Interplay of irrigation strategies and sowing dates on sunflower yield in semi-arid Mediterranean areas

Sunflower (Helianthus annuus L.) is one of the most cultivated oil crops in the world. Given its high dependence on water availability, its cultivation in the Mediterranean area is severely threatened by climate change: very hot and dry weather conditions currently occurring in the Mediterranean area have a negative impact on sunflower yield. Many studies have pointed to earlier sowing dates as a promising strategy to prevent summer drought stress causing sunflower yield losses, but the literature on winter sowing dates is scarce. The aim of this research was to quantify the interplay between sowing date (winter time included) and water regime to sustain sunflower cultivation in the Mediterranean area. A field experiment and a modeling study were carried out to evaluate the effects of different sowing dates (00SD: ‘conventional sowing date’ in March/April and ‘earlier sowing dates’ in December-January-February, depending on years) under two different water regimes (irrigated vs. rainfed) on quantitative traits of high oleic cultivars of sunflower. Field experiments revealed that sowing in late February - mid March was the most effective strategy in terms of achene productivity. Achene production by sunflower was also simulated using EPIC under a baseline climatic scenario and for 4 hypothetical sowing dates (D1: 10th January, D2: 10th February, D3: 10th March, D4: 10th April) and different irrigation strategies. The most effective sowing date was D3 under rainfed conditions, confirming the results of the field study. Irrigation from 20 days before anthesis up to flowering significantly improved achene yield for the early sowing dates (D1 and D2), which almost reached their respective yield potentials. This confirms that an earlier sowing date could be a viable management strategy in Mediterranean areas with little water availability.