The world population is forecast to rise, needing a remarkable increase in food production. As agriculture is among the most water-demanding sectors, such augmentation could negatively affect water resource. Thus actions should be taken both to improve the water efficiency of current cropping systems and to seek alternative water sources for agriculture. The improvement of water efficiency in agriculture has been long investigated. Soilless culture, especially hydroponics, is characterized by a particular attention to the water resource. A different approach is represented by alternative water sources, i.e. seawater, considered as a realistic option in agriculture, either desalinized or blended with freshwater. This study compared the water footprint (WF) of the chicory crop (Cichorium intybus L. var. silvestre) grown in the following cropping systems: a conventional soilless system using freshwater (blue-hydroponics); conventional soil cultivation (blue-pots and open field); a soilless system integrated with a 10% share of seawater (sea-hydroponics); pots irrigated with a 10% share of seawater (sea-pots).By adding seawater to irrigation, we also introduced the "seawater footprint" concept, discussing the environmental implications of the provenience of the irrigation water. Our results showed a significant reduction in WF in both blue-hydroponic and sea-hydroponic (i.e. 64% and 75%, respectively) systems compared to soil cultivation with sea-hydroponics providing the best result in terms of biomass production and water saving. By contrast, sea-pots' performances in terms of WF were significantly lower (at P <= 0.05), with an increase of WF of 104% compared to open field cultivation. As the seawater share led to very different results in the two systems, it can be speculated that seawater is not the only reason for the sea-pots' poor performance. Nevertheless, the combination of poor results in terms of both biomass production and water saving and the detrimental effects of salinity on soil make the option of soil cropping with seawater unrealistic. However a controlled use of seawater in soilless culture could reduce, without any negative environmental concern, the freshwater withdrawal dedicated to food production. Moreover, our results also suggested a higher salt tolerance in hydroponic conditions compared to soil cultivation for the tested crop.
