• Journal of Bio-Environment Control
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• v.20 no.2
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• pp.93-100
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• 2011

Maintenance of adequate soil water potential during the period of crop growth is necessary to support optimum plant growth and yields. A better understanding of soil water movement within and below the rooting zone can facilitate optimal irrigation scheduling aimed at minimizing the adverse effects of water stress on crop growth and development and the leaching of water below the root zone which can have adverse environmental effects. The objective of this study was to evaluate the feasibility of using a portable irrigation controller with an Watermark sensor for the cultivation of drip-irrigated vegetable crops in a greenhouse. The control capability of the irrigation controller for a soil water potential of -20 kPa was evaluated under summer conditions by cultivating 45-day-old tomato plants grown in three differently textured soils (sandy loam, loam, and loamy sands). Water contents through each soil profile were continuously monitored using three Sentek probes, each consisting of three capacitance sensors at 10, 20, and 30 cm depths. Even though a repeatable cycling of soil water potential occurred for the potential treatment, the lower limit of the Watermark (about 0 kPa) obtained in this study presented a limitation of using the Watermark sensor for optimal irrigation of tomato plants where -20 kPa was used as a point for triggering irrigations. This problem might be related to the slow response time and inadequate soil-sensor interface of the Watermark sensor as compared to a porous and ceramic cup-based tensiometer with a sensitive pressure transducer. In addition, the irrigation time of 50 to 60 min at each of the irrigation operation gave a rapid drop of the potential to zero, resulting in over irrigation of tomatoes. There were differences in water content among the three different soil types under the variable rate irrigation, showing a range of water contents of 16 to 24%, 17 to 28%, and 24 to 32% for loamy sand, sandy loam, and loam soils, respectively. The greatest rate increase in water content was observed in the top of 10 cm depth of sandy loam soil within almost 60 min from the start of irrigation.

• Korean Journal of Soil Science and Fertilizer
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• v.39 no.5
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• pp.303-306
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• 2006

This experiment was investigated the influence of water stress in growth and yields of safflower. The water stress treatment was early growth stage(Mar. 20~Apr. 18), middle growth stage(Apr. 29~May 28) and last growth stage(Jun. 8~Jul. 7) for 30 days, respectively. Stem length of plant was 127 cm in normal irrigation(control) state and that of growth middle stage at drought state was 96 cm, to be shorted more 31 cm than that of normal irrigation state, also other growth rate of plant was decreased, relatively. Number of effective flower bud per $m^2$ was 224 ea in normal irrigation state, 114 ea in growth middle stage at drought state. Yield of seed at drought state decreased 37% and 13% in growth middle stage(222 kg/10a) and last stage(307 kg/10a) than 353 kg/10a in normal irrigation state. According to the result, it could be estimated that optimum irrigation time(0.05 MPa) was 23days after non-rainfall at early growth stage(from sowing seed time to 30 days after sowing seed), 10 days in middle growth stage(41-70 days after sowing seed) and 9 days in last growth stage(81-110 days after sowing seed), to prevent the damage of drought.

• Korean Journal of Agricultural Science
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• v.15 no.1
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• pp.36-46
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• 1988

Twelve soybean cultivars were cultivated in the 1/2,000a. Wagner pots with irrigation and without irrigation for 30 days after flowering, and the differences of plant growth and bean yield among cultivars were compared. And to investigate the varietal differences in the rate of photosynthesis under different relative humidity, 6soybean cultivars were cultivated in 1/2,000a. Wagner pot and the rate of photosynthesis of each soybean cultivar at flowering time was measured under the relative humidity of 80, 70, 60, 50 and 40%. The results obtained are summarized as follows; 1. The days to maturity of the soybean cultivars were shortened by non-irrigation treatment. The response of the maturing dates to non-irrigation was significantly different among the soybean cultivars. The days for maturing of Paldal, Danyeob and Eundaedu were delayed 2 days but those of Jangbaek and Tamahomare were delayed about 7 to 8 days under non-irrigation treatment. 2. The stem length, stem diameter, number of nodes of the mainstem, number of branches and number of branch nodes of all soybean cultivars were decreased by non-irrigation treatment. The number of branches and the number of branch nodes were especially severely influenced by non-irrigation treatment. 3. The number of pods per plant and the number of perfect pods was significantly reduced by non-irrigation treatment but the number of imperfect pods was increased. The non-irrigation treatment reduced the number of pods per plant by 58.0% and the ratio of the number of the perfect pods per plant by 46.6% relative to the ordinary cultivation with irrigation. 4. The grain yield of all cultivars was significantly reduced by the non-irrigation treatment, and average grain yield of soybean cultivars cultivated under non-irrigation treatment was 35.9% of that of soybean cultivars cultivated with irrigation. The influence of non-irrigation treatment was lowest in Paldal and significantly high in Tamahomare and Jangbaek. 5. The rate of photosynthesis of soybean leaves was significantly different among cultivars and was also influenced by relative humidity. Ratio of the photosynthetic amount of soybean leaves at 40% RH to the maximum photosynthesis at optimal humidity was 97.2% in Paldal, 96.4% in Danyeob and 88.8% in Baekun. 6. At 40% relative air humidity, highly significant correlations were found among the photosynthesis rate, the amount of transpiration and the respiration rate.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.473-473
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• 2011

Group method of data handling neural networks model (GMDH-NNM) is used to estimate daily reference evapotranspiration (ETo) using limited climatic variables such as max temperature ($T_{max}$), min temperature ($T_{min}$), mean wind speed ($W_{mean}$), mean relative humidity ($RH_{mean}$) and sunshine duration (SD). And, for the performances of GMDH-NNM, it consists of training and test performances, respectively. The training and test performances are carried out using daily time series data, respectively. From this research, we evaluate the impact of GMDH-NNM for the modeling of the nonlinear time series data. We should, thus, construct the credible data of the daily ETo data using GMDH-NNM, and can suggest the methodology for the irrigation and drainage networks system. Furthermore, this research represents that the strong nonlinear relationship such as ETo modeling can be generalized using GMDH-NNM.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.44 no.3
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• pp.282-287
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• 1999

The object of this study was to determine the difference of the time course changes of transpiration, diffusion resistance and photosynthetic rate of rice at several different growth stages subjected to soil moisture stress (SMS) and recovery by irrigation. A japonica rice cultivar 'Dongjinbyeo', was grown under flooded condition in a plastic container filled with silty loam soil. At 5 main growth stages, the container was treated by SMS until initial wilting point (IWP) and then reirrigated. The duration of SMS until IWP were the longest, 13 days for tillering stage, and the shortest, 7 days for panicle initiation and meiosis stage. The transpiration rate rapidly decreased during SMS and the transpiration rate at IWP of the stressed plant showed 10∼20% compared with control, and the transpiration rate of stressed plant at most growth stages also recovered rapidly after irrigation and then reached 100% of control within a week. The shoot photosynthetic rate in all growth stages rapidly decreased by SMS, and the rates at IWP of stressed plants were de-creased nearly to 0%, beside the treatment at tillering stage. The recovery degree of photosynthetic rate by irrigation ranged from 20 to 90%, showed higher at early growth stages of SMS treatment than that of later stages. At all growth stages the leaf diffusion resistance of stressed plants was over 3 times that of the control resulting from a rapid increase at 3 to 5 days after draining for SMS, and showed quick recovery by irrigation within 3 days after drainage. The above physiological parameters changed in close relation with the decrease of the soil matric potential after SMS. These results indicate that at all main growth stages of rice plants the transpiration and photosynthesis reduction by stomatal closure reponded sensitively to the first stage of SMS closely related with decrease of soil water potential, while those recovery pattern and recovered degree by irrigation are little different by growth stage of rice.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.2
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• pp.25-36
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• 2018

Drip irrigation system is a low energy cost method which can efficiently save and supply water by dropping water slowly on the crop's root zone during crop growth. In the drip irrigation system, disk filters take an important role to physically remove impurity (inorganic and suspended organic) particles present in agricultural water which can cause emitter clogging. For the purpose, both top-and-bottom surfaces of the disk are grooved in micron size flowing from outside to inside. However, many congested flow paths in disk filter media incur higher head loss of inflow water resulting in relatively decreasing velocities depending on operation time than sand and mesh filters. Therefore, it is important to optimize the structure of disk filter in micro irrigation system. The head loss of disk filter media takes also charge of more than 60 % of total head loss in whole disk filter. This study is to find the appropriate cross-sectional shape of the disk groove to minimize the head loss by executing the experiment. The experiment used three disk filters that have similar filter body but have a half-elliptic and two kinds of triangular cross sections. The experimental results showed that the disk filter with half-elliptic cross sections of disk grooves have less head loss than the disk filter with regular triangular one.

• Journal of Korean Society on Water Environment
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• v.25 no.1
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• pp.69-75
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• 2009

Water stress has become a major concern in agriculture. Korea suffers from limited agricultural water supply, and wastewater reuse has been recommended as an alternative solution. A study was performed to examine the effects of microorganism concentration in the ponded-water of a paddy rice field with reclaimed-water irrigation for evaluating the microbial risk to farmers and neighborhood children. Most epidemiological studies were performed based on an upland field, and they may not directly applicable to paddy fields. Beta-Poisson model was used to estimate the microbial risk of pathogen ingestion. Their risk value increased significantly high level after irrigation and precipitation. It implies that agricultural activities such as plowing, and fertilizing, and precipitation need be practiced a few days after irrigation considering health risks. The results about field application of the microbial risk assessment using E. coli showed difference according to monitoring time and treatment plot. Result of the microbial risk assessment showed that risk values of ground-water and reclaimed secondary wastewater irrigation were lower than directly use of wastewater treatment plants' effluent. This paper should be viewed as a first step in the application of quantitative microbial risk assessment of E. coli to wastewater reuse in a paddy rice farming.

• Journal of Biosystems Engineering
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• v.39 no.1
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• pp.39-46
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• 2014

Purpose: Monitoring and control of environmental condition is highly important for optimum control of the conditions, especially in greenhouses and plant factories, and the condition is not uniform within the facility. Objectives of the study were to investigate variability in soil water content and to provide information useful for better irrigation control. Methods: Experiments were conducted in a strawberry-growing greenhouse (greenhouse 1) and a cherry tomato-growing greenhouse (greenhouse 2) in winter. Soil water content, electrical conductivity (EC), and temperature were measured over the entire area, at different distances from an irrigation pump, and on ridge and furrow areas. Results: When measured over the entire greenhouse area, soil water content decreased and temperature and electrical conductivity increased over time from morning to afternoon after irrigation. Water content decreased by distance from the irrigation pump up to 70 m and increased after that, and temperature showed an inverse pattern. Soil water contents on the ridge were lower than those on the furrow, and the differences were 10.2~18.4%, indicating considerable variability. The lowest EC were observed on the furrow and highest values were observed on the ridge. Soil water contents were less and temperature levels were greater at the window side than in the center locations. Conclusions: Selection of number and location of soil water content sensor would be the first step for better water content monitoring and irrigation control. Results of the study would provide basic data useful for optimum sensor location and control for underground greenhouse environment.

• Journal of People, Plants, and Environment
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• v.23 no.5
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• pp.507-519
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• 2020

Background and objective: This study analyzed the growth characteristics, in relation to the soil moisture content, of trees planted in an environment with limited soil depth to provide the baseline data for effective irrigation management. Methods: The experimental treatment was divided into soil moisture contents (SMC) of 20%, 15%, 10%, 5%, and 1%, and the respective watering times were set accordingly. As for plant materials, Nandina domestica, Euonymus alatus, Thuja occidentalis, Hibiscus syriacus, Pinus densiflora, and Pyracantha angustifolia, were chosen for this study, because they are highly likely to be used in urban street environments. Results: The minimum irrigation point suitable for each species was determined by considering various aspects of visual quality and water efficiency in terms of plant growth, including characteristics such as height, root diameter, rootlet development, and weight. Our results indicate that N. domestica should be watered so that the moisture content of the soil is of at least 5%, based on the balance between the stem and roots, as well as on visual quality. E. alatus and P. angustifolia are suitable for watering that results in at least 10% SMC, considering the height, root growth, weight, and visual quality of plants. As for T. occidentalis, it showcases moderate growth with a soil moisture content of at least 5%. Finally, the minimum irrigation time required to obtain 15% SMC is appropriate, in terms of plant growth, fresh weight, and visual quality, for H. syriacus and P. densiflora. Conclusion: This study suggested a basic irrigation guideline for container gardens where trees planted in environments with limited soil depth can be managed so that they are visually appropriate and in good condition of growth.

• KCID journal
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• v.2 no.1
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• pp.101-107
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• 1995