Evaluation of interseeded forbs and pasture composition in Alabama cool-season grazing systems

Abstract

Diversification of Southeastern pasture systems with cool-season annual forbs has been proposed as a low-input pathway toward improved sward composition and reduced enteric methane emissions through plant secondary metabolite (PSM) contributions. Two studies evaluated whether candidate PSM-producing forbs could be reliably established in a southeastern production system without negative animal impacts. A two-year grazing trial at the Sand Mountain Research and Extension Center in Crossville, Alabama compared ‘AU Merit’ hairy vetch (Vicia villosa Roth), ‘Florida broadleaf’ mustard (Brassica juncea (L.) Czern.), and ‘Purple Top’ turnip (Brassica rapa L.) interseeded into ‘KY31’ tall fescue (Schedonorus arundinaceus [Schreb.] Dumort., nom. cons.). A small-plot study evaluated twelve (nine additional) coolseason forb species across three site-years. Additionally, a third methodological study compared two non-destructive methods of estimating botanical composition against hand-separation of clipped forage samples. Hairy vetch was the only species to reliably establish in both the grazing study and small-plot studies, increasing the planted forb fraction (18.7% of standing dry matter biomass; P < 0.0001) above the control, lowering the weed fraction (10.4% of standing dry matter biomass; P < 0.0001) below turnip paddocks, and increasing crude protein (14.9%; P = 0.0056) above brassica treatments without measurable effects on animal health or performance. Point-step transects produced the strongest non-destructive association with forb mass (R2 = 0.75; P < 0.0001). These results support hairy vetch as a low-input diversification candidate for Southeastern tall fescue pastures.