Winter Sweetclover to Improve Sustainable Switchgrass Biomass Production.

Sweetclover (Melilotus albus and M. officinalis) is a potential companion crop for biomass production with switchgrass (Panicum virgatum).  Sweetclover fixes nitrogen and has minimal competition with warm season grasses. In Iowa switchgrass is actively growing from mid May until October, leaving a potential cool-season niche for sweetclover.  Sweetclover is a cold tolerant biennial, in the wild it frequently germinates in the fall, vernalizes during the winter, then flowers and dies in early summer.  It can germinate at any time in the growing season but flowers and dies in the following year.  Fall germination may be most favorable for biennial sweetclover to benefit a switchgrass cropping system.  Spring plantings of sweetclover are known to establish within ‘Cave In The Rock’ switchgrass stands.  Fall plantings are expected to establish also but are untested.  Biennial sweetclover such as ‘Madrid’ M. officinalis could germinate in established switchgrass stands after planting in October, and would die during seed maturation in the following May.  How much benefit the sweetclover will contribute to switchgrass yields, the long term fate of a sweetclover seed bank in switchgrass, and the management challenges are unknown. However, winter sweetclover in switchgrass is worthy of further study in Iowa and other parts of the United States.