The Emerging Flora Does Not Reflect the Soil Reinfestation Potential: Integrating Phytosociology and the Seed Bank in Cropping Systems

The integrated assessment of the emerging weed community and the soil seed bank is essential for understanding the persistence and reinfestation potential of weeds in agricultural systems. This study aimed to evaluate the phytosociological structure and the germinable seed bank under no-tillage, conventional tillage and fallow systems, associated with chemical desiccation with glyphosate and mechanical mowing at pre-sowing, over four agricultural seasons (2017/2018 to 2020/2021) in Erechim, RS, Brazil. Phytosociology was assessed using the random quadrat method, and the seed bank was evaluated through seedling emergence from soil samples collected from the 0–10 and 10–20 cm layers. A total of 23,913 individuals were recorded in the phytosociological survey, with predominance of Lolium multiflorum (61.9%) and Sida rhombifolia (21.5%). In the seed bank, 5812 seedlings emerged, of which 56.7% occurred in the 0–10 cm layer. Desiccation reduced the emergence of L. multiflorum by 34.7% in the surface layer compared with mowing. The similarity index between phytosociology and the seed bank was 0.35, showing that the community observed in the field does not fully represent the reinfestation potential stored in the soil.