Stale seedbed preparation for sustainable weed seed bank management in organic cropping systems

Stale seedbed preparation is a neglected agronomic strategy used to decrease weed seed banks. The experiments aimed to verify the quantity-qualitative seed bank reduction after different soil tillage typologies: rotary culti- vator, rotary harrowing and spike tooth harrowing (tillage depth in each case uniformed to about 15 cm). Tillage was carried out during the spring-summer period, with five tillage sequences spaced about 30-40 days. The weed seedbank analysis (10-30 cm) showed that beyond a 10 cm soil depth, the buried seeds were unaffected irre- spective of the kind of soil tillage since no seed depletion was observed. In contrast, weed seed bank was heavily depleted in the shallowest soil layer (0-10 cm) due to the germination trigger induced by the soil aeration and by the consequent increase of oxygen availability after tillage. This seed bank reduction, was proportional to the degree of soil crumbling induced by the different tillage methods and it was higher in the case of the smaller soil clods size. Each weed species showed the highest emergence dynamics when soil tillage was carried out during the periods most suitable to meet the respective thermal requirements. Indeed the earliest soil tillage in April triggered germination and emergence of microthermal weeds, while those carried out in May and June triggered the emergence dynamics of weeds characterized by higher thermal requirements. The emergence rate, after the stale seedbed preparation, showed high values overall in the case of deep soil crumbling. In addition the extent of soil crumbling was positively related to the biodiversity of the emerged weed communities. The weed species that were the least sensitive to stale seedbed preparation were those characterized by small seeds and conse- quently those species would be more difficult to reduce through stale seedbed preparation.