Evolution of soil structure at field-scale on a silt loam in Northern Germany

Compaction is considered as one of the major threats to soil quality and health. The use of heavy farm machinery may compact the soil, reducing the pore volume and simultaneously increasing soil bulk density. In this context, a multitude of internal (soil-related) and external factors are at play and influence soil physical properties like bulk density, which is a widely used indicator of compaction.

Undisturbed soil samples were collected on a North German farm from six individual fields, all located within the same area of ~1.2 km². All fields display loess-derived soils, similar in soil type, texture and management (same farmer).  Since 1995, samples were extracted from ~20 and ~40 cm (~35 cm as of 2016) representing top- and subsoil.

For one of the fields, there are approximately 15 observations within a timeframe of roughly 20 years. For the topsoil, a trend of decreasing bulk density was observed, whereas the subsoil showed a trend for the opposite behaviour, with bulk density increasing over time. Soil compaction and thus increased bulk densities are expectable on agricultural fields managed with heavy machinery. However, for the topsoil, regular tillage accompanied by soil loosening might have caused the decrease in bulk density over time. From a soil structural and stability point of view, this might nonetheless not be beneficial.