How much area of a field is compacted? An approach for estimate the headland zones at regional scale

Soil compaction is a severe soil degradation process that affects important soil functions. Understanding how much area is already compacted is important for grasping the scale of this issue.

In intensive, highly mechanised agriculture, a field is typically divided into a core field and a headland according to traffic intensity. However, studies that provide data on the area affected by compaction often only analyse the core field, ignoring the headlands. However, the headlands exhibit the highest intensity of field traffic (wheel load and wheel pass frequency), which is associated with a high risk of soil compaction.

This study focuses on deriving compacted headlands area using field geometry and working width at regional scale. Germany, a nation of modern agriculture, served as the study area. Firstly, field boundaries and working widths (tramlines) were digitised across Germany in QGIS. To take regional variations into account, 11 soil regions were selected, with two 3x3 km squares in each region serving as the digitisation boundary. In a second step, Python scripts were coded to calculate the position and size of the headlands as well as the different traffic intensity zones within the headland. According to Ward et al. 2020, headlands can be differentiated into three zones: (i) the turning zone, (ii) the transition zone, and (iii) the field edge. The turning zone exhibits the highest compaction risk.

The results show that, on average, 19.9% of a field is occupied by the headland. Depending on the size and geometry of the field, this area share can vary significantly, ranging from 3.5% to 100%. On average, the turning zone accounts for 9.8% of the total field area. The transition zone and the field edge account for 4.7% and 5.5%, respectively.

This study reveals that headlands occupy a significant proportion of agricultural land in Germany. Due to high traffic intensity, headlands are prone to soil compaction. Therefore, the headland area should be considered in the spatial assessment of soil compaction. As traffic intensity varies within the headland, the 'turning zone' is a realistic area in which severe soil compaction can be assumed. This part of the field should therefore be included in the spatial estimation of areas already affected by compaction, thereby increasing the percentage of compacted soils assumed in previous studies that excluded headlands.