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Delaying tillage and incorporation of arable crop residues in autumn may limit accumulation of soil mineral nitrogen (SMN) and reduce nitrogen (N) leaching. However, on clay soils, high water content during late tillage can impair soil structure and fertility. This study investigated the effects of tillage timing on SMN (0–90 cm depth), soil physical properties in the topsoil and yield in two Swedish clay soils differing in clay content. SMN generally increased during autumn and also with earlier tillage. On a heavy clay soil (Ultuna; ∼60% clay), SMN increased throughout winter until spring and the amount of N leached was probably small. In contrast, on a clay loam soil in southernmost Sweden (Rydsgård; ∼35% clay), SMN decreased during winter by up to 26 kg ha−1. In general, measured soil water content (w) was lower than 0.9 × plastic limit (PL) at the time of early tillage (mouldboard ploughing or stubble cultivation), while it exceeded 0.9 PL at the time of normal and late tillage. The proportion of small aggregates produced by tillage was negatively correlated to relative soil water content at the time of tillage (w/PL). Conventional methods to determine soil physical qualities (bulk density, saturated hydraulic conductivity, aggregate tensile strength) did not show any clear differences between treatments. However, plant emergence and yield were significantly reduced after late compared with early tillage at Ultuna, a trend that has persisted from 2000 until the present. These results suggest that the suitability of delayed autumn tillage as a means to reduce SMN accumulation and N leaching varies between Swedish clay soils. A reduction in N leaching can be achieved on lighter clay soils in warmer and moister areas, whereas the effects may be small on heavier clay soils in central Sweden, where repeated late tillage carries a risk of yield reduction. [ABSTRACT FROM AUTHOR]

Abstract: Few previous studies explicitly deal with the effect of tillage depth in non-inversion tillage. Swedish experiments on different tillage depths (5–10 compared with 15–20cm) in non-inversion tillage on a range of soil types (mainly classified as Eutric Cambisols) were used to study effects on soil properties and crop yield, with mouldboard ploughing as the reference. On-site measurements of penetration resistance (all sites) and saturated hydraulic conductivity (eight sites) were made in 14 experiments of three years or more. Data from a total of 115 experimental years during 2006–2011 were used to analyse interactions between tillage depth, crop, soil type and precipitation on crop yield. The three most common crops were winter wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and oilseed rape (Brassica napus L.). Data on draught requirement were also collected (in three experiments). At the selected sites, there were mainly only small differences in crop yield between tillage depths, but on two sites with clay soil yield was significantly reduced by increased tillage depth. In an overall trend, increased tillage depth slightly seemed to decrease yield on heavier soils. The reaction of different crops was little affected by tillage depth. Decreasing tillage depth generally increased penetration resistance (approximately double at 10–15cm depth for shallow discing compared to ploughing) and reduced saturated hydraulic conductivity in the topsoil. Increasing tillage depth from 5–10cm to 15–20cm more than doubled the draught requirement. Mean yield for non-inversion tillage was only 1–2% lower than for mouldboard ploughing, despite a large increase in penetration resistance. There was also a poor correlation between penetration resistance and crop yield relative to mouldboard ploughing. There was no clear interaction between precipitation and tillage treatment in the effect on crop yield. Overall, on Swedish soils, there seems to be little need for soil loosening in non-inversion tillage. A shallow working depth can be recommended, especially on heavier soils. [Copyright &y& Elsevier]

Rapid and uniform crop establishment is a prerequisite for efficient crop production and minimal environmental impact. Extensive experiments were carried out in shallow plastic boxes placed in the field directly on the ground for studies of the effects of seedbed properties on emergence of small-grain cereal crops in a cool, temperate climate. This paper presents studies of the seedbed as a protective layer against evaporation and the requirements for good emergence under dry weather conditions. Without rainfall after sowing, nearly complete emergence of barley (Hordeum vulgare L.) was obtained, when rapidly germinating seed was placed on a moderately compacted basal layer containing at least 5% (w/w) plant-available water and covered by a 4 cm deep surface layer consisting of aggregates < 5 mm. This applied even when initial water content in the surface layer was below the wilting point and potential evaporation was high. If the soil at 4 cm depth is drier or if a sufficiently fine seedbed cannot be obtained, then seedbed and sowing depth should be somewhat greater, and if the soil is wetter, then the depth may be smaller. There were only small differences in emergence between surface layers consisting of aggregates < 2 mm, 2-4 mm or 2-5 mm, or dominated by these aggregate fractions, but when the surface layer consisted of coarser aggregates, emergence was usually much lower. Determinations of water losses from the soil during the experimental period showed that the differences in emergence were caused by differences in efficiency of the seedbed to control evaporation. The results indicate that, in an initially wet soil, it is always possible to find a time and method for seedbed preparation and sowing that lead to good emergence of small-grain cereal crops, even with a lengthy period without rainfall after sowing. [ABSTRACT FROM AUTHOR]

Rapid and uniform crop establishment is a prerequisite for efficient crop production and minimal environmental impact. Experiments were carried out in shallow plastic boxes placed directly on the ground in the field for studies of the effects of seedbed properties on emergence of various crops. This paper presents an analysis of the time required for germination and emergence under near-optimal seedbed conditions. The crops studied were barley, oats, wheat, pea, rape seed, white mustard, sugar beet, red clover and timothy. The time required for germination generally increased with size of the seeds, presumably because larger seeds needed more water to initiate germination. This applied both when comparing different crops and different seed sizes of the same crop. However, considerable differences occurred between seed lots of the same crop and there were greater differences between seed lots of the same crop than between the three small grain crops studied. Growth rate of the seedlings generally increased with seed size, presumably because of increased energy content in the seed. Consequently, the most rapid emergence was obtained from small seeds at shallow sowing and from large seeds at deep sowing. The crops studied had a minimum temperature for germination and seedling growth close to 0 °C. Under optimal seedbed conditions, thermal time required for 50% germination of barley was typically about 65 °C days over this base temperature and for seedling growth about 6 °C days cm-1. From 4 cm sowing depth, about 80 °C days were required for emergence but with considerable variations between seed lots. For rape seed or white mustard about 40 °C days were required for germination and about 8 °C days cm-1 for the seedling growth. [ABSTRACT FROM AUTHOR]

Abstract: Soil water content during tillage can have a large impact on soil properties and tillage outcome. Measurement of soil relief in relation to fixed elevation points provides a non-destructive method of monitoring loosening/compacting processes during the year. The main objective of this study was to determine the effect of soil water content during primary tillage on soil physical properties. The treatments included mouldboard and chisel ploughing of a clay soil on three occasions in the autumn, with gradually increasing water content (0.76, 0.91 and 1.01×plastic limit). Soil surface height was measured by laser within a 0.64m2 area from fixed steel plates after each tillage occasion, and before and after seedbed preparation in the following spring. The measurements of surface height were compared with measurements of other soil physical properties, such as bulk density, saturated hydraulic conductivity and seedbed properties. Tillage at the lowest water content (0.76×plastic limit) produced the greatest proportion of small aggregates, and generally the most favourable soil conditions for crop growth. Soil loosening, as measured by increase in soil height during primary tillage, was highest for mouldboard ploughing and for tillage at the lowest water content. Differences between tillage treatments decreased with time, but were still significant after sowing in the spring. Natural consolidation during winter was smaller than the compaction during seedbed preparation in the spring. No significant differences in bulk density were found between treatments, and thus soil surface height was a more sensitive parameter than bulk density determined by core sampling to detect differences between treatments. Late tillage under wet conditions caused a greater roughness of the soil surface and the seedbed base, which was also found in the traditional seedbed investigation. The effect of tillage time on seedbed properties also resulted in a lower number of emerged plants in later tillage treatments. The laser measurements were effective for studying changes in soil structure over time. The results emphasize the need to determine changes in soil physical properties for different tillage systems over time in order to model soil processes. [Copyright &y& Elsevier]

In this paper we describe the susceptibility of Swedish subsoils to compaction and discuss strategies for prevention of traffic-induced subsoil compaction against the background of experiences from wheeling experiments conducted in Sweden during recent years. The susceptibility of Swedish subsoils to compaction must be considered high because subsoils are often wet during field operations and machinery with high wheel loads is used. The risk of subsoil compaction could be reduced by technical solutions, such as the use of dual and tandem wheels instead of single wheels, low tyre inflation pressure or tracks. However, each of these solutions has its limitations. Results from several wheeling experiments on different soils indicate that residual deformations occur even when the applied stress is lower than the precompression stress. Hence, soil compaction could not be avoided completely by limiting the applied stress to the precompression stress. [ABSTRACT FROM AUTHOR]

Abstract: The objective of the present study was to measure the specific draught (force per cross-sectional area of worked soil) and energy use for soil fragmentation for different tillage implements and soil conditions. Draught was calculated from measurements of fuel consumption and speed during tillage with a mouldboard plough and a chisel plough set to working depths of 13, 17 and 21cm, and a disc harrow. Tillage was carried out at three different water contents (“Wet”, “Moist” and “Dry”) on two sites. The average working depth was calculated from weighing the loose soil within a 0.25-m2 frame. Specific area of the soil was determined by sieving. Soil strength was measured in situ using a shear vane and a penetrometer. Average working depth was much less than the set working depth for the chisel plough. Specific draught was generally the lowest for the mouldboard plough and the highest for the chisel plough, and increased with decreasing soil water content. The specific draught was strongly correlated to soil cohesion, but not to penetration resistance. The proportion of coarse aggregates after tillage was the highest for the mouldboard plough and the lowest for the moist soil. The energy use for soil fragmentation was in most cases the lowest for the disc harrow, while there were small differences between the chisel and the mouldboard ploughs. The results show that the mouldboard plough is energy efficient for loosening soil, while the disc harrow is energy efficient for soil fragmentation during primary tillage. Tillage at an intermediate water content, close to the plastic limit, gave the largest proportion of small aggregates and consequently the lowest energy use for soil fragmentation. [Copyright &y& Elsevier]

Due to its persistence, subsoil compaction should be avoided, which can be done by setting stress limits depending on the strength of the soil. Such limits must take into account soil moisture status at the time of traffic. The objective of the work presented here was to measure soil water changes during the growing period, use the data to calibrate a soil water model and simulate the soil susceptibility to compaction using meteorological data for a 25-year period. Measurements of soil water content were made in sugarbeet (Beta vulgaris L.) from sowing until harvest in 1997 on two sites classified as Eutric Cambisols in southern Sweden. Sampling was carried out at 2-week intervals in 0.1 m layers down to 1 m depth, together with measurements of root growth and crop development. Precompression stress of the soil at 0.3, 0.5 and 0.7 m depth was determined from uniaxial compression tests at water tensions of 6, 30, 60 and 150 kPa and adjusted as a logarithmic function of the soil water tension. Soil water content was simulated by the SOIL model for the years 1963–1988. Risk calculations were made for a wheel load of 8 t and a ground pressure of 220 kPa, corresponding to a fully loaded six-row sugarbeet harvester. Subsoil compaction was expected to occur when the major principal stress was higher than the precompression stress. The subsoil water content was very low in late summer, but increased during the autumn. At the end of August, there was practically no plant available water down to 1 m depth. There was in general good agreement between measured and simulated values of soil water content for the subsoil, but not for the topsoil. In the 25-year simulations, the compaction risk at 50 cm depth was estimated to increase from around 25% to nearly 100% between September and late November, which is the period when the sugarbeet are harvested. The types of simulation presented here may be a very useful tool for practical agriculture as well as for society, in giving recommendations as to how subsoil compaction should be avoided. [Copyright &y& Elsevier]