Productivity and Animal Performance On Tall Fescue and Rye-Ryegrass Pastures Under Conventional Nitrogen Fertilization and Interseeding with Legumes.

Tall fescue (Festuca arundinacea Schreb.) and rye (Secale cereale L.)-ryegrass (Lolium multiflorum L.) mixtures are the most commonly grown cool-season pasture grasses for cattle production in Oklahoma. The increasing cost of nitrogen fertilizer, however, has resulted in 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 interseeding forage legumes on forage and animal production of tall fescue (PDF 584) and rye (‘Maton II’)-ryegrass (‘Marshall’) pastures in south-central Oklahoma. Forage legumes utilized were ‘Apache’ arrowleaf clover (Trifolium vesiculosum Savi), ‘Estes’ button medic (Medicago orbicularis [L.] Bartal. - rye-ryegrass pastures only),’Durana’ white clover (T. repens L. - tall fescue pastures only), Austrian winter pea (Pisum sativum subsp. arvense L.), and ‘AU’ hairy vetch (Vicia villosa Roth). The pasture treatments were arranged in three replications of a completely randomized design. The grazing periods were November 2008 through January 2009 (rye-ryegrass) and April 2009 through June 2009 (tall fescue). While not statistically different (P = 0.2), rye-ryegrass pastures tended to have greater total season forage yield (average 5476 kg ha^-1) compared to tall fescue pastures (average 3497 kg ha^-1). There were no differences in forage yield between rye-ryegrass + legumes and rye-ryegrass + N fertilizer treatments or tall fescue + legumes and tall fescue + N fertilization treatments throughout the grazing season. There were no differences in total gain (average 41.6 kg animal^-1), average daily gain (average 0.75 kg animal^-1 d^-1), or days on pasture (average 57 d) among pasture treatments. This may be due to extremely dry weather conditions experienced during this growing season.  These experiments will need to be conducted over several years along with an economic analysis before conclusions can be made regarding using legumes to replace N fertilizer.