• Journal of the Korean Geosynthetics Society
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• v.12 no.2
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• pp.13-23
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• 2013

The Korean Peninsula is considered as a seasonal frozen area that is thawed in the spring and frozen in the winter. The influence of fines of the frost susceptibility of subgrade soils were established by laboratory freezing tests simulating closely the thermal conditions in the field. During the winter season, the climate is heavily influenced by the cold and dry continental high pressure. Because of siberian air mass, the temperature of January is $-6{\sim}-7^{\circ}C$ on average. This chilly weather generate the frost heaving by freezing the moisture of soil and damage potential of the geotechnical structure. In the freezing soil, the ice lenses increase the freeze portion of soil by absorbing the ground water with capillary action. However, the capillary characteristics differ from the sort of soil on the state of freezing condition. In this study, ten soil samples are prepared. The basic physical property tests were performed by following the Korean Industrial Standard and the soil specimens were classified by the Unified Soil Classification System (USCS). These classified soils are used to perform the laboratory opened systems freezing test in order to determine the frost heaving characteristics of soils such as unfrozen water content, heaving amount, and freezing depth.

• Korean Journal of Plant Resources
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• v.33 no.5
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• pp.419-427
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• 2020

Ligusticum chuanxiong Hort. is included in Umbelliferae family, it is one of the Korean traditional medicinal plants as the roots have been used to treat diseases. In this study, the growth characteristics and active compound contents of L. chuanxiong were compared among the different forest sites. As a result, root diameter and root length of L. chuanxiong was the highest in Jeongseon. Also, the fresh weight and dry weight of L. chuanxiong were the highest in Jeongseon. The total content of active compound was 23.27 mg/g the highest in Bonghwa, and 21.59 mg/g in Jeongseon, 15.87 mg/g in Hamyang was accumulated. In this study compares three forest site for cultivating of L. chuanxiong in different climate zone that the best site to product yield were Jeongseon. In this sites were located in higher altitue and lower temperature than other sites, also there were shown that lower soil moisture contents and well-drained soil. It was shown yield and active compound contents of L. chuanxiong was influenced by micro-environment conditions like as altitude, temperature, soil conditions.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1115-1123
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• 2008

When constructing projects such as road embankments, bridge approaches, dikes or buildings on soft, compressible soils, significant settlements may occur due to the consolidation of these soils under the superimposed loads. The compressibility of the soil skeleton of a soft clay is influenced by such factors as structure and fabric, stress path, temperature and loading rate. Although it is possible to determine appropriate relations and the corresponding material parameters in the laboratory, it is well known that sample disturbance due to stress release, temperature change and moisture content change can have a profound effect on the compressibility of a clay. The early research of Tezaghi and Casagrande has had a lasting influence on our interpretation of consolidation data. The 24 hour, incremental load, oedometer test has become, more or less, the standard procedure for determining the one-dimensional, stress-strain behavior of clays. An important notion relates to the interpretation of the data is the ore-consolidation pressure ${\sigma}_p$, which is located approximately at the break in the slope on the curve. From a practical point of view, this pressure is usually viewed as corresponding to the maximum past effective stress supported by the soil. Researchers have shown, however, that the value of ${\sigma}_p$ depends on the test procedure. furthermore, owing to sampling disturbance, the results of the laboratory consolidation test must be corrected to better capture the in-situ compressibility characteristics. The corrections apply, strictly speaking, to soils where the relation between strain and effective stress is time independent. An important assumption in Terzaghi's one-dimensional theory of consolidation is that the soil skeleton behaves elastically. On the other hand, Buisman recognized that creep deformations in settlement analysis can be important. this has led to extensions to Terzaghi's theory by various investigators, including the applicant and coworkers. The main object of this study is to suggestion the modified compression index value to predict settlements by back calculating the $C_c$ from different numerical models, which are giving best prediction settlements for multi layers including very thick soft clay.

• The Korean Journal of Ecology
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• v.26 no.3
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• pp.129-134
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• 2003

Amounts of CO₂ fixed by net primary production and released by soil respiration were determined on big-cone pine plantation. Net primary production, which was determined by allometric method, was converted into CO₂. CO₂ evolution in forest ecosystems are mainly through soil and root respiration. In order to separate root respiration from soil respiration, root-free sites were made in stand. Litter removal sites were prepared to estimate CO₂ evolution through litter layer. Respiration was measured at every two weeks intervals from April 2001 through April 2002, and soil temperature and soil moisture were measured at the same time. Net primary production of this big-cone pine plantation was 25.7 t·ha/sup -1/·yr/sup -1/. The amount of CO₂ fixed by this plantation was 42.5 t CO₂·ha/sup -1/·yr/sup -1/, The amount of CO₂ released by soil respiration was 5.0 t CO₂·ha/sup -1/·yr/sup -1/. The relative contribution of root respiration and litter layer respiration to total respiration was 46% and 32%, respectively. Net amount of fixed CO₂ was 37.5 t CO₂·ha/sup -1/·yr/sup -1/ in this big-cone pine plantation. From this result, this big-cone pine plantation play a carbon sink source from the atmosphere.

• Korean Journal of Weed Science
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• v.12 no.3
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• pp.200-222
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• 1992

The results of recent researches for improvement of seedling stand in direct seeded rice on the dry paddy in Korea were summarized as the following ; a variety to be cultivated should be chosen the characteristics of high percentage germination under low temperature, shorter period of shoot emergence, and better growth of the mesocotyl and shoots. Meanwhile, there was 40% increase in seedling stand at the treatment of removal of the seed awn under using the drill seeder. After seeding the rice seed covered with soil of 3cm depth was better seedling emergence and also there was the hightest seedling emergence at the 70% of moisture content of the soil. In addition, the application of the Release containing GA 10% enabled to increase the seedling stand and furthermore it was effective under deep seeding depth. The optimum seeding date should be seeded around May 10 when mean air temperature is above 12-13$^{\circ}C$ so that may establish more less 70% in seedling stand. Based on an appropriate seedling stand of 150/$m^2$, the optimum seeding rate was 5kg/10a. It was the best in seeding method using drill seeder and the most desirable recommended seeding method was the drill seeder in terms of seedling stand. In order to improve seedling stand water management was more effective in canal irrigation and in drainage at 6hr after irrigation following by the seeding process. On the other hand, for the increase of seedling stand under flooded condition a variety might have characters being better germination at low concentration of dissolved oxygen and vertically deeper growing of the crown root. Also, seedling stand was able to increase with the seed coating of $CaO_2$in the flooded soil. It was possible to be seeded on the early part of May being mean air temperature of avove 10$^{\circ}C$ and the optimum seeding rate was 5kg/10a. For an effective water management water would be flooded up to 3cm depth for 2-3 weeks after seeding. The rice plant grown under the direct seeded cultivation might be not so much strong in lodging resistance compared to that grown under the transplanting and moreover direct seeded rice cultivation under flooded condition would be more weak growth of the rice plant than that on dry paddy. Meanwhile, the lodging would be affected by the seeding rate, the soil depth after seeding. and seeding method even in the same variety. In particular, roots in the lodging pattern of direct seeded rice cultivation under flooded condition were largely distributed on the soil surface so that resulted easily in the lodging. In general, the lodging resistance would be greater as seeding rate and amount of N fertilizer application are lower and soil depth after seeding is higher. Among the introduction of different seeding method the high ridged drill seeding method on dry paddy soil resulted in the lowest in the lodging index and also it was lower in the drill seeding method than in the scattering seeding method under flooded condition. In case of more than 150 seedlings per $m^2$ there was a severe lodging due to high lodging index at the 3rd and 4th internodes. The effective lodging prevention was able to at the treatment of the Inabenfide at 45 days before heading and the Uniconazol at 15 days before heading which caused the shortage by 10-15cm in culm length. Also, fertilizer management using split application of nitrogen would be contributed the reduction of lodging at the rate of 20-30-20-20-10%(basal-5th leaf stage-7th leaf stage-panicle initiation stage-heading stage) on the dry paddy soil.

• Magazine of the Korean Society of Agricultural Engineers
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• v.32 no.3
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• pp.39-46
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• 1990

This paper was analized the thermal conductivity of polystylene (TENSAR- GEOGRID) embeding into the subbase through frost penetration depth, frost heave, change of bearing capacity, and soil moisture movement due to freezing, thawing and icing actions, and their results were as follows : 1.The change of temperature into the sub-base was much increased by the Tensar-Geogrid insertion, and the frost penetration and frost heave were decreased as the thinner of the insulation thickness but the thawing velocity of melting period was appeared to be faster in case of non-insulated. 2.The frost heave had a close relationship with the thickness of insulations which was reasonably included anti-frost effects. 3.The moisture content during the freezing period of upper layer of the insulation insertion was increased by 15 per cent but it was returned to initial state of the thawing period, and at the down layer temporarily increased by 10 per cent and returned to the original state at once. 4.The insulation was acted as a function of distribution of surcharge, and the settlement of the sub-base was about 1.5 mm under 15 tonnage of load and which was included within the allowable limits. 5.The sliding resistance due to the icing which was induced by the insulation insertion into the sub-base was appeared as more 40 per cent than noninsulation area, so that the insulations should be restricted on the place such as mountains, curved and cross area which were required the braking power under the traffics.

• The Korean Journal of Ecology
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• v.18 no.4
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• pp.471-481
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• 1995

The weed population dynamics as affected by contrasting conventional tillege (CT) and no-tillage (NT) practices with a minimum herbicide application was studied in Athens, Georgia, U.S.A. Common chickweed (Stellaria media) was the most common spring weed while johnsongrass (Sorghum halepense), sicklepod (Cassia obtusifolia), and pigweed (Amaranthus retroflexus) accounted for 89∼97％ of net production during summers of 1983 and 1984. Total weed production in summer of 1984 was 2∼5 times greater than that of 1983. Weed production was greater in NT plots than in CT plots in summer of 1983, but reverse was the case in summer of 1984. In spring, net production in NT plots was greater than that in CT plots, especially, in 1985. Species diversity was consistently higher in NT plots, but in the wet summer of 1984 the pattern was different, with higher diversity in CT plots. Weed species diversity was higher in the spring rye crop than in the summer grain sorghum crop. The larger but less diverse weed populations in summer of 1984 indicated that these populations experienced competitive exclusion. Under the favorable summer moisture conditions the three dominant species grew so vigorously and quickly as to exclude many less common species that were able to survive under the drier conditions in 1983. The three dominant species not only excluded other weeds in 1984 but also greatly reduced crop production. The perennial johnsongrass was equally successful, or even more so, in CT plots as in NT plots. Plowing did not kill johnsongrass rhizomes but tended to break them up, thus increasing the number of individual plants that appear after the plowing. It means that johnsongrass was not controlled by the plowing. In summer of 1983, a moderate amount of weedy growth was maintained with a minimum amount of gerbicide application in NT and CT plots. It is possible that a small mixed weed population would be beneficial by providing cover for predatory and parasitic arthropods, and by reducing soil temperature and moisture losses.

• The Korean Journal of Pesticide Science
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• v.4 no.4
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• pp.56-60
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• 2000

A study was performed to determine the maintenance conditions of the earthworm, Lumbricus rubellus, for the acute toxicity test. To fine out climatic and soil conditions, the earthworms were maintained in artificial soil consisting of sand, clay mineral and peat at different levels of conditions for 14 days. Lumbricus rubellus led to an increase of biomass at temperature $22{\pm}2^{\circ}C$, soil pH $7.0{\pm}1$ and moisture 40%. And four fungicides were tested for acute toxicities to Lumbricus rubellus, according to the optimum condition. The test earthworms were exposed to each pesticide with various concentration gradients. After 14 days, the number of surviving earthworms and their weight alteration during the test period was determined. The 14-day $LC_{50}$ values for the Lumbricus rubellus, of carbendazim, benomyl, thiophanate-methyl and thiabendazole were determined to be 59, 53, 64 and 36 mg/ kg soil dry weight, respectively.

• Korean Journal of Agricultural Science
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• v.2 no.2
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• pp.433-444
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• 1975

This study was conducted to investigate the strength of lime soil mixtures for varied' curing temperatures(20, 30, 40, 50, $60^{\circ}C$) and lime content (3, 6, 9, 12%) in four lime-stabilized soils(KY : Sand, MH : Sand, SS: Sandy loam. JJ : Loam). The experimental results obtained from unconfined compressive strength tests are as follows; 1. The optimum moisture content increased and maximum dry density decreased with the increase of the lime content. 2. The lime content for the maximum strength of SS and JJ soils showed at the 9 percent lime content, but KY and MH soils didn't show the tendency of increase and decrease by the lime content and curing period. The rate of decrease of the soaked unconfined compressive strength showed the lower value in accordance with lime content. 3. According to increase in curing temperatures in curing temperatures at 30, 40, 50, $60^{\circ}C$, the unconfined compressive strength of lime soil mixtures increased, the rate of increase initially increased at a rapid rate, and showed that around 120 hours were sufficient curing time to complete hardening. 4. The average maximum temperature of Korea being around $30^{\circ}C$ from July to August, thus these months are ideal construction periods to increase the strehgth of lime soil mixtures. 5. Accelerated curing times equivalent to 28-day normal curing decreased in accordance with the increase of curing temperature, and showed shorter in lime soil mixtures than soil cement. 6. Accelerated curing times versus normal curing times are formed as a linear, its slope decreased in accordance with the increase of curing temperature, it may be expressed as follows: (1). $30^{\circ}C$ : t=2.63d-1.4(r=0.99) (2). $40^{\circ}C$ : t= 1.76d-0.8(r=0.97) (3). $50^{\circ}C$ : t=1.35d-3.2(r=0.94) (4). $60^{\circ}C$ : t=0.49d+1.8(r=0.91) in which t ; Accelerated curing time d ; Normal curing time.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.54 no.4
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• pp.390-396
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• 2009

To select optimal shade material in paddy soil, growth characteristics and ginsenoside contents were investigated in new cultivar, 'Cheonpoong' of three-year-old ginseng cultured under three kinds of shade materials such as three-layered blue and one-layered black PE (polyethylene) net (TBPN), blue PE sheet (BPSS), and aluminium-coated PE sheet (APSS). The order of light transmission ratio and air temperature by shade materials were BPSS > APSS > TBSB among three shade materials. Average soil water tension in PDC and IDC was 64 mbar (absolute soil moisture, 25%) and 123 mbar (absolute soil moisture, 17%), respectively, and soil water tension in IDC was changed more distinctly than that of PDC by season and shade materials. Yield in PDC was distinctly decreased more than that in IDC because of the increase of discolored-leaf and rusted-root ratio. BPSS and TBPN among three shade materials were the most effective on the increase of yield in PDC and IDC, respectively. Ratio of rusty-colored root showed not significant difference by drainage class and shade materials. Contents of panaxatriol ginsenoside (Rg1, Re and Rf) were decreased in PDC, while it of panaxadiol ginsenoside (Rb1, Rc and Rd) were increased in IDC. Total ginsenoside contents of IDC was distinctly higher than that of PDC, and BPSS showed the highest contents among three shade materials regardless of poorly and imperfectly drainage class.