Higher Number Of Passes Research Articles

The Distribution of Soil Compaction with Depth and the Response of a Perennial Forage Crop

As a result of the great intensity of vehicular traffic to which perennial forage crops are subjected, the avoidance of long-term induced subsoil compaction is difficult. The object of this work was to study the alternatives of using either a light tractor with a high number of passes or a heavier one with a reduced amount of wheeling on the field. Field tests were carried out on grassland on a Typic Argiudol with a soil moisture below but near field capacity. Three different numbers of passes, with two tractors with different weights but the same ground pressure, were used to obtain six different traffic intensities. In the soil profile analysed, ranging from 0 to 600mm, bulk density and penetration resistance were measured before and after traffic. Six months later grassland yield was evaluated, both in and out of the vehicle track. Decreases in grass yield ranging from 7 to 25%, were measured in out-of-track areas, and 52 to 76% in intrack areas. If results are compared for the same number of passes, then the heavier tractor appears to give either the same or a greater reduction in grassland yield than the lighter tractor. If the results are compared on a basis of traffic intensity, the picture is less clear but it seems likely that the lighter tractor, with a larger number of passes, can do as much or even greater damage than the heavier tractor with fewer passes.

The effect of vehicle weight on the distribution of compaction with depth and the yield of Lolium/Trifolium grassland

Although research has demonstrated that traffic by vehicles on soils with high moisture contents causes subsoil compaction and a negative impact on grassland productivity, knowledge is lacking regarding the interactive effects of using a light tractor with a high number of passes or a heavier one reducing wheeling on the field. Research was conducted in 1994–1995 in Buenos Aires State, Argentina to establish the effect of the tractor axle load on the distribution of subsoil compaction independently of the influence of ground contact pressure and to evaluate the effect of densification upon grassland production. The main species present were annual ryegrass ( Lolium multiflorum Lam.) (60%) and white clover ( Trifolium repens L.) (38%). The grassland was trafficked with two tractors of the same design and similar pressures on the soil contact area of the drive wheels, but with one of them having 1.8 times the mass of the other, 4.2 Mg and 2.3 Mg, respectively. The work was performed on a fine clayey, illitic, thermic Typic Argiudoll (Centeno series), at a high moisture content using three different numbers of passes for each tractor: one, five and ten. Cone index and bulk density to 600 mm in the profile were measured to identify changes in soil compactness. Dry matter yield per hectare was used to indicate the response of grassland production. Independent of pass numbers, the heavier tractor always produced greater increases in bulk density for the 300–600 mm depth range. Grass responses to compaction were significant for all treatments, either in the lane of the tractor, where the average decrease in dry matter production was 74%, or adjacent to tyre imprints, where the grass yield was reduced by 18%. For the same number of traffic passes, the heavier tractor increased bulk density at the 300–600 mm depth compared with the lighter tractor. However, the lighter tractor, with a larger number of passes, produced as much or even greater compaction than the heavier tractor with fewer passes.

The effect of surface topography on the wear of steel

The pattern of roughness and wear has been obtained by varying the speed, the number of passes and the pre-roughness of the samples in both dry and lubricated sliding conditions. Three-dimensional graphs of wear versus speed versus sliding time and roughness of the worn surfaces were produced and a linear relation between the variation of the roughness and the amount of wear at a high number of passes has been determined. The initial dry wear rate is influenced by the prior surface roughness. In the case of lubricated conditions the influence of prior roughness is not pronounced. In dry sliding the smooth surfaces in the running-in stage roughen and the rough surfaces become smoother, while in lubricated conditions both surfaces become smoother in the first few passes. Sliding perpendicular to the lay produces rougher surfaces and more wear than is the case in the parallel direction.