Evolution of soil structure under no-tillage and ploughing

Since 1994 plow tillage is compared to no-tillage on six crop rotation plots in the long-term field trial Oberacker at the Inforama Ruetti in Zollikofen. The deep cambisol of the trial plots consists of 15 % clay and 3 % organic matter. From 2000 to 2004 soil physical parameters have been investigated in order to assess the effects of the two tillage systems on soil structure. Diagrams showing at the same time the share of wheeled area and the amount of soil stress under the wheel tracks are used to compare possible impacts of the two ploughing systems «in furrow» and «onland» on soil structure and to make suggestions for improvements.Determination of bulk density, macropore volume and air permeability allow for conclusions regarding the size and arrangement of voids in the soil and show favourable effects of no-tillage on structural properties of the subsoil and partly negative effects of this tillage system on topsoil.Apart from the determination of conventional soil mechanical stability parameters like precompression stress, the new parameters «remaining total pore volume» and «remaining macropore volume» are suggested to improve the interpretation of compression test results, particularly regarding functional aspects. These parameters characterizing soil structural stability emphasize the generally favourable properties of the subsoils in the «Oberacker» trial and indicate improvements in topsoil stability caused by no-tillage.