Effects of crop method and harvest seasons on yield and quality of green asparagus under tunnel in southern Italy

A three-year research (2007-2009) was carried out on green asparagus under tunnel in Campania (southern Italy), with the purpose to verify both the chance to practise organic management and annual double harvest, in order to extend the eco-compatible production period and to avoid expensive imports. Comparisons among eight experimental treatments were made. Treatments were obtained by factorial combination of two crop methods (conventional and organic) and four spring and summer harvest periods of 90-day whole duration (75 days in spring plus 15 in summer; 60 days in spring plus 30 in summer; 45 days in spring plus 45 in summer; as a control, 90 days in spring), arranging a split plot design with three replicates. The conventional management caused the highest yield, as a consequence of the higher spear number per plant, while the organic management resulted in both spear calibre and mean weight increase. Organic spears showed higher level of residues and sugars but a lower content of nitrate and fiber. The treatment concerned with 75-day harvest in spring and 15 in summer proved the best double harvest combination, causing the highest comprehensive yield (11.5 t•ha-1), not different from the control harvested only in spring for 90 days. Summer spears showed higher values of optical residue, glucose, fructose, vitamin C and some mineral nutrients; instead, spring spears attained lower nitrate and average fiber content. Asparagus annual double harvest revealed interesting economically, but the profits are strictly related to the prices of summer spears, which were evidently higher in summer than in spring in the three years of research.