Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 10, 2011
Publication Date: September 19, 2011
Citation: Rao, S.C., Northup, B.K. 2011. Growth and nutritive value of grass pea in Oklahoma. Agronomy Journal. 103:1692-1696. 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 cool-season annuals during the late spring 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. Grass pea is a cool-season annual grain legume has been noted for its tolerance to dry conditions and adaptability to difficult environments. Study was conducted to determine and compared, the seasonal patterns of biomass production and quality of both forage and seed between improved Mediterranean grass pea lines and locally adapted grass pea cultivar “AC-Greenfix”. Environmental conditions, especially total precipitation and distribution played an important role in the performance of Mediterranean lines. Locally adapted AC-Greenfix produced more leaf and stem biomass across years and averaged over sampling dates (2230 vs 1695 lbs/acre for the 10 Mediterranean lines). Some Mediterranean lines produced more seed and greater N concentration than ‘AC-Greenfix’, but varied with growing season, indicating diversity in adaptation to southern Great Plains growing conditions. Additional crop development is needed for these Mediterranean lines to perform with the same consistency as ‘AC-Greenfix’ in the southern Great Plains.
Technical Abstract: Cool-season grass pea (GP) has some potential to provide as late spring forage in the southern Great Plains (SGP), but genetic materials for development of new cultivars is limited. Our objective was to evaluate seasonal forage production and grain yield for 10 new Mediterranean-origin GP lines, in central Oklahoma. Replicate (n=3) plots (3 x 10 m) were lightly disked, fertilized (60 kg ha-1 P2O5), and sown at 60 kg ha-1 in 60 cm rows with GP lines 190, 288, 289, 290, 299, 387, 390, 736, B22, B111, and AC-Greenfix (control) that were treated with inoculum (Rhizobium leguminosarum) during early March in 2007, 2008 and 2009. Whole plant samples were collected, 59, 73, 94 and 115 days after seeding. Biomass collected on d 115 was separated into seed and non-seed biomass. Biomass accumulation, N concentration and non-grain digestibility showed significant (p<0.05) line, year, and sampling date effects. Grain biomass, N concentration and digestibility also showed significant line and year effects. As noted at every sampling date, AC-Greenfix produced the most non-grain biomass each year [2499 kg ha-1 for AC- Greenfix vs an average of1899 (±145) kg ha-1 for the other 10 lines]. Line x year interactions for grain biomass were, statistically significant, with 2008 being the most productive year for all lines. Additional crop development is needed for these new Mediterranean GP lines to perform with the same consistency as AC-Greenfix in the SGP.