Effect of plant spacing on growth and yield of lettuce (Lactuca sativa L.) in a soilless production system

Abstract

Lettuce production in re-circulating hydroponic systems is done on a limited scale in South Africa with conflicting information on the recommended spacing for optimal yield and quality in such systems. The development and yield of four lettuce (Lactuca sativa L.) cultivars ‘NIZ 44–675’, ‘Nou-gatine’, ‘Tango’ and ‘Natividad’ at five different inter- and intra-row spacings namely: 10x20 (50 plants m-2), 10x25 (40 plants m-2), 15×20 (30 plants m-2), 20×20 (25 plants m-2) and 20x25 (20 plants m-2) cm were evaluated during May/June 2008. The experimental layout was a randomized complete block design and each treatment combination was replicated three times. There was a significant interaction between spacing and cultivar regarding leaf fresh and dry mass while all cultivars reacted similarly to different spacings on other yield parameters. Plant population significantly affected plant height, fresh and dry leaf mass, leaf area and leaf number m-2, with significantly higher values of all variables at the closest spacing (50 plants m-2). The results indicate that an increase in plant population results in a significant increase in yield and yield components of leafy lettuce, with all cultivars producing the highest yield at a spacing of 50 plants m- 2 during winter production. Cultivar differences observed showed that ‘NIZ 44–675’ and ‘Tango’ performed better than ‘Nougatine’ and ‘Natividad’, mostly due to higher leaf area, fresh mass, plant height and leaf number.