Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 25, 2005
Publication Date: September 15, 2005
Citation: Rao, S.C., Northup, B.K., Mayeux, H.S. 2005. Candidate cool-season legumes for filling forage deficit periods in the Southern Great Plains. Crop Science. 45:2068-2074. Interpretive Summary: Livestock producers have a goal of grazing high quality forages year-round to reduce the use of expensive stored feeds. In the southern Great Plains, winter wheat and warm-season perennial grasses are the primary forages for livestock production. Wheat pasture is grazed from November through April, and the warm-season pastures in June through September. This system has a major forage deficit in May and early June, when cattle must be fed until warm-season pasture is ready. Forages that can fill this gap are needed to support improved grazing systems in the region. In 2001 through 2003, we evaluated how the cool-season annual legumes grasspea ('AC-Greenfix') and lentil ('Indian Head') functioned at producing forage during May and June, and nutritive value of the forages. We inoculated and planted these cultivars on 15 March of each year in 650 square foot plots and collected plant samples on five dates in May and June. We used the samples to describe production, and analyzed them for nitrogen content and digestibility. We found that both cultivars were able to produce high quality forage during three years with spring drought. However, grasspea outperformed lentil, reaching a maximum yield of 5710 (versus 1792) lb/acre by 75 days after planting. Nitrogen content (ranging from 2.3 to 5.5%) and digestibility (79%)of hay produced by the cultivars were similar. The higher level of production means grasspea could better fill the spring forage gap, and function as part of more efficient wheat-based forage systems used in the southern Great Plains.
Technical Abstract: This study evaluated seasonal forage production and nutritive value of the cool-season annual legumes grasspea (Lathyrus sativus L. cv 'AC-Greenfix') and lentil (Lens culinaris Med. cv 'Indian Head') grown to fill the spring forage deficit period of the southern Great Plains. Data were collected from March to June in 2001 through 2003 at the USDA-ARS Grazinglands Research Laboratory, Oklahoma. Cultivars were inoculated and planted (60-cm row spacing) annually on 15 March (75 kg/ha for grasspea; 25 kg/ha for lentil) in 60 m^2 plots. Aboveground biomass was collected on five dates [45 to 95 days after seeding (DAS)], dried 60 h at 65°C, weighed, and used to calculate aboveground standing crop. Samples were ground (1.0 mm) and analyzed for nitrogen (N) and in vitro digestible dry matter (DDM) concentrations. Standing crop and N concentration showed significant (P<0.05) interactions between DAS, cultivars and years. Significant (P<0.05) DAS x cultivar and DAS x year interactions were noted in DDM. Grasspea outperformed lentil and reached its maximum yield of 6415 vs 2013 kg/ha, respectively, on 75 DAS before declining. Nitrogen concentration (23 to 55 mg/kg) and DDM [786(±3) g/kg] of the two cultivars was similar during the growing season. The higher level of production gives grasspea greater potential as a component of wheat-based forage systems in the southern Great Plains, particularly for filling the deficit period during late spring.