نبذة مختصرة : With the increase in population and improvement in diet diversity, there is a growing need for the quantitative and qualitative development of oil seeds. Camelina (Camelina sativa), an oil seed plant from the Brassicaceae family, is an ideal candidate as it contains 50 to 60% unsaturated fatty acids and omega-3 fatty acids, and has the ability to thrive in adverse environmental conditions. By introducing this new oil plant into cultivation programs, it can significantly contribute to the production of high-quality edible or non-edible oil in the developing countries such as Iran. However, achieving maximum grain yield and appropriate fatty acid composition in camelina oil relies heavily on selecting the appropriate planting date. Additionally, providing necessary nutrients, particularly nitrogen, to the plants is a key aspect of agricultural management to achieve desired quality and quantity of crop products. This research aims to investigate the impact of planting date and different levels of chemical and biological nitrogen fertilizers on the growth characteristics, yield, and oil content of camelina plants in the Eghlid, south of Iran. Materials and Methods This research was conducted in the cropping year of 2021-2022 at the Eghlid Agricultural Research Station in Fars province, south of Iran (Long. 52 42, Lat. 30 55, and Alt. 2375 m above sea level). The experiment was performed as a split-plot design based on a randomized complete block design with three replications. The main plots included different nitrogen fertilizers at four levels: 100% chemical nitrogen (250 kg/ha urea), 75% chemical nitrogen (187 kg/ha urea) + nitrogen biofertilizer, 50% chemical nitrogen (125 kg/ha urea) + nitrogen biofertilizer, and non-use of nitrogen fertilizer (control). The sub-plots included four planting dates: September 11, 2021, September 26, 2021, April 9, 2022, and April 24, 2022. The experimental plots (sub-plots) were determined to be 5 x 2 meters. Each plot consisted of 4 stacks with a distance of 50 cm between them. The distance between sub-plots was 50 cm, the distance between main plots was 150 cm, and the distance between replications (blocks) was 300 cm. On both sides of each stack, seeds were planted in two rows with a distance of 25 cm to achieve a density of 120 plants/m2 . One-thirds of the urea nitrogen fertilizer was added to the plots of each treatment before planting, one-thirds at the 6- 8 leaf stage, and the remaining third at the stemming stage of camelina. In the biofertilizer treatment, the camelina seeds were inoculated with biofertilizer containing Azotobacter sp. and Azospirillum sp. before being sown. The cumulative growth degree days of seedling emergence, flowering, and ripening, as well as plant height, chlorophyll index, grain yield, yield components and seed oil percentage were evaluated. Results and Discussion With delaying planting from September 11, 2021, to April 24, 2022, the GDD (Growing Degree Days) for camelina emergence decreased, additionally, a delay in planting led to a shorter growth period until full flowering of the camelina plants. Planting in September 26, 2021, led to the longest growth period until full maturity of the camelina plants, while spring planting resulted in a decreased length of the growth period until maturity. The highest plant height (43 cm) was achieved in the presence of 75% chemical fertilizer + biofertilizer nitrogen and the lowest (41 cm) was in the absence of nitrogen fertilizer application. The planting date of September 11, 2021 and April 24, 2022 showed the highest (43 cm) and lowest (37 cm) plant height of camelina. The decrease in plant height during the late planting date was primarily due to the decrease in internode elongation as a result of changes in day length and a shorter vegetative growth period. The highest chlorophyll index (66) was achieved by using 100% nitrogen chemical fertilizer, while the lowest chlorophyll index (52) was observed in the control, lack of fertilizer application. This trait decreased when the planting was delayed. The delay in planting led to a decrease in leaf area, resulting in a decrease in the chlorophyll index during the late planting date. No application of nitrogen fertilizer had the highest seed oil percentage (29.4%), while the application of 75% chemical fertilizer + biofertilizer nitrogen resulted in the lowest oil percentage (18.5%). The delay in planting from early autumn to late spring led to a decrease in the seed oil percentage. This decrease can be attributed to increase in nitrogen content, which promotes the formation of nitrogenous protein precursors. Consequently, more photoassimilates are allocated to protein formation, reducing the available photoassimilates for fatty acid synthesis and, ultimately, limiting oil production capacity. The decrease in oil percentage observed in the most delayed planting dates is likely due to the increase in temperature during the seed filling stage and the reduction in net photosynthesis. Mean comparison of the interaction between nitrogen fertilizer and planting date on camelina grain yield showed that applying 75% chemical fertilizer + biofertilizer nitrogen, compared to no nitrogen fertilizer, on planting dates of September 11, 2021, September 26, 2021, April 9, 2022, and April 24, 2022, increased grain yield of camelina by 80, 100, 150, and 190 percent, respectively. Conclusions The Findings show that in the Eghlid region, autumn-sown camellia out-yields spring-sown one. Additionally, by using a combination of 75% chemical fertilizer and nitrogen biofertilizer, a higher grain yield is achieved compared to using 100% nitrogen chemical fertilizer alone. Considering the importance of production of oilseed plants, like camellia, in Iran and the need for sustainable plant production programs, it appears that growth-promoting bacteria can play a significant role in reducing the need for nitrogen fertilizers. [ABSTRACT FROM AUTHOR]
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