Effect of nitrogen management on wild and domestic genotypes of cardoon for agro-energy purpose

In the last decade, among the species proposed for the production of renewable energy, a growing interest has been directed toward the cardoon, due to the high biomass that can be obtained even in marginal environments without irrigation and with low input nitrogen. Studies carried out in Italy and in other Mediterranean countries demonstrated the high variability of the cardoon response in terms of biomass and seed production performance, in relation to the genotype and the cultivation environment. Given the need to use marginal land for bioenergy crops to avoid competition with food crops, a trial in a marginal area of the Sub-Appennino Dauno (southern Italy) was carried out, to identify genotypes that are best suited to this environment and alternative strategies to fulfil crop nitrogen requirements. The trial was carried out during 2012-2013 on a two-year-old crop in rainfed conditions, to compare three nitrogen management strategies and four genotypes: i) unfertilized control (N0), one nitrogen level (50 kg ha-1, N1), and unfertilized with the intercropping with subterranean clover (Trifolium brachycalycinum Katzn. and Morley) in order to exploit the nitrogen-fixing capacity (TB); ii) a wild cardoon (Cynara cardunculus L. var. sylvestris Lamk) landrace (RCT10) and 3 lines (CDL07, CDL09, CDL10) of domestic cardoon (C. cardunculus L. var. altilis DC.). A split plot with three replications experimental design was adopted. Drought during the growing season played a crucial role in the experiment. 'CDL07' performed better in terms of above ground dry biomass (AGDB) with 9.0 Mg ha-1 with respect to the other genotypes (5.4 Mg ha-1, on average). On the contrary, grain yield was the highest in 'RCT10' (2.0 Mg ha-1) and the lowest in 'CDL10' (0.6 Mg ha-1). N1 performed better both for AGDB yield (10.7 Mg ha-1) and seed yield (2.2 Mg ha-1). Conversely, TB provided very low yield (1.4 and 0.2 Mg ha-1, AGDB and seed yield, respectively) because of adverse effect of competition of subterranean clover for water. Results confirmed high variability in biomass and seed yield of different genotypes and the limiting role of the water availability in environments such as those Mediterranean. The intercropping with subterranean clover as eco-sustainable strategy for nitrogen supply is not suitable in dry areas.