• 한국농공학회지
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• 제40권5호
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• pp.37-42
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• 1998

This study was performed to evaluate the characteristics of volume change is unsaturated clayed soil. The medium-plastic clay was selected and compacted by 50% of Proctor standard compaction energy at 6% higher moisture content than its OMC. A series of isotropic compression tests and triaxial shear tests were performed. The results of the study are summarized as follows. At each matric suction, when the matric suction was increased, the yield stress was increased and slope of volume change was decreased. The more net mean stress was, the less the quantity of volume change was. In shear test, the volumetric strain was much rapidly changed in large matric than in low matric suctions. But the effect of matric suction to volume change disappeared under high net mean stress. At lower deviator stress the more matric suction was, the higher volume change was. But As the matric suction was increasing, the behavior of the unsaturated clayey soil was similar to that of saturated clayey soil. Volume change in the unsaturated clayey soil can be represented as a unique plane in three-dimensional space, which is the axes of net mean stress, matric suction and void ratio.

• 한국기후변화학회지
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• 제7권4호
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• pp.397-405
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• 2016

For better understand of the soil respiration characteristic in ecosystem, it is necessary to accurately determine the daily, monthly and seasonal $CO_2$ flux related to various environmental factors. In general, soil respiration is being measured on a sunny day. But soil respiration is known to be affected by soil temperature and soil moisture content. In case of forestry, changes in soil moisture content are entirely dependent on rainfall. If we calculated the monthly soil respiration measured based on sunny days data only, it could be a factor that loses credibility soil respiration. On this study, we measured soil respiration on Pinus koraiensis plantation at Mt. Taehwa of Gwangju, Gyeonggi-do on sunny and rainy days in 2012, using Automatic Open-Closed Chamber system (AOCC) and portable $CO_2$ analyzer (GMP343). Then we computed the regression equations using sunny days data, precipitation less than 10 mm data, and precipitation over 10 mm data. At first, there were no significant differences in observed data and computed data. But less than 10 mm precipitation, computed data was 26.5% lower than observed data. Precipitation over 10 mm, on the other hand, the former was 29.3% higher than the latter. In each case, it showed significant differences between observed and computed data (p<0.05). So if we computed regression equation using soil respiration measured sunny days only, about 30% of annual soil respiration could be overestimated. Through further study, we suggest the subdivision and computation of regression equation on the basis of the rainfall intensity.

• 한국농공학회지
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• 제24권1호
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• pp.63-72
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• 1982

To maintain an optimum condition for the plant growth on upland soil, the irrigation planning after the natural rainfall should be given enormous considerations on the rainfall effectiveness. This study has been intended to develop the computer model for estimating the effec- tiveness of the rainfall. The computer model should also estimated the infiltration due to the rainfall and the soil moisture deficiency at the root zone of the plant. For this purpose, the experiments of infiltration using rainfall simulator and the observations of the change of soil moisture content before and after rainfall were carried out. Needed input data for the developed model include final infiltration capacity and field capacity of the soil, porosity of the top soil, root depth of the plant, rainfall intensity and duration, and the Horton's decay coefficient. Among the needed input data for the developed model, final infiltration capacity and Horton's decay coefficient were determined by the experiments of infiltration. And from the result of the experiments, it is found that there is a great correlation between initial infiltration capacity and initial moisture content. And it is also found that the infiltration due to rainfall can be estimated with the Horton's equation. The developed model was tested by the experimental data with two rainfall intensities. Tests were conducted on the different root depths at each rainfall. Observed and estimated effective rainfalls were found to have great correlation. The result of the experiments showed that the effectiveness of the rainfall were 100%, so the comparisons were conducted by the comsumption rates of infiltration at each depth. The developed model can be also used for estimating the deficiency of rainfall, if the rainfall is not sufficient to the needed soil moisture. But, test was not carried out.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.321-321
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• 2017

Water availability in rainfed lowlands (RFL) is strongly affected by climate change. In RFL, rice plants are exposed to soil moisture fluctuations (SMF) but rarely to simple progressive drought as widely believed. Typical RFL field is characterized by a about 5-cm thick high bulk density hardpan layer underneath the cultivated layer at about 20 cm depth that impedes deep root development. Root system has the ability to develop in response to changes in SMF, known as phenotypic plasticity. We hypothesized that genotypes that can adapt to RFL have root plasticity. The roots can sharply respond to re-wetting after drought period and thus penetrate the hardpan layer when the hardpan is wet and so becomes relatively soft, and thus access water under the hardpan. This study aimed to identify CSSLs derived from a cross between Sasanishiki and Habataki which adapted to such RFL conditions. We used 39 CSSLs together with the parent Sasanishiki, which were grown in hydroponics and pot under transient soil moisture stresses (drought and then rewatering), and compared with continuously well-watered (WW) (control) up to 14 days after sowing (DAS), and 20 DAS, respectively. Based on the results of hydroponics and pot experiments, we selected a few lines, which were grown in the soil-filled rootbox with artificial hardpan layer and without artificial hardpan. For the rootbox without artificial hardpan, plants were grown under WW and transient soil moisture stresses for 49 DAS. While the rootbox with artificial hardpan, the plants were grown under WW (control) and SMF (WW up to 21 DAS, 1st drought (22-36 DAS), rewatering (37-44 DAS), and followed by 2nd drought (45-58 DAS)). Among the 39 CSSLs, only CSSL439 (SL39) consistently showed significantly higher shoot dry weight (SDW) than Sasanishiki under transient soil moisture stress conditions as well as SMF conditions in all the experiments. Furthermore, under WW, SL39 consistently showed no significant differences from Sasanishiki in shoot and root growth in most of traits examined. SL39 showed significantly greater total root length (TRL) than Sasanishiki under transient soil moisture stress, which is considered as phenotypic plasticity in response to rewatering after drought period. Such plastic root development was the key trait that effectively contributed to root elongation and branching during the rewatering period and consequently enhanced the root to penetrate hardpan layer when the soil penetration resistance at hardpan layer reduced. In addition, using the rootbox with artificial hardpan layer ($1.7g\;cm^{-3}$, heavily compacted), SL39 showed greater root system development than Sasanishiki under SMF, which was expressed in its significantly higher TRL, total nodal RL, and total lateral RL at hardpan layer as well as at below the hardpan layer. These results prove that SL39 has plasticity that enables its root systems to penetrate hardpan layer in response to rewatering. Under SMF, such root plasticity contributed to its higher gs and Pn.

• 한국농공학회논문집
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• 제65권3호
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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.

• 한국환경과학회지
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• 제21권8호
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• pp.931-938
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• 2012

The effects were investigated of different lengths and numbers of slitwalls in drainless containers on growth and change in soil moisture volumes on the growth of Diffenbachia amoena 'Marianne' and Begonia rex. Drainless containers filled with amended soil, with square shape ($240mm{\times}240mm$) were used, as well as three different sets of slitwalls (2, 4 or 8, respectively) in addition to non-slitwall containers. Two indoor foliage plants were grown in slitwall containers in randomized blocks with 3 replications in greenhouse conditions, from March to September, 2009. Soil moisture volumes per container were measured by weighing containers every 2 hours during the day. The change in soil moisture volumes showed considerable differences among slitwalls tested in comparison to control containers before and after twice-weekly irrigation. Particularly, the differences in the S2 (195mm, slitwall 2) containers were significantly greater than other containers tested. For Diffenbachia amoena 'Marianne', plant height, length of leaf, dry weight and fresh weight were higher with S2 containers than with those grown in other containers tested. The Begonia rex with the best quality in terms of plant height, length of leaf and width of leaf was grown in S8 (360mm, slitwall 8) containers. Particularly, statistical analysis has indicated that shoot fresh weights of Begonia rex grown in S8 were 3-fold higher than those grown in CS8 containers. The different results obtained within the two species led us to hypothesize a species-specific influence on indoor foliage plant performance. However, plants of both species grown in slitwall containers showed good results compared with plants grown in non-slitwall containers.

• 한국환경과학회지
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• 제5권6호
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• pp.727-738
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• 1996

An one dimensional atmosphere-canopy-soil interaction model is developed to estimate of the heat budget parameter in the atmospheric boundary layer. The canopy model is composed of the three balance equations of energy, temperature, moisture at ground surface and canopy layer with three independent variables of Tf(foliage temperature), Tg(ground temperature), and qg(ground specific humidity). The model was verilied by comparative study with OSUID(Oregon State University One Dimensional Model) proved in HAPEX-MOBILHY experiment. Also we applied this model in two dimensional land-sea breeze circulation. According to the results of this study, surface characteristics considering canopy acted importantly upon the simulation of meso-scale circulation. The factors which used in the numerical experiment are as follows ; the change for a sort of soil(sand and peat), the change for shielding factor, and the change for a kind of vegetation.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2019년도 추계학술대회
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• pp.19-19
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• 2019

It is necessary to maintain stable crop productions under the unsuitable environments, because the drought and flood may be frequently caused by the global warming. Therefore, it is agent to improve the crop growth model corresponded to soil moisture status. Chili pepper (Capsicum annuum) is one of the useful crop in Asia, and then it is affected by change of precipitation in consequence drought and flood occur however crop model to evaluate water stresses on chili pepper is not enough yet. In this study, development of crop model under different soil moisture status was attempted. The experiment was conducted on the slope fields in the greenhouse. The water level was kept at 20cm above the bottom of the container. Habanero (C. chinense) was used as material for crop model. Sap bleeding rate, SPAD value, chlorophyll content, stomatal conductance, leaf water potential, plant height, leaf area and shoot dry weight were measured at 10 days after treatment (DAT) and 13 DAT. Moreover, temperature and RH in the greenhouse, soil volume water contents (VWC) and soil water potential were measured. As a result, VWC showed 4.0% at the driest plot and 31.4% at the wettest plot at 13 DAT. The growth model was calculated using WVC and the growth analysis parameters. It was considered available, because its coefficient of determination showed 0.84 and there are significant relationship based on plants physiology among the parameters and the changes over time. Furthermore, we analyzed the important factors for higher accuracy prediction using multiple regression analysis.

• Journal of Forest and Environmental Science
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• 제35권4호
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• pp.213-222
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• 2019

Climate change has been intensifying and affecting forest ecosystems. Over the years, the intensity and frequency of climate change have increased and the effects of climate change have been aggravating due to cumulative greenhouse gases such as CO₂, which has resulted in several negative consequences, drought being the main threat among all. Drought affects forest ecosystems directly and indirectly. Insufficient soil moisture, due to drought, may affect the growth of plants and soil respiration (SR), and soil temperature may increase because of desiccated soil. In addition, the mortality rate of plants and soil microorganisms increases. As a result, these effects could reduce forest productivity. Thus, in this article, we have presented various research studies on artificial drought using throughfall exclusion, and we have mainly focused on SR, which is significantly related to forest productivity. The research studies done worldwide were sorted as per the main groups of Köppen-Geiger climate classification and intensively reviewed, especially in tropical climates and temperate climates. We briefly reviewed the properties among the exclusion experiments about the temperate climate, which mostly includes Korean forests. Our review is not a proof of concept, but an assumption for adequate investigation of drought effects in the Korean forest.

• 아시안잔디학회지
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• 제4권1호
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• pp.49-55
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• 1990

Experiments were conducted to investigate the relationships between the soil freezing depth and the accumulated degree-day of temperature below $0^{\circ}C$ at 17 locations during 1989-1990 winter season in kangwon province. The observed results are as follows : 1.When accumulated degree-day of temperature below at was 141t at late January soil freezing depth of sunny place was 46.5cm, that of shaded lot was 59 cm, and that of marginal place sunny or shaded area was 55cm, in Chun cheon. 2.Accumulated degree-day of temperature below at of Dae gwangryong area was more than that of Un-du, whereas soil freezing depth of Dae gwangryong was lower that of Un-du. It was considered that snow covering worked as heat insulator. 3.Soil freezing depth of vinyl mulching on Zoysia turf was less by around 2Ocm than that of non-vinyl mulching. Rice hulls covering of 4Ocm showed the great heat insulation effects with the soil freezing depth of 1.5cm at sunny place and 6.5cm at shaded lot compared to that of 47cm at sunny and 59.5 cm at shaded place bare ground. 4.Among investingated areas, Dunae, Honeg seong gun was the deepest soil freezing, 89cm with $569^{\circ}C$ of accumulated degree-day of temperature below $0^{\circ}C$ at late February. 5.dehydration of Juniperus C. var. Kaizuca, Euonymus japonica, and Chamaecyparis pisifira at winter season was around 5 %, however dehydration of Vinca minor was more than 10 %. A Studies on the Soil Freezing Depth and Change of Moisture contents in evergreen Plants upon subzero Temperature in Kangwon area.(2)