Calcified Seaweed

this
http://apps.rhs.org.uk/advicesearch/profile.aspx?PID=144
would suggest  about 25% more  calcified seaweed than the amount of lime you would apply.

The amount you need depends on the ph of your soil, of course 

Calcified Seaweed balanced organic fertilizer with trace elements.

To raise the ph to a level suitable for brassicas it is better to use lime but compared with lime it is very useful in the plot for increasing trace elements 

calcium, nitrogen and phosphorus elements N, P and K availability by 16%, 8% and 30%