Mechanical degradation of soil structure during intensive tillage

Soil structure is a collection of durable aggregates formed from particles of sand, silt, and clay. It is their stability that determines soil fertility, as the arrangement of pores within and between aggregates defines water, air, and biological regimes. Intensive tillage inevitably transfers excess energy to the soil, which destroys these structures and deforms the soil matrix.

Three factors of mechanical destruction of soil aggregates

When agricultural machinery passes over the field, the soil is subjected to critical stress. Structural destruction occurs under the influence of several physical factors, which can act either individually or in combination:

• Mechanical abrasion and crushing: the working components of implements create zones of intense stress in the soil. When pressure or shear exceeds the strength limit of an aggregate, it crumbles into fine particles or the original mineral components.
• Impact effect: when implements are operated at high speeds, soil particles collide with immense force. The energy of these impacts overcomes the cohesive forces provided by clay and organic matter.
• Vibrational loading: prolonged vibration from machinery on wet soil causes its over-compaction. In this process, large macro-aggregates are destroyed, and the released particles settle into a denser arrangement.

Consequences of degradation: from crust to soil "asphyxiation"

When aggregates are destroyed, the balance of soil pores is sharply disrupted. Large macropores, which should ensure water infiltration and gas exchange, become clogged with fine silt and dust particles. This leads to three critical consequences for an agronomist in the field:

• Loss of water permeability (colmatage): released silty particles clog the pores between the remaining aggregates. Water stops infiltrating into deep horizons, stagnates on the surface, and triggers erosion.
• Deterioration of water-holding capacity: structureless soil loses the ability to effectively retain soil moisture against gravity, causing crops to suffer even during short-term droughts.
• Surface crust formation: raindrops wash out colloids on the surface of de-structured soil, and subsequent drying cements them into a dense crust that blocks air access and hinders emergence.

Siltation of macropores cuts off free oxygen access to the soil profile, creating zones of local hypoxia. Under these conditions, anaerobic bacteria become active, reduction processes are initiated, and products of incomplete oxidation accumulate, including organic acids toxic to roots. At the same time, the release of carbon dioxide, formed during the respiration of roots and microbiota, is slowed down. An excess of carbon dioxide combined with a deficiency of oxygen creates a stressful environment that strictly limits the yield potential of the crop.