Comparison of milk thistle (Silybum marianum) and cardoon (Cynara cardunculus) productivity for energy biomass under weedy and weed-free conditions

Abstract

• Milk thistle and cardoon achieved satisfactory biomass yields without irrigation. • Both crops expressed high competition and allelopathy against weeds. • Weeds competition slightly reduced productivity of both crops. • Cardoon achieved greater potential energy yield than milk thistle. Milk thistle ( Silybum marianum [L.] Gaertn.) and cardoon ( Cynara cardunculus L.) are energy plants. However, no studies have been conducted to investigate which of these crops could provide sufficient biomass under reduced inputs (regarding irrigation, fertilization and weed management), although this knowledge is essential for the farmers for decision-making. A 3-year field study was conducted in central Greece to compare the productivity of milk thistle (native ecotype) with that of cardoon (var. C12) under weedy and weed-free conditions, without fertilization and irrigation. During the 3 years of cultivation, cardoon and milk thistle produced a total of 24.56 t ha −1 and 20.89 t ha −1 dry biomass, respectively, in weed-free treatments. Weed competition slightly reduced the productivity of both crops. Therefore, the corresponding biomass yields in weedy treatments were 19.70 and 15.49 t ha −1 . The gross calorific value of milk thistle and cardoon biomass ranged from 15.5 to 16.1 MJ kg -1 and 16.5 to 17.3 MJ kg −1 , respectively. The average across-year potential energy yield in weed-free treatments was 111,870 MJ ha -1 for the milk thistle and 135,330 MJ ha -1 for the cardoon. The corresponding potential energy yields in weedy treatments were 80,130 MJ ha -1 and 113,550 MJ ha −1 . Conclusively, milk thistle and cardoon could provide satisfactory dry biomass for energy use in semi-arid Mediterranean fields without irrigation or weed control inputs (assisted by their high allelopathic potential). Additionally, the cardoon outperformed the milk thistle in productivity.