Seeding rate, row spacing, and nitrogen rate effects on perennial ryegrass seed production

Seeding rates (SRs) and row-spacing widths (RSWs) in perennial ryegrass (Lolium perenne L.) seed production are variable and the impacts of these factors on perennial ryegrass seed yield and plant growth characteristics are not well characterized. Experiments were conducted during 2010 and 2011 in first-year seed production fields near Roseau and Roosevelt, MN, where five SRs (1.3, 2.6, 5.2, 7.8, and 10.4 kg pure live seed [PLS] ha⁻¹), three RSWs (10, 20, and 30 cm), and three N rates (67, 112, and 157 kg N ha⁻¹) were evaluated in a split-split plot design under nonirrigated conditions. The 30-cm RSW resulted in 45% greater stem rust incidence, 8% fewer fertile tillers, and up to 2% greater 1000-seed weight (TSW) vs. the 10-cm RSW. For every unit of N applied, N increased biomass by 4 to 25 kg ha⁻¹, fertile tillers by 3.7 tillers m⁻², and seed yield by up to 4.7 kg seed ha⁻¹, depending on environment. The 7.8 and 10.4 kg PLS ha⁻¹ SRs combined with the 10-cm RSW, 157 ha⁻¹ N rate, and other management factors, nearly eliminated weeds (<2% weed cover) compared with with wider RSWs and lower SRs. Weed cover was always inversely correlated with early-season vegetative cover (EVC). Seeding rates of 2.6 kg PLS ha−1 and greater resulted in similar seed yields suggesting that early-season plant density is not as important for seed yield as other management factors such as N rate, which significantly improved seed yield in three environments.