Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 8, 2009
Publication Date: May 5, 2009
Citation: Rao, S.C., Northup, B.K. 2009. Capabilities of four novel warm-season legumes in the southern Great Plains: Grain production and quality. Crop Science. 49:1103-1108. Interpretive Summary: Yearling stocker cattle are a key part of agriculture in the southern Great Plains where they graze different forages to gain weight before entering feedlots for finishing. Stockers grazing warm-season grasses during the late summer must graze forage with low protein contents, which limit their growth, so protein supplements are supplied to improve weight gains. Commercial urea or protein blocks (cottonseed meal or alfalfa pellets) are the traditional supplements, but they cost three to four times the value of farm-grown, high protein feed. There is a need to explore legumes not normally grown in the Great Plains as sources of protein that may reduce the costs of growing stocker cattle. The annual tropical grain legumes mung bean, cowpea, guar, and pigeon pea were compared to soybean during 2004 through 2006, as sources of high quality feeds. Average grain yields ranged from 1280 lb/acre for cowpea to 1835 lb/acre for pigeon pea, under largely dry growing conditions. Soybean produced 1570 lb/acre of grain. The amounts of crude protein were highest for soybean grain (37.5%), and ranged from 23.1% to 27.5% in guar, mung bean and cowpea grain. Pigeon pea grain had the lowest levels of crude protein (21.3%). Grain digestibility was highest for soybean (97%) followed by mung bean, cowpea, and guar (92% to 94%), while pigeon pea grain was least digestible (89%). The amounts of crude protein noted in these legumes exceeded the levels (16% to 20%) found in most types of commercial supplement. Therefore, the four tropical legumes tested are all capable of producing grain that easily meets the protein requirements of all classes of stocker cattle grazed in the southern Great Plains.
Technical Abstract: Grain legumes could serve as a low cost nitrogen (N) and energy source for animal production in the southern Great Plains (SGP). This study evaluated the yield and nutritive value of grains 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) annually in mid-June 2004 through 2006. Seeding rates were varied to achieve 10 seeds m-1 row length. Grain was harvested at the end of growing seasons (90 to 120 days since planting), and grain samples were ground (1.0 mm) and analyzed for N concentration and in vitro digestible dry matter (IVDDM). Significant (P<0.05) year x legume interactions were recorded for all characteristics, with variable legume responses among years. Guar produced both the highest (2730 kg /ha in 2004) and lowest (897 kg/ ha in 2005) and consistently the lowest in pigeon pea (33.3 to 34.9 g/ kg). Soybean grain had the highest IVDDM (968 to 969 g/ kg), while pigeon pea had the consistently lowest digestibility (890 to 894 g/ kg). The four novel legumes produced grains that meet the nutritional requirements for all classes of stocker or feeder cattle.