Effects of seeding time and stand suppression methods on the success of legume introduction into existing grass pasture

Sod-seeding legumes into unproductive pasture can be an effective, low-disturbance rejuvenation strategy; however, legume establishment success is often low. The aim of this study was to examine the effects of seeding time and vegetation suppression methods on legume establishment at plot and field scale sod-seeding. A small plot trial at Touchwood Hills was set up to evaluate the effects of seeding time and vegetation suppression methods on the legume establishment, forage yield, and nutritive value. Three on-farm field-scale trials were seeded near Morse, Elrose, and Touchwood Hills, Saskatchewan to assess stand establishment of yellow flowering alfalfa ( Medicago falcata L .), purple flowering alfalfa ( Medicago sativa L.), and sainfoin ( Onobrychis viciifolia Scop.). At the field scale, the legume establishment success was variable, with upper slope and knoll landscape positions often having lowest plant counts, reflecting drier soil conditions. In the small plot trial, herbicide suppression using glyphosate (2.2 L/ha) consistently resulted in the highest emergence (4.8 plants m ⁻² ) across legume species ( P < 0.001), followed by fall dormant seeding (1.4 plants m ⁻² ), and lowest (0.2 plants m ⁻² ) for spring seeding without sod suppression. Forage dry matter (DM) yield in the seeding year was reduced by 69%–76% after herbicide application compared to other treatments, whereas forage nutritive value improved, with lower fiber and higher crude protein ( P < 0.001). Herbicide suppression provided the greatest seedling establishment but reduced forage DM yield in seeding year. Limited legume establishment at the field scale indicates the need for strategies to reduce competition from the existing stand.