ARS | Publication request: Capabilities of four novel warm-season legumes in the southern Great Plains: biomass and forage quality

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 22, 2009
Publication Date: May 22, 2009
Citation: Rao, S.C., Northup, B.K. 2009. Capabilities of four novel warm-season legumes in the southern Great Plains: Biomass and forage quality. Crop Science. 49:1096-1102.

Interpretive Summary: Double-cropping summer annual legumes after winter wheat is a common agricultural practice in several areas of the USA. However, double cropping is not common in the southern Great Plains (SGP). Producers in the SGP rely on wheat forage for fall grazing by yearling stocker cattle, in addition to harvesting a grain crop in June. The dry conditions during summer fallow after wheat (June to August) means soil water available for growing summer forage may be limited. This study determined the forage production pattern and nutritive value of four summer annual grain legumes compared to soybean during the summer fallow period of winter wheat in SGP during 2003 through 2006. We found continuous double cropping of legume biomass varied during four dry to normal years. Biomass production for medium to long duration soybean, pigeon pea and guar averaged 3560, 3439 and 3321 kg/ha as compared to short season cow pea and mung bean (2918 and 2405 kg/ha, respectively). Mung bean and cow pea accumulated the least N (70 and 65 kg N/ha) where as soybean, guar and pigeon pea yielded 100, 93 and 77 kg N/ha. Digestibility of cow pea, mung bean soybean and guar were similar (757 to 825 g/kg), while pigeon pea was least digestible (634 g/kg). Any of these legumes tested could be incorporated in to range of farming systems and give producers options other than soybean as a source of forage, or biological N for following cereal crops.

Technical Abstract: Grain legumes could provide high nitrogen (N), late summer forage for stocker cattle in the southern Great Plains (SGP). This study evaluated the forage yield and nutritive value of tropical annual legumes novel to the SGP. Included were cultivars of pigeon pea ([Cajanus cajan (L.) Millsp.], cv. ‘GA-2’), guar ([Cyamopsis tetragonoloba (L.) Taub.] cv. ‘Kinman’), cowpea ([Vigna unguiculata (L). Walp.], cv. ‘Chinese red’), mung bean ([Vigna radiata (L.) Wilcz.], cv. ‘Berkins’), and the grain soybean [Glycine max (L.) Merr.] ‘Hutcheson’ as a control. Seeds were inoculated and planted (60-cm row spacing at 10 seeds m-1 row length) annually in mid-June 2003 through 2006. Aboveground samples were collected on six dates, from 45 to 120 days since planting (DSP). Samples were dried and aboveground biomass was calculated. Samples were then ground to 1.0 mm, and analyzed for N and in vitro digestible dry matter (IVDDM) contents. Biomass production varied during four dry to normal years. Soybean, pigeon pea and guar averaged 3560, 3439 and 3321 kg ha-1 while mung bean and cowpea averaged 2918 and 2405 kg ha-1, respectively. Mung bean and cowpea accumulated the least N (70 and 65 kg N ha-1). Soybean, guar and pigeon pea yielded 100, 93 and 77 kg N ha-1, respectively. Digestibility of cowpea, mung bean, soybean and guar were similar (757 to 825 g kg-1), while pigeon pea was least digestible (634 g kg-1). These novel legumes could provide producers in the SGP with options other than soybean for generating forage and biological N.