Prediction of soil structures produced by tillagePrédiction des structures du sol produites par labourageVoraussage der durch bodenbearbeitung erzeugten bodenstrukturen

A statistical method for describing the distribution of aggregates and voids within tilled soil is used as the basis for a prediction technique. Transforms of aggregate-void and void-void transition probabilities are used in such a way that factors can be defined which describe how the soil structure differs under a range of circumstances. A standard structure is defined for a given soil as that which is produced at the 5 cm depth by one pass of a set of tines working at 10 cm depth when tillage is done at a speed of 1.4 m/s in soil at a water content equal to the plastic limit and which has previously grown a cereal crop. Factors are defined which describe deviations from this standard structure as a function of depth in the tilled layer, implement type, previous use of the soil, number of implement passes, water content at time of tillage, and subsequent compaction of thettilled layer. Application of the inverse transform then enables estimates of the distributions of aggregates and voids in the tilled layer to be predicted for required, specified conditions.     

Effect of rainfall on the surface micro-relief of tilled soil

Surface micro-reliefs after four different tillage treatments were measured with a relief meter. Measurements were taken at the time of tillage and on four successive dates. The relief measurements were used to calculate the autocorrelation functions, the power spectra, and the distributions of surface slopes. Changes in parameters of these functions are related to estimates of the cumulative rainfall kinetic energy between the readings and the tensile yield stress of aggregates from the tilled soil. The effect of rainfall was to reduce the roughness to a given proportion in a time which was independent of the initial roughness of the surface, and hence independent of the type of implement used.     

Predicting soil fragmentation during tillage operation using fuzzy logic approach

One of the main characteristics of the soil structure, which affects the plant growth and its yield, is its aggregates size. Correct tillage operations leads to prevention from soil degradation and help to maintain and improve its physical, chemical, and biological characteristics. In this paper, a model based on fuzzy logic approach was used to describe the soil fragmentation for seedbed preparation in the composition of primary and secondary tillage implements of subsoiler, moldboard plow and disk harrow as conventional tillage composition in the region. Field experiments were carried out at educational and research farms of faculty of agriculture, University of Mohaghegh Ardabili. In this paper, an intelligent model, based on Mamdani approach fuzzy modeling principles, was developed to predict soil fragmentation during tillage operation. The model inputs included soil moisture content, tractor forward speed and soil sampling depth. The fuzzy model consisted of 50 rules, in which three parameters of root mean square error (RMSE), relative error (ɛ), and coefficient of determination (R²) were used to evaluate the fuzzy model. These parameters were calculated 0.167%, 3.95%, and 0.988%, respectively. According to the results of this research, the fuzzy model can be introduced as one of the methods for predicting soil fragmentation during the tillage operation with high accuracy.     

Reverse-rotational rotary tiller for reduced power requirement in deep tillage

In this paper details of rotary tillage regarding the movement of tilled soil are presented. A noticeable reduction of tillage power requirement was achieved during rotary tillage. The soil movement depended upon the direction of rotation and the ratio of tilling depth (H) to blade radius (R). With the differences in the soil movement, four kinds of rotary tilling patterns were determined. Increase in operating power generally resulted when a large amount of tilled soil was re-tilled in the zone of blade rotation. Improvement of backward throwing of the soil was required for power reduction, especially in deep tillage. A backward throwing model of soil by the blade was developed on the basis of trochoidal motion of the blade and sliding motion of the soil over a scoop-surface on the horizontal portion of the blade. The throwing model estimated the conditions for avoiding re-tillage, such as direction of rotation and shape of scoop-surface. The throwing model was applied to the design of the shape of the scoop-surface which enabled maximum backward throwing of the soil sufficient to avoid re-tilling. At tilling depths greater than 300 mm, reverse rotation with the new shaped blades brought about a tillage power reduction by about a half compared to forward or reverse rotation with conventional blades.     

Spatial distribution of soil forces on moldboard plough and draft requirement operated in silty-clay paddy field soil

Spatial distribution of soil forces on the surface of plough is an important aspect that can help engineers for improving efficiency of tillage implement. It was analyzed at eleven different points of the moldboard plough with the help of sensors accompanied with the virtual instrument developed in LabView software with the aid of other supporting instruments. It was observed that soil forces increased with an increase in speed and depth. Depth changed soil forces more at upper parts than lower parts whereas speed affected rear parts more than the front part of the plough. Draft forces followed almost similar trend and least value of 308.17 N experimental draft force was found at 1 m/s speed and 5 cm depth under 33% moisture content. Cumulative soil forces found too smaller than the draft as they represented the force spatial distribution of specific parts of plough. It was observed that sensor technology provided real time picture of force variation during tillage process that could save time and effort.     

Soil-blade dynamics in reverse-rotational rotary tillage

Soil cutting and the clod crack formation process during reverse-rotational rotary tillage in a heavy clay soil were investigated. Of particular interest was the relationship between clod crack formation and tillage resistance during sequential rotations of the tillage blade. Investigation of the crack formation process is helpful to develop and to design more effective and high performance tillage methods. This paper describes two new discoveries. The first is that the tillage resistance showed a higher cross-correlation between sequential rotations within a certain distance of tilling, while there was little or no cross-correlation between different tillage plots that were separated more than 0.4 m. The forward distance of untilled soil that was disturbed by the tillage blade was estimated to be 36.4 mm. This is the distance of two tillage pitches. The second discovery involved the blade frequencies during tilling. Fluctuation in tillage resistance frequencies of a single blade was nearly equal to the predicted occurrence of crack intervals on the tilled clod's surface. This frequency was 120 Hz. When these frequencies were translated into the distance along the trochoid trajectory of the blade cutting edge, they were the same as the length of the clods tilled by the reverse-rotational rotary tiller. These minute vibrations in the tillage resistance were considered the important indexes for recognizing the tilled soil conditions and the tilled clod failure on the reverse-rotational rotary tiller. The analytical results of this paper will be utilized for the active occurrence of the cracks regarding with natural frequency of the blade and the operation condition of the reverse-rotational rotary tiller.     

Influence of the axle load, tyre size and configuration on the compaction of a freshly tilled clayey soil

Enhancement of the potential root growth volume is the main objective of farmers when they establish a conventional tillage system. Therefore, the main function of primary tillage is to increase soil’s structural macroporosity. In spite of this, during secondary tillage operations on these freshly tilled soils, the traffic on seedbeds causes significant increases in soil compaction. The aim of this paper was to quantify soil compaction induced by tractor traffic on a recently tilled non consolidated soil, to match ballast and tyre size on the tractors used during secondary tillage. The work was performed in the South of the Rolling Pampa region, Argentina. Secondary tillage traffic was simulated by one pass of a conventional 2WD tractor, using four configurations of bias-ply rear tyres: 18.4×34, 23.1×30, 18.4×38 and 18.4×38 duals, two ballast conditions were used in each configuration. Soil bulk density and cone index in a 0 to 600 mm profile were measured before and after traffic. Topsoil compaction increased as did ground pressure. Subsoil compaction increased as total axle load increased and was independent from ground pressure. At heavy conditions, topsoil levels always showed higher cone index values. From 150 to 450 mm depth, the same tendency was found, but with smaller increases in the cone index parameter, 22 to 48%, averaging 35%. Finally, at the deepest layer considered, 600 mm, differential increases due to the axle load are great enough as to be considered similar to those found in the upper horizon, 36 to 64%, averaging 55%. On the other hand, bulk density tended to be less responsive than cone index to the traffic treatments. Topsoil compaction can be reduced by matching conventional bias-ply tyres with an optimized axle weight.     

Effects of tillage systems on compaction and crop yield of Albic Luvisol in Croatia

This four-year experiment was conducted in north-west Slavonia (agricultural area of Croatia) to evaluate the effects of different tillage systems on compaction of silty loam soil (Albic Luvisol). The compared tillage systems were: (1) conventional tillage (CT), (2) conservation tillage (CM), (3) no-tillage system (NT), and the crop rotation was corn (Zea mays L.) – winter wheat (Triticum aestivum L.) – corn – winter wheat. For detecting the soil compaction, bulk density and penetration resistance were measured during the growing seasons. In all seasons and tillage systems, the bulk density and penetration resistance increased with depth and the greatest increase from surface to the deepest layer in average was observed at CT system. The bulk density and penetration resistance increased at all tillage systems during the experiment, but the greatest increase was also observed at CT system. The greatest bulk density (1.66 Mg m⁻³) and the greatest increase of 6.4% were observed at CT system in the layer 30–35 cm. In the first season, the bulk density was the greatest at NT system, but during the experiment the lowest average increase of 1.9% was observed at this system. The greatest penetration resistance of all measurements (5.9 MPa) was observed in the last season at CT system in depth of 40 cm. The lowest average increase of penetration resistance 11.4% was also observed at NT system. The highest yield of corn in the first season was achieved with CT system while in other seasons the highest yield of winter wheat and corn was achieved with CM system.     

Productivity of tillage loosening and separating machines in an aggregate with tractors of various capacities

Currently, chemical methods of weed control are increasingly being replaced by mechanical weeding. One of the promising mechanical devices for weed control is a rotary loosening and separating stratifier. This tillage machine can provide high quality tillage to a depth of up to 18 cm. Its performance is determined by the width of the grip of the gun and the speed of movement and is limited by the traction capabilities of the tractor. Using the Goryachkin formula for the traction resistance of a tillage machine, the authors obtained the dependence of productivity on the width of the grip and the speed of movement at different depths of tillage. The obtained dependencies on the example of tractors John Deere 8330, HTZ 16131-05 and MTZ 1523.3 showed the presence of a pronounced maximum, which led to the solution of the optimization problem. The article presents a method for calculating the optimal width of the grip and the speed of movement that ensure the maximum productivity of the tillage machine, depending on the depth of processing and the specific resistance of the soil. The use of optimal parameters of the tillage machine allows you to increase its productivity by 2–3 times.     

Soil strength as affected by tillage system and wheel traffic in wheat -corn rotation in central Anatolia

This paper discusses the loading of a typical central Anatolian soil by the most commonly used corn and wheat production agricultural equipment. It further describes the effect that loading and soil conditions have on soil strength, namely compaction, and proposes techniques for minimizing undesired soil compaction. Experiments were carried out on a typical central Anatolian medium-textured imperfectly drained clay loam soil (Cambisol). Three different tillage methods and subsequently the same field operations were used for each rotation. Shear strength, penetration resistance, bulk density and moisture variations were detected in four sampling periods at each rotation. Tillage reduced the soil strength with the mouldboard plough causing the greatest loosening. However, natural processes and the vehicular traffic caused the soil to be re-compacted to about the same values as before. In any of the cases the obtained parameters did not exceed the critical values for plant growth except the penetration resistance in the 20–30 cm depth layer during corn production.     

An investigation of the bevameter soil physical measurements in the prediction of soil tool draft

The relationship between the parameters measured during soil testing using the bevameter system and the horizontal forces acting on a simple soil-cutting blade were investigated. Field experiments were conducted on untilled, compacted soil and on recently-tilled soil. On both soils, five sites were randomly chosen and bevameter and draft measurements were performed The parameters measured were modulus of soil deformation, wet and dry bulk density, soil moisture content, tool operating depth, tool operating velocity and horizontal draft. A statistical analysis of the data indicated that a mathematical model for predicting draft should contain the following variables: operating depth, dry bulk density and modulus of deformation. A linear regression analysis of draft versus modulus of deformation showed significance at the 95% confidence level on the untilled sites at all measured depths. A similar analysis of the tilled site indicated significance at the 70 mm depth only. The usefulness of the bevameter deformation modulus as an indicator of draft was found to be limited to shallow depths.     

Water flow between soil aggregates

Aggregated soils are structured systems susceptible to non-uniform flow. The hydraulic properties depend on the aggregate fabric and the way the aggregates are assembled. We examined the hydraulic behavior of an aggregate packing. We focused on conditions when water mostly flows through the aggregates, leaving the inter-aggregate pore space air-filled. The aggregates were packed in 3 mm thick slabs forming a quasi two-dimensional bedding. The larger aggregates were wetted with water and embedded in smaller aggregates equilibrated at a lower water content. The water exchange between wet and drier aggregates was monitored by neutron radiography. The three-dimensional arrangement of the aggregates was reconstructed by neutron tomography. The water flow turned out to be controlled by the contacts between aggregates, bottle-necks that slow down the flow. The bottle-neck effect is due to the narrow flow cross section of the contacts. The water exchange was simulated by considering the contact area between aggregates as the key parameter. In order to match the observed water flow, the contact area must be reduced by one to two orders of magnitude relative to that obtained from image analysis. The narrowness of the contacts is due to air-filled voids within the contacts.     

Total axle load effects on soil compaction

Theoretical and applied research has shown that the pressure at a point in the subsurface soil is a function of both the surface unit pressure and the extent of the area over which it is applied (total load). Thirty years ago, most of the soil compaction from vehicle traffic was in the plow layer and was removed by normal cultural practices. As equipment has increased in size and mass, machine designers have increased tire sizes to keep the soil surface unit pressure relatively constant. However, the increase in total axle loads is believed to have caused an increase in compaction at any given depth in the soil profile, resulting in significant compaction in the subsoil.Two tires of different sizes, a standard agricultural tire and a flotation tire were used to support equal loads. Soil pressures were measured at three depths in the soil profile directly beneath each of the tires. Two soils were used and each was prepared first in a uniform density profile, and then they were prepared with a simulated traffic pan (layer of higher density) at a depth of approximately 30 cm.Results showed that the presence of a traffic pan in the soil profile caused higher soil pressures above the pan and lower pressures below it than was the case for a uniform soil profile. The soil contact surface of the flotation tire was approximately 22% greater than the agricultural tire. The greater contact surface did reduce soil pressures at the soil surface, of course, but the total axle load was still the dominant factor in the 18–50 cm-depth range used in this study.     

The reference shrinkage curve of clay soil

The objective of this work is to develop and validate a model that predicts the reference soil shrinkage curve, that is one without crack volume contribution, as a necessary preliminary step in future estimation of soil crack volume from soil shrinkage data. Current soil shrinkage models are based on the approximation of soil shrinkage data by some a priori taken mathematical expressions and justified by the fitting of their parameters to the data. However, the crack volume entering the data is not single valued and depends on shrinkage conditions. Unlike that the reference shrinkage curve is single valued. For soils with sufficiently high clay content when there are no large pores (lacunar pores) inside the intra-aggregate clay, the reference shrinkage curve is derived from the assumption of the rigid superficial (interface) layer of aggregates with changed pore-size range and distribution compared with the intra-aggregate matrix. This consideration is based on accounting for contributions of the interface aggregate layer and intra-aggregate matrix to the soil volume and water content during shrinkage. The reference shrinkage curve is predicted by eight fundamental physical immediately measured parameters of (i) the intra-aggregate matrix (including clay content); (ii) the aggregate structure; and (iii) the mean silt-sand grain size or mean interface layer thickness. The model was validated using the data for eight soils. In addition to the major potential application for estimating a soil crack volume, the model explains differences between the observed shrinkage curves of soil and pure clay, and it can have other numerous applications.     

Morphology of horizontal cracks in swelling soils

Horizontally formed cracks in the network of cracked swelling soils tend to influence water and solute transport. An approach is suggested for estimating the mean width and volume of horizontal cracks. It is assumed that the nearly horizontal cracks appear as a result of inhomogeneous soil subsidence caused by rapid drying and shrinkage of thin layers at the walls of vertical cracks. Compared with the moist soil matrix, at the same soil depth, horizontal cracks originate as ruptures in stretched layers of the drying walls of vertical cracks. A characteristic of the average inhomogeneity of soil subsidence, i.e., the mean potential relative subsidence (MPRS) depending on the soil depth is defined. It is calculated on the basis of linear shrinkage in the clay soil matrix and at the walls of vertical cracks of different depths, and on two geometrical parameters of crack networks. They are namely the maximum crack depth and the thickness of the upper intensive-cracking layer. The absolute value and sign of the derivative of the MPRS function with respect to soil depth determine the specific volume of horizontal cracks (horizontal-cracks porosity), and their mean width as functions of depth. Model predictions are obtained using published data on variation of linear shrinkage with depth in 19 soil profiles. For lack of data specific to horizontal-crack characteristics model, predictions were compared with data on vertical cracks and subsidence at the soil surface. Satisfactory agreement was obtained for all soil depths up to the maximum crack depth.     

A model of stress distribution and cracking in cohesive soils produced by simple tillage implements

The objective of this research was to describe the mechanical behavior of soil under the action of a tillage tool, with the purpose of finding a relation between the tool geometry and the resultant soil structure. The problem was solved using fundamental principles of soil mechanics and force equilibrium analysis. As a result, a mathematical model was developed which describes three stress zones within the cut soil volume: shear failure, tension failure, and no internal failure. The model was programmed into a computer to generate maps of normal and shear stresses to visualize the three failure zones. The model was tested by cutting soil with flat tillage tools in a laboratory soil bin, and it proved to provide reliable predictions of the pattern of soil shear and tension failure.     

贵州石漠化地区棕黄色粘性土团聚体稳定性研究

   以贵州省普定县碳酸盐岩石漠化研究试验区（陈旗村）的棕黄色粘性土为研究对象,考虑了初始含水率和浸润时间两个影响因素,对研究区土体中占绝对优势的>5mm的大颗粒团聚体进行了共计16组湿筛法试验。结果表明：棕黄色粘性土团聚体遇水破裂的过程主要发生在被浸润初期,初始含水率越小的土壤,经雨水浸润后,大颗粒团聚体破裂得越快越彻底;而原本就比较湿润的土体,团聚体的稳定性则较好。因此,对碳酸盐岩石地区石漠化的防治,应着重考虑气候长期干燥、蒸发量对水土流失的影响。

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The development and influence of gas bubbles in phreatic aquifers under natural flow conditions

In a phreatic aquifer, bubbles may result from the entrapment of air during groundwater recharge and/or bacterial metabolism. The calculated critical depth of about 1 m at which bubbles are most likely to be found in a granular aquifer, coincides with the depth of 0.60 m of an almost stagnant water layer (specific discharge 1 × 10^-6 cm sec^-1) found at the water table region under natural flow conditions. Bubbles clog pores and therefore reduce the hydraulic conductivity without significantly reducing the volumetric water content. Stagnation at the water table region results since prevailing pressures (in the order of 10^-1 atmospheres) are not sufficiently large to move bubbles through porous media in a water environment.     

Effect of multiple passes of tractor with varying normal load on subsoil compaction

A field experiment was conducted on alluvial soil with sandy loam texture, in a complete randomized design, to determine the compaction of sub-soil layers due to different passes of a test tractor with varying normal loads. The selected normal loads were 4.40, 6.40 and 8.40 kN and the number of passes 1, 6, 11 and 16. The bulk density and cone penetration resistance were measured to determine the compaction at 10 equal intervals of 5 cm down the surface. The observations were used to validate a simulation model on sub-soil compaction due to multiple passes of tractor in controlled conditions. The bulk density and penetration resistance in 0–15 cm depth zone continuously increased up to 16 passes of the test tractor, and more at higher normal loads. The compaction was less in different sub-soil layers at lower levels of loads. The impact of higher loads and larger number of passes on compaction was more effective in the soil depth less than 30 cm; for example the normal load of 8.40 kN caused the maximum bulk density of 1.53 Mg/m³ after 16 passes. In 30–45 cm depth layer also, the penetration resistance increased with the increase in loads and number of passes but to a lesser extent which further decreased in the subsoil layers below 45 cm. Overall, the study variables viz. normal load on tractor and number of passes influenced the bulk density and soil penetration resistance in soil depth in the range of 0–45 cm at 1% level of significance. However, beyond 45 cm soil depth, the influence was not significant. The R² calculated from observed and predicted values with respect to regression equations for bulk density and penetration resistance were 0.7038 and 0.76, respectively.     

Characteristic loading of light mouldboard ploughs at slow speeds

A study on four mouldboard ploughs, that are commonly used with animal traction in Kenya, was conducted. Draught, suction and torsion loads were measured and specific draught evaluated in field tests on four sites with typical agricultural soil conditions. Draught and suction are the horizontal and vertical components of the reaction to soil force, respectively, while torsion is the resisting moment about the plough shank. The objective was to quantify these parameters and to study their characteristics under variable conditions at operation, at speeds up to 1.12 m/s and tillage depths between 0 and 150 mm in an attempt to optimize the design, selection and utilization of mouldboard ploughs for animal traction in Kenya. It was found that depth of tillage is the most critical factor, and draught and suction increased significantly with depth while specific draught increased or decreased depending on the soil type. Draught and specific draught increased significantly with speed. The increase in suction with depth probably implies an increased stability in the ploughing operation, while its reduction with speed indicates a potential instability of plough control with varying speeds. Consequently, aiming for steady motion in the utilization of animal traction may aid in the optimization. It was also found that ploughs with a high specific draught (kN/m) are expected to experience higher torsional loads on the shanks. The characteristic draught, specific draught and suction loads of the ploughs were described by quadratic functions in speed and depth of tillage with coefficients of determination (R₂) ranging from 0.55 to 0.99. A significant difference in the coefficient of variation of draught loads in the three soil types probably implies that optimal duration for use of animal traction in tillage should be dependent on soil type.