Performance of Steers Grazing Tall Fescue and Rye-Ryegrass Pastures with Nitrogen Fertilizer or Interseeding Annual Legumes.

Tall fescue (Festuca arundinacea Schreb. = Lolium arundinaceum [Schreb.] S.J. Darbyshire) and the mixture of rye (Secale cereale L.) and ryegrass (Lolium multiflorum L.) are commonly grown pasture grasses for cattle production in Oklahoma.  Increasing costs of nitrogen fertilizer has resulted in renewed interest in forage legumes as alternative and economical sources of N.  The objective of this study was to determine the effects of conventional N fertilization compared to inclusion of forage legumes on animal production on perennial tall fescue ‘PDF 584’ (TF) and annual rye ‘Maton II’-ryegrass ‘Marshall’ (RRG) systems in south-central Oklahoma.  Forage legumes included ‘Apache’ arrowleaf clover (Trifolium vesiculosum Savi), Austrian winter pea (Pisum sativum subsp. arvense L.), and hairy vetch (Vicia villosa Roth).  Pasture treatments were arranged in three replications of a completely randomized design, and the experiment was conducted during two grazing seasons in 2008-09 and 2009-10. There were no differences in forage availability between RRG treatments or between TF treatments in 2008-09, and there were no differences in total grazing days (TGD) or average daily gain (ADG) among treatments.  However, gain ha^-1 was greatest on RRG + legumes and RRG + N.  In 2009-10, TF + legumes had the least available forage from fall through winter, and generally the least in TGD, gain ha^-1, and ADG. Forage availability was greatest for RRG + N in March 2010, but there was no difference in forage availability from April through June.  TF + N had the most TGD and was among the greatest in gain ha^-1 but was among the least in ADG, while both RRG systems were intermediate in TGD and among the greatest in gain ha^-1 and ADG.  This experiment will be conducted again in 2010-11 with complete economic analysis before conclusions can be made regarding using annual legumes to replace N fertilizer.