Sorry Stoker no you need to use fresh compost each year if you are growing in a bag. The previous years tatties will have used all the nourishment. Put the spent soil on your garden or in the compost.

I agree MG. There wont be much left in the compost for this year.

I grow potatoes in pots and I use fresh compost every year, for the same reasons as above.

you could possibly grow another plant in it as thats how crop rotation works as some plants use other plants waste . hardly worth it in a bag so moon grower sais sprinkle it on your garden etc lol .