Thus, seeds on the soil surface were retrieved five times (0,
3, 6, 9, and 12 months after maturation) during the 12-month afterripening
period, whereas surface-lying seeds that were buried in
May (to simulate burial by spring tillage) were exhumed in August
(9 months after maturation) and November (12 months after
maturation) retrieval dates during the 12-month after-ripening
period