FROST-SEEDING LEGUMES INTO ESTABLISHED SWITCHGRASS - ESTABLISHMENT, DENSITY, PERSISTENCE, AND SWARD COMPOSITION

Legumes incorporated into established switchgrass (Panicum virgatum L. ) could provide symbiotic N, improve herbage quality, and extend the g razing season. Almost no information exists for legume renovation of s witchgrass by frost-seeding. The objective of this study was to identi fy cool-season legumes that can be established into switchgrass by fro st-seeding, yet not provide excessive competition to the associated gr ass. Six legumes [biennial 'Polara' white-flowered sweetclover (Melilo tus alba Medik.), biennial 'Madrid' yellow-flowered sweetclover (Melil otus officinalis Lam.), 'Norcen' birdsfoot trefoil (Lotus corniculatus L.), Redland II' medium red clover (Trifolium pratense L.), 'Apollo S upreme' alfalfa (Medicago sativa L.), and a 50:50 mixture of Redland I I red clover and Norcen birdsfoot trefoil] were inoculated with rhizob ia and frost-seeded into established 'Cave-in-Rock' switchgrass in mid -March of 1991 and 1992. These mixtures were compared with switchgrass fertilized at four N levels (0, 60, 120 and 240 kg ha(-1)). Successfu l legume establishment was observed, with an average of 24 and 25% of viable seed producing seedlings by June for 1991 and 1992 seedings, re spectively Mean legume density was 160 and 170 plants m(-2) by June of the seeding year (YR 1) and 95 and 55 plants m(-2) by June of the sec ond year (YR 2) for 1991 and 1992 seedings, respectively. Legume renov ation of switchgrass stands did not affect grass stem density by July YR 1. Mean forage stand composition (based on stem counts) was 87, 67, and 45% legume in June, July, and August YR 2, respectively, for 1991 seedings, and 54, 29, and 23% legume during the same time periods for 1992 seedings. Legumes did not seriously reduce switchgrass stem dens ity, although red clover, birdsfoot trefoil, and their mixture were mo re competitive than others. Legumes can be successfully introduced int o established Cave-in-Rock switchgrass by frost-seeding and they will persist for at least 2 yr with favorable weather.