Evaluation of sunn hemp performance and nutritive value in Maine, USA

Background Sunn hemp ( Crotalaria juncea L. and Crotalaria ochroleuca G. Don) was evaluated as a warm‐season legume to mitigate the “summer slump” in Maine's forage production caused by heat and moisture deficit stress. Methods This study compared three cultivars: “Crescent Sunn,” “Loei,” and “Red Mini,” at 60 and 90 days after seeding over the 2024 and 2025 growing seasons to measure biomass, nitrogen (N) fixation, and nutritive value. Results Environmental conditions significantly impacted performance; biomass accumulation in 2024 was 4296 kg dry matter (DM) ha −1 , whereas the drought‐stressed 2025 season produced 1099 kg DM ha −1 . Notably, drought increased the percentage of N derived from the atmosphere (52% in 2025 vs. 33.8% in 2024) and improved forage nutritive value by increasing crude protein and digestibility. Crescent Sunn and Loei consistently outperformed Red Mini; across all cultivars, delaying harvest to 90 days increased total biomass but elevated lignin levels and reduced digestibility. Conclusions Sunn hemp is a resilient forage and N source for northern temperate regions; management should target a 60‐day harvest for high‐quality animal feed or a 90‐day harvest for maximum cover crop biomass.