Soil properties and sugar beet growth as affected by repeated passes of heavy machinery and soil tillage

摘要

High wheel loads applied in agricultural field management cause major concern regarding the risk of subsoil (below 30 cm soil depth) compaction. However, investigations on potential cumulative effects of repeated passes of heavy machinery in the course of regular rotational crop management are scarce. Conservation tillage is expected to be effective against subsoil compaction compared to mouldboard ploughing, but experimental evidence for this assumption is rare as well. Therefore, a complex field traffic experiment (unwheeled/wheeled) consisting of three consecutive wheelings with a six-row sugar beet tanker harvester (one pass per year at 70-100 % field capacity) was included in a long-term tillage trial (MP = mouldboard ploughing 30 cm deep, SM = shallow mixing with a cultivator 10 cm deep). In 18-23 cm soil depth, penetration resistance was higher and air capacity and pneumatic conductivity (both measured on soil cores drained to a water tension of 6.2 kPa) were lower in SM than in MP treatment. Simultaneously, sugar beet yield was diminished by SM treatment. In the subsoil pneumatic conductivity was enhanced by SM treatment compared to MP. Regardless tillage, three wheelings with the harvester decreased air capacity and pneumatic conductivity of topsoil and subsoil. In contrast, penetration resistance and sugar beet yield were just slightly or not affected by wheeling. Conclusively, the results indicate that repeated passes with present-day sugar beet harvesters with high wheel load under moist to wet conditions may cause subsoil structure degradation on loessial soils. Under these wheeling conditions shallow conservation tillage practices obviously did not result in a higher resistance of the soil to mechanical stresses compared to mouldboard ploughing.