Soil compaction by uniaxial loading and the survival of the earthworm Aporrectodea caliginosa

Earthworms are the major component of the soil fauna in temperate agro-ecosystems. Land use and soil management are widely reported to influence earthworm populations. We report simple laboratory experiments in which earthworm survival was tested against uniaxial loads for a range of soil conditions. Across all the experimental conditions 86% of earthworms survived. While greater loads (up to 800 kPa) over longer exposure times (up to 60 s) decreased survival; even under the most severe test conditions 33% of earthworms survived. Our results suggest that decreased earthworm populations in compacted soil are not due to uniaxial loading alone, but may be the result of shearing the soil during loading or from changes to the soil properties.     

Genetic analyses of herding traits in the Border Collie using sheepdog trial data

The aim of this study was to evaluate the quality of the data provided from sheepdog trials in Norway, estimate heritabilities, repeatabilities and genetic correlations for the traits included in the trial and make recommendations on how sheepdog trials best can be utilized in the breeding of Border Collies in Norway. The analyses were based on test results from sheepdog trials carried out in Norway from 1993 to 2012. A total of 45 732 records from 3841 Border Collies were available, but after quality assurance only a third was left. The results demonstrated little information in the data. Heritabilities varied between 0.010 and 0.056 with standard errors ranging from 0.010 to 0.023, while repeatabilities ranged from 0.041 to 0.286. There is a need to assure the quality of data to improve the information in the test results. We recommend adding new traits based on the Herding Trait Characterization scheme evaluated in Sweden, and on traits from the predatory motor pattern, regarded as common for all dogs. These new traits may be scored across the elements that make up the current trial system, which should be kept in place to stimulate participation in the genetic evaluation scheme.     

Shrinkage behaviour of transiently- and constantly-loaded soils and its consequences for soil moisture release

Soils under loaded conditions may have different shrinkage behaviour from that of load‐free soils. In this study, we applied two kinds of mechanical stress (σ) on repacked homogeneous soil samples: transient and constant stresses, simulating the traffic load during tillage and the overburden pressure, respectively. Three transient stresses were applied on the soil surface with 150, 400 and 1400 kPa, while the constant stresses ranged from 1.8, 3.8, 5.5, to 7.3 kPa. We hypothesized that the two stresses play different roles in soil shrinkage behaviour as depicted by void ratio (e) and moisture ratio (?), as compared with load‐free soil. Thus, our aim was to build up the relationship between e, ? and σ. For a swelling soil, total pores can be divided into rigid and non‐rigid components according to their swelling and shrinkage capacity relative to soil moisture. The non‐rigid pores compacted by the transient stress can be regained in the subsequent wetting at load‐free conditions, whereas the compacted rigid pores do not recover. The reduction in rigid pores does not alter the soil pore shrinkage capacity. The shrinkage curves of transiently‐loaded soils are therefore parallel to each other with an identical coefficient of linear extensibility (COLE) and the same shrinkage slope, although their structural shrinkage phase narrows with an increase of stress. However, the constant stress compresses non‐rigid pores readily through suppressing their swelling capacity during wetting as well as compacting rigid pores. If the change of rigid pores is negligible, the shrinkage curves of constantly‐loaded soils converge at the zero shrinkage or the dry‐end point with the load‐free soil shrinkage. If the reductions of rigid and non‐rigid pores are both considered, the soil shrinkage combines the part of parallel shrinkage derived from the reduced rigid pores and the intersected shrinkage resulted from the altered non‐rigid pores. On the basis of different shrinkage behaviours resulting from the two mechanical stresses, we propose numerical formulae to illustrate a series of curves for the e‐?‐σ relationship. The different changes in rigid and non‐rigid pores cause soil water release differently.     

Determination of pre-compression stress of a variously grazed steppe soil under static and cyclic loading

In many land use systems all over the world soil deformation is a major problem due to increasing land use intensity. On arable soils machine traffic is continuously intensified with respect to load and wheeling frequency leading to (sub-)soil compaction and deeper soil degradation concerning hydraulic or pneumatic functions. Altered soil functions, in particular reduced hydraulic conductivities and impeded aeration, may decrease crop growth and productivity as well as the filtering and buffering capacity of soils. Prevented gas exchange and longer lasting anoxia in soils due to the reduced pore continuity and pore functioning also affects global change processes. In order to evaluate potential risks for irreversible soil deformation, it is necessary to quantify their mechanical stability. A commonly applied method is the determination of the pre-compression stress, commonly under static loading conditions in oedometer tests. The determination of pre-compression stresses under static loading may not quite resemble the conditions encountered in the field where soils are loaded repeatedly with a sequence of short intermittent loading–unloading–reloading events. Such dynamic loading conditions are encountered, e.g. at multiple wheel passes or in grassland soils due to animal trampling. In this study we present a comparison of a standard (static loading) and a modified (cyclic/dynamic loading) oedometer test using data of a Calcic Chernozem from the Inner Mongolian steppe under various grazing intensities. Static loading lasted for 10 min per loading step, while the dynamic/cyclic loading was carried out by 30 s loading and following 30 s unloading (=1 cycle) for in total 20 cycles. Differences between statically and cyclically determined pre-compression stresses at an identical time of loading show lower values for the statically determined pre-compression stress values compared to those determined cyclically. Among the dynamically determined pre-compression stresses, the values decrease with increasing number of loading steps and loading time, respectively. This is particularly true for the ungrazed sites.Thus, it could also be proofed that increased grazing intensities lead to structure deformation and increased sensitivity to wind- and water erosion followed by severe land degradation of grassland soils, particularly in semi-arid areas. Furthermore, hydraulic effects, e.g. positive pore water pressure due to intense shearing and kneading processes induced by grazing animals can enhance this structural deterioration.Thus, dynamic or cyclic loading results in an intense soil deformation which also causes serious changes in ecological and soil physical properties like hydraulic conductivity or gas flux.     

Structural stabilization of soil backfill with quicklime

The application of quicklime (CaO) to soil backfill for the amelioration of poorly aerated grave soils (sandy loam) was tested in a cemetery in Germany. Two grave simulations (soil pits 9 m × 2 m × 1.6 m, l × w × d) were set up. Variation sans was only excavated and refilled, while in variation qlm, 20 kg quicklime per m³ soil were added to the backfill. Soil matric potential and gas composition were recorded over a period of 24 months in the two refilled pits and in the surrounding undisturbed soil (ref) at the 50 cm and 135 cm depths, respectively. Soil samples were taken in the beginning from ref and in three‐month intervals from the treatments sans and qlm. Soil pH and CaCO₃ content, as well as bulk density (ρ_B), air capacity (AC), air conductivity (k_l), and saturated hydraulic conductivity (k_s) were measured. Excavation and backfill of the untreated soil (sans) led to an increase in ρ_B at the 50 and 90 cm depths and decreases in AC, k_l, and k_s when compared to ref. Quicklime application led to an increase in pH, the formation of CaCO₃ in the formerly carbonate‐free soil, consistently reduced ρ_B, and increased AC, k_l and k_s. Although the quicklime application did not lead to notably more negative matric potentials, it increased the O₂ concentration in the soil air and reduced the CO₂ concentration to zero. The results show that the application of quicklime helps the structural amelioration of cemetery soils even at relatively low clay contents.     

High-Tc superconductors in the two-dimensional limit:

The free modulation of interlayer distance in a layered high-transition temperature (high-Tc) superconductor is of crucial importance not only for the study of the superconducting mechanism but also for the practical application of high-Tc superconducting materials. Two-dimensional (2D) superconductors were achieved by intercalating a long-chain organic compound into bismuth-based high-Tc cuprates. Although the intercalation of the organic chain increased the interlayer distance remarkably, to tens of angstroms, the superconducting transition temperature of the intercalate was nearly the same as that of the pristine material, suggesting the 2D nature of the high-Tc superconductivity.     

Magnetic Field and Plasma Observations at Mars: Initial Results of the Mars Global Surveyor Mission

The magnetometer and electron reflectometer investigation (MAG/ER) on the Mars Global Surveyor spacecraft has obtained magnetic field and plasma observations throughout the near-Mars environment, from beyond the influence of Mars to just above the surface (at an altitude of approximately 100 kilometers). The solar wind interaction with Mars is in many ways similar to that at Venus and at an active comet, that is, primarily an ionospheric-atmospheric interaction. No significant planetary magnetic field of global scale has been detected to date (<2 x 10(21) Gauss-cubic centimeter), but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of Mars is reported.     

Einfluss des Porenwasserdruckes auf die Zugfestigkeit von Bodenproben

Effect of pore water pressure on tensile strength Direct tensile testing with measurements of the pore water suction was used to investigate the relationship between tensile strength and suction. The tests were conducted on a till and a clayey soil, both homogenized. A closer view is focused on the relationship between material strain and the development of suction. Beyond, the factor χ of the effective stress equation for unsaturated soils by Bishop (1959), which was calculated by the data of tensile strength and corresponding matric suction is compared to the volumetric χ of the tested soil specimens. It could be shown, that the pore water pressure changes with strain. Therefore, not the initial suction of a soil is relevant for its failure but the actual one that can be measured in the failure zone at the moment of fracture. In addition the application of the volumetric χ in the effective stress equation compared to the χ derived from tensile testing leads to an 1.6 to 2.8 fold overestimation of the contribution of matric suction to soil tensile strength.     

Effect of repeated tractor wheeling on stress/strain properties and consequences on physical properties in structured arable soils

The discussion about the effect of repeated short time wheeling on long-term changes in soil structure and pore functioning reveals a great uncertainty. On the one hand it is told that soil structure elements are rigid and do not undergo intense changes in pore functions as a consequence of the short loading interval during each single wheeling. On the other hand, the complete deterioration of the structure elements and pore functions is assumed to occur, which also results in changes of the shrinkage pattern, soil strength including even strength regain. Consequently, the effect of wheeling on soil deformation and stress/strain distribution was investigated in a soil bin which contained Hiwassee clay at the NSDL, Auburn. If the soil is very strong due to aggregation, plow pan formation or dryness, soil stress applied by repeated wheeling results in an increased primarily vertical soil particle displacement in the Hiwassee clay soil while during repeated wheeling (up to 10×) a more pronounced displacement linked with a more intense movement of particles can be proofed. With increasing number of wheeling events, new platy or again coherent structure elements are formed, which create a very different pore system. The more intense is soil wheeling, the smaller is the saturated hydraulic conductivity and the higher is the unsaturated one at a given pore water pressure value. Such changes are the more pronounced the more completed is the rearrangement of the still existing aggregates into new units like plates. Due to shear because of the three-dimensional soil displacement even under dry conditions such aggregates can be redisturbed and a coherent but very compacted soil horizon can be formed. Under those conditions the values of bulk density are even higher than the Proctor density.