Morad Shaban - Young researchers club, Boroujed branch, Islamic Azad University, Boroujerd, Iran

The physiological process of germination depends on several environmental factors such as temperature, water potential, light, nutrients and smoke. Water and temperature are determinant factors for seed germination. Both factors can, separately or jointly, affect the germination percentage and germinationrate. The effect of temperature on germination and water potential on germination canoften be described by the thermal time and hydrotime models, respectively. The germination and growth behavior of different seeds under the influence of different physical parameters have been explained by differentmodels. Thermal-time describe effect of temperature on seed germination. The ability to germinate rapidly at low temperatures has been proposed as one of many mechanisms thatconfer a competitive advantage to this species. Previous studies of this phenomenon, however, have been limited to relativelysimple comparisons of total germinability and germination rate under selected constanttemperaturetreatments.Hydro-time models describe effect of water potential on seed germination as have been combined to form hydrothermal-time model that can describe seed germination patterns. Historical patterns of seedbed microclimate and predicted germination response may be useful in assessing andoptimizing alternative field planting scenarios. Inclusion of weather forecasting and seedbed modeling may providereal-time management options for improving rangeland seeding success.

Hydro-time, Seed and termal-time