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This work aimed, to evaluate the structural behavior of Oxisols based on the least limiting water range (LLWR) and establish relations with corn crop. The experiment was carried out in a randomized block design with five treatments and four replications. Soil samples collected at the layer of 0-0.20 m depth in a Haplustox (LVd) and an Eutrustox (LVef) were used. The compaction treatments consisted of T0= no additional compaction; T1 and T2= two and four passes with a 4 t tractor, respectively; T3 and T4 = two and four passes with a 10 t tractor, respectively. The range of LLWR variation in the LVd was the lowest one and varied from 0.01 to 0.04 m3 m-3, whereas in the LVef varied from 0.03 to 0.13 m3 m-3 for the critical soil penetration resistance (PRc) of 2 MPa. It was observed that critical bulk density (BDc) values were 1.76 and 1.40 Mg m-3 in the LVd and the LVef, respectively. The highest frequency of bulk density (BC = BDc) occurred from the T1 to T4 (LVd) and from the T2 to T4, however, a reduction in corn yield was not observed. The determination of the LLWR was efficient and complementary for identifying more favorable or more impeditive conditions to compaction in the LVef for the corn crop development in relation to the LVd. [ABSTRACT FROM AUTHOR]

Abstract: Farmers may desire a high cone index soil for tractive purposes or a low cone index (CI) soil for root penetration and seedling emergence. The function of any agricultural tractor is to provide mobility for itself and to power an implement. The aim of this paper was to (a) assess the impact of two tractors with different tyre sizes and axle loads on motion resistance (MR) and on the CI for three different soil mechanic conditions and (b) determine the existing relationships between MR and ground pressure parameters and tyre sinkage. Traffic was simulated with one pass on clay soil for a front-wheel assist tractor (FWA, load=77.7kN) and a four-wheel drive tractor (4WD, load=98.01kN) on three soil conditions: direct sowing systems, ploughed and seedbed. The outlined hypotheses were as follows: (1) there is a direct relationship between the subsoil compaction and the MR force of the FWA and 4WD tractors, and (2) the power loss produced by the MR depends on the soil mechanics. The experiment was conducted in the eastern section of the Rolling Pampa region of Argentina at 34°36′S, 58°40′W. MR, rut depth (RD) and CI were measured. The MR mean values of the 4WD were 9.30, 6.59 and 2.31kN for ploughed, seedbed and direct sowing soil, respectively, whereas the values for the FWA were 10.41, 7.91 and 4.67kN, respectively. For the three soil conditions, no significant differences were found in the RD between the 4WD and FWA. For the topsoil level (0–150mm), one FWA pass caused mean values in the CI of 2150, 1835 and 1780kPa for direct sowing, seedbed and ploughed soil, respectively, whereas for 4WD the values were 1890, 1640 and 1587kPa, respectively. For the subsoil (150–600mm), 4WD caused higher CI values than the FWA. The CI mean values of the 4WD were 2477, 2240 and 1890kPa for direct sowing, seedbed and ploughed soil, respectively, whereas the values for the FWA were 2240, 1870 and 1770kPa, respectively. For the different soil conditions, the subsoil compaction increased as the total axle load increased, independently from the ground pressure. Moreover, for both tractors, a greater MR force was observed in the soil with the lowest bearing capacity. The smallest power loss ratio due to MR and engine power was found with the 4WD. [Copyright &y& Elsevier]

Abstract: The aim of this paper was to quantify soil compaction induced by tractor traffic on two tillage regimes: conventional tillage and direct drilling. Traffic was simulated with one pass of a conventional 2WD tractor, using four configurations of cross-ply rear tyres: 18.4–34, 23.1–30, 18.4–38 and 24.5–32, and four configurations of radial tyres 18.4R34, 23.1R 30, 18.4R 38 and 24.5R 32, with two ballast conditions used in each configuration. The experiment was conducted in the east of the Rolling Pampa region, Buenos Aires State, Argentina at 34°25′S, 59°15′W; altitude 22m above sea level. Rut depth after traffic and soil bulk density and cone index in a 0–450-mm profile were measured before and after traffic. Considering topsoil level, in two tillage regimes, all treatments induced significant values of soil compaction as compared to the control plot without traffic. Subsoil compaction increased as total axle load increased and was independent of ground pressure. For the same tyre configuration, radial tyre caused less soil compaction than the cross-ply. [Copyright &y& Elsevier]

Abstract: The main function of deep tillage is to alleviate subsoil compaction, but how long do the benefits of this technique remain? Traffic on loose soil causes a significant increase in soil compaction. Subsoiling and chisel plowing were carried out at 450 and 280mm depth, respectively on a compacted soil in the west Rolling Pampas region of Argentina. The draft required, physical soil properties, root growth, sunflower (Helianthus annus L. Merr.) yield and traffic compaction over the subsequent two growing seasons were measured. Cone penetrometer resistance was reduced and sunflower yields increased following deep tillage operations. Subsoil compaction caused changes to the root system of sunflower that affected shoot growth and crop yields. Although subsoiling and chiseling had an immediate loosening effect, it was evident that after just 2 years, when traffic intensity was >95mgkmha−1, re-compaction and settling had occurred in the 300–600mm depth range. [Copyright &y& Elsevier]