A new agro-industry compost as medium for growing baby-leaf lettuce in floating systems

© 2018 International Society for Horticultural Science. All Rights Reserved. Many diseases, including damping off, which is caused by fungi such as Pythium spp., can affect the production of small leafy vegetables (baby leaf) in floating systems. Agro-industry composts could be used as an alternative to peat, the traditional substrate in floating systems. More particularly, the use of composts with suppressive effects may help to control these pathogens and reduce the use of chemicals, contributing to a more sustainable production system. The objective of this work was to investigate the suppressive capacity of agroindustry compost (C14) compared with peat in the pathosystem Pythium irregulare-lettuce grown in two types of polystyrene trays (cell plug and styrofloat). The commercial red lettuce cultivar `Antoria¿ was cultivated in an unheated greenhouse covered with thermal polyethylene, while each type of tray (cell plug and styrofloat) contained a different volume of substrate, 31.5 and 32.4 cm3, respectively. When plants were harvested 35 d after sowing, no significant differences were observed in plant growth between peat and compost under non-inoculated conditions. Under inoculated conditions, compost increased plant aerial growth, particularly fresh weight, leaf area and plant height in both types of trays. Plants grown in cell-plug trays were more affected by the pathogen than those grown in styrofloat trays, because of the larger amount of substrate in the other type of tray. The nitrate content was significantly reduced in plants grown in styrofloat trays filled with C14 under inoculated conditions. These results suggest that the compost helped to prevent pathogen infection and promoted lettuce growth in a floating system.