Resilient potatoes

I obviously didn't dig up all my potatoes last season . Pulled the covers off the plot this morning to find lots of potato plants, yellow from no sunlight but growing strong. I wasn't planning on planting potatoes this year, so maybe this is a blessing in disguise.

As the soil hasn't been prepared for them and they are in the same area as last year, what would be the best fertiliser to use on them to get a good crop?

I'll have to do a better job this year with harvesting

Thanks mum. A job for the morning I guess