Yield and quality of lettuce grown in floating system using different sowing density and plant spatial arrangements

Baby leaf vegetables (rocket, lamb's lettuce, headless lettuce, endive, escarole, water cress) are mostly requested for mixed salads. Small-size leafy vegetables can be profitably cultivated in a floating system to obtain fresh market products or ready-to-use salads that are arousing more and more interest in consumers. Among hydroponic methods, the floating system is the easiest and cheapest way to produce baby leaf vegetables when soil cultivation is not feasible any more. When recirculation of nutrient solution (NS) is used, this system shows high water and fertiliser efficiency and low environmental impact. In the present study two cultivars of lettuce (Lactuca sativa L. var. longifolia) were used: 'Ronda' and 'Amadeus'. The growing cycle was carried out in the greenhouse in March-April 2000. The growing set-up consisted of benches containing the NS and the floating boards. Two plant densities were adopted: 316 and 620 plant/m(2). The latter was obtained using two different plant spatial arrangements. After 40 days of growth, fresh leaf yield was on average near to 6 kg/m(2). Leaf dry matter content was on average 5 g/100 g of fresh weight (f.w.) without any differences between treatments. Contents of inorganic anions and cations were determined both in leaves and roots. Nitrate (NO3) content was generally lower than 2,000 mg/kg of f.w. and was not influenced by the treatments. Water consumption was near to 80 L/m(2) regardless of plant density, while WUE resulted on average 3.5 g of leaf dry matter produced per litre of water consumed.