.H. Choi, and D.K. Park. 2002. Cooling efficiency and growth of tomato as affected by root zone cooling methods in summer season. J. Bio-Env. Con. 11:81-87.
12. Moon, J.H., Y.K. Kang, and H.D. Suh. 2007. Effect of root-zone cooling on the growth and yield of cucumber at supraoptimal air temperature. Acta Hort. 761:271-274.
13. Morgan, L. 2011. Root zone chilling. http://www.thctalk.com/ cannabis-forum/archive/index.php/t-50357.html.
14. Na, T.S., K.J. Choi, B.K. Yun, M.S. Cho, H.G. Kim, and H.J. Kim. 2011. Cooling effect on bell pepper on glass house in summer. Kor. J. Hort. Sci. Technol. 29:79. (Abstr.)
15. Rylski, I. and M. Spigelman. 1982. Effects of different diurnal temperature combinations on fruit set of sweet pepper. Scientia Hort. 17:101-106.