Traditional and soilless culture systems to produce corn salad (Valerianella olitoria L) and rocket (Eruca sativa Mill.) with low nitrate content

In the latest 20 years, Traditional Culture System (TCS) in soil has been increasingly substituted by Soilless Culture System (SCS), based on growing media. This system allows to obtain higher qualitative and quantitative standards, to standardize cultural techniques, to increase earliness, to reduce nitrate content of leafy vegetables and to reduce production costs and environmental impact. The traditional culture system (TCS) was compared to a SCS, with two plant densities (1067 and 2134 plants/m(2)), on corn salad (Valerianella olitoria L.) and rocket (Eruca sativa Mill.). TCS was simulated in polystyrene trays filled with local soil and peat (1:1 v/v), overhead irrigation and weekly fertilization. For SCS, 40-cell trays were filled with perlite and peat (1:1 v/v), floated in a nutrient solution during growing cycle. Production was significantly influenced by culture system x plant density. SCS allowed to enhance earliness: SCS produced marketable corn salad in 70 days and rocket in 72 days, while TCS would have required an extended growing period. Corn salad and rocket plants grown in SCS produced more than two-fold and four-fold in terms of fresh mass in comparison with plants grown in TCS, respectively. The plants grown in SCS with the highest plant density gave the greatest production (corn salad 1667 g m(-2); rocket 2182 g m(-2)). Leaf nitrate content was significantly influenced by the culture system. The leaves of plants grown with TCS contained less NO3- than those grown with SCS, in a ratio of 1:2.5 and 1:1.6 for corn salad and rocket, respectively. Leaf nitrate content was 333 and 449 mg kg(-1) f.w. for corn salad and rocket grown in SCS, respectively. With both culture systems the nitrate content was much lower than 2500 mg kg(1) f.w., which is the maximum content allowed by the EU regulation for lettuce.