PERFORMANCE OF FORAGE SOYBEANS IN THE SOUTHERN GREAT PLAINS

Authors: Rao, Srinivas; Mayeux Jr, Herman; Northup, Brian

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2005
Publication Date: 9/15/2005
Citation: Rao, S.C., Mayeux, H.S., Northup, B.K. 2005. Performance of forage soybeans in the southern great plains. Crop Science. 45:1973-1977.

Interpretive Summary: A primary goal of grazing-based forage production systems is to provide high quality forage year-round, reducing costs of storage and purchasing preserved forage or concentrated feeds. The primary forage resources for livestock production in the southern Great Plains is winter wheat and warm-season perennial grasses. Winter wheat forage is available during winter and early spring. Warm-season grasses are productive only in late spring and early summer, and their quality declines during mid and late summer. This research attempts to replace or reduce costs of harvested forages and concentrated feeds during the forage deficit periods to improve net returns for livestock producers. We evaluated the seasonal forage production pattern and nutritive value of three forage-type soybeans (Derry, Donegal and Tyrone) and the common seed-type cultivar Hutcheson. All three forage cultivars produced 15 to 47% greater leaf and 43 to 129% greater stem yield than the seed soybean 120 days after seeding. Among the forage soybean cultivars, Tyrone produced greater forage yield and lower seed yield at maturity. Forage quality of whole plants was similar for all cultivars. We demonstrated that among the forage cultivars, Tyrone has the potential to provide high quality and quantity of forage in late summer and early fall when other forages are unproductive.

Technical Abstract: Pasture for livestock in the southern Great Plains is often in short supply during the late summer. This study compared seasonal patterns in forage production, forage quality, and seed yield of three recently developed cultivars of forage soybean (Glycine max L.) (Donegal, Derry and Tyrone) to the seed cultivar Hutcheson. Inoculated seeds were planted at 60 kg ha-1 in rows (10 m long) with 60 cm spacing, in June 2001, 2002, and 2003, after harvest of no-till winter wheat. Whole plant samples were collected on six sample dates from 52 days after seeding (DAS) to 120 DAS. At 120 DAS, forage soybeans Derry, Donegal and Tyrone leaf and stem accumulations were 15, 46, and 47% and 43, 69, and 126% greater than those of the seed soybean, respectively. Seed soybean initiated flowering 15 days earlier than forage soybeans, resulting in lower leaf and stem yield. Forage quality of whole plants (N concentration and dry matter digestibility) were similar across cultivars. Seed yield of Tyrone was lowest (690 kg ha-1), as compared to Donegal (1180 kg ha-1), Hutcheson (985 kg ha-1), or Derry (939 kg ha-1). Nitrogen concentration and digestible dry matter of seed of all cultivars were similar. We concluded that forage soybean cultivars could provide greater forage biomass for livestock in the southern Great Plains during late summer and early fall when perennial warm season grasses are less productive.