Heavy machinery jeopardises the promises of conservation agriculture

“Conservation agriculture” is described by the FAO as a farming system that promotes minimum soil disturbance (i.e. no tillage), maintenance of a permanent soil cover, and diversification of crop species. It enhances biodiversity and natural biological processes above and below the ground surface, which contribute to increased water and nutrient use efficiency and to improved and sustained crop production.

An important component of this type of agriculture is no-till farming, which means that a crop is sown directly into the residues from the previous crop without ploughing or other tillage, something that is currently applied to approximately 15 percent of the world's arable land. No-till farming offers economic and environmental advantages compared to conventional tillage, but global studies have shown that the method can lead to persistent yield losses for some crops.

A new study now demonstrates that the promise of beneficial and sustainable soil management may be undermined by a gradual and invisible threat of subsoil compaction. The threat stems from the episodic passage of heavy machinery such as harvesters.

“Our analyses show that almost 40 percent of global no-till lands are under high subsoil compaction risk, particularly in the USA, Brazil and Canada”, says Thomas Keller, professor of soil mechanics and soil management at the Swedish University of Agricultural Sciences. “No-till farming is primarily applied in regions with large fields and farms, which often involves large and heavy machinery. The most sensitive areas are those where the soil is often moist, which increases the risk of compaction, or where the soil naturally recovers slowly after compaction damage”.

In their article in the journal PNAS, Thomas Keller and his colleagues from the United States and Austria describe how subsoil compaction gradually increases when compaction events occur more frequently than the natural rates of soil structure recovery. The researchers also write that there are data that suggest that subsoil compaction is a factor that could explain the yield losses seen in some crops (e.g. corn) in systems that use no-till.

The researchers conclude that avoiding soil compaction must become a central component of conservation agriculture and other systems that focus on soil health. They also highlight that progress made with autonomous light-weight vehicles offer a potential to avoid excessive loads on the soil.

Conservation agriculture is not widespread in Sweden, but heavy machinery is still a problem

Soil compaction is a problem regardless of whether the soil is tilled or not prior to seeding. In Sweden, the risk of soil compaction is relatively high, because heavy machinery is used and Sweden has a comparatively humid climate.

– With this study, we want to draw attention to a problem that is invisible and that leads to a gradual deterioration of arable land. This affects not only the yield but also the soil's water-regulating function. Soil compaction can both reduce the amount of plant-available water during droughts and increase the risk of surface runoff and flooding during heavy rainfall, says Thomas Keller.

Contact person

Thomas Keller, Professor
Department of soil and environment
Swedish University of Agricultural Sciences, Uppsala
thomas.keller@slu.se, +46 76 8363117, +46 18 671692

The scientific article

T. Keller, S. Bickel, & D. Or. 2025. The invisible subsoil compaction risk under no-till farming, Proc. Natl. Acad. Sci. USA. 122 (46) e2515473122, https://doi.org/10.1073/pnas.2515473122.

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Harvesting winter wheat at SLU. Photo: Jenny Svennås-Gillner