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1
Huang, Xuewen. "Analysis of effects of soil properties, topographical variables and management practices on spatial-temporal variability of crop yields." Diss., Connect to online resource - MSU authorized users, 2008.
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Macdonald, J. A. "Soil and environmental variables affecting the land-atmosphere exchange of methane." Thesis, University of Edinburgh, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.654211.
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Rates of methane (CH4) oxidation (-) and emission were measured from a range of soil types and land uses to investigate the soil and environmental variables which affected the land-atmosphere exchange of CH4. The influence of soil characteristics, land use, inputs of nitrogen (N) and sulphur (S) and temporal variations in soil water content and temperature on CH4 flux were examined in the field using a static chamber technique, and in the laboratory using soil cores. The flux of CH4 was measured from a range of sites in the UK, Cameroon and Borneo, including temperate and tropical forest, agricultural land, moorland and blanket bog. In mineral soils, rates of CH4 oxidation ranged from a maximum uptake of -27.2 ng m-2 s-1 in an undisturbed forest in Cameroon, to a small net emission of 0.8 ng m-2 s-1 from an agricultural field in Scotland. In peats, soil water content controlled the magnitude and direction of flux within sites by affecting the degree of anaerobicity of the peat and hence the depth of the CH4 oxidising layer. Other factors such as peat depth and substrate quality influenced inter-site variability. The contribution of CH4 produced by termites to the CH4 budget was investigated in undisturbed and disturbed forests in Cameroon and Borneo. In summary, rates of CH4 oxidation from mineral soils were low and covered a small range relative to CH4 emission rates from peat. Rates of CH4 oxidation were significantly inhibited by anthropogenic disturbance such as deforestation, conversion to agriculture, and inputs of N. Spatial variability was controlled by the bulk density of the soil, both in temperate and tropical climates, demonstrating the importance of the gaseous diffusion status of the soil and the secondary role of temperature in regulating oxidation rates. Seasonal variability affected both CH4 emission and oxidation rates. The relative influence of soil water content and temperature on the CH4 flux varied between sites and was dependent on the soil type.
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Baban, Serwan M. J. "The derivations of hydrological variables (including soil moisture) from satellite imagery." Thesis, University of East Anglia, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292298.
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Kichler, Corey Mitchell Zech Wesley C. "Assessment of equipment performance variables for improved management during tillage operations." Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SPRING/Civil_Engineering/Thesis/Kichler_Corey_32.pdf.
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Al-Ghanem, Abdulhakim M. F. "AN EVALUATION OF SELECTED TEST VARIABLES ON STRAIN RATE FOR DRAINED TRIAXIAL TESTING ON TAILINGS MATERIALS (SOIL MECHANICS)." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/275399.
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Roberts, Philip Andrew 1962. "The effects of system variables on soil-vapor extraction of benzene and p-xylene in an unsaturated desert soil." Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/278316.
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Water-unsaturated column experiments using benzene and p-xylene were performed with a desert soil sample (fc = 0.001) to simulate the removal of volatile organic compounds (VOC) by soil-vapor extraction. Higher flow rates of air were found to facilitate quicker VOC removal but lower flow rates were more efficient. Initial concentrations had no effect on the rate of VOC removal. Sorption of both compounds by the solid phase at 18 and 10 percent wetness was similar to that reported for saturated systems. At these moisture contents, Kp the for benzene averaged 0.03 cm 3/g and that for p-xylene averaged 0.61 cm 3/g. At the driest soil condition, higher than predicted sorption of benzene (Kp = 0.12 cm3/g) is attributed to VOC sorption on dry mineral sites. Mechanisms that limited transport of both compounds are assumed to be intra-aggregate aqueous diffusion and desorption. (Abstract shortened with permission of author.)
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Jian, Jinshi. "Global soil respiration: interaction with macroscale environmental variables and response to climate change." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/92195.
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The response of global soil respiration (Rs) to climate change determines how long the land can continue acting as a carbon sink in the future. This dissertation research identifies how temporal and spatial variation in environmental factors affects global scale Rs modeling and predictions of future Rs under global warming. Chapter 1 describes the recommend time range for measuring Rs across differing climates, biomes, and seasons and found that the best time for measuring the daily mean Rs is 10:00 am in almost all climates and biomes. Chapter 2 describes commonly used surrogates in Rs modeling and shows that air temperature and soil temperature are highly correlated and that they explain similar amounts of Rs variation; however, average monthly precipitation between 1961 and 2014, rather than monthly precipitation for a specific year, is a better predictor in global Rs modeling. Chapter 3 quantifies the uncertainty generated by four different assumptions of global Rs models. Results demonstrate that the time-scale of the data, among other sources, creates a substantial difference in global estimates, where the estimate of global annual Rs based on monthly Rs data (70.85 to 80.99 Pg C yr-1) is substantially lower than the current benchmark for land models (98 Pg C yr-1). Chapter 4 simulates future global Rs rates based on two temperature scenarios and demonstrates that temperature sensitivity of Rs will decline in warm climates where the level of global warming will reach 3°C by 2100 relative to current air temperature; however, these regional decelerations will be offset by large Rs accelerations in the boreal and polar regions. Chapter 5 compares CO2 fluxes from turfgrass and wooded areas of five parks in Blacksburg, VA and tests the ability of the Denitrification-Decomposition model to estimate soil temperature, moisture and CO2 flux across the seasons.
Cumulatively, this work provides new insights into the current and future spatial and temporal heterogeneity of Rs and its relationship with environmental factors, as well as key insights in upscaling methodology that will help to constrain global Rs estimates and predict how global Rs will respond to global warming in the future.Ph. D.
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Korre, Anna. "A methodology for the statistical and spatial analysis of soil contamination in GIS." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266111.
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Templeton, Benjamin Sean. "Environmental And Stand Variables Influencing Soil CO2 Efflux Across The Managed Range Of Loblolly Pine." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/31529.
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Managed loblolly pine forests comprise an important pool in the global carbon cycle. Understanding the influences upon inputs and outputs of this pool, including the effects of management activities, will allow landowners to understand how carbon can be sequestered in their stands. Specific to this study, we sought to create multivariate models of the output of carbon from the soil in the form of soil CO2 efflux (Rs) and a component of that total efflux, heterotrophic respiration index (Rh), from data collected across the managed range of loblolly pine in the Southeastern U.S. We also performed tests of significance on controlled subsets of these data for the effects of fertilization and of thinning. Finally, we sought a connection between stand leaf area index (LAI) and total soil CO2 efflux or heterotrophic respiration. Our models indicated variability in both Rs and Rh across latitude and physiographic province, respectively, within this range. The Rs (R2 = 0.56) model included temperature, latitude, a soil moisture by temperature effect, soil nitrogen, and bulk density variables. The Rh (R2 = 0.50) model included soil moisture, a temperature by moisture interaction, and physiographic province. Rs was not significantly affected by either fertilization or thinning, yet Rh was influenced by both (negatively and positively, respectively). This indicates a shift in relative contributions of heterotrophic respiration and root respiration components to Rs in response to these treatments. Heterotrophic respiration was shown to have a weak negative response (R2 = 0.04) to increasing stand LAI.Master of Science
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Hammer, Rachel Lynn. "Soil Respiration and Related Abiotic and Remotely Sensed Variables in Different Overstories and Understories in a High Elevation Southern Appalachian Forest." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/93272.
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Forests have the ability to sequester carbon from our atmosphere. Soil respiration (Rs) plays a role in a forest's ability to do so as it is a significant source of carbon dioxide back to the atmosphere. Therefore, understanding the process of Rs under varying conditions is gaining more attention. As of now we have a relatively good understanding of Rs under managed forest ecosystems such as pine plantations. This particular study examined Rs under different overstories and understories in a high elevation Southern Appalachian forest in order to get a better understanding of Rs under a natural hardwood system. The four vegetation types under consideration were an eastern hemlock (Tsuga canadensis L. Carriere) dominated overstory, a hardwood overstory with little to no understory, a mountain laurel (Kalmia latifolia L.) dominated understory, and a cinnamon fern (Osmundastrum cinnamomeum (L.) C.Presl) dominated understory. Differing temporal variations of Rs were observed under the vegetation types. We found monthly differences in rates among vegetation type however, an overall annual difference in Rs rates between vegetation types was not observed. This simply indicates the importance of observing Rs under different time scales to get a better understanding of its variation. We also calculated vegetation indices from remotely-sensed data to explore any relationships to Rs as well as if the indices themselves could improve out model. A vegetation index is a number that is calculated for every pixel in a remotely sensed image and represents plant vigor or abundance. Few significant relationships were found between the indices and Rs. Future work may want to better understand vegetation indices' spatial extent and accuracy in order to find whether they may be beneficial in Rs estimation. Understanding the influence of varying vegetation type and soil temperature and moisture on Rs will ultimately improve our ability to predict what drives changes in carbon fluxes.Master of Science
Forests have the ability to sequester carbon from our atmosphere. Soil respiration (Rs) plays a role in a forest’s ability to do so as it is a significant source of carbon dioxide back to the atmosphere. Therefore, understanding the process of Rs under varying conditions is gaining more attention. As of now we have a relatively good understanding of Rs under managed forest ecosystems such as pine plantations. This particular study examined Rs under different overstories and understories in a high elevation Southern Appalachian forest in order to get a better understanding of Rs under a natural hardwood system. The four vegetation types under consideration were an eastern hemlock (Tsuga canadensis L. Carriere) dominated overstory, a hardwood overstory with little to no understory, a mountain laurel (Kalmia latifolia L.) dominated understory, and a cinnamon fern (Osmundastrum cinnamomeum (L.) C.Presl) dominated understory. Differing temporal variations of Rs were observed under the vegetation types. We found monthly differences in rates among vegetation type however, an overall annual difference in Rs rates between vegetation types was not observed. This simply indicates the importance of observing Rs under different time scales to get a better understanding of its variation. We also calculated vegetation indices from remotely-sensed data to explore any relationships to Rs as well as if the indices themselves could improve out model. A vegetation index is a number that is calculated for every pixel in a remotely sensed image and represents plant vigor or abundance. Few significant relationships were found between the indices and Rs. Future work may want to better understand vegetation indices’ spatial extent and accuracy in order to find whether they may be beneficial in Rs estimation. Understanding the influence of varying vegetation type and soil temperature and moisture on Rs will ultimately improve our ability to predict what drives changes in carbon fluxes.
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Kohrt, Jonathon. "Expression of Glyphosate Resistance in Two Amaranthus Species as Influenced by Application Variables of Glyphosate." OpenSIUC, 2013. https://opensiuc.lib.siu.edu/theses/1119.
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The expression of glyphosate resistance can vary within single field populations of common waterhemp and Palmer amaranth. This variability in expression can translate into control ranging from 20 to 80%, which could be the difference in a minor versus a major failure in weed management. Certain application parameters that have been previously associated with glyphosate efficacy, such as glyphosate application time of day and plant stress may exacerbate this variability and lead to failed control of plants on the lower end of the resistance spectrum. Greenhouse research was conducted in 2011 to determine the influence of glyphosate application time of day on the expression of resistance in common waterhemp and Palmer amaranth. Control of both glyphosate-susceptible (GS) and -resistant (GR) weed species showed similar trends in response to glyphosate with respect time of application. Decreased sensitivity of all Amaranthus biotypes was greatest at 9:00 pm and may be attributed to an observed shift in leaf orientation from horizontal to vertical at the time of glyphosate application in response to low-light conditions. The altered leaf orientation most likely reduced herbicide spray coverage. The magnitude of resistance, the difference in the sensitivity of the resistant versus susceptible biotypes, was unaffected by glyphosate application time of day; however, these results indicate that even in resistant populations glyphosate applied at suboptimal times of day such as the evening can cause a further increase in weed escapes from glyphosate. Greenhouse and field experiments were conducted in 2011 and 2012 to determine the influence the soil nutrient amendments on glyphosate sensitivity and growth rate and of GS and GR common waterhemp and Palmer amaranth. In both the GR and GS biotypes of common waterhemp the sensitivity to glyphosate was increased as fertilizer was introduced. However, only the sensitivity of the susceptible biotype of Palmer amaranth was increased with the addition of fertilizer. The lack of response in the GR Palmer amaranth population to fertilizer can be associated with the fact that due to carrier volume limitations enough glyphosate could not be applied to achieve 50% control. The magnitude of resistance was decreased numerically with the addition of fertilizer in both weed species; however, only in common waterhemp was the magnitude of resistance significantly different with the use of high rates fertilizer. The use of fertilizer also had an influence on the growth rate and dormancy of axillary buds. Lateral branching (broken dormancy in axillary buds) was increased in both common waterhemp and Palmer amaranth with the addition of fertilizer. Converting dormant buds to active meristems favors glyphosate translocation and could be responsible for increased glyphosate efficacy. In the field, glyphosate efficacy in GR common waterhemp and Palmer amaranth was also increased with addition of fertilizer; however, this effect was variable. Optimizing the efficacy of glyphosate when applied to even mixed populations of GS and GR Palmer amaranth and common waterhemp can reduce surviving weeds that can produce seed and perpetuate the frequency of glyphosate resistance in the field. Furthermore, greater efficacy of glyphosate may translate into relatively less significant failures in glyphosate applications allowing for successful rescue herbicide treatments and minimal impact on crop yield compared with a complete glyphosate failure with dramatic implications on reduced crop yield and increased weed seed production.
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Madaeni, Fatemehalsadat. "Detecting the trends in meteorological variables and investigating their effects on runoff over the last 50 years." Thesis, KTH, Mark- och vattenteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-99342.
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There is now a general consensus among scientists on occurrences of more and intense climatic disasters, floods and droughts, everywhere in the future. To act sooner and smarter against these negative impacts, we must shift our focus in better understanding of the future climate change and possible implications of that to better manage our water resources. Certainly, there is a link between the future effects of climate change on water resources and trends of climatic variables. In this study, by using Mann-Kendall trend analysis method, it is concluded that from 1961 to 2010 only temperature has an upward trend, in all the seasons and yearly, in all the 16 studied stations from north, middle and south of Sweden. Furthermore, runoff simulated by HBV model shows increasing trend in summer and winter which is in partially agreement with the recorded one that discerns a growth in the mentioned seasons, as well as yearly. What is more, potential evapotranspiration estimated by FAO Penman-Monteith equation and actual one simulated by CoupModel reveal a rise in spring for the former and both spring and winter for the latter. Other meteorological variables do not show any significant trend, while intensive precipitation increased in winter and summer in the majority of the stations. Comparing the runoffs simulated by CoupModel and HBV model shows that HBV works better for three selected stations which can enforce the claim that HBV works better for smaller fields.
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Tesfa, Teklu K. "Distributed Hydrological Modeling Using Soil Depth Estimated from Landscape Variable Derived with Enhanced Terrain Analysis." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/616.
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The spatial patterns of land surface and subsurface characteristics determine the spatial heterogeneity of hydrological processes. Soil depth is one of these characteristics and an important input parameter required by distributed hydrological models that explicitly represent spatial heterogeneity. Soil is related to topography and land cover due to the role played by topography and vegetation in affecting soil-forming processes. The research described in this dissertation addressed the development of statistical models that predict the soil depth pattern over the landscape; derivation of new topographic variables evaluated using both serial and parallel algorithms; and evaluation of the impacts of detailed soil depth representation on simulations of stream flow and soil moisture. The dissertation is comprised of three papers. In paper 1, statistical models were developed to predict soil depth pattern over the watershed based on topographic and land cover variables. Soil depth was surveyed at locations selected to represent the topographic and land cover variation at the Dry Creek Experimental Watershed, near Boise, Idaho. Explanatory variables were derived from a digital elevation model and remote sensing imagery for regression to the field data. Generalized Additive and Random Forests models were developed to predict soil depth over the watershed. The models were able to explain about 50% of the soil depth spatial variation, which is an important improvement over the soil depth extracted from the SSURGO national soil database. In paper 2, definitions of the new topographic variables derived in the effort to model soil depth, and serial and Message Passing Interface parallel implementations of the algorithms for their evaluation are presented. The parallel algorithms enhanced the processing speed of large digital elevation models as compared to the serial recursive algorithms initially developed. In paper 3, the impact of spatially explicit soil depth information on simulations of stream flow and soil moisture as compared to soil depth derived from the SSURGO soil database has been evaluated. The Distributed Hydrology Vegetation Soil Model was applied using automated parameter optimization technique with all input parameters the same except soil depth. Stream flow was less impacted by the detailed soil depth information, while simulation of soil moisture was slightly improved due to the detailed representation of soil depth.
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Alharbi, Abdulaziz. "The effect of mulching on the surface energy balance and key soil physical variables,under Sub-humid and Semi-acrid conditions." Thesis, University of Reading, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.533770.
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Lata, Mary Elizabeth. "Variables affecting first order fire effects, characteristics, and behavior in experimental and prescribed fires in mixed and tallgrass prairie." Diss., University of Iowa, 2006. http://ir.uiowa.edu/etd/72.
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Leeper, Ronnie. "Near-surface Atmospheric Response to Simulated Changes in Land-cover Vegetation Fraction, and Soil Moisture over Western Kentucky." TopSCHOLAR®, 2009. http://digitalcommons.wku.edu/theses/108.
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A series of land-use-land-cover-change (LULCC) based sensitivity experiments, including changes in vegetation type, fractional vegetation (FV), and soil moisture (SM), over Western Kentucky were conducted to investigate atmospheric response to land-use. The choice of land-use for this study was chosen in the context of Western Kentucky’s historical LULCC. For this study, vegetation types considered were grassland, forest, and bare soil with further variations in FV for grassland and forest at 25, 50, 75, and 100 % and systematic increases and decreases in volumetric SM of 0.05, 0.10, and 0.15 m3 m-3. To the author’s knowledge, this is the first assessment of its kind that incorporates these types of LULCC in a single study. In addition, typical anthropogenic land-use change often incorporates several types of LULCC. Moreover, this assessment provides a robust analysis of the impacts LULCC has on atmospheric processes over Western Kentucky.
To simulate the importance of land-use on atmospheric processes, a well known meso-scale model developed by the National Center for Atmospheric Research (NCAR) and the Pennsylvania State University (PSU) MM5 coupled with an intermediately complex land surface model (LSM) Noah was used. The purpose of this research is to investigate the impact of multiple types of LULCC on planetary boundary layer (PBL) evolution, PBL stability, near surface 3D-wind fields, temperature, and moisture. Furthermore, it is anticipated that multiple types of LULCC will provide more insight into the complex nonlinear land-atmosphere interactions from atmospheric, air quality, and climatology perspectives.
Modeling analysis revealed the importance of land-use on atmospheric processes. Changes in all three types of LULCC (land-cover, FV, and SM) altered the distribution of surface energy and moisture, PBL structure, 3D-wind fields, and PBL stability. In general, it was found that LULCC that enhanced (diminished) ET rates reduced (increased) sensible heat flux, atmospheric temperature and, and PBL heights below (above) control (CTRL). For instance, the conversion of land-cover from CTRL to grassland reduced 2 m temperature and PBL heights by 0.60 °C and 228 m respectively compared to CTRL due to an evaporative advantage (lower stomata resistance). Multiple types of land-use change were found to either offset or enhance overall modeled response to LULCC. A reduction in FV to 25 % over grassland diminished ET despite the evaporation advantage of grassland and increased 2 m temperature and PBL heights with respect to CTRL by 3.3 °C and 504 m. These results significantly altered horizontal and vertical wind fields, affecting moisture advection and the development of meso-scale circulations. Compared to CTRL, these differences were enhanced over drier soils, but muted over moist soils. Moreover, the impact of LULCC on atmosphere evolution was not only dependent on the type of LULCC, but also on the current state of other unaltered land surface features such as vegetation type, FV, and SM.
Alterations to modeled PBL development, as a result of LULCC, can have important impacts on a region’s climatology and air quality. Simulated changes in typical PBL moisture and temperature through time can affect local and regional climatology. Depending on the type of LULCC, these alterations in climate may lead to localized cooling. In addition, it was further hypothesized that changes in PBL height can affect air quality. Given the capping inversion layer at the top of the PBL, changes in PBL heights can significantly affect air quality with lower (higher) PBL heights diminishing (enhancing) air quality. Moreover, this research prescribes the importance of considering LULCC in atmospheric assessments of climatology and air quality, including pollutant dispersion and trajectory modeling.
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Tenywa, Moses Makooma. "Soil erosion overland flow processes on spatially variable soils /." The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu148784853136528.
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Rachman, Seaful, and n/a. "Infiltration under different landuse types at the Upper Ciliwung watershed of West Java, Indonesia." University of Canberra. School of Resource, Environmental and Heritage Sciences, 1992. http://erl.canberra.edu.au./public/adt-AUC20041215.124610.
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Infiltration, the process of water movement through the soil surface is one of most important hydrological processes to be considered in watershed management. The process depends on rainfall, soil, vegetation and
topographic conditions. The last three variables can be influenced by human land-uses. This study is concerned with the influence of landuse
types (categories) on infiltration at the upper
Ciliwung watershed of West-Java, Indonesia. Sixty six infiltration measurements were carried out in 5 types of land-uses i.e. natural forest, agriculture, settlement, productive (old) tea and new tea plantation areas. The measurements were done using ring infiltrometers. The data
obtained were expressed in the form of Philip's equation I = st1I2 + At, where I is cumulative infiltration; S is sorptivity; t is time; A is a parameter which was calculated from saturated hydraulic conductivity (K). Crown cover, slope gradient and soil variables such as soil moisture, organic carbon content, total porosity,
bulk density were also analysed from each of the 66 sites. The results of the study shows that land-use types have significant influence on these soil variables and on infiltration. Crown cover and human activities in term of land management are among the most important factors which affect soil condition. These variables mostly influence total porosity of soil which is the most important variable to determine sorptivity and hydraulic conductivity. High percentage of crown cover and less human activity
in forest area result in high accumulation of litter and humus and high total porosity of soil. On the other hand, settlement and new tea plantation areas have comparatively low crown cover and more frequent human activity which
result in soil compaction. Discriminant function analysis of land-use categories shows that the soil under forest is very distinct from the soils under other land-use types. However, the soils under the remaining land-use types are
more similar to each other, especially between the soil of settlement and tea plantations.
The rank of infiltration rate from the highest to the lowest magnitude is as follows; natural forest, agriculture, productive tea plantation, new tea plantation and settlement areas. Infiltration rates under natural forest and agriculture are significantly different from each
other as well as from those in the last three land- use types. However, there are no significant differences in infiltration rates among the last three land-use types. The result of this study also provides basic information
for landuse management and further research in
order to solve soil and water conservation and management problems in the watershed.
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Mohamed, Abdel-Mohsen Onsy. "Performance of an anisotropic clay under variable stresses." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75342.
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In the true triaxial test procedure used for testing laboratory-prepared kaolinite clay samples, undrained (with constant mean stress) strength tests were conducted to study the yield and failure of the clays. The principle concern focussed around the influence of orientation of particle bedding plane on the development of yield and failure characteristics of the clay. As the true triaxial cell permits variations of the three principal stresses, it was possible to study the soil response in any chosen quadrant of the principal space.As a consequence to what is mentioned above, two types of consolidated undrained true triaxial tests were conducted in this study. In the first type, specimens were trimmed from the block sample with 90, 60, 30 and 0 degree orientation angles of particle's bedding planes; these angles were measured with respect to the direction of the major principal stress axis. For each degree of inclination, specimens were tested with three confining pressures 207, 276 and 345 kPa, and for each value of confining pressure, the loading path was varied from compression to tension.
The degree of dissociation between the stress and strain increment vectors was seen to depend on both initial and stress induced anisotropy.
Most important of all, a constitutive relationship for anisotropic kaolinite clay was derived on the basis of the observed experimental behaviour of soil samples under loading.
Additionally, anisotropy is characterized by a double transformation technique. The first transformation accounts for the directional dependency whilst the second transformation concerns itself with anisotropy of the base vectors. The relative joint invariant principle is used to calculate the degree of dissociation during the loading process. The variation of the dissociation angle during the loading process can be considered as a measure of the evolution of the resultant anisotropy. The model has shown to provide viable predictions of the stress-strain relationships obtained from true triaxial tests on an anisotropic kaolinite clay for: (a) different inclinations of particle's bedding planes, (b) different stress paths in one sector, (c) different stress paths in other sectors, and (d) the failure surfaces for different inclinations of particle's bedding planes in the octahedral plane. (Abstract shortened with permission of author.)
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Varella, Hubert Vincent. "Inversion d’un modèle de culture pour estimer spatialement les propriétés des sols et améliorer la prédiction de variables agro-environnementales." Thesis, Avignon, 2009. http://www.theses.fr/2009AVIG0638/document.
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Les modèles de culture constituent des outils indispensables pour comprendre l’influence des conditions agropédoclimatiques sur le système sol-plante à différentes échelles spatiales et temporelles. A l’échelle locale de la parcelle agricole, le modèle peut être utilisé dans le cadre de l’agriculture de précision pour optimiser les pratiques de fertilisation azotée de façon à maximiser le rendement ou le revenu tout en minimisant le lessivage des nitrates vers la nappe. Cependant, la pertinence de l’utilisation du modèle repose sur la qualité des prédictions réalisées, basée entre autres sur une bonne détermination des paramètres d’entrée du modèle. Dans le cadre de l’agriculture de précision, les paramètres concernant les propriétés des sols sont les plus délicates à connaître en tout point de la parcelle et il existe très peu de cartes de sols permettant de les déterminer de manière précise. Néanmoins, dans ce contexte, on peut disposer d’observations acquises automatiquement sur l’état du système sol-plante, telles que des images de télédétection, les cartes de rendement ou les mesures de résistivité électrique du sol. Il existe alors une alternative intéressante pour estimer les propriétés des sols à l’échelle de la parcelle qui consiste à inverser le modèle de culture à partir de ces observations pour retrouver les valeurs des propriétés des sols. L’objectif de cette thèse consiste (i) dans un premier temps à analyser les performances d’estimation des propriétés des sols par inversion du modèle STICS à partir de différents jeux d’observations sur des cultures de blé et de betterave sucrière, en mettant en oeuvre une méthode bayésienne de type Importance Sampling, (ii) dans un second temps à mesurer l’amélioration des prédictions de variables agro-environnementales réalisées par le modèle à partir des valeurs estimées des paramètres. Nous montrons que l’analyse de sensibilité globale permet de quantifier la quantité d’information contenue dans les jeux d’observations et les performances réalisées en matière d’estimation des paramètres. Ce sont les propriétés liées au fonctionnement hydrique du sol (humidité à la capacité au champ, profondeur de sol, conditions initiales) qui bénéficient globalement de la meilleure performance d’estimation par inversion. La performance d’estimation, évaluée par comparaison avec l’estimation fournie par l’information a priori, dépend fortement du jeu d’observation et est significativement améliorée lorsque les observations sont faites sur une culture de betterave, les conditions climatiques sont sèches ou la profondeur de sol est faible. Les prédictions agro-environnementales, notamment la quantité et la qualité du rendement, peuvent être grandement améliorées lorsque les propriétés du sol sont estimées par inversion, car les variables prédites par le modèle sont également sensibles aux propriétés liées à l’état hydrique du sol. Pour finir, nous montrons dans un travail exploratoire que la prise en compte d’une information sur la structure spatiale des propriétés du sol fournie par les mesures de résistivité électrique, peut permettre d’améliorer l’estimation spatialisée des propriétés du sol. Les observations acquises automatiquement sur le couvert végétal et la résistivité électrique du sol se révèlent être pertinentes pour estimer les propriétés du sol par inversion du modèle et améliorer les prédictions des variables agro-environnementales sur lesquelles reposent les règles de choix des pratiques agricolesDynamic crop models are very useful to predict the behavior of crops in their environment and are widely used in a lot of agro-environmental work. These models have many parameters and their spatial application require a good knowledge of these parameters,especially of the soil parameters. These parameters can be estimated from soil analysis at different points but this is very costly and requires a lot of experimental work. Nevertheless,observations on crops provided by new techniques like remote sensing or yield monitoring, is a possibility for estimating soil parameters through the inversion of crop models. In my work, the STICS crop model is studied for the wheat and the sugar beet and it includes more than 200 parameters. After a previous work based on a large experimental database for calibrate parameters related to the characteristics of the crop, I started my study with a global sensitivity analysis of the observed variables (leaf area index LAI and absorbed nitrogen QN provided by remote sensing data, and yield at harvest provided by yield monitoring) to the soil parameters, in order to determine which of them have to be estimated. This study was made in different climatic and agronomic conditions and it reveals that 7 soil parameters (4 related to the water and 3 related to the nitrogen) have a clearly influence on the variance of the observed variables and have to be therefore estimated. For estimating these 7 soil parameters, I chose a Bayesian data assimilation method (because I have prior information on these parameters) named Importance Sampling by using observations, on wheat and sugar beet crop, of LAI and QN at various dates and yield at harvest acquired on different climatic and agronomic conditions. The quality of parameter estimation is then determined by comparing the result of parameter estimation with only prio rinformation and the result with the posterior information provided by the Bayesian data assimilation method. The result of the parameter estimation show that the whole set of parameter has a better quality of estimation when observations on sugar beet are assimilated. At the same time, global sensitivity analysis of the observed variables to the 7 soil parameters have been performed, allowing me to build a criterion based on sensitivity indices (provided by the global sensitivity analysis) able to rank the parameters with respect to their quality of estimate. This criterion constitutes an interesting tool for determining which parameters it is possible to estimate to reduce probably the uncertainties on the predictions. The prediction of the crop behaviour when estimating the soil parameters is then studied. Indeed, the quality of prediction of agro-environmental variables of the STICS crop model (yield, protein of the grain and nitrogen balance at harvest) is determined by comparing the result of the prediction using the prior information on the parameters and the result using the posterior information. As for the estimation of soil parameters, the prediction of the variable is made on different climatic and agronomic conditions. According to the result of parameter estimation, assimilating observations on sugar beet lead to a better quality ofprediction of the variables than observations on wheat. It was also shown that the number ofcrop seasons observed and the number of observations improve the quality of the prediction
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Neto, André Torre. "Estudo e implementação de um sistema de monitoramento remoto de variáveis edafo-ambientais." Universidade de São Paulo, 1995. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-14102014-114617/.
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Este trabalho descreve o desenvolvimento e a implementação de um sistema de aquisição automática de variáveis edafo-ambientais, que inclui a transmissão de dados, em tempo real ou posterior para as facilidades computacionais de um laboratório. Esses dados alimentam um programa de modelamento do transporte de pesticidas no solo, o qual é executado em uma estação de trabalho RISC/UNIX. O sistema foi projetado e implementado considerando uma arquitetura serial multiponto, que permite a leitura de até 240 sensores. A transmissão de dados e realizada por dois enlaces, um via radio (3 Km) e outro via linha telefônica discada (130 Km). Unindo esses enlaces, ha um microcomputador PC, que se convencionou chamar de Unidade Remota de Armazenamento. O sistema de aquisição opera sob a supervisão da Unidade Remota. Para isso, foi criado um programa em ambiente gráfico (Windows), o qual assume que os sensores edáficos estejam distribuídos em até quatro parcelas. Esse programa tem as funções de: a) controlar os parâmetros do sistema de aquisição de dados, como intervalo entre amostragens e faixa de leitura dos sensores; b) verificar a consistência dos dados; c) permitir a complementação de dados, com entradas manuais relativas a aplicação de pesticidas e chuvas artificiais; d) armazenar localmente os dados em memória de massa; e) enviar dados para o laboratório, quando requisitados; f) monitorar leituras em tempo real e g) indicar possíveis falhas do sistema. O enlace via linha telefônica serve não somente para a transferência dos dados, mas também possibilita que as funções da Unidade Remota sejam observadas e controladas a distância. O sistema está em operação no campo (Estação Experimental de Pindorama, do IAC) há mais de dois anos. Estão sendo adquiridos dados climatológicos, temperatura do solo e potencial mátrico, em intervalos de 10 minutos. No decorrer desse período, os danos causados por efeitos secundários de relâmpagos durante tempestades resultaram em várias interrupções na operação do sistema. Apesar de terem sido tomadas as precauções usuais, como circuitos de proteção de linha, aterramento adequado do sistema e instalação de pára-raios, estes esforços não foram totalmente eficientes e devem ser melhoradosThis work describes the development of an automatic data acquisition system for environmental variables that includes the transmission of the acquired data in real time or later time to the computational facilities of a laboratory. These data are to be supplied for a modeling of pesticide transport in soil program that is executed in a RISC/UNIX workstation. The system was devised and implemented considering multipoint serial bus architecture and reads up to 240 sensors. The data transmission is performed through a two-link telemetry chain, radio (3 km) and telephone line (130 km). A personal computer named Remote Storage Unit (RSU) was used to join these links. The data acquisition is supervised by the RSU. In order to execute this task a graphics user interface based program (Windows) was created. The program presupposes the distribution of the soil sensors in up to four plots. This program performs the functions of: a) controlling the data acquisition system such as sample intervals and sensors range; b) verifying the consistency of data; c) allowing the complementation of data with manual entries related to artificial rains and pesticide applications; d) locally storing the data in mass memory; e) sending these data to the laboratories, when requested; f) real time monitoring of readings; and g) indicating any system failure. Besides the data transmission the telephone line link can also be used to operate the RSU remotely. The system is operating in the field (Estação Experimental de Pindorama, IAC) for more than two years. Climatologically variables, soil temperature and soil matric potential are being measured at 10 minutes sample interval. During this test period the system operation was interrupted several times due to secondary effects of lightning. Despite of the usual taken cares as line-protection circuits, adequate system grounding and the installation of lightning rods these efforts were not efficient and must be improved
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Michaud, Aubert Raymond. "Soil erodibility indices for Southern Quebec soils derived under variable intensity rainfall simulation." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66178.
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Zhang, Xiaoxian. "Simulating water flow in variably saturated soils containing fractures and soil pipes." Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285396.
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Chintala, Rajesh. "Lime induced changes in the surface and soil solution chemistry of variable charge soils." Morgantown, W. Va. : [West Virginia University Libraries], 2008. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5552.
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Thesis (Ph. D.)--West Virginia University, 2008.Title from document title page. Document formatted into pages; contains ix, 128 p. : ill. (some col.). Includes abstract. Includes bibliographical references.
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Habte, Michael Andebrhan Civil & Environmental Engineering Faculty of Engineering UNSW. "Numerical and constitutive modelling of monotonic and cyclic loading in variably saturated soils." Awarded by:University of New South Wales. Civil and Environmental Engineering, 2006. http://handle.unsw.edu.au/1959.4/24204.
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A fully coupled, effective stress based elasto-plastic model is presented for a rigorous analysis of flow and deformation in variably saturated porous media subjected to monotonic and cyclic loading. The governing equations are derived based on the effective stress concept, equations of equilibrium, and conservation equations of mass and momentum using a systematic macroscopic approach. Both elastic and elasto-plastic constitutive equations are developed. All model coefficients are identified in terms of measurable parameters. The governing equations presented are general in nature, embodying all previously presented formulations in the field. A unified bounding surface plasticity model is developed to describe the stress-strain behaviour of variably saturated soils subjected to monotonic and cyclic loading. The model is formulated incrementally within the critical state framework using the effective stress approach. The model takes into account the effects of both plastic volumetric strain and matric suction on the hardening of the bounding surface. Cyclic behaviour is captured through a new mapping rule in which the point of stress reversal is taken as the centre of projection. The effect of particle crushing at high stresses is considered through a three-segmented critical state and isotropic compression lines. A non-associative flow rule is employed to generalise application of the model to all soils. Solution to the governing equations is obtained numerically using the finite element approach, with the finite difference method employed for the time integration of the rate equations. The elasto-plastic constitutive equations are integrated explicitly using Euler???s forward and the modified Euler integration schemes. Yield surface correction schemes are adopted to improve accuracy of the solution. Essential elements of the proposed model are validated by comparing numerical predictions with experimental data from the literature for fully and partially saturated soils subjected to monotonic and cyclic loadings in drained, undrained, isotropic and deviatoric conditions. The results demonstrate capability of the coupled model to predict essential characteristics of variably saturated soils subjected to monotonic and cyclic loadings in a unified manner.
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Gonçalves, Paulo Henrique Lopes. "Influência de variáveis biofísicas nas taxas de respiração de solos em floresta tropical da Amazônia Oriental." Universidade Federal de Viçosa, 2009. http://locus.ufv.br/handle/123456789/5233.
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The Amazon rainforest has great biological diversity and it is among the most complex forest ecosystems of the planet. Any forest system is composed of physical components (climatic, edaphic, topographical and among others) and by biological components (animals and plants). Because of the interdependence of these components it is difficult to understand the functioning of the system as a whole. Despite the Amazon forest being the largest continuous reserve of tropical rainforest in the world, there is still little understanding about its functioning, particularly in relation to the carbon cycle. Recent studies have demonstrated the importance of carbon stocks in the soil as a source and potential sink of CO2. However, few experimental studies have been conducted on the quantification of these fluxes and their seasonal variations associated with biophysical variables that influence the magnitude of these fluxes. The objectives of this study are: a) To analyze the seasonal variations of soil rates of respiration with litter in areas of black soil (TP) and yellow Oxisol (LA); b) To identify the function of dependency between the soil respiration rates at the soil surface, with soil temperature, soil moisture and litter production; c) To make a comparation of flux estimates of soil allocated carbon in sites of black soil and yellow Oxisol. The results showed a seasonal variation of the flux soil CO2, the sites of yellow oxisol and black soil in fluxes in both response to the observed seasonality in rainfall, soil temperature and soil moisture. The magnitudes of the CO2 fluxes in the LA site ranged from 1.52 to 3.98 μmol.m-2.s-1 with an average of 2.84 ± 0.20 μmol.m-2.s-1 in LA, while the CO2 fluxes in the TP site ranged from 1.95 to 5.73 μmol.m-2.s-1 and with an average of 3.73 ± 0.35 20 μmol.m-2.s-1. The rainfall in these periods was 37 mm in August and 373 mm in April. The average temperature near the soil surface, in August and April, were 25.3° C and 23.9° C, respectively, while soil moisture ranged from 12.5 % to 21.5 % in respective months. The magnitudes of soil CO2 fluxes, in general, were greater in the rainy season in both experimental sites. The hourly fluxes of soil CO2 in the LA site showed little variation between daytime and night, time in august while in April (rainy season) there was evidence of a diurnal variation. The results of this study indicate a greater allocation of C in TP site compared to the LA site.
A floresta tropical amazônica tem grande diversidade biológica e está entre os mais complexos ecossistemas florestais do planeta. Qualquer sistema florestal é composto por componentes físicos (climáticos, edáficos, topográficos entre outros) e por componentes biológicos (animais e plantas). A interdependência entre esses componentes dificulta a compreensão do funcionamento do sistema como um todo. Apesar da floresta amazônica ser a maior reserva contínua de floresta tropical úmida do mundo, ainda há pouco entendimento sobre o seu funcionamento, particularmente em relação ao ciclo do carbono. Pesquisas recentes têm demonstrado a importância do carbono no solo como estoque, fonte e potencial sumidouro de CO2. Todavia, poucos estudos experimentais têm sido realizados sobre a quantificação desses fluxos e suas variações sazonais associadas com variáveis biofísicas que influenciam a magnitude desses fluxos. Os objetivos deste trabalho são: Analisar as variações sazonais das taxas de respiração na superfície do solo com liteira em áreas de terra preta (TP) e de latossolo amarelo (LA); Identificar a relação de dependência das taxas de respiração na superfície do solo com a precipitação pluvial, temperatura do solo, umidade do solo e produção de liteira; Comparar as estimativas de carbono alocado no solo entre as áreas de TP e de LA. Os resultados evidenciam uma variação sazonal dos fluxos de CO2 do solo, tanto nas áreas de LA como nas áreas de terra preta, em resposta à sazonalidade observada no regime pluviométrico, e da temperatura e umidade do solo. As magnitudes dos fluxos de CO2 variaram de 1,52 a 3,98 μmol.m-2.s-1 e média de 2,84 ±0,20 μmol.m-2.s-1 em LA e em TP os fluxos variaram de 1,95 a 5,73 μmol.m- 2.s-1 e média de 3,73 ±0,35. A precipitação pluvial nesses períodos foi de 37 mm em agosto e 373 mm em abril. A temperatura média do solo próximo à superfície, nos meses de agosto e abril, variou de 25,4o C a 23,9o C, respectivamente, enquanto a umidade do solo variou de 12,5 % a 21,5 % para os respectivos períodos. As maiores magnitudes dos fluxos de CO2 do solo, de um modo geral, ocorreram no período chuvoso em ambas as áreas experimentais. Os fluxos horários de CO2 na área de LA em agosto (menos chuvoso) apresentaram pequena variação entre o período diurno e noturno, enquanto em abril (chuvoso) a variação nos fluxos foi bem mais acentuada. Os resultados desse trabalho indicam uma maior alocação de C na TP em relação a LA, provavelmente pela maior quantidade de matéria orgânica na superfície do solo.
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Muthineni, Srinivas. "Two Dimensional Numerical Modelling Of Variably Saturated Flows." Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/255.
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The prediction of moisture and contaminant transport through unsaturated soil to ground water is becoming increasingly important in the fields of hydrology, agriculture and environmental engineering. Computer aided simulation techniques enables one to conduct a series of systematic numerical experiments to analyze flow phenomenon in subsurface hydrology under various physical and chemical processes. The flow movement depends upon medium characteristics, initial and boundary conditions, which reflect, physical processes occurring below the ground. To understand the effects of physical process an efficient and accurate model is needed. Thus the model developed must be able to handle varied initial and boundary conditions. In this regard, infiltration into a very dry soil becomes a very important problem of study.
Most of the earlier numerical models developed are concentrated on the development of an efficient algorithm or the modelling of a particular process which govern the flow in unsaturated or saturated-unsaturated homogeneous medium. Not much work has been done on the analysis of variably saturated flow in layered soil medium. Models to simulate unsaturated flow through dry soils, especially through layered soils with varied boundary conditions are very limited. Further, not much studies have been reported in the literature on the prediction of seepage face development and the phreatic surface movement in variably saturated media with layering. These aspects are very important in determining the flow field and the discharge from the domain. A detailed literature review covering above aspects has been made and is reported in this thesis.
In the present work, two dimensional numerical models to predict the movement of wetting front in unsaturated domain and the movement of the phreatic surface in homogeneous and layered porous media under various initial and boundary conditions are developed based on finite difference and finite volume techniques. These models can handle flow in both rectangular flow domains and radial flow domains. The initial condition settings include the handling of very dry soil medium without any transformation of the governing equation, handling of infiltration and constant head conditions at the boundaries under steady state as well as transient scenarios. The models are also able to handle various soil moisture characteristics which depict the nonlinear behaviour between hydraulic conductivity, moisture content and pressure head in a soil media.
A mixed form of the governing partial differential equation is used in the present study as it leads to better mass conservation. The finite difference model uses a central difference approximation for the space derivatives and an Eulerian backward difference approximation for the time derivative. The fully implicit formulation is solved iteratively using Strongly Implicit Procedure after making Picard approximation for the highly nonlinear coefficients. The process of infiltration into an initially dry soil leads to the development of a steep wetting front. As the finite volume technique is naturally an upwind method, it is expected to play a positive role in modelling such processes accurately. Hence, a finite volume model is also developed by approximating the convective part using a MUSCL approach and a fully implicit central difference method for the diffusive part of the governing equation.
The models developed are validated using both experimental data and numerical solutions for problems reported in the literature. The validation problems cover a wide range of physical scenarios such as: infiltration into a very dry soil, infiltration into a dry soil column with gravity drainage, development of water table mound, steady state drainage in a sand filled wedge shaped tank with seepage face development and transient seepage face development in a rectangular domain. Five test problems are used for the validation of the models. The developed models perform very well for the test problems considered, indicating the models' capability in handling such situations. The results obtained by using the present models for simulating flow through highly unsaturated (very dry) soils show that the models perform very well when compared with models which use transformation techniques to handle such problems. The performance of the present models in comparison with the experimental data and numerical models available in the literature show the suitability of the present models in handling such situations.
The present models are also used to analyse various types of unsaturated flow problems with varying initial and boundary conditions. The boundary conditions considered are no flow and /or free flow conditions along the left, right and bottom boundaries with infiltration condition along a part of the top boundary. For the various cases considered in the present study, infiltration rate varies from 5 cm/day to 50cm/day through an initially very dry soil of -15000 cm pressure head in homogeneous and layered soils. Different types of soil media considered vary from sandy loam, loam and clay with horizontal and vertical layering of these soils. A total number of 14 cases are analysed. The results are discussed in terms of pressure head variation in the flow domain along with moisture redistribution for all the cases under consideration. It is observed from these studies that the infiltration rate play an important role on the wetting front movement through layered soils depending on the type of layering and the boundary conditions considered. The soil properties of various layers affect the movement of wetting front by changing the direction of movement. Even though the wetting front movement is predominantly vertical, there is a tendency for the wetting front to move in the horizontal direction as it moves from a coarse soil to fine soil. It is also observed that the vertical layering of soils with different hydraulic conductivity helps in redirecting the flow towards the bottom boundary through the neighboring coarser layers.
As finite volume method is more suitable for simulating sharp fronts, it is expected to perform better than finite difference method for simulating infiltration into very dry soils. So, a comparison is made between the performance of these two models by using the above test problems. It is observed from these studies that the performance of both the models are same except that the finite volume method takes much more CPU time than the finite difference model. Considering the type of problems tested, it is observed that for modelling unsaturated and saturated-unsaturated flows, finite difference method is better in comparison to finite volume method. It may be due to the predominant diffusive characteristics of the governing equation even while modelling flow through very dry soils.
Proper estimation of the seepage height is an important aspect in finding the discharge through the porous medium. It is observed from the literature that the use of a saturated flow model in such situations can lead to an underestimation of the discharge through the porous medium. This effect is more important when dealing with small dimension problems. It is also observed that various parameters which govern the moisture movement through saturated-unsaturated regions affect proper estimation of the seepage face height and there by discharge. Various factors like effect of boundary conditions, type of soil layering, problem dimension and aspect ratio on seepage face development and the associated phreatic surface formation is studied in the present work. It is seen from the present study that the seepage face development is more in rectangular flow domain than in radial flow domain for both homogeneous and layered soils. It is also seen that the seepage face development in rectangular problems are more sensitive than radial flow problems for various factors considered. The seepage height is also influenced by the tail water level. It is seen from the present study that as the tail water level increases the seepage face reduces with no seepage face development for some of the cases studied. This influence is relatively less for radial flow problems. As the length of the domain increases the seepage height decreases. It is seen that for different cases with same horizontal dimension, as the height of the domain increases the seepage face height also increases. This phenomenon is observed for both homogeneous and layered soil medium. The influence of the aspect ratio, which is the ratio of the length to height of the domain indicate that as the aspect ratio increases the seepage height decreases. The type of the soil layering is observed to have a very strong influence on the seepage face development. The study for understanding the effect of soil layering on the development of seepage face and phreatic surface suggest that as the coarseness of the material increases, the phreatic surface become flatter and its steepness increases with the fineness of the soil.
The present model is also used for studying the transient phreatic surface movement and the seepage face development. This is studied for homogeneous and layered rectangular soil medium. The present study is used to understand the effect of specific storage on the phreatic surface movement and the seepage face development. The studies indicate that the influence of specific storage on the seepage face development is insignificant in homogeneous soils with only very little effect in the early time for longer domains. It is also observed that the influence of the specific storage is significant in the case of layered soils. This effect depends on the type of layering and the problem dimension and is observed to have influence for relatively longer period. This observation suggests the importance of specific storage on transient seepage face development. When the specific storage effect is considered the drainage of the soil become faster resulting in a faster decline of the phreatic surface with time. The influence of specific storage is also studied considering the problem dimension effect. It is seen that as the aspect ratio increases, the effect of specific storage on the phreatic surface development decreases. The studies with change in the upstream boundary condition from a constant head to a no flow condition indicate that the effect of specific storage has no significant influence on the phreatic surface development for both homogeneous and layered soils.
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Kramer, Gisieli. "AVALIAÇÃO ESPAÇO-TEMPORAL DAS RELAÇÕES ENTRE ECOSSISTEMAS TERRESTRE E AQUÁTICO: ESTUDO DE CASO DA BACIA DA UHE PASSO REAL DA REGIÃO SUL DO BRASIL." Universidade Federal de Santa Maria, 2009. http://repositorio.ufsm.br/handle/1/9315.
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The UHE Passo Real reservoir, founded in 1973 (158,0 MW capacity), with a flooded area of 221 km2 (CEEE, 2008), presents different types of water and an intense agricultural exploitation in the uptake area. In this study, we aimed at interpreting, analyzing and correlating soil use and soil cover in distinct uptake watersheds and agricultural periods with TSS concentration and Secchi depth in different parts of the reservoir. The soil maps showed the three watersheds that flow into the reservoir:
Jacuí, Jacuí-Mirim and Ingaí. In these maps there were the vegetative development period in March/2009 and the post-harvest period in May with exposed soil. TM Landsat 543/RGB images were used to identify the kinds of soil use. The categories of soil use were: forest areas, cultures, field,exposed soil and water. The TSS variable (using a filtering method) was measured in 22 points
(February, April and June/2009) in four samples: Jacuí, Jacuí Mirim, Ingaí and the main reservoir axis. In the images classification, the culture category was higher in the three watersheds in March: Jacuí Mirim 61,46% (total area =157.182,75 ha), Ingaí 56,51% (114.671,16 ha) and Jacuí 49,55% (423.430,47 ha). In May, the category of exposed soil was higher: Jacuí Mirim 75,55%, Ingaí 68,78%
and Jacuí 65,77%. The highest average TSS was found in June (higher precipitation) in the Jacuí sample (Ma= 9,33 mg/L). The low TSS values were frequently found in February, for example, Jacuí sample (Ma=4,33mg/L). The data from SD samples were coherent with TSS data considering that water transparency was higher when the sediments concentration was lower. It was found that soil use and soil cover in the studied area are predominantly rural, mainly due to soybean and corn crops in
February and the beginning of winter pasture in May. Even if Jacuí Mirim and Ingaí watersheds presented a higher percentage of exposed soil in May, the Jacuí watershed presents higher TSS flush and TSS concentrations because of a larger uptake area and a lower aquatic flow volume. Overall, the aquatic dynamics at the UHE Passo Real is related to the water flow from the uptake watersheds and it
suggests distinct aquatic compartments that result in different colors of water.O reservatório da UHE Passo Real, inaugurado em 1973 (capacidade 158 MW) e área inundada de 221 km2 (CEEE, 2008) apresenta diferentes tipos de água e uma intensa exploração agrícola na área de captação. Os objetivos da pesquisa compreenderam a interpretação, análise e relação do uso e cobertura da terra em distintas bacias de captação e fases agrícolas com a concentração dos sólidos em suspensão (TSS) e a profundidade do Disco de Secchi (DS). Os mapas de uso da terra caracterizaram as três principais bacias de captação que deságuam no reservatório: Jacuí, Jacuí-Mirim e Ingaí. Esses mapas contemplaram a fase do desenvolvimento vegetativo das culturas agrícolas em março/2009 e a fase pós-colheita em maio com domínio de solo exposto. Imagens de satélite TM Landsat 543/RGB foram utilizadas para identificar as formas de uso da terra. As classes de uso foram assim definidas: áreas florestais, culturas, campo, solo exposto e água. A variável TSS (processada pelo método da filtragem) foi medida em 22 pontos (fevereiro, abril e junho/2009) separados em quatro grupos amostrais: grupo Jacuí, Jacuí Mirim, Ingaí e eixo principal do reservatório. Na classificação das imagens a classe cultura destacou-se nas três bacias em março: 61,46% Jacuí Mirim (área total da bacia=157.182,75 ha), 56,51% Ingaí (114.671,16 ha) e 49,55% Jacuí (423.430,47 ha). Em maio, a classe solo exposto sobressaiu-se com 75,55% na bacia do rio Jacuí Mirim, 68,78% no Ingaí e 65,77% no Jacuí. A maior média dos valores de TSS foi encontrada em junho (maior média de precipitações) para o grupo amostral Jacuí (Ma= 9,33 mg/L). Os valores baixos de TSS foram registrados, em geral, em fevereiro, a exemplo do grupo amostral Jacuí (Ma=4,33mg/L). Os dados dos grupos amostrais do DS apresentaram consistência com os dados do TSS uma vez que a transparência da água foi maior na medida em que a concentração de sedimentos foi menor. Observou-se que os usos e coberturas da terra na área de estudo são predominantemente rurais, principalmente pelo cultivo da soja e do milho em fevereiro e início do plantio das pastagens de inverno em maio. Embora as bacias dos rios Jacuí Mirim e Ingaí apresentaram maiores porcentagens de solo exposto em maio, na bacia do rio Jacuí registrou o maior efeito do sistema terrestre sobre o aquático com a ocorrência de maiores concentrações de TSS. Isto deve-se ao efeito de maior área de captação e menor volume do compartimento aquático de deságüe. Sobretudo, a dinâmica que ocorre no ambiente aquático do reservatório da UHE Passo Real está relacionado com a entrada de água das bacias de captação e sugerem distintos compartimentos aquáticos pelo modo mistura que resultam diferentes colorações na água.
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Ara?jo, Virg?nia Farias Pereira de. "Arthropoda de solo em um ecossistema semi-?rido da regi?o neotropical: composi??o, variabilidade temporal e estratifica??o." Universidade Federal do Rio Grande do Norte, 2009. http://repositorio.ufrn.br:8080/jspui/handle/123456789/13047.
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Previous issue date: 2009-02-17Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
Caatinga is an important laboratory for studies about arthropods adaptations and aclimatations because its precipitation is highly variable in time. We studied the effects of time variability over the composition of Arthropods in a caatinga area. The study was carried out at a preservation area on Almas Farm, S?o Jos? dos Cordeiros, Para?ba. Samples were collected in two 100 m long parallel transects, separated for a 30 m distance, in a dense tree dominated caatinga area, between August 2007 and July 2008. Samples were collected in each transect every 10 m. Ten soil samples were taken from each transect, both at 0-5 cm (A) and 5-10 cm (B) depth, resulting in 40 samples each month. The Berlese funnel method was used for fauna extraction. We registered 26 orders and the arthropods density in the soil ranged from 3237 to 22774 individuals.m-2 from January 2007 to March 2008, respectively. There was no difference between layers A and B regarding orders abundance and richness. The groups recorded include groups with few records or that had no records in the Caatinga region yet as Pauropoda, Psocoptera, Thysanoptera, Protura and Araneae. Acari was the most abundant group, with 66,7% of the total number of individuals. Soil Arthropods presented a positive correlation with soil moisture, vegetal cover, precipitation and real evapotranspiration. Increases in fauna richness and abundance were registered in February, a month after the beginning of the rainy season. A periodic rain events in arid and semiarid ecosystems triggers physiological responses in edafic organisms, like arthropods. Edafic arthropods respond to time variability in the Caatinga biome. This fauna variation has to be considered in studies of this ecosystem, because the variation of Arthropods composition in soil can affect the dynamics of the food web through time
A Caatinga ? um importante laborat?rio para estudos sobre as adapta??es e aclimata??es de Arthropoda, devido a uma alta varia??o temporal da precipita??o. Foram verificados os efeitos da variabilidade temporal sobre a composi??o de Arthropoda em uma ?rea de caatinga. O estudo foi realizado na Reserva Particular do Patrim?nio Nacional (RPPN) Fazenda Almas, S?o Jos? dos Cordeiros, Para?ba. A coleta foi realizada em dois transectos paralelos de 100 m, distantes 30 m entre si, em ?rea de caatinga arb?rea densa, durante o per?odo entre agosto de 2007 e julho de 2008. Em cada transecto, foram determinados 10 pontos de coleta, distanciados 10 m entre si, onde se retiraram 10 amostras do solo entre 0 e 5 cm (A) e 5 e 10 cm (B) de profundidade, totalizando 40 amostras mensais. O m?todo do funil de Berlese foi utilizado na extra??o da fauna. Foram registradas 26 ordens e a densidade de Arthropoda do solo variou de 3237 a 22774 indiv?duos.m-2 em janeiro de 2007 e mar?o de 2008, respectivamente. N?o houve diferen?a significativa entre as camadas A e B com rela??o a abund?ncia e riqueza de ordens. Grupos com poucos registros ou que n?o haviam sido inventariados na regi?o da caatinga foram registrados, como Pauropoda, Psocoptera, Thysanoptera, Protura e Araneae. Acari foi o grupo mais abundante com 66,7% do total de indiv?duos. Os Arthropoda de solo apresentaram correla??o positiva com a umidade do solo, cobertura vegetal, precipita??o e evapotranspira??o real. Foram registrados aumento na riqueza e na abund?ncia da fauna em fevereiro, um m?s ap?s o in?cio das chuvas. A ocorr?ncia de chuvas peri?dicas em ecossistemas ?ridos ou semi-?ridos aciona respostas fisiol?gicas em organismos ed?ficos, como os Arthropoda. Portanto, os Arthropoda ed?ficos respondem a variabilidade temporal em ?rea de caatinga. Esta varia??o da fauna tem implica??es potencialmente importantes no estudo do ecossistema, pois as mudan?as na composi??o de Arthropoda do solo podem afetar a din?mica da rede alimentar ao longo do tempo
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Pereira, Paulo Ricardo Brum. "Distribuição espacial do carbono no solo e avaliação dos fluxos dos gases de efeito estufa (CO2, CH4 e N2O) em áreas de vegetação de Cerrado, Pinus spp e Eucalyptus spp na Estação Experimental de Mogi Mirim (IF/SMA-SP)." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/64/64134/tde-18112010-170343/.
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Objetivou-se neste trabalho avaliar a variabilidade espacial e temporal do carbono no solo produzindo um mapa, sobre esse tema para toda a área da Estação Experimental de Mogi Mirim (EE Mogi Mirim), juntamente com a análise dos fluxos dos gases de efeito estufa (CO2, N2O e CH4) e a relação desses dois fenômenos com as variáveis do solo nos diferentes usos da terra. Para se alcançar objetivo proposto com relação aos estoques de carbono e avaliação das variáveis do solo foi feita a coleta e o prepara das amostras nas profundidades de 00 até 30 cm, foi feito o georreferenciamento e determinação dos teores de carbono, densidade do solo, calculo dos estoques de carbono e determinação da cor do solo. Por sua vez para o estudo e entendimento dos fluxos dos gases de efeito estufa (GEE), comparou-se um talhão considerado sem perturbação (Talhão 41) e a partir desse talhão avaliou-se comparativamente em uma seqüência com ambientes com histórico de uso da terra representativo da área com manejos. Os fluxos dos gases CO2, N2O e CH4 foram medidos utilizando-se câmaras estáticas. Nos resultados obtidos foi aplicada a estatística descritiva clássica e geoestatistica para avaliar a freqüência e distribuição dos dados. Resultados relativos as variáveis do solo mostram que praticamente a grande maioria tende a diminuir com a profundidade (Ca, soma das bases, CTC, acidez potencial e carbono). Por sua vez o pH é sempre muito alto nas 3 camadas e a saturação por bases e o magnésio são muito baixos e permanecem inalterados em todas as profundidades. A variabilidade espacial dos estoques de carbono possui características isotrópicas. Especificamente na profundidade 00 - 10 cm, o modelo teórico que melhor se ajustou foi o exponencial, na profundidade 10 - 20 cm foi o esférico e na profundidade 20 - 30 cm foi o exponencial. Os estoque de C na profundidade 00 10 cm, tiveram como média 22.8 ton C/ ha-1, sendo o maior valor de 42.9 ton C/há-1 e o menor valor de 10.3 ton C/há-1. Na profundidade 10 - 20cm, a média do estoque de carbono foi de 14.9 ton C/há-1, sendo o maior valor de 31.5 ton C/há-1 e o menor valor de 6.99 ton C/há-1. Na profundidade 20 -30 cm, a média do estoque de carbono foi de 11.45 ton C/há-1, sendo o maior valor de 25.28 ton C/há-1 e o menor valor de 6.3 ton C/há-1. Os resultados das análises dos fluxos do gás carbônico, como um todo mostra que a respiração do solo variou entre 75.3 e 164.4mgC m-2 h-1. Relativo aos fluxos de N2O os valores médios para as emissões variaram entre 8,85 e 51,94 \'mü\'gN m-2 h-1, enquanto que a absorção variou, entre -1,32 e - 4,59 \'mü\'gN m-2 h-1. Os resultados dos fluxos do gás metano médio ficaram entre 4,63 e 31,51 mgC m-2 h-1, enquanto que os valores de oxidação média ficaram entre -5,41 e -22,79 mgC m-2 h-1The aim here is to evaluate the spacial and transient variability of carbon in soil, producing a map about this subject for all the area of the Experimental Station of Mogi Mirim (Estação Experimental de Mogi Mirim EE Mogi Mirim), with the emissions analyzes of greenhouse gases effect (CO2, N2O e CH4), and the relation between these phenomenon with the soil variables in different uses of the land. In order to reach the proposed objective related to the carbon storages, and the variable evaluation of the soil, a sample collect and preparation were made at a depth from 00 to 30cm. It was also made the georeferencial and the carbon levels determination, density of soil, the estimate of carbon storages, and the determination of soil color. The study and understanding of the greenhouse gas emissions (GGF), a área considered without disturbing, and from it a comparative evaluation in a sequence of environments with historical land use representative of the management area. The CO2, N2O and CH4 gas emissions were measured by using static chambers. In the results obtained, it was applied the classic statistic description and geostatistics to evaluate the frequency and the distribution of data. Results related to the soil variables show that the major trend to decrease, according to the depth (Ca, sum of bases, CTC, potential acidity, and carbon). On the contrary, the pH is always very high in 3 layers, and the saturation for bases and the magnesium are very low, maintaining unchangeable in all depths. The variability of the carbon storages have isotropic characteristics. Specifically in depth 00 - 10cm, the theorical model that better adjusted was the exponential; in depth 10 - 20cm, it was the spherical, and in depth 20 - 30cm it was the exponential. The carbon storage in depth 00-10cm had as na average 22.8ton C / ha-1, being the highest value of 42.9 ton C/ha-1, and the lowest value of 10.3 ton C/ha-1. In depth 10 - 20 cm, the average of carbon storage was 14.9 ton C/ha-1, being the highest value of 31.5 ton C/ha-1, and the lower value of 6.99 ton C/ha-1. In depths of 20 - 30cm, the average of carbon storage was of 11.45 ton C/há-1, being the highest value of 25.28 ton C/ha-1, and the lowest of 6.3 ton C/ha-1 The analyze results of carbon gás emissions as a whole, shows that the soil breath varied between 75.3 e 164.4 . mgC m-2 h-1 . Regard to N2O emissions, the average values to emissions varied between 8.85 and 51.94 \'mü\'gN m-2 h-1, while the absorption varied, between -1.32 e - 4.59 \'mü\'gN m-2 h-1. The results of average methane gas were between 4.63 e 31.51 mgC m-2 h-1, while the average oxidation values were between -5.41 e -22.79 mgC m-2 h-1
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Kamat, Madhusudan Sunil. "Soil moisture change due to variable water table." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54922.
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The thesis numerically models and investigates the effect of a variable water table on the soil moisture content. The modelling is done using COMSOL and Richards' equation. The temporal variation plots can be used to find the capillarity of the soil and its impact on other phenomenon such as vapor intrusion and infiltration.
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Munhoz, Juliana Soares Biruel. "Caracterização da produtividade florestal e dos padrões de crescimento de Pinus taeda L. no sul do Brasil através de análise de tronco." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/11/11150/tde-28042011-162045/.
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Visando caracterizar a dinâmica de crescimento do Pinus taeda no sul do Brasil, este estudo teve os seguintes objetivos: i) determinar os principais fatores edafo-climáticos e do povoamento associados à ampla variação de produtividade da espécie; e ii) caracterizar padrões de crescimento e uniformidade, do plantio até 9 anos em diferentes regiões edafoclimáticas. Para isso, foram selecionadas 24 parcelas sem desbaste (700m²), com aproximadamente 1450 árvores ha-1, entre 8 a 10 anos de idade, do projeto PPPIB (Produtividade Potencial do Pinus no Brasil), as quais estão localizadas em Jaguariaíva-PR, Ponta Grossa-PR, Rio Negrinho-SC e Três Barras-SC. O clima destas regiões é temperado úmido, com precipitação média anual de 1477mm, com temperaturas máxima, média e mínima de 24,3ºC, 17,9ºC e 12,7ºC. Todas as variáveis biométricas foram determinadas através do banco de dados de inventário (2006-2009), dados de cubagem, análise de tronco (discos), de anéis de crescimento (baguetas) e massa específica aparente (densitometria de raios-X). Coletaram-se solos (0-20cm) nas parcelas de inventário, e obtiveram-se os dados climáticos de estações meteorológicas locais. Através das análises de disco determinaram-se os índices de sítio (idade base 10 anos), e através da bagueta e densitometria de raios-X, estimaramse o padrão de crescimento de todas as parcelas em volume (m³ha-1) e matéria seca (Mgha-1) e seus Incrementos Médios Anuais e Correntes Anuais até o 9º ano. A uniformidade foi avaliada através do coeficiente de variação de volume das árvores dentro das parcelas (CVV) e da percentagem de biomassa em 50% das árvores mais finas (PB50), dos 2 aos 9 anos. As regiões apresentaram grande variação das propriedades físico-químicas do solo, como profundidade (30-140cm), teor de matéria orgânica (23 a 65g dm-3), teor de argila (20 a 85%), quantidade de N (500 a 5300kg ha- 1), e quantidade de P (9 a 84kg ha-1). Aos 9 anos de idade todas parcelas não haviam culminado seu crescimento, e o incremento médio anual com casca (IMAc9), o estoque de biomassa do lenho e índice de sítio de idade base 10 (IS10) variaram de 15 a 35m³ ha-1 ano-1, de 55 a 130Mg ha-1, e 12 a 19m, respectivamente, com maiores valores em Três Barras. Esta caracterização não era possível de ser detectada antes do 6º ano, mostrando que as decisões silviculturais ou genéticas precoces em Pinus precisam ser cuidadosamente consideradas. A produtividade (IMA) foi positivamente relacionada com o IS10, e ambos estiveram relacionados com os maiores teores de matéria orgânica do solo, quantidade de nitrogênio disponível e menores médias de temperatura mínima e déficit hídrico. As florestas mais produtivas se mostraram também mais uniformes (menores CVV e maiores PB50), mas confundidas com material genético superior. Assim, o estudo corrobora o papel dos nutrientes, solos de boa drenagem, e condição climática amena e com baixo déficit hídrico na explicação da elevada produtividade do P.taeda no sul do Brasil, comparativamente a sua região de origem. Baseado nestes resultados, estudos de fertilização, material genético e uso rotineiro de análise do tronco, associado à densitometria de raios-X, podem ser recomendados para o P. taeda.The study was designed to characterize the growth dynamics of Pinus taeda in south of Brazil and had the following objectives: i) determine the main edaphic, climatic and stand factors associated with the range in productivity of the species; and ii) characterize the growth patterns and uniformity, from planting until 9 years-old, across different edaphic and climatic regions. A total of 24 unthinned plots were selected (700m2), with stocking of 1450 trees ha-1, between 8 and 10 years old, from the PPPIB project (Pine Potential Productivity in Brazil), and are located in Jaguariaíva-PR, Ponta Grossa-PR, Rio Negrinho-SC and Três Barras-SC. The climate of these regions is temperate humid (Cfb), with mean annual precipitation of 1477mm, and maximum, mean and minimum temperatures of 24.3ºC, 17.9ºC e 12.7ºC. The biometric variables were assessed using inventory datasets (2006-2009), destructive sampling, bole analysis (disks), growth rings (stem coring), and specific gravity (X-ray densitometry). Soil samples (0-20cm) were collected on inventory plots, and climatic data were obtained from local weather stations. Site index (base age 10 years) were determined using bole disks, and growth patterns of all plots (m3ha-1), dry mass (Mgha-1), mean and current annual increments until 9th year were determined using stem coring and X-ray densitometry. Stand uniformity was evaluated using tree volume coefficient of variation within plots (CVV) and percentage of biomass for the 50% thinnest trees (PB50), from ages 2 to 9. Regions showed a wide range of soil physical and chemical properties, such as soil depth (30-140cm), organic matter levels (23 a 65g dm-3), clay content (20 a 85%), amount of N (500 a 5300kg ha-1), and amount of P (9 a 84kg ha-1). At 9 years old all the plots did not reached their maximum growth; and mean annual increment with bark (IMAc9), standing stem biomass and site index at base age 10 (IS10) ranged from 15 to 35m³ ha-1 year-1, 55 to 130Mg ha-1, and 12 a 19m, respectively, with higher values on Tres Barras region. This characterization was not possible to be detected before the 6th year, showing that early silvicultural and genetic decisions in Pinus need to be carefully considered. The productivity (IMAc9) was positively related with IS10, and both were related with higher levels of soil organic matter and available nitrogen, and with lower averages of minimum temperatures and water deficit. The most productive forests showed to be more uniform also (lower CVV and higher PB50), but confounded with superior genetic material. Therefore, the study corroborates with the role of nutrients, well drained soils, mild climatic conditions and low water deficit to explain the high yileds of P.taeda in Brazil, comparatively to its original region. Based on these results, studies of fertilization, genetic material and more frequent use of bole analysis, associated with X-ray densitometry, might be recommended for P. taeda.
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Redin, Cristina Gouvêa. "EFEITOS DO PASTOREIO SOBRE A VEGETAÇÃO NATURAL EM FRAGMENTO DE SAVANA ESTÉPICA PARQUE, RIO GRANDE DO SUL, BRASIL." Universidade Federal de Santa Maria, 2013. http://repositorio.ufsm.br/handle/1/8719.
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Despite occupying a prominent place in the southern flora, the region belonging to the State Park Espinilho inserted within Steppe Savanna Park domains still is poorly investigated by science. Vegetation characteristics such as dense herbaceous extract and the presence of isolated trees configure it as favorable to livestock activity. Taking advantage of this fact, the aimed of the present study was to analyze the floristic and edaphic changes imposed by grazing. For this we select two areas, one under grazing and other excluded from this activity for five years, both areas contain a sample unit of 2ha subdivided into 200 plots of 100m² subunits. An inventory of the woody and regenerating extract was conducted in 100 of these sampling units and the data of other variables were collected in 50 subunits. The dissertation was divided in two chapters with the objective of analyzing the similarity, the structural and floristic changes in regenerating and woody vegetation (Chapter I) and evaluate changes in physical properties of the soil and total aerial herbaceous biomass between areas, as well as investigating possible correlations between these variables and the abundance of the main species present in regeneration (Prosopis affinis Spreng. and Vachellia caven (Molina) Seigler & Ebinger (Chapter II). Through studies on structural and phytosociological attributes we can see remarkable differences between areas mainly on the diameter structure of vegetation and floristic composition of natural regeneration and being Vachellia caven the specie better adapted to grazing than Prosopis affinis. As a result expressed by Jaccard index, the similarity between areas is average (75%). Regarding the physical variables of soil and total aboveground herbaceous we found significant differences between areas evidenced by Student's T-tests. The Spearman correlation test show positive correlation between Vachellia caven and soil conditions on grazed area and negatively correlated to total aboveground biomass of herbaceous extract which proves its better adaptation to grazing and intolerance to more levels of soil shading. Based on exploratory ordination analyses (PCoA) we can infer that there is a big difference between the two study areas that were shaped by remarkable changes in soil physical components, herbaceous vegetation and abundance of Prosopis affinis and Vachellia caven occurring just over five years of exclusion.Apesar de ocupar lugar de destaque na flora sulina, a região pertencente ao Parque Estadual do Espinilho, inserido dentro dos domínios fitogeográficos da Savana Estépica Parque, ainda é pouco investigada pela ciência. Características da vegetação, tais como denso estrato herbáceo e a presença de árvores isoladas, configuram-na como propícia à atividade pecuarista. Valendo-se desse fato, o presente estudo objetivou analisar alterações florísticas e edáficas, impostas pelo pastoreio. Para tanto, foram selecionadas duas área de estudo, uma sob pastoreio e outra excluída dessa atividade a cinco anos, ambas contendo uma unidade amostral de 2 ha, subdividida em 200 subunidades amostrais de 100 m². Foi realizado inventário do estrato arbóreo e regenerante em 100 dessas subunidades amostrais e coleta de dados das demais variáveis em 50 subunidades. A dissertação foi dividida em dois capítulos com objetivos específicos de analisar a similaridade, alterações estruturais e florísticas na vegetação arbórea e regenerante (Capítulo I), avaliar alterações em propriedades físicas do solo e biomassa aérea total do estrato herbáceo entre as áreas, bem como investigar possíveis correlações entre essas variáveis e a abundância das principais espécies presentes na regeneração (Prosopis affinis Spreng. e Vachellia caven (Molina) Seigler & Ebinger) (Capítulo II). Por meio de estudos referentes a atributos fitossociológicos e estruturais, pode-se perceber notáveis diferenças entre as áreas, principalmente quanto à estrutura diamétrica da vegetação e composição florística da regeneração natural, sendo Vachellia caven a espécie melhor adaptada ao pastejo, ao contrário de Prosopis affinis. O resultado para similaridade entre as áreas, conforme expresso pelo índice de Jaccard, é de média similaridade (75%). Em relação às variáveis físicas do solo e biomassa aérea total do estrato herbáceo constataram-se diferenças significativas entre áreas, evidenciadas por meio de testes-T de Student. Os testes de correlação, realizados pelo método de Spearman, mostram que Vachellia caven correlaciona-se positivamente com condições de solo conferidas à área com pastoreio e negativamente com a biomassa aérea total do estrato herbáceo, o que comprova sua melhor adaptação ao pastoreio e intolerância aos maiores níveis de sombreamento do solo. É possível ainda inferir mediante análises exploratórias de ordenação (PCoA) que há uma total distinção entre as duas áreas de estudo, configurada pelas notáveis alterações ocorrentes ao longo de apenas cinco anos de exclusão nos componentes físicos do solo, estrato herbáceo e abundância de Prosopis affinis e Vachellia caven.
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Bey, Clarissa Rachel. "Scale-Dependent Environmental Influences on Linked Mussel-Fish Assemblages in Big Darby Creek, OH." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1376918254.
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Wraith, Jon M. "Soil Temperature Influence on Water Use and Yield Under Variable Irrigation." DigitalCommons@USU, 1989. https://digitalcommons.usu.edu/etd/1996.
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The need for efficient use of water resources has increased the importance of optimum soil water usage in agricultural systems. Soil temperature has been shown to be important in influencing the early development of many plant species. Many agricultural regions have suboptimal soil temperature regimes for plant growth, and some cultural practices have been shown to reduce near-surface soil temperatures. The seasonal influence of soil temperature on soil water extraction and aboveground and belowground plant growth under variable irrigation was investigated at the USU Greenville Farm in Logan, UT. Soil surface mulches and buried heat cables were used to modify soil temperature. A line-source sprinkler system provided a gradient of water application.
During 1987 yields were mainly influenced by irrigation. During 1988 greater soil temperature differences resulted in significant plant growth and yield responses. Soil water depletion corresponded to soil temperature treatments during the early part of the growing seasons. Depth of maximum soil water depletion was about 20 cm deeper for warm treatments. Water uptake rates of earlier-maturing plants in warm treatments were reduced later in the season, so that cumulative seasonal soil water depletion was similar for all temperature treatments. Although depth of rooting was somewhat greater under high than low irrigation during 1988, low irrigation treatments depleted soil water to greater depth. There was no interactive response of plant growth and yield or of soil water depletion to soil temperature and irrigation treatments.
Modifications were made to a computer simulation model of the soil-plant-atmosphere system in order to more mechanistically simulate plant water uptake and to include influences of soil temperature on seasonal rooting growth and soil water extraction. The model adequately simulated both the pattern and magnitude of soil temperature influences on soil water depletion, and conclusions drawn from model simulations agreed with field observations during 1987 and 1988.
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Muhl, Sara Ann. "Alien grass invasion of Renosterveld : influence of soil variable gradients." Thesis, Stellenbosch : Stellenbosch University, 2008. http://hdl.handle.net/10019.1/2991.
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Thesis (MScConsEcol (Conservation Ecology and Entomology))--Stellenbosch University, 2008.This thesis examines the role of agricultural activity in the process of invasion of west coast renosterveld fragments by annual alien grass species. This highly endangered vegetation type has less than 5% remaining, it is vital to understand the mechanisms allowing invasion of annual alien grasses in order to effectively prevent the loss of the many rare and endemic species found in west coast renosterveld. This study was divided into three major components. Firstly the distribution of indigenous and alien plant species in relation to fence lines, separating active agricultural fields from untransformed vegetation, was described. Regression analysis was used to test for relationships between distances from agricultural fields and soil physical and chemical characteristics in natural vegetation. Cover by annual alien invasive grasses in untransformed vegetation decreased significantly with distance away from agricultural land. Secondly alien and indigenous grass seed banks were sampled along the transects, at the same sites, in order to establish whether the seed banks correlated with above ground cover. Results varied among sites and seed banks were correlated with the vegetation cover at only one site. It appears that there are a multitude of factors determining the distribution of annual alien grass cover. Thirdly a greenhouse experiment established the role that nitrogen plays in the success of the alien grass Avena fatua. This species was grown in competition with three indigenous species, an annual forb (Dimorphotheca pluvialis), a geophyte (Oxalis purpurea) and an indigenous perennial grass (Tribolium uniolae) at three levels of soil nitrogen. The geophyte was largely unaffected, while growth of the annual and indigenous perennial grasses was negatively affected by competition with A. fatua. Nitrogen did not seem to affect competitive interactions. Management of these renosterveld patches, in order to conserve them effectively, will require a multi-faceted approach, including prevention of further invasion and removal of invasive grasses already present.
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Brown, Tabitha Therisa. "Variable rate nitrogen and seeding to improve nitrogen use efficiency." Thesis, Washington State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10043121.
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Increased nitrogen (N) fertilizer additions to modern agricultural cropping systems will be necessary to feed a growing world population. However, greater nitrogen use efficiency (NUE) is required if agroecosystems are to continue to provide certain ecosystem services (e.g., greenhouse gas emission reductions and water quality goals). The aim of this research was to investigate the role of variable rate N and seeding of winter wheat (Triticum aestivum) for optimizing yield-water-NUE relationships across heterogeneous landscapes. Field plot studies were conducted at the Cook Agronomy Farm (CAF) near Pullman, WA during the 2010, 2011 and 2012 winter wheat harvest years. A randomized complete block split plot N rate x seeding rate experiment with N fertilizer rate as main plot and seeding rate as subplot was employed across three landscape positions. Assessed were evidence of “haying-off”, depletion of available water resources, and the link between yield, protein, and NUE response to landscape by N fertilization rate by seeding rate treatment combinations. A performance classification was developed to evaluate wheat performance with regard to N utilization efficiency (Gw/Nt) and N uptake efficiency (Nt/Ns) components of the NUE.
Evidence of haying-off in winter wheat was medium to high for drier landscape positions, particularly during low precipitation years and likely occurs in these landscapes most years. Treatment impacts on NUE varied by year and landscape but overall NUE decreased by 14 to 22 kg grain yield per kg N supply as N rate increased from 0 to 160 kg N ha-1 across three landscape positions and two site years (2011 and 2012). Target NUE and maximum anthesis biomass could be achieved with a 34 to 68% reduction in typical seeding rates. The NUE-based performance classification was helpful in identifying environmental or management conditions contributing to low or high NUE indicating potential to be used as an evaluation tool. This research also included a policy fellowship focused on N2O emission reductions and greenhouse gas offset credits that could be generated from adoption of variable rate N for wheat and concluded that offset credits alone would not provide enough incentive for adoption of variable rate N.
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Reed, Philip Edward 1959. "A variable moduli probabilistic constitutive model for soils." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276754.
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Measurement of stress - strain relationships in soil systems usually incorporate varying degrees of uncertainty. These uncertainties arise from laboratory testing mechanisms, sampling disturbances, errors performed by operators or technicians performing the tests, etc. Currently, deformation analyses have been modeled using several deterministic techniques. However, because of the uncertainties involved, there is a need to adapt these numerical methods into probabilistic models. This thesis develops a probabilistic constitutive model based on a variable moduli deterministic technique. First-order, second-moment stochastic methods are used to estimate a mean stress - strain curve and its ±1 standard deviation from raw data obtained on nearly identical, remolded sand samples. Probabilistic estimations for Bulk and Shear moduli are determined from the estimated mean curves and are used to develop a probabilistic constitutive model. Through the use of a probabilistic constitutive matrix, a stochastic equation is produced which can relate strains to any stress state imposed on a particular soil. This is verified through an example.
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Turpin, Karine. "Macropore flow and soil hydraulic properties as affected by manurebiosolids injector implements under variable soil physical conditions." Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/27062.
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The aim of this study was to investigate, at various soil water contents, the tillage effects of two different types of injectors on soil hydraulic properties of a loamy clay soil located in Winchester, Ontario, Canada. The two injectors considered are the AerWay SSD (A) and the Kongskilde Vibro-Flex (K). The soil-properties changes associated with the injectors were assessed at ten different soil water contents for both injectors.
The first part of this research involves the evaluation of field saturated hydraulic conductivity (Kfs), matrix flux potential (&phis;m), bulk density (rhob) and volumetric water content (theta) for undisturbed soil (U) and for soil disturbed by injector (D). The field saturated hydraulic conductivities measured on disturbed soil for the Kongskilde (DK) were in 80% of the cases lower than those measured on undisturbed soil (UK). In contrast, Kfs measured on disturbed soil for the AerWay (DA) were higher in 90% of the cases. These results indicate that the Kongskilde reduces the infiltration capacity of the soil, which may be the result of reduced effective porosity via the smearing of the soil surface. They also indicate that the AerWay is facilitating infiltration, most likely by fracturing the soil surface.
The second part of this study involves a dye tracer experiment conducted on disturbed soil to evaluate the movement pathways of water through soil. In contrast to the AerWay, no relation could be established between liquid transport variables and the water content at which the Kongskilde was run. Greatest depths of penetration observed for the AerWay treatment occurred at run average water contents above 29.7 % vol. and below 19.7 % vol. Sorptive capacity of the upper layers was maximized when soil water contents were between 21.7 % vol. and 31.3 % vol.
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Norton, E. R., L. J. Clark, and H. Borrego. "Evaluation of Variable Rate Fertilizer Applications in an Arizona Cotton Production System." College of Agriculture, University of Arizona (Tucson, AZ), 2005. http://hdl.handle.net/10150/198174.
Full textAbstract:
A project was initiated in the 2004 cotton (Gossypium hirsutum) growing season in an effort to accomplish two major objectives. The first was to continue with phosphorus (P) fertilization evaluations that have taken place in the Upper Gila River Valley for the past four seasons by continuing to document the effects of P fertilization on crop yield and fiber quality. The second objective was to investigate the feasibility of utilizing a Global Positioning Systems (GPS) and Geographic Information Systems (GIS) technology for making variable rate (VR) applications of P fertilizers based upon yield data from the previous cropping season. Yield maps from a cotton picker mounted yield monitoring system were collected from the 2003 growing season and used to develop prescription applications of P fertilizers in the 2004 season. The project was established with four treatments including a control (Treatment 1 - 0 P fertilizer applied); a VR application treatment (Treatment 2 - received 52 lbs P/acre on average); a high Uniform Rate (UR) application (Treatment 3 - 75 lbs P/acre); and a low UR application (Treatment 4 - 45 lbs P/acre). These treatments were arranged in a randomized complete block design with four replications. The size of each experimental unit was 0.7 acres. Lint yield results indicated a positive response to applied P fertilizers with treatments 2, 3, and 4 producing significantly higher yields than the control. Lint yield was not significantly affected by fertilizer application technique. Yield differences among the treatments receiving P fertilizer were minimal, particularly among treatments 2 and 3. However, it is important to note that the amount of P fertilizer used in treatment 2 was reduced by 27% with the use of the VR application technique. This produces an approximate $7/acre savings to the grower. This project will be continued in the 2005 growing season and will be expanded to investigate VR application technology in nitrogen (N) fertilization also.
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Al-Yaari, Amen Mohammed. "Global-scale evaluation of a hydrological variable measured from space : SMOS satellite remote sensing soil moisture products." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066678/document.
Full textAbstract:
L'humidité du sol (SM) contrôle les bilans d’eau et d’énergie des surfaces continentales et joue ainsi un rôle clé dans les domaines de la météorologie, l'hydrologie et l'écologie. La communauté scientifique en télédétection micro-ondes a fait des efforts considérables pour établir des bases de données globales de l’humidité du sol en surface (SSM) découlant d'instruments micro-ondes actifs et passifs. Parmi ces instruments, SMOS (Soil Moisture and Ocean Salinity), lancé en 2009, est le premier satellite passif conçu spécifiquement pour mesurer SSM à partir d’observations en bande L (1.4 GHz) à l'échelle globale. La validation des données SMOS SSM sur différentes régions climatiques et pour des conditions environnementales variées est une étape indispensable avant qu’elles soient utilisées de manière opérationnelle. En effet, une meilleure connaissance de la précision des estimations de SSM et des incertitudes associées permettra non seulement d'améliorer les produits SMOS SSM, mais aussi d'optimiser les approches de fusion de données utilisées pour créer des produits multi-capteurs long terme. De tels produits sont développés dans le cadre du programme Climate Change Initiative (CCI) de l'Agence spatiale européenne (ESA) pour l’ensemble des variables climatiques essentielles (ECV), dont SSM. A la suite des chapitres d'introduction I à III, les résultats de cette thèse sont présentés en trois chapitres. Le chapitre IV présente une comparaison des produits SSM issus des capteurs passifs SMOS (bande L) et AMSR-E (bande C) en prenant pour référence les estimations SSM du système d'assimilation SM-DAS-2 du Centre Européen pour les Prévisions Météorologiques à Moyen Terme (CEPMMT). Cette évaluation est menée sur la période d’observation commune à SMOS et AMSR-E (2010- 2011), en utilisant des indicateurs classiques (corrélation, RMSD, Biais). En parallèle, le chapitre V présente une comparaison des produits SMOS SSM avec les produits SSM issus du capteur actif ASCAT en bande C en utilisant comme référence les simulations SSM d’un modèle des surfaces continentales (MERRA-Land), et en utilisant des indicateurs classiques, des méthodes statistiques avancées (triple collocation), et des diagrammes de Hovmöller sur la période 2010-2012. Ces deux évaluations ont montré que la densité de la végétation (paramétrée ici par l’indice foliaire LAI) est un facteur clé pour interpréter la cohérence entre le produit SMOS et les produits AMSR-E et ASCAT. Cet effet de la végétation a été quantifié pour la première fois à l’échelle globale pour les trois capteurs micro-ondes. Ces deux chapitres ont également montré que les trois capteurs SMOS, AMSR-E et ASCAT ont des performances complémentaires selon la densité de végétation et qu’il y a ainsi un potentiel intéressant en terme de fusion des jeux de données micro-ondes passifs et actifs. Dans le chapitre VI, avec l’objectif général d’étendre vers le passé les séries de données SSM de SMOSL3 et de développer un jeu de données SSM homogène sur 2003-2014, nous avons évalué l’utilisation d’une approche de régression linéaire multiple appliquée aux mesures de températures de brillance de AMSR-E (2003 - 2011). Les coefficients de régression ont été calibrés avec les produits SSM issus de SMOS sur 2010-2011. Le produit SSM résultant, qui fusionne les observations SMOS et AMSR-E, a été évalué par comparaison avec un produit SSM AMSR-E et les produits SSM MERRA-Land sur 2007-2009. Ces résultats préliminaires montrent que la méthode de régression linéaire est une approche simple et robuste pour construire un produit SSM réaliste en termes de variations temporelles et de valeurs absolues. En conclusion, cette thèse a montré que le potentiel de synergie entre les systèmes micro-ondes passifs (AMSR-E et SMOS) et actifs (ASCAT) est très prometteur pour le développement et l'amélioration de longues séries temporelles SSM à l'échelle mondiale, telles que celles produites dans le cadre du programme CCI de l'ESASoil moisture (SM) plays a key role in meteorology, hydrology, and ecology as it controls the evolution of various hydrological and energy balance processes. The community of scientists involved in the field of microwave remote sensing has made considerable efforts to build accurate estimates of surface SM (SSM), and global SSM datasets derived from active and passive microwave instruments have recently become available. Among them, SMOS (Soil Moisture and Ocean Salinity), launched in 2009, was the first ever passive satellite specifically designed to measure the SSM, at L-band (1.4 GHz), at the global scale. Validation of the SMOS SSM datasets over different climatic regions and environmental conditions is extremely important and a necessary step before they can be used. A better knowledge of the skill and uncertainties of the SSM retrievals will help not only to improve the individual products, but also to optimize the fusion schemes required to create long-term multi-sensor products, like the essential climate variable (ECV) SSM product generated within the European Space Agency’s (ESA's) Climate Change Initiative (CCI) program. After the introductory Chapters I to III, this dissertation consists of three main parts. Chap. IV of the dissertation evaluates the passive SMOS level 3 (SMOSL3) SSM products at L-band against the passive AMSR-E SSM at C-band by comparing them with a Land Data Assimilation System estimates (SM-DAS-2) produced by the European Centre for Medium Range Weather Forecasts (ECMWF). This was achieved over the common period 2010-2011 between SMOS and AMSR-E, using classical metrics (Correlation, RMSD, and Bias). In parallel, Chap. V of the dissertation evaluates the passive SMOSL3 products against the active ASCAT SSM at C-band by comparing them with land surface model simulations (MERRA-Land) using classical metrics, advanced statistical methods (triple collocation), and the Hovmöller diagram over the period 2010-2012. These two evaluations indicated that vegetation density (parameterized here by the leaf area index LAI) is a key factor to interpret the consistency between SMOS and the other remotely sensed products. This effect of the vegetation has been quantified for the first time at the global scale for the three microwave sensors. These two chapters also showed that both SMOS and ASCAT (AMSR-E) had complementary performances and, thus, have a potential for datasets fusion into long-term SSM records. In Chap. VI of the dissertation, with the general purpose to extend back the SMOSL3 SSM time series and to produce an homogeneous SM product over 2003-2014 based on SMOS and AMSR-E, we investigated the use of a multiple linear regression model based on bi-polarization (horizontal and vertical) brightness temperatures (TB) observations obtained from AMSR-E (2003 - 2011). The regression coefficients were calibrated using SMOSL3 SSM as a reference over the 2010-2011 period. The resulting merged SSM dataset was evaluated against an AMSR-E SSM retrievals and modelled SSM products (MERRA-Land) over 2007-2009. These first results show that the multi-linear regression method is a robust and simple approach to produce a realistic SSM product in terms of temporal variation and absolute values. In conclusion, this PhD showed that the potential synergy between the passive (AMSR-E and SMOS) and active (ASCAT) microwave systems at global scale is very promising for the development of improved, long-term SSM time series at global scale, such as those pursued by the ESA’s CCI program. It also provides new ideas on the way to merge the different SSM datasets with the aim of producing the CCI (phase 2) long-term series (a coherent "SMOS-AMSR-E" SSM time series for the period 2003 -2014), that will be evaluated further in the framework of on-going ESA projects
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Tsegaye, Tezera. "Modelling the effect of variable soil impedance on pea root growth." Thesis, University of Aberdeen, 1992. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU045142.
Full textAbstract:
Experiments were conducted: (i) to investigate varietal differences in pea (Pisum sativum L.) root response to mechanical impedance, (ii) to study the effect of mechanical impedance on root growth and morphology and (iii) to predict root growth in soils whose mechanical impedance varied temporally and spatially by adapting the Diggle (1988), ROOTMAP, model. Pea varieties whose root growth rates did not differ under unimpeded conditions had their root growth rates reduced by significantly different proportions in response to mechanical impedance. Highly significant correlations between first order lateral elongation rate and diameter were observed for pea roots grown in moist vermiculite. There was also evidence that regular stimulation of the root tip is required to trigger lateral emergence. An experimental procedure for obtaining ROOTMAP input parameters was devised and the growth and distribution of pea roots grown for 29 days in soil whose mechanical impedance varied with time and depth as a result of soil drying out, was successfully predicted. These findings highlight the potential that exists for selecting and breeding varieties based on root characters that confer insensitivity of response to mechanical impedance and for using ROOTMAP to investigate the growth response of different crop varieties in realistic soil scenarios.
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Cobb, Chester Ray. "Estimating Nitrogen Efficiency of Swine Lagoon Liquid Applied to Field Crops Using Continuously Variable Irrigation." NCSU, 2002. http://www.lib.ncsu.edu/theses/available/etd-05082002-125033/.
Full textAbstract:
Application of anaerobic swine (Sus scrofa domesticus) lagoon liquid onto cropland by irrigation is a common method of waste disposal and treatment. Currently, the application rate of swine lagoon liquid is based on the N concentration of the lagoon liqu id and the N required by the receiver crop to obtain a realistic yield. In North Carolina, only 50% of the total N in the swine lagoon liquid applied by irrigation is considered available for plant use during the first year after application. Uncertaint y exists as to whether this coefficient accurately predicts the amount of plant-available N. Therefore, research was conducted in the Coastal Plain of North Carolina to determine the efficiency of N uptake by corn (Zea mays L.) and soybean (Glycine max M errill) receiving swine lagoon liquid through irrigation. The line-source sprinkler irrigation method was used to provide a continuous variable N rate, ranging from 0 to 290 kg N/ha, across the field during 1999 and 2000. Ammonia volatilization losses r anged from 6 to 22% during irrigation. Crop yield and grain N recovered were affected more by the amount of liquid than N applied in 1999. Nitrogen recovered in grain in 1999 was <15% for both corn and soybean at 168 kg N/ha of either swine lagoon liqui d or ammonium nitrate. In 2000 at the 168 kg N/ha rate, grain N removal by corn, nonnodulating soybean, and nodulating soybean was 28, 25, and 39% from swine lagoon liquid and 45, 31, and 56% from ammonium nitrate. Based on yields and grain N removed by corn and nonnodulating soybean in 2000, N from applied swine lagoon liquid, accounting for N losses during irrigation, was about 70% as effective as ammonium nitrate. Symbiotic N2 fixation by the soybean was reduced by 60% when applied N reached 175 kg N/ha for both ammonium nitrate and swine lagoon liquid. While nodulating soybean removed more grain N than did either corn or nonnodulating soybean in 2000, soil inorganic N concentrations at the end of the growing season were higher for the nodulating s oybean. Therefore, it is not conclusive if soybean would be a better receiver crop than corn for swine lagoon liquid. Based on the results of this study, using the 50% available N coefficient of the lagoon liquid comes close to predicting plant-availabl e N when N losses during irrigation are around 25%. Nitrogen losses during irrigation can significantly affect plant-available N when applied N is based on the N concentrations of the lagoon liquid.
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Nolte, Kurt, Mark C. Siemens, and Pedro Andrade-Sanchez. "Integrating Variable Rate Technologies for Soil-applied Herbicides in Arizona Vegetable Production." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2011. http://hdl.handle.net/10150/146756.
Full textAbstract:
5 pp.Precision herbicide application is an effective tool for placing soil incorporated herbicides which have a tendency for soil adherence. And while field implementation depends on previous knowledge of soil textural variability (soil test and texture evaluations), site-specific technologies show promise for Arizona vegetable producers in non-uniform soils. Regardless of the method used for textural characterization, growers should keep in mind that textural differences do not change in the short/medium term, so the costs associated with defining texture-based management zones can be spread over many years.
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Manning, Grant Russell. "Relations between spatial variability of soil properties and grain yield response to nitrogen fertilizer in a variable Manitoba soil-landscape." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ45091.pdf.
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Brunke, Michael A., Patrick Broxton, Jon Pelletier, David Gochis, Pieter Hazenberg, David M. Lawrence, L. Ruby Leung, Guo-Yue Niu, Peter A. Troch, and Xubin Zeng. "Implementing and Evaluating Variable Soil Thickness in the Community Land Model, Version 4.5 (CLM4.5)." AMER METEOROLOGICAL SOC, 2016. http://hdl.handle.net/10150/612995.
Full textAbstract:
One of the recognized weaknesses of land surface models as used in weather and climate models is the assumption of constant soil thickness because of the lack of global estimates of bedrock depth. Using a 30-arc-s global dataset for the thickness of relatively porous, unconsolidated sediments over bedrock, spatial variation in soil thickness is included here in version 4.5 of the Community Land Model (CLM4.5). The number of soil layers for each grid cell is determined from the average soil depth for each 0.9 degrees latitude x 1.25 degrees longitude grid cell. The greatest changes in the simulation with variable soil thickness are to baseflow, with the annual minimum generally occurring earlier. Smaller changes are seen in latent heat flux and surface runoff primarily as a result of an increase in the annual cycle amplitude. These changes are related to soil moisture changes that are most substantial in locations with shallow bedrock. Total water storage (TWS) anomalies are not strongly affected over most river basins since most basins contain mostly deep soils, but TWS anomalies are substantially different for a river basin with more mountainous terrain. Additionally, the annual cycle in soil temperature is partially affected by including realistic soil thicknesses resulting from changes in the vertical profile of heat capacity and thermal conductivity. However, the largest changes to soil temperature are introduced by the soil moisture changes in the variable soil thickness simulation. This implementation of variable soil thickness represents a step forward in land surface model development.
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Svedin, Jeffrey David. "Characterizing the Spatial Variation of Crop Water Productivity for Variable-Rate Irrigation Management." BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/6878.
Full textAbstract:
Irrigated agriculture is the primary consumer of limited worldwide freshwater resources. Drought, growing world populations, and environmental demands compete with irrigation for freshwater resources"”threatening sustainable global food, fuel, and fiber production. This escalating global crisis demands that agriculture produce more food using less water. Traditional irrigation management has used technology to apply uniform irrigation rates across landscapes"”ignoring natural environmental variation. This provides inherent inefficiencies of over- or under- irrigation within individual fields. Variable-rate irrigation (VRI) is modern technology that employs global positioning systems and geographic information systems to match irrigation to spatially variable crop water demands within a field. Although commercially available, VRI lacks scientifically validated decision support systems to determine spatially and temporally variable crop water demand. The purpose of this research is to explore spatial and temporal variations in crop water demand to inform growers utilizing VRI. This research consists of four seasons of winter wheat (Triticum aestivum L.) production on a commercial farm in Idaho that employs a VRI system. In Chapter 1, the spatial variation of crop water productivity (CWP, the grain produced per unit of water consumed), is characterized for two seasons (2016-2017) and we propose a unique conceptual strategy for VRI management targeted at CWP. Observed CWP ranged from 4.1-21 kg ha-1 mm-1 with distinct spatial variation that, when considered together with grain yield, were shown to be useful for VRI management. During the 2017 growing season, VRI zones conserved 25% of irrigation compared to traditional uniform irrigation management. In the second chapter the spatial variation of soil water holding capacity (SWHC) was measured at 90 sampling points throughout the field. Then, during the 2016-2017 growing seasons, the spatial and temporal variation of soil moisture were modelled to characterize crop stress and its influence on grain yield. Soil within the field showed large spatial variation of SWHC, ranging from 147-369 mm. Under uniform irrigation in 2016, the natural variation of TAW created 21 day variation in the onset of crop stress throughout the field and under VRI in 2017 the onset of crop stress spanned 56 d. Surprisingly the variations in TAW did not statistically influence yield in 2016, and in 2017 the rate of irrigation predicted yield and TAW again did not statistically predict yield. This suggests that other environmental variables should be included when delineating irrigation zones and rates for VRI.
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Brouwers, Luke Bernhard. "Geotechnical Centrifuge Modelling of Variably Saturated Flow at The Soil-Rock Interface." Diss., University of Pretoria, 2017. http://hdl.handle.net/2263/63229.
Full textAbstract:
The underlying mechanisms governing unsaturated flow from soil into fractured rock in
the intermediate fractured vadose zone is still poorly understood despite occurring in
numerous areas of application. To gain a better understanding of these mechanisms, a
series of physical experiments using a geotechnical centrifuge are performed. The
centrifuge model comprises of two Perspex® sheets bent to form a clean smooth parallel
1mm aperture single discrete fracture that is inclined 90º, 75º and 60º from horizontal,
where dry sand is placed on top and water is supplied as continuous and intermittent
influx styles. The presence of the interface shows the development of perched water
system and saturated wetting front along the interface, which supports the capillarydominant
conceptual models for the fractured vadose zone. Breaching through the
interface occurred from preferential feeding pathways in the soil as multiple point
sources in the fracture and flow regimes composing of droplets, tendrils with droplet
formation and numerous types of rivulets indicating that fluxes within the fracture
range between 1 x 10-8 < Q < 1 x 10-4 m3/s per m. Changing the influx styles did not
alter the flow mechanisms occurring within the fracture. However, intermittent influx
did provide larger saturated wetting fronts along the interface while continuous influx
promotes flow instability within the fracture. Altering the fracture inclination influenced
the dominant flow mechanisms within the fracture but full saturation is never achieved
but rather only a potential 5 - 30% cross-sectional area contributes to flow, which
further decreases with depth due to merging of rivulets in upper regions of the fracture.
Although the results from the geotechnical centrifuge model may not be scaled to
prototype conditions due to similitude not being achieved between the Capillary and
Bond numbers, observations of breaching of the soil-rock interface, flow mechanisms
and flow instabilities within the fracture are similar in both the 1g and 20g experiments
indicating gravity driven flow instability maintains similitude and the geotechnical
centrifuge model offers a representative indication of natural conditions. The
contrasting support for both conceptual models regardless of fracture inclination
indicates that variably saturated flow at the soil-rock interface is a combination of the
two current conceptual models, with capillary flow dominating in soil material and the
dominant flow regime present within the fracture dependant on the interaction of
interfacial capillarity, gravitational and viscous forces. Ultimately the improved
conceptualisation and understanding gained from these experiments will benefit
hydrogeological as well as geotechnical areas of application such as hillslope hydrology,
contaminant transport, groundwater recharge, slope stability, differential settlement,
waste disposal, rock mass stress distributions, grouting and seepage into excavations.Dissertation (MSc)--University of Pretoria, 2017.
Water Research Commission
Geology
MSc
Unrestricted
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Dadfar, Humaira. "The influence of variable B horizon thickness (tonguing) on solute transport through undisturbed soil columns." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq24456.pdf.
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Aikio, S. (Sami). "Plant adaptive strategies in relation to variable resource availability, soil microbial processes and ecosystem development." Doctoral thesis, Oulun yliopisto, 2000. http://urn.fi/urn:isbn:9514256824.
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Abstract
Plants have evolved various adaptive strategies for balancing the benefits and costs of having a high affinity for resources, plasticity of growth allocation and mycorrhizal symbiosis. The relative growth rates of mycorrhizal and non-mycorrhizal plants were modelled for stable and variable nutrient availability. Mycorrhizal plants had higher growth rates at low and non-mycorrhizal plants at high nutrient availability. Variation in nutrient availability reduced the growth rate of mycorrhizal plants due to a high affinity for nutrients. However, mycorrhizal plants may be able to buffer against external fluctuations and therefore experience less environmental variation than non-mycorrhizal plants. Non-mycorrhizal plants may even benefit from variation.
The optimal allocation of growth between shoot and roots depends on the availability of energy and nutrients. The optimisation model predicted that the requirement for phenotypic plasticity of shoot/root allocation is greatest in environments with low resource availability. Plants with a high affinity for resources required more plasticity in order to tolerate variation than plants with a low affinity. The model predicted a trade-off between the ability to deplete resources and the ability to tolerate resource fluctuations.
Changes in the availability and ratio of resources lead to changes in the structure and composition of vegetation during primary succession. The field study of the forested phases of the land uplift island Hailuoto showed a successional change in the vegetation from the dominance of bryophytes and deciduous dwarf shrubs to dominance by lichens and evergreen dwarf shrubs. The humus layer became thinner and the availability of nutrients declined, while the C/N ratio of soil organic matter increased during succession indicating a decline in the quality of organic matter. The increased soil respiration rate indicates a successional increase in the energetic costs of decomposing organic matter.
Nutrients mediate both direct and indirect trophic interactions. Indirect interactions of nutrient cycling are not explicit in continuous time models. A transformation to a discrete time model was shown to make the indirect interactions explicit as transition probabilities and allowed their dynamic contribution to be evaluated with an elasticity analysis. The importance of indirect interactions was greater in tundra than temperate forest and increased with the rate of nutrient cycling.