Tillage and cover crop effects on weed management and community changes in organic tomato cropping system

The adoption of no-till practices in organic vegetable production has been challenged by an ineffective cover crop management and absence of season-long weed control. The objectives of our research were to determine the effects of tillage (no-till vs conventional tillage), winter soil cover (bare soil vs cover crop) and weed control approaches on weed abundance, season-long suppression, diversity and community composition in organic tomato cropping system. The trial, implemented as a split-split plot design, was conducted during 2015-2016 season under Mediterranean conditions (Pisa, Italy). The results showed the success of the combination of roller- crimper and flaming in inhibiting the regrowth of the cover crop (Trifolium squarrosum L.) and preparing a dead mulch in no-till plots (NT) suitable for direct transplanting of tomato. However, weeds were able to regrow shortly after transplanting and no decrease in weed abundance, as percent weed cover, by the dead mulch was registered further in the season, although the clover controlled initially 53% of weed abundance. Among the weed species present, the dead mulch enhanced selectively the emergence of Artemisia vulgaris L. and Daucus carota L. When used as green manure in conventionally tilled plots (CT), the clover had no residual effect on weeds. Compared with CT, the soil cover of weeds in NT was around 40% higher. Likewise, weed biomass at harvest time in NT was much higher than CT and the resulting competition was highly noticeable on tomato plant biomass. Regarding weed diversity, NT increased weed species richness and induced changes in the weed flora composition during the season. It was well demonstrated that no- till practices are challenging in fields with high weed seed bank and perennial weed species. The dead mulch may offer also good growth conditions for some weed species mainly in terms of nutrients availability and humidity. Effective cover crop suppression strategies are possible in organic conservation systems while good stands of high biomass at the right sowing and killing time remain crucial for a longer weed management.