Weed seedbank and vegetation dynamics in summer crops under two contrasting tillage regimes

Knowledge of the weed seedbank composition, dynamics and relationships with the emergent weed community, is necessary to improve weed management practices. Field research was made over three years in a maize ( Zea mays L.)-soybean ( Glycine max (L.) Merr.) crop rotation under two contrasting tillage regimes [conventional (CT) and no-till (NT)] to evaluate (i) changes in the weed seedbank and in the emerged community and (ii) to determine if the soil seedbank composition has any predictive value for the composition of the emergent weed community. The experiment was a randomised complete block design. Each year, after crop planting, samples of the seedbank were taken, then the seeds were extracted by washing soil samples through a sieve. Weed emergence was recorded during the first month after planting. Data were analysed with Principal Components Analysis and diversity was estimated using the Shannon index. Although the most abundant species found in the seedbank were always present in the above-ground community, percentage recruitment varied markedly between tillage regimes and years. The degree of soil disturbance, timing of tillage practices, crop rotation and planting date act as filters which allow or prevent the germination and emergence of weeds. The results indicated that knowledge of soil seedbank composition alone has relatively little predictive value for the composition of the emergent weed community.