• Journal of Korea Water Resources Association
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• v.46 no.6
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• pp.569-583
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• 2013

This study is to evaluate the future climate change impact on hydrological components in the Seolmacheon ($8.54km^2$) mixed forest catchment located in the northwest of South Korea using SWAT (Soil and Water Assessment Tool) model. To reduce the uncertainty, the model was spatially calibrated (2007~2008) and validated (2009~2010) using daily observed streamflow, evapotranspiration, and soil moisture data. Hydrological predicted values matched well with the observed values by showing coefficient of determination ($R^2$) from 0.74 to 0.91 for streamflow, from 0.56 to 0.71 for evapotranspiration, and from 0.45 to 0.71 for soil moisture. The HadGEM3-RA future weather data of Representative Concentration pathway (RCP) 4.5 and 8.5 scenarios of the IPCC (Intergovernmental Panel on Climate Change) AR5 (Assessment Report 5) were adopted for future assessment after bias correction of ground measured data. The future changes in annual temperature and precipitation showed an upward tendency from $0.9^{\circ}C$ to $4.2^{\circ}C$ and from 7.9% to 20.4% respectively. The future streamflow showed an increase from 0.6% to 15.7%, but runoff ratio showed a decrease from 3.8% to 5.4%. The future predicted evapotranspiration about precipitation increased from 4.1% to 6.8%, and the future soil moisture decreased from 4.3% to 5.5%.

• Korean Journal of Soil Science and Fertilizer
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• v.25 no.1
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• pp.8-15
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• 1992

An experiment was conducted to find out effect of soil water condition on shoot and root growth and P, K uptake by soybean plants. Soybean plants were grown under different soil water table levels, 20cm, 40cm and 60cm below the soil surface using minirhizotron with 20cm in diameter, and well irrigated and water stressed conditions using 1/2000a Waganer pots. Three soybean plants, Paldal culfivar, were grown and sampled at the early growing period, 37 days after planting, and at the harvesing period, 115 days after planting. Shoot and root growth were restricted by water stresed condition and by excessive soil water condition with the 20cm water table. Little difference in shoot and root growth were found between well irrigated condition and 40cm or 60cm water table conditions. The P and K contents in shoot under water stressed condition were higher than well irrigated condition at the early growing period but reversed at later harvesting period. The dry weight and length of roots were more severely restricted by water stress than those of shoots. Root morphological difference was found by anatomical observation. Normal cortex was developed under the well irrigated condition, while abnormal cortex with aerenchyma formed by lysis under excessive water conditions of 20 or 40cm water talbes. Aerenchyma was formed at outer skirt of pericycle. Role of formation of aerenchyma of soybean roots might be an adaptation to excessive soil water condition and possibly related to survival of soybean roots growing under near flooding condition on dikes of paddy lands.

• Korean Journal of Soil Science and Fertilizer
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• v.16 no.2
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• pp.168-178
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• 1983

Influence of several dehydration treatments on original structure and water behavior in the process of drying were investigated employing three hawaiian volcanic ash soils and four synthetic minerals. These three soils were developed under different rainfall condition and contained three different amount of amorphous materials in them. Measurement of water losses by oven drying at $105^{\circ}C$, $P_2O_5$ drying, freeze drying, and critical point drying revealed that more water losses were noted by oven drying than by three other drying techniques and the differences of water losses between oven and $P_2O_5$-drying were closely related to amoun: of amorphous materials in them, showing the order of Kaiwiki > Hilo > Kawaihae. This indicates that dehydration of amorphous materials by elevated temperature ($105^{\circ}C$) excluded water beyond that in the adsorbed (hygroscopic) state. The effect of dehydration treatments on initial structure was visualized by scanning electron microscopy. The micrographs showed that oven-and $P_2O_5$-dried samples formed into large mass of sub-angular blocky, dense, and closed crumbs, while the freeze dried and critical point dried samples resulted in less shrinkage, and small, fluffy and open spongy structure. However, critical point drying technique produced bulkier, softer, and greater open structure samples than even freeze drying. Additional Index Words: original structure, synthetic minerals, critical point drying, $P_2O_5$ drying. 1. This is a part of author's Ph.D. dissertation submitted to the University of Hawaii, Honolulu, Hawaii 96822 in 1979. 2. Professor of Agricultural Chemistry, Korea University.

• Korean Journal of Soil Science and Fertilizer
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• v.28 no.3
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• pp.227-232
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• 1995

The model equations including scaling factors to estimate the soil water characteristics curve(SWCC) without direct measurement of soil water tension were developed. Scaling were applied to a data set of soil water content, soil water tension, particle size distribution, and OM contents of the 134 soil samples with the 10 soil textural classes. The capability of the model equations was tested on another 205 soil samples. The parameter, ${\theta}^*$, of soil water contents was used by scale transformation as follows : ${\theta}^*=[{\theta}i-{\theta}(1.5MPa)]$/$[{\theta}(10KPa)-{\theta}(1.5MPa)]$ Using ${\theta}^*$ a model equation to estimate SWCC, which was applicable to all textural classes, was developed as follows: $H(0.1MPa)=0.13{\cdot}({\theta}^*)^{-2.04}$. Other model equations to estimate the water content at the soil water tension of 10KPa [${\theta}(10KPa)$] and 1.5MPa [${\theta}(1.5MPa)$], which are required to ${\theta}^*$ were developed by using scale factors of sand(S) and silt(Si) content and organic matter content(OM) as foilows : ${\theta}(10KPa)=26.80-3.99ln[S]+2.36{\sqrt{[Si]}}+2.88[OM]$ ($R=0.81^{**}$) ${\theta}(1.5KPa)=15.75-2.86ln[S]+0.55{\sqrt{[Si]}}+0.70[OM]$ ($R=0.76^{**}$) The measured and estimated values of ${\theta}(1/30MPa)$ on the 205 soil samples were highly correlated on 1 : 1 corresponding line with $R=0.85^{**}$.

• Journal of Korean Society of Forest Science
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• v.75 no.1
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• pp.51-54
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• 1986

The good growth of Populus alba ${\times}$ P. glandulosa is shown at the foothill of the mountain where good soil moisture is available, but its growth is poor at the upper part of the mountain where soil moisture is limitted. Stomatal frequency, stomatal size and transpiration rates that affect soil moisture demand were determined in order to know how this character is inherited from its parents. Number of stomata per $mm^2$, length and width of stomata from the abaxial leaf and transpiration rate ($g/cm^2$) per day in P. alba ${\times}$ P. glandulosa showed intermediate values between those of their parents, while P. alba showed the highest values and P. davidiana the lowest values. The values of stomatal frequency of P. alba ${\times}$ P. glandulosa were close to the expected mean values of parents in the $x^2$ test, and in the regression analysis the transpiration rates for the hybrid and its midparent had strong relationship with 0.97 of regression coefficient. The fact that these intermediate characteristics were observed in the hybrid suggests incomplete dominance in the hybrid. It is concluded that soil moisture demand in P. alba ${\times}$ P. glandulosa and its parents is closed related to stomatal frequency, stomatal size and transpiration rate.

• Korean Journal of Soil Science and Fertilizer
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• v.22 no.1
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• pp.1-5
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• 1989

This study was carried out by using laboratory data to calculate Soil Moisture Control Section (SMCS) for medium textured topo-sequential soils derived from porphyry in Milyang area. The soils studied were characterized by loam to silty clay loam, and the moisture content at -1/3 bar in the solum ranged around 21.06% to 32.42%. The moisture contents per centimeter of soil layer within a solum calculated at field capacity (FC) ranged from 0.11cm to 0.19cm. The upper boundaries of SMCS of the soils calculated on the basis of FC as the water content at -1/3 bar, ranged from 16.2cm to 21.2cm and the lower boundaries from 44.4cm to 63.8cm, and the depth of SMCS were from 27.7cm to 42.6cm in the soil profiles. The Bongsan soil on the summit had shallower in the boundaries and narrower in the depth of SMCS than the soils on side-slopes or on valley.

• Korean Journal of Soil Science and Fertilizer
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• v.43 no.6
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• pp.880-885
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• 2010

Importance of climate change and its impact on agriculture and environment has increased with a rise of greenhouse gases (GHGs) concentration in Earth's atmosphere. Nitrous oxide ($N_2O$) emission in upland fields were assessed in terms of emissions and their control at the experimental plots of National Academy of Agricultural Science (NAAS), Rural Development Administration (RDA) located in Suwon city. It was evaluated $N_2O$ emissions at different soil water content, soil temperature, and mineral N conditions in a upland cultivating red pepper and soy bean. The results were as follows: 1) There were significant correlation between amount of $N_2O$ emissions and soil temperature, soil water content and mineral N conditions showed $0.528^{**}$, $0.790^{***}$ and $0.937^{***}$ in red pepper field and $0.658^{***}$, $0.710^{***}$ and $0.865^{***}$ in soybean field, respectively. 2) From the contribution rate analysis as to contribution factors for $N_2O$ emission, it appeared that contribution rate was in the order of mineral N (71.9%), soil moisture content (23.6%), and soil temperature (4.5%) in pepper field and mineral N (65.5%), soil moisture contents (19.2%), and soil temperature (15.2%) in soybean field.

• Journal of Biosystems Engineering
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• v.8 no.1
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• pp.9-16
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• 1983

This study was conducted to find out the effects of such parameters as specific draft resistance, slip rate, and fuel consumption rate on plowing performance in paddy fields spread with chopped rice straw. The plowing operation by an 8 P.S. power tiller was carried out in 6 different fields having the soil moisture content of 27~36 percent in dry basis in clay loam soil texture, and applying chopped rice straw of 10, 20, 30 and 60cm in length in the spring of 1982. The effects of soil hardness and moisture content on the plowing performance were also investigated. The results of the study are summarized as follows; 1. The minimum draft during the plowing operation was 110kg in the 30cm rice straw plot having the soil moisture content of 32 percent in dry basis. 2. The multiple regression equation of the specific draft(D) as a function of soil moisture content(M) and cutting length of rice straw(L) was obtained as follows. $D=14.1978-0.8565M+0.0661LxM-2.9685L+0.0133M^2+1.093L^2$ 3. In the 30cm rice straw plot with the soil moisture content of 32 percent in dry basis, the minimum specific draft resistance and the rate of slip were 0.35kg per $cm^2$ and 16 percent respectively. The specific draft resistance varied sensitively in accordance with the soil moisture content, and the slip rate of power tiller was dependent upon the cutting length of rice straw rather than the soil moisture content. 4. The highest plowing performance was 5.3 ares per hour at the soil moisture content of 35 percent and soil hardness of 10kg per $cm^2$. The relationship between the plowing performance and the soil moisture content was obtained by a quadratic equation. 5. The minimum fuel consumption rate in the plowing operation was recorded 6.5 liters per 10 ares in 30cm chopped rice straw plot with the soil moisture content of 32 percent in dry basis.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.30 no.1
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• pp.33-38
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• 1985

This experiment was carried out to study in stomatal behaviour of wheat (Chokwang) upon the different soil water potentials, lodging and two different nitrogen treatment. Stomatal aperture was measured at flowering stage under diurnal course with two hour intervals, Stomatal apertures were differently changed according to soil water potentials and leaf position on the stem, showing the rapid closure of stomata at low soil water potential and the narrow opening at low leaf position of stem. Wider stomatal opening appeared at the plot of optimal nitrogen application than that of low nitrogen. It was greatly decreased in opening of stomata at plants lodged, appearing that plant investigated of six days after lodging showed less than 50% than that normal plants, which indicated peculiar decrease of low leaf position of stem at afternoon of diurnal course.

• Journal of Korea Water Resources Association
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• v.37 no.2
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• pp.133-144
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• 2004

A Tank Model composed of 4 tanks with soil moisture structure was applied to Daecheong Dam and Soyanggang Dam watersheds. Calibration and verification were repeated 332 and 472 times for each watershed using SCE-UA global optimization method for different calibration periods and objective functions. Four different methods of evapotranspiration calculation were used and evaluated. They are pan evaporation, 1963 Penman, FAO-24 Penman-Monteith, and FAO-56 Penman-Monteith methods. Tank model with soil moisture structure showed better results than the standard tank model for daily rainfall-runoff simulation. Two types of objective function for model calibration were found. Proper calibration period are 3 years, in which dry year and flood year are included. If a calibrationperiod has an inadequate runoff rate, the period should be more than 8 years. The four methods of eyapotranspiraton computation showed similar results, but 1963 Penman method was slightly inferior to the other methods.