Visual assessment of soil structure: Part II. Implications of tillage, rotation and traffic on sites in Canada, China and Germany

The aim of the paper was to utilize methods of visual structure assessments in conjunction with soil physical measurements for the analysis of the impact of tillage, rotation and traffic on topsoil structure. The study was conducted in long-term-experiments on the Elora rotation (ER) and Elora Landscape (EL) sites in Canada, the Luancheng (LS) site in China and the Dedelow (DT) site in Germany. Texture of soils ranged from loamy sand (DT) to sandy loam (EL, ER) to silt loam (LS), climate ranged from clearly sub-humid (LS), slightly sub-humid (DT) to humid (EL, ER). Two common variants of tillage were compared on all sites: (1) Moldboard Ploughing (MP) and (2) No-Till (NT). Within the plots, wheeltracks were analysed separately on ER and DT sites. On ER site, different rotation variants were sampled. On EL site, large alfalfa and corn plots and the driveway in between were sampled at different slope positions. Methods of visual structure analysis of Peerlkamp, Diez and Shepherd were tested along with measurements of dry bulk density (DBD), initial infiltration rates and soil penetrometer and shear resistance. Both visual structure assessment and measurements indicated significant differences between variants of tillage and traffic on DT and ER sites. Differences between alfalfa (good structure) and corn rotation (less favourable structure) were also significant on EL and ER sites. Soils in Germany and Canada were partly compacted, under wheeltracks in particular. Most favourable topsoil structure conditions were found under MP plots, most unfavourable structure was detected under wheeeltracks and NT plots. On LS site in China (loess soil, lower weights of machinery) visual structure was overall favourable and no significant differences between tillage variants were found. However, MP plots indicated the beginning of subsoil compaction. Crop yields confirmed differences between tillage variants. Yields of cereals were significantly higher (350-800kgha⁻¹) under MP as compared with NT on ER and DT sites due to a better air capacity. It may be concluded that (i) results of visual assessments were coincident with those of soil physical measurements and can complement them, (ii) under intensively mechanised soil management in sub-humid to humid regions, NT can lead to sub-optimum topsoil structure states, (iii) subsoil compaction is a risk of MP on all soils, and (iv) controlled traffic and the inclusion of perennials into the rotation may be advantageous for soil structure.