Letteratura scientifica selezionata sul tema "Sandy top soil"

Soil survey and fertility capability classification (FCC) were carried out in an area mostly underlain by the beach ridge sands (BRS) parent material in Akwa Ibom State, Nigeria. The study applied the FCC in agricultural land use planning for efficient land management and optimal agricultural productivity of the beach soils. Field and laboratory data were obtained from 40 pedons located across eight Local Government Areas on the BRS parent material. From the results of field and laboratory studies, 11 FCC units were identified in the area. Based on similarities in certain soil profile characteristics, the 11 FCC units were grouped into four agro-ecological units (AEUs): (i) poorly drained FCC units with sandy topsoil over sandy subsoil, grouped to form AEU-A, covered 65.00% of study area; (ii) well drained FCC units with sandy topsoil over sandy subsoil, formed AEU-B and covered 22.50% of study area; (iii) poorly drained FCC units with sandy topsoil over loamy subsoil or loamy top- and sub- soils, formed AEU-C and covered 7.50% of study area; (iv) well drained FCC units with sandy topsoil over loamy subsoil, which formed AEU-D, occupied 5.00% of study area. The result of this study has shown that FCC can be employed as a simple but efficient tool in agricultural land use planning. Major soil profile characteristics used to differentiate land units within the beach sands area of Akwa Ibom State are drainage and texture.

The soil water behavior of sandy soils was studied under semiarid conditions in the Shendong mining area (China). The soil water content (θ) was measured under different depths and topographies using an HH2 moisture meter. The infiltration process was studied using a Guelph soil permeameter. A set of hydrodynamic variables was calculated in the laboratory. The θ of the first 20 cm was the lowest and increased with depth. The content of soil water increased from the top slope to the bottom slope. The infiltration experiments showed that the steady state infiltration rate was >40 mm h−1 in most cases. Owing to the higher contents of sand and soil macropores at the top of the slope and the top 0–20 cm of surface soil, the initial infiltration rate and steady infiltration rate were higher. The average available water capacity was 18.28%, which was consistent with the predominance of a sandy textural fraction. The results of a soil water retention curve and a rainfall simulation experiment showed that there was a low soil water retention capacity throughout the whole profile. This study contributes to the understanding of several aspects of the soil water behavior of sandy soils and provides key information for environmental management and land reclamation under semiarid conditions in the Shendong mining area.

Non-ionic surfactants have been well researched as a tool to ameliorate water repellent conditions. However, few studies have evaluated the risks and benefits of non-ionic surfactant applications in wettable soil. The objective of this study was to evaluate the effects of a surfactant in modifying the wetting pattern in soils of different textures and organic matter contents. The experimental treatments consisted of (1) four different soil textures including sandy, sandy loam, sandy clay loam and silt loam, (2) four different organic matter contents (0.2, 0.7, 1.2 and 1.7% by weight), and (3) irrigation water treatments with or without surfactant (IrrigAid Gold). The experiment was carried out in Plexiglas boxes with one drip emitter under the soil surface. The results demonstrated the superiority of surfactant application on increasing water distribution in the soil profile for all soil textural classes. Silt loam texture had the highest side wetted area and wetting depth 45min after the initiation of irrigation. Upward capillary water movement and top wetted area significantly decreased in the surfactant treatment across all soil textures except in sandy soil. As organic matter content increased, top wetted area decreased. These findings clarified the potential ability of surfactant in increasing water infiltration in non-repellent soil in an in vitro system.

SUMMARYEstimates on soil organic carbon (SOC) and nitrogen (N) stocks in soils cannot be directly calculated from routine soil analyses, since these often lack measurements on soil bulk density (Bd). Hence, flexible pedotransfer functions are required that allow the calculation of SOC stocks from gravimetrically determined SOC contents. The present paper aimed to: (1) quantify SOC and N stocks in grassland topsoils for a Northern Dutch region dominated by dairy farming and (2) analyse the relationships between SOC and bulk density at the field level. As estimates of SOC and N stocks are potentially affected by soil compaction, the combined measurements on soil bulk density and soil organic matter (SOM) were also evaluated with respect to critical limits for soil compaction using soil density (Sd) for sandy soils and packing density (Pd) for clay soils. The SOC and Bd measurements were done in the upper 0·1–0·2 m of grasslands at 18 dairy farms, distributed across sandy, clay and peat soils. Both farm data and grassland management data were collected. Non-linear regressions were used to analyse relationships between Bd and SOM. Significant non-linear relationships were found between gravimetric SOC contents and bulk density for the 0–0·1 m layer (R2=0·80) and the 0·1–0·2 m layer (R2=0·86). None of the fields on sandy soils or clay soils indicated signs for limited rooting in the topsoil although some fields appear to approach the critical limit for compaction for the 0·1–0·2 m layer. Stocks of SOC in the top 0·2 m at farm level were highest in the peat soils (21·7 kg/m2) and lowest in the sandy soils (9·0 kg/m2). Similarly, N stocks were highest for farms on peat soil (1·30 kg/m2) and lowest for farms on sandy soil (0·60 kg/m2). For the sandy soils, the mean SOC stock was significantly higher in fields with shallow groundwater tables.

The infiltration behaviour and physical properties of a hardsetting sandy loam soil at Cowra, N.S.W., following 2 years of different tillage treatments are reported. Soil that had not been cultivated for 25 years was also investigated at an adjacent pasture site. Infiltration of simulated rainfall at the end of the wheat-growing season gave moisture profiles that were quite different for cultivated, direct drilled and pasture soils. The moisture profile for the cultivated soil suggested the presence of an impeded layer which retarded the movement of infiltrated rain to the subsoil. Porosity measurements confirmed the presence of a layer with significantly fewer macropores (> 300 �m diameter) at the 50-100 mm depth in the cultivated soil, when compared with the direct drilled soil. The old pasture soil had significantly higher porosity (> 300 �m diameter) in the top 100 mm. Aggregate stabilities and organic carbon contents were measured in narrow increments to 150 mm depth for the three different soils, and revealed that a surface 25 mm layer of high organic carbon and highly stable macro-aggregates was present in the pasture and direct drilled soils but absent in the cultivated soil. The unstable surface layer in the conventionally cultivated soil was a consequence of the mixing and inverting action of cultivation and was not due to a net loss of organic carbon from the profile. The organic carbon content of the pasture soil was not significantly different from the direct drilled soil below 50 mm; however, it was significantly lower than the conventionally cultivated soil between 50 and 150 mm depth. These results indicate a need to adopt tillage practices that can preserve the top 25 mm layer of such fragile soils.

Development of Typic Haplorthods in a heathland area in Denmark responded over a short period of time (decades) to changes of vegetation. Part of the heath, Hjelm Hede, was left undisturbed and was invaded by trees, mainly oak and a few aspen and conifers. Another part of the heath was planted with Norway and Sitka spruce 60–70 yr ago. The soils under heath, oak and spruce were studied. Major differences were found, some visible in the field and others detectable in the laboratory. Under oak, relative to heath, horizon boundaries were less distinct, pH increased in the top horizons, organic carbon and C/N ratio decreased, and iron and aluminum contents in the upper B horizons decreased. Compared with the original heath podzol, the soil under spruce had a lower pH in the O, E and upper B horizons, higher organic carbon content and C/N ratio in the top horizons, increased cementation, and a placic horizon. However the pyrophosphate-extractable iron and aluminum content was significantly lower than in any of the other soils. The soil under oak showed "depodzolization" features, whereas the soil under spruce was increasingly podzolized, though the podzolization mechanism might be different from that under heath. Analyses of phenolic compounds in the soil water were consistent with these conclusions. The three main components of substituted benzoic acids were gallic acid, protocatechuic acid and coumaric acid, which are all strongly complexing agents believed to take part in the podzolization process. Generally, the highest concentrations were found under spruce and the lowest under oak.Key words: Vegetation-induced soil changes, Spodosols, phenolic compounds

The %C within the top sandy 0.15 m of a sodic Hydrosol under native trees consisted of a constant %C in uncharged organic matter and a %C in negatively charged organic matter decreasing linearly with depth, as did the specific volume of the soil. The kaolinitic clay present was strongly bonded together. In an adjoining canefield cleared 10 years earlier, incorporation of burnt cane residues to 0.35 m had more than doubled the CEC of the soil, but had not generated structural porosity. The clay in the top 0.15 m remained strongly bonded together. The rate of increase in the specific volume of the sandy soil under trees with %C was twice that reported for surface aggregates of a silty soil from rotation plots on a Chromosol, and of sectioned clay cores from a Ferrosol under softwood scrub.The rate of increase in the specific volume of pores ≤30 μm diameter with %C was measured by the water retention of aggregates at 10 kPa suction, and was 50% more for the sandy soil than for the silty soil. The difference is ascribed to the dominance of mycorrhizal fungi under trees compared with bacteria under grass. Both agents are presumed to link particles together through acidic polysaccharide gel. Subsequent air-drying then leaves pores stable to wetting and drying. It is suggested that the increase in the plastic limit of silty soils is mainly due to pores stabilised in this way. Pores in decomposing plant residues coated with inorganics could also contribute.

Abstract. Several simple soil water models with four layers or less, typical of those used in GCMS, are compared to a complex multilayered model. They are tested by applying a repeating wetting/drying cycle at different frequencies, and run to equilibrium. The ability of the simple soil models to reproduce the results of the multilayer model vary according to the frequency of the forcing cycle, the soil type, the number of layers and the depth of the top layer of the model. The best overall performance was from the four layer model. The two layer model with a thin top layer (0.1 m) modelled sandy soils well while the two layer model with a thick top layer (0.5 m) modelled clay soils well. The model with just one layer overestimated evaporation during long drying periods for all soil types.

Abstract This research article represents the recompacted dense sand sample behaviour and stress distribution in the direct shear box. In Lithuania, sand is quite common on a construction site, in general about 32%. To reduce the influence of the shear box design on the experimentally determined values of the soil strength parameters, it is necessary to know the regularities of the change of the normal load acting in the shear plane. Three different normal stresses of 50, 100, and 200 kPa were applied to the dense sand in the direct shear boxes during experimental and numerical simulation. The results showed an obvious evidence of non-uniformity of stress for standard and raised specimens. The numerical analysis exhibited that when the sample is loaded only with a vertical load, approximately 75% of that load is transferred to the sample bottom, 84% to the shear plane, and 95% to the top. At the end of the shear test, the vertical force in the shear plane reaches maximum, the normal stress is higher by 13.5% than applied on the sample top. The shear strength of sandy soils were influenced by box size and sample height too. The improved shear box apparatus allows to estimate the vertical load at shear plane.

Universal soil loss equation (USLE) soil erodibility (K) factors were computed from drumlin soils in the Cape Caribou River area, Labrador. Soil erodibility variation was investigated, using Mann-Whitney and Kruskal-Wallis tests, for three stratifications: (i) topographic position (TOP), (ii) mineral soil horizon (HOR), and (iii) soil texture (TEX). Topographic position with two substrata, drumlin summits (SUM) and drumlin side slopes (SID), was not significant. Horizons A, B and C and textural classes loamy sands (LS), sandy loams (SL) and loams (L) were significant. A log linear likelihood chi-square (G2) model was applied to investigate relationships of HOR and TEX. Partitioning of the G2 statistic revealed both significant and non-significant cells in the cross tabulation. Some sampling considerations for the determination of K factors are discussed. It is concluded that accepted field methods could enhance K factor determination in Labrador forest soil environments. Key words: Soil erodibility, K factor, drumlins, Labrador

Humans are modifying animal populations, indirectly accelerating or reducing the geomorphic alterations caused by animals. Species have been monitored and studied with focus on domesticated animals but little research has been undertaken on wild animals. This study analyses the geomorphic impact of elephants on Tembe Elephant Park, so that the changes they cause to the landscape may be quantified. To conduct this research four sites were chosen: an area where elephants had been excluded for twenty-five years, where excluded for five years, where elephants exist at present and where elephants mud wallow. Three of the four study sites were classed as sand forest (twenty-five-years exclusion, five-years exclusion and where elephants exist) and were analysed and compared to determine the similarities and differences in climate, microclimate, vegetation and the soil’s physical and chemical properties. The wallow site was not compared to any other study site, but was observed and mapped to quantify the geomorphic impact of elephants wallowing. When the sand forest sites were compared the climate, vegetation type and soil were found to be similar. Where elephants were present: the vegetation was inconsistent in basil cover, canopy height, structure and class. Soils were more compacted with a low infiltration rate, higher temperature, lower soil moisture, higher pH and a lower electric conductivity and air relative humidity was the highest. Where elephants have been excluded for twenty-five years, the opposite trends arose from the data analysis. The vegetation was consistent in basil cover, canopy height, structure and class, and the soils were less compacted with a high infiltration rate, low temperature, higher soil moisture, lower pH and a higher electric conductivity. The microclimate showed a trend where the air relative humidity was the lowest. At the elephant wallow site data showed that the wallows were in general circular in shape, 52.5m3 of soil was removed per month for the last nine months and the surface area of the wallows increased by 165.5m2 per month for nine months from April to December 2008. All the results from this study show that the elephant activity in Tembe Elephant Park has geomorphic consequences. From the results, it is possible to conclude that the geomorphic impacts of elephants on Tembe Elephant Park are contributing to a nutrient cycle shift in the sand forest biome, as they change aspects of the vegetation, microclimate, soil and landscape, which are the foundation of the cycle.
Dissertation (MA)--University of Pretoria, 2011.
Geography, Geoinformatics and Meteorology
MA
Unrestricted

Organic matter decomposition in terrestrial system is of vital importance for nutrient cycling and ecosystem function. Soil microorganisms are the key drivers of decomposition which regulates the availability of inorganic nutrients through immobilisation and mineralisation. The size of the soil organic C pool is twice that of C in the atmosphere and more than twice of that in vegetation. Thus, organic matter decomposition in soil greatly influences the C flux between soil and the atmosphere. Therefore understanding factors influencing organic matter decomposition is important for climate change mitigation and soil fertility. In this thesis, the effects of residue mixing, removal of water-extractable organic C, clay subsoil addition to sandy soil and drying and rewetting on decomposition were investigated. Organic matter decomposition is influenced by both internal and environmental factors. Plant residues are an important source of soil organic C and decomposition of plant residues has been studied extensively. However, residues from different species or above- and below-ground residues are often mixed and less is known about factors influencing decomposition of residue mixtures. Shoot and root residues of three Australian native perennial grass species [Wallaby grass (Danthonia sp); Stipa sp and Kangaroo grass (Themeda triandra)] and barley (Hordeum vulgare L.) were mixed to create nine different residue mixtures (1:1 mixture). Soil respiration was measured over 18 days. Cumulative respiration in residue mixtures differed from the expected value (average of cumulative respiration of individual residues) in most cases with synergistic interactions occurring in 56 % of the mixtures (expected < measured value), antagonism in 22 % (expected > measured value). Synergism occurred when residues with relative similar decomposition rate were mixed, while antagonism occurred when the decomposition rate of individual residues differed strongly. Furthermore, a negative correlation was found between the change in microbial biomass C (MBC) and available N concentration between the start of the experiment and day 18 and cumulative respiration on day 18. The interaction with respect to cumulative respiration was not reflected in MBC and available N concentrations. Cumulative respiration and MBC concentration were greater in soil amended with residues with higher water-extractable organic C (WEOC) concentration, compared to those with lower WEOC concentration, either individually or as in mixtures. Between 2 and 30 % of organic C in residues is water-extractable and its importance in stimulating decomposition has been shown previously. Water-extractable organic C can be leached by heavy rainfall or irrigation, but little is known about the effect of addition of residues from which the WEOC was removed by extraction or leaching on microbial activity and biomass. Shoot residues of barley (Hordeum vulgare L.) were extracted five times for maximal removal of WEOC or were leached up to eight times to partially remove WEOC. Maximum WEOC removal decreased both soil respiration and MBC concentration in the first week, but MBC concentration at the end of the experiment was greater with extracted residues compared to the original residues. With leached residues, partial removal also reduced respiration rate in the first 10 days. However, MBC concentration was greatest with residue leached eight times, suggesting great substrates utilisation efficiency. In South Australia a large area of land is covered by sandy soils (3.2 million ha), with a heavy textured soil underneath, so called ‘duplex soil’. Due to the lack of binding sites for organic matter and nutrients and large pore size, sandy soils are often characterised by low organic matter content, low nutrient and water retention capacity and rapid organic matter decomposition. Addition of clay-rich subsoil to sandy soil has been shown to increase crop yield and water retention in sandy soils. Additionally, clay particles could bind organic matter. However, little is known about the effect of clay subsoil addition to sandy soil on soil respiration after addition of residue mixtures. Clay subsoil was added to a sandy top soil at 10 and 30 % (w/w). Residues of barley (Hordeum vulgare L.) and two native perennial grass species (Danthonia sp and Themeda triandra) were added individually or as 1:1 mixture. Increasing clay addition decreased cumulative respiration and extractable C concentration in soil with individual residues and mixtures. No interaction was observed in terms of cumulative respiration in sandy soil alone, but at addition of 10 % clay subsoil, antagonism occurred in two residue mixtures, and at 30 % clay addition synergism occurred in one of the mixtures. It can be concluded that clay soil addition to sandy soil does not only alter decomposition rate but also interactions in residue mixtures. In Mediterranean climate such as in South Australia long periods of dry and hot weather are interrupted by occasional rainfall or irrigation. Although the effect of drying and rewetting (DRW) has been studied extensively, the factors determining the respiration flush upon rewetting and total cumulative respiration are not fully understood. A sandy soil amended with different proportion of clay subsoil (0, 5, 10, 20, 30, and 40 %) was exposed to a single DRW event. Expressed per g soil, cumulative respiration in the constantly moist control (CM) decreased with increasing clay soil addition rate, but cumulative respiration in the DRW treatment did not vary among clay soil treatments. However, when expressed per g total organic C (TOC), cumulative respiration in the DRW treatment increased with increasing clay subsoil addition rate. Addition of clay subsoil increased water retention capacity during drying, thus microbial activity. The respiration flush one day after rewetting was greater than the respiration rate in CM only in treatments with 20-40 % clay addition rate. The response of respiration to DRW may be influenced by land management due to its effect on the soil organic C pool and differ between soil size fractions. An incubation experiment was conducted with soils collected from two plots with a long history of different management (wheat-fallow rotation and permanent pasture). The soils were sieved to 4-10 mm and <2 mm to obtain two size factions. There were five moisture treatments with the same length (48 days). The CM treatment was maintained at 50 % of maximum water-holding capacity (WHC) throughout. In the DRW treatments, the number of dry and moist days was equal but the number of DRW events ranged from one to four (1 to 4DRW). Cumulative respiration per g TOC at the end of the experiment was greater in the <2 mm than in the 4-10 mm fraction in both soils and was highest in CM and 1DRW. In wheat soil, cumulative respiration decreased from 1DRW to 3DRW, whereas it decreased only between 2 to 3DRW in pasture soil. Cumulative respiration in the second moist period was greater in 3DRW than in 2DRW (8 and 12 prior moist days) whereas cumulative respiration in the third moist period was greater in 4DRW than in 3DRW (12 and 16 prior moist days). It can be concluded that the response of respiration to drying and rewetting is more strongly influenced by management than size fraction. Cumulative respiration upon rewetting is influenced not only by the number of DRW cycles but also the number of moist days prior to rewetting. Three incubation experiments were carried out to assess the relationship between cumulative respiration per g TOC and the number of moist or dry days with the two soils used in the previous experiment. In the first experiment, the CM and DRW treatments had the same total length (10 days) with different proportions of moist and dry days in the DRW treatments. The second and third experiment had DRW cycles of dry and moist period of equal length with one cycle in Experiment 2 and two cycles in Experiment 3. Soil in the CM was maintained at 50 % of WHC throughout for all experiments. Total cumulative respiration per g TOC was greater in wheat than in pasture soil which can be explained by the greater proportion of particulate organic matter in the former. In the first experiment, cumulative respiration in the dry period was not influenced by the number of dry days, but cumulative respiration in moist period increased with number of moist days. Total cumulative respiration in the DRW cycle was negatively correlated with the number of dry days and positively correlated with the number of moist days. Cumulative respiration in DRW treatments was lower than in CM when the proportion of moist days was less than 50 % of the total length with the difference becoming greater with decreasing proportion of moist days. In both the second and the third experiment, total cumulative respiration increased with increasing number of days with a greater increase in CM than in DRW treatments. When subjected to two DRW cycles in the third experiment, total cumulative respiration in each DRW cycle was also positively correlated with the number of moist days with the slope greater in first than in the second DRW cycle. In conclusion, cumulative respiration in DRW cycles is mainly a function of the number or proportion of moist days and little influenced by soil management. An incubation experiment was conducted with the soil from the wheat-fallow rotation to determine the influence of number of dry and moist days and their distribution in two DRW cycles on respiration rate and cumulative respiration in each DRW cycle. The number of moist and dry days ranged in either the first or second DRW cycle between 10 and 35. The constantly moist treatments were maintained at 70 % of WHC throughout. Cumulative respiration in CM was greater than that in DRW treatments with the difference greater in treatments with varying number of dry days than those with varying number of moist days. Cumulative respiration in the dry period differed little among DRW treatments. The flush of respiration upon rewetting increased with number of prior dry days. Respiration rates in the moist period of the first cycle were higher than in the second cycle only up to 17 days, indicating that the effect of prior substrate utilisation in 5 moist days in the first cycle is limited to first 17 days in the moist period of second cycle. Cumulative respiration in the moist period increased with the number of prior dry or moist days with the increase greater in treatments varying in number of moist days than those varying in number of dry days. Cumulative respiration was greater when the number of moist or dry days varied in the first than in the second cycle. It is concluded that the number of dry days influences the size of the respiration flush after rewetting, while the number and distribution of moist days affect cumulative respiration. To summarise, the studies described in this thesis showed: • Cumulative respiration in residue mixtures relative to that of the individual residues depends on residue type and soil clay content. • Removal of WEOC from residues reduces initial respiration rates but not always cumulative respiration. • Addition of clay to sandy soil not only reduces cumulative respiration but also alters respiration in dry and moist periods of DRW cycles. • Cumulative respiration in DRW treatments is mainly influenced by the length of the moist period: (i) total length of the moist period determines total cumulative respiration at the end of the DRW treatments, and (ii) number of prior moist days influences respiration in the subsequent cycles.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2015

The static cone penetration tests are quite extensively used for carrying out in-situ geotechnical investigations both for onshore and offshore sites especially where the soil mass is expected to comprise of either soft to medium stiff clays or loose to medium dense sands. The wide use of the cone penetration tests (CPT) in geotechnical engineering has resulted in a great demand for developing necessary correlations between the cone penetration resistance and different engineering properties of soils. The successful interpretation of the cone penetration test data depends mainly on the various empirical correlations which are often derived with the help of a controlled testing in calibration chambers. The calibration chambers have been deployed in various sizes (diameter varying from 0.55 m to 2.10 m) by a number of researchers. It is quite an expensive and time consuming exercise to carry out controlled tests in a large size calibration chamber. The task becomes even much more difficult when a sample comprising of either silt or clay has to be prepared. As a result, most of the reported cone penetration tests in calibration chambers are mainly performed in a sandy material. Taking into account the various difficulties associated with performing tests in large calibration chambers, in the present study, it is attempted to make use of a miniature static cone penetrometer having a diameter of 19.5 mm. This cone was gradually penetrated at a uniform rate in a triaxial cell in which a soil sample of a given material was prepared; the diameter of the cone was intentionally chosen smaller so that the ratio of the diameter of the cell to that of the cone becomes a little larger. Two different diameters of the cells, namely, 91 mm and 140 mm, were used to explore the effect of the ratio of chamber (cell) size to that of the cone size. In addition, the rate of penetration rate was also varied from 0.6 mm/minute to 6.0 mm/minute (the maximum possible rate for the chosen triaxial machine with the larger cell) to examine the effect of the rate of the penetration of the miniature cone on the tip resistance. By using the chosen experimental setup, a large number of static miniature cone penetrometer tests were carried out on four different materials, namely, (i) clean sand, (ii) sand with 15% silt, (iii) sand with 25% silt, and (iv) sand with 15% fly ash. The cone tip resistance for each material was obtained for a wide range of three different relative densities. The effective vertical pressure (σv) for the tests on different samples was varied in between 100 kPa and 300 kPa. The variations of the tip resistance with axial deformation in all the cases were monitored so as to find the magnitude of the ultimate tip resistance. In contrast to the standard cone, the diameter of the piston shaft was intentionally kept a little smaller than that of the cone itself so as to restrict the development of the piston resistance. For each cell (chamber) size, two different sizes of the pistons were used to assess the resistance offered by the penetration of the piston shaft itself. It was noted that the resistance offered by the chosen piston shaft is not very substantial as compared to that of the cone tip itself. Most of the experimental observations noted from the present experiments were similar to those made by the penetration of the standard size cone in a large calibration chamber. The ultimate tip resistance of the cone was found to increase invariably with an increase in the magnitude of σv. An increase in the relative density of the soil mass leads to an increase in the value of qcu. For the same range of relative densities, an addition of fly ash in the sample of sand, leads to a considerable reduction in the magnitude of qcu. Even with the addition of 25% silt, the values of qcu were found to become generally lower as compared to clean sand and sand added with 15% silt. An employment of a larger ratio of the diameter of the cell to that of the miniature cone leads to an increased magnitude of qcu. An increase in the penetration rate from 0.6 mm/min to 6.0 mm/min, was found to cause a little increase in the magnitude of qcu especially for sand added with fly ash and silt. The effect of the penetration rate on the results was found to increase continuously with a reduction in the rate of penetration. At higher penetration rates, in a range closer to those normally employed in the field (20 mm/sec), it is expected that the rate of penetration of the cone will not have any substantial effects on the magnitude of qcu for clean sands. The magnitude of qcu obtained in this thesis at different values of σv for all the cases with the use of the miniature cone were compared with the two widely used correlations in literature. It is found that except for dense sands, in most of the cases, the present experimental data lie generally in between the two correlation curves from literature; for dense sands the measured values of qcu were found to be significantly lower than the chosen correlation curves. It was noted that with the use of the miniature cone penetrated in a given sample prepared in a triaxial cell, it is possible to obtain reasonably an accurate estimate of the tip resistance of the standard cone especially for loose to medium dense states of all the materials. Further, from the analysis of all the tests results, it was noted that approximately a linear correlation between qcu/σv and soil friction angle (φ) for different chosen materials exists provided the dependency of the φ on the stress level is taken into account. As compared to the standard cone penetrometer which is usually employed in the field, the miniature cone used in this study is expected to provide a little conservative estimate, of the tip resistance of the standard static cone penetrometer with reference to the different materials used in this study on account of the facts that (i) there is a reduced area behind the cone, (ii) the ratio of the diameter of the calibration chamber (cell) to that of cone is not very high, (iii) the chosen size of the cone is smaller than the standard cone, and (iv) the chosen penetration rate is much smaller than the standard rate of penetration. Further, in the case of clean sand, an attempt has also been made in this thesis, with the help of a number of direct shear tests at different stress levels, to generate an expression correlating peak friction angle, critical state friction angle, relative density of sand and vertical effective stress. A correlation has been generated with the help of which, the value of peak dilatancy angle can be obtained from the known values of peak friction angle and critical state friction angle. In confirmation with the available information in literature, this exercise on clean sand has clearly indicated that a decrease in the magnitude of vertical effective stress leads to an increase in the values of both peak friction angles and peak dilatancy angles.

A research program was undertaken to quantify the effect of flow induced erosion on the stability of natural river banks along the Red River in Manitoba. The Erosion Measurement Device (EMD) was designed and built in the Geotechnical Laboratory of University of Manitoba to approximate the erosion rate profiles of soil samples from nine sites along the RedRiver. Two simulations of a natural flood event and one of the same flood with the operation of the Floodway were then used to determine the difference in the lower toe erosion and the slopes reduction of the global factor of safety. These results indicate that the operation of the Floodway does not have negative impact on the stability of river banks upstream of the Floodway inlet.

Soil Essentials is a practical reference for farmers and land managers covering soil issues commonly encountered at the farm level. Written in a straightforward style, it explains the principles of soil management and the interpretation of soil tests, and how to use this information to address long-term soil and enterprise viability. This book demonstrates how minerals, trace elements, organic matter, soil organisms and fertilisers affect soil, plant and animal health. It shows how to recognise soil decline, and how to repair soils affected by nutrient imbalances, depleted soil microbiology, soil erosion, compaction, structural decline, soil sodicity and salinity. The major problem-soils – sodic soils, light sandy soils, heavy clay soils and acid sulphate soils – are all examined. With this information, farmers and land managers will be able to consider the costs and financial benefits of good soil management.

The Australian Soil Classification provides a framework for organising knowledge about Australian soils by allocating soils to classes via a key. Since its publication in 1996, this book has been widely adopted and formally endorsed as the official national system. It has provided a means of communication among scientists and land managers and has proven to be of particular value in land resource survey and research programs, environmental studies and education. Classification is a basic requirement of all science and needs to be periodically revised as knowledge increases. This third edition of The Australian Soil Classification includes updates from a working group of the National Committee on Soil and Terrain (NCST). The main change in this edition accommodates new knowledge and understanding of the significance, nature, distribution and refined testing for soils comprising deep sands, leading to the inclusion of a new Order, the Arenosols. The introduction of the Arenosols Order led to a review and changes to Calcarosols, Tenosols and Rudosols. The Australian Soil Classification is Volume 4 in the Australian Soil and Land Survey Handbooks Series.

Framboids may be the most astonishing and abundant natural features you have never heard of. These microscopic spherules of golden pyrite consist of thousands of even smaller microcrystals, often arranged in stunning geometric arrays. There are probably 10³⁰ on Earth, and they are forming at a rate of 10²⁰ every second. This means that there are a billion times more framboids than sand grains on Earth, and a million times more framboids than stars in the observable universe. They are all around us: they can be found in rocks of all ages and in present-day sediments, soils, and natural waters. The sulfur in the pyrite is mainly produced by bacteria, and many framboids contain organic matter. They are formed through burst nucleation of supersaturated solutions of iron and sulfide, followed by limited crystal growth in diffusion-dominated stagnant sediments. The framboids self-assemble as surface free energy is minimized and the microcrystals are attracted to each other by surface forces. Self-organization occurs through entropy maximization, and the microcrystals rotate into their final positions through Brownian motion. The final shape of the framboids is often actually polygonal or partially facetted rather than spherical, as icosahedral microcrystal packing develops. Their average diameter is around 6 microns and the average microcrystal size is about 0.1 microns. There is no significant change in these dimensions with time: the framboid is an exceptionally stable structure, and the oldest may be 2.9 billion years old. This means that they provide samples of the chemistry of ancient environments.

AbstractTo better understand the depositional context of Late Pleistocene human tracks found at archaeology site EjTa-4 on Calvert Island, on the Pacific Coast of Canada, we present here the results of an experiment designed to recreate the conditions by which these tracks were formed, preserved and then revealed through excavation. Based on radiocarbon ages on small twigs and the analysis of sediments and microfossils, the interpretation of the site formation processes relate that the tracks were impressed into a clayey soil substrate just above the high tide line between 13,317 and 12,633 calBP. The features were subsequently encapsulated by black sand, which washed over the tracks from the nearby intertidal zone during a storm event. To test this interpretation, we enlisted the aid of high school student volunteers to recreate the conditions by which the tracks were formed. A clayey substrate was prepared in a laboratory setting at the University of Victoria and a few plant macrofossils were placed on top it. This was followed by having the students create tracks in the clay, which were then covered with a layer of sand. Upon excavation of these experimental tracks, we found that they had a very similar character to those found in the field, including the pressing of macrofossils into the clay by the weight of the track maker. These results support the interpretation and chronological assessment of the depositional events that occurred during late Pleistocene times at archaeology site EjTa-4.

Before I went to Bihar I knew little about embankments. I had seen levees in California, in the Sacramento–San Joaquin Delta and in the Central Valley. There, if you stand on an embankment on one side of the river, you can look across and see a matching embankment. Some have been set back from the river a half of a mile or so; but even then it is easy to grasp in a glance the relatively linear triad of a river and its pair of embankments. The first embankment I saw in Bihar after miles of bumping along in the back seat of a gray Tata Sumo SUV in the April heat was a steep-sided loaf of sand, maybe twelve feet above the adjacent land. I scrambled to the top and looked around. The Kamla River glared below, reflecting a hazy but intense sun. It flowed lazily between the embankment and a wide stretch of sand a few inches above the water. Together the water and the sandbank narrowed as they receded into the distance. I didn’t see another embankment. I was disoriented by the incessantly jarring ride and the heat, but I recall asking where the other embankment was. A gesture directed my eyes toward the horizon of low trees and brush and sandy soil. Nothing was very distinguishable in the monochromatic haze of dust and heat. Over the next two days my eyes and brain continued to struggle in vain to make sense of what I was seeing by comparing the north Indian state of Bihar to California. California rivers are powerful and can flood portions of the flat Central Valley, but they are in no way comparable to the rivers that rush out of the towering Himalaya. The Sierra Nevada ranges from five to twelve thousand feet. At twelve thousand feet in the Himalaya, one is still in the “middle hills,” where in spring there are forests of rhododendron trees blooming.

In reality, there can be no generic definition of an “ideal soil” because a soil’s performance is influenced by the local climate, landscape characteristics, grape variety, and cultural practices and is judged in the context of a winegrower’s objectives for style of wine to be made, market potential, and profitability of the enterprise. This realization essentially acknowledges the long-established French concept of terroir: that the distinctiveness or typicity of wines produced in individual locations depends on a complex interaction of biophysical and human cultural factors, interpreted by many as meaning a wine’s sense of place. As discussed in “Soil Variability and the Concept of Terroir” in chapter 1, because of this interaction of factors that determine a particular terroir, it is not surprising that no specific relationships between one or more soil properties and wine typicity have been unequivocally demonstrated. While acknowledging this conclusion, it is still worthwhile to examine how variations in several single or combined soil properties can influence vine performance and fruit character. These properties are: • Soil depth • Soil structure and water supply • Soil strength • Soil chemistry and nutrient supply • Soil organisms Provided there are no subsoil constraints, the natural tendency of long-lived Vitis vinifera, on own roots or rootstocks, to root deeply and extensively gives it access to a potentially large store of water and nutrients. In sandy and gravely soils that are naturally low in nutrients, such as in the Médoc region of France, the Margaret River region in Western Australia, and the Wairau River plain, Marlborough region, New Zealand, the deeper the soil the better. A similar situation pertains on the deep sandy soils on granite in the Cauquenas region, Chile. However, such depth may be a disadvantage where soils are naturally fertile and rain is plentiful, as in parts of the Mornington Peninsula, King and Yarra Valley regions, Victoria, Australia, and the Willamette Valley region in Oregon (see figure 1.11, chapter 1), because vine growth is too vigorous and not in balance.

Shallow foundation structures in marine environments can rarely be placed on top of the sea floor. Weak soils usually need to be excavated to place the structure on more stable ground. Steep but stable slopes of the resulting pit meet both economic and ecologic aims as they minimise material movement and sediment disturbance. This paper focuses changes of geometry of submarine slopes in non-cohesive soils (erosion, sedimentation, breach failure, liquefaction failure) due to surface waves. After Terzaghi the angle between slope and the horizontal of the ground surface of cohesionless soil is at most equal to the critical state friction angle, as obviously true for dry soil. However, it can be observed that natural submarine slopes of sandy soils are always mildly sloped. During the construction of artificial submarine pits under offshore conditions it should be considered that the long-term slope-inclination is less than onshore due to hydrodynamic actions (e. g. flow, waves, earthquakes). Large surface waves cause excess pore water pressures within the soil body, leading to a reduction of effective stresses and in case of submarine slopes to changes of the slope geometry depending on wave length L, wave height H, water depth h and soil properties (permeability k, relative density Dr). During our preliminary work we investigated such processes based on the coupling of linear wave theory and linear quasistatic consolidation theory (e.g. [1]). With the help of numerical modelling we solved corresponding equations considering also materially nonlinear consolidation. However, deformations were always limited by used Lagrangian-FEM. Recent developments at our Institute enable the use of an Eulerian-FEM approach with an u-p-Formulation for fully saturated soil [2]. This allows larger deformations of the subaqueous slope to be numerically investigated.

Shallow foundation structures for offshore wind turbines offer ecological benefits compared to pile foundations as less noise is emitted at sea floor level during construction process. On the other hand, shallow offshore foundations can rarely be placed on top of the sea floor. Weak soils usually need to be excavated to place the foundation structure on more stable ground and thus, anthropogenic submarine slopes result. Steep but stable slopes meet both economic and ecologic aims as they minimise material movement and sediment disturbance. After Terzaghi [1] the angle β between slope and the horizontal of the ground surface of coarse-grained soil is at most equal to the critical state friction angle φc. However, it can be observed that natural submarine slopes of sandy soils are always much more shallow. Particularly fine-grained, cohesionless or almost cohesionless soils failed in the past, although the slope angle was much smaller than the critical state friction angle φc. Artificial (temporary) slopes do not appear and behave as natural submarine slopes, since the latter are already shaped by perpetual loads of waves, tide and mass movements. Physical simulations of different scales are used to analyse the stability of artificial submarine slopes with sandy soil of the North Sea. The study focuses on gravitational forces and impacts from the excavation processes. The simulations and theoretical considerations result in suggested slope angles for future shallow offshore foundations of wind farms in the North Sea.

Shallow foundation structures offer ecological benefits compared to pile foundations as less noise is emitted at sea floor level during construction process. On the other hand, shallow offshore foundations can rarely be placed on top of the sea floor. Weak soils usually need to be excavated to place the foundation structure on more stable ground and thus, anthropogenic submarine pits result. Steep but stable slopes of the pit meet both economic and ecologic aims as they minimise material movement and sediment disturbance. According to Terzaghi [1] the angle β between slope and the horizontal of the ground surface of cohesionless soil is at most equal to the critical state friction angle φc. However, it can be observed that natural submarine slopes of sandy soils are always much more shallow. Artificial (temporary) slopes do not appear and behave as natural submarine slopes, since the latter are already shaped by perpetual loads of waves, tide and mass movements. Physical simulations of different scales were presented at the OMAE 2011 [2] to analyse the stability of artificial submarine slopes of sandy soil in the North Sea. The laboratory tests focused on gravitational forces and impacts from the excavation processes. This paper presents additional numerical simulations of wave-induced bottom pressure on the suggested submarine foundation pits. Furthermore, in-situ tests will be performed in 2012 and 2013. Both dredging process and resulted foundation pits will be considerably surveyed.

The dynamic response of a jacket-supported offshore wind turbine under coupled wind, wave, and current fields during Hurricane Sandy is the subject of this study. To illustrate the detailed procedure related to the response evaluation of a 5-MW offshore wind turbine with a jacket support structure, we consider a single site where the water depth is 50 m. Loads are computed using two simulation tools, FAST and Abaqus, with partial coupling. Aerodynamic loads on the turbine rotor are first evaluated using a wind turbine model in FAST with a fixed base; then, these rotor aerodynamic loads are applied as point loads at the top of a model of a tower that is supported by a jacket structure in Abaqus. Based on stochastic simulations, we discuss the applicability of the Abaqus jacket modeling and describe the characteristics and comparisons of the aerodynamic and hydrodynamic effects on loads on the jacket members. Details related to the structural model and soil-pile interaction model employed in the analyses are also discussed.

Abstract Top hole construction is a critical part of any well design, especially for subsea wells. It is considered to be the foundation for the well, and it is crucial for ensuring well integrity. Uncertainties and conditions of the seabed and top layers could compromise the stability of the chosen solution. This paper describes the first implementation of the conductor anchor node (CAN®) technology in sand-based conditions and demonstrates its positive impact on the drilling performance for an offshore exploration well in the North Sea. The main challenges identified in the top-hole design for this well were the presence of boulders down to 65 m below the seabed, and hard soil that consisted mainly of very dense sand and high strength sandy-clay layers. Different solutions were evaluated using a risk-based approach, looking to optimize operational performance and decrease the environmental footprint. A technology which consists of a pre-installed short conductor within a CAN was chosen. This solution enabled the operator to establish a competent well foundation above the boulder interval and increase operational efficiency by reducing the critical rig time. However, the CAN technology had not been deployed in this type of soil previously. Thus, the feasibility of its installation became one of the main milestones of the project. This was made possible due to a set of contingencies and modifications that were the result of a strategic collaboration among the parties involved. The CAN was successfully installed by a crane vessel before the rig arrived at location, and the set of contingencies and modifications mentioned in this paper were decisive to ensure it reached the required penetration depth. Furthermore, this paper demonstrates that the CAN technology was crucial for the project to achieve top performance results and become one of the fastest exploration wells drilled in the Norwegian basin. This solution reduced uncertainties related to the conductor cementing, load and fatigue capacities, and deep surface casing cement. Improvement in the drilling performance is determined by estimating the decrease in drilling time, materials and consumables. Those results are then used to perform a cost comparison which demonstrates that the CAN technology reduced the top-hole construction cost significantly on this offshore well. In addition, the reduction in the well environmental footprint is quantified, and its contributions to the projects health and safety goals are highlighted.

Abstract The installation of shallow foundation systems for offshore wind turbines like gravity foundations requires the excavation of the weak top soil of the seabed to place the structure on more stable ground. This excavation can be done through suction dredging resulting in a pit. Different slope angles of this pit can be realized using this technique. As the failure mechanisms of artificial submarine slopes using suction dredging are barely investigated, relatively small final slope angles of max. 10 degree are reached to guarantee stability. Nevertheless, small-scale experiments show that submarine slopes with overcritical slope inclinations can be stable for a while when prepared with suction dredging. Steeper inclinations would significantly reduce the disturbance of the marine fauna and the amount of sand to be removed and therefore meet both economic and ecological interests. The investigations of the failure mechanism in the submarine slope during suction dredging are carried out with a coupled Euler-Lagrange approach, namely the combination of the Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). This method enables the computation of particle-particle as well as the fluid-particle interaction forces and hence their influence on the investigated submarine slope behavior. The calculations are carried out with the open source software package CFDEM® coupling, which combines the discrete element code LIGGGHTS® with CFD solvers based on OpenFOAM®. Additionally, small scale model tests of suction dredging of sandy submarine slopes are carried out. The displacement of the soil grains is monitored with a high-speed camera. To take into account effects of contractancy and dilatancy, a loosely and a densely packed sand are investigated and the influence of the packing density on the failure mechanism is evaluated. The experimentally gained results will be compared to the numerical ones to evaluate the capability of the coupled CFD-DEM method to depict the failure behavior of submarine slopes during suction dredging.

Road transport is one of the biggest soil polluter. There are a lot of investigations of soil pollution near highways, but soil pollution near gravel roadsides needs more experimental research. In this experimental study we selected gravel road Juseviciai – Budvietis – Derviniai and analyzed soil pollution near this road. Soil samples were collected on both sides of the road by making the transversal profile, the sampling points move away of the road at a distance 1; 2; 5; 10 meters, the samples were collected in 600 meters long strip. All samples were collected by using the envelope principle, samples were taken from the top of the soil layer 0–10 cm depth. It was established that Mn concentration in the soil sample, which was taken from the middle of gravel road carriageway, reached 238,5 mg/kg – it means 1,79 times less than background value. This value is more than 6 times less than maximum allowed concentration and quit close to the values, which were established on both sides in the soil close to gravel road. The modelling of Mn concentration where made in appropriate scale of mathematical model – 15 meter to both sides of gravel road, the width of the road – 4 meters. The simulated soil volume is 34 x 14 meters, the soil type – medium-coarse sandy loam. It was modeled that after one year Mn concentration in the soil, close to gravel road remains 1,3 times less than background value (at a constant Mn emission in the environment). Moving away from driveway till 10–15 meters the concentration of Mn decrease to 200 mg/kg in the soil depth of 0,5 m. After 10 years this concentration will reach 1 meter depth. Bet there would be no changes of Mn concentration in the groundwater level.

Multi-layered soil conditions often exist in offshore practice. In some sites a thin layer of medium dense sand lays between firm to stiff clay layers. In these cases the ultimate bearing capacity of foundations can be increased due to the strong sand layer by comparing with foundations in uniform clay. However, there is also a potential of reduction in foundation capacity when the foundation punches through the sand layer. The punch-through failure can occur during either pre-loading or storm loading. In this study, the continuous penetration of spudcan foundations on clay-sand-clay soils was investigated by large deformation finite element analysis. The numerical simulation was carried out using Remeshing and Interpolation Technique with Small Strain (RITSS) model. The clays obey Tresca failure criterion for undrained analysis and the sands obey Mohr-Coulomb yield criterion for drained analysis. The friction angle of the sand was taken as φ = 32° and 40° with its dilation angle ψ = 2° and 10° respectively. The effects of the relative height of the top soft clay and the relative thickness of the middle sand layer on the load-displacement responses were investigated. The soil flow mechanisms at various penetration depths were also discussed.

The United States Army produces a significant amount of classified paper waste that is pulverized to a fine consistency unsuitable for recycling. However, cheap, high quality organic materials such as classified paper waste are useful as soil amendments. The objective of this research was to evaluate the utilization of pulverized classified paper waste as a soil amendment to improve soil health and increase establishment of desirable native grasses on degraded Army training lands. Paper was applied at rates of 9 to 72 Mg ha⁻¹ to two soil types at Fort Polk, LA: an alfisol (very fine sandy loam - Fine, smectitic, thermic Chromic Vertic Hapludalfs) and an ultisol (loamy fine sandy - Loamy, siliceous, semiactive, thermic Arenic Paleudults). These are common soil orders found on military training lands nationwide and represent fertile (alfisol) and unfertile (ulitsol) soils. Vegetation and soils were monitored over 2 growing seasons. No increase in heavy metals were observed in soils. Extensive analysis showed very low levels of regulated contaminants in the paper, but most were below detection limits. The ultisol site showed improved soil physical and chemical properties, while desirable vegetation benefitted from nutrient immobilization at the alfisol site. Based on the results of this study, applying pulverized paper waste to soil at a rate of 35.9 Mg ha⁻¹ is recommended. Application of paper waste to soils had no adverse environmental effects, improved soil physiochemical properties, and facilitated establishment of desirable native vegetation.

The first phase of the study was designed to determine the adsorption rate of viruses and microspheres to sandy and loamy soils and determine the adsorption efficiency of various viruses to soil. The adsorption of viruses to sandy and loamy soils has been found virus type dependent. The poorest adsorption was observed for MS2 bacteriophage while the greatest adsorption was observed for PRD-1. Adsorption sites on the soil material were not found as limiting factors for adsorption of viruses on soil material. The effect of water quality on adsorption has been found as virus type dependent. The adsorption process of microspheres to soil material has been found to be similar to that of viruses and occurs within a very short period of time. Carboxylated (negatively charged) microspheres seems to adsorb more efficiently than plain microspheres to soil material. At low temperatures (10oC), and under saturated conditions no virus die-off was observed, therefore under these conditions virus can survive for long period of time. At 23oC, and saturated conditions, the greatest die-off was observed for MS2 bacteriophage, whereas, negligible die-off was for PRD-1 bacteriophage and hepatitis A virus. Considering the survival results MS2 bacteriophages is not suitable as indicator for pathogenic viruses persistence in soil material. Furthermore, temperature, is more important than any other factor for the inactivation of viruses.

Concentrated flow erosion in rills, pipes, ephermal gullies, and gullies is a major contributor of downstream sedimentation. When rill or gullies form in a landscape, a 3- to 5-fold increase in soil loss commonly occurs. The balance between the erosive power of the flow and the erosion resistance of the bed material determines the rate of concentrated flow erosion. The resistance of the bed material to detachment depends primarily on the magnitude of the interparticle forces or cohesion holding the particles and aggregates together. The effect of soil properties on bed material resistance and concentrated flow erosion was evaluated both in the laboratory and field. Both rill erodibility and critical hydraulic shear were greater when measured in 9.0 m long rills under field conditions compared with laboratory mini-flumes. A greater hydraulic shear was required to initiate erosion in the field compared to the mini-flume because of the greater aggregate and clod size and stability. Once erosion was initiated, however, the rate of erosion as a function of hydraulic shear was greater under field conditions because of the greater potential for slaking upon wetting and the greater soil surface area exposed to hydraulic shear. Erosion tests under controlled laboratory conditions with the mini-flume allowed individual soil variables to be studied. Attempts to relate rill erosion to a group soil properties had limited success. When individual soil properties were isolated and studied separately or grouped separately, some trends were identified. For example, the effect of organic carbon on rill erodibility was high in kaolinitic soils, low in smectitic soils, and intermediate in the soils dominated by illite. Slow prewetting and aging increased the cohesion forces between soil particles and decreased rill erodibility. Quick prewetting increased aggregate slaking and increased erodibility. The magnitude of the effect of aging depended upon soil type. The effect of clay mineralogy was evaluated on sand/clay mixtures with montmorillonite (M), Illite (I), and kaolinite (K) clays. Montmorillonite/sand mixtures were much less erodible than either illite or kaolonite sand mixtures. Na-I and Na-K sand mixtures were more erodible than Ca-I and Ca-K due to increased strength from ionic bonding and suppression of repulsive charges by Ca. Na-M was less erodiblethan Ca-M due to increased surface resulting from the accessibility of internal surfaces due to Na saturation. Erodibility decreased when salt concentration was high enough to cause flocculation. This occurred between 0.001 mole L-1 and 0.01 mole L-1. Measuring rill erodibility in mini-flumes enables the measurement of cohesive forces between particles and enhances our ability to learn more about cohesive forces resisting soil detachment under concentrated water flow.

The critical shear stress and erodibility of soil are fundamental parameters for modeling embankment breaching. Unfortunately, very few studies have examined the erosion characteristics of soils consisting predominantly of particles larger than sand. This report presents results of an experimental study in which the erosion characteristics of gravelly soils were measured. A flume apparatus was developed in which 0.45-m-square samples were extruded into confined flow. A mechanical laser system allowed the measurement of scour in real time, resulting in a continuous and automated erosion test. The critical shear stress of a uniform gravel was found to match the expected values based on the Shields diagram, while tests that were composed largely of gravel but contained other soils, such as sand, silt, and clay, varied significantly with the critical shear stress and erodibility, depending highly on the characteristics of the finer soils.

Sodium affected soils, along with salt-affected soils, are distributed widely in irrigated areas of the arid and semi-arid region of the world. Some of these soils can and must be reclaimed to meet the increasing demand for food, and existing irrigated lands must be managed to reduce salinization and alkalization associated with deteriorating irrigation water quality. This project was conducted for examining ways to reduce the use of chemical amendments and large quantities of leaching water for reclaiming sodic soils or for preventing soil sodification, We hypothesized that sodicity of calcareous soils irrigated with moderately sodic irrigation water can be controlled by maximizing dissolution of soil CaCO3. The work performed in Israel has shown that dissolution of CaCO3 can be enhanced by elevating the CO2 partial pressure in soils, and by increasing pore water velocity. The concentration of Ca in pore water was at an order of 1.5 mmolc L-1 at a CO2 partial pressure of 5 kPa, which is sufficient to maintain SAR below 4 at salinity of irrigation water of 0.5 dS m-1 or less. Incorporation of crop residue at a flesh weight of 100 Mg ha-1 reduced the exchangeable Na percentage from 19 to 5%, while it remained 14% without crop residue application These findings indicate a possibility of preventing soil sodification with appropriate crop rotation and residue management without chemical amendments, provided that soils remain permeable. In the case of highly sodic soils, dissolution of CaCO3 alone is usually insufficient to maintain soil permeability during initial leaching. We examined the effect of salinity and sodicity on water infiltration, then developed a way to estimate the amendments required on the basis of water infiltration and drainage characteristics, rather than the traditional idea of reducing the exchangeable Na percentage to a pre-fixed value. Initial indications from soil column and lysimeter study are that the proposed method provides realistic estimates of amendment requirements. We further hypothesized that cultivation of salt-tolerant plants with water of elevated salinity can enhance reclamation of severely Na-affected soils primarily through improved water infiltration and increased dissolution of CaCO3 through respiration. An outdoor lysimeter experiment using two saline sodic Entisols sodded with saltgrass for two seasons did not necessarily support this hypothesis. While there was an evidence of increased removal of the exchangeable Na originally present in the soils, the final salinity and sodicity measured were lowest without sod, and highest when sodded. High transpiration rates, coupled with low permeability and/or inadequate leaching seemed to have offset the potential benefits of increased CaCO3 dissolution and subsequent removal of exchangeable Na. Although vegetative means of reclaiming sodic soils had been reported to be effective in sandy soils with sufficient permeability, additional study is needed for its use in saline sodic soils under the high evaporative demand. The use of cool season grass after initial salt leaching with CaCl2 should be explored. Results obtained from this project have several potential applications, which include the use of crop residues for maintaining sodium balance, the use of CaCl2 for initial leaching of poorly permeable clayey sodic soils, and appraisal of sodicity effects, and appropriate rates and types of amendments required for reclamation

Vibration compaction is the most effective way of compacting coarse-grained materials. The effects of vibration frequency and amplitude on the compaction density of different backfill materials commonly used by INDOT (No. 4 natural sand, No. 24 stone sand, and No. 5, No. 8, No. 43 aggregates) were studied in this research. The test materials were characterized based on the particle sizes and morphology parameters using digital image analysis technique. Small-scale laboratory compaction tests were carried out with variable frequency and amplitude of vibrations using vibratory hammer and vibratory table. The results show an increase in density with the increase in amplitude and frequency of vibration. However, the increase in density with the increase in amplitude of vibration is more pronounced for the coarse aggregates than for the sands. A comparison of the maximum dry densities of different test materials shows that the dry densities obtained after compaction using the vibratory hammer are greater than those obtained after compaction using the vibratory table when both tools were used at the highest amplitude and frequency of vibration available. Large-scale vibratory roller compaction tests were performed in the field for No. 30 backfill soil to observe the effect of vibration frequency and number of passes on the compaction density. Accelerometer sensors were attached to the roller drum (Caterpillar, model CS56B) to measure the frequency of vibration for the two different vibration settings available to the roller. For this roller and soil tested, the results show that the higher vibration setting is more effective. Direct shear tests and direct interface shear tests were performed to study the impact of particle characteristics of the coarse-grained backfill materials on interface shear resistance. The more angular the particles, the greater the shear resistance measured in the direct shear tests. A unique relationship was found between the normalized surface roughness and the ratio of critical-state interface friction angle between sand-gravel mixture with steel to the internal critical-state friction angle of the sand-gravel mixture.

experimental methods for quantifying effects of water content and other dynamic environmental factors on bacterial growth in partially-saturated soils. Towards this end we reviewed critically the relevant scientific literature and performed theoretical and experimental studies of bacterial growth and activity in modeled, idealized and real unsaturated soils. The natural wetting-drying cycles common to agricultural soils affect water content and liquid organization resulting in fragmentation of aquatic habitats and limit hydraulic connections. Consequently, substrate diffusion pathways to soil microbial communities become limiting and reduce nutrient fluxes, microbial growth, and mobility. Key elements that govern the extent and manifestation of such ubiquitous interactions include characteristics of diffusion pathways and pore space, the timing, duration, and extent of environmental perturbations, the nature of microbiological adjustments (short-term and longterm), and spatial distribution and properties of EPS clusters (microcolonies). Of these key elements we have chosen to focus on a manageable subset namely on modeling microbial growth and coexistence on simple rough surfaces, and experiments on bacterial growth in variably saturated sand samples and columns. Our extensive review paper providing a definitive “snap-shot” of present scientific understanding of microbial behavior in unsaturated soils revealed a lack of modeling tools that are essential for enhanced predictability of microbial processes in soils. We therefore embarked on two pronged approach of development of simple microbial growth models based on diffusion-reaction principles to incorporate key controls for microbial activity in soils such as diffusion coefficients and temporal variations in soil water content (and related substrate diffusion rates), and development of new methodologies in support of experiments on microbial growth in simple and observable porous media under controlled water status conditions. Experimental efforts led to a series of microbial growth experiments in granular media under variable saturation and ambient conditions, and introduction of atomic force microscopy (AFM) and confocal scanning laser microscopy (CSLM) to study cell size, morphology and multi-cell arrangement at a high resolution from growth experiments in various porous media. The modeling efforts elucidated important links between unsaturated conditions and microbial coexistence which is believed to support the unparallel diversity found in soils. We examined the role of spatial and temporal variation in hydration conditions (such as exist in agricultural soils) on local growth rates and on interactions between two competing microbial species. Interestingly, the complexity of soil spaces and aquatic niches are necessary for supporting a rich microbial diversity and the wide array of microbial functions in unsaturated soils. This project supported collaboration between soil physicists and soil microbiologist that is absolutely essential for making progress in both disciplines. It provided a few basic tools (models, parameterization) for guiding future experiments and for gathering key information necessary for prediction of biological processes in agricultural soils. The project sparked a series of ongoing studies (at DTU and EPFL and in the ARO) into effects of soil hydration dynamics on microbial survival strategy under short term and prolonged desiccation (important for general scientific and agricultural applications).

Soil water wettability or water repellency is a phenomenon that can affect infiltration and, ultimately, runoff. Thus, there is a need to develop a model that can quantitatively capture the influence of water repellency on infiltration in a physically meaningful way and within the framework of existing infiltration theory. The analytical model developed in this study relates soil sorptivity (an infiltration parameter) with contact angle (a direct measure of water repellency) for variably saturated media. The model was validated with laboratory experiments using a silica sand of known properties treated to produce controlled degrees of water repellency. The measured contact angle and sorptivity values closely matched the model‐predicted values. Further, the relationship between the frequently used water drop penetration time test (used to assess water repellency) and sorptivity was illustrated. Finally, the direct impact of water repellency on saturated hydraulic conductivity was investigated due to its role in infiltration equations and to shed light on inconsistent field observations. It was found that water repellency had minimal effect on the saturated hydraulic conductivity of structureless sand. A quantitative model for infiltration incorporating the effect of water repellency is particularly important for post‐fire hydrologic modeling of burned areas exhibiting water repellent soils.