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

Abstract

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.

Keywords

drought Maine / nitrogen fixation / nutritive value / sunn hemp

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2026 The Author(s). Grassland Research published by John Wiley & Sons Australia, Ltd on behalf of Chinese Grassland Society and Lanzhou University.