Stress distribution and soil displacement under a rubber-tracked and a wheeled tractor during ploughing, both on-land and within furrows

Abstract

Ploughing is a field operation considered to be associated with severe soil compaction. Two experiments were carried out in Denmark on Eutric Cambisols with a Claas Challenger 2-65 E rubber-tracked tractor with a total weight of 185 kN. In Experiment A, the vertical stress under the track during ploughing was measured by stress sensors at 0.1 m depth in order to study stress distribution. In Experiment B, the vertical soil displacement and vertical normal soil stress during ploughing were measured simultaneously at three different depths. The tracked tractor was compared to a wheeled tractor with a total weight of 97 kN. The rubber-tracked tractor and the wheeled tractor were pulling a plough with 12 and 7 bodies, respectively. The tracked tractor ploughed on-land, whereas the wheeled tractor ploughed both on-land and conventionally (two wheels running in the furrow). In Experiment A, vertical stress was found to be much higher under the rear than under the front part of the tracks. It was caused by unsuitable adjustment of the plough to the tractor for given field conditions. By lowering the point of application of the draught force induced by the plough, maximum vertical stress was reduced from 304 to 158 kPa. However, the vertical stress was concentrated under the supporting rollers and wheels as well as under the centre line of the track, so that maximum stress was 3.8 times higher than average stress. In Experiment B, the vertical stress was higher below the wheeled tractor than below the tracked tractor, which had been adjusted as in Experiment A. No significant difference in maximum vertical soil stress was found between the tracked tractor and the wheeled tractor ploughing on-land at any depth. The vertical stress at 0.3 and 0.5 m depth was significantly higher during conventional ploughing (i.e. under the in-furrow wheels) than during on-land ploughing. The higher vertical stress also resulted in larger vertical soil displacement at 0.3 m depth under the in-furrow wheels when ploughing conventionally than under the on-land ploughing tractor. At 0.5 m depth, no residual vertical soil displacement occurred because the soil strength was very high. The results clearly demonstrated that on-land ploughing may reduce the risk for subsoil compaction compared to conventional ploughing. Using tracks instead of wheels may further reduce this risk. However, this is only the case if the tractor is well balanced. Thus, each particular tillage tool should be adjusted to the tractor, also with respect to the soil type and the field conditions.