Effects of band steaming on weed control, weed community diversity and composition and yield in organic carrot at three Mediterranean sites

Band steaming is a non-chemical weed control method of increasing interest for highly remunerative, low competitive crops. This study aimed to test the field ap- plication of a new prototype of band-steaming machine in three organic fields under contrasting Mediterranean environmental conditions. Trials were conducted in car- rot under real-field conditions to investigate the effects of three steaming doses and one control (no steaming) on weed vegetation and crop yield. Soil temperature at steaming application, weed density at species level during carrot crop growth, and weed and carrot biomass at harvest were sampled at each site. Band steaming sig- nificantly affected total weed density: when comparing the untreated control with the highest steam dose, weed density reduction ranged from 62% (−492 plants m−2) at site II to 94% (−146 plants m−2) at site III. Generally, diversity of weed communities decreased with increasing steaming dose, indicating a progressive species filtering effect: Fumaria officinalis L. and Sonchus oleraceus L. were filtered by steaming appli- cation at site I, while Polygonum lapathifolium L. and Portulaca oleracea L. were filtered at sites II and III. Weed community composition was affected by steaming dose at two sites out of three. Small seeded species (seed mass <1.5 mg) were less tolerant of steaming than species with large seeds. Through reduction in weed density, steam application gave carrot a competitive advantage, increasing fresh yield from 47% at site III (+3,646 g m-2) to 92% at site II (+1,866 g m-2), compared with yields at non- steamed plots.