Yield response of sunflower to irrigation and fertilization under semi-arid conditions

Until recently, irrigation of traditionally rainfed crops such as sunflower in the semi-arid regions of southern Spain was limited to supplementary irrigation given the very limited water supply. This was primarily due to a poor understanding of the irrigation management of this crop. However, thanks to irrigation and N-fertilization research carried out between 2012 and 2014 in southern Spain, functions of sunflower yield response to irrigation and N-fertilization have been determined, thus identifying the optimal irrigation and fertilization scheduling to optimize both yield and water productivity. The study found that irrigation volumes of around 60-80% of the optimum and N-fertilization doses of around 100 and 150 units of N, depending on if stressed or non-stressed conditions were found, provided the maximum yield. Significant interactions between irrigation and N-fertilization supply were demonstrated, as N crop status also depended on the water stress conditions, with N deficiencies detected when water supply was limited, demonstrating the utility of using the nutritional crop status for combined fertilization and irrigation recommendations. Likewise, sowing date affected the yield response of sunflower to water supply, with early sowing dates resulting in higher yields (an increase of around 11.4% compared to traditional sowing dates) due to the mitigation of heat and water stress during the flowering period. Irrigation practices for sunflower under semi-arid conditions have demonstrated significant benefits, especially with limited rainfall supply. However these practices must be combined with N-fertilization practices in order to maximize input efficiency. Optimized irrigation and fertilization practices for sunflower must therefore be encouraged as a way to achieve a similar performance as traditional irrigated crops. (C) 2016 Elsevier B.V. All rights reserved.