M. A. Islam, T. J. Butler, J. T. Bushong, and M. W. Rowland. The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401
Incorporating self-reseeding summer legumes into cool-season and warm-season grass swards can improve forage distribution, increase animal performance, and decrease reliability on nitrogen fertilizer. Examples for such legumes are smooth-seeded wild bean (Strophostyles leiosperma) and trailing wild bean (S. helvula). They are native to USA and have tremendous potential to provide high quality forage during summer in the southern Great Plains when grasses are low in quality. However, limited information is available on their agronomic management including the choice of appropriate inoculants. A preliminary field study with a combination of different soil pH (5.1, 5.7, 5.9 and 6.3) and Rhizobia inoculants (control; a general cowpea inoculant, EL; a Strophostyles specific inoculant, ST) suggest that smooth-seeded wild bean can grow in a wide range of soil pH whereas trailing wild bean prefers neutral soil pH. Trailing wild bean had the highest nodule counts with the Strophostyles specific inoculant while smooth-seeded wild bean did not inoculate at any of the inoculant treatments. A greenhouse study was conducted with the aim to identify appropriate Rhizobia bacteria for both species. Two bacterial inoculants (EL, ST) with a control and two different soils of pH 7 (clay and sandy) were used in the study. Soils were sterilized before imposing treatments. The design of the experiment was a completely randomized block with three replications. The experiment was harvested at 30 days after emergence. Both species in both soils produced significantly (P < 0.0001) highest number of nodules (averaged 47 plant-1) in ST inoculant compared to EL (6 plant-1) or control (1 plant-1) treatment. Similar trends were also observed in the dry matter yield of both species however little difference was noticed between EL and control treatment. The results thus confirm that wild beans should be inoculated with Strophostyles specific inoculant for effective nodulation and nitrogen fixation.