Pappi of cardoon (Cynara cardunculus L.): The use of wetting during the harvesting aimed at recovering for the biorefinery

The pappi of cardoon (Cynara cardunculus L.) flowers form a crown of plumose filaments which aid the wind dispersal of the seeds connected to them. The high cellulose content of this fraction can be a valuable raw material for fiber or pulp products. During threshing, the pappi are discharged together with the other biomass, but as they are liable to blow away, they fly away during discharging and from the windrow. As the biomass is baled within 3-4 h after harvesting, the objective of the study was to test a wetting system applied to a combine and the effect of some adjuvant in limiting pappi dispersal caused by the wind. The system included a water tank (1 m3), an electric pump, a flow regulator, and three pairs of nozzles to spray the solution onto the threshed material discharged from the rear of the combine. Four adjuvants in two concentrations were used to extend the retention time. The percentage of retention was evaluated on an artificial surface (plastic panels) and on the crop residues left in the windrows behind the combine. The retention time analysis was made one (T1) and four hours (T4) after harvesting. On the plastic panels, the pappi treated just with water showed a low level of sticking because the covered area had decreased by 92.9% at T1 compared to the time of harvesting (T0). The amount of pappi remaining on the windrow at T4 proved the efficacy of one of the adjuvants (AL-02) in limiting dispersal (52.8 kg ha−1), bearing in mind that without wetting (untreated), the amount remaining was seven times less (7.51 kg ha−1). Therefore, wetting appears a feasible option, compared to no treatment, to keep a certain amount of pappi on the soil. In order to reduce the dispersal and to increase the recovery of the pappi, the combine (equipped with the wetting system) should be rapidly followed by a baler, before the wetting effect disappears.