ABSTRACT: Ascophyllum extract application can promote plant growth and root yield in carrot associated with increased root-zone soil microbial activity

Acadian Seaplants Ltd., 30 Brown Avenue, Dartmouth, Nova Scotia, Canada B3B 1X8 (e-mail: zalam@uoguelph.ca); and 2Atlantic Food and Horticulture Research Centre,
Agriculture and Agri-Food Canada, 32 Main Street, Kentville, Nova Scotia, Canada B4N 1J5.
Received 1 May 2013, accepted 9 October 2013. Published on the web 10 October 2013.

Alam, M. Z., Braun, G., Norrie, J. and Hodges, D. M. 2014. Ascophyllum extract application can promote plant growth and root yield in carrot associated with increased root-zone soil microbial activity. Can. J. Plant Sci. 94: 337􀀁348. Root growth and soil microbial activity were examined in two cultivars of carrot following treatment with Ascophyllum nodosum marine-plant extract. Field experiments were established in grower-managed fields of Maverick and Pronto carrots during 2010 and 2011. Soluble Ascophyllum extract powder (SAEP) was applied weekly, bi-weekly or tri-weekly at rates of 0 (control), 0.25, 0.50, 0.75 or 1.0 g L􀀂1 over 11 to 13 wk. Results indicate that SAEP treatment increased root yields of Maverick and Pronto by about 20 and 15%, respectively, reduced proportion of smaller roots and improved harvest index (HI). Maximum yield was found at or above 0.50 g L􀀂1 SAEP for Maverick and at 0.75 g L􀀂1 for Pronto. Soil microbial colony counts, respiration and metabolic activity increased following SAEP applications, but varied with SAEP rate and application frequency. Using the Biolog microbial analysis system, maximum average well colour development (AWCD), substrate diversity (H), substrate evenness (E), and substrate richness (S) responses to extract treatment generally showed successive increases at 0.50, 0.75 and 1 g L􀀂1 SAEP at tri-weekly application frequencies. With more frequent applications, rates below 1 g L􀀂1 led to greater microbial growth, respiration and functional activities. Principal component analysis (PCA) showed a strong relationship between carrot growth, soil microbial populations and activity parameters. These results suggest that seaweed extract application can result in an increase in soil microbial activity associated with increased yield in carrots.