Sunn hemp (Crotalaria juncea L.) is a tropical legume that produces plant biomass and nitrogen (N) quickly. Our objectives were to assess the growth of a new sunn hemp cultivar breed to produce seed in a temperate climate and determine the residual N eﬀect on a rye (Secale cereale L.) cover crop in east-central Alabama from 2007 to 2009. Plant populations, plant height, stem diameter, biomass production, and N content were determined for two sunn hemp planting dates, following corn (Zea mays L.) and wheat (Triticum aestivum L.) harvest, across di ﬀerent seeding rates (17, 34, 50, and 67kg/ha). Rye biomass was measured the following spring. Sunn hemp biomass production was inconsistent across planting dates, but did relate to growing degree accumulation. Nitrogenconcentrationswere inversely relatedtobiomassproduction,and subsequentNcontentscorrespondedto biomasslevels.