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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.