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A model for the one-dimensional consolidation of saturated clayey soils, considering creep, is proposed, based on the consolidation mechanism idealized by Terzaghi (1941). The effective vertical stress is divided into two parts: one corresponding to the "solid" contacts, and other relating to the "viscous" contacts, the void ratio changes being caused by variations solely in the solid portion. Based on experimental evidence, a non-linear viscosity law was adopted, described by a hyperbolic function, in addition to its dependence on the void ratio. The resulting differential equation system is solved through the Finite Difference Method. The main "secondary effects of time" – experimental deviations from the classical Terzaghi (1925) theory – were able to be reproduced using the model, as well as experimental results that support other categories of consolidation models, such as the isotache- and C α / C C -based models. A good fit was obtained for the results of long-term laboratory tests in clays from different parts of the world that reached the end of secondary consolidation. A good prediction was also reached for the evolution of settlements from the experimental embankment on the soft soils of Lilla Mellosa, monitored since 1947 in Sweden. [ABSTRACT FROM AUTHOR]

Liming with 'structure lime', comprising approximately 80–85% ground limestone and 15–20% slaked lime, has been promoted in subsidised environmental schemes in Sweden since 2010 to increase clay aggregate stability and mitigate particulate phosphorus losses to surface waters. To date, approximately 65,000 ha have been structure-limed. Apart from stabilising aggregates, liming may also improve other physical properties, such as soil strength. This study examined the effect of increasing application rate (0–16 t ha-1) of structure lime on soil strength, approximated by horizontal (draught requirement) and vertical (penetrometer resistance) measurements, in eight field soils (clay content 26–38%) to which structure lime had been applied two, three, four or six years previously. Draught requirement when cultivating with a multipurpose cultivator significantly decreased (by 11%) with the highest application rate of structure lime (16 t ha-1) compared with an unlimed control. This reduced the wheel power requirement by 7.1 kW and diesel consumption by 1.2–1.4 L ha-1, and lowered CO 2 emissions by 3–4 kg ha-1. To clarify the general effect of structure liming, the mean value of all limed treatments was compared with that of the unlimed control. This showed that structure liming in general significantly reduced the draught requirement (by 7%). However, penetrometer resistance measurements revealed no significant effects of structure liming and no relation between draught requirement and penetrometer resistance measurements. Overall, the results indicate that structure liming can reduce fuel consumption, due to easier soil tillage, and thus lower CO 2 emissions. • Cultivator draught requirement was measured in structure limed field trials. • A towing eye with sensors that can measure forces in three directions was used. • Structure liming reduced horizontal draught requirement by 7%. • Reductions corresponded to decreases of 1.2–1.4 L diesel ha-1 and 3–4 kg CO 2 ha-1. • Structure liming did not affect penetrometer resistance in this study. [ABSTRACT FROM AUTHOR]

The structure of agricultural topsoils varies considerably throughout the year due to interactions between climatic and biological factors and agricultural management practices. Tillage generally decreases soil density and increases macroporosity, but the resulting arrangement of clods and aggregates is unstable and the soil eventually reverts back to its denser pre-tillage condition. Accounting for post-tillage changes in soil structure and related hydraulic properties could greatly improve model predictions of hydrological and transport processes. Model testing, development and parameterization is, however, currently hampered by a lack of direct measurements of the changes occurring in the structural pore system. We subjected repacked samples of soil collected from the harrowed layer of nine different fine- and medium-textured Swedish mineral soils to subsequent wetting and drying cycles in the laboratory. Initial wetting and equilibration at −30 cm pressure potential was followed by three cycles of simulated rainfall (5 mm h −1 for 4 h) and equilibration. X-ray tomography was used to quantify changes in surface and total porosity, pore size distribution (PSD) and connectivity of structural pores. Total porosity decreased (by 2–24%) in all soils except for two clay soils where in one case the porosity increased slightly (3%) and remained unchanged in the other. In six of the soils, the PSD shifted significantly towards smaller pore sizes, and in four of these soils the connectivity of the pore network decreased. Soil surface porosity decreased most markedly in two silt loam soils (by 73% and 75%). For the nine soils changes were strongly correlated with silt content. Only weak correlations were found between the changes in total porosity and soil texture and organic carbon content. Changes in the PSD appeared to be mainly controlled by the initial structure of the sample created at the time of tillage and sample preparation. [ABSTRACT FROM AUTHOR]

• Manure rate had little influence on the improvement of soil physical properties. • Improvement in soil gas transport and Ksat by manure varied with soil and crop type. • Silty soil had better improvements by manure addition than sandy and clayey soil. Manure application and crop rotation are common agricultural practices that can alter soil physical properties and affect soil functions. In this study, we assessed the effect of long-term manure fertilization (24 to 126 years) and crop type on soil hydraulic, aggregate and pore structural properties. Samples were collected from three long-term experiments (LTEs) in Sweden (silty clay, SiC), Germany (silt loam, SiL) and Denmark (sandy loam, SL). Measurements included water retention, air permeability and gas diffusivity measured at five matric potentials −3, −5, −10, −30 and −50 kPa, saturated hydraulic conductivity (K sat), bulk density (ρ b), and water-stable aggregates (WSA). The treatments at the three LTEs included various manure rates and crop sequences (winter wheat, maize, spring barley, and grass/clover). Results showed that long-term manure addition reduced ρ b by an average of 3–6% for all three sites, and improved soil water retention, plant available water and WSA for most investigated plots. However, increasing manure rates for the SiL and SL sites did not result in further improvements in soil water retention, ρ b and water-stable aggregates. The effect of manure on soil pore size distribution, gas transport, and K sat varied with soil and crop type. Manure increased the porosity of pores < 30 µm in the two fine-textured sites and increased the porosity of pores > 30 µm for wheat and maize plots in the SL site. Manure improved gas transport and K sat in the wheat plots and decreased these properties in the barley plots regardless of soil texture. The maize plots in the SL site had well developed pore structure, while the pore structure in the SiL site was relatively poor. Grass plots had poorer gas transport than maize plots in the SL site despite the manure addition. The study shows that improvements in soil physical and chemical properties arising from manure application largely depend on the crops grown and the soil texture. [ABSTRACT FROM AUTHOR]