Yield of new hemp varieties for medical purposes under semi-arid Mediterranean environment conditions

Under the effects of climate change new drought tolerant crops are imperative to introduce in irrigated agricultural areas of Mediterranean countries. In this sense, hemp (Cannabis sativa L.) represents an alternative in many semi-arid agricultural areas of Mediterranean basin because of its low water requirements and cost effectiveness when it is developed under non controlled conditions. The aim of this work was to evaluate the potential yield of five new hemp varieties (Sara, Pilar, Aida, Theresa, and Juani) cultivated under high tunnel conditions in a semi-arid Mediterranean area, and also to study the effect of plant density on active biomass production and cannabinoids biosynthesis (cannabidiol, CBD and cannabigerol, CBG) at different plant positions. The trial was conducted under plastic macro-tunnels during two seasons (2014 and 2015), from May to October. The agronomic response and the chemical profiles of the studied varieties were evaluated at the end of each season. Moreover, it was monitored the differentiation in terms of active biomass production and cannabinoids biosynthesis in different plant organ positions (at upper, medium, and lower). Additionally, during the second season, three different plant densities (PD1, 9,777; PD2, 7,333; and PD3, 5,866 plants· ha-1) were tested in order to define the the best of them for maximizing CBD and CBG productions. The findings highlighted significant differences in yield between cultivars within the CBD and CBG. Moreover, plant density was a determinant factor related to active biomass production and cannabinoids contents, PD3 representing a suitable strategy to maximize the cannabinoids production minimizing the requirements of rooted apical cuttings. These results allowed concluding that these new hemp cultivars together with the adopted agronomic practices in this experience would be very appropriate for CBD and CBG productions, being determinant to consider the plant density and the cultivar for both studied chemotypes.