• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.131-131
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• 2017

작물의 체온인 엽온은 작물의 증발산량 또는 작물의 스트레스와 관련이 있으며, 일반적으로 일사, 풍속, 습도 등 기상조건과 잎의 크기, 형태 등 생리작용 등에 의해 지배된다. 엽온을 작물의 수분스트레스지수, 증발산량 등을 산정하기 위한 인자로 많이 활용되고 있으며, 최근 ICT 기술의 발달로 인해 열영상 카메라, 적외선 센서 등을 활용해서 실시간 측정을 하고, 정보를 작물 생육환경 제어에 활용하는 연구들이 많이 이루어지고 있다. 본 연구에서는 시설오이를 대상으로 캐노피 온도(Canopy temperature, $T_c$)와 대기온도(Air temperature, $T_a$)간의 상관관계, 또 ($T_c-T_a$)와 포화수증기압차(Vapor pressure deficit, VPD)와의 관계를 분석하였다. 대기온도와 상대습도를 이용하여 산정된 VPD가 엽온에 미치는 영향을 분석한 결과, 엽온 증가에 따라 VPD가 증가하였으며, 캐노피와 대기온도간의 차이 또한 VPD간에 음의 상관관계($R^2=0.82{\sim}0.89$)가 나타났는데, 이는 대기온도에 따른 엽온과 포화수증기압의 상승이 원인인 것으로 나타났다. ($T_c-T_a$)와 VPD값을 이용하면 작물 수분스트레스(Crop Water Stress Index, CWSI)를 산정할 수 있는 데, 결과값을 분석한 결과 $T_c$와 $T_a$의 차가 적은 경우 CWSI값이 증가함을 알 수 있었다. 향후 연구에서는 추가적으로 다양한 재배환경에서의 캐노피 온도, 포화수증기압차, 그리고 CWSI를 산정하여, 적정 생육 환경조성을 위한 지표로 활용할 계획이다.

• Journal of Ecology and Environment
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• v.35 no.3
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• pp.213-225
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• 2012

Sap flux density (SFD) measurements were used, in combination with morphological characteristics of trees and forest structure, to calculate whole-tree transpiration, stand transpiration (St) and mean canopy stomatal conductance (Gs). Analysis based on the relationships between the morphological characteristics of trees and whole tree water use, and on the responses of SFD and Gs to short wave radiation (RR), vapor pressure deficit (VPD) and soil water content (SWC) during drought and non-drought periods were conducted. The results showed a strong positive correlation between whole tree transpiration and both tree diameter at breast height (DBH) ($r^2$ = 0.95, P < 0.05) and sapwood area (SA) ($r^2$ = 0.98, P < 0.05). Relationships between SFD and DBH ($r^2$ = 0.25), as well as SA ($r^2$ = 0.17) were weak. Daily SFD of Quercus serrata Thunb was closely related to VPD and RR. Although operating at different time scales, RR and VPD were important interacting environmental controls of tree water use. SFD increased with increasing VPD (<1 kPa) and RR. SWC had a considerable effect on stand transpiration during the drought period. The relationships between SFD, VPD and RR were distorted when SWC dropped below 35%.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.183-183
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• 2017

Pan evaporation (Epan) is an important indicator of water and energy balance. Despite global warming, decreasing annual Epan has been reported across different continents over last decades, which is claimed as pan evaporation paradox. However, such trend is not necessarily found in seasonal data because the level of contributions on Epan vary among meteorological components. This study investigates long-term trend in seasonal pan evaporation from 1908 to 2016 across South Korea. Meteorological variables including air temperature (Tair), wind speed (U), vapor pressure deficit (VPD), and solar radiation (Rs) are selected to quantify the effects of individual contributing factor to Epan. We found overall decreasing trend in Epan, which agrees with earlier studies. However, mixed tendencies between seasons due to variation of dominant factor contributing Epan were found. We also evaluated the reference evapotranspiration based on Penman-Monteith method and compared this with Epan to better understand the physics behind the evaporation paradox.

• Journal of Biosystems Engineering
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• v.42 no.1
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• pp.23-43
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• 2017

Purpose: As application-specific wireless sensor networks are gaining popularity, this paper discusses the development and field performance of the GHAN, a greenhouse area network system to monitor, control, and access greenhouse microenvironments. GHAN, which is an upgraded system, has many new functions. It is an intelligent wireless sensor and actuator network (WSAN) system for next-generation greenhouses, which enhances the state of the art of greenhouse automation systems and helps growers by providing them valuable information not available otherwise. Apart from providing online spatial and temporal monitoring of the greenhouse microclimate, GHAN has a modified vapor pressure deficit (VPD) fuzzy controller with an adaptive-selective mechanism that provides better control of the greenhouse crop VPD with energy optimization. Using the latest soil-matrix potential sensors, the GHAN system also ascertains when, where, and how much to irrigate and spatially manages the irrigation schedule within the greenhouse grids. Further, given the need to understand the microclimate control dynamics of a greenhouse during the crop season or a specific time, a statistical assessment tool to estimate the degree of optimality and spatial variability is proposed and implemented. Methods: Apart from the development work, the system was field-tested in a commercial greenhouse situated in the region of Punjab, India, under different outside weather conditions for a long period of time. Conclusions: Day results of the greenhouse microclimate control dynamics were recorded and analyzed, and they proved the successful operation of the system in keeping the greenhouse climate optimal and uniform most of the time, with high control performance.

• Horticultural Science & Technology
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• v.32 no.3
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• pp.390-399
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• 2014

The objective of this study was to establish a processing technology for preserved leaves based on the results from the examination of the optimal period and condition for dye-absorbing treatment for Eucalyptus cinerea F. Mull. ex Benth. (silver dollar eucalyptus) being used frequently as plant material for flower design. Cut foliages of E. cinerea with uniformly matured leaves were cut into 20 cm lengths and their lower stem parts were placed in dye solution in growth chambers with different temperatures (10, 20, 30, and $40^{\circ}C$), vapor pressure deficits (VPD; 0.23, 0.70, 1.17, and 1.61 kPa), and photoperiods (0, 6, 12, 24 hours) for 3, 6, 9, and 12 days, and then dried in a room of $20^{\circ}C$ for three days. Lower temperature during preserving dye treatment reduced the changes in leaf color compared with fresh leaves and decreased ${\Delta}E$ value. Especially, high temperature increased red degree (a) and decreased yellow degree (b) due to browning. Lower VPD reduced the change in leaf color compared with fresh leaves and decreased ${\Delta}E$ value. Shorter photoperiod reduced the change in leaf color compared with fresh leaves and decreased ${\Delta}E$ value. The ${\Delta}E$ value increased with increasing absorbing duration under three environmental conditions. The flexibility of stem and leaves after dipped into preserving dye solution and dried for 3 days increased with decreasing temperature, VPD and dipping duration. Therefore, the optimal environment condition for dye treatment was 0.23-0.70 kPa VPD at $10-20^{\circ}C$ in the darkness, and the optimal and economical duration was 3 days. These conditions reduced the speed of water loss by decreasing transpiration, so yellowing or browning by rapid water loss deteriorated the quality of preserved leaves out of these ranges.

• Journal of Bio-Environment Control
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• v.22 no.1
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• pp.35-41
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• 2013

This study was conducted to provide data necessary for reducing the condensation on greenhouse covering in winter season. The variation of VPD (Vapor Pressure Deficit) and condensation flux was analyzed in experimental tomato greenhouse. VPD values in experimental plastic greenhouse were greater than 0.2 kPa of disease prevention threshold, and lower than 0.5 kPa of threshold for dehumidification. The surface temperature of inside covering was slightly higher than the average temperature of outside and above curtain, and changed according to outside temperature. The humidity above curtain was nearly 100% and good condition for condensation. The humidity below curtain was 75~90% and comparatively stable condition for growing. The condensation flux value in experimental greenhouse corresponded with result of Seginer and Kantz (1986).

• Journal of Forest and Environmental Science
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• v.21 no.1
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• pp.92-97
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• 2005

This research was carried out to elucidate the characteristics of stomatal transpiration, water efficiency, vapor pressure deficit of leaves by the light intensity Kalopanax pictus leaves. The results obtained are summarized as follows: 1. In the upper leaves of Kalopanax pictus seedlings, the stomatal transpiration rate increased continuously with increasing light intensity, but in the middle and lower leaves. it was saturated at $100{\mu}mol\;m^{-2}S^{-1}$. At the light saturated point. the stomatal transpiration rate was in the following order: the upper ($1.29mmol\;H_2O\;m^{-2}S^{-1}$) middle ($0.56mmol\;H_2O\;m^{-2}S^{-1}$) lower leaves ($0.31mmol\;H_2O\;m^{-2}S^{-1}$). 2. In the upper leaves, water use efficiency rapidly increased to $600{\mu}mol\;m^{-2}S^{-1}$, and then decreased. In the middle and lower leaves, it increased to $400{\mu}mmol\;m^{-2}S^{-1}$, and then showed a constant values. 3. The vapor pressure deficit (VPD) in according to leaf positions was linearly decreased with increasing photosynthetic photon flux density (PPFD).

• Journal of Practical Agriculture & Fisheries Research
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• v.17 no.1
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• pp.93-100
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• 2015

This study was performed to examine the high temperature adaptability with CO₂ treatment for tomato under the condition of greenhouse cultivation during summer season. The indoor condition of CO₂ concentrations were controlled as control, 500 ppm, and 1,000 ppm for the greenhouse with the maximum air temperature of 44℃. With the observation of VPD (vapor pressure deficit) and CWSI (crop water stress index) by leaf-air temperature difference according to CO₂ treatment concentration, the plants with the CO₂ concentration of 1,000 ppm performed less water stress than those with the CO₂ concentrations of control and 500 ppm. The plants without CO₂ treatment performed the severest degree of water stress.

• Journal of Bio-Environment Control
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• v.27 no.1
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• pp.46-53
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• 2018

This study was conducted to determine which greenhouse provided good environmental conditions for strawberry production, and performed better at conserving energy. Temperature, RH, VPD, $CO_2$, solar radiation, yield, and fuel consumption were the parameters analyzed. The temperatures of both greenhouses were well controlled in order to provide optimal day and night temperatures for strawberry production. The air inflated double layer greenhouse had higher RH values (more than 90% at night), which led to higher disease occurrence, in comparison to the conventional double layer greenhouse. Furthermore, the air inflated double layer greenhouse had lower VPD values than the conventional double layer greenhouse. Therefore, better RH and VPD were observed in the conventional double layer greenhouse. Higher $CO_2$ concentration was observed in the air inflated double layer greenhouse while the conventional double layer greenhouse ventilated better than the air inflated greenhouse, because of its side ventilators. Moreover, higher solar radiation in the conventional double layer greenhouse resulted in higher yield, in comparison to the air inflated double layer greenhouse. Thus, we can conclude that the conventional double layer greenhouse provided a better environment for crop growth, in comparison to the air inflated double layer greenhouse. Regarding fuel consumption, the air inflated double layer greenhouse had lower fuel consumption than the conventional double layer greenhouse. Therefore, from an energy consumption point of view, we can conclude that the air inflated double layer greenhouse performed better than the conventional double layer greenhouse.

• Journal of Bio-Environment Control
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• v.25 no.4
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• pp.351-358
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• 2016

This study investigated the effect of different relative humidity (RH) regimes on graft healing of grafted seedlings of watermelon (Citrullus vulgaris Schrad.). Two watermelon cultivars ('Speed' and 'Sambok Honey') were grafted onto the 'RS-Dongjanggun' bottle gourd rootstock (Lagenaria siceraria Stanld.) and the grafted seedlings were maintained under one of three relative humidity regimes, 95-96% [1.1-0.8 (day) or $0.8-0.6(night)\;g{\cdot}m^{-3}$ vapor pressure deficit (VPD)], 97-98% [ 0.7-0.4 (day) or $0.5-0.3(night)\;g{\cdot}m^{-3}$ (VPD)], or 99-100% [0.3-0.0 (day) or $0.2-0.0(night)\;g{\cdot}m^{-3}$ (VPD)] according to the Mollier diagram based on the air temperature of $25^{\circ}C\;day/18^{\circ}C\;night$ with 16 h photoperiod per day. Among the RH treatments, 97-98% significantly increased plant height and fresh weight of the rootstock and scion of the 'Speed' and it also enhanced the graft union connection of both cultivars after two days of grafting. However, plant height and thickness of the scion of 'Sambok Honey' was increased by the 99-100% RH treatment. Furthermore, both cultivars grown in the 95-96 and 97-98% RH treatments consisted of lower levels of endogenous $H_2O_2$ and less activities of antioxidant enzymes which illustrated the occurrence of less oxidative stress. Hence, the results of this study identified the optimal RH level for the graft healing of watermelon seedlings.