• Journal of the Society of Disaster Information
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• v.16 no.3
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• pp.577-585
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• 2020

Purpose: The presence of the matric suction in unsaturated soil increases the stability of the slope, but the reduction of the matric suction due to precipitation can cause sudden slope failure, resulting in a major disaster. In this paper, engineering characteristics in unsaturated state were analyzed for granite weathering soil, which is the representative mountain soil of Korea. Method: Experiments and analysis were conducted on granulated weathering soil as unsaturated shear strength relationships for moisture characteristic curves, unsaturated injection curves, and matric suction under unsaturated conditions. Result: It was analyzed that a rapid change in the matric suction for volumetric water content occurs compared to the case where the particle size distribution is poor and the particle size distribution is good. A good case for the particle size distribution indicates a relatively small permeability coefficient at the same matric suction capacity compared to a poor case. The greater thematric suction, the greater the shear strength. Conclusion: For Korea's representative soil, granulated weathering soil, the functional characteristic curves, unsaturated permeability coefficients, unsaturated shear strength, etc., which are engineering characteristics in unsaturated state, were tested to secure each correlation.

• Journal of Bio-Environment Control
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• v.24 no.3
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• pp.153-160
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• 2015

The objectives of this study were to determine optimal length of off-time between irrigation cycles to improve irrigation efficiency using a frequency domain reflectometry (FDR) sensor-automated irrigation (FAI) system for tomato (Solanum lycopersicum L.) cultivation aimed at minimizing effluent from coir substrate hydroponics. For treatments, the 5-minute off-time length between 3-minute run-times (defined as 3R5F), 10-minute off-time length between 3-minute run-times (defined as 3R10F), or 15-minute off-time length between 5-minute run-times (defined as 5R15F) were set. During the 3-minute or 5-minute run-time, a 60mL or 80mL of nutrient solution was irrigated to each plant, respectively. Until 62 days after transplant (DAT) during the autumn to winter cultivation, daily irrigation volume was in the order of 3R5F (858mL) > 5R15F (409mL) > 3R10F (306mL) treatment, and daily drainage ratio was in the order of 3R5F (44%) > 5R15F (23%) > 3R10F (14%). Between 63 and 102 DAT, daily irrigated volume was in the order of 5R15F (888mL) > 3R5F (695mL) > 3R10F (524mL) with the highest drainage ratio, 19% (${\pm}2.6$), at the 5R15F treatment. During the spring to summer cultivation, daily irrigation volume and drainage ratio per plant was higher in the 3R5F treatment than that of the 3R10F treatment. For both cultivations, a higher water use efficiency (WUE) was observed under the 3R10F treatment. Integrated all the data suggest that the optimal off-time length is 10 minutes.

• Korean Journal of Soil Science and Fertilizer
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• v.36 no.1
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• pp.1-7
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• 2003

Time domain reflectometry (TDR) is a newly developed method for measuring simultaneously solute concentrations and volumetric water content of soil. Bulk electrical conductivity ($EC_a$) of soil is obtained from TDR signal using several equations proposed, and electrical conductivity of soil solution ($EC_w$) can be calculated using the linear relationship $EC_a=EC_w\theta(a\theta+b)+EC_s$ between $EC_a$ and $EC_w$ at constant soil water content. The objectives of this study were to evaluate $EC_a$ proposed by several workers and to obtain the empirical constants (a, b, and $EC_s$) for $EC_w$ of the soils from A, Bl, and B2 horizon of an agricultural field (Coarse loamy, Fluvaquentic Eutrudepts). The $EC_a$ proposed by Yanuka et al. responded most sensitively to the KCl solute concentrations. The empirical constants of a, b, and $EC_s$ for $EC_w$ were -0.249, 1.358, and 0.054 for A horizon, -2.518, 2.708, and 0.097 for Bl horizon, and 2.490, -0.250, and 0.103 for B2 horizon, respectively. Therefore, the results of this study showed that Yanuka et al. equation was most useful one in determining $EC_a$, from TDR signal for agricultural soil with low salinity and that the empirical constants for the calculation of $EC_w$, from $EC_a$ can be obtained through a simple calibration experiment.

• Journal of the Korea Organic Resources Recycling Association
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• v.18 no.4
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• pp.31-37
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• 2010

Livestock manures have a potential to be a valuable resource with an efficient treatment. In Korea, 42 million tons of livestock manure were generated in 2008, and 84 % of them were used for compost and liquid fertilizer production. Recently recycling of livestock manure for biogas production through anaerobic digestion is increasing, but its utilization in agriculture is still uncertified. In this study, there was applied co-digestate to the paddy for rice cultivation based on N supplement. Co-digestate was fertilizer fermented with pig slurry and food waste combined with the ratio of 70:30(v:v) in its volumetric basis. For assessing the safety of co-digestate, it was monitored the contents of co-digestate for seasonal variation, resulted in no potential harm to the soil and plant by heavy metals. The results showed that soil applied with co-digestate was increased in exchangeable potassium, copper and zinc mainly due to the high rate of pig slurry in co-digestate applied. Considering high salt content due to the combination with food waste, strict quality assurances are needed for safe application to arable land though it has valuable fertilizer nutrient. Leachate after treatment showed that the concentration of nitrate nitrogen washed out within two weeks. Considering the salt accumulation results in soil, it is highly recommended that the application rate of co-digestate should not exceed the crop fertilization rate based on N supplement. With these results, it was concluded that co-digestate could be used as an alternative fertilizer for chemical fertilizer. More study is needed for the long-term effects of co-digestate application on the soil and water environment.

• Journal of Animal Environmental Science
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• v.16 no.2
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• pp.135-142
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• 2010

The composting of layer manure is economical and efficiently process. In this study, the variation of composting characteristics in layer manure was investigated according to air supply capacity. The fermented compost was added in layer manure and mixed with sawdust inside composting reactors. The level of air supply capacity was varied in the range of $50{\sim}200\;{\ell}/m^3/min$. During composting the temperature variations of composting piles was different the temperatures of composting piles for T-1 ($50\;{\ell}/m^3/min$) and T-2 ($100\;{\ell}/m^3/min$) were reached at $40^{\circ}C$ and $50^{\circ}C$ within 2 days, respectively. For T-3 ($150\;{\ell}/m^3/min$) and T-4 ($200\;{\ell}/m^3/min$), their temperatures was $60^{\circ}C$ within same days and maintained during 8 days. Water contents decreased according to the air supply capacity; 8.9%, 15.4%, 18.0% and 18.6% for T-1, T-2, T-3 and T-4. The weight ratios of T-1, T-2, T-3 and T-4 were reduced to 12.8%, 15.6%, 18.1% and 17.9%, respectively. The decreasing volumetric ratios of T-1, T-2, T-3 and T-4 were 18.0%, 21.0%, 22.3% and 22.0%. The oxygen discharge concentrations during composting were 12 ppm for T-1, T-2 and 9 ppm for T-3 and T-4. After composting, fertilizer components such as total nitrogen (TN) and phosphorous pentoxide ($P_2O_5$) were examined at each air supply capacity. Nitrogen contents of the T-1, T-2, T-3 and T-4 were 0.75%, 0.74%, 0.72% and 0.64%. Also, The contents of $P_2O_5$ were 0.35%, 0.40%, 0.38% and 0.42% for T-1, T-2, T-3 and T-4.

• Korean Journal of Agricultural and Forest Meteorology
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• v.22 no.2
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• pp.57-67
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• 2020

Pinus densiflora is the most widely distributed tree species in South Korea. Its ecological and socio-cultural attributes makes it one of the most important tree species in S. Korea. In recent times however, the distribution of P. densiflora has been affected by dieback. This phenomenon has largely been attributed to climate change. This study was conducted to investigate the responses of growth and physiology of P. densiflora to drought and nitrogen fertiliz ation according to the RCP 8.5 scenario. A Temperature Gradient Chamber (TGC) and CO₂. Temperature Gradient Chamber (CTGC) were used to simulate climate change conditions. The treatments were established with temperature (control versus +3 and +5℃; aCeT) and CO₂ (control: aCaT versus x1.6 and x2.2; eCeT), watering(control versus drought), fertilization(control versus fertilized). Net photosynthesis (P_n), stomatal conductance (g_s), biomass and relative soil volumetric water content (VWC) were measured to examine physiological responses and growth. Relative soil VWC in aCeT significantly decreased after the onset of drought. P_n and g_s in both aCeT and eCeT with fertiliz ation were high before drought but decreased rapidly after 7 days under drought because nitrogen fertilization effect did not last long. The fastest mortality was 46 days in aCeT and the longest survival was 56 days in eCeT after the onset of drought. Total and partial biomass (leaf, stem and root) in both aCeT and eCeT with fertiliz ation were significantly high, but significantly low in aCeT. The results of the study are helpful in addressing P. densiflora vulnerability to climate change by highlighting physiological responses related to carbon allocation under differing simulated environmental stressors.