Soil porosity and gas transport properties after 19 years of no-till and conventional tillage

No-till and conventional plough tillage have been compared since 1994 in the Oberacker longterm field experiment at Inforama Ruetti in Zollikofen (Switzerland) on a slightly humic sandy loam soil. Crops were grown in a six-year crop rotation in a strip trial with six adjoining plots. Nineteen years into the trial, undisturbed cylindrical samples were taken at 10 cm and 40 cm depth from both cropping systems. The sampling was supplemented with reference samples from the permanent-grassland strips between the experimental plots. The samples were used to determine air-filled porosity (εa), relative gas diffusivity (Dp/D0) and air permeability (ka) at five different matrix potentials between –30 and –500 hPa. For no-till and the permanent-grassland strips, pore-system and gas-transport characteristics were similar in both the topsoil and subsoil, although less favourable in the topsoil. By contrast, conventionally tilled soils exhibited a clear stratification: εa, Dp/D0 and ka were more favourable in the topsoil and less favourable in the subsoil than for no-till and the permanent grassland strips, respectively. With no-till, the biopore-rich subsoils tended to lead to higher yields than under conventional tillage. In an evaluation of impacts of cropping systems on soil quality, the entire soil profile (i.e. topsoil and subsoil) should be studied, and key soil functions such as productivity should be included in the assessment.