Sunflower response to tillage and soil residual nitrogen in a wheat-sunflower rotation under rainfed Mediterranean conditions

A field study was carried out to determine the effects of tillage systems on sunflower yield over 9 years, and the effects of tillage systems and residual N on sunflower yield and yield components over 4 years, in a wheat-sunflower rotation under rainfed Mediterranean conditions. Tillage treatments included no tillage (NT) and conventional tillage (CT). Nitrogen fertiliser rates were 0, 50, 100, and 150 kg N/ha, applied only to wheat. A split-plot design with 4 replications was used. The weather had a marked influence on sunflower biomass and seed yield. Rainfall over October-May was directly related to seed yield. In contrast, seed oil content was inversely related to mean temperature during the flowering season (June). Sunflower yield displayed no significant reponse to residual N derived from the fertiliser N applied to the preceding wheat crop. The tillage system did not exert a consistent influence on sunflower yield; thus, continuous no-tillage may represent an economically and environmentally viable alternative to conventional tillage for sunflower production under rainfed Mediterranean conditions.