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Received: October 1st, 2022 ; Accepted: March 15th, 2023 ; Published: March 17th, 2023 ; Correspondence: jyri.olt@emu.ee The process of tractor wheels slipping is accompanied by two forms of ground deformation: displacement and shearing. From the point of view of preserving the structure of the soil environment, wheel slip should be limited to displacement only. The limit of soil strength [σo] at this deformation can be a standardizing parameter. In this article an analytical dependence is developed, which allows using the parameter [σo] to establish the maximum permissible level of slipping of wheeled tractors. Of the soil parameters, the specified dependence includes the coefficient of sliding friction between the particles of soil medium and the coefficient of wheel rolling resistance on a particular agrotechnical background. Theoretical studies have established that the greater the value of this coefficient, the smaller should be the maximum permissible value of tractor slipping with a more economical effect on the soil environment. Compared to a tractor with a nominal drawbar pull of 14 kN, the use of a heavier tractor with a drawbar pull of 30 kN is possible with higher values of maximum permissible towing. This result is due to the magnitude of the vertical load on the wheel of the heavier tractor, which gives it a greater friction force between the tire wheel and the ground and allows the same contacting traction force to be realized at a lower level of slipping. The results of mathematical modeling using the developed analytical relationships indicate that with increasing the value of the angle of placement (slope) of the tractor wheel to the longitudinal axis of symmetry, the maximum permissible level of its slipping should be less. This will help to reduce the value of deformation (longitudinal shift) of the soil by the tractor during its working movement. When using the ground shear strength limit [σo] у as a limiting parameter for increasing the pitch and height of the tractor tire, as well as the width of the tractor wheel tyre, the maximum permissible level of its towing is more than 15%, which is an undesirable fact.

Saabunud / Received 04.05.2021 ; Aktsepteeritud / Accepted 07.06.2021 ; Avaldatud veebis / Published online 07.06.2021 ; Vastutav autor / Corresponding author: Jüri Olt jyri.olt@emu.ee The experimental research was carried out on a specially designed laboratory-and-field test unit with the use of a hydraulic vertical rotor drive and strain-gauge equipment mounted on a tractor as well as the set of interchangeable coupling pieces for setting the machine's operating duty. Research into the process of breaking two adjacent potato row beds with the vanes of a vertical rotor has been undertaken. A design and process schematic model has been proposed for the operation of the potato harvester. Experimental research into the geometrical parameters of the potato row has been carried out to select the design parameters of potato harvesters. Based on the results obtained during the experimental investigations, the rational ranges have been established for the work process of the rotary potato harvester, the methods of engineering clod breaking tools have been developed. Following the completion of the full factorial experiment, regression functions have been generated. Their analysis has proved that the following factors have the greatest impact on the optimisation parameters: the rotor diameter and the clearance between the rotor and the spherical discs. The following parameters have been optimised based on the response surface analysis: soil separation ratio S = 93.5%, tuber damage rate Pb = 0.97%, total power consumption by unit operation Nа = 18.27 kW, at the following pre-set values of the factors: nр = 77 min–1, Vm = 2.2 m∙s–1, dр = 0.825 m, l2 = 0.3 m. The maximum discrepancy between the results of the theoretical and experimental investigations for determining the design and process parameters of the potato harvester does not exceed 15%. The completed economic testing has proved the advantages of the experimental potato harvester as compared to the existing ones. That said, the separation ratio of the pilot machine is equal to S = 91.4%, which is 23% higher than in the reference case, while its tuber damage rate is equal to 1.14%, which is 5.0% better than in the reference case. The recommendations for the selection of the rational operation duty of the rotary potato harvester as well as the methods for the engineering analysis of the design and process parameters of clod breaking tools have been developed.

Saabunud / Received 06.07.2020 ; Aktsepteeritud / Accepted 03.08.2020 ; Avaldatud veebis / Published online 03.08.2020 ; Vastutav autor / Corresponding author: Jüri Olt e-mail: jyri.olt@emu.ee Operations to apply mineral fertilisers to the soil are an important part of practically every form of agricultural technology. The current global trend of transitioning to bridge and gantry-type agricultural systems leaves the unanswered relevant question of the effectiveness of the technological process of applying mineral fertilisers to the soil. This is relevant because, in gantry agriculture, a section of the arable soil is separated as an engineering area. This is why the main difference in gantry agriculture from traditional methods of the bulk spreading of fertiliser onto a field is that, with gantry systems, the amount of fertiliser that lands within the engineering zone are limited. This significantly affects the manufacturing costs involved in the entire area of agricultural technology and, as a result, the production costs of the end product. This study aimed to research the patterns that are apparent in affecting the parameters involved in the use of gantry-type equipment when applying fertiliser with the parameters and operational modes of a specially-developed electric spreader of mineral fertilisers. The physical object of the study was the agricultural gantry equipment that had been developed by the authors. This equipment, which is used for spreading fertiliser, was in the form of a tractor-mounted, suspended, single-disc spreader which was known as JarMet, and which had especially been modified to run from an electrical supply. The study indicated that the biggest influence on the speed of rotation of the centrifugal disc in the mineral fertiliser spreader stems from its height above the ground, the distance of track of the agricultural gantry itself, and the aerodynamic coefficient of the fertiliser. It was determined that, for the agricultural gantry with a distance of tracks of 3.5 m, a sufficient angular speed of the single-disc centrifugal tool is 15.5 rad·s−1, with a power demand for driving this at 0.35 kW·h. When using agricultural gantries of this type with an extended track width of up to 6 m, the necessary angular speed of the centrifugal tool for spreading fertiliser increases exponentially, to 318.2 rad·s−1, with the power demand for driving it increasing to the third power.

Saabunud / Received 08.02.2020 ; Aktsepteeritud / Accepted 05.03.2020 ; Avaldatud veebis / Published online 07.03.2020 ; Vastutav autor / Corresponding author: Jüri Olt e-mail: jyri.olti@emu.ee At the stage at which agricultural gantry systems are being designed, developed, and studied, the question of a rational choice of tyres for such systems is relevant, as tyres are the most important part of an agricultural gantry system and have a significant effect on most of its operating properties. The methods that can be used for choosing tyres for traditional mobile-powered equipment are already well established by scientific experience, but the movement of agricultural gantry systems in permanent artificial tracks creates somewhat different conditions and demands for a pneumatic tyre when compared to a traditional tractor moving along agricultural soil. This is why the development of methods that will assist in finding rational parameters for the pneumatic tyres of agricultural gantry systems that are moving along compacted soil in permanent artificial tracks is an urgent and relevant task. The purpose of the study is to optimise the parameters for the tyres of agricultural gantry systems in terms of their being able to travel on compacted soil in permanent artificial tracks. Theoretical studies and the synthesis of the parameters for a pneumatic wheel to work with an agricultural gantry system took place by modelling on a PC the performance conditions of such a vehicle. The basis for the study methods was formed by the fundamentals of tractor theory and theoretical mechanics, using the software program Mathcad. The traction factor of an agricultural gantry system's pneumatic wheel was used as the performance criterion for the effectiveness of the work being done by the wheel. The physical object of study was an agricultural system that has been developed by us. As a result of the study, it was determined that the solving of the task that has been set out - using an analysis of partial derivates of the function of the efficiency of an agricultural gantry system's wheel – makes it possible to quickly and effectively determine the rational optimum points for its pneumatic tyre's parameters. It was determined that, for the agricultural gantry system at hand, and in view of the maximum efficiency of its pneumatic wheel, the wheel's tyre width must be within the range of 0.20–0.30 m and its diameter must be within the range of 0.90–1.25 m. With those ranges, it is recommended that the tyre's inflation pressure be increased from 100 kPa to 160 kPa because the partial derivates of the function of the efficiency at those parameters would decrease to near zero. It has been proven that the choice of tyre type for agricultural gantry systems should be based first on the choice of its width and then its load-bearing capacity – its diameter. The proposed methods for finding rational parameters for pneumatic wheels make it possible to determine the tyre parameters for all kinds of agricultural gantry systems which will be required to travel on compacted soil in permanent artificial tracks. For the agricultural gantry system that has been developed by us, using tyres of the 9.5R32 type provides the highest levels of efficiency, i.e. at a factor of 0.86.

Received: September 6th, 2021 ; Accepted: January 30th, 2022 ; Published: February 17th, 2022 ; Correspondence: jyri.olt@emu.ee The paper presents the results of the research into the properties of blue melilot (Melilotus caeruleus (L.) Desr.) and fenugreek (Trigonella foenum graecum L.) with regard to the set of their economy-and-biology and biochemical indices in relation to the dates of their sowing. It has been established that the two species under consideration feature wide ranges of index variability depending on the sowing term and the weather conditions. The earliest ripening terms have been recorded for species in case of summer sowing dates (decade I of June), when short growing season lengths of 36–37 days were observed. At the same time, in terms of heavy plant herbage yield obtained from species in the green conveyor system, the early spring (decades II–III of April) and late spring (decade I of May) sowing terms are more suitable providing a herbage yield of 5.7–6.9 t ha–1 in case of blue melilot and 7.3–9.3 t ha–1 for fenugreek, with a solids content of 12.4–28.4%, total sugars of 2.5–5.0% and vitamin C - 38.0–51.8 mg (100 g)-1 . For the purpose of obtaining the spice named ‘Greek hay’ (foenum Graecum), a better choice is to cultivate fenugreek with early spring (decades II–III of April) and late spring (decade I of May) sowing times, as in this case a greater vegetation mass develops, resulting in a plant dry weight yield of 1.3–1.4 t ha–1. An increase in the total precipitation by 1 mm has contributed to the variation of the herbage yield within the range of 15.0 to 77.3 kg ha–1, dry matter yield - 0.693 to 25.9 kg ha–1. High seed yield has been noted in case of sowing the species in early spring (decades II–III of April), where the seed yield of blue melilot was equal to 0.4 t ha-1, fenugreek - 2.0 t ha-1 , their 1,000 seeds having a weight of 0.71 and 9.7 g, respectively.

Received: August 1st, 2022 ; Accepted: September 8th, 2022 ; Published: September 9th, 2022 ; Correspondence: jyri.olt@emu.ee A new design of the harrow with screw-type operating tools is presented in the paper. It describes the theoretical and experimental investigations carried out for the purpose of optimising the design and process parameters of the harrow with screw-type operating tools. Such optimisation will provide for improving the soil fertility, when burying chaff and other plant residues as organic fertilisers into the soil during its tillage. On the basis of the results obtained in the comprehensive experimental investigations, new regression relations have been generated. These relations provide for determining the proportion of the field surface, where the after harvesting residues have been completely buried in the soil with the harrow with screw-type operating tools. It has been established that the dominant effect on the relative amount of the field surface area S with completely worked-in plant residues is produced by the soil tillage depth h, then follows the factor of the screw-type operating device battery approach angle β. The pitch distance Т of the screw-type operating device has the smallest effect. The results of the completed research prove that increasing the pitch distance Т of the screw-type operating tool from 0.18 m to 0.26 m results in the decrease in the area S of the field surface with the plant residues buried in the soil by 1.4%. An increase in the approach angle β from 20° to 40° results in the increase in the field surface area S with the plant residues completely worked into the soil by 5.6%. Increasing the soil tillage depth from 0.08 m to 0.12 m results in the increase in the above-mentioned surface S by 7.1%. The simultaneous action of the factors of the tillage depth h and the approach angle β results in the percentage of the surface S rising from 72% to 82%.

Received: May 7th, 2022 ; Accepted: June 28th, 2022 ; Published: July 9th, 2022 ; Correspondence: jyri.olt@emu.ee The aim of research is to analyse the process of the wide span vehicle motion on the treads of the permanent process track with the use of the traction method of turn. The completed studies have proved that the plane-parallel motion of a wide span vehicle solely with the use of the traction method of turn on the treads of the permanent process track requires a significantly smaller difference between the moments applied to the wheels on the right side and on the left side of the vehicle, as compared to that of a crawler tractor. This difference is in proportion to the width of its wheel base that has a relatively smaller length. It has been established that the use of solely tractionbased turn does not provide for the adjustment of the motion trajectory through the lateral (planeparallel) displacement of the fore-and-aft axis of the agricultural wide span vehicle. The oscillations in the lateral displacement of the agricultural wide span vehicle in the process of its motion are lowfrequency ones. The main variance spectrum of these oscillations is concentrated within the range of frequencies of 0–2 s −1. At the same time, the maximum transverse displacement of the agricultural wide span vehicle equal to 1.3 10−5 m N−1, occurs also at low frequencies. In view of the fact that the main variance spectrum of the oscillations of the tangential forces applied to the wheels on the left and right sides of the agricultural wide span vehicle is concentrated exactly within a low frequency range, only the high accuracy of the system using a laser beam can ensure its satisfactory steerability.

Received: January 25th, 2022 ; Accepted: April 6th, 2022 ; Published: April 18th, 2022 ; Correspondence: jyri.olt@emu.ee The gap between two technological operations should be minimal in the production environment. For this, special combined (multi-operational) machine-and-tractor units (MTU) are used. Their agricultural machines have sequentially installed working devices for various technological purposes. In the absence of such MTUs, single-operation units are used. Such units more often have different working widths. For their simultaneous operation in the same field, the first unit (for example, a sowing unit) must have a wider width than the second one (for example, a rolling one). In practice, the opposite case occurs more often when the first unit's working width is less than the second unit's working width. As a result, the first machine-and-tractor unit delays the work of the second one. This article aims to develop the algorithm for the simultaneous operation of two machine-and-tractor units of different field performance. The first of them (a sowing unit) has a working width of 3.6 m, and the second (a rolling one) is 6.1 m. As a result, the following has been established using the example of processing a field of 80 hectares: the second unit should start its work (i.e., rolling the crops) when the first one (sowing) has sown a certain area. According to the formula proposed in the article, the size of this area is 44 hectares. Under natural working conditions, the second unit (rolling) started its work after the first (sowing) unit has sown 44 hectares of the field area. As a result, both units have completed the entire area with a half-hour gap, i.e., practically simultaneously and without delay from each other.

Received: March 6th, 2021 ; Accepted: May 12th, 2021 ; Published: May 14th, 2021 ; Correspondence: jyri.olt@emu.ee The authors have set an aim in relation to the development of a novel rotary potato harvesting machine design and the substantiation of rational design and process parameters for the clod crushing tools in the machine in order to improve its separation capacity. A novel design solution has been suggested for the process of crushing the two adjacent potato rows with the vanes of the vertical rotor and the expediency of using the methods of crushing clods in the two adjacent potato rows in advance has been justified. Also, the more rational placement of the clod crushing tools in the potato harvesting machine has been suggested. Following the completed research, the geometrical parameters of the vertical rotor have been substantiated, in particular, its diameter dр = 0.65–1.0 m and height hzag = 0.27 m. Additionally, the process parameters have been substantiated for some other tools crushing the clods, in particular, the angle of inclination of the share’s working face, which has to be equal to 10°, the elevator belt width bel = 1.05 m, the linear velocity of the belt Vp = 1.95 m s –1 , the belt agitation amplitude Аst = 18 mm. If the soil moisture content is equal to W = 18.4%, the soil separation rate rises insignificantly, when the rotor diameter increases within the range of 0.65–1.0 m, moreover, at Vm = 1.0 m s –1 it varies within the range of 85.3–87.2%, at Vm = 1.5 m s –1 – within the range of 87.0–92.7%, at Vm = 2.0 m s –1 – within the range of 86.0–89.1%. The best performance is achieved at a rotor rotation frequency of nр = 100 min–1 and a translational velocity of Vm = 1.5 m s –1 , in which case the soil separation rate S is equal to 93.5%. The tuber damage rate Pb decreases from 4.2% to 1.5%, as the rotor diameter dр increases from 0.65 m to 1.0 m, the translational velocity of the machine Vm – from 0.8 to 2.2 m s –1 at the rotor rotation frequency nр = 50–100 min–1.

Received: August 27th, 2021 ; Accepted: October 6th, 2021 ; Published: October 7th, 2021 ; Correspondence: jyri.olt@emu.ee Disking is one of the methods of soil cultivation, provides its effective crumbling, loosening, partial mixing and soil inversion. This ensures that crop residues on the soil surface are shredded and intermixing with loosened soil particles. Since, in addition to crop stubble, weeds are also counted as crop residues, soil disking, along with the use of herbicides, is often regarded as the most effective method of controlling the weediness of the agricultural background. Despite the fact that numerous studies on the disk harrow working process are available, insufficient attention has been paid to the study of the stability of harrow machine-tractor units, especially trailed ones. The purpose of this study is to establish the theoretical patterns that would provide for selecting the trailed disk harrow parameters that ensure the desired directional stability of the implement, which, in its turn, helps to achieve the desired qualitative performance of the disk harrowing machine-tractor unit. The principles of the theory agricultural machine, analytical mechanics, higher mathematics, as well as methods of PC-assisted numerical calculations have been used. According to the results of the study, it has been established that sufficient directional stability of the trailed disk harrow can be ensured if its working width B, the distance from the hitch point to the centre of resistance (parameter d) and the operating speed 𝑉𝑜 are properly selected. Determining the above-mentioned parameters of the disk harrow with the use of the obtained new analytical relations ensures achieving just their optimal combination, which provides for the maximum field productivity of the harrow machine-tractor unit with the satisfactory stability of disk harrow movement in the horizontal plane.

Received: February 13th, 2021 ; Accepted: April 15th, 2021 ; Published: April 19th, 2021 ; Correspondence: jyri.olt@emu.ee The output capacity of the machine for top spreading the soil with solid mineral fertilisers can be raised by means of increasing its working width. The authors have carried out field trials and field experiment investigations with the MVU-8 granulated mineral fertilizer spreading machine equipped with two prototype units of the centrifugal fertiliser spreading tool, in which the axis can be tilted at different angles to the vertical line. In accordance with the results of the completed investigations, it has been established that setting the axial tilt angle of the centrifugal operating device in the fertiliser spreading tool within the range of 25–30° provides for achieving a productivity of the combined tractor-implement unit for applying mineral fertilisers at a level of 35–40 ha per working shift hour. The best performance in the fertiliser application with regard to both the working width and the fertiliser placing distribution uniformity is ensured at angles of inclination of the disc in the fertiliser spreading tool with respect to the horizontal plane within the range of 25–30°. At these angles, the uneven distribution of the fertiliser over the working width is equal to 19.2%, the uneven distribution of the fertiliser along the unit’s line of travel is equal to 8.9%, while the deviation in the dosage of the applied fertilisers from the set value is equal to 7.5%.

Received: October 7th, 2021 ; Accepted: December 10th, 2021 ; Published: December 10th, 2021 ; Correspondence: jyri.olt@emu.ee Improving the quality of sugar beet harvesting to a great extent depends on the first operation in the process, which involves cutting and harvesting sugar beet tops. This technological process is performed with the use of either the haulm harvesting modules of beet harvesters or top harvesting machines as separate agricultural implements, which are aggregated with a tractor. At the same time, front-mounted harvesters are as widely used as trailed asymmetric implements, in which case the aggregating tractor moves on the already harvested area of the field. The purpose of this work is to determine the optimal design and kinematic parameters that would improve the stability in the performance of the technological process of harvesting sugar beet tops by means of developing the basic theory of the plane-parallel motion performed by the rear-trailed asymmetric top harvester. As a result of the analytical study, an equivalent scheme has been composed, on the basis of which a new computational mathematical model has been developed for the plane-parallel motion of the asymmetric top harvester in the horizontal plane on the assumption that the connection between the wheeled tractor and the rear-trailed top harvester is made in the form of a cylindrical hinge joint. Using the results of mathematical modelling, the system of linear second-order differential equations that determines the transverse movement of the centre of mass of the aggregating wheeled tractor and the rotation of its longitudinal symmetry axis by a certain angle about the said centre of mass as well as the angle of deviation of the rear-trailed asymmetric top harvester from the longitudinal symmetry axis of the tractor at an arbitrary instant of time has been obtained. The solving of the obtained system of differential equations provides for determining the stability and controllability of the motion performed by the asymmetric machine-tractor unit, when it performs the technological process of harvesting sugar beet tops.

Received: April 15th, 2021 ; Accepted: July 21st, 2021 ; Published: July 22nd, 2021 ; Correspondence: jyri.olt@emu.ee In the paper, the results are presented obtained in the research into the fresh bulbs and the dried products of 9 onion varieties cultivated in the conditions of the Ukrainian Forest Steppe area with regard to their economical biology, biochemical, marketability and organoleptic indices. The varieties that are most suitable for convection drying and long-term storage have been identified. It has been established that the marketability of both the fresh bulbs and dried products depends on the masses of the bulbs. The Bronze d’Amposta and Harmony varieties deliver the greatest amount of marketable output (94.0 and 93.2%) featuring marketable bulbs with masses of 67.4 g and 70.4 g, respectively (r = 0.82). As the bulb mass increases, the amount of non-standard (r = -0.81) and small (r = -0.76) particles in the dried product decreases substantially. It has been found that the content of solid matter and sugars in fresh bulbs has effect on the yield and quality of the dried and reconstituted products. The Harmony and Skvirskaya varieties, the bulbs of which during the vegetation season build up 12.9% and 13.8% of solid matter, respectively, are distinguished by the highest dry product yield - 17.1 and 16.8%, respectively. Correlation has been established between the contents of solid matter and sugars in fresh bulbs (r = + 0.58). During the tasting of reconstituted onion products, the highest scores were awarded to the samples produced from the Skvirskaya and Harmony varieties - 7.0 points each on the 9-point scale, as their bulbs had accumulated over 7.0% of sugars (total). Judging by the aggregate of the researched indices, the Harmony and Skvirskaya varieties of onions are the most suitable for convection drying. It has been established that the preservation of onions in the conditions of stationary buried storage without artificial cooling depends on the duration of storage and the specific varietal features. Within the five months of the test storage, the preservation of bulbs of all the varieties was high and varied within the range of 80–93%. Longer storage is expedient only in case of the Harmony, Skvirskaya and Gospodinya, for which the bulb preservation rates for a seven month storage period has been shown to be equal to 90.2, 88.4 and 87.2%, respectively. It has been proved that the quantity of healthy bulbs depends to a significant extent on the solid matter content in the bulbs (r = 0.93).

Received: February 2nd, 2021 ; Accepted: March 27th, 2021 ; Published: April 7th 2021 ; Correspondence: jyri.olt@emu.ee One of the important conditions in securing the high quality, when performing the work process of vibrational root lifting, is to avoid damaging the roots. It is obvious that the greatest probability of damaging and even breaking the lifted root arises, when the tool interacts with the root body during their first contact and in the time of the root passing in the throat between the operating shares. The aim of the study is to substantiate the rational design length for the working throat of the vibrational root lifter in its interaction with the sugar beet root while lifting the latter from the soil. As a result of the completed research, the minimum permissible tool oscillation frequencies have been determined for the specific values of the lifter’s translational velocity and the working throat rear part length, at which the event of the vibrational lifting tool gripping the root will occur at least one time. For example, when the length of the lifter’s working throat rear part is equal to 0.1 m and the oscillation frequency is equal to ν = 20.3 Hz, the satisfactory quality of the vibrational root lifting process is ensured, when the velocity of the translational motion performed by the vibrational lifter stays within the range of 1.3–2.55 m s –1 . In order to ensure the good quality of the vibrational root lifting process at the lifter’s translational velocity equal to V = 2.0 m s –1 and the frequency of its tool’s oscillations equal to ν = 10 Hz, it is necessary that the length of the lifter’s working throat rear part is equal to 0.2 m, at a tool oscillation frequency of 6.7 Hz - 0.3 m. As a result of the completed numerical calculations, the permissible values have been determined for the tool oscillation frequency, which can be recommended for the translational velocities within the range of 1.3–2.2 m s –1 , taking into account the limitation set for the tool oscillation frequency by the pre-condition of the guaranteed gripping of each root by the digging shares.

Received: May 25th, 2021 ; Accepted: June 22nd, 2021 ; Published: June 28th, 2021 ; Correspondence: jyri.olt@emu.ee The topic of the paper is the determination and justification of the rational design and kinematic parameters of clod breaking tools in rotary potato harvesters with the aim of improving their separating efficiency. A new mathematical model has been developed for the motion of a soil particle on the working surfaces of the cone-shaped and cylindrical vanes in the rotary tool of the new design developed by the authors. Differential equations have been generated for the motion of a soil clod as a material particle from the moment of its arrival to the surface of the vane until the moment of its departure from the said surface. As a result of the completed investigations, relations have been established between the time of contact and absolute displacement of the soil particle and the velocity of its departure from the rotor vane surface, on the one hand, and the kinematic and design parameters of the rotor, on the other hand. For example, when the machine translation velocity increases, the absolute displacement of the soil particle within the interval from the time zero to the moment of its departure from the vane surface increases from 0.59 m to 0.65 m, the velocity of soil particle departure from the vane surface - from 1.61 m s–1 to 1.81 m s–1. The highest values of the absolute displacement of the soil particle and the velocity of its departure from the vane surface are achieved at a machine translation velocity of 2.0 m s–1. The time of the contact between the material particle and the vane surface decreases with the rise of the translation velocity. When the rotor rotation frequency varies within the range from 20 min–1 to 100 min–1, the absolute velocity, with which the soil particle leaves the vane surface, rises to 4 m s–1. The duration of the contact between the material particle and the vane reaches its maximum value of 0.33 s, when the rotor rotation frequency varies within the range of 30–40 min–1.

Received: July 18th, 2021 ; Accepted: September 3rd, 2021 ; Published: September 6th, 2021 ; Correspondence: margus.arak@emu.ee The functional working tool on the blueberry harvester is its rotating picking reel. Its working element is the picking rake which is attached to the picking reel. A total of four rakes are attached to the picking reel. A picking rake includes an axis which is attached in an articulated manner between the reel’s end discs, and pin-shaped teeth which are rigidly attached to it. The picking rake’s tooth must be made of a fully flexible material to prevent damage to the blueberry plant. The aim of this research was to determine the flexure of test specimens (plastic rods) which have been constructed from a fully flexible material of different conditions, along with the suitability for use of such flexible material as the teeth on the picking rake. As a result of this study, it became clear that, based on the results from flexure, durability, and residual deformation tests, it is more expedient to choose Ertacetal C (POM-C) as the material for the picking reel’s tooth, with a diameter of 4.3 mm.

Received: February 2nd, 2021 ; Accepted: March 27th, 2021 ; Published: April 7th, 2021 ; Correspondence: jyri.olt@emu.ee Improving the efficiency in the work process of mineral fertilizer dressing is a topical problem in today’s agricultural industry. The authors have developed a design of the fertilizer spreading tool with a tilted axis and carried out field experiment investigations on it. It has been established by the results of the investigations that the non-uniformity in the spreading of mineral fertilizers along the line of their departure from the fertilizer spreading tool with a tilted axis is most strongly affected by the disc rotation frequency. The obtained results provide for selecting the optimum parameters and modes of operation for the tool under consideration in the situation, when it is installed in fertilizer placing machines. Also, it has been established that increasing the spreading disc rotation frequency in such a tool from 600 to 800 rpm results in the growth of the effective range of mineral fertilizer spreading along the placing line at a level of 10.5 m. Increasing the disc’s angle of inclination to the horizontal plane to 20º results in the rise of the effective fertilizer spreading range at a level of the 48th tray (24 m) inclusive as well as the increase of the distance between the tool and the tray that contains the maximum share of the spread fertilizers (5.1%) to 24 trays (12 m). At a constant rotation frequency of the disc in the tilted-axis fertilizer spreading tool, in all its kinematic modes of operation, an increase in the angle of its disc’s inclination to the horizontal plane results in the rise of the indices representing the distribution of the mineral fertilizers over the trays along the line of their placing. The width of the mineral fertilizer spreading can be controlled by adjusting the rotation frequency of the disc in the tilted-axis fertilizer spreading tool, when it is set at an angle to the horizontal plane, similar to how it is done in state-of-the-art fertilizer placing machines with horizontally positioned discs in their centrifugal spreading tools. The rotation frequency of the disc in the tilted-axis fertilizer spreading tool has the most significant effect on the coefficient of variation incidental to the distribution of the mineral fertilizers along the line of their placing.

Received: October 6th, 2020 ; Accepted: December 11th, 2020 ; Published: December 16th, 2020 ; Correspondence: jyri.olt@emu.ee From the point of view of energy saving, research into agricultural gantry units equipped with new implements specially adapted for operation in such systems and capable of efficiently functioning in controlled traffic (permanent lane) and wide span (gantry) systems is an important and topical issue in soil tillage science. The range of wide span systems includes harrowing units for fallow land tillage. This paper describes the experimental determination of the operating characteristics of the harrowing unit, in which a gantry implement carrier propels harrows for fallow land tillage, for the purpose of establishing the compliance of their parameters with the fundamental principles of the effective implementation of the controlled traffic and wide span soil management. The experimental investigations were done using strain-gauge and control-and-measuring equipment with analogue-to-digital conversion of the signals received from the sensing elements. An agricultural wide span unit with a track width of 3.5 m and harrows for fallow land tillage were investigated. The results show the harrowing unit is well adapted to operation in controlled traffic and wide span soil tillage systems and delivers high quality performance of the harrowing process. The latter effect is also due to the fact that the gantry travels on the compacted tracks which have a few surface irregularities compared to cultivated soil. The coefficient of variation of the draught force applied to the hook of the gantry during harrowing operations did not exceed 10%. This is evidence of the high stability (low variability) of the harrowing process, which has a positive effect on the motion stability of the harrowing unit based on the gantry tractor.

The theoretical and experimental research into the micro-damaging of cereal crop seeds in the process of their harvesting by combine grain harvesters in relation to the strains, forces and stresses imparted to them by the threshing tools has been carried out. The propagation of deformations and cracks in the seeds as well as the nature of their strength and the damage that is sustained, when the critical load is applied, have been investigated. It has been established that the onset of cracks, the direction of their propagation and their quantity in the bodies of grain seeds depends in the majority of cases on the direction of action of the external forces and the specifics of the seeds’ internal biological properties. It has been established that the strength of the grain seed is, apart from the arisen cracks, also under the significant effect of the microtraumas in the germ, endosperm as well as the seed coat and shell. Theoretical calculations have been carried out on the PC and the effect that the drum and rotor threshing apparatus have on the deformation and damage sustained by cereal crop seeds has been substantiated. The said calculations and the obtained graphic relations support the results of the experimental investigations and prove that the macro- and especially micro-damage sustained by the seeds of winter wheat and rye is different, when they are threshed with the use of different types of threshing apparatus, which has a considerable impact on the final quality of the harvested cereal crop seeds. The results obtained in the experimental investigations, field and laboratory tests on the topic of the effect of mechanical loading on the sustained damage and quality of seeds indicate that the damage rate accounted for the work processes of the reaping and postharvest treatment of the cereal crop heaps of different winter wheat varieties with the use of rotor threshing apparatus is 3.1% as compared to the drum threshing apparatus – 6.4%, that is, 2 times lower. The total amount of the seeds with microtraumas collected in the hopper after threshing amounts to 23.0% and 54.0%, respectively, which is a significant difference. Similar results have been obtained in the experimental investigations on the effect of the equipment on the sustained damage and quality of seeds in the cleaning, chemical treatment and sowing of cereal crops.

The aim of the study was to determine the optimal design and kinematic parameters of the separator that cleans potatoes from impurities and has a design of the spiral type. The authors have devised a highly efficient design of the spiral type potato heap separator, in which the motion of the potato tubers takes place in the channel formed by two spiral members made in the form of cylindrical spiral springs. In order to substantiate the optimal kinematic and design parameters of the new spiral type potato heap separator, the authors have generated a mathematical model of the motion of a single potato tuber on the cleaning surface formed by two spirals. As a result of solving the obtained analytical expressions, the graphical relations between the parameters of the investigated process of the motion of a single potato tuber body situated between two adjacent spirals have been plotted, which has enabled selecting the optimal design and kinematic parameters of the spiral separator. It has been established in the completed investigation that the angular velocity of rotation of the cleaning rolls has to be within the range of 27 40 rad s -1 in order to ensure the efficient transportation and cleaning of the potato tuber with a diameter of 50 mm that moves on the surface of the spiral with a radius of 75 mm wound from the round bar with a diameter of 15 mm, in case the spirals are mounted with an eccentricity of 10 mm. By analysing the kinematics of motion of the potato tuber on the surface of the spiral type cleaning machine, in case the tuber contacts the spirals at two points, it has been established that the increase of the angular velocity of rotation of the spirals results in the respective growth of the transportation capacity of the cleaning tool, while the separating efficiency at the same time becomes reduced to some extent.

The aim of this study is to provide for the intensification of the process of removing impurities from the potato heap by oscillating devices, which takes place, when potato tubers are cleaned in the spiral separator during their lifting. The authors have devised a new design of the spiral separator, which can be used in the process of lifting potatoes from the soil. It comprises cantilever cleaning spiral springs, which in their simultaneously rotary and oscillatory motion clean and transport the potato tubers with good quality. However, the removal of impurities from the cleaning area and the cleaning of the side surfaces of potato tuber bodies from the stuck soil can be significantly more effective, if the spiral springs perform their oscillatory motions in the longitudinal and vertical plane during their operation more intensively. In order to achieve that, the authors have worked out a new theory of the oscillatory motion of the cleaning spiral working under the action of the potato heap. That promotes the intensification of the process of cleaning potato bodies from the stuck soil. The authors have generated a new partial differential equation, which describes the oscillations of the cantilever cleaning spiral. The PC-assisted numerical solving of the said differential equation and further numerical modelling have made it possible to obtain the analytic expressions of the relations between the change in the helix pitch distance of the cleaning spiral and its deformation, in particular, the simultaneous longitudinal extension and transverse bending. That result, in its turn, provided for finding the maximum limit amount of the above-mentioned deformation under the condition that the potato tubers may not fall through the spaces between the spiral turns, taking into account the design and kinematic parameters of the cleaning spiral itself, the material it is made of and the process-dependent mode of operation of the separator. As a result of the PC-assisted numerical modelling, it has been found that the total deflection of the spiral on its length varies within the range of 0 to 0.05 m under the following parameters: angular velocity of rotation of the spiral ω = 30 rad s-1, density of the material of the spiral ρ = 7,700 kg m-3, elastic modulus Е = 2∙1011 Pa, cleaning spiral bar stock radius r = 8.5 mm and a uniform load intensity of 1000 N m-1. Such variation ensures the good quality of cleaning and transportation of potato tubers. According to the results of the PC-assisted numerical calculations, the helix pitch distance of a cleaning spiral with the above parameters and the original helix pitch distance S = 48 mm, due to the spiral’s deformation under the proposed transverse oscillations, can change up to 54 mm, which makes impossible for potato tubers to fall out of the cleaning unit. Experimental studies fully support the results from the theoretical calculations to determine the displacement of the ends of the cleaning unit’s spiral springs.

Increased cost-effectiveness in crop production can be achieved by automating technological operations. This is also the case for berry cultivation in plantations. Starting any berry cultivation automation process should, quite naturally, begin with fertilisation, since this is the first technological operation to be carried out during the vegetation period and is a relatively simple one. The main task here is to apply the correct amount of fertiliser under the canopy of plants. Blueberry plantations that have been established on milled peat fields have plants that have been planted in parallel rows at a pre-designated interval. The fertilisation of plants must take place individually in the first years of their growth, so that each plant is fertilised separately. This form of fertilisation can be referred to as precision fertilisation. The aim of this paper was to provide an overview of the levels of technology now available when it comes to precision fertiliser equipment and to introduce the concept of a new precision-automated fertiliser unit, while also justifying the efficiency of using automated equipment. The automated fertiliser unit that is to be designed will be autonomous, will move unmanned through the plantation, and will include the necessary sub-systems for the precision fertilisation of individual plants, such as a plant detection system, a fertilising nozzle, a motion system and, additionally, a service station. On the basis of the results obtained, it can be argued that the use of an automated precision fertilisation unit increases productivity levels by approximately 2.25 times and decreases the specific fertiliser costs by approximately 8.4 times when compared with the use of a portable spot fertiliser.

One of the promising ways of efficiently applying high power intensity tractors is their design and utilisation in the form of modular traction vehicles comprising two modules: the power module and the process module. In order to provide for the sufficient manoeuvrability of the modular traction vehicle, when its process module passes a turn, the latter is equipped with vertical and horizontal hinge joints. The freedom of the process module’s rotation with respect to the power module in the horizontal plane through the agency of the above-mentioned vertical hinge joint is restrained by a hydraulic cylinder, in which the chambers above and below the piston are connected via a throttle valve with a hydraulic resistance coefficient of about 1.03×106 N m s rad–1 . This paper is concerned with the theoretical and experimental research into the stability of motion (on turn spaces as well as in the transport mode) of a modular combined unit, when its velocity changes and/or the slip resistance coefficient of the tyres on the wheels of the process module, in which the hydraulic cylinder is equipped with a throttle valve with the above-mentioned hydraulic resistance coefficient, changes.

Retention of soil moisture is an urgent topic of the day in the cultivation of agricultural crops. Using fallow fields is one of the ways to solve the named problem, but the tilling of such fields requires observing some special conditions, in particular, the capillary effects in their upper soil layers must be cut down. For that purpose, the authors have proposed a special harrow equipped with the tools capable of fulfilling the above-mentioned task. The authors have carried out extensive field experiment research into the tillage of fallow soils with the use of the said implement. In order to apply the implement, a new harrow unit has been developed. The results obtained during the experiment research have been processed with the use of statistical methods and it has been established that the depth of harrowing in the tilled field decreases, when the operating speed of the combined unit under consideration increases to 3.3 m s –1 . At the same time, the variances of oscillations of the parameter under research in accordance with the Cochran's C test remain uniform. Also, the frequency of the harrowing depth oscillations changes insignificantly. That is supported by the correlation lengths of the normalized correlation functions of the process under consideration, which, at the above-mentioned operating speed, stay within the sufficiently narrow range of values: 0.16–0.20 m. According to the results of the experimental investigations, the maximum value of the normalized cross-correlation function for the relation between the oscillations of the field harrowing depth and the oscillations of the field’s longitudinal profile does not exceed 0.12. This testifies to the absence of any substantial interrelation between the said two stochastic processes, which is quite reasonable in view of the small values of the variance and period of the oscillations of the field’s longitudinal profile. The probability of the new combined tractor and harrow unit maintaining the tolerance of the fallow field cultivation depth oscillations within the range of ± 1 cm is equal to 82%. Within each 1.85 m of the distance travelled by the combined soil cultivation unit under consideration, only one instance of the field cultivation depth deviating from the ± 1 cm tolerance can be expected.

Saabunud / Received 08.10.2020 ; Aktsepteeritud / Accepted 15.12.2020 ; Avaldatud veebis / Published online 31.12.2020 ; Vastutav autor / Corresponding author: Jüri Olt yri.olt@emu.ee The experimental investigations carried out in field production conditions have proved that the process of cleaning potato tubers from extraneous material with the use of a spiral separator takes place due to the active conveyance of the heap by the turns of the cantilever mounted cleaning spiral springs. The cleaning spiral springs not only rotate at the set angular velocity, but simultaneously their cantilevered ends perform oscillatory motion, which arises due to the deflection of their longitudinal axes under the action of the weight of the potato heap fed into the work zone of the separator. The results obtained in the process of the field experiment investigations carried out by the authors have provided for obtaining the relations that enable selecting the optimum design and kinematic parameters of the spiral-type potato cleaning devices for the targeted separation rate and, accordingly, estimating their impact on the quality of the performed work process.

The analysis of the performance of biofuel is aimed at evaluating the energy efficiency of operating the engine with the use of biodiesel fuel as function of the fuel’s composition and other physical-and-chemical parameters. The mathematical models and analysis techniques known to the authors do not take into account the effect that the use of different bio-diesel fuels has on the operation of the engine and, therefore, need refinement in terms of the mathematical expressions and empirical formulae that describe the physical processes taking place in the engine’s cylinders. The aim of the study is to improve the mathematical relations taking into consideration the physical-and-chemical parameters of different types of fuel. The research methods proposed in the article are based on step-by-step consideration of the mathematical models of processes that follow each other, with due account for their possible overlapping, which jointly have an effect on the engine’s output indices. The boundary conditions and parameter increments are pre-set in electronic work sheets. Thus, it becomes possible, using the refined mathematical model, to calculate the main performance indices of the diesel engine with due account for the changes in the physical-and-chemical parameters of the fuel. The novelty of the described approach is in the possibility, through the use of the refined model and taking into account the data on the composition of the fuel and the design and operation parameters of the engine, to calculate the indices that allow evaluating the efficiency of use of specific fuels in the internal combustion engine under consideration. In results, formulas for the calculation of the effective power of the engine, fresh air charge density, excess air factor, effective specific fuel consumption and combustion pressure have been developed. Combustion pressure modelling and experimental data is presented.

The paper describes the development of a mathematical model for the motion of a seed mixture particle in the aspiration channel of the separator after the particle passes the cone-shaped spreader and enters the workspace of the aspiration channel in the pneumatic dynamics and vibration unit devised by the authors. The unique feature of the proposed new design is the presence of the central pipe with sail members in the aspiration channel. The sail members in the air stream generate the self-oscillatory mode of motion of the central pipe, which results in the efficient separation of the grain seed mixture into the required fractions. On the basis of the prepared equivalent schematic model, the differential equations of the motion of a seed mixture particle in the process of aspiration separation have been generated. Basing on the results of the PC-assisted numerical modelling of the motion paths, on which the material particles (seeds) of the heavy and medium fractions travel, it has been established that they move on different courses, and the course of the heavy fraction seeds is such that, after they pass the cone-shaped spreader and advance further in the air stream through the space of the aspiration channel, they move closer to the pipe of the aspiration channel. Also, their velocities and accelerations are greater than the same kinematic parameters of the medium fraction seeds. The seeds of the light fraction move upwards under the action of the air stream and leave the aspiration separator at its top.

This paper presents the results acquired from the study of eight carrot hybrids which are suitable for growing in the climatic zone of woodland steppes, while considering a set of economical and/or biological, biochemical, and organoleptic properties. The carrot hybrids that were studied have a wide range of variation in their economic value indicators, which makes it possible to grow them for storage and processing in various soils and climate conditions without irrigation. The most productive carrot hybrids are White Sabine F1 and Yellowstone F1 with a commercial yield of 55.8–58.7 t hа–1 and an average taproot weight of 118.7–136.2 g. The levels of preservation of the taproot of the hybrids White Sabine F1 and Purple Haze F1 after seven months of storage in conditions that involved the use of a stationary pit storage facility was at 81.4% and 80.2% respectively. The use of the taproots of the hybrids Yellowstone F1 and Viking F1 for drying ensures a yield of a high-quality, biologically-valuable finished product with a yield of 11.4–11.7%. Dry hybrid Evolyutsiya F1 and Mars F1 carrots contain more than 40 mg (100 g)–1 of β-carotene.

The topic of the paper is the theory of the forced transverse oscillations performed by the root fixed in the soil under the action of the harmonic perturbing force vectored at right angle to the root’s centreline and along the line of the translational motion performed by the lifter. On the basis of applying the Ostrogradsky-Hamilton variational principle and using the equivalent schematic model developed by the authors, the expressions have been obtained that allow to determine the amplitude of the forced transverse root body oscillations as function of the perturbing force amplitude value as well as the soil’s elastic deformation and damping coefficients. The ranges of the elastic soil deformation coefficient values, at which the resonant behaviour is observed, that is, at which the forced elastic root body oscillation amplitude value exceeds the tolerance limits, have been determined for the 10, 15 and 20 Hz frequencies of the perturbing force produced by the vibrational lifting tool. That said, the mentioned oscillation amplitude values can vary from 0.58 to 0.45 m, which is sufficient to result in the root breaking. Moreover, it has been proved that, with the increase of the perturbing force frequency, the resonant behaviour ranges shift towards the increased values of the elastic soil deformation coefficient. Therefore, such elastic soil deformation coefficient ranges should be avoided in case of the lifting tool design proposed in the paper. As regards the damping properties of the soil, it has been proved that they do not cause any resonance phenomena.

Drying and processing wet particulate food production waste, such as distillery dreg, brewer's grains, beet pulp, spent coffee and barley slurry etc. for their further use as cattle fodder or fuel is an important and topical problem, which needs effective solutions. As a solution of the problem, the authors have developed improved equipment and a fluidised bed vibration drier, which ensures reaching the required output of the work process and final moisture content in the waste at a minimum power and material intensity and features the combination of the high feasibility with the high reliability of design. In order to validate the improved drying work process together with the optimum parameters of the vibration drier, theoretical investigations based on the mathematical model of the process developed by the authors have been carried out. The process of the vibration drier’s frame oscillating together with the waste has been examined, which has resulted in the generation of the differential equation that analytically describes the said process. The work process under consideration has been researched into from the thermophysical point of view using the specific initial data typical for the specific food producer. The research has resulted in obtaining the following design and process parameters of the vibration drier, in particular, for its heating pipes: diameter rt = 0.1 m; length lt = 5 m; number nt = 20, heat-transfer factor Kp = 30 and the final temperature of the dried food production waste to2 = 80 °C. The listed parameters provide for reaching the required final moisture content in the dried food production waste. Also, new relations have been generated for determining the principal process parameters of the improved drier (productive capacity, heat consumption, mass of heat carrier, waste conveyance speed, sizes and masses of the drier’s actuating elements). The obtained relations can be applied in the further theoretical and experimental research on the drier as well as the development of standard methods for its design and calculation.

The practice of separating grain mixtures with the use of the difference in the aerodynamic properties of their components has proved that the process of separating mixtures in the aspiration separator is the most promising one with regard to the improvement of quality and intensification of production. The authors have developed a new improved design of aspiration seed separators, in which the work process of separating seed material is performed with the use of vibration processes. In this seed material separator, the constant force air flow that acts on the sail members on the central pipe of the separator, when seeds are fed for processing, generates self-excited oscillations in the pipe, which produces centrifugal forces of inertia in the seed feeding system. As a result of the mentioned effect, the propelling force in the process under study substantially increases, accelerating the seeds of different fractions, which differ in their masses, to different velocities. The motion paths of the seed particles change accordingly, heavier particles moving closer to the vertical axis of the aspiration channel, which provides for increasing the efficiency of separation of the seeds of different fractions from each other. In this paper, a new mathematical model is developed for the motion of a seed mixture material particle in the operating space of the separator’s aspiration channel. The mathematical modelling of the process of vibration and aspiration separation has indicated that the separation of the motion paths of the medium and heavy fractions takes place within the range of 20–40 mm; the flying speed of the particles is equal to 3.2–8.0 m s–1, respectively; and their acceleration is equal to 1.8– 3.3 m s–2, which provides the necessary conditions for the accurate and high quality separation into the required fractions. In view of the found differences between the kinematic characteristics of the separated fractions of the grain mixture, the diameter of the pipeline for the medium fraction is to be within the range of 90–100 mm, for the heavy fraction – 50–70 mm.

This paper outlines a theory that involves the vibrational wave transportation of bulk grain during the course of passing that grain under an infrared radiation source, in a working thermal radiation drying chamber, and using a vibrational wave transporter belt that has been developed by the authors of this paper. The main outstanding feature of the proposed design is the presence of mechanical off-centre vibration drives which generate the vibration in the working rollers at a preset amplitude and frequency, thereby generating a mechanical wave on the surface of the flexible transporter belt which ensures the movement of bulk grain along the processing zone which itself is being subjected to infrared radiation. A calculation method was developed for the oscillation system that is used in conjunction with the vibrational transportation of the grain mass, in order to be able to determine the forces that may be present in the vibrational system and to prepare the differential calculations for the movement of the vibrational drive’s actuators, utilising for this purpose Type II Lagrange equations. The solving of the aforementioned integral equations on a PC yielded a number of graphical dependencies in terms of kinetic and dynamic parameters for the vibrational system described above; the analysis of those dependencies provided a rational structural, along with kinetic and dynamic indicators. According to the results that were taken from theoretical and experimental studies on the functioning of the developed infrared grain dryer combined with a vibrational exciter, stable movement for its working roller takes place if the angular velocity of a drive shaft is changed within the range of between 50–80 rads–1 , whereas the amplitude of the indicated oscillations falls within the range of 3.0–4.0 mm. It has been discovered that a rational speed when transporting soy seeds during infrared drying falls between the range of between 0.15–0.60 cm s -1 , whereas the amplitude of the indicated oscillations falls within the range of 3.0–4.0 mm. An increase of this parameter within the stated limits increases the time that it takes to achieve the stage in which a constant drying soy speed is reached by more than 2.5 times (from 205 seconds to 520 seconds), stabilising the figure at a level of 520 seconds, which makes it possible to recommend a range of transport speeds of between 0.15–0.40 cm s –1 under infrared radiation for the seeds in order to achieve the required moisture content with a single pass of the produce on the wave transporter. With that in mind, the power consumption levels for the vibrational exciter do not exceed 50W, while the angular velocity of the drive shaft’s rotation falls within the range of between 100– 120 rads–1 . The results of the experimental study that has been conducted indicated that a rational transportation speed for the soy seeds on the wave transporter under infrared radiation is between 0.15–0.40 cm s –1.

Article The results of experimental studies and operational tests of the sugar beet harvesting process carried out recently reveal that the latest models of beet harvesters produced in Europe and America cause considerable loss of the sugar-bearing mass. The source of this loss is mainly the poor topping of the crowns of standing sugar beet roots, more specifically the excessively low point at which the tops are cut off, which results in the straight out loss of sugar-bearing mass. Thus, there is need to search for such engineering solutions that would avoid both the loss of sugar-bearing mass and the presence of residual haulm on the roots. The aim of this study was to reduce the loss of sugar-bearing mass in the process of topping sugar beet root crowns. The results of this research into the distribution of the heights that root crowns protrude above the soil surface have confirmed the hypothesis that it follows the normal distribution. Based on the results, it has been established that this distribution has the following statistical parameters: mean deviation a = 20–30 mm, mathematical expectation m = 40...60 mm. The laboratory unit developed for this work and the field studies performed with it have provided sufficient evidence to develop a new system to automatically adjust the topping height on state-of-the-art root crop harvesters.

Article The most common technology of removing the sugar beet haulm in the world is a continuous cut of the entire mass of the green haulm with further additional removal of the upper parts of the sugar beet heads, which is carried out without extracting the roots from the ground. This is the scheme according to which most top harvesting machines, manufactured in the world, now operate. However, we have found in our studies that, due to additional cutting off the upper parts of the root crop heads, up to 10% of the sugar-bearing mass is lost. Besides, there is an urgent need for immediate processing of the sugar beet root crops, as losses of the sugar juice occur, and bacteria enter inside of the root crop through the cut-off part, causing rotting. Therefore, a more favourable operation for harvesting root crop tops is not cutting off their heads but cleaning them from the residues of the foliage. In addition, the operation of cleaning the sugar beet roots from the residues of the foliage is subject to rather high requirements due to the absence of the green and dry residues on the heads of the roots, as well as the losses and damage of the root crops themselves. The purpose of this investigation is to develop a theory of the force interaction of the flexible cleaning blade with the sugar beet head in the process of its cleaning when the blade is mounted on the vertical driving shaft. The methods used of the investigation are those of modelling, higher mathematics and theoretical mechanics, as well as programming and numerical calculations on the computer. As a result of the research, an equivalent scheme was developed and a mathematical model was constructed describing the force interaction of the flexible cleaning blade with the surface of the sugar beet root.

Article This article focuses on the evaluation of a rod improvement which is considered in detail below. The rod in question is part of an hydraulic cylinder manufacturing process which takes place on CNC machines. The need for ensuring a process improvement in this area arose because the rod often breaks down under operational conditions. It was found that the cause of this is a finishing operation in the existing production process. The effect of charging which occurred during the grinding process brings about the embedding of abrasive particles into the workpiece surface layer. Therefore, at the running-in stage, the mating surfaces on the rod and the system being used to seal the rings both experience intense wear in their contact areas, with this being caused by abrasive microparticles which serves to reduce the performance characteristics of the part in question. However, even if we dispense with the grinding process, ensuring the necessary roughness of Ra = 0.63 μm at the machining stage alone will present problems of their own for a number of reasons. First and foremost is the connection with the phenomenon that results in an autooscillation processes which is generated by the manufacturing system, as well as the formation of flow chips during machining on CNC machines. In this regard, in order to avoid any negative factors creeping into the process, we propose that a new approach be taken in achieving the necessary surface roughness, one which is based on the suppression of the auto-oscillation process during machining by means of creating a selective metastable structure. At the machining stage, any inhomogeneous structure in the local chip formation area will be destroyed, thereby suppressing the auto-oscillation process and reducing the surface roughness. Eventually, the proposed method will allows the grinding operation to be dispensed with entirely from the manufacturing process.

Article The density of the plants of Dolichos bean significantly influenced the economically valuable indicators, because there is always competition for light, moisture and nutrients between plants in the life process. The period from mass sprouting to the technical ripeness was reduced with increasing the plant density. Such a pattern was characteristic of all phases of the growth and development of the Dolichos bean. The plants with high population (71 thousand units ha-1) took short period (60 and 119 days) from germination to the beginning of technical and biological ripeness, respectively, turned out to be the earliest ripening crops. The plants are better illuminated, the soil nutrition conditions are improved and the sanitary-hygienic climate of the crops improves with thinned crops, thereby plant productivity has raised. However, the average yield of scapulabeans and unripe Dolichos seeds is regulated by the density of the plants, and increased in density due to the greater number of plants. The optimum density for Dolichos bean was 71 thousand plants per hectare, at which yields of green shoots and green peas were formed 7.3 and 3.3 t ha-1, respectively.

Article Saabunud / Received 08.04.2019 ; Aktsepteeritud / Accepted 06.06.2019 ; Avaldatud veebis / Published online 12.06.2019 ; Vastutav autor / Corresponding author: Jüri Olt e-mail: jyri.olt@emu.ee The aim of the current research is to provide an overview of the trends in the park of agricultural machinery in Estonia during the period 2010–2018. For this purpose, data obtained from the registers of Agriculture and Transport of Statistics Estonia have been used. The article outlines, firstly, changes in the number of agricultural holdings by the size of arable land and growing area of grain, secondly, changes in the number of tractors and grain harvesters, including the number of new tractors and harvesters sold over the years, thirdly, the preferences of holdings for tractors and grain harvesters, and fourthly, the categorization of new tractors and grain harvesters by the manufacturing company in the given time period. What is more, developments concomitant with trends in the park of agricultural machinery have been described.

Article For the purposes of carrying out field experiments using the vertical-type cleaner with its elastic cleaning blades to remove haulm residues from the crowns of standing roots, the programme for this process and the technique behind it have both been developed by basing the process on the measurement of the volume of haulm residues that are left on the root crowns after they have been cleaned by a cleaning tool that operates at pre-set values in terms of its translational velocity, its height above the soil surface, and its rate of revolution. In addition, the cleaner’s energy-and-force performance has also been determined. In this process, the new laboratory and the field experimental unit have been put together. The unit comprises a rearmounted root crown cleaner of the rotary type with a vertical axis of rotation. During the field experiments, the general-purpose tractor which carries it moves at a pre-set velocity as registered by the track measuring wheel; the general height of the cleaning tool’s position is set within the specified range by the use of two pneumatic feeler wheels that are equipped with adjustment mechanisms. The results of the completed investigations have been statistically processed with the use of the regression analysis and correlation analysis methods. On the basis of the developed multiple-factor experiment technique, empirical mathematical models have been generated in the form of regression equations for the process of cleaning the crown’s of sugar beet roots. In accordance with the results of the calculations, it has been established that the translational velocity of the implement has the greatest level of impact on the volume of haulm residue that remains on the spherical surfaces of root crowns after cleaning. The rate of rotation for the vertical cleaning rotor and its height above the soil surface which are controlled by the two pneumatic feeler wheels have a lesser effect on the process under consideration.

Article One of the principal problems in the harvesting of potatoes is the cleaning of the lifted heap from soil and plant impurities. The low quality in the performance of this harvesting work process operation is the main cause of the withdrawal from fields of considerable amounts of fertile soil. In order to facilitate choosing the optimal parameters for the new design of the spiral potato heap cleaning unit, a mathematical model of sieving the soil impurities through its cleaning spirals has been developed. The obtained analytical expressions have been solved with the use of a PC and the results have been used for plotting the graphic relations between the parameters of the examined process of a variable-mass body’s motion on the surface of a spiral, which have made it possible to select the optimal design and kinematic parameters of the spiral cleaning unit under consideration. The obtained graphic relations indicate that the rate of sieving in the spiral separator depends on many factors, including the initial mass, the design dimensions (spiral’s radius, helix angle etc.), the frictional properties of the surface, the angular parameters of the position of the potato heap elements on the spiral’s surface, and the angular velocity of the rotational motion of the spiral roll itself.

Article In order to increase substantially the quality of the potato heap separation, it is necessary to carry out the theoretical substantiation of the spiral separator’s parameters with regard to the impact interaction between the product and the tools of the un it under the condition of not damaging the tubers. An equivalent schematic model of the impact interaction between a potato tuber and the surface of the rebounding conveyor has been devised. Taking into account the coefficient of restitution of the tuber’s velocity in case of an impact, new analytical expressions have been obtained for determining the magnitude and direction of the potato tuber’s velocity after the impact. They provided the basis for applying the principle of momentum at impact and obtainin g the analytical expressions that allow determining the impact impulse and impact force at the impact of the tuber on the surface of the rebounding conveyor and, eventually, the dynamic constraints on the permitted velocity of the tuber prior to the impact interaction under the condition of not damaging it. A new analytical mathematical model of the impact interaction of the potato tuber during the potato heap separation has been developed. On the basis of the obtained theoretical results, studies have been carried out on the rational kinematical parameters of the high - quality performance of the above - mentioned work process under the condition of keeping the potato tubers undamaged .

Article The increase of the efficiency and quality of performance of the work process of potato heap separation can be achieved by means of improving the design of the vibrational spiral separator and substantiating theoretically its rational parameters under the condition of eliminating damage to the potato tubers. An equivalent schematic model of the interaction between the potato tuber and the surface of the cantilever spiral springs has been devised. On the basis of the model, the kinematic characteristics of the tuber’s flight and its impact contact with the elastic surface of the over mounted rebounding conveyor have been investigated. A new analytical mathematical model of the potato tuber’s flight from the surface of the spiral separator and its subsequent encounter with the rebounding conveyor mounted above the spiral springs has been developed. New analytical dependences have been obtained for finding out the distance and height of the potato tuber’s flight to the point of impact contact as well as the trajectory equation fo r the travel to the said contact, which makes it possible to obtain the kinematic constraints imposed on the allowed rate of travel under the condition of not damaging the tuber. On the basis of the obtained analytical dependences, the kinematic parameters of the improved design of the spiral potato harvester separator in its interaction with a potato tuber under the condition of not damaging the latter have been investigated .

Article Cleaning potato tubers from soil impurities and plant debris after digging them out of soil is a topical problem in the work process of potato production. Therefore, the engineer ing of new designs of potato heap separators necessitates the further studying of them and the optimisation of their kinematic and design parameters, which must not only ensure the high quality of cleaning, but also rule out the possibility of damaging the tubers. The aim of this study is to determine the design and kinematic parameters of the improved design of the spiral potato separator, which will ensure the high quality of cleaning and rule out the possibility of damaging the tubers, on the basis of th e development of the new theory of potato tuber’s motion on the surface of the separator. An analytical study has been carried out resulting in the construction of the equivalent schematic model of the interaction between the potato tuber and separator, th e tuber being approximated by a material point on the surface formed by the two cantilevered spirals, which are the separator’s tools. The separator’s spirals are driven to rotate and at the same time they can perform oscillations in the vertical and axial plane under the action of the varying load generated by the continuous feeding of the potato heap for separation. In the model, the forces acting on the potato tuber’s body are applied to it, the coordinate axes that have been selected and appropriately o riented are shown. A system of equations has been set up for the constructed equivalent schematic model, comprising three differential equations of the potato tuber body’s motion on the surface of the trough formed by the two cantilevered spirals. The dete rmined kinematic and design parameters will allow to raise the quality of cleaning potato tubers from soil impurities and plant debris. .

Article The theoretical basis of the agricultural material drying techniques has been formed in the world for two and a half centuries. Nevertheless, despite the multitude of studies well presented in the literature, the i ndustry still lacks universally recognized methods of design calculation for the majority of drying problems. Presumably, this is due to the fact that the dehydration of foodstuffs is one of the most energy - intensive and complicated work processes. In the process of thermal treatment during the drying, the physical state of the water in the treated item changes, the properties of the item itself are altered. Recently, the drying of foodstuffs by means of infrared (IR) radiation has been gaining ever wider a cceptance. At the same time, the technologies for dehydrating foodstuffs and materials are now far ahead of the theory of drying. Not only the classical literature on the drying problems, but even special studies on the subject cannot provide any specific recommendations for the design of installations with the electro - magnetic principle of energy input. Whereas that is exactly the type of installations that are now actively making headway, while offering serious challenges in their modelling. For that reas on, experimenting has until now been the only reliable way of their studying. Despite the available extensive scientific literature on the drying, including works on IR units, the practical issues of engineering IR driers have not been tackled. All the exi sting studies consider solely particular cases. This study discusses the process of drying the fixed bed of rapeseeds with the use of the electromagnetic infrared emitter. The energy intensity of the process and the optimum thickness of the product bed are determined. The aim of the paper is to examine the effect that the operating condition parameter s (energy input intensity, temperature, grain bed thickness) have on the drying kinetics and the energy characteristics of the process. The methods of research are based on the thermophysical analysis of the material’s structure. The experimental studies were carried out with the use of monitoring and measuring equipment, up - to - date methods and instruments, including solutions developed by the authors. The analy tical treatment was performed with the use of the software packages: MathCAD, Excel. The sample testing and examination took place in the laboratory and the methods were in compliance with the applicable standards. A comprehensive experimental investigatio n of the effect that the operating parameter s (specific load and power) have on the rape seed IR - drying kinetics had been accomplished.

Article A mathematical model has been developed representing the motion of a seed drill combination simultaneously performing the preceding banded placement of mineral fertilisers. Such a combined unit comprises the gang-up wheeled tractor, the fertiliser distribution module behind the tractor attached to it with the use of a hitch and intended for the banded placement of mineral fertilisers and the grain drill behind the fertiliser distribution module attached to it also with the use of a hitch. For the components of this dynamic system the coordinates of their centres, their masses as well as the external forces and the reactions of the soil surface applied to them have been determined. In order to use the original dynamic equations in the form of the Lagrange equations of the second kind, the generalised coordinates and kinetic energy relations have been determined. Following the necessary transformations, a system of six differential equations of motion has been generated, which characterises the behaviour of the combined machine unit during its plane-parallel motion. In this system, two line coordinates and one angular coordinate characterise the behaviour of the propulsion and power unit (wheeled tractor), while three angular coordinates characterise the rotations of the draft gear and the centres of the machines integrated with its use.

Article The reduction of power consumption in the ploughing operations can be achieved by way of improving the grip properties of the implement-carrying tractors, which is facilitated by setting up ploughing units for operation on the ‘push-pull’ principle. The aim of the current research is to substantiate the set-up and parameters of the ploughing unit with a front-mounted plough basing on the theoretical investigation of the stability of its motion in the horizontal plane. The methods of research include obtaining the amplitude- and phase-frequency response characteristics of the dynamic system in order to analyse the stability of its motion under the action of external statistically random perturbations. Also, the methods of software development and PC-based numerical computation are applied. The results of the study prove that the increase of the ploughing unit’s travel speed results in the considerable rise of the gain of the amplitude of the tractor’s heading angle oscillation in response to the oscillation of the angular displacement of the front-mounted plough in the horizontal plane. The phase-frequency response displays the same behaviour, changing substantially together with the unit’s travel speed. Raising the coefficient of resistance to tyre slip of the tractor’s rear wheels from 100 to 130 kPa and the front wheels from 140 to 175 kPa results in a minor decrease of the amplitude of oscillation of the tractor’s heading angle φ. The ploughing unit has the best response to the input effect, i.e. the oscillation of the front-mounted plough’s angular displacement βp, when it operates using the 1+5 combination. The increase of the number of front-mounted plough bodies from 1 to 3 results in the substantial growth of the tractor’s heading angle oscillation amplitude. Taking into account the way, in which the ploughing unit as a dynamic system responds to the input perturbance, the increase of its travel speed can be restricted not by the condition of its motion stability, but solely by the agrotechnical requirements applied to such a process operation as ploughing. The ploughing unit’s motion stability substantially improves in case of higher air pressure in the tyres on the tractor’s front and rear wheels. This effect is especially pronounced in the perturbance oscillation frequency range (0...1.5 s –1 ) that covers the main part of its dispersion.