Introduction: Conventional agriculture has altered the dynamic balance of agroecosystems by decreasing soil fertility, reducing biodiversity, and putting human and animal health at risk due to chemical residue in agricultural products. To reduce these negative environmental impacts, sustainable agricultural systems have been promoted to protect resources and biodiversity. One of the effective strategies is the integrated management of organic and chemical fertilizers in sustainable agricultural systems. Flax is an oil plant of the Linaceae family, which is extensively used in the modern pharmaceutical and food industries. Flax seeds contain protein and oil. Considering the negative effect of the excessive use of chemical fertilizers on the quality of medicinal and oil plants, most food and pharmaceutical companies prefer materials derived from sustainable and organic systems. Therefore, this study was carried out to investigate the effects of integrated application of organic and chemical fertilizers on yield components, yield, and oil content of flax.
Materials and Methods: The field experiment was laid out in 2018-2019 growing seasons at the Research field of the University of Kurdistan, Iran (longitude 47° 18' E, the latitude of 35° 19' N and 1865 m altitude). The region has a semi-arid climate according to the Köppen climate classification. The experiment was carried out in a randomized complete block design with ten treatments and three replications. The experimental treatments included control, chemical fertilizer, farmyard manure, digested fertilizer, humic acid, farmyard manure + humic acid, digested fertilizer + humic acid, chemical fertilizer + humic acid, farmyard manure + chemical fertilizer, and digested fertilizer + chemical fertilizer. Each experimental plot consisted of six rows, 4 m long and at 35 cm row spacing. The amount of manure, urea, superphosphate triple, and digested fertilizer was 10 ton/ha, 150 kg/ha, 50 Kg/ha and 4 ton/ha respectively. Fifty percent of fertilizers were applied in the integrated treatments. The concentration of humic acid was 0.5 per thousand. The site was irrigated immediately after sowing the seeds and a drip irrigation system was used once a week. Weeding was done by hand as required. Quantitative traits were measured at the maturity stage.  Seed samples were collected after the harvest process. To extract the flax oil, a Soxhlet extraction with n-hexane solvent was used. The obtained data underwent analysis of variance (ANOVA) using SAS statistical software (SAS Version 9.1), where means were compared using LSD.
Results and Discussion: The results showed that treatments had a significant effect on the most measured traits in this study. The integrated treatments significantly increased plant height, capsule number per plant, sub-branches number, biological yield, grain yield, oil percentage, and oil yield. The traits consisted of grain number per capsule, primary branches, and 1000 grain weight of flax were not affected by the treatments significantly. The highest value of biological yield (2440 kg/ha) and grain oil content (30%) was recorded in the integrated treatments of digested fertilizer + chemical fertilizer and digested fertilizer +humic acid, respectively. The integrated treatments of digested fertilizer + humic acid, farmyard manure + humic acid, chemical fertilizer + humic acid, humic acid, and digested fertilizer + chemical fertilizer significantly increased grain oil content by 36.66, 34.84, 29.63, 28.73, and 26.92 % compared to control, respectively. The highest value of grain yield (688.3 kg/ha) and oil yield (185.9 kg/ha) was obtained in the integrated treatment of humic acid + chemical fertilizer. The lowest of mentioned characteristics belonged to the control treatment. The integrated treatments of humic acid + chemical fertilizer and farmyard manure + chemical fertilizer significantly increased grain yield by 30.46 and 29.43% compared to control, respectively. The integrated treatment of chemical fertilizer + humic acid increased oil yield by 19.39, 33.69, 30.01, and 19.64 % compared to chemical fertilizer, farmyard manure, digested fertilizer, and humic acid, respectively. Environmental conditions and plant nutrition are effective factors on the growth and yield of crops. It can be said that combined treatment increased the positive effect of organic fertilizers and there were synergistic interactions between them.
Conclusion: The integrated treatments of organic and chemical fertilizers improved the flax characteristics compared to chemical fertilizers application singly. Overall reasonable management of fertilizers not only improved flax yield but only protected environmental safety.