Calcified seaweed question

[Digeroo]

Bought some calcified seaweed,

Promotes stronger root systems and vigorous plant growth

Scattered some around my brassicas.  Several weeks later it still seems to be there does not look as if it has changed.  I did not think I needed to dig it in, because you are supposed to be able to sprinkle it on paddocks. 

When will it disappear?  it is not doing the plants much good if it simply sits on top of the soil.  Does not appear to be water soluble.  Not clear how the plants get anything from it.

[Digeroo]

[goodlife]

It is much slower acting than conventional lime...and it will need to be raked into surface for it to able to 'interact' with the soil fauna before it start to have any effect.

[Digeroo]

Perhaps it is a good thing if it takes longer, every else washing out too quickly.