Effects of tillage and cover crops on the germinable weed seedbank in organic vegetable production

Organic crop production practices that limit replenishment of the weed seedbank can benefit vegetable producers by reducing future weed pressure. Cover cropping combined with conservation tillage can suppress weeds; however, reduced soil disturbance may also influence weed seedbank dynamics. Therefore, a four-year study was conducted in a field transitioning to organic certification to evaluate how two conservation tillage systems (no-tillage, NT; strip-tillage, ST) and two conventional tillage systems (bare-ground, BG; black polyethylene mulch, BP), all used in combination with winter cover crops, affected the density and composition of the germinable weed seedbank. The study followed an eggplant (2012 and 2014) and sweet corn (2013 and 2015) rotation. Tillage method significantly affected weed seed density, plant class (broadleaf vs. grass/sedge) densities, and species-level composition. Germinable seedbank densities were highest in NT and ST and consistently lowest in BP, with BG intermediate. Broadleaf densities were greater in conservation tillage systems, whereas grasses and sedges were more abundant under conventional tillage. Goosegrass, carpetweed, yellow woodsorrel, and fall panicum accounted for more than 88% of the germinable seedbank across all years, and their relative abundances varied among treatments. Species richness increased over time in conservation tillage plots and was significantly greater in NT and ST by the final year of the study. The results suggest that increased soil disturbance under conventional tillage reduces germinable weed seedbank density, while conservation tillage promotes higher richness and shifts in the relative abundance of key weed species.