Vetch emergence rate low

Most of the Bigflower Vetch seed has not emerged. Emergence:#sown is very low, less than 1:10.
I don't know whether this is due to seedling death, poor germination or germination delay due to seed dormancy. Maybe I'll do a little digging in the sown rows and see what I find.
If this is due to inherited dormancy, I could select for no dormancy by just saving seed from these early sprouters - If recessive, then all their offspring will be early sprouters, if dominant, then some percentage of intercrossed offspring would also be early sprouters.