Jong Hwa Shin

Modeling of Transpiration of Paprika (Capsicum annuum L.) Plants Based on Radiation and Leaf Area Index in Soilless Culture

Modeling of crop transpiration is important to manage the irrigation strategy in soilless culture. In this study, the transpiration of paprika plants (Capsicum annuum L.) grown in rockwool was analyzed considering the relationship between incident radiation (RAD) and leaf area index (LAI). Coefficients of the simplified Penman-Monteith formula were calibrated in order to calculate the transpiration rate of the crop (Tr). Transpiration rate per floor area was measured by weighing plants with load cells. The following model was developed: Tr = a [1 − exp(−k × LAI)] × RAD /λ + b for estimating transpiration of paprika. Determination coefficient for the linear regression between estimations and measurements of daily transpiration was 0.80 with a slope of 0.93. In validation, the model showed high agreement between estimated and measured values of daily transpiration. Radiation showed a great effect on transpiration of paprika plants. The results indicated the simplified Penman- Monteith formula could be used to predict water requirements and improve irrigation control in soilless culture. However the model coefficients require parameter adjustments for specific climate and crop conditions.

Sweet Pepper (Capsicum annuum L.) Canopy Photosynthesis Modeling Using 3D Plant Architecture and Light Ray-Tracing.

Canopy photosynthesis has typically been estimated using mathematical models that have the following assumptions: the light interception inside the canopy exponentially declines with the canopy depth, and the photosynthetic capacity is affected by light interception as a result of acclimation. However, in actual situations, light interception in the canopy is quite heterogenous depending on environmental factors such as the location, microclimate, leaf area index, and canopy architecture. It is important to apply these factors in an analysis. The objective of the current study is to estimate the canopy photosynthesis of paprika (Capsicum annuum L.) with an analysis of by simulating the intercepted irradiation of the canopy using a 3D ray-tracing and photosynthetic capacity in each layer. By inputting the structural data of an actual plant, the 3D architecture of paprika was reconstructed using graphic software (Houdini FX, FX, Canada). The light curves and A/Ci curve of each layer were measured to parameterize the Farquhar, von Caemmerer, and Berry (FvCB) model. The difference in photosynthetic capacity within the canopy was observed. With the intercepted irradiation data and photosynthetic parameters of each layer, the values of an entire plants photosynthesis rate were estimated by integrating the calculated photosynthesis rate at each layer. The estimated photosynthesis rate of an entire plant showed good agreement with the measured plant using a closed chamber for validation. From the results, this method was considered as a reliable tool to predict canopy photosynthesis using light interception, and can be extended to analyze the canopy photosynthesis in actual greenhouse conditions.

Transpiration, Growth, and Water Use Efficiency of Paprika Plants (Capsicum annuum L.) as Affected by Irrigation Frequency

Irrigation frequency is one of the major factors required for adequate irrigation control in soilless culture. In order to investigate the effect of irrigation frequency on transpiration, growth, fruit yield, and water use efficiency, the paprika plants (Capsicum annuum L.) were compared under different irrigation frequencies based on solar radiation in soilless culture systems. The plants were grown on rockwool slabs following the vertical trellis “V” technique. Irrigation started whenever cumulative solar radiation reached the set value. Two set values of 120 J·cm−2 (high irrigation frequency, HIF) and 160 J·cm−2 (low irrigation frequency, LIF) were applied from 25 days after transplanting. Irrigation amount was controlled to keep a drain ratio at 20–30% of the total supply in order to avoid the salt accumulation in the root medium. Total water amount supplied to the plants in LIF was 94% of that in HIF. Transpiration in LIF or HIF was similar to that of estimated transpiration by Penman-Monteith equation, but slightly lower or higher value was observed, respectively. Leaf area and marketable fruit yield were not affected by the irrigation treatment. The both ratios of total transpiration to marketable fruit yield and total irrigation to marketable fruit yield were a little higher in LIF than in HIF. We concluded that water use efficiency in HIF was considered to be similar to or a little higher than that in LIF, but irrigation frequency did not affect the growth and production of paprika plants in open-loop system.

Changes in electrical conductivity and moisture content of substrate and their subsequent effects on transpiration rate, water use efficiency, and plant growth in the soilless culture of paprika (Capsicum annuum L.)

The moisture content (MC) and electrical conductivity (EC) in substrates are major root-zone environmental factors that affect the transpiration rate and subsequent plant growth in soilless culture. For maintaining optimum root-zone environments, efficient real-time irrigation control is required based on the substrate EC, substrate MC, and transpiration. The objectives of this study were to clarify the relationship between substrate MC and EC and analyze the changes in substrate EC, plant growth, and water use efficiency under different moisture control regimes. Irrigation systems maintaining three regimes of substrate MC (70–85, 60–85, and 50–85%) were set as treatments, and a conventional irrigation using accumulated radiation served as a control. Subsequent changes in the substrate EC and transpiration rate were continuously measured at different substrate MCs, and the relationships between these variables were derived. The transpiration rate was most sensitive to substrate EC at general cultivation conditions of a substrate EC of 2.5 to 4.5 dS·m−1 and a substrate MC of 60 to 85%. The transpiration rate tended to decrease with increasing substrate EC and decreasing substrate MC. More water was consumed in a higher substrate MC, which was controlled within a narrow range of MC. However, substrate EC was well-controlled below 4.5 dS·m−1 in a substrate MC of 70 to 85%. The relationship between the range of substrate MC and the increase in substrate EC was obtained using equations. Although more water was supplied for the control with a substrate MC of 70 to 85%, fruit productivity tended to increase compared to the other substrate MC treatments (60–85 and 50–85%). From the results, it is hypothesized that precise control of root-zone environments can be used to increase fruit productivity and water use efficiency and to minimize plant water stress as well.

Temperature and long-day lighting strategy affect flowering time and crop characteristics in Cyclamen persicum

Long-day treatments such as day extension (DE) and night interruption (NI) lighting during short day and cold seasons can promote the growth and flower development of Cyclamen persicum and cyclic NI lighting (CL) can reduce the lighting cost as compared with continuous NI. To compare the effect of CL with continuous NI or DE under different temperatures, cyclamen (Cyclamen persicum Mill.) ‘Metis Red’ was grown until full bloom at 12, 16, or 20°C during dark period in combination with six photoperiods: 9-hour short days (08:00–17:00) with natural sun light (SD), SD + 6-hour DE (17:00–23:00), SD + 2-hour (23:00–01:00) or 4-hour (22:00–02:00) NI, and 10% [6 min on and 54 min off (6/54) for 4-hour] or 20% [6 min on and 24 min off (6/24) for 4-hour] CL. Compact fluorescent lamps used as the light source delivered about 3 mol·m−2·s−1 PPFD at the canopy level. Plants grown at 20°C during the dark period had visible buds and open flowers earlier by 7 days than those grown at 16 or 12°C. The NI and CL hastened flower bud initiation and flowering, and promoted plant growth as compared with SD at each growing temperature. Plants grown at 16 and 12°C with all NI treatments had the higher numbers of flower buds, leaves, and flowers than those grown at 20°C under SD. Using CL lighting and 16°C could reduce cyclamen production costs during winter by as much as 83% as compared to a natural light and 20°C. Therefore, CL can substitute for continuous NI or heating that enhances the flowering of cyclamen during SD and cold seasons, reducing heating and lighting costs.

Analysis of Year-round Cultivation Characteristics of Artemisia princeps in Greenhouse and Enhancement of Eupathilin Content by Environmental Stress

Mugwort (Artemisia princeps) is a medicinal plant that has a substance called euphatilin, which is effective for cell damage and gastritis recovery. The objectives of this study were to investigate the annual growth characteristics of Artemisia princeps in greenhouse and to increase the eupatiline content by environmental stresses. Growth and eupatilin content of the plants were compared after 6 weeks of seedling and subsequent 8 weeks of greenhouse cultivation. Photosynthesis of mugwort plants did not saturate even at a relatively high light intensity of 1,200μmol m·s. Growth rate of the plants reached its highest at two weeks after transplanting and began to decrease since 8 weeks after transplanting. The plants showed typical characteristics of a perennial herbaceous plant as they were sensitive to seasonal changes. In particular, the plants showed high growth and eupatilin content in spring and summer as vegetative growth periods, but flowering and wintering caused considerable decreases in growth and eupatilin content in fall and winter. Therefore, application of night interruption is essential for year-round cultivationof the plant. Two stresses and a elicitor were treated: drought stresses by stopping irrigation at 5, 6, 7, and 8 days before harvest; salt stresses with nutrient solution concentrations of 2, 4, 6, 8, and 10 dS·m by adding sodium chloride at 3 days before harvest; and foliar applications of methyl jasmonates of 12.5, 25, 50, and 100μM at 3 days before harvest. Significant increase in eupatilin content was observed at drought stresses of 7and 8-days of irrigation stop and foliar application of 25μM methyl jasmonate, while no significant increase observed at salt stresses. From the results, it was confirmed that the environmental treatments can improve the productivity and quality of Artemisia princeps as a phamaceutical raw material. Additional key words : drought stress, greenhouse, growth, methyl jasmonate, photosynthetic rate, salinity stress

Precise, Real-time Measurement of the FreshWeight of Lettuce with Growth Stage in a PlantFactory using a Nutrient Film Technique

The measurement of total fresh weight of plants provides an essential indicator of crop growth for monitoring production. To measure fresh weight without damaging the vegetation, imagebased methods have been developed, but they have limitations. In addition, the total plant fresh weight is difficult to measure directly in hydroponic cultivation systems because of the amount of nutrient solution. This study aimed to develop a real-time, precise method to measure the total fresh weight of Romaine lettuce (Lactuca sativa L. cv. Asia Heuk Romaine) with growth stage in a plant factory using a nutrient film technique. The total weight of the channel, amount of residual nutrient solution in the channel, and fresh shoot and root weights of the plants were measured every 7 days after transplanting. The initial weight of the channel during nutrient solution supply (Wi) and its weight change per second just after the nutrient solution supply stopped were also measured. When no more draining occurred, the final weight of the channel (Ws) and the amount of residual nutrient solution in the channel were measured. The time constant (τ) was calculated by considering the transient values of Wi and Ws. The relationship of Wi, Ws, τ, and fresh weight was quantitatively analyzed. After the nutrient solution supply stopped, the change in the channel weight exponentially decreased. The nutrient solution in the channel slowly drained as the root weight in the channel increased. Large differences were observed between the actual fresh weight of the plant and the predicted value because the channel included residual nutrient solution. These differences were difficult to predict with growth stage but a model with the time constant showed the highest accuracy. The real-time fresh weight could be calculated from Wi, Ws, and τ with growth stage. Received: August 25, 2015

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.