Summer forage capabilities of tepary bean and guar in the southern Great Plains

Authors: BAATH, GURJINDER - Oklahoma State University; Northup, Brian; Gowda, Prasanna; ROCATELI, ALEXANDRE - Oklahoma State University; SINGH, HARDEEP - Oklahoma State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2020
Publication Date: 4/6/2020
Citation: Baath, G.S., Northup, B.K., Gowda, P.H., Rocateli, A.C., Singh, H. 2020. Summer forage capabilities of tepary bean and guar in the southern Great Plains. Agronomy Journal. 112(4):2879-2890. https://doi.org/10.1002/agj2.20220.
DOI: https://doi.org/10.1002/agj2.20220

Interpretive Summary: Winter wheat and different warm-season grasses, such as native prairie, Bermudagrass, and Old-World bluestem have long been important for grazing yearling stocker cattle in the U.S. southern Great Plains (SGP). While these sources of grazed pasture can provide high quality forage for stockers, there are issues in their use as pasture. One serious issue is the drop in forage quality of warm-season grasses during late summer (July to mid-September), which limit weight gain by stockers. This drop in nutritive value of warm-season grasses has resulted in a continuing search for new species that have the capacity to produce useful amounts of high quality forage during late summer. In this study, we explored a series of less-common grain legumes that are available Worldwide, to identify those that may be capable of producing nutritious late-summer forage in the SGP. We compared 3 cultivars of both tepary bean (a grain legume grown in South America to northern Mexico), and guar (a grain legume from India that is grown in many countries for grain or forage) to soybean. We grew these cultivars and soybean on two different soils (low fertility upland, and fertile lowland) in central Oklahoma during 2016 and 2017, and compared the amount of forage produced, leaf to stem ratios of forage, and measures of forage quality. We found that tepary bean possessed the best overall capacity for producing adequate yields of forage, combined with high and consistent quality when grown as a summer forage. The cultivar ‘Black’ of tepary bean outperformed both soybean and the guar varieties in amount of forage produced, combined with high leaf-to-stem ratios (5850 lb/acre; 3.1 lb leaf to 1.0 lb stem), which makes tepary bean a more effective forage for stocker cattle. Soybean produced leaves of greater quality than the other legumes, but forage of soybean had large amounts of low-quality stems, which reduced the digestibility of soybean forage. The guar varieties had the lowest leaf-to-stem ratios, which would also limit their value as forage. Therefore, we concluded that tepary bean, a less common grain legume, could serve as an alternate forage for producers in the SGP in place of soybean. There is a need for future research to define improved management practices for growing tepary bean for grazing or hay.

Technical Abstract: Low nutritive value of perennial warm-season grasses often causes limitation to weight gains of stocker cattle grazing in the U.S. Southern Great Plains (SGP). Exploration of less-common and novel grain legumes may identify species capable of generating nutritious summer forage to fill gaps when high quality forage is limited. This two-year field experiment compared seasonal changes in forage biomass, leaf-to-stem ratio, and chemical composition of three varieties each of tepary bean (Phaseolus acutifolius) and guar (Cyamopsis tetragonoloba) to soybean (Glycine max) when grown on different soil types in central Oklahoma. Tepary bean cv. Black outperformed soybean and guar varieties by producing greater amounts of forage (6537 kg ha-1) with a larger leaf-to-stem ratio (3.1) at 65 days after planting. The biomass yields and leaf nutritive value of soybean were greater than the other tested legumes, but had large amounts of low-quality stems with the lowest in vitro true digestibility (529-581 g kg-1) during both years. Guar varieties had the lowest leaf-to-stem ratio (1.3-1.5 kg kg-1) throughout the growing seasons, which could limit its value for grazing compared to other legumes. We concluded tepary bean could serve as an alternate forage option to soybean for producers in the SGP. Tepary bean possessed the best overall capacity for producing adequate yields of forage, combined with high and consistent nutritive values when grown as a summer forage. Future research should focus on defining improved management practices for growing tepary bean in extensive production settings for grazing or hay.