You can build a contrast matrix for all pairwise comparisons you're interested in, consider "H X" in place of the original "X" design matrix (H is the contrast matrix), and do it basically by hand. Or you can just do a pairwise t-test as described in the link hereafter.
as far as I know, it's not possible to run pairwise comparisons in vegan using adonis().
I guess you could do it artificially by selecting each time different subsets of data with couples of treatments (e.g. SF+BF, SF+HF and so on). But maybe it requires some kind of adjustments (not sure about that).
Anyway, you can find several discussions on this issue. For example here:
My p-value from adonis was significant, but the pairwise.perm.manova did not show a significant p-value among my 6 groups comparisions...is it possible?
Hi Katia, it is definitely possible that your overall MANOVA is significant and none of your pairwise comparisons are significant. p-values from pairwise comparisons are generally adjusted by some p.adjust method to make them more conservative because of the increasing chance of making a type II error.