Subsoil compaction caused by machinery traffic on a Swedish Eutric Cambisol at different soil water contents

Field traffic may reduce the amount of air-filled pores and cavities in the soil thus affecting a large range of physical soil properties and processes, such as infiltration, soil water flow and water retention. Furthermore, soil compaction may increase the mechanical strength of the soil and thereby impede root growth.

The objective of this research was to test the hypotheses that: (1) the degree of soil displacement during field traffic depends largely on the soil water content, and (2) the depth to which the soil is displaced during field traffic can be predicted on the basis of the soil precompression stress and calculated soil stresses. In 1999, field measurements were carried out on a Swedish swelling/shrinking clay loam of stresses and vertical soil displacement during traffic with wheel loads of 2, 3, 5 and 7 Mg at soil water contents of between 11 and 35% (w/w). This was combined with determinations of soil precompression stress at the time of the traffic and predictions of the soil compaction with the soil compaction model SOCOMO. Vertical soil displacement increased with increased axle load. In May, the soil precompression stress was approximately 100 kPa at 0.3, 0.5 and 0.7 m depth. In August and September, the soil precompression stress at 0.3, 0.5 and 0.7 m depth was 550–1245 kPa. However, when traffic with a wheel load of 7 Mg was applied, the soil displacements at 0.5 m depth were several times larger in August and September than in May, and even more at 0.7 m depth. An implication of the results is that the precompression stress does not always provide a good indication of the risk for subsoil compaction. A practical consequence is that subsoil compaction in some soils may occur even when the soil is very dry. The SOCOMO model predicted the soil displacement relatively well when the soil precompression stress was low. However, for all other wheeling treatments, the model failed to predict that any soil compaction would occur, even at high axle loads.

The measured soil stresses were generally higher than the stresses calculated with the SOCOMO model. Neither the application of a parabolic surface load distribution nor an increased concentration factor could account for this difference. This was probably because the stress distribution in a very dry and strongly structured soil is different from the stress distribution in more homogeneous soils.     

土壤质地对玉米不同生理指标水分有效性的影响

为确定土壤质地对玉米不同生理指标水分有效性的影响,该文利用3种土壤（重壤土、中壤土和砂壤土）的盆栽控水试验和1种土壤（重壤土）的田间小区控水试验,研究了玉米不同生理指标随相对土壤含水率（土壤含水率占田间持水率的比）的动态变化。结果表明：3种土壤中各生理指标相对值在相对土壤含水率降低到土壤水分阈值之前保持不变,低于此阈值时随相对含水率的进一步降低而线性降低,且均可用分段函数来拟合（R2=0.824～0.999）。土壤水分有效性大小排序为：砂壤土＞中壤土＞重壤土,而且瞬时生理指标的土壤水分阈值低于日变化和整个试验阶段的累积指标。因此土壤质地和不同生理指标的时间尺度都会影响玉米生理指标对土壤水分有效性的响应。     

Strength attributes and compaction susceptibility of Brazilian Latosols

In this study, strength attributes and compaction susceptibility of the main classes of Brazilian Latosols (Oxisols), under native vegetation, were studied using the load bearing capacity models relating precompression stress, compression index and water potential through statistical regression models. These models were developed based on the results of the analysis of undisturbed soil samples collected at the B horizon at the different sites. The results showed that the maximum value of the compression index was 0.53 for the Acric Red Latosol, indicating its higher susceptibility to soil compaction. The Dystrocohesive Yellow Latosol had the highest load bearing capacity, while the Acric Red Latosol had the lowest one. The Dystrocohesive Yellow Latosol due to its high load bearing capacity and bulk density (mechanical resistance) behave similarly to hardsetting soil, in which the plants root system has severe physical restrictions to explore deeper horizons during the dry periods. Differences in the load bearing capacity and compaction susceptibility were found to be influenced by soil structure which is associated with clay mineralogy in these very weathered-leached soils and water potential. The study also showed that soil compression index is influenced by water potential and clay mineralogy also. Our work has laid a foundation for estimation of compaction susceptibility of Latosols.     

Physical resilience of soil to field compaction and the interactions with plant growth and microbial community structure

Soil compaction has deleterious effects on soil physical properties, which can affect plant growth, but some soils are inherently resilient, whereby they may recover following removal of the stress. We explored aspects of soil physical resilience in a field‐based experiment. We subjected three soils of different texture, sown with winter wheat or remaining fallow, to a compaction event. We then monitored soil strength, as a key soil physical property, over the following 16 months. We were also interested in the associated interactions with crop growth and the microbial community. Compaction had a considerable and sustained effect in a sandy loam and a sandy clay loam soil, resulting in an increase in strength and decreased crop yields. By contrast compaction had little effect on a clay soil, perhaps due initially to the buoyancy effect of pore water pressure. Fallow clay soil did have a legacy of the compaction event at depth, however, suggesting that it was the actions of the crop, and rooting in particular, that maintained smaller strengths in the cropped clay soil rather than other physical processes. Compaction generally did not affect microbial communities, presumably because they occupy pores smaller than those affected by compaction. That the clay soil was able to supply the growing crop with sufficient water whilst remaining weak enough for root penetration was a key finding. The clay soil was therefore deemed to be much more resilient to the compaction stress than the sandy loam and sandy clay loam soils.     

Mechanisms of soil vulnerability to compaction of homogenized and recompacted Ultisols

Soil compaction is a main cause of soil degradation in the world and the information of soil compaction in subtropical China is limited. Three main Ultisols (quaternary red clay, sandstone and granite) in subtropical China were homogenized to pass through 2 mm sieve and recompacted into soil cores at two bulk densities (1.25 and 1.45 g cm⁻³). The soil cores were equilibrated at different matric potential values (−3, −6 and −30 kPa) before subjected to multi-step compaction tests. Objectives of this study were to determine how different initial soil conditions and loading time intervals influence pre-compression stress and to evaluate an easy measure to determine soil vulnerability to compaction. It became evident that the soil strength indicator, pre-compression stress, was affected by soil texture, initial soil bulk density and matric potential. The coarser the soil texture, the lower the bulk density and the higher the matric potential, the lower was the pre-compression stress. The pre-compression stress decreased exponentially with increasing initial soil water content. Soil water content and air permeability decreased after compaction. The amount of water loss was affected not only by soil texture, bulk density and initial water content but also by loading time interval. These results indicate soil pore structure and hydraulic conductivity changed during compactions. The applied stress corresponding to the highest changes of pore water pressure during compaction had a significant linear relationship with the pre-compression stress (R=0.88, P<0.001). The correlation was ascribed to that the changes in pore water pressure describe the dynamics of the interactive effects of soil pore characters and soil water movement during compaction. The results suggested the evaluation of soil vulnerability to compaction have to consider the initial soil condition and an easy method to measure the changes in pore water pressure can be applied to compare soil strength and soil vulnerability to compaction.     

The variation of soil critical state parameters with water content and its relevance to the compaction of two agricultural soils

Examination of the previously published results of laboratory compression tests on a loam and a sandy loam has shown that as the water content and degree of saturation of a soil increase, the gradient of the virgin compression line, expressed in terms of specific volume and log of spherical pressure, increases and its intercept decreases. The water contents of the soils ranged from 5% to 30% and the degrees of saturation ranged from 10% to 40%. For both soils the gradient of the recompression line for previously compressed soils was shown to decrease with decreasing initial specific volume (increasing density) and to approach zero at a specific volume of 1.5 (dry bulk density of 1750 kg/m₃). It was deduced that the position of the critical state line also varies with soil water content and that the critical state theory can be extended to unsaturated soils and therefore be of use in predicting the mechanical behaviour of agricultural soil during cultivation and compaction.     

不同含水率高易溶盐含量的伊犁黄土流变特性

流变学研究方法可以揭示黏弹性物质的流动和变形规律,常被应用于土体结构的力学稳定性及长期变形参数研究。为了深入探究伊犁黄土类土的黏弹性和结构稳定性,该研究采用流变仪对不同含水率和易溶盐(Na₂SO₄)含量的伊犁黄土类土进行了稳态和动态流变试验,引入Bingham模型对小剪切速率下的流变曲线进行了拟合,并分析解释了稳态和动态流变试验的演化过程。同时,讨论了含水率及易溶盐含量对稳态和动态流变参数的影响规律,定量分析了流变参数与各变量之间的关系。结果表明：稳态剪切过程中土体由固态向类固态转化,并最后趋于流态,具有剪切变稀行为;随着含水率及易溶盐含量增大,屈服应力和黏度均减小,且屈服应力在300～1 100 Pa之间。随着含水率和易溶盐含量增大,动剪切强度参数和黏弹性参数均线性减小,土体的结构稳定性降低。当剪切应变小于0.1%时,土体处于线性黏弹区,损耗因子变化不大;剪切应变大于0.1%时,损耗因子逐渐增大。高含水率及高易溶盐含量的土壤最先到达屈服点,说明高含水率和高易溶盐含量不利于土体结构的稳定性。随着含水率的增大,易溶盐含量对流变参数的影响程度变小...     

Physico-mechanical properties and yield of silage corn as affected by soil compaction and tillage methods

Experimental investigations were conducted over three years to test the hypothesis that soil compaction affects the physical and mechanical properties of corn ears and corn cobs. Field experiments were made on sub-drained clay and sandy loam soils at Macdonald College Farm in Quebec Province of Canada. The mechanical properties of corn ears and corn cobs were determined from quasi-static force-deformation analysis performed with a universal Instron testing machine.

The results showed that soil compaction treatments did not significantly influence corn cob elastic modulus and strength in simple bending nor in radial compression. Cob moisture content did not significantly change as a result of the application of various traffic treatments. However, corn cob diameter and pith diameter were both significantly affected by soil compaction.

Corn ear moisture content and bending strength were not significantly affected by soil compaction. However, corn ear yield in all three years was found to be dependent on the amount of soil compaction applied.

Also studied were the effects of various tillage methods in ameliorating the deleterious effects of soil compaction on crop yield and crop quality. It is concluded that a judicious choice of tillage machinery system can minimize the reductions in ear yield due to soil compaction.     

A method for predicting soil susceptibility to the compaction of surface layers as a function of water content and bulk density

Identifying the vulnerability of soils to compaction damage is becoming an increasingly important issue when planning and performing farming operations. Soil compaction models are efficient tools for predicting soil compaction due to agricultural field traffic. Most of these models require knowledge of the stress/strain relationship and of mechanical parameters and their variations as a function of different physical properties. Since soil compaction depends on the soil's water content, bulk density and texture, good understanding of the relations between them is essential to define suitable farming strategies according to climatic changes. In this work we propose a new pedotransfer function for 10 representative French soils collected from cultivated fields, a vineyard and forests. We investigate the relationship between soil mechanical properties, easily measurable soil properties, water content and bulk density. Confined compression tests were performed on remoulded soils of a large range of textures at different initial bulk densities and water contents. The use of remolded samples allowed us to examine a wide range of initial conditions with low measurement variability. Good linear regression was obtained between soil precompression stress, the compression index, initial water content, initial bulk density and soil texture. The higher the clay content, the higher the soil's capacity to bear greater stresses at higher initial water contents without severe compaction. Initial water content plays an important role in clayey and loamy soils. In contrast, for sandy soils, mechanical parameters were less dependent on initial water content but more related to initial bulk density. These pedotransfer functions are expected to hold for the soils of tilled surface layers, but further measurements on intact samples are needed to test their validity.     

FEM analysis of subsoil reaction on heavy wheel loads with emphasis on soil preconsolidation stress and cohesion

Heavy sugarbeet harvesters may compact subsoil. But it is very difficult to study this by field experiments that resemble agricultural practice. Therefore, an analysis was made by a finite element method (FEM) for a relevant calcaric fluvial soil profile, the mechanical properties of which were largely known. Measuring data of this Lobith loam soil includes preconsolidation stress, compression index and swelling index, all as a function of depth. Using these three types of soil parameters calculations have been done for tyre sizes, inflation pressures and wheel loads that occur with heaviest sugarbeet harvesters available on the European market in 1999. Because no values on soil cohesion were available, the calculations were done for several cohesion levels. The results include the detection of regions with Mohr–Coulomb plasticity and regions with cap plasticity (compaction hardening). For the soil studied—a typical soil strength profile for arable land with ploughpan in the Netherlands in the autumn of 1977—all studied combinations of wheel load and inflation pressure did not induce compaction in and below the ploughpan. The size of the region with Mohr–Coulomb plasticity decreased with increasing cohesion. It appeared from a sensitivity analysis that, although soil modelling may use a great number of soil parameters, the most important parameters seem to be: preconsolidation stress and cohesion. There is an urgent need for data of these parameters that are measured on a great range of subsoils and subsoil conditions.     

Guidelines for safe trafficking and cultivation, and resistance–density–moisture relations of three disturbed soils from Alberta

The Atterberg limits and the Proctor compaction test are used by engineers for classifying soils and for predicting stability of building foundations. Field capacity and wilting point (agronomic limits) are used to indicate available water for plant uptake. Few studies have related the engineering criteria to the agronomic ones with regard to compaction hazard for soils. This study investigated the relationships between Atterberg limits, agronomic limits and the critical moisture content (moisture content at Proctor maximum density) for three disturbed soils (sandy loam and clay loam soils from a reclaimed Highvale mine site, and a silt loam soil from a grazing site at Lacombe) of different textures. Relationships between bulk density, moisture content and penetration resistance for these soils were also investigated. For the sandy loam and loam soils, the field capacity was close to the critical moisture content but lower than the plastic limit. Therefore, cultivation of these two soils at moisture contents close to field capacity should be avoided since maximum densification occurs at these moisture contents. Overall, the critical moisture content or field capacity would be a better guide for trafficking of sandy loam and loam textured soils than the Atterberg limits. For the clay loam, field capacity was within the plastic range. Thus trafficking this soil at field capacity would cause severe compaction. In conclusion, either field capacity or plastic limit, whichever is less, can be used as a guide to avoid trafficking at this moisture content and beyond. For the sandy loam and loam soils penetration resistance significantly increased only with increased bulk density (P≤0.05). For the clay loam soil, penetration resistance was positively related to bulk density and negatively related to moisture content.     

有机质与黏粒含量对黑土压缩-回弹特性的影响

为探明有机质和黏粒对黑土压缩-回弹行为的影响,以典型黑土区耕作土壤为研究对象,通过人工添加腐植酸、人工分离-提取-添加黏粒、恒温恒湿培养的方法各配制3个梯度的重塑土。采用室内固结的方法,通过压缩系数、压缩指数及回弹指数的测定与分析,研究了2种含水量条件下黑土压缩与回弹对有机质和黏粒含量变化的响应行为。结果表明:(1)压缩指数均随有机质含量的增加而增大,且在高含水量时二者呈极显著正相关,有机质含量最高时压缩指数为0.246 3,但有机质含量对回弹无显著影响。(2)无论含水量高低,压缩指数均与黏粒含量呈极显著正相关,而回弹指数随着黏粒含量的增加逐渐降低,且在低含水量时二者呈显著负相关。(3)含水量不同,有机质与黏粒对黑土压缩-回弹特性的影响亦不同;黏粒对黑土压缩-回弹行为的影响更为显著。     

基于准静态压缩的果实黏弹塑性模型

目前对果实黏弹塑性特征与模型进行表征比较困难。基于果实等速压缩变形特征,提出了一表征其黏弹塑性的流变模型。该模型包括3个非线性弹簧元件、一个黏性元件以及一个滑块元件。结合压缩应力—应变试验曲线特征与模型特性提出了模型参数的数值确定方法。采用梨果实全果肉、带核果肉两种试样进行试验,获得了其黏弹塑性模型参数。结果表明试验与理论模型结果非常吻合,果核对其黏弹塑性有较大影响。采用本模型结合试验结果能较准确简便地确定类似特性果实的流变特征参数。研究结果为果品黏弹塑性流变特性分析以及模型表征提供了一种新的方法。     

Quantification of the effects of soil compaction on water flow using dye tracers and image analysis

Abstract. Soil compaction has long been considered to be a problem in arable land, primarily because it causes damage to soil structure, which can lead to serious reduction in crop yields. However, few studies have sought to investigate the effects of soil compaction on the water transport regime of modified soil pore systems. We attempted to quantify the effects of soil compaction on the initiation of preferential flow by using dye tracers and image analysis. A laboratory methodology involving rainfall simulation enabled us to quantitatively evaluate differences in the mechanisms of water flow between two soil types at several degrees of compaction. The results suggested significant differences in the types of water flow pathways between clay loams and sandy loams at different extents of compaction. In the sandy loam, it was concluded that a high degree of compaction led to an increased likelihood of preferential flow, whereas a more uniform movement of soil water occurred at less compaction. By contrast, preferential routing of soil water was recorded in the clay loam, except at the highest measured compaction. The results indicate that the visual techniques of dye tracing and image analysis could enable improved understanding of flow pathways of soil water associated with soil compaction.     

初始含水量和容重对黑土压缩特性的影响

东北黑土区农业机械化水平高,农机作业压实导致的土壤结构和物理性状退化问题日益严重,压缩特性是定量分析土壤压实过程的有效手段,但目前黑土压缩特性随初始含水量和初始容重的变化规律尚不明确。为了解初始含水量和初始容重对黑土压缩特性的影响程度及其变化关系,该研究以重塑黑土为对象,设0.15、0.20、0.25、0.30、0.35、0.40 g/g共6个初始含水量水平,设1.00、1.10、1.20、1.30、1.45、1.60 g/cm³共6个初始容重水平,使用固结仪进行单轴压缩试验测定土壤压缩曲线,分析初始含水量和容重对压缩特性影响。结果表明,土壤初始含水量、容重及两者交互作用均极显著影响重塑黑土压缩特性(P<0.001),据此建立了预测压缩特性的土壤传递函数。黑土的预固结压力为10.42～1 106.17 kPa,与初始含水量显著线性正相关、与初始容重显著线性负相关(P<0.05);压缩指数为0.311～0.852,与初始含水量和容重呈二元多项式方程的关系,随初始容重的增大而降低,在中等含水量时最大;回弹指数为0.007～0.321,与初始含水量正相关,与...     

Subsoil compaction by heavy sugarbeet harvesters in southern Sweden: III. Risk assessment using a soil water model

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.     

双氰胺对不同质地红壤中碳酸氢铵的硝化抑制作用研究

通过室内好气培养试验,研究了双氰胺(DCD)对施入不同质地红壤中碳酸氢铵的硝化抑制作用。结果表明,添加DCD明显提高了相应处理的铵态氮含量,降低了硝态氮含量。无论加入DCD与否,砂壤土中碳酸氢铵的硝化时间大约都需7周;轻粘土中碳酸氢铵的硝化时间为35.d,加入硝化抑制剂后硝化时间可延长2周;而中壤土中至培养结束时仍有较高的铵态氮,故铵的硝化时间有待进一步研究。DCD对碳酸氢铵的硝化抑制效果中壤土优于砂壤土、轻粘土;在砂壤土和轻粘土中,DCD对低浓度铵态氮处理的硝化抑制效果好;而在中壤土中对高浓度的抑制效果好。     

铁矿尾砂配施有机物料对褐土压缩及回弹特性的影响

铁矿尾砂作为工业废弃物已经应用于农业生产，可以改善土壤结构；农业机械作业造成的土壤压实、破坏土壤结构是影响作物产量的主要原因之一。论文旨在探讨铁矿尾砂配施有机物料对褐土压缩—回弹特性的影响，将混有铁矿尾砂和有机物料的土壤以18%含水率培养一昼夜，按1.25 g/cm3容重装入土工试验专用环刀，采用快速固结试验方法，进行单轴压缩试验。结果表明，随铁矿尾砂施用量增加，在低应力时，土壤孔隙比减小量（?e）变大；在高应力时，土壤 ?e 变小。预固结压力值（Pc）和压缩指数（Cc）均随铁矿尾砂施用量增加而降低，Pc和Cc变化范围分别为72.91～119.30 kPa、0.445～0.720，二者均与有机质含量呈极显著正相关关系；与砂粒含量呈极显著负相关关系（P<0.01）。回弹指数（Cs）变化范围为0.0109～0.0169，与有机质及砂粒含量均无显著相关关系，有机物料是影响土壤回弹指数的主要因素。较对照相比，20%铁矿尾砂配施有机物料处理使压缩指数降低12.77%，预固结压力值和回弹指数分别提高6.93%和22.14%，降低压实风险。     

Effect of magnetized water on infiltration capacity of different soil textures

The infiltration process is important in the planning and management of irrigation systems. This study was performed in Mazandaran province, Iran, to compare the effect of magnetized and non‐magnetized irrigation water on cumulative infiltration and final infiltration rate of three soil textures. Magnetized water was obtained by passing the water through a strong permanent magnet installed on a feed pipeline. The results showed that the effects of soil texture and magnetized irrigation water on cumulative water infiltration and final infiltration rate was significant (P < 0.01). Cumulative water infiltration and final infiltration rates with magnetized water were greater than that of non‐magnetized water. The cumulative water infiltration rate after 4 h for magnetized and non‐magnetized water was 26.4 and 12.7 cm in clay soil, 37.6 and 20 cm in silty loam soil and 40.8 and 29.3 cm in sandy loam soil, respectively. The final infiltration rates after 4 h for magnetized and non‐magnetized water were 0.05 and 0.023 cm/min in clay soil, 0.063 and 0.036 cm/min in silty loam soil and 0.076 and 0.046 cm/min in sandy loam soil, respectively. Therefore, magnetized irrigation water had most effect on the infiltration capacity of clay soil.     

Interpretation of uniaxial,confined compression test data for agricultural topsoils

Traditionally, soil strength is estimated from uniaxial, confined compression tests by procedures adopted from classical soil mechanics. The heterogeneity of agricultural topsoil calls for an alternative approach. Undisturbed soil cores were collected in the plough layer of 14 soils in arable agriculture. Soil texture ranged from coarse sandy to silty loam soils with a maximum of 20% clay. The samples were drained to either of six matric potentials in the range from − 30 to − 300 hPa. Uniaxial, confined compression was applied to ∼800 kPa with strain-controlled stress application (1 mm min⁻¹). Measured strain was fitted to stress by the Morgan-Mercer-Flodin (MMF) model. The model fitted data remarkably well for all samples. Three fitting parameters of the model reflected physical characteristics of soil reaction to stress. The estimates of soil compressibility calculated from the model at 10 kPa (C₁₀) correlated closely and linearly to the C_s index considered to reflect elastic deformation in classical studies of soil compression tests. Soil bulk density and content of soil organic matter decreased C₁₀ as well as compressibility at 100 (C₁₀₀) and 400 kPa (C₄₀₀). A complex pattern in the effects of soil texture and soil moisture on compressibility was revealed. The pattern in strain-stress data is interpreted as a reflection of a gradual transition from elastic to plastic deformation of the mixture of structural units. The MMF model is suggested for interpretation of strain-stress data from uniaxial, confined compression tests. This implies use of stress in a linear scale.