Forage Production of Grass--Legume Binary Mixtures on Intermountain Western USA Irrigated Pastures.

Well-managed irrigated pasture production can be optimized without nitrogen (N) fertilizer. The objective was to determine mixture and planting ratios of tall fescue (Schedonorus arundinacea Schreb.) (TF), meadow brome (Bromus riparius Rehm.) (MB), orchardgrass (Dactylis glomerata L.) (OG), timothy (Phleum pratense L.) (TIM), and perennial ryegrass (Lolium perenne L.) (PRG) with alfalfa (Medicago sativa L.) (ALF), birdsfoot trefoil (Lotus corniculatus L.) (BFTF), or cicer milkvetch (Astragalus cicer L.) (CMV) that maximize productivity. Planting ratios were 0:100 (grass:legume), 25:75, 50:50, 75:25, and three 100:0 grass monocultures fertilized at 0, 67, and 134 kg N ha^-1. Seasonal production of TF-ALF was 12.69 Mg ha^-1, equal to TF fertilized at 134 kg N ha^-1. ALF mixtures with MB, OG, TIM, and PRG produced 12.57, 10.97, 11.77, and 10.74 Mg ha^-1, respectively, and 8 to 40% more than grasses receiving 134 kg N ha^-1. Production of BFTF mixtures with TF, MB, and OG were 11.69, 11.45, and 9.95 Mg ha^-1, respectively, equal to their respective grass monoculture receiving 134 kg N ha^-1. The BFTF-TIM and BFTF-PRG mixtures averaged 12% more forage than grass monocultures receiving 134 kg N ha^-1. Production of CMV-grass was similar to that of grasses receiving 67 kg N ha^-1. Seasonal forage distribution was more uniform in ALF- and BFTF-grass mixtures, averaging 30% more at the second and third harvests than fertilized grasses. The TF and MB legume mixtures averaged 7% more production in the 50:50 planting ratios than the other two grass-legume mixtures, while the 50:50 and 25:75 ratios of OG and TIM-legume mixtures averaged 12% more than the 75:25 and the 25:75 PRG-legume planting ratio averaged 9% more than the 50:50 and 75:25. Forage production of grass-legume mixtures can equal or exceed fertilized grass monocultures and with more uniform distribution over the growing season. [ABSTRACT FROM AUTHOR]