"Potato Fertiliser" ???

I went to our local garden club on Sunday and bought a few things for the allotment, one of these items was labelled "potato fertiliser". I bought a small bag (a couple of kilos in weight) in preparation for planting my spuds this weekend.

Only when I got home did I think! There were no instruction, so my question to the good people of this forum is: How much and when? I was thinking of liberally sprinkling it in and around the planting hole and maybe adding it to the mulch later in the year when the tubers start to bulk up?

Before anyone says go back and ask the people you bought it from? I will, but I cant get down there for a few weeks and it will be too late by then!

Thanks in advance.

Thats great, thanks Salmo!