Seeding rate and reseeding potential of ball clover in binary mixtures with annual ryegrass

Legumes can form symbiotic associations with rhizobia and fix atmospheric nitrogen (N), contributing N to forage systems when grown in mixtures with non‐N‐fixing species. Ball clover (BC; Trifolium nigrescens Viv.) is a cool‐season annual legume with strong reseeding potential due to its production of hard seed. We evaluated BC seeding rates (2, 4, or 6 lb ac −1 ) in mixtures with annual ryegrass (RG; Lolium multiflorum Lam.) to identify an optimal rate for pasture production systems and compared these mixtures with RG monocultures receiving either 0 or 45 lb N ac −1 (RG + N). Seeding rates did not affect herbage accumulation during establishment or in the following year. However, BC + RG mixtures produced less herbage accumulation than RG + N during establishment (1280 vs. ≥2800 lb ac −1 ) following reseeding (2900 vs. 1720 lb ac −1 ). RG grown in a mixture exhibited intermediate δ 15 N values (1.62‰, on average) between RG and RG + N, indicating the uptake of both soil‐derived N and N transferred from BC fixation. Seeding BC at 4 or 6 lb ac −1 increased the legume proportion in the sward to ∼50%, enhanced biological N fixation (BNF; 24.8 lb N ac −1 , average), and resulted in total shoot N yields comparable with RG + N. Therefore, seeding BC at 4 lb ac −1 provides benefits comparable with seeding at 6 lb ac −1 at a lower cost, whereas seeding at 2 lb ac −1 represents the most economical option, with a lower clover proportion (30%) and BNF (16 lb N ac −1 ) during the establishment year.