Effect of autumn sowing date on growth and seed yield of sunflower (Helianthus annuus L.) cultivars under environmental conditions of the north of Khuzestan province, Iran

To evaluate the effect of autumn sowing date on seed yield of sunflower cultivars, a field experiment was carried out as strip plot arrangement in randomized complete block design with three replications in safiabad agricultural and natural resources research and education center of Dezful, Iran during two growing seasons (201718 and 2018-19). Seven sowing dates (6th Sep., 23rd Sep., 7th Oct., 22nd Oct., 6th Nov., 21st Nov. and 6th Dec.) were assigned to vertical strips and five sunflower cultivars (Azargol, Barzegar, Progress, Farokh and Lakomka) were randomized in horizontal strips. Mean comparison of sowing date and cultivar interaction showed that the highest growth duration (204 days) belonged to sowing date of 21st Nov. and cv. Progress. The lowest growth duration (118 days) was for cv. Farokh in sowing date of 6th Sep. Delay in sowing date led to decrease in head diameter and thousand seed weight of all sunflower cultivars. Delaying in the sowing date also led to shorter plant height. The highest (42.8%) and the lowest (37.7%) seed oil content was observed in the first (6th Sep.) and the last (6th Dec.) sowing dates, respectively. Cv. Azargol (41.9%) and cv. Farokh (38%) had the highest and the lowest seed oil content. Mean comparisons of sowing date and cultivar showed that the highest seed yield (2985 kg.ha-1) belonged to the first sowing date (6th Sep.) and cv. Progress. The lowest seed yield (232 kg.ha-1) obtained from cv. Lakomka in 6th Dec. sowing date. The results of this experiment showed that the period of 6th until 23rd Sep. is suitable sowing date window for autuom sowing sunflower in the north of Khuzestan province.