• Korean Journal of Soil Science and Fertilizer
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• v.30 no.4
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• pp.314-327
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• 1997

A 2-dimensional soil water flow model was developed to describe the migration of soil moisture in drip-irrigated root zone employing cylindrical coordinate system. Several natural phenomena were incorporated into the model such as transpiration, various types of evaporation, and ponding due to the increase in irrigation rate. Model was solved numerically by finite difference method. The model was verified in several ways leading to the conclusion that it can describe the soil moisture migration in drip-irrigated root zone fairly well. From sensitivity analysis, vertical migration of soil moisture was found to move faster than the horizontal one, which indicates the vertical location just under the dripping point are adequate for measuring points of soil moisture. The pot shape of soil moisture in irrigated zone was proved to be caused by evaporation at the soil surface. Also, it was found that the hydraulic conductivity has greatly influential to the soil moisture migration, and that the soil moisture continues to migrate vertically after irrigation stops.

• Water for future
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• v.10 no.1
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• pp.53-70
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• 1977

The analysis performed here is aimed to increase the familiarity of hydrologic process especially for the small basins which are densely gaged. Kyung An and Mu Shim river basins are selected as a representative basin according to the criteria which UNESCO has established back in 1964 and being operated under the auspice of Ministry of Construction. The data exerted from these basins is utilized for the determination of characteristics of procipitation and runoff phenomena for the small basin, which is considered as a typical Korean samall watershed. The study found that the areal distribution of preciptation did not show any significant deviation from the point rainfall. Since the area studied is less than 20 km#, the pointrainfall may be safely utilized as a representative value for the area. Also the effect of elevation on the precipitation has a minor significance in the small area where the elevation difference is less than 200m. The methodology developed by Soil Conservation Service for determination of runoff value from precipitation is applied to find the suitability of the method to Korean river basin. The soil cover complex number or runoff curve number was determined by comsidering the type of soil, soil cover, land use and other factors such as antecedent moisture content. The average values of CN for Kyung An and Mushim river basins were found to be 63.9 and 63.1 respectively under AMC II, however, values obtained from soil cover complex were less than those from total precipitation and effective precipitation about 10-30%. It may be worth to note that an attention has to be paid in application of SCS method to Korean river basin by adjusting 10-30% increase to the value obtained from soil cover complex. Finally, the design flood hydrograph was consturcted by employing unit hydrograph technique to the dimensionless mass curve. Also a stepwise multiple regression was performed to find the relationship between runoff and API, evapotranspiration rate, 5 days antecedentprecipitation and daily temperature.

• The Journal of Engineering Geology
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• v.20 no.1
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• pp.61-70
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• 2010

In case of groundwater recharge estimation using water table fluctuation method, specific yield affects the accuracy and confidence level of recharge rate. Nevertheless, there have been few studies on the method for the accurate estimation of specific yield in Korea. Specific yield estimated from the relationship between rainfall and groundwater levels is reasonable compared to the other methods. However, lots of factors such as artificial pumping, evapotranspiration by the plants, and a sudden increase in water levels by a heavy rainfall can affect the pattern of groundwater levels' fluctuation and make an over-estimated or under-estimated specific yield. This study obtained a reasonable specific yield by using a daily or 12 hourly average of rainfall and groundwater levels measured in a dry season.

• Journal of The Korean Society of Grassland and Forage Science
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• v.17 no.1
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• pp.43-50
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• 1997

The aim of the study is to describe the fate and transformation of nitrogen in grassland ecosystems. Field experiments were conducted using sandyloam soil under variabling conditions: Zen, fertilization, reduced slurry application(l20kg N $ha^{-1}\;yr^{-1}$), usual sluny application (240 kg N $ha^{-1}\;yr^{-1}$).Soil water samples were gathered with 120cm ceramic cups with initial pressure of 0.5 bar. Samples were collected twice a month and analysed for NO, colormetrically. Percolation was calculated as the difference between precipitation and potential evapotranspiration, and leaching as the product of percolation and nitrate content of the water h m the ceramic cups. The N$H_4$-N content in soil had no significant effect on slurry application, but high slurry application on grassland resulted in high N$O_3$-N content in soil. The NO, concentration in soil water was remarkably variable during the year. The average N$O_3$, concentration during experiment became the lowest(8.5 mg/e ) without slurry application and highest with 240kOa cattle sluny(25.3 mg4 ). For each of the three different amounts of cattle sluny applied (0, 120, and 240kOa), the amount of N$O_3$-N leached per year were 12, 23 and 29kg/ha respectively. On grassland under the climatic conditions of Allgau showed enormous nitrate leaching, which has a p a t potential of polluting the ground water. The high pool of mineral N in the soil are the source for N$O_3$ leaching. The leaching of N$O_3$ cannot be avoided completely, but minimized by optimizing N fertilization rate.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.2
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• pp.37-46
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• 2014

Water for crop growth were supplied by irrigation in protected cultivation and these are accumulated in the soil and utilized for crop evapotranspiration. The study for analyzing soil moisture characteristics is necessary for adequate irrigation water and soil water management in protected cultivation. Soil moisture content, irrigation water quantity and meteorological data were monitored to analyze soil moisture increment and extraction characteristics in terms of soil layers and cucumber crop growth stages. In first cropping period, the total amount of irrigation water was 5.07 mm/day, soil moisture increment was 4.82 mm/day and soil moisture extraction was 5.56 mm/day. In second cropping period, the total amount of irrigation water was 4.82 mm/day, soil moisture increment was 4.65 mm/day and soil moisture extraction was 4.73 mm/day. Soil moisture extraction rate from 0 to 75 cm is 90.3 % in first cropping period and 79.1 % in second cropping period. The majority irrigation water were consumed in root zone, however, about 15 % of soil moisture were losses by infiltration in lower soil layer. Soil moisture extraction and extraction pattern of cucumber crop calculated in this study can be utilized as a basic data for irrigation water management in protected cultivation.

• Magazine of the Korean Society of Agricultural Engineers
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• v.16 no.4
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• pp.3555-3571
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• 1974

This experiment of which aim contribute to plan irrigation system so as to increase forage crop yields, was conducted to estimate evapotranspiration amount of forage crops and to find out system of consumed water in a pasture-ground. The results obtained by this study are as follows: 1. The general weather conditions which, were closely related to the evapotrannpiration of forage crops were nearly same as those of the average year with the exception that temperature of May and June were slightly low. 2. According to the investigation of potential evapotranspirations (P.E) or forage crops and its changes during growing periods, changes of tenday P.E. were high significant according to the harvesting period. P.E of Alfalfa of which yield was the largest was the biggest. Althrough the correlations between P.E. and meteorological factors were irregular oming to three-time harvesting, correlation between ten-day evapotraspiration amount and copper plated pan evaporation or solar radiation was high positive significant. 4. Predicting formulas of P.E. were led by weather factors, and also relatione between P.E. and weather factors were showed as figure. from the these formulas, P.E. may be calculated by weather factors. 5. Predicting formulas of P.E. were led by mean temperature and copper plated pan evaporation, and by mean temperature and solar radiation. As computed values and measured values showed in figure, these formulas were high signiflent. 6. In the total consumed soil water duration of 10 days which, was non-rain period from 12th to 21th of August, Alfalfa was the largest 48.1mm, second, Orchard grass 40.1mm and Fescue 37.6mm, and Ladino clover was the smallest 37.1mm, also, order of each forage crop yield amound. was same to the abov. Order of soil moisture extraction rate of soil layer of all the for forage crops dulation of ten-day was soil layer 1 which was largest, soil layer 2, 3, and 4 Reviewing the the first five-day and the second five day, in the first five-day, order of that of all the forage crops was same to the above, but in the second five-day, that of soil layer 2 or 3 was more than the of soil layer 1.

• Journal of The Korean Society of Agricultural Engineers
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• v.65 no.3
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• pp.57-67
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• 2023

A flash drought is a rapid-onset drought that develops over a short period of time as weather and environmental factors change rapidly, unlike general droughts, due to meteorological abnormalities. Abnormally high evapotranspiration rates and rapid declines in soil moisture increase vegetation stress. In addition, crop yields may decrease due to flash droughts during crop growth and may damage agricultural and economic ecosystems. In this study, Flash Drought Intensity Index (FDII) based on soil moisture data from Gravity Recovery Climate Experiment (GRACE) was used to analyze flash drought. FDII, which is calculated using soil moisture percentile, is expressed by multiplying two factors: the rate of intensification and the drought severity. FDII was developed for domestic flash drought events from 2014 to 2018. The flash drought that occurred in 2018, Chungcheongbuk-do showed the highest FDII. FDII was higher in heat wave flash drought than in precipitation deficit flash drought. The results of this study show that FDII is reliable flash drought analysis tool and can be applied to quantitatively analyze the characteristics of flash drought in South Korea.

• Journal of Biosystems Engineering
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• v.25 no.3
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• pp.213-220
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• 2000

Grafting of fruit-bearing vegetables has been widely used to increase the resistance to soil-borne diseases, to increase the tolerance to low temperature or to soil salinity, to increase the plant vigor, and to extend the duration of economic harvest time. After grafting, it is important to control the environment around grafted seedlings for the robust joining of a scion and rootstock. Usually the shading materials and plastic films are used to keep the high relative humidity and low light intensity in greenhouse or tunnel. It is quite difficult to optimally control the environment for healing and acclimation of grafted seedlings under natural light. So the farmers or growers rely on their experience for the production of grafted seedling with high quality. If artificial light is used as a lighting source for graft-taking of grafted seedlings, the light intensity and photoperiod can be easily controlled. The purpose of this study was to develop a prototype system for the graft-taking enhancement of grafted seedlings using artificial lighting and to investigate the effect of air current speed on the distribution of air temperature and relative humidity in a graft-taking enhancement system. A prototype graft-taking system was consisted by polyurethane panels, air-conditioning unit, system controller and lighting unit. Three band fluorescent lamps (FL20SEX-D/18, Kumho Electric, Inc.) were used as a lighting source. Anemometer (Climomaster 6521, KANOMAX), T-type thermocouples and humidity sensors (CHS-UPS, TDK) were used to measure the air current speed, air temperature and relative humidity in a graft-taking system. In this system, air flow acted as a driving force for the diffusion of heat and water vapor. Air current speed, air temperature and relative humidity controlled by a programmable logic controller (UP750, Yokogawa Electric Co) and an inverter (MOSCON-G3, SAMSUNG) had an even distribution. Distribution of air temperature and relative humidity in a graft-taking enhancement system was fairly affected by air current speed. Air current speed higher than 0.1m/s was required to obtain the even distribution of environmental factors in this system. At low air current speed of 0.1m/s, the evapotranspiration rate of grafted seedlings would be suppressed and thus graft-taking would be enhanced. This system could be used to investigate the effects of air temperature, relative humidity, air current speed and light intensity on the evaportranspiration rate of grafted seedlings.

• Journal of Korean Society of Water and Wastewater
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• v.34 no.6
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• pp.503-512
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• 2020

Identifying the water circulation status is one of the indispensable processes for watershed management in an urban area. Recently, various water circulation models have been developed to simulate the water circulation, but it takes a lot of time and cost to make a water circulation model that could adapt the characteristics of the watershed. This paper aims to develop a water circulation state estimation model that could easily calculate the status of water circulation in an urban watershed by using multiple linear regression analysis. The study watershed is a watershed in Seoul that applied the impermeable area ratio in 1962 and 2000. And, It was divided into 73 watersheds in order to consider changes in water circulation status according to the urban characteristic factors. The input data of the SHER(Similar Hydrologic Element Response) model, a water circulation model, were used as data for the urban characteristic factors of each watershed. A total of seven factors were considered as urban characteristic factors. Those factors included annual precipitation, watershed area, average land-surface slope, impervious surface ratio, coefficient of saturated permeability, hydraulic gradient of groundwater surface, and length of contact line with downstream block. With significance probabilities (or p-values) of 0.05 and below, all five models showed significant results in estimating the water circulation status such as the surface runoff rate and the evapotranspiration rate. The model that was applied all seven urban characteristics factors, can calculate the most similar results such as the existing water circulation model. The water circulation estimation model developed in this study is not only useful to simply estimate the water circulation status of ungauged watersheds but can also provide data for parameter calibration and validation.

• Asian Journal of Turfgrass Science
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• v.25 no.1
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• pp.79-88
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• 2011

The purpose of this study was to obtain information on rates and salinity levels of irrigation for growth of Kentucky bluegrass by minimizing the hazard of salt accumulation in the sand based growing medium. Root zone profile consists of 20 cm sand based top soil, 20 cm of coarse sand as layer to interrupt capillary rise and 10 cm of reclaimed paddy soil as a base of the root zone profile. Topsoil was a mixture of dredged sand and peat with a ratio of 95%: 5% by volume. The columns were soaked into 5 cm depth saline water reservoir with salinity level of 3-5 $dSm^{-1}$. Salinity levels of irrigation water were 0, 2 and 3 $dSm^{-1}$. Irrigation rates were 3.8, 5.7 and 7.6 mm $day^{-1}$ which were equivalent to 70%, 100% and 130% of average ET (evapotranspiration) rate of Kentucky bluegrass, and irrigation interval was 3 days. Salt accumulation was due to irrigated water and moved up water from shallow water base. At the end of second year, the accumulation of salt in the rootzone showed ECc of3.86, 4.7 and 5.1 $dSm^{-1}$, and SAR of 19.2, 23.9 and 27.5 when the salinities were 0, 2 and 3 dS $m^{-1}$, respectively. Irrigation rates of 100% and 130% of ET rate with saline water did not decrease ECe and SAR in growing media. The growth of KEG was influenced by irrigation rate in the $1^{st}$ year, however, salinity level was more critical in the $2^{nd}$ year. Compared to non-saline water, saline water of 2 and 3 dS $m^{-1}$ resulted in decreased visual quality by 3.2% and 16.5%, by 6.4% and 39.3% in clipping weight, and by 5.5% and 5.0% in root mass, respectively.