Seedbank reduction after different stale seedbed techniques in organic agricultural systems

Little information is available on the stale seedbed effect on seedbank reduction. This weed management is of increasing interest overall in organic agricultural systems where is no possible to use herbicides. The emergence dynamics and related seedbank reduction were evaluated following adoption of two different stale seedbed techniques (with or without irrigation), made during the spring-summer season in 2001 in organic agricultural systems. As expected, emergence was strongly stimulated by irrigation and soil tillage.When the no-tillage technique was adopted (control), the absence of soil disturbance resulted in extremely low emergence levels, associated with a reduction in the number of the relative species. Consequently, analysis of the residual seedbank of the shallow layer (0- 10 cm) of the control (no-till) showed only small reduction (about 1%). In contrast, the tillage-only experiment led to a reduction of about 5% in the same soil layer. However only with the irrigation, a drastic reduction in the amount of seeds (roughly half) was achieved. In particular, grasses showed the highest seedbank reduction rates. Despite this different effectiveness of the stale seedbed techniques, the soil layers at greater depths (10-20 and 20- 30 cm) were found to be completely unaffected, independently of the agronomic practices carried out. Qualitative analysis of exhumed seeds demonstrated that greatest “forcing of germination” (tillage + irrigation) resulted in a percentage increase of “deep-dormant” seeds as a consequence “non-dormant” seeds decrease. Although stale seedbed appeared to be only partially effective, we believe that if this agrotechnique is properly carried out and repeated at the appropriate times, it promises to be successful in agricultural systems where herbicides are excluded.