Influence of soil physical and chemical properties on mechanical characteristics under different cultivation durations with Mollisols

The degree of soil compaction is affected not only by the agricultural machinery but also by the soil physical, chemical, and mechanical properties. We hypothesized that the changes in the soil physical (clay content) and chemical properties (soil organic matter, SOM) due to long-term tillage operations would cause corresponding variations in the soil mechanics properties. The in-situ undisturbed soil samples were firstly adopted to detect soil properties as affected by long-term conventional tillage of Mollisol (black soil), and explore the relationship between soil physico-chemical properties and mechanical properties with 4 different cultivation duration croplands (0, 17, 30, and 40 yr). Then, artificial modified soil samples were further used to verify this relationship and confirm the predominate factor influencing compression-rebound behavior at 3 levels of SOM and clay contents, respectively, at 2 levels of gravimetric water contents. The compression index (Cc) and rebound index (Cᵣ) were determined using a fast oedometer test. We found that with cultivation duration extending, the clay content and soil bulk density increased, while the SOM, Cc and Cᵣ gradually decreased. The laboratory simulation tests also showed that the compressibility was higher when SOM or clay content was higher; while the soil resilient capacity was lower when the SOM was lower or clay content was higher. In conclusion, the decrease of SOM and the increase of clay content due to long-term cultivation could increase the risk of soil compaction and weaken its recovery capacity. SOM is predominant in influencing the soil mechanical properties relative to clay content. Maintaining and/or increasing SOM may improve the mechanical properties of arable Mollisols.