Early spuds

Just wondered if any one else has had problems with early spuds this year. The plot had beans, peas and carrots last year and was dug over last autumn and 4 barrowloads of well rotted horse manure added. (the plot is big enough for 21 tubers). I used my favourite Arran Pilot seed bought from one of the well known suppliers. They were planted end of March and were slow starting and when growing the tops were small and did not flower, and some tops died off. Just started digging and am getting 2 or 3 eggsize spuds per plant. I woud normally expect at least twice this yeald.
I would appreciate any advice or comments.

TIA

 

Funny you should say that - I had three types of spuds growing in bags. I had a fudge around in there to get some for dinner and found one measly potato about as big as a sprout! Also had a few peas, 18gms to be precise! Not exactly a feast! Plus 2 raspberries and 4 blackcurrants but at least they were from new shrubs just planted this year.