Spatio-temporal modelling of wheel load carrying capacity (WLCC) to mitigate soil degradation at regional scale

Soil compaction caused by intensive field traffic is one of the main threats to agricultural soils. Soil compaction occurs when the applied soil stress is higher than the soil strength. Both, soil strength and stress, are highly variable in space and time. While soil strength mainly depends on environmental conditions (e.g. weather, soil type, crop type), soil stress results from the used machinery. One key parameter for the applied soil stress is the wheel load which results from the machinery setup. The wheel load carrying capacity (WLCC) approach takes this into account and specifies the maximum wheel load until soil stress does not exceed the soil strength.

The objective of this study is to model and analyse the dynamic variation of WLCC at regional scale for a 5-year period (2016-2020). We selected a study area (~2000 km²) with highly mechanized agriculture in Northern Germany where the main crops are cereals, maize and sugar beets. Sentinel-2 images were used to derive the crops for the 5-year period. We calculated the WLCC using an advanced version of the SaSCiA-model (Spatially explicit Soil Compaction risk Assessment) for each day of the 5 years.

The results show a high temporal dynamic characteristic of the WLCC during the crop rotation at regional scale. The relatively dry years 2016 and 2018 increased the maximum allowable wheel load, especially during harvesting of maize and sugar beets in autumn. In all 5 years, spring was the time with the lowest WLCC. At this time, however, high soil stresses occur due to the application of slurry and digestates, which is associated with high soil compaction risk. The spatial variation of WLCC depends on the one hand on soil properties such as soil texture. On the other hand, the used crop has a high effect on the WLCC due to different soil water utilization.

Based on the spatio-temporal analysis of WLCC at regional scale, an assessment can be performed to reduce the soil compaction risk either by increasing the soil strength or by decreasing the soil stress. We show exemplarily how the adjustment of tire inflation pressure affects the WLCC. Finally, this study may contribute to understand WLCC dynamics in crop rotations at regional scale and may help to mitigate further soil compaction.