Optimum Soil Moisture Content Research Articles

The Preliminary Study on The Effect of Coarse Particles Content on OMC and Maximum Dry Unit Weight: A Case of Aceh’s Fill Materials

Empirical evidence suggests that the percentage of coarse fraction content on soil has an influence on the soil optimum moisture content (OMC) and soil maximum dry density (MDD). This phenomenon is used as a basis to examine the characteristics of Aceh’s fill materials. The major objective of the present study is to determine the relationship between coarse-grained content and OMC and MDD of the Aceh’s fill materials. This relationship is important in the justification of soil suitability as materials for engineering construction. Thirty (30) soil samples from various locations in the Province of Aceh have been collected and tested. The tests carried out include soil physical properties tests and standard compaction test. In the case of a relationship between soil coarse fraction content and soil OMC or MDD, two general findings have been deduced. The first finding of the present study shows that the soil OMC decreases when the content of coarse-grained particles in the soil increases. The later finding shows a positive correlation between coarse particles content and the soil MDD which the increase of the content of coarse-grained particles in the soil will increase the value of the soil’s MDD. In conclusion, the coarse particles content affects the OMC and MDD of Aceh’s fill materials

Re-examination of compaction parameters of fine-grained soils

The reported methods for prediction of compaction parameters of fine-grained soils are critically re-examined in this paper. It is shown that correlations involving just any one index property do not yield satisfactory prediction of optimum moisture content and maximum dry unit weight of soil at any rational compactive effort. By defining a fine-grained soil by its liquid limit and plastic limit, the interrelationship between compaction energy and compaction parameters is brought within a definite framework. Plastic limit is found to influence the maximum dry unit weight of soil to a greater extent than the liquid limit at all energy levels considered in the study. On the other hand, the optimum moisture content–compaction energy–index property relationship is more complex. The degree of accuracy of optimum moisture content prediction is improved when separate correlation equations are used for low-to-medium plastic and highly plastic soils.

Leachability of Heavy Metals from Steel Mill Sludge Incorporated in Fired Clay Brick

The reuse of sludge in clay brick material is a long-term approach to sludge disposal for economic and environmental sustainability. In this study, steel mill sludge collected from Kluang, Johor was used to be investigated to replace clay as brick material. The raw material has been characterized using X Ray Fluorescent (XRF) analysis. The optimum moisture content (OMC) and maximum dry density (MDD) of the soil used was performed by using Standard Proctor Compaction Test in order to verify percentages of water used during brick manufacturing. Brick were manufactured into different percentages which are control brick (0%) and steel mill sludge brick with 5%, 10% and 15% of steel mill sludge waste. Manufactured brick was dried and fired in a furnace at 1050 °C. The results showed that zinc (Zn) and copper (Cu) are the higher heavy metal concentrations detected in steel mill sludge. Meanwhile, leachability test showed that heavy metals leached from steel mill sludge brick are low under permissible limit and complied with United States Environmental Protection Agency (USEPA).

English

Actual evapotranspiration and crop coefficient (Kc) of Amaranthus cruentus grown in weighing lysimeter was determined under a screen house. The weighing lysimeter was made of a cylindrical plastic of circular cross-sectional area of 0.076 m2 and diameter 0.3 m. Climatic variables such as solar radiation, relative humidity, air temperature and wind speed were collected for the estimation of reference evapotranspiration (ETr) using the FAO-Penman Monteith model. Actual crop evapotranspiration (ETc) was measured directly from the daily drop in the level of water in the burette that was connected to the lysimeter. Crop factor (Kc) was estimated from the ratio of ETc /ETo.  The ETc of the crop rose gradually from the period of emergence (4.5 mm week-1) during the 1 week after planting (WAP) to a maximum value of 14.3 mm week-1 during the 7 WAP. Kc for the emergence and maturity stages of Amaranthus cruentus were 0.15 and 0.36, respectively. The highest leaf area index (LAI) and leaf coverage area were 11.39 and 0.866. The optimum soil moisture content for the highest Kc value (0.36) was 11.7%. The output of this research will be useful for farmers who are into vegetable production for enhanced productivity at farm levels.   Key words: Lysimeter, Amaranthus cruentus, crop factor, soil water content, leave area index.

COMPARATIVE STUDY BETWEEN SOME DIFFERENT POTATO HARVESTING MACHINE IN SMALL HOLDINGS

Field experiments were carried out to compare between some different potato harvesting machines (agitator potato ‎digger, elevator potato digger and chisel plow) and evaluate their performance ‎under field conditions. Potato harvesting machines performance was conducted ‎under four different soil moisture contents (9, 11, 13 and 16%) ‎and thee different digging depths (22, 27 and 32 cm). Digging ‎operation was carried out at four different forward speeds (1.3, 1.8, 2.5‎and 3.0 km/h.). Harvesting performance was evaluated in terms of potato ‎losses, productivity, harvesting efficiency, energy requirements and harvesting cost. The ‎experimental results reveal that the use of both agitator digger and elevator potato digger maximize harvesting efficiency and minimize losses and cost comparing with chisel plow under the following conditions: The suitable digging depth to dig all potato tubers is 32 cm., the optimum soil moisture content suitable for digging potato is 13‎‎%, ‎the proper forward speed for operating potato ‎diggers is 2.5 km/h.

Test method for determination of optimum moisture content of soil and maximum dry density

A method for accurately determining the optimum water content of soil and the corresponding maximum dry density has been developed using a small number of soil samples, based on the physical parameters of the confined compression modulus of soil. The peak value of the compression modulus on the force-compression modulus curve is used to determine the optimum moisture content and maximum dry density. The proposed method is validated using four different types of soils: Qinghai-Tibet clay, SiO2-clay, Lanzhou loess, and Qinghai-Tibet sand soil. The results show that as opposed to conventional compaction methods, the new method allows for accurate determination of the optimum water content and the maximum dry density for various types of soil. Additionally, for certain moisture contents, when the compaction of soil is the greatest, clay and SiO2-clay attain the theoretical saturation status, whereas sand soil and loess do not.

Study of the Moisture Equilibrium of Highway Expansive Soil Embankments

AbstractTo investigate the moisture equilibrium of expansive soil embankments, a series of stress-dependent soil-water characteristic curve (SWCC) tests, one-year field monitoring on a trial covered expansive soil embankment, and numerical simulations of the process of moisture equilibrium of a covered expansive soil embankment under atmospheric effects over a period of ten years are conducted. The results show that (1) The effect of the stress state on the equilibrium moisture of expansive soil is clearly in the suction range of 0–3 MPa; (2) In the first year of service, the moisture content of the core of an expansive soil embankment increases gradually, the extent of moisture content fluctuation increases with increasing proximity to the slope side, and the differential settlement of the embankment is observed; (3) The moisture content of the core reaches a steady state, i.e., the moisture equilibrium state, on the sixth year of service; (4) The optimum moisture content of an expansive soil compacted i...

Effect of Ecological Factors on Seed Germination of Alien Weed Tridax procumbens (Asteraceae)

Aims: To determine the effects of light, temperature, pH, salt stress, moisture content, depth of seed burial, and storage periods on its seed germination of Tridax procumbens seeds. Study Design: The seeds of T. procumbens were collected in October December 2012 from several paddy fields along Thailand. Seeds collected from many randomly selected plants were unsoiled and stored at room temperature until used in the experiments. Place and Duration of Study: The experiment was conducted in Faculty of Science and Technology, Phranakhon Rajabhat University, between January 2013 and May 2014. Methodology: To increase understanding of its rapid spread, the influences of light, temperature, pH, salt stress, moisture content, depth of seed burial, and storage periods on its seed germination have been evaluated. Results: The seeds were obviously stimulated germination by light in T. procumbens, with highest germination rate at an alternating under the 12 h light/12 h dark regime, but a few seeds still germinated in the dark. The seeds germinated at a constant temperature in the range of 5–45oC and reached a maximum at 25oC. The seeds germinated over a wide pH range (4–10), with the highest germination rate at 7. The optimum soil moisture content for germination was around 540%. The species was moderately tolerant of salt stress, with NaCl solution concentration > 0.15 mol L. The highest seedling emergence occurred for seeds placed from 0 to 2 cm deep, and no seedlings emerged from a 3-cm burial depth. Original Research Article Vanijajiva; JAERI, Article no. JAERI.2014.003 31 The seeds of T. procumbens have no apparent dormancy and retain a high viability after room storage for 450 days. Conclusion: This study has demonstrated that T. procumbens are adapted to a wide range of environmental conditions.

羊草和紫花苜蓿生长特征及光合特性对不同土壤水分的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 羊草和紫花苜蓿生长特征及光合特性对不同土壤水分的响应 DOI: 10.5846/stxb201301290188 作者: 作者单位: 北京师范大学,北京师范大学资源学院,北京师范大学资源学院,北京师范大学,北京师范大学资源学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(40871031, 41025001); 长江学者和创新团队发展计划(IRT1108); 中央高校基本科研业务费专项 Effects of soil moisture content on morphological and photosynthetic characteristics of Leymus chinensis and Medicago sativa Author: Affiliation: Beijing Normal University,,,Beijing Normal University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用人工控制实验,对12%(T1)、16%(T2)和20%(T3)3种土壤水分条件下羊草和紫花苜蓿的净光合速率Pn、实际光化学量子效率ФPSⅡ、光化学淬灭qP、非光化学淬灭qN、水分利用效率WUE、株高、分枝分蘖数、生物量等参数进行测定.结果表明,在实验范围内,(1)ФPSⅡ 和qP共同影响净光合速率,羊草和紫花苜蓿净光合速率对土壤水分的响应不同,紫花苜蓿的土壤水分生态幅要比羊草窄,羊草生长的最适土壤含水量为20%,随着土壤含水量的降低,净光合速率呈单调递减趋势;紫花苜蓿的最适土壤含水量为16%,其净光合速率与土壤含水量之间呈非线性关系,存在明显阈值.(2)适宜土壤含水量有助于羊草和紫花苜蓿株高和分枝分蘖的生长.(3) 在土壤水分低于适宜土壤含水量范围时,羊草和紫花苜蓿有相似的响应机制,都通过增加根系生物量来适应环境胁迫. Abstract:Leymus chinensis and Medicago sativa are the two most significant perennial artificial grasses of the farming-pastoral ecotone of north China and are crucial for the development of animal husbandry in this area. In this region, water is an important ecological factor that limits plant ecophysiology and the growth of L. chinensis and M. sativa. To maximize the productivity of artificial grassland in this area, it is necessary to explore the mechanisms of the morphological and photosynthetic response characteristics of L. chinensis and M. sativa to water stress. Response characteristics, including the fluorescence characteristics, water use efficiency, biomass and biomass allocation to drought, are studied in this paper. This was done in order to propose the optimum soil moisture content for the growth of, and high economic benefits from, L. chinensis and M. sativa in the chestnut soil of the farming-pastoral ecotone of north China. Data on the morphological and photosynthetic characteristics of L. chinensis and M. sativa were collected from a controlled field experiment in the Taipusi Banner in Inner Mongolia. A water control experiment was applied from the 9th week to the 13th week of the field experiment to evaluate leaf net photosynthetic rate (Pn), actual photochemical efficiency of photosystem Ⅱ complex in the light (ФPSⅡ), photochemical quenching (qP), non-photochemical quenching (qN), water use efficiency (WUE), plant height, branch number and tiller number per plant, biomass and biomass allocation in modules of L. chinensis and M. sativa. The experiment consisted of three soil moisture gradients of 12%, 16% and 20%. The results indicated that, within the soil moisture range of the experiment: (1) the responses of Pn to soil moisture content of L. chinensis and M. sativa were different from each other, and the highest Pn depended on the highest ФPSⅡ and qP. The most suitable soil moisture content for the growth of L. chinensis was 20% and with a decrease in soil moisture content, the Pn of L. chinensis also decreased in a linear relationship; conversely, the optimum soil moisture content of M. sativa was 16%, and as soil moisture decreased, the Pn of M. sativa showed a non-linear relationship with an obvious threshold value. To some extent, the ecological amplitude of soil moisture of M. sativa was narrower than that of L. chinensis. (2) The appropriate soil moisture content for plant growth was attributed to plant height, branching and tillering. (3) The adaptive strategies of L. chinensis and M. sativa were similar, in that they adapt to environmental stress through increased root biomass when the soil moisture content was below the appropriate range. Pn, ФPSⅡ, qP, qN, WUE, morphological characteristics, biomass and biomass allocation in modules of L. chinensis and M. sativa would be changed with the changed soil moisture, which indicates that an optimum soil moisture content should be created for maximizing the growth of M. sativa and L. chinensis during production to obtain high economic benefits for the farming-pastoral ecotone of north China. 参考文献 相似文献 引证文献

Interaction of Carbon Dioxide Enrichment and Soil Moisture on Photosynthesis, Transpiration, and Water Use Efficiency of Soybean

Soybean (Glycine max (L.) Merrill) is one of the most important oil and protein sources in the world. Interactive effect of elevated carbon dioxide (CO2) and soil water availability potentially impact future food security of the world under climate change. A rhizotron growth chamber experiment was conducted to study soil moisture interactions with elevated CO2 on gaseous exchange parameters of soybean under two CO2 concentrations (380 and 800 μmol·mol－1) with three soil moisture levels. Elevated CO2 decreased photosynthetic rate (11.1% and 10.8%), stomatal conductance (40.5% and 36.0%), intercellular CO2 concentration (16.68% and 12.28%), relative intercellular CO2 concentration (17.4% and 11.2%), and transpiration rate (43.6% and 39%) at 42 and 47 DAP. This down-regulation of photosynthesis was probably caused by low leaf nitrogen content and decrease in uptake of nutrients due to decrease in stomatal conductance and transpiration rate. Water use efficiency (WUE) increased under elevated CO2 because increase in total dry weight of plant was greater than that of water use under high CO2 conditions. Plants under normal and high soil moisture levels had significantly higher photosynthetic rate (7% to 16%) favored by optimum soil moisture content and high specific water content of soybean plants. Total dry matter production was significantly high when plants grown under elevated CO2 with normal (74.3% to 137.3%) soil moisture level. Photosynthetic rate was significantly and positively correlated with leaf conductance and intercellular CO2 concentration but WUE was significantly negatively correlated with leaf conductance, intercellular CO2 concentration and transpiration rate. However, the effect of high CO2 on plants depends on availability of nutrients and soil moisture for positive feedback from CO2 enrichment.

外来杂草小花山桃草种子休眠萌发特性研究

PDF HTML阅读 XML下载 导出引用 引用提醒 外来杂草小花山桃草种子休眠萌发特性 DOI: 10.5846/stxb201303150425 作者: 作者单位: 河南科技大学林学院,浙江农林大学林业与生物技术学院,河南科技大学林学院,浙江农林大学林业与生物技术学院,河南科技大学林学院 作者简介: 通讯作者: 中图分类号: 基金项目: 河南科技大学博士基金资助(09001076); 河南科技大学科学研究基金项目(2007ZY025) Seed dormancy and germination characteristics of Gaura parviflora, an exotic weed species in China Author: Affiliation: Forestry College,Henan University of Science＆Technology,School of Forestry and Biotechnology, Zhejiang A,Forestry College,Henan University of Science＆Technology,School of Forestry and Biotechnology, Zhejiang A,Forestry College,Henan University of Science＆Technology Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:种子萌发和出苗是植物一生中对环境胁迫最为敏感的阶段,外来植物在这一时期对环境条件的适应能力是决定其入侵能力大小的关键因素之一.通过室内外试验研究了小花山桃草种子休眠特性以及贮藏时间、果皮、温度、pH 值、水势、盐分和埋土深度对其种子萌发、幼苗生长和出苗的影响.结果表明:小花山桃草蒴果中4 粒种子的大小差异显著(P < 0.01),但它们的活力和萌发率差别不大,4 粒种子活力均高达96%以上.休眠解除后,萌发率均高达98%以上;坚硬果皮的机械阻碍是引起种子休眠的主要原因;在室温储藏条件下,种子萌发率随贮藏时间的增加先增加后降低.贮藏1个月,萌发率提高到54%(贮藏前为0).贮藏3-6 个月时,萌发率达最大值(98.5%-99%).贮藏1a后,萌发率和萌发速度显著下降,但萌发率仍高达90%以上;在室外,有10.5%的蒴果前两粒种子(果实柱头端)同时萌发出苗.室外埋藏1a后,蒴果中未萌发的3 粒种子的发芽率分别为45.5%、90.5%和88.5%;小花山桃草种子萌发的温度范围为5-35 ℃,15-25 ℃最适于种子萌发,25 ℃最有利于幼苗生长;小花山桃草能忍受一定的盐胁迫和干旱胁迫,盐浓度和水势为0.15 mol/L和-0.5 MPa时,种子萌发率分别为33.5%和9%.种子萌发和幼苗生长最适宜的土壤含水量为50%;小花山桃草对pH 值具有较广泛的适应性,在pH 值为5-9范围内均可萌发;小花山桃草种子在土壤表面的出苗率为43%,埋土深度2 cm时,出苗率最高(89.5%),埋土深度大于10 cm时,不再出苗.小花山桃草种子休眠萌发特征以及出苗特点是其快速入侵的基础.研究结果为预测小花山桃草潜在分布范围以及提出科学合理的综合治理措施提供了理论依据. Abstract:Seed germination and early seedling growth are the stages in a plant's life cycle during which it is most sensitive to environmental stresses. The adaptability of an alien plant at this stage to unfavorable environmental conditions is one of the key factors determining its invasiveness. In this study, experiments were conducted to evaluate the effects of dormancy features, storage time, pericarp, temperature, pH, osmotic stress, salt stress and seed burial depth on seed germination, seedling growth and seedling emergence in Gaura parviflora. Although the four seeds of each capsule were found to differ significantly with respect to weight (P < 0.01), their vigor and germination rates were similar to one another. Seed vigor was greater than 96%, and germination was higher than 98% after release from dormancy. The pericarp of G. parviflora affected seed germination via physical obstruction, and was the major cause of seed dormancy. After storage at room temperature, G. parviflora seed germination initially increased; at longer storage times, however, it decreased. Prior to storage, no germination occurred. After one month of storage, germination rates as high as 54% were observed, with maximum germination (98.5%-99%) taking place after 3-6 months of storage. Germination rate and germination speed decreased significantly after one year of storage, although the germination rate was still greater than 90%. The first two seeds of G. parviflora capsules germinated (10.5%) and emerged at the same time under outdoor conditions. After one year of burial in the soil, germination rates of the remaining second, third and fourth ungerminated seeds averaged 45.5%, 90.5% and 88.5%, respectively. Gaura parviflora seeds germinated at temperatures ranging from 5 ℃ to 35 ℃, with optimum germination occurring at 15-25 ℃, and optimum seedling growth taking place at 25 ℃. Gaura parviflora seeds were fairly tolerant of high salt stress and low water potential, with germination rates of 33.5% and 9% observed at a salinity level of 0.15 mol/L and an osmotic potential of -0.5 MPa, respectively. The optimum soil moisture content for seed germination and seedling growth was 50%. Gaura parviflora seeds were able to germinate over a broad range of pH values, ranging from pH 5 to 9. When seeds were placed on the soil surface, the seedling emergence rate was 43%. Maximum seedling emergence (89.5%) occurred at a burial depth of 2 cm. No seedlings emerged when a burial depth of 10 cm was used. Seed dormancy, seed germination and seedling emergence are the critical factors responsible for the rapid invasion characteristics of this species. Our results should be helpful for predicting potential distribution areas of G. parviflora and for developing effective management strategies for this species. 参考文献 相似文献 引证文献

Stabilization of Clayey Soil with Lime and Waste Stone Powder

Clay soils are commonly stiff in dry state but lose their stiffness when saturated with water. Soft clays are characterized by low bearing capacity and high compressibility. In this research, waste stone sludge obtained from slab stone processing, from stone washing plants were recycled for Stabilization of clayey soil with lime. Thus, the effectiveness of using waste stone powder and lime in stabilizing fine-grained clayey soil (CL) was investigated in the laboratory. The soil samples in natural state and when mixed with varying percentages of lime and waste stone powder were used for the laboratory tests that included atterberg limits tests, grain size analysis, standard Proctor compaction tests, unconfined compression tests and California bearing ratio tests. The results show significant reduction in plasticity and changed the optimum moisture content and maximum dry density of clayey soil with increasing percentage content of waste stone powder and lime. The results of the unconfined compressive strength (UCS) and California bearing ratio (CBR) tests show that at the different curing times, the addition of waste stone powder and lime caused an increase in the value of UCS up to 6% waste stone powder content and 7% lime content, and increase in the value of CBR to 6% waste stone powder content and 9% lime content, thereafter, the values of UCS and CBR decreased.

Effect of Natural Resin on Strength Parameters of Sandy Soil

Nowadays, strength characteristics of soils have more importance due to increasing building loads. In some projects, geotechnical properties of the soils should be improved. Geotechnical engineers generally use waste materials to improve soil properties but most of these materials have toxic substances such as heavy metal slags, fly ash, silica fume and industrial resins. In this study, the effects of the addition of a plant gum, named as astragalus, grown commonly in Central and East Anatolia, Iran, Iraq, Turkmenistan and Transcaucasia, on the stability and strength parameters of cohessionless soil were investigated. Astragalus is a pure natural and environmental friendly material. Ground water directly affected by soil additives which used for soil improvement. In this investigation, properties of a cohessionless soil were stabilized by using astragalus. In order to find out which rate of the additive caused maximum strength parameters of the soil samples which prepared by using four different replacement amounts of 0%, 3%, 5% and 10% by weight of soil. Maximum dry densities and optimum moisture contents were determined for each mixture. Strength parameters of each mixture were also determined. According to experimental study, adding 1% of astragalus content is convenient for sandy soil when considered strength parameters and economical respect of additive material. I. I NTRODUCTION Human beings use soil as building and foundation material to build homes and roads through the ages. Geotechnical properties of an soil can be improved in two ways: compaction and mixing with additive material such as lime, cement, fly ash, natural materials etc. In this paper, geotechnical properties of an embankment soil were improved. The soil was taken from a commercial sand pit in Elazig City. Effects of a plant gum, named as astragalus, on the strength parameters of the sandy soil were studied. Geotechnical properties of the sandy soil were determined. Maximum dry density and optimum moisture content of the sandy soil also found out. Samples were prepared by using four different replacement amounts of 0%, 1%, 3%, 5% and 10% by weight of soil. All samples were prepared at optimum moisture content. Shear box tests were conducted on these samples. The existing soil at a construction site cannot always be totally suitable for supporting structures. For this reason

MANUFACTURE AND EVALUATION OF A LOCAL SIMPLIFIED POTATO DIGGER

Filed experiments were carried out to manufacture a simplified potato digger from locally available materials and evaluate its performance under laboratory and field conditions. Digger performance was conducted under four different soil moisture contents (d.b.) of (9, 11, 13 and 15 %) and three different digging depths of (22, 27 and 32 cm). Digging operation was carried out at four different forward speeds of (0.9, 1.6, 2.2 and 2.8 km/h). Digger performance was evaluated in terms of potato losses, digging efficiency, energy requirements and digging cost. The experimental results reveal to the following: The suitable digging depth to dig all potato tubers is 27 cm. The optimum soil moisture content suitable for digging potato is 11 %. The proper forward speed for operating the manufactured potato digger is 2.2 km/h.

시멘트 혼합 노상토의 강도특성

본 연구에서는 플라이애쉬 및 시멘트를 이용하여 강화된 하부노상의 압축강도와 탄성계수를 평가하였다. 실내실험용 시편 제작은 현장 다짐조건을 가장 잘 모사할 수 있는 선회다짐기를 이용하였다. 실험에 사용된 흙은 천안(제4지방산업단지 진입도로 확장공사)공사 현장에서 채취한 흙으로 공학적 분류는 SP에 속한다. 소일시멘트의 배합은 미리 시행된 다짐시험을 통해 측정된 최적함수비상태의 흙에 시멘트, fly ash를 각각 4%, 8%, 12%를 혼합하였고 7일, 14일, 28일 양생하여 실험을 실시하였다. 압축강도 및 탄성계수 평가를 위해 일축압축시험, 자유단 공진주 시험, LFWD(Lightweight Falling Weight Deflectometer)를 수행하였다. 실험결과, 시멘트의 함량이 높을수록 높은 강도를 보이며, 양생시간이 길수록 압축강도의 증가폭이 큰 것으로 나타났고, Fly ash의 경우 큰 폭의 강도증가는 보이지 않았으나, 28일 이후의 강도가 점진적으로 증가하는 것으로 나타났다. 탄성계수 역시 시멘트 함량이 높을수록 증가폭이 큰 것으로 나타났다. 1축 압축시험에 의한 탄성계수와 자유단 공진주시험에 의한 탄성계수를 비교한 결과 두 결과 값은 유사한 패턴의 그래프를 보였고, Fly ash는 단기적으로는 큰 영향은 없지만, 28일 양생으로 증가추세를 보였다. In this research, unconfined compressive strength and stiffness of modified subgrade soil by cement or fly ash were evaluated. Gyratory compactor, which could simulate the field compaction, was adopted to make the test specimen. The testing soil from Cheonan area was used and its classification was SP. The optimum moisture content and maximum dry unit weight of soil were determined, and cement or fly ash was added, 4%, 8% and 12%. Curing times, such as 7, 14 and 28 day were adopted. An unconfined compressive test, an impact resonant test and an LFWD(Lightweight Falling Weight Deflectometer) were carried out to evaluate the strength or stiffness of modified soil. The strength of modified soil increased as the amount of cement and its curing time were increased. However, the strength or stiffness of fly ash modified soil was not significant. The correlation of unconfined compressive test and impact resonant test was relatively good.

Regression model for prediction of optimum moisture content and maximum dry unit weight of fine grained soil

In the present paper, log linear regression models have been developed to estimate the maximum dry unit weight and optimum moisture content of fine grained soil. The parameters such as compaction energy, specific gravity, liquid limit, and grain size (grain size, corresponding to 50% finer particles) are showing the significant contribution for both the models for predicting the maximum dry unit weight as well as optimum moisture content of fine grained soil. All possible regression techniques have been performed for predicting the best models. The above models are useful within the range of 318.10 - to 10832.10 kJ/m³, 2.60 to 2.80, 30.81 - to 213.27%, and 0.0008 - to 0.019 mm for compaction energy, specific gravity, liquid limit, and grain size (Grain size, corresponding to 50% finer particles) respectively.

Effect of temperature, soil moisture content and type of cutting on establishment of sweet potato cuttings

Effective rooting is essential for successful crop establishment from cuttings. The objective of this study was to determine the effect of temperature and soil water content on the root and shoot growth during the early establishment of sweet potato cuttings. Root growth and development were examined in a phytotron at four temperatures (20, 24, 28 and 32 °C constant) and with four types of cuttings (3 node cutting vertically planted, 3 node cutting planted upside down, 3 node cutting horizontally planted and 1 node cutting planted horizontally). The cuttings were allowed to establish and grow for three weeks. The highest total root length (3.59 m plant-1) was recorded in the 24 °C growth chamber and was significantly longer than the roots from the other temperature treatments. The highest root dry mass (0.22 g plant-1), shoot dry mass (1.7 g plant-1), leaf area (578 cm2) and total dry mass (2.0 g plant-1) were also obtained from the 24 °C growth chamber. The three node cuttings planted vertically produced the longest total root length of 3.66 m plant-1 which was significantly longer than those of the other cutting types. The highest root dry mass, shoot dry mass, leaf area, vine length, leaf number, and total dry mass were also obtained from the vertically planted three node cuttings. To determine the response to soil moisture content, cuttings were sealed and allowed to establish and grow in plastic bags containing sandy soil at 100, 80, 60 and 40% of field water capacity. After 12 and 20 days in a growth chamber at 28 °C the plants were harvested. The 80% of field capacity moisture regime was found to be the optimum soil moisture content for sweet potato root growth. With the soil water content at field capacity and at 40% of field capacity root development was somewhat suppressed. The results illustrated the capacity of sweet potato cuttings to establish successfully under a range of ambient temperatures and soil moisture contents.

The effect of various environmental and design parameters on methane oxidation in a model biofilter.

Methane from landfills built with RCRA (Resource Conservation and Recovery Act) covers is frequently vented directly to the atmosphere. Alternatively, landfill gasses could be vented through a layer of soil that could serve as a biofilter to oxidize CH4 to carbon dioxide and water. Properly designed soil biofilters may reduce atmospheric CH4 emissions from landfills and help reduce the accumulation of greenhouse gasses in the atmosphere. This study was conducted to investigate the performance of a lab-scale model biofilter system using soil as the filterbed medium in packed columns to measure the effect of a variety of environmental and design factors on the CH4 oxidation capacity of a soil biofilter. Biofilter performance was tested under a variety of environmental and design conditions. The optimum soil moisture content for CH4 oxidation in a loamy sand was 13% by weight. Addition of NO3-N did not affect the CH4 oxidation rate. Soil depths of 30 cm and 60 cm were equally efficient in CH4 oxidation. When the CH4 loading rate was decreased, the percentage of CH4 oxidized increased. The maximum CH4 oxidation rate was 27.2 mol m(-2) d(-1) under optimum conditions.

Temperature and soil moisture content effects on the growth of Lumbricus terrestris (Oligochaeta: Lumbricidae) under laboratory conditions

The growth of Lumbricus terrestris was determined under varying temperatures and soil moisture contents under laboratory conditions. Our objective was to identify the optimum soil moisture or temperature that would aid in the reproduction of L. terrestris for inoculations in areas devoid of this species. A laboratory experiment using different growth chambers for temperature control with varying soil moisture contents was conducted at the National Soil Tilth Laboratory in Ames, IA. Five temperatures, three different soil moisture contents, and horse manure as a food source were selected and replicated 10 times. It was found that 30°C were fatal to L. terrestris after 14 d and 25°C after 182 d. Regardless of temperature, worms reared under high soil moisture content (30%) developed faster and increased in mass than those reared at 20 or 25% soil moisture content over 266 d. Optimum temperature and soil moisture content for mass rearing of L. terrestris was identified at 20°C and at 30% soil moisture content for these Iowa soils.

Methane Oxidation at Low Temperatures in Soil Exposed to Landfill Gas

AbstractSoil exposed to elevated methane concentrations can develop a high capacity for methane oxidation. Methane oxidation at high and low methane concentrations is performed by different types of methanotrops and therefore oxidation rates found at low temperatures at the atmospheric methane content cannot be extrapolated to soils exposed to high methane concentrations. Four sandy soils with different organic matter content (1–9% w/w) from two landfills in Denmark were investigated in batch experiments in the laboratory to determine the response of methane oxidation at low temperatures and different soil moisture regimes. At 2°C the methane oxidation rates were 0.005 to 0.17 µmol g−1 h−1, and calculations showed that it was possible to oxidize all the produced methane at older landfills, even during the winter. Therefore, methane oxidation in top covers of landfills is an alternative to gas recovery at smaller and older landfills in northern Europe. Equations have been developed that describe the dependency of temperature and soil moisture content for each soil. The oxidation rates depended significantly on the soils (and thereby organic matter content), temperature, and soil moisture content. Soil moisture was the most important factor. However, high Q10 values indicate that temperature also was important. The four soils tested had optimum soil moisture content between 11 and 32%. At increasing organic matter content, both the optimal soil moisture content and the maximum oxidation rate increased.