Identifying the position of the compacted layer by measuring soil penetration resistance in a dryland farming region in Northeast China

Topsoil is disturbed by ploughing, the effects of infiltration, the movement of fine particles from the topsoil to the subsoil, and direct pressure from agriculture machinery, all creating an abrupt delineation in the form of a compacted layer with very low permeability. Spatial variability of soil properties, such as soil structure and penetration resistance (PR), can help identify the compacted layer. However, there are no quantitative methods to describe this layer. In this study, PR was used to survey different soil types. A Mann–Kendall (M-K) test of PR data was used to identify the presence and position of the compacted layer in a dryland farming region of Northeast China. Our results demonstrated that PR was mainly affected by bulk density and soil water content. Compared with the topsoil, PR was more significantly affected by water content in deeper soil layers. An M-K test of the PR curve can provide a more reliable and objective assessment of the thickness of the plough layer and location of the compacted layer than field observation. Our data indicated that there was a compacted layer in the soil profile in the study areas and the spatial variability of the compacted layer was heterogeneous. The plough layer was shallow, and the compacted layer was thicker in areas with frequent use of agricultural machinery. Moreover, frequent use of agricultural machinery resulted in a PR of the plough and compacted layers that was greater than that in other areas. Information on identifying the position and thickness of the compacted layer and the factors influencing their spatial distribution can be used to create effective soil management options and improve conditions for the development of plant roots in dryland farming regions.