Effects of rake angle of chisel plough on soil cutting factors and power requirements: A computer simulation

A computer simulation was conducted to predict the effects of rake angle of a chisel plough and soil bulk density on angle of soil failure plane, rupture distance, width of side crescent, frictional, overburden, cohesion and adhesion soil cutting factors, draft forces and drawbar power requirements. The experimental work was carried out in two locations. Soil of the first location was sandy clay with the soil bulk densities of 1.75 and 1.70 g/cm³ for firm and loose soil conditions, respectively, with an angle of internal friction of 30° and a surface friction angle of 20°, cohesion of 2.5 kN/m² and adhesion of 1.2 kN/m². Soil of the second location was clay loam with the soil bulk densities of 1.65 and 1.50 g/cm³ for firm and loose soil conditions, respectively, with an angle of internal friction of 34° and a surface friction angle of 23°, cohesion of 2.4 kN/m² and adhesion of 1.14 kN/m². The prediction showed that the angle of failure plane found to decrease with the rake angle. The rupture distance decreased with the rake angle from 15° to 55° and then increased as the rake angle increased over 55°. The width of the side crescent increased as the rake angle increased and the maximum value and the minimum value were recorded at 75° and at 15°. Values of frictional and overburden factors decreased as rake angle increased. The maximum and minimum values were recorded at 15° and 75°, respectively. The values of cohesion factor increased as rake angle increased. The maximum value was recorded at rake angle of 75° and the minimum value was recorded at rake angle of 15°. Adhesion factor was found to change inversely with the rake angle from 15° to 55° and then to change directly with the rake angle over 55°. The draft force decreased with the rake angle and reached its minimum value at 45° rake angle. Over 45°, the draft force increased and reached its maximum value at 75° rake angle. The draft increased with soil bulk density. The power required for moving the plough recorded the maximum value at rake angle of 15°, while the minimum value was recorded at 55° rake angle. The values of power increased with decrease of soil bulk density. The predicted values demonstrated some deviations from the experimental values of the draft force and the drawbar power.     

Comparison of various coulter‐type ground‐driven rotary subsoilers in terms of energy consumption and soil disruption

Hardpans below the normal tillage depth inhibit root penetration and cause drainage problems. Subsoiling is commonly used to disrupt hardpans and provide pathways for water and roots to enter the subsoil. The objective of this study was to develop and compare various types of ground‐driven rotary subsoilers that adequately disrupt compacted soil profiles for conservation tillage systems. To accomplish these objectives, four different coulter‐type ground‐driven rotary subsoilers were designed and manufactured by dividing a 1.2 m diameter coulter into multiple blades. Minimizing the soil resistance was one of the main considerations in forming the shape and number of blades on the coulters. An experiment was conducted in a soil bin to determine the effects of ground‐driven rotary subsoilers on soil disturbance and energy requirements. Treatments were four different types of subsoilers: coulter without blade (CNB), coulter with 5 blades (C5B), coulter with 7 blades (C7B) and coulter with 9 blades (C9B), and two tillage depths (25 cm and 38 cm). To determine the differences between subsoilers, soil disturbance, cone index, bulk density and draft were measured. The C5B subsoiler required considerably less draft, draft power and vertical force for both operation depths followed by the C7B, C9B and CNB subsoilers. The CNB subsoiler left the soil surface clean with no spoil while the coulters with blades caused spoils on the soil surface. The soil disruption paths of the coulters with blades have an advantage for row crops due to limited above‐ground disturbance if seeds can be placed in the middle of the disrupted zone.     

凸齿镇压器与土壤相互作用的三维动态有限元分析

为分析凸齿镇压器与土壤的相互作用、预测不同的作业参数对凸齿镇压器作业效果的影响,该文利用有限元方法,在Abaqus软件中建立了凸齿镇压器与土壤相互作用的三维动态有限元模型。该模型在分析过程中使用任意拉格朗日-欧拉方法对网格进行自适应划分,以解决土体局部变形引起单元畸变而导致分析中断的问题。根据凸齿镇压器的2种工作模式,对模型设置不同的边界条件,探讨不同载荷对凸齿镇压器沉降量和所需牵引力的影响以及不同沉降量对所需载荷及牵引力的影响。搭建了基于室内土槽的凸齿镇压器牵引试验平台,通过土槽试验对有限元分析结果的有效性进行验证。结果表明,有限元求解的牵引力与实测值相对误差为3.4%,并且有限元分析模型运行结果能准确反映土壤的形貌变化特征;任意拉格朗日-欧拉方法有效解决了单元扭曲导致分析不收敛的问题;在恒定速度下,凸齿镇压器的沉降量和所需水平牵引力随着载荷的增大而增大,同样,沉降量的增大导致了所需载荷和牵引力的增加。该三维有限元模型可用于预测凸齿镇压器工作过程中的所需牵引力和土壤表面微形貌加工的作业效果,可为探索凸齿镇压器与土壤相互作用的机理,对凸齿形状进行改良与优化、以及作业条件与参数的选择提供参考依据。     

An approach for draft prediction of combination tillage implements in sandy clay loam soil

A methodology to predict the draft requirements of combination tillage implements in any soil and operating conditions was developed. This methodology required the draft requirements of individual tillage implements in undisturbed soil condition and draft utilization ratio of the rear passive set of combination tillage implement, which is defined as the ratio of the drafts of the rear passive set operating in combination and individually. Laboratory experiments were conducted to measure the draft requirements of a reference tillage tool (single disk), three scale-model individual (moldboard plow, cultivator and disk gang) and two combination (moldboard plow with disk gang and cultivator with disk gang) tillage implements at different depths (5, 7.5 and 10 cm), speeds (1.2, 2.2, 3.2 and 4.2 km/h), wet bulk densities (in the range of 1.27–1.85 g/cm³) and cone index penetration resistance values (in the range of 445–1450 kPa) in soil bin filled with sandy clay loam soil. The average draft utilization ratio of the reference tillage tool obtained were analyzed by both orthogonal and multiple regression techniques to develop the regression equation considering soil properties, operating and tool parameters. The developed draft equation based on the above mentioned methodology was verified with the data obtained for the draft of scale-model and prototype combination tillage implements in the laboratory and field conditions, respectively. It was found that the developed equation predicted the draft of both combination tillage implements within an average absolute variation of 18.0 and 13.5%, respectively.     

A nonlinear 3D finite element analysis of the soil forces acting on a disk plow

This study aimed to compare predicted soil forces on a disk plow with measured forces within the tillage depth of clay (90 g kg⁻¹ sand, 210 g kg⁻¹ silt, 700 g kg⁻¹ clay) and sandy loam (770 g kg⁻¹ sand, 40 g kg⁻¹ silt, 190 g kg⁻¹ clay) soils. The model assumed the effects of both tilt angle and plowing speed. Two plowing speeds (4 and 10 km/h) at three tilt angles (15°, 20° and 25°) were compared and the draft, vertical, and side forces determined. A 3D nonlinear finite element model was used to predict the soil forces while a dynamometer was used to measure them on a disk plow in the field. An incremental method was used to deal with material nonlinearity and the Trapezoidal rule method was used to analyze the dynamic response of soil during tillage. Field tillage experiments were conducted to verify the results of the finite element model. It was found that increasing the tilt angle of the plow increased the draft and vertical forces and decreased the side force. Increasing plowing speed increased the draft and side forces and decreased the vertical force. Generally, the results from the finite element model were found to be compatible with the experimental results in clay soil, while in sandy loam the differences between predicted and measured data were probably due to problems of measuring soil mechanical characteristics in the triaxial test.     

Comparison of tillage forces and wear rates of pressed and cast cultivator shares

The draft force, vertical up force and wear rate of 5-mm-thick pressed steel shares were compared with those of 10-mm-thick cast steel shares. The tests were conducted using a range of soil types and moisture contents over several years. Because they were made of a harder material, the cast shares lost mass at 0.48 of the rate of the pressed shares, irrespective of the soil type or condition. However, the cast shares, because they were made from thicker material, had a blunter cutting edge which in moist soil conditions increased the draft and vertical up forces.

The results showed the wear rate (based on distance) to be independent of the speed of tillage but the soil type and condition had a large effect on the wear rates and tillage forces.     

An improved technique for agricultural implement draught analysis

Agricultural implement draft requirements show considerable spatial variability due to variations in soil properties and fracturing of soil. A large sample size is necessary to obtain a representative mean draft value for a given soil type and condition because of this variability. Moreover, empirical polynomial/multi-linear regression models for implement draft are often subjected to multi-collinearity problems. Proper design of experiments can assist in the complete elimination of these multicollinearity problems. An implement test procedure has been developed which addresses the problems of soil variability and multi-collinearity. Proper choice of values for independent variables in the experimental design phase can assist in transforming these variables to an orthogonal domain which completely overcomes multi-collinearity problems. The orthogonal regression technique using transformed variables and the conventional polynomial/multi-linear regression techniques using real variables were used to analyze draft data for a moldboard plow in a Capay clay soil to illustrate advantages of the orthogonal technique.     

Effect of amplitude and frequency on soil break-up by an oscillating tillage tool in a soil bin experiment

Experiments were conducted in a soil bin to study the effect of amplitude and frequency of an oscillating tillage tool on fragmentation of Kharagpur sandy clay loam soil. It was observed that the maximum utilization of energy occurs at an oscillation frequency close to the natural frequency of the soil. Therefore, optimum values of frequency and amplitude of oscillation were determined on the basis of maximum clod surface produced per unit of energy input. The oscillating tillage tool produced smaller soil aggregates than a non-oscillating one. At a given amplitude of oscillations, increase in frequency above the natural frequency of soil did not increase soil break-up further. At any frequency, soil break-up increased with increase in amplitude. At a tool oscillation frequency equal to the natural frequency of soil the equation MWD = A₀exp(−K₀r), where MWD is the mean weight diameter of soil aggregates, r is the amplitude of the oscillations, A₀ is MWD of soil aggregates produced by an identical rigid tool and K₀ is a constant, described the data on soil break up adequately.     

Effect of soil characteristics, seeding depth, operating speed, and opener design on draft force during direct seeding

Direct seeding practices that promote soil and water conservation and reduce input costs have become an increasingly accepted alternative to conventional tillage systems in western Canada. The objective of the present study was to determine the relative importance of soil characteristics, seeding depth, operating speed, and opener design on draft forces during direct seeding in central Saskatchewan. Draft was measured for nine different openers operated at 1–5 cm seeding depths and three ground speeds in four untilled Chernozemic soils that differed in soil moisture and/or texture. The average increase in opener draft for all fields was 4% for each km h⁻¹ increase in speed. Although the range in soil consistency was small, there was a 24% increase in draft in heavy clay compared to sandy loam soil. Draft force of the average opener increased by nearly 20% for each centimeter increase in seeding depth. However, highly significant interactions among most of the variables investigated indicated that the relative performance of openers was not consistent for the range of conditions evaluated. Large differences among the draft forces of different openers operated at different depths in soils with different consistencies were particulary noteworthy. For example, a 4.5-fold increase in the draft of a low versus a high draft opener operated at 1.25 versus 5.0 cm seeding depth at 7.5 km h⁻¹ in moist, heavy clay soil emphasized the large influence that opener design and seeding depth have on tractor power requirements and direct seeding input costs.     

Draught and vertical forces obtained from dynamic soil cutting by plane tillage tools

An understanding of the relationship between tool forces and speed is important in evolving management strategies for optimum performance. The effect of speed on tillage tool forces were studied experimentally for wide (width=25.4 cm, depth=15 cm) and narrow (width=5.1 cm, depth=22.9 cm) plane tillage blades operating in a Dystric Fluvisol (silty sand texture) in a soil bin. The tools were tested at two depths (10 cm and 15 cm for wide blade, 11.4 cm and 22.9 cm for narrow blade), two rake angles (45° and 90°) and eight speed levels (0.25, 0.5, 0.75, 1.00, 1.25, 1.50, 1.75 and 2.00 m/s). The variables were combined in a 2×2×8 factorial experiment with three replications. The performance of three theoretical models based on the trial wedge approach in predicting the experimental results was evaluated. The first model (Model 1), based on Soehne's approach (with modification for the three-dimensional analysis) assumes that the soil fails in a series of shear planes, forming a wedge that is trapezoidal in shape. The equilibrium of the wedge boundary forces produce the force required for failure. The second model (Model 2), based on Mckyes' approach assumes that soil failure is by the formation of a centre wedge flanked by two side crescents. Equilibrium of the boundary forces on the wedge and crescents produce the forces as a function of an unknown failure angle which is obtained by minimizing the weight component of the total force. Model 3, based on Perumpral's approach assumes the same failure wedge as Model 2 but the total cutting force is minimized instead. Experimental results show that the tool force (draught and vertical force) is a function of the speed and the square of speed whereas the three models assume it to be a function of the square of speed only. The models were not very accurate in predicting the experimental results. The average percent deviation of the predicted forces from the observed values were 43%, 40% and 66% for Models 1, 2 and 3, respectively. Thus, Model 2 had more general agreement with experimental observations. The models were better in predicting the forces (draught and vertical force) for the narrow tool with average percent deviations of 33%, 28% and 46% for Models 1, 2 and 3, respectively, as compared to 53%, 51% and 85% for the wide blade.     

Properties of soils from the Swedish long-term fertility experiments: VI. Mapping soil electrical conductivity with different geophysical methods

Abstract

Swedish long-term soil fertility experiments were used to investigate the effect of texture and fertilization regime on soil electrical conductivity. In one geophysical approach, fields were mapped to characterize the horizontal variability in apparent electrical conductivity down to 1.5 m soil depth using an electromagnetic induction meter (EM38 device). The data obtained were geo-referenced by dGPS. The other approach consisted of measuring the vertical variability in electrical conductivity along transects using a multi-electrode apparatus for electrical resistivity tomography (GeoTom RES/IP device) down to 2 m depth. Geophysical field work was complemented by soil analyses. The results showed that despite 40 years of different fertilization regimes, treatments had no significant effects on the apparent electrical conductivity. Instead, the comparison of sites revealed high and low conductivity soils, with gradual differences explained by soil texture. A significant, linear relationship found between apparent electrical conductivity and soil clay content explained 80% of the variability measured. In terms of soil depth, both low and high electrical conductivity values were measured. Abrupt changes in electrical conductivity within a field revealed the presence of ‘deviating areas’. Higher values corresponded well with layers with a high clay content, while local inclusions of coarse-textured materials caused a high variability in conductivity in some fields. The geophysical methods tested provided useful information on the variability in soil texture at the experimental sites. The use of spatial EC variability as a co-variable in statistical analysis could be a complementary tool in the evaluation of experimental results.     

Methods for measuring soil velocities caused by a sweep

A field experiment was conducted to measure surface soil velocity and to determine the relation between soil aggregate velocities at the tool surface and at the soil surface.

A technique incorporating use of both a video camcorder and wood blocks was developed to measure surface soil velocity. Soil velocity direction at the tool surface was measured from scratch marks on the tool. Velocity measurements were made for three sweeps with different rake angles operated at three speeds and two depths.

Surface soil moved in either of two modes: V-flow (upward and laterally in the shape of one leg of the letter V) or snowplow (initially moving upward and subsequently being buried in a wave of soil). Surface soil velocities were uncorrelated with velocities on the tool surface, indicating that soil flow paths over the sweep were not parallel. The ratio of vertical to lateral soil flow at the tool surface increased with larger rake angle and was greater than the ratio at the soil surface. At the soil surface, vertical velocity was greater near the nose than near the wing tip and velocity parallel to the travel direction increased with increased speed and rake angle.     

受迫振动深松机性能参数优化与试验

为解决目前深松作业机具耕作阻力大、深松深度不稳定、耕作质量不高的问题,该文采用振动减阻原理设计研制了受迫振动深松机。通过分析深松铲的结构和运动过程,建立深松铲的数学模型;确定影响深松牵引阻力的参数;采用正交试验方法得出影响受迫振动参数的最优组合:前进速度2 km/h,振动频率为10 Hz,振动角度为12°。为了验证性能参数最优组合的正确性,开展了受迫振动深松机性能参数检测试验。试验结果表明:振动深松前后,土壤各土层容重均下降,表层土下降达21.74%;在15~25 cm土层含水率增加16.02%;深松后地表平整,耕深稳定变异系数为7.37%,稳定性系数92.63%,振动深松作业后测得土壤扰动系数为57.11%,土壤蓬松度为36.96%,土壤蓬松度和扰动系数均达测试指标的要求。采用受迫振动能使振动深松机显著降低牵引阻力9.09%,减阻效果明显。该研究对深松机振动特性分析与性能参数设计提供了参考。     

Design and performance of an adjustable three-point hitch dynamometer

Mounted implements necessitate the use of a three-point hitch dynamometer to measure the forces between the tractor and implements. In this work, an adjustable three-point hitch dynamometer was designed to fit most of the implements (standard and non-standard) available in Jordan. The dynamometer consists of three telescoping beams connected to a central T-shaped box. The system provides variable width and height of the dynamometer to satisfy a wide range of implement dimensions. Strain gages attached to cantilever beams were connected to a Wheatstone bridge in such a manner that only draft force is measured. The dynamometer was calibrated and several field tests were conducted to measure the force required to pull a chisel plow in a Jordanian clay loam soil at various depths and speeds. Different sets of strain gages can be attached and arranged in the bridge so that only the lateral or vertical forces can be measured.     

The efficacy of three techniques to alleviate soil compaction at a restored sand and gravel quarry

Reinstated soil at restored sites often suffers from severe compaction which can significantly impede root development. Several methods, such as ripping and complete cultivation, are available to alleviate compaction that may occur as a result of soil reinstatement. This paper examines the effectiveness of the industry standard industrial ripper and a prototype modern ripper, the Mega‐Lift, in comparison with the recommended best practice method of complete cultivation. An investigation of the penetration resistance of the soil at a restored sand and gravel quarry was carried out using a cone penetrometer and a ‘lifting driving tool’ (dropping weight penetrometer) 3 years following cultivation. All the cultivation treatments reduced soil compaction to some degree compared with the untreated control. However, the penetration resistance values suggest that rooting would be restricted at relatively shallow depths in the plots cultivated using the industrial and Mega‐Lift ripper; penetration resistance exceeded 2 MPa within the first 0.33 m. Complete cultivation maintained penetration resistance values of less than 2 MPa within the depth limit of the penetrometer of 0.42 m. In addition, the results from the ‘lifting driving tool’ indicate that soils treated using complete cultivation remained significantly looser than those treated with the ripper to a depth of at least 0.80 m. The results demonstrate that complete cultivation remains the most effective method of alleviating soil compaction on restored sites, although it is recognized that its relatively high cost may restrict the uptake of the technique.     

Unity of mechanisms of water and wind erosion of soils

An equation for the threshold velocity of the water or wind flow at which erosion of a homogeneous model soil begins was derived on the basis of accepted and explicitly formulated suppositions and limitations and tested using experimental data. The validity of the proposed mechanisms and equations describing the lifting force of the soil-eroding water or wind flow and the interaggregate cohesion in a model homogeneous incoherent soil was confirmed. The limit for the decrease in the threshold flow velocity with decreasing size of the soil particles (aggregates) was theoretically substantiated. The first unified equation of the threshold velocity of the water or wind flow for a homogeneous model soil in dimensionless variables was derived and experimentally justified.     

On-the-go measurement of soil water content and mechanical resistance by a combined horizontal penetrometer

A combined horizontal penetrometer was designed for the on-the-go and simultaneous measurement of soil water content and mechanical resistance. The maximum sampling rate for both sensors was 10 Hz and the maximum operating depth was 20 cm. For the water-content sensor, its measurement principle depends on the electric field of the fringe-capacitance. In order to evaluate the applicability of this combined penetrometer, four experiments in the field were carried out. These experiments included: (1) soil water content profiles test; (2) soil compaction measurement test; (3) effect of the operating velocity on the water content and resistant force measurement; (4) effect of operating depth on the force measurement. The experimental results show that the combined horizontal penetrometer is a practical tool since it can provide more useful information of soil physical properties.     

Double extended octagonal ring (DEOR) drawbar dynamometer

A drawbar dynamometer is required to measure drawbar forces in field research on energy inputs for agricultural field equipment. In this study, a 2D double extended octagonal ring (DEOR) drawbar dynamometer with a draft capacity of 180 kN was developed. The two extended octagonal rings were oriented vertically on either side of the tractor drawbar which provided a better match of strain to expected drawbar draft and vertical load than could be achieved with a horizontal orientation in previous designs. Strain distributions in the extended octagonal rings were analyzed using a finite element method to locate optimal strain gage positions to minimize cross sensitivity between draft and vertical force measurements. The DEOR was fabricated from high strength ANSI 4130 steel. Vertical and draft calibrations of the DEOR dynamometer were done in a laboratory universal testing machine. Calibration results show that the DEOR dynamometer had a linearity of 0.99 and negligible cross sensitivity for both horizontal and vertical outputs. The DEOR dynamometer was tested in a field to measure the draft and vertical force of a sweep-type liquid manure injector. No mechanical problems were observed for the dynamometer in the field test and its draft outputs were comparable to those reported in the literature for manure injectors.     

渗流潜蚀作用临界发生条件的推导

为了进一步深入了解渗流潜蚀作用的发生条件及其机理,首先在对国内外文献进行广泛调研的基础上,将“管涌”、“渗透压密”、“流土”、“突涌”等几种最为常见的渗流潜蚀作用的概念模型进行了严格界定,将流土及突涌发生时的渗流方向扩展到任意方向。其次,通过受力分析,利用解析方法推导了“管涌”、“渗透压密”、“流土”、“突涌”等渗流潜蚀作用发生的临界条件,并对其他地下径流作用下发生的潜蚀作用进行了讨论。最后,指出由于渗流潜蚀作用发生环境的多样性,对其发生临界条件的判断应就其具体受力情况来具体分析。根据渗流潜蚀作用临界发生条件推导得出的相关结果,为潜蚀作用的进一步研究提供了理论基础。