Germination and Seedling Emergence of Three Semiarid Western North American Legumes

Abstract

Few seed sources of North American forbs are available for revegetation/restoration of degraded western rangelands adapted to annual precipitation zones less than 300 mm, and those that are available are mainly wildland collected. The amount of time and resources necessary to make wildland collections in quantity results in high seed prices and variable seed quality, such that forbs have been under-represented in rangeland seeding mixes. We have previously identified western prairie clover (Dalea ornata Douglas ex Hook.), Searls’ prairie clover (Dalea searlsiae A. Gray), and basalt milkvetch (Astragalus filipes Torr. ex A. Gray) as native species adapted to low precipitation zones in the western United States for which field-grown seed production would potentially reduce seed costs and increase availability. A series of glasshouse experiments were conducted to determine the effects of scarification, planting depth, and soil composition on germination and seedling emergence of these species. All three species produce hard seeds, and scarification was necessary to increase germination and seedling emergence. Compared with a 6-mm planting depth, a planting depth of 19 mm retarded the rate of emergence for all species but only reduced the total seedling emergence for basalt milkvetch. With seed scarification in sandy soils, prairie clover seedling emergence exceeded 80% while basalt milkvetch was less than 10%. With seed scarification in soils with higher clay content, prairie clover total seedling emergence reduced to 58–70% while basalt milkvetch increased to approximately 30%. Along with enhancing stand establishment in seed production fields, these data will assist land managers in planning for optimal establishment of these species in rangeland revegetation/restoration projects.