Impedance measurement is a widely used technique for monitoring ion species in various applications. In plant cultivation, the impedance system is used to measure the electrical conductivity (EC) of nutrient solutions. Recent research has shown that the quality and quantity of horticultural crops, e.g. tomato, can be optimized by controlling the salinity of nutrient solutions. However, understanding the detailed response of a plant to a nutrient solution is not possible until the fruit is fully grown or by sacrificing the stem. To overcome this issue, horticultural crop cultivation requires real-time monitoring of the EC inside the stem. Using this data, the growth model of a plant could be constructed, and the response of the plant to external environment determined. In this paper, we propose an implantable microneedle device equipped with a micro-patterned impedance measurement system for direct measurement of the EC inside the tomato stem. The fabrication process includes silicon-based steps such as microscale deposition, photolithography, and a deep etching process. Further, microscale fabrication enables all functional elements to fulfill the area budget and be very accurate with minimal plant invasion. A two-electrode geometry is used to match the measurement condition of the tomato stem. Real-time measurement of local sap condition inside the plant in which real-time data for tomato sap EC is obtained after calibration at various concentrations of standard solution demonstrate the efficacy of the proposed device.

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Abstract. The average annual and winter ambient air temperatures in Korea have risen by 0.7 and 1.4°C, respectively, during the last 30 years. Radish (Raphanus sativus), one of the most important cool season crops, may well be used as a model to study the influence of climatic change on plant growth, because it is more adversely affected by elevated temperatures than warm season crops. This study examined the influence of transplanting time, nitrogen fertilizer level, and climate parameters, including air temperature and growing degree days (GDD), on the performance of a radish cultivar 'Mansahyungtong' to estimate crop growth during the spring growing season. The radish seeds were sown from April 24 to May 22, 2012, at internals of 14 days and cultivated with 3 levels of nitrogen fertilization. The data from plants sown on April 24 and May 8, 2012 were used for the prediction of plant growth as affected by planting date and nitrogen fertilization for spring production. In our study, plant fresh weight was higher when the radish seeds were sown on 24 th of April than on 8 th and 22 nd of May. The growth model was described as a logarithmic function using GDD according to the nitrogen fertilization levels: for 0.5N, root dry matter = 84.66/(1 + exp (-(GDD -790.7)/122.3)) (r 2 = 0.92), for 1.0N, root dry matter = 100.6/(1 + exp (-(GDD -824.8)/112.8)) (r 2 = 0.92), and for 2.0N, root dry matter = 117.7/(1 + exp (-(GDD -877.7)/148.5)) (r 2 = 0.94). Although the model slightly tended to overestimate the dry mass per plant, the estimated and observed root dry matter and top dry matter data showed a reasonable good fit with 1.12 (R 2 = 0.979) and 1.05 (R 2 = 0.991), respectively. Results of this study suggest that the GDD values can be used as a good indicator in predicting the root growth of radish.Additional key words: base temperature, growing degree days (GDD), root dry matter

Air temperature and light conditions are important factors not only to produce high-quality seedlings but also to promote energy efficiency in a plant factory with artificial lighting. In this study, we conducted two experiments in order to investigate the favorable conditions of air temperature, light intensity and photoperiod for the production of cucumber scions and rootstocks in a plant factory with artificial lighting. Cucumber scions and rootstocks were cultivated in two combined treatments: the combination of three different levels of difference between the day and night temperature (DIF), 25/20, 26/18 and 27/16 °C and five different light intensity conditions of photosynthetic photon flux, 50, 100, 150, 200 and 250 μmol·m−2·s−1 was set for the first experiment, and the combination of three different photoperiod conditions, 12, 16 and 20 h·d−1 and five different light intensity conditions, 50, 100, 150, 200 and 250 μmol·m−2·s−1 was set for the second experiment. In the air temperature and light intensity treatments, the hypocotyl elongation of cucumber scions and rootstocks was affected more largely by light intensity than DIF. The highest DIF treatment (27/16 °C) affected negatively on the accumulation of dry mass. On the contrary, the smallest DIF treatment (25/20 °C) was favorable for seedling growth due to lesser stress by rapid change of air temperature between photo- and dark-period. In the photoperiod and light intensity treatments, an increased DLI (daily light integral) promoted the growth of scions and rootstocks. Under the same DLI condition, the growth of scions and rootstocks increased with increasing photoperiod and decreasing light intensity. In both of experiments, while the dry weight increased with increasing the light intensity, the light use efficiencies were reduced by increasing the light intensity. Considering the growth and quality of seedlings and energy efficiency, the optimal environment conditions were represented by 25/20 °C of air temperature, 150 μmol·m−2·s−1 of light intensity and 16 h·d−1 of photoperiod.

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