A closer look at the plough pan: what is it exactly? Is ploughing the only cause? And what about the no-tillage pan? [Practice Abstract]
Ploughing is often criticized for its impact on soils, particularly for the risk of forming a ‘plough pan’, a compacted, repeatedly smoothed layer typically found at a depth of 25–30 cm.
However, this risk is not limited to ploughing alone, and has been observed on several
occasions during the ABC group’s (Belgian agroecological initiative) field trials: compacted or smoothed layers can also be found at various depths in non-ploughed soils.
The origin of these compacted or impermeable zones is often linked to:
1. Choice of tillage implements (use of wings, rotary tools, or deep tillage performed
repeatedly at a constant depth)
2. Timing and soil conditions (particularly when operations are carried out on moist or wet soils)
3. Soil type, as clay-rich soils are generally more prone to smearing and compaction, while high organic matter content tends to reduce these effects
The presence of compacted or smeared layers affects plant development. Soil water dynamics are partially or completely altered (water accumulation above the compacted or smeared horizon), and vertical root growth is restricted, forcing plants to explore only the upper soil layer. This results in increased susceptibility to drought stress, limited access to nutrients, and deformation of taproots in root crops.
In some cases of very shallow tillage – as sought in conservation agriculture systems – this smearing can occur just a few cm below the surface and hinder crop establishment. This was observed in one of the ABC group’s trials: during a pea sowing following shallow rotary tillage, the peas rooted only within the top 4 cm of soil and did not survive the dry period that followed establishment.
Keywords: Arable, Low input farming, Reduced tillage, Transdisciplinary research
Country: Belgium
