[5-1130-P] Other Categories (5th)

[5-1130-P-24] Proposal of temperature control technology in pot cultivation for the citrus fruits

*Ryuta IBUKI¹, Yoshimichi Yamashita², Sachie Horii², Norihiro Hoshi², Madoka Chiba¹ (1. Miyagi University(Japan), 2. National Agriculture and Food Research Organization(Japan))

Keywords:pot cultivation, thermal management

Disaster area of Fukushima restarted farming mainly by the large-scale rice production corporation by farmland accumulation and the flower farmer using pipe house, which have little concern about reputational damage. For effective use of pipe house, there is a need for new crops that can be grown in pipe house at times other than floriculture and rice seedlings. With this situation as the background, we focused on pot cultivation. It has been considered to cultivate ‘citrus fruits’, which is cultivated in warmer regions under meteorological conditions by cultivation using pots, outdoors in summer and in a pipe house in winter. In addition to alleviating the northern limit of temperature-based cultivation, we are exploring new thermal management techniques for the pot cultivation environment. A difference was observed in the condition depending on the presence or absence of the whole covering sheet on the ‘citrus fruits’ (e.g. ‘Citrus sphaerocarpa’, etc.) in pot placed in the pipe house from 2017 to 2018, and the plant growth was good at the tree with the covering. Then, from 2018 to 2019, we investigated the thermal effect of the covering. ‘Citrus sudachi’ grown in pots (diameter 385 mm, depth 310 mm, black soil and pumice in the bottom of pots) was wintered, and the temperature and heat transfer conditions in the cultivation environment were compared for the presence or absence of the covering. The leaf surface temperature with an infrared radiation thermometer and the 10 cm depth soil temperature with a T-type thermocouple were examined during the winter (February 4 to March 4, 2019). The lowest, average and the highest (T_min,T_a, T_max) were surveyed, with leaf temperatures of (-7 °C, 7 °C, 38 °C) in the covering tree, (-6 °C, 8 °C, 41 °C) in the control area, with the soil temperature (1 °C, 11 °C, 29 °C) under the covering tree, and (1 °C, 12 °C, 33 °C) in the control. From this, it was found that the cover texture contributes to the suppression of the high temperature of 3 to 4 °C during the day rather than the heat retention effect at night. In addition, we also investigated the time-dependent change of the temperature distribution of the soil in the pot placed in the pipe house from February 4 to February 26, 2019. The soil temperatures in pot at the inner side of the south sidewall, the center and the inner side of the north wall were measured at intervals of 10 minutes using a T-type thermocouple for a depth of 2 cm, 10 cm and 20 cm. The inner side of the south wall surface is the hottest and the maximum value on a fine day is extremely high, showing 50 to 60 °C. On the other hand, the daily maximum value of the pot center 10 cm deep showed a value 20 to 30 °C lower than that of the south side wall surface. Also, the time to reach the maximum temperature at the point showed a delay of about 3 hours as compared with the wall surface. During the period, the soil temperature changes at the center of the pot is delayed while the air temperature goes up with the sunrise during the daytime. According to Konakahara(1975), due to strong winds and physiological changes in the tree, low land temperatures in the land-planted ‘Citrus Unshiu’ inhibit water supply from the roots, and the amount of transpiration exceeds water supply, resulting in poor water balance in the tree. The balance tends to occur, the decrease of the water content in the leaves becomes remarkable, and quantitatively the effect starts to be seen at the soil temperature of 10 °C or less, and the effect becomes remarkable at that of 5 °C or less. In the measurement, the time when the central soil temperature exceeded 5 ° C was after 11:00, and the time exceeding 10 ° C was after noon. On the other hand, the temperature difference between the air and the center of the pot was maximum in the morning and was 20 to 30 °C. This is consistent with the case of Konakahara, and suggests the need to manage the ground temperature and temperature difference, taking into consideration the high temperature of the daytime inside the house even in winter. Based on these results, we considered that more sophisticated control of temperature distribution and heat transfer in the pot throughout the year will contribute to the improvement of productivity in pot cultivation. For example, the water content of the soil, which affects the thermal conductivity, is considered to have a large effect, and measurements were performed to understand the change in the water content in the pot. This work was conducted under "A Scheme to Revitalize Agriculture and Fisheries in Disaster Area through Deploying Highly Advanced Technology" by the Ministry of Agriculture, Forestry and Fisheries, Japan.