Sunn Hemp (Crotalaria juncea L.) Interseeding Approaches in Tall Fescue Pasture Systems

Incorporating warm-season legumes such as sunn hemp (SH: Crotalaria juncea L.) into tall fescue (TF: Lolium arundinaceum (Schreb.) Darbysh.) paddocks may improve summer herbage accumulation (HA) and nutritive value when TF becomes dormant. This study evaluated the effects of interseeding methods, nitrogen rates, and harvest timing on the HA and nutritive value of SH interseeded into established TF pasture over two growing seasons (2016–2017) at Forage Systems Research Center, Linneus, Missouri. Three interseeding methods, pure tall fescue control (PF), strip-kill drill (SK), and mowed-drill (MD), were evaluated in combination with two nitrogen rates (full rate, F; zero rate, Z) and three harvest timings (45, 55, and 65 days after planting, DAP) in a split-split-plot randomized complete block design. HA varied between years, with SK producing the greatest yield in 2016 (2489 kg DM ha−1) but declining significantly in 2017 (1697 kg DM ha−1; p < 0.001) due to unfavorable establishment conditions. Harvest at 65 DAP consistently maximized HA across both years, while earlier harvest timings (45–55 DAP) produced greater crude protein, in vitro true digestibility, and neutral detergent fiber digestibility and lower fiber concentrations, indicating a trade-off between yield and nutritive value with advancing harvest timing. Interseeded treatments consistently produced lower fiber concentrations and greater IVTD than PF, though effects on NDFD varied by year and method. The MD method required fewer field operations and inputs compared to SK, eliminating the need for herbicide application and specialized equipment, while producing HA and nutritive value were not significantly different from PF under nitrogen fertilization. Overall, SH interseeding can improve summer HA and nutritive value in TF-based systems, with the MD method offering the most practical approach for producers.