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With depleting resources, it is essential to increase the application of Agriculture 4.0 principles and technologies. Blueberry cultivation includes various operations, one of them being fertilization. To precisely discharge the correct amount of fertilizer, a volumetric dispenser utilizing a straight fluted roller could be considered as an option. The aim of this research is to verify whether such a dispenser could be used for precision fertilization with solid granular fertilizers. The output of the dispenser was measured on different conditions with three NPK fertilizers. Based on statistical analysis, the required 10% discharge uniformity cannot be achieved and it is necessary to modify the dispenser or use another one.

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.

The cultivation and harvesting of sugar beets (roots and leaves) is one of the most labour and energy consuming work processes in the agricultural industry. The most important task in sugar beet farming is to improve the quality of sugar beet root crop harvesting and reduce energy costs for harvesting. This primarily concerns reductions in losses and damage of root crops, as well as a reduction in their contamination; in this case, the loss of fertile soil will be excluded, which will be removed from the fields together with the contaminated root crops. These issues present a multifaceted scientific and technical problem, which must be solved by searching for new working elements of sugar beet harvesting machines. Despite the modern level of construction of beet harvesters and their working bodies that has been achieved, there is a need to find further ways to improve them. Further research should deal with the improvement of general constructional schemes of new beet harvesters, with thorough theoretical justification of their constructions and technological parameters. The newly developed theories of functioning of improved constructions of sugar beet harvesters and their working bodies require thorough experimental verification. This will give grounds to use the obtained theoretical dependences for the final goal—analysis and generalisation of their rational parameters. Theoretical research must play a fundamental role in the mechanical and technological substantiation of the root lifting process. It must be used as the basis for developing rational kinematic and dynamic operation conditions in order to achieve the required quality of the performed work process as well as streamlined energy consumption. At the modern stage of the development of agricultural mechanisms, the methods of mathematical model generation based on the use of the theoretical and analytical mechanics and the application of up-to-date mathematical tools and computer technology have to be employed in the analysis and synthesis of the parameters of implements and agricultural machines overall. Thus, the modern methods of theoretical research into the implements of sugar beet harvesters have to be based, first, on the state-of-the-art perception of the principles of the processes that take place when the roots are lifted from the soil and, second, on the possibility of describing these processes more comprehensively and systematically with the use of modern mechanical and mathematical methods. Undoubtedly, such a description only has to be provided for the principal and essential moments of the mentioned processes, while the insignificant and incidental factors must be completely neglected. Further, on the basis of the analytically determined rational parameters of the lifting implements of sugar beet harvesters, which are subsequently experimentally validated and refined, highly reliable prototypes must be designed, which then have to be widely used by the agricultural engineering plants and companies. Therefore, this treatise presents the fundamentals of a new theory of the lifting tools of sugar beet harvesters—in particular, vibrational lifters based on the modern methods of mechanics and mathematics. It has been a long time since the first attempts were made (in the 1970s) to analytically describe the oscillating processes that take place during the vibrational lifting of sugar beet roots from the soil. The theory of the vibrational lifting of root crops has, overall, not been developed to a sufficient extent; the mathematical model specifically used for the process of root extraction from the soil by the vibrational lifter has not been devised. Until recently, it had been assumed that the experimental methods of determining the amplitude and frequency of oscillation of the vibrational faces—which could only have relatively limited values, subject to the reliability of the vibrational actuator—completely ensured the optimality of this whole process. However, at the present time, under the conditions of significant improvements in the reliability of designs and changes in the kinematic parameters of harvesting (for example, the increase in the travel speed to levels of up to 2.5 m·s−1 ), the obtained values of the parameters of vibrational lifters can by no means be considered optimal. Therefore, a goal has been set to develop, first of all, a new theory of vibrational root lifting based on the generation of mathematical models, which would describe the interaction between the digging shares on the one hand and the root’s body and the soil on the other hand. At the same time, the theory has to provide the mathematical descriptions of all stages of said interaction, starting from the stage of the lifter approaching the root body fixed in the soil (as in elastic medium), proceeding to the interaction of the root body with only one digging share of the lifter (asymmetric gripping of the root), followed by the interaction with both the share surfaces (symmetric gripping), and finally the eventual translation of the root along the lifting tool’s throat towards the level of the soil surface. Additionally, as a matter of principle, the theory needs to consider different (possible) directions of the oscillating motions of the digging shares of the vibrational attachment—i.e., the longitudinal and transverse ones.

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.

Book of Abstracts. 12th International Conference on Biosystems Engineering 2021, May 5–7, 2021 Tartu, Estonia. Estonian University of Life Sciences.

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.