Young Yeol Cho

Uptake of nutrients and water by paprika (Capsicum annuum L.) as affected by renewal period of recycled nutrient solution in closed soilless culture

One of the problems in closed soilless cultures is to find a solution in order to reduce ion imbalance in recycled nutrient solutions when the drained nutrient solution is re-used. To reduce ion imbalance in recycled nutrient solutions, determination of renewal period is required, since uptake of individual ion by plants changes throughout the growing period. The aims of this study are to determine the appropriate renewal period to reduce ion imbalance in the recycled nutrient solution and to investigate the uptake of nutrients and water by the paprika plant and to measure fruit yield and mineral contents in plant as influenced by renewal period of recycled nutrient solution in a closed soilless culture. Paprika plants were grown in rockwool slabs with either 4-, 8-, or 12-week renewal period in the closed as compared to the open hydroponic system (control). The electrical conductivity (EC), pH, and volume of the nutrient solutions were measured every three days. The nutrient solution in the reservoir tank was constantly maintained at EC 2.5 dS·m−1 and pH 5.5–6.5. As results, the uptake of K+ was significantly influenced by the renewal period. Changes of cation and anion ratio in the recycled nutrient solution could be reduced by discharging every 4 weeks. The significantly lowest fruit yield was observed in a closed hydroponic system using a 12-week renewal period. Regarding the ion balance in the recycled nutrient solution, renewing every 4 weeks was found to be the most effective in this study. However, considering the yield along with nutrients and water uptake, a 8-week interval could also be used.

Growth characteristics of sowthistle (Ixeris dentata Nakai) under different levels of light intensity, electrical conductivity of nutrient solution, and planting density in a plant factory

The objective of this study was to investigate the growth characteristics of sowthistle (Ixeris dentata Nakai) under different levels of light intensity (photosynthetic photon flux, PPF), electrical conductivity (EC) of nutrient solution, and planting density for efficient production in a closed-type plant factory system. Growth and yield of the plants were analyzed at EC 1.5 and 2.0 dS·m−1 with PPF 100 and 200 μmol·m−2·s−1. Further, growth and yield were measured under four different planting densities: a 15-cm between-row distance with within-row distances of 10, 15, 20, and 25 cm. Shoot dry weight and leaf photosynthetic rate all increased with increasing EC and light intensity. Shoot fresh and dry weights, chlorophyll content, and leaf photosynthetic rate were maximal at EC 2.0 dS·m−1 with PPF 200 μmol·m−2·s−1. For all planting densities, number of leaves and leaf width were not significantly different. Shoot fresh and dry weights per plant were not significantly different, however, shoot fresh and dry weights per area decreased with increasing plating densities. A linear relationship was observed between the number of leaves and days after transplantation. Based on the results, we suggest a nutrient solution of EC 2.0 dS·m−1, PPF 200 μmol·m−2 · s−1, and planting density of 15×10 cm for maximal growth and yield of sowthistle in a closed-type plant factory.

Estimation of growth and yield for single-stemmed rose ‘Vital’ in a single stem system

In ornamental crop production, growth models as a function of environmental factors can be used as a valuable tool for predicting the timing of a phenological event for the average of a population, for the optimization of environmental conditions inside a growing system, and for making cultural decisions for increasing crop production. The feasibility of an expolinear growth equation was evaluated by predicting the crop growth of single-stemmed rose ‘Vital’ in a single stem system using recirculating nutrient solution. The objectives of this study were to determine a suitable environmental variable and growth parameters, i.e. maximum crop growth rate (Cm), maximum relative growth rate (Rm), and the lost time (tb) for expolinear growth equation using biomass data obtained from 4 experiments with different seasons [cut on Oct. and Nov. in 2004 (Expts. 1 and 2), and Apr. and Jun. in 2005 (Expts. 3 and 4)] and then to predict the crop growth based on an empirical model as a function of the environmental variable and plant density (plants/m2) using estimated parameters of the expolinear growth equation. The growth parameters were estimated by fitting the expolinear growth equation as a function of time, thermal units (TUs, °C·d), or daily incident photosynthetically active radiation (PAR, MJ·m−2·d−1) to observed the biomass per unit area (m2) using a nonlinear regression procedure with Gauss-Newton method. The use of TUs as a variable of expolinear growth equation improved the accuracy of the model and gave a better estimate of growth parameters as compared with those of time or incident PAR integral. Although the fitted expolinear growth equation effectively described the measured fresh and dry mass per unit area, we concluded that TUs was an appropriate variable of expolinear growth equation for single-stemmed rose ‘Vital’ considering some advantage, such as a cheap and easy way for growers to measure the microclimate inside a greenhouse for cut-flower rose production. This study also investigated the effects of TUs and plant density (67, 89, and 107plants/m2) on the growth of single-stemmed rose ‘Vital’ in a single stem system by adjusting the expolinear equation. The growth parameters, Cm, Rm, and tb were estimated by fitting the expolinear growth equation to the measured dry mass measurements obtained from 3 experiments (Expts. 1, 2, and 3) at three different plant densities. Parameters Cm and tb showed a curvilinear relationship with plant density over three experiments and were fitted to the quadratic function. The Rm was substituted with the mean value of the estimated values at each plant density, 0.0082, because there were no significant differences in Rm values among plant density treatments. The estimation of dry mass per unit area by the expolinear growth equation as inputs of TUs and plant density agreed well with the validation data, but the model tended to overestimate dry mass per unit area. The measured dry mass showed a linear relationship with fresh mass regardless of plant densities. The shoot fresh mass per m2 was estimated by an empirical relationship between shoot fresh mass and dry mass using the estimated shoot dry mass. The estimated and measured shoot dry mass and fresh mass showed a reasonably good fit with 1.142 (R2 = 0.988) and 1.168 (R2 = 0.976), respectively.

Application of quadratic models for establishment of adequate temperature ranges in germination of various hot pepper (Capsicum annuum L.) cultivars

Appropriate temperature control of seeds leads to uniform germination and efficient management of the production of seedling grafts, which are required for successful cultural practices. In this study, the base, optimum, and maximum temperatures of four hot pepper cultivars were used as scions as well as four hot pepper cultivars used as rootstocks were estimated using a quadratic model. Seeds of the cultivars were germinated in growth chambers at constant temperatures of 20°C, 25°C, 30°C, and 35°C. Cumulative germination was described using a logistic function. The base, optimum, and maximum temperatures were estimated by regressing the inverse of the time to 50% germination (1/GR50) against temperature. Although germination rates varied according to cultivar and temperature, the highest germination rates were observed at temperatures of 25°C and 30°C. Wongang 1 was the most tolerant at low temperature, whereas Koregon PR-380 and Wongang 1 were the most tolerant at high temperature. Further, we suggest appropriate combinations of scion and rootstock cultivars based on our cardinal temperature results for the eight hot pepper cultivars.

Development of an expolinear growth model for pak-choi using the radiation integral and planting density

The objectives of this study were to develop a growth model of pak-choi using an expolinear function and to estimate the effect of the radiation integral and planting density on the crop growth rate. The growth and yield of hydroponically grown pak-choi (Brassica campestris ssp. chinensis) were investigated at four different planting densities (27, 33, 44, and 67 plants/m2). The shoot dry and fresh weights per m2 increased with increasing planting density and could be expressed as expolinear functions based on the daily photosynthetically active radiation (PAR). A linear relationship was observed between the shoot dry weight and fresh weight, regardless of the planting density. The maximum crop growth rate and light use efficiency (LUE) increased with increasing planting density, but the lost daily PAR integral decreased. The maximum relative growth rate was not significantly different among the planting densities. Using the relative growth rate per the daily PAR integral and LUE, an expolinear growth model of pak-choi was developed. The measured and estimated shoot dry weights exhibited strong agreement with Y = 1.010·X (R2 = 0.982***) using the PAR and leaf area index as inputs. The expolinear growth model was determined to be useful for quantifying the growth and yield of pak-choi in controlled environments.