Weed Seedbank Dynamics and Species Turnover as Influenced by Long-Term Herbicide Programs in Wheat Fields

Abstract

Weed seedbank dynamics and species turnover were evaluated in wheat (Triticum aestivum L.) fields under long-term herbicide-based management programs to assess their impact on weed community persistence and compositional shifts. Soil seedbank samples collected from different depths were analyzed for density, species composition, and viability, while field emergence patterns were monitored across cropping seasons. Results indicated a significant reduction in total seedbank density under continuous herbicide use; however, this was accompanied by a shift in species composition toward herbicide-tolerant and resistant weed biotypes. Annual broadleaf weeds declined in dominance, while certain grass weeds and opportunistic species increased in relative abundance, indicating directional species turnover driven by selection pressure. Vertical distribution analysis revealed a concentration of viable seeds in upper soil layers due to reduced soil disturbance in conservation-based herbicide programs. Temporal emergence patterns showed reduced but more synchronized weed flushes, often occurring during early crop establishment stages. Repeated herbicide applications resulted in simplified weed communities with lower species richness but higher dominance indices, reflecting reduced ecological diversity. Evidence of persistent seedbank fractions suggested incomplete depletion despite long-term chemical control, highlighting the role of dormancy and seed longevity in sustaining weed populations. The study demonstrates that while herbicide programs effectively reduce overall weed pressure, they also drive shifts in community structure and selection for tolerant species. These findings emphasize the need for integrated weed management strategies combining chemical, cultural, and mechanical approaches to prevent herbicide-driven species turnover and maintain sustainable weed control in wheat-based agroecosystems.