Tire pressure and wheel load are both easily managed parameters which play a significant role in tillage operations for limiting slip which involves energy loss. To a great extent, this aspect affects the fuel consumption and the time required for soil tillage. The study was focused on the tire pressure and extra weight variation effect on fuel consumption and work productivity for soil tillage at normal tractor wheels slippage (7-15%). The experimental research unit composed of an 82.3 kW 4WD tractor and a reversible 4-bodies plough is presented. Tests were carried out on a stubble loam, where slip of tractor driving wheels was  15%, tractor front ballast mass was varied in the range from 0 to 520 kg and inflation pressure in the tires from 240 kPa to 100 kPa. Dependences of tractor performance indicators on ballast mass and tires inflation pressure are presented. When tractor tire slip varies in the range from 7 to 15 percent (which is normal slip in the soil), reducing the tires inflation pressure decreases the driving wheel slip and fuel consumption, while increases work productivity. Increasing the additional mass of the tractor (adding ballast weights) decreases the driving wheel slip, increases work productivity, but also increases fuel consumption and soil compaction.

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Tractors are the main machines in agricultural production processes. Agricultural tractors commonly employ a four-wheel drive transmission. To reach maximum efficiency in production works, tractors are loaded by as high thrust as possible. The consequence of it, quite often, is that the slippage of driving wheels grows to the limit that is not allowed. To reduce the slippage, various ways are pointed out in terramechanics. One way is to increase the tractor's weight by adding ballast. The other way is to increase the contact area between tires and the supporting surface. The slippage can be also reduced with traction control and other relevant systems. These methods, which help to reduce slippage, also affect tire deformation. When proportion of tires deformation is not the same as proportion of their sizes, the consequence is change of the lead of front wheels. In this paper analysis is presented, how the lead of front wheels affects the work of MFWD tractor in different conditions. Test results are presented for a MFWD tractor, how the lead of front wheels varies depending on deformation ratios between front and rear tires. For a MFWD tractor, values of deformation ratio between front and rear tires were determined, which ensured effective and which produced unreasonable values of lead of front wheels.

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Oilseed winter rape is often replaced by winter wheat in benefit to crop rotation. The high-cut and rigid oilseed winter rape stubble with large roots mass often is the main challenge of clear post-harvesting shallow tillage, especially in clay loam soil at minimum expenditure of fuel consumption. In most cases the disc harrow is used to interblend the stubble and plant residues into soil. If the shallow tillage is done well, the mineralization takes place and winter rape stubble does not have the negative influence on the sowing of the next rotation crop. The aim of this study was to determine the dependence of fuel consumption that is required to achieve the preferred level of shallow tillage in clay loam soil after the harvest of oilseed rape. The fuel consumption was investigated with a disc harrow (4 m width), depending on the disc angle and forward speed. The investigated tractor "CASE IH 135" with dual wheels was equipped with a data acquisition system and was used to measure the fuel consumption, speed and implement draft. This research has developed the correlation of stubble and other plant residue incorporation ratio (from 0.47 to 0.86) to fuel consumption (from 2.7 to 5.9 l•ha-1) that was dependent on the draft force of the aggregate regime. The sufficient post-harvest tillage quality level, in this case the plant residue incorporation ratio was taken into account, is possible to reach with the minimal fuel consumption per hectare, when the disc angle is 10° at the working speed 3.5 m•s-1 .