Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2016
Publication Date: 3/1/2016
Citation: Jones, T.A., Johnson, D.A., Bushman, B.S., Connors, K.J., Smith, R.C. 2016. Seed dormancy mechanisms in basalt milkvetch and western prairie clover. Rangeland Ecology and Management. 69:117-122.
Interpretive Summary: Until now, the success of seed-field establishment for the native legume, basalt milkvetch, has been sporadic. Only a few seed fields of NBR-1 basalt milkvetch have been established from seed, with most fields having been established with greenhouse-grown transplants, a laborious and expensive process. An additional problem is that transplanting success of basalt milkvetch is highly variable and sometimes features a high rate of mortality. In contrast, much greater success has been obtained with transplanting the native legume western prairie clover. Mechanical scarification and prechilling treatments were applied to seed to try to improve germination percentage of both species. Both species responded to mechanical scarification, but only basalt milkvetch responded to prechilling. The utility of prechilling basalt milkvetch seed was also demonstrated in the field. Most rangeland restoration efforts in the Great Basin region involve "dormant" seedings that are planted in late fall to intentionally delay germination until the following spring, when soil moisture is greatest. Dormant seedings obviate the need for prechilling before planting because the seed overwinters in the ground. However, our results highlight the importance of scarifying seed of both western prairie clover and basalt milkvetch before seeding both rangelands and seed fields. These findings make it possible to successfully establish seed fields of these species and elucidate seed treatments that increase establishment success in rangeland restoration seedings.
Technical Abstract: A greater diversity of native legumes and forbs is desirable for rangeland restoration practice in the Intermountain Region of the western U.S. However, for such diversity to materialize in the seed marketplace and to be effective in restoration practice, plant materials are needed that can be germinated reliably in the seed field and on restoration sites. We measure germination response of two native legumes, basalt milkvetch (Astragalus filipes Torr. ex A. Gray) and western prairie clover (Dalea ornata [Douglas] Eaton & Wright), to eight germination treatments. Treatments were a factorial combination of 1) seed scarification with sandpaper (or unscarified), 2) a substrate of moist sand (or blotter paper), and 3) a 3-wk prechill at 5 degrees (or non-prechilled). Germination increased lineraly throughout the 10-week course of the experiment for all treatment combinations of both species. Scarification increased germination of western prairie clover, but prechilling and substrate had no effect. In contrast, prechilling, scarification, and a sand substrate all increased germination of basalt milkvetch. Hence, the prechilled/scarified/sand treatment combination displayed the highest germination for all 10 weeks (30-43%), and the non-prechilled/unscarified/blotter paper treatment combination always germinated lowest (1-3%). Results were consistent with a physical dormancy (hard-seededness) mechanism that limits germination of western prairie clover and combination of physical and physiological mechanisms that limit germination of basalt milkvetch. Of the two species, we have found basalt milkvetch to be much more difficult to establish from seed. By prechilling acid scarified seed in moist sand, basalt milkvetch was successfully established in two field trials seed in mid-April. Mechanical (sandpaper) scarification without prechilling was equally effective. By scarifying and prechilling basalt milkvetch seed to address both physical and physiological dormancy mechanisms, respectively, this seed-treament protocol may be "scaled up" to produce large quantities of germinable seed.