The invisible subsoil compaction risk under no-till farming

Thomas Keller, Samuel Bickel, and Dani Or

PNAS; November 10, 2025; 122 (46) e2515473122; https://doi.org/10.1073/pnas.2515473122

Significance

No-till (NT), a key component of conservation agriculture, is presently practiced over 15% of global arable land. NT offers economic and ecological advantages over conventional tillage; however, it may result in persistent yield losses for certain crops. Here, we highlight an invisible threat to sustainable soil management under NT due to subsoil compaction. We describe a subsoil compaction risk driven by compaction events due to heavy farm vehicles occurring at intervals shorter than soil structure recovery times. Our analyses show that nearly 40% of global NT lands face a high subsoil compaction risk. Mitigating this risk through scaling of farm machinery to soil mechanical limits is essential to sustaining and realizing the full ecological and agronomic benefits of conservation agriculture.

Abstract

No-till (NT) is a key component of conservation agriculture aiming at producing crops with minimal soil disturbance. This land management practice offers numerous economic and ecological advantages over conventional tillage as evidenced by its rapid expansion since the 1960s, now practiced on 15% of the global arable land. Nevertheless, various crops exhibit persistent yield losses even decades after transition to NT. Here, we demonstrate that the promise of beneficial and sustainable soil management may be undermined by a gradual and invisible threat of subsoil compaction. We report on a risk of subsoil compaction stemming from the episodic passage of heavy machinery (e.g., harvesters). The threat is of dynamic and asymmetric nature whenever compaction events occur more frequently than the natural rates of soil structure recovery, resulting in a gradual increase in soil degradation. Our analyses show that nearly 40% of global NT lands (0.8 million km²) are under high subsoil compaction risk (primarily in heavily mechanized Canada, United States of America, and Brazil). Awareness and mitigation of subsoil compaction by scaling field operations to soil mechanical limits and adoption of smaller robotic vehicles will contribute to a sustainable and holistic conservation agriculture.

See: https://www.pnas.org/doi/10.1073/pnas.2515473122

Figure 1: Loads of modern farm machinery induce high stress levels into deep soil layers with associated enhanced risks of soil compaction in the root zone. (A) Simulated vertical stress under the tire of a large tractor (Left) and a modern combine harvester (Right). The 50 kPa isobar indicates a critical stress level to prevent soil deformation under moist conditions (22). Root system of winter wheat (Triticum L.) at harvest is shown for comparison (redrawn from ref. 23). (B) Illustrative examples of measured depth profiles of cone penetration resistance, indicative for root elongation rates (24), in NT and plowed soils from field experiments in the United States of America [Left; (25)] and from farmers’ fields in Sweden (Right; see Materials and Methods). Symbols show means per depth and horizontal bars are SE.