SEEDBANK PERSISTENCE AND SEEDLING EMERGENCE OF 7 WEED SPECIES IN AUTUMN-SOWN CROPS FOLLOWING A SINGLE YEARS SEEDING

Seedbanks and seedling emergence, resulting from seeds shed in wheat crops and ploughed in, were monitored in two experiments for 3-4 years in successive autumn sown crops, in which herbicides were used to prevent re-seeding. Populations of Galium aparine, Papaver rhoeas, Lamium purpureum, Myosotis arvensis, Veronica persica, Viola arvensis and Veronica hederifolia were studied in separate plots. The numbers of viable seeds in the soil declined exponentially; G. aparine and V. hederifolia declined most, and P. rhoeas and V. arvensis least rapidly. Total weeds (all species) over the 3-4 years, (obtained by adding successive numbers of seedlings recorded in each autumn or winter), represented 3-4% of the first year seedbank for the combined species. Few seedlings emerged in the first year after seeding due to effective burial by the initial ploughing. The species showing the greatest emergence in the first year, relative to seedbank size, were G. aparine and V. hederifolia. Other, smaller seeded, species produced their main seedling flushes in the second and third years after seeding. It is concluded that poor weed control in one year is likely to result in large weed infestations for up to four years and probably longer for some species.