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Rubber-tracked vehicles are becoming increasingly popular in agriculture. Rubber-tracked undercarriage systems are typically fitted instead of tyres on heavy agricultural vehicles, with the aim of e.g. decreasing soil stress and soil compaction risks. Therefore, accurate prediction of soil stresses below rubber-tracked systems is important. Here, we present a model for prediction of vertical stress distribution at the rubber track–soil interface. In the model, the rubber-tracked undercarriage system consists of a front and rear wheel (idler and drive wheel) and a number of support rollers. The stress distribution in the longitudinal direction under a wheel or roller is described by harmonic oscillation, with the dynamic contact length being a function of wheel or roller diameter. In the lateral direction, the stress distribution is modelled by a linear function, with the maximum stress under the centre line of the track. Model input parameters include the load on the track, track width, track length (distance between front and rear axles), number of support rollers and wheel and roller diameter. The model, which is written in Visual Basic and implemented as a macro in an Excel spreadsheet, then computes the vertical stress at the rubber track–soil interface based on these inputs and the stress distribution generated in the contact area can be used to simulate soil stresses. The model provides realistic estimates of the vertical stress at the contact between rubber track and soil, thereby improving predictions of soil stress and the compaction risks of rubber-tracked agricultural vehicles. [ABSTRACT FROM AUTHOR]

Several previous field studies in temperate regions have shown decreased soil respiration after conventional tillage compared with reduced or no-tillage treatments. Whether this decrease is due to differences in plant residue distribution or changes in soil structure following tillage remains an open question. This study investigated (1) the effects of residue management and incorporation depth on soil respiration and (2) biological activity in different post-tillage aggregates representing the actual size and distribution of aggregates observed in the tilled layer. The study was conducted within a long-term tillage experiment on a clay soil ( Eutric Cambisol) in Uppsala, Sweden. After 38 y, four replicate plots in two long-term treatments (moldboard plowing (MP) and shallow tillage (ST)) were split into three subplots. These were then used for a short-term trial in which crop residues were either removed, left on the surface or incorporated to about 6 cm depth (ST) or at 20 cm depth (MP). Soil respiration, soil temperature, and water content were monitored during a 10-d period after tillage treatment. Respiration from aggregates of different sizes produced by ST and MP was also measured at constant water potential and temperature in the laboratory. The results showed that MP decreased short-term soil respiration compared with ST or no tillage. Small aggregates (< 16 mm) were biologically most active, irrespective of tillage method, but due to their low proportion of total soil mass they contributed < 1.5% to total respiration from the tilled layer. Differences in respiration between tillage treatments were found to be attributable to indirect effects on soil moisture and temperature profiles and the depth distribution of crop residues, rather than to physical disturbance of the soil. [ABSTRACT FROM AUTHOR]

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]

Rapid, uniform crop establishment is a precondition for efficient crop production. In order to develop guidelines for seedbed preparation and sowing, extensive experiments were carried out in plastic boxes placed in the field directly on the ground for studies of the effects of seedbed properties on crop emergence. This paper deals with the effects on emergence of cereals caused by surface-layer hardening, induced by simulated rainfall (irrigation) after sowing followed by dry weather. The experimental crop was spring barley (Hordeum vulgare L.). Soils for the experiments (Eutric Cambisols, silt loam or clay loam in most cases) were collected from the surface layer of farm fields in various parts of Sweden. On soils with high silt content, irrigation after sowing often caused slumping and subsequent hardening of the whole seedbed. On clay soils, usually only a shallow surface crust formed. The earliest irrigation had the most negative effects on crop emergence. On a silt loam soil with unstable structure, irrigation with only 5 mm reduced emergence to under 20%. Later or heavier irrigation was often less negative, as it allowed the plants to emerge before the surface layer dried and hardened. Deep sowing greatly increased the negative effects on emergence, whereas soil aggregate size usually had negligible effects. It was concluded that when sowing in practice, seedbed preparation and sowing depth should be chosen to promote the fastest possible emergence. Sowing immediately before rain should be avoided, as should shallow sowing that requires rain for the seed to germinate. [ABSTRACT FROM AUTHOR]

Abstract: Tillage experiments were carried out in order to study the effect of water content on the aggregate size distribution produced by tillage, and to investigate the relationship between the soil structures produced by tillage and Dexter''s index of soil physical quality, S. Tillage with a mouldboard plough was done on four different soils over a range of naturally occurring water contents. The aggregate size distribution and the specific surface area produced by tillage were obtained by sieving. We define the optimum water content for tillage, θ OPT, as the water content at which the specific surface area of the aggregates produced is maximum. This is consistent with the water content at which the amount of small aggregates produced is greatest and the proportion of clods produced is smallest. For the four investigated soils, θ OPT was found to be close to the water content at the inflection point of the water retention curve, and in the vicinity of 0.8θ PL (where θ PL is the lower plastic limit). At water contents either lower or higher than θ OPT, the specific surface area produced was smaller. The specific surface area produced at θ OPT was found to be strongly correlated with the index of soil physical quality, S. The specific surface area produced is larger the greater S, i.e. the better the soil physical quality. Consistently, the proportion of small aggregates produced at θ OPT is larger and the proportion of clods produced at θ OPT smaller, the greater S. No clods (>50mm) are produced on soils with good physical quality. [Copyright &y& Elsevier]

Abstract: Autumn tillage strategies designed to reduce leaching losses of nitrogen (N) from arable fields were examined on a medium clay soil (approx. 40% clay) in terms of their effects on accumulation of soil mineral N (SMN) during autumn and winter, crop N uptake, grain yield (spring-sown cereals) and soil structure over the long term (1997–2004). Tillage strategies included mouldboard ploughing (20–25cm depth) and stubble cultivation (10–12cm depth) in different combinations and timing, together with different options for straw management and catch crops. Postponing mouldboard ploughing from early September to early November significantly decreased SMN content during autumn and winter, although levels were generally low in all treatments. On average, the soil profile down to 90cm depth contained 30kgNha−1 in November and 27kgNha−1 in December with early mouldboard ploughing, while the corresponding figures for late mouldboard ploughing were 16 and 21kgNha−1. Stubble cultivation stimulated N mineralisation but the increase in SMN from tillage in September to November was only 3kgha−1 after stubble cultivation, compared with 8kgha−1 after mouldboard ploughing. Stubble cultivation before late mouldboard ploughing resulted in 6kgha−1 higher SMN during autumn than late ploughing without preceding cultivation. Postponement of mouldboard ploughing significantly decreased grain yield by on average 11% and this negative effect accumulated over time. A catch crop compared with no catch crop reduced SMN during autumn and winter by 3–5kgha−1 and had no significant yield effect. Effects of straw incorporation were small and could not be significantly proven either for SMN or yield. Transport of SMN to deeper layers was generally limited and SMN did not decrease during winter, indicating a minor impact of tillage time on N leaching risk. No significant changes in soil physical parameters were detected, but the results indicated poorer soil structure after tillage in late autumn compared with early autumn in terms of higher soil bulk density, lower aggregate stability in water, and lower infiltration rate. Overall, considering the short-term and long-term negative effects on yield and possibly soil structure, the benefit of delaying tillage seems small on this clay soil. [Copyright &y& Elsevier]

Abstract: Soil disturbance by tillage and traffic often adversely affects aggregate stability, leading to colloid and particle mobilisation, which may result in crusting, low water infiltration rate and sediment transport. Hence, minimising soil tillage is an important step in conserving soil quality. This study investigated readily dispersible clay (RDC) and particle transport as affected by shallow tillage or mouldboard ploughing in five Swedish long-term reduced tillage experiments that had been underway for 15–31 years at the time of soil sampling. The soils of the experimental sites are Eutric and Dystric Cambisols. RDC of soil samples, collected in 0–10cm and 12–17cm depth, from mouldboard ploughed (MP) and shallow tillage (ST) plots was compared by measuring turbidity. Particle transport was also determined in undisturbed soil columns (20cm in diameter and 20cm high) from these treatments. RDC and particle transport were significantly lower for ST than for MP at three sites where clay content was above 30%. Particle transport in two soils (clay content above 40%) increased with irrigation events, indicating that preferential transport dominated in unsaturated soil columns, but matrix flow and, consequently, particle dispersion increased as the soil approached saturation. Despite more organic C accumulation in the upper 0–10cm of ST than in the 12–17cm soil layer, clay dispersion was lower in the latter. Particulate P (Total P−dissolved P) was well-correlated to turbidity, suggesting that analysis costs often can be cut by only measuring turbidity. Shallow tillage generally produced positive environmental effects without negative effects on crop yield, especially on soils with high clay content. [Copyright &y& Elsevier]