Improving growing substrates by adding the seaweed Cystoseira baccata

Abstract

We examined the impact of adding the seaweed Cystoseira baccata (Ochrophyta, Sargassaceae) in various forms to two different growing substrates: pine bark and gorse compost. Specifically, we examined the influence of the seaweed on the physical and chemical properties of the substrates, and on their agronomic performance on a lettuce crop. The seaweed was used in a 20% (v/v) proportion and three different forms, namely: fresh (FS), washed fresh (WFS), and washed and dried (WDS). The mixed substrates exhibited no signs of instability. FS and DWS increased the total water retention capacity of pine bark by 20% and 27%, respectively. Adding the seaweed in any of its three forms to this type of substrate, which is poor in nutrients and has a low electrical conductivity (EC), significantly increased its P, K, Mg and Na contents, as well as its EC (from 0.08 dS m–1 in the control substrate to 0.69, 0.12 and 0.27 dS m–1 in those containing FS, WFS and WDS, respectively). On the other hand, only in fresh form (FS) altered the salinity and total K content of a substrate rich in nutrients and salts such gorse compost (from 0.89 to 1.42 dS m−1 in terms of EC and 0.59% to 0.98% in K). All mixtures performed well as substrates for a lettuce crop. Those containing DWS increased aerial mass in gorse compost, while any of the tested formats increased aerial mass in pine bark