Inverkan av hjullast och ringtryck på tryck och deformation i jordprofilen, främst matjorden

Compaction of farmland can in many cases be negative. A poorer water infiltration in the soil profile, bad conditions for root growth, slower decomposition rate of organic material, and an increase in traction power are some of the negative effects. The most serious compaction is the one appearing below the depth of tillage, as it will exist for many years. The factors having the greatest influence on the amount of soil compaction is the wheel load, the tyre equipment used, the tyre inflation pressure and the water content in the soil. Factors discussed in this report are wheel load, tyre inflation pressure, the stress in the soil, the stress distribution in the contact area and the impact of these parameters on the amount of compaction. Three different experiments were carried out on three sites in the autumn in 2002. The first experiment was carried out at Svenstorp farm in southern Sweden. During dry conditions the stress and the deformation in the soil was measured under a 3-row, a 6-row and a 9-row sugar beet harvester that were driving with different loads. The 6-row harvester was also driven with different tire inflation pressures. Saturated hydraulic conductivity, macroporosity and bulk density was measured in the topsoil after a single pass with the harvesters. The second experiment took place at Krenkerup farm in southern Denmark. Two different systems for sugar beet harvesting were evaluated. The first system contained one big harvester only that had a loading capacity of 28 tons and a total weight of 55 tons. Because of the great loading capacity, it was able to bring the sugar beets to the end of the field. The other system contained a smaller harvester, with a total weight of 27 tons and two field trailers that were supporting the harvester all the time. The measurements were concentrated on stress and deformation in the subsoil and also stress and stress distribution in the topsoil under the different tyres. The last experiment took place at Ultuna, Uppsala, Sweden. In this experiment the stress and the stress distribution in the topsoil was measured when driving with different wheel loads and tyre inflation pressures. The results from Svenstorp showed the positive effects of a reduced tyre inflation pressure on soil stress, saturated hydraulic conductivity and macro porosity in the topsoil. Traffic by the 6-row harvester, driving with a high tyre inflation pressure, was resulting in the lowest rate of saturated hydraulic conductivity, independently of the load. Also the boogie wheels of the 3- row harvester were resulting in low infiltration rates, independently of the load. The measurements at Krenkerup showed that one passage over the soil with the big harvester deformed the soil more at both 30 cm and 70 cm depth, than one passage with the small harvester followed by the field trailer. The highest stress both at 30 cm and 70 cm depth was measured under one of the three tyres of the big harvester. There was a very even stress distribution between the three axles of the field trailer. Measurements at Ultuna showed that a higher wheel load resulted in a higher stress in the topsoil, even though the tyre inflation pressure was kept constant. A lower tyre inflation pressure resulted in a more even stress distribution in the contact area. The main conclusions of this study are: 1) A reduced tyre inflation pressure will greatly reduce compaction of the topsoil. 2) The deformation in the soil was greater after passing once with a 55 ton harvester than after passing once with a 27 ton harvester plus a field trailer. 3) An increase in wheel load resulted in a higher stress in the topsoil, even though the tyre inflation pressure was kept the same