Seedling Emergence as Related to Temperature and Moisture Tension

Mixtures of seed that provide quick germination and seedling growth during most seasons are important for controlling erosion and establishing an aesthetically pleasing turf in highway corridors. To aid in selection of species for mixtures, we designed an experiment to determine total emergence and rates of emergence of several grass and legume species and cultivars under various soils moisture and temperature regimes. Rates of seedling emergence for 12 grass and legume species or cultivars were determined in the laboratory on a Groseclose (clayey, mixed, mesic, Typic, Hapludult) subsoil maintained at soil water potentials of −1/3, −3, −6, and −9 bars and at 21 and 28 C over a 19-day period. Abruzzi rye (L), German millet (L.), perennial and annual ryegrasses (L. and Lain), weeping lovegrass (Schrad. Nees), and redtop (L.) were considered aggressive species. After 4 days at −1/3 bar of soil water potential, seedling emergence for these species ranged from 54 to 100% emergence and by day 6 total emergence was the highest for all groups at either temperature. Intermediate species included creeping red rescue (L.) Kentucky bluegrass (L.), Kentucky 31 tall rescue (Schreb.), crownvetch (L.) at 21 C, and common bermudagrass (L.) at 28 C. Emergence at 21 C and −1/3 bar generally began on day 3 or 4 and near maximum emergence rates of the intermediate species occurred by day 8 at 21 C and −1/3 bar. Total emergence was less than observed for the aggressive group. Emergence was also sharply reduced at −6 and −9 bars as compared to Abruzzi rye, German millet, and perennial ryegrass. Common bermudagrass at 21 C and Sericea (G. Don.), and crownvetch at 28 C had few seedlings emerge until day 8 in the soil maintained at −1/3 bar, and their total emergence was the lowest of all species with near maximum occurring between day 10 and 13; therefore, they were considered non-aggressive species. Generally, as temperature and moisture tension increased, the rate of emergence and total emergence of all species declined. Of the aggressive species, only Abruzzi rye, German millet, and perennial ryegrass had above 50% relative emergence after 19 days at a soil water potential of −9 bars and 21 C. Seed mixtures for different planting seasons should be designed with species adapted to various temperature and moisture extremes.