Ameliorate Secondary Dormancy of Leguminous Cover Crop Species for Use in Commodity Production Systems through Recurrent Phenotypic Selection.

Winter cover crops provide a range of benefits; among these are increasing nutrient scavenging and decreasing soil erosion. Establishment of cover crops following a corn production system requires planting these cover crops in early September and terminating them the following March. While cool-season legumes (CSL) are popular winter cover crop options, germination is restrained by secondary dormancy. This study compares germination, establishment, and biomass accumulation of unselected (US) and heat-selected (HS) populations from three CSL species [crimson clover (Trifolium incarnatum L.; CC), berseem clover (T. alexandrinum L.; BC), and hairy vetch (Vicia villosa Roth.; HV)]. Efficacy of selection in reducing secondary dormancy was assessed in replicated trials during winter 2016 and 2017. Laboratory studies evaluated germination of US and HS germplasm at 20° and 40°C, while field experiment evaluated germination and establishment of US and HS seedlots, across four plating dates. All statistical analyses were conducted using PROC MIXED, α=0.05. Laboratory germination results, showed HS HV and HS CC had a significant increase in velocity of germination at 40°C (VOG₄₀) after one cycle of selection. Following two cycles of selection, all CSL species showed significant increases in VOG₄₀ compared to their US counterparts. In 2016 field trials, there were no significant differences in germination between HS and US populations when planted before October. October planting date showed a significant increase in germination of US BC compared to the HS population. November planting date showed a significant increase in germination of HS HV compared to US population. In 2017 field trials, US BC showed a significant increase in germination in August and September compared to the HS population. September planting date showed a significant increase in germination in HS CC compared to its US counterpart. However in 2017, plant area of HS HV was greater with the earliest planting date.