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Mathieu Lamandé

Horizontal stresses below two agricultural vehicles

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Deformation of the pore system in the subsoil due to mechanical stress applied by agricultural machinery is persistent for at least decades. Application of normal stress exceeding subsoil strength leads to a reduction of capacity soil properties (i.e. air-filled porosity) by compaction, while shear stress larger than soil strength may affect intensity soil properties (i.e. air permeability) by soil deformation not necessarily associated with compaction. In previous experiments in field conditions, isotropic compaction was observed below the center of tires, while shearing took place below the edge of tires. Stress distribution at the tire/soil contact is not uniform. Dimensions and inflation pressure are key factors for the ability of agricultural tires to distribute the wheel load. Our hypothesis was that the risk of shearing increases with the tire inflation pressure and the number of wheels. We measured horizontal stress at two depths (0.3 and 0.5 m) below tires of two slurry spreaders: one self-propelled machine equipped with wide tires (1.050 m) and low inflation pressure (150 kPa) but carrying a high wheel load (120 kN), and one tractor towing a three-axle slurry spreader equipped with 0.7 m wide tires, loaded with 73 kN and with high inflation pressure (300 kPa). Effect of traffic on soil structure was assessed by air permeability measurements on soil cores sampled at nine locations across the tracks (within as well as outside the tire-soil contact area) and at three depths (0.3, 0.5 and 0.7 m). The maximum rooting depths of spring barley was recorded below the center of the tire, below the edge of the tire, and outside the tracks. Horizontal stresses had about the same magnitude for 0.3 and 0.5 m depths for the self-propelled machine, while it was much higher at 0.3 than at 0.5 m for the tractor-trailer combination. At 0.3 m depth it was significantly higher for the tractor-trailer system than for the self-propelled machine. Generally, air permeability was reduced in the track of the tractor-trailer system, while no significant reduction was observed for the self-propelled system. Outside but close to the tracks, the latter system increased the air permeability (significantly at 0.3 m). Also the tractor-trailer system tended to increase the air permeability outside the track (significant when compared to the in-track values). Both systems reduced significantly the maximum rooting depth below the center and at the edge of the tire as compared to non-trafficked soil, while there was no difference between machinery systems. This study was only an appetizer for further research on the effect of horizontal stress on soil structure, as many factors were confounded (wheel load, inflation
Original languageEnglish
Publication year2015
Number of pages1
Publication statusPublished - 2015
Event20th International Soil Tillage Research Organization Conference (ISTRO) 14-18th, September, 2015 Nanjing, P.R. CHINA - Kina, Nanjing, China
Duration: 14 Sep 201518 Sep 2015


Conference20th International Soil Tillage Research Organization Conference (ISTRO) 14-18th, September, 2015 Nanjing, P.R. CHINA

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