Legume cover crop management and organic amendments application: Effects on organic zucchini performance and weed competition

• Climatic conditions influenced vetch management and fertilizer effects.
• Roller crimped vetch showed a decrease in weed biomass in comparison with green manure.
• Using roller crimper under cooler conditions reduced zucchini competitive ability.
• The combined use of anaerobic digestate and vetch ensured a proper crop N nutrition.

In organic farming it is crucial to reach the best compromise between yield and sustainability of agronomical strategies. To this end, this two-year study evaluated the effects of legume cover crop management (no cover; vetch grown as green manure; roller crimped vetch) and organic amendments (no fertilizer; compost; animal manure; digestate fertilizer) application on organic transplanted zucchini and weed biomass productions, N dynamics, N balance and competitive interactions. In the first year, the vetch incorporated as green manure treatment showed the highest zucchini yield and weed biomass, as well as the highest crop N uptake reduction in presence of weeds. The roller crimped cover crop showed a decrease in weed biomass by more than 65% compared to green manure, and higher productivity than the no cover treatment. Animal manure and digestate fertilizers showed the highest yield, soil mineral N contents and crop N uptake, even if no variation in competitive ability was recorded. Conversely, the second year showed the potential limits of the roller crimping technique under cooler conditions, implying a reduction in zucchini yield performances and competitive ability. Among the experimental fertilizers, the digestate showed comparable results than commercial fertilizer for yield, but significantly higher than N0 (by 31%) and, when combined to vetch management, also in terms of N balance. This study illustrates the effectiveness of combination of different agronomical strategies to obtain adequate yield and weed impact reduction.