Productivity and phytotoxicity of six sunflower hybrids and their residues effects on rotated lentil and ivy-leaved speedwell

Sunflower (Helianthus annuus L.) is an important energy plant, but the yields of crops grown in rotation with sunflower may be reduced due to its residues phytotoxicity. A 2-years field study was conducted to determine the productivity and extract phytotoxicity of six sunflower hybrids (Arena PR, PR64E83, Opera PR, Ontil, Faborh and Falcon). The effects of their incorporated in soil residues on lentil (Lens culinaris Medik.) and on ivy-leaved speedwell (Veronica hederifolia L.) were also investigated. Sunflower hybrids differed in leaf area index, quantum yield of photosystem II and dry biomass. Among hybrids, Faborh and Falcon were the most productive regarding seed (6.1 t ha−1) and oil (2.6–2.7 t ha−1) yields. In rotation, ivy-leaved speedwell emergence and growth were not affected or were stimulated by sunflower residues, while plant number and fresh weight of weed-free lentil were reduced by 22.6% and 28%, respectively. When lentil was grown in competition with ivy-leaved speedwell, the corresponding reductions were 12.4 and 43.5%. At harvest, lentil dry biomass and seed yield were reduced by 7.3 and 13%, respectively, by sunflower residues. The corresponding reduction in ivy-leaved speedwell treatments were 29.4 and 24%. In laboratory conditions, the lower water extract concentration (1.25 g 100 mL−1) of all hybrids stimulated lentil root length, as well as speedwell growth. On the contrary, the concentrations of 2.5 and 5 g 100 mL−1 caused significant inhibition of lentil root length, as well as of ivy-speedwell germination and growth. Conclusively, the sunflower hybrids Faborh and Falcon could provide sufficient seed and oil yield for biodiesel production in irrigated Mediterranean fields. However, lentil yields in rotation cropping system with sunflower may be reduced, while weeds, such as ivy-leaved speedwell, may be enhanced.

► We investigated productivity and phytotoxicity of six sunflower hybrids.
► The sunflower residues effects on rotated lentil were also determined.
► The hybrids Faborh and Falcon achieved sufficient seed and oil yield.
► Lentil emergence and yield were reduced by sunflower residues.
► However, ivy-leaved speedwell growth was enhanced.