Soil structure depends on several factors, among which are farming system and soil tillage. The state of aggregation determines the water-air relations in soil and influences the thermal conductivity, porosity and density of soil, availability of nutrients, as well as biological processes, etc. In the field experiment with conservation tillage for onion we studied the influence of various methods of conventional tillage, no tillage, and disking as well as the biomass of the inter-harvest plants on the aggregation and structure of soil. Secale cereale and Vicia sativa cultivated as inter-crop cover plants favourably influenced the soil aggregation. It was expressed by greater share of valuable soil aggregates (ø1–5 mm) and better soil structure index in comparison with conventional tillage (CT), without plant mulches. The leaving of mulches from cover plants on the surface of the soil from fall to spring and direct sowing on onion without tillage (NT) decreased soil cloddiness index. The positive influence of plant mulches on soil structure was mainly observed after wintering and in the initial period of onion vegetation. The changes in indicators of soil aggregation under the influence of mulching and simplifications of the soil tillage system for vegetables were predominantly recorded in the soil arable layer of 0–20 cm.

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