Introduction: Oil production is very important in the economy of any country, because oil consumption in the world has an increasing pattern. . However, in Iran, there is only about 10% self-sufficiency in oil production, and to meet the needs, it is necessary to import this important food item. For this reason, in recent years, more attention has been paid to the cultivation of oilseeds. Water deficit stress in the stage of reproductive growth severely reduces the yield of rapeseed because the number of seeds and the weight of seeds decrease. In some areas of Khuzestan province, rapeseed is mainly cultivated as a suitable plant for crop diversification and creating plant diversity. On the other hand, periodic conditions in Khuzestan province cause this plant to be cultivated outside the recommended planting date. This issue causes the growth period of rapeseed to coincide with the growth of some other crops. In this situation, some irrigation turns are necessarily allocated to other plants (including wheat which is in the pollination stage and okra which is in the germination stage), which causes rapeseed to face water shortage stress, even in the Flowering is possible. Based on this, it is necessary to apply appropriate management methods to reduce the effects of drought stress on rapeseed during the flowering stage.Thus, the current research was aimed to evaluate the response of rapeseed to organic fertilizer (cow manure) and potassium, and the possible effect of these food sources on reducing the effects of drought stress in the flowering stage on the quantitative and qualitative yield of rapeseed.
Materials and Methods: In this study, which was carried out during 2022-23 growing season at Payame Noor University of Shadegan, the effect of cow manure and potassium on the yield of rapeseed and oil under different irrigation conditions was evaluated. The experiment was split split plot with three replications, in which irrigation (full irrigation and interruption of irrigation during the flowering stage) was applied in the main plot, cow manure (0.0, 15 and 30 t ha-1) in the sub plot and potassium fertilizer (0.0 , 75 and 150 kg/ha) were placed in the sub-sub plot. To evaluate the effect of treatments on rapeseed, grain yield and grain yield components (including number of spikelet per plant and number of seeds per spikelet, 1000-grain weight), harvest index, biological yield and water productivity were measured. The quality of the grain was also determined by measuring the amount of protein and oil of the grain.
Results and Discussion: Drought stress during the flowering stage decreased the number of spikelet per plant, the number of grain per spikelet and consequently the grain yield by 27.3%, 19.2% and 19.6% respectively. By water shortage at flowering stage, the protein percentage of rapeseed increased from 24.2 to 27.6 percent. With the consumption of 30 t ha^-1 cow manure, the number of silique per plant, the number of grain per silique, and the grain yield increased by 27.4, 57.4, and 14.1 percent, respectively. In terms of grain quality, the use of cow manure improved the oil percentage and yield (10.4% and 24.2%, respectively), but the protein percentage of rapeseed decreased with the use of cow manure. Rapeseed grain quality increased in terms of oil percentage and oil yield in response to potassium consumption (4.3% and 25.8% for oil percentage and yield, respectively). Water productivity in drought stress conditions was about 39% higher than in full irrigation conditions. In any case, the highest water productivity was obtained by applying drought stress and using 30 t ha^-1 of cow manure. Under full irrigation conditions, rapeseed had the lowest water productivity and the use of cow manure could not significantly improve water productivity in rapeseed.
Conclusion: Drought stress reduced components of grain yield, grain yield and grain quality (based on oil percentage) of rapeseed. The consumption of potassium and cow manure led to the improvement of the studied traits. The use of cow manure (at the rate of 30 tons per hectare) in drought stress conditions resulted in achieving the highest water productivity. Therefore, it is recommended to use 30 t ha^-1 of cow manure and 150 kg ha^-1 of potassium fertilizer to achieve the highest yield and quality of rapeseed in conditions of interruption of irrigation during the flowering stage.