Changes in Seed Dormancy in Soil after Seed Rain of Datura stramonium

To investigate the level of datura seed dormancy in the soil after the seed rain, a factorial experiment based on randomized complete blocks design was conducted in three replications, during 2011–2012 in Karaj. Factors comprised three moisture regimes (moisture levels inclouded 1- dry (H1), 2- alternate wetting and drying (H2), 3- moisture (H3)) and four temperatures of seed storage (temperatures in four months of the seed rain to restart growth integrated December and January (T1), February and March (T2), April (T3) and at the end of May and June (T4)) in a factorial combination were applied on Datura seed mass. After applying each treatment, germination tests at temperatures of 8, 14, 20, 28 and 35°C were performed. Then according to the estimated parameters, the relationship between temperature and moisture with Hydro-Thermal models which was investigated. Results indicated that response of germination percentage adequately described with segmented functions, continually. When the seeds were completely at dry conditions, a gradual increased in temperature increases the rate of germination. However, this increase was negligible compared with the increase observed in response to the two other levels of moisture levels (H2- H3). No germination was found at temperatures 4 & 7°C, irrespective of moisture levels. While with increasing temperature up to 15 and 23°C, the rate of germination increased considerably, especially for alternate wetting and drying conditions.