Extended Abstract
Introduction
Linseed (Linum usitatissimum L.) is a valuable medicinal and oilseed crop, rich in oil (30–48%), omega-3 fatty acids, vitamin E, and high-quality proteins. Its seeds contain essential amino acids and possess anti-inflammatory and anti-cancer properties. Recently, linseed cultivation has gained renewed interest in Iran. However, conventional agriculture has led to unstable ecosystems due to heavy reliance on synthetic inputs such as pesticides and chemical fertilizers. This unsustainable approach necessitates alternative nutrient management strategies that are more eco-friendly. Biofertilizers, which contain beneficial bacteria and fungi (e.g., nitrogen-fixing Azotobacter, phosphate-solubilizing bacteria), offer an effective solution for enhancing soil fertility, nutrient uptake, and plant productivity while minimizing environmental harm. Vermicompost, rich in organic matter and nutrients, and nano-fertilizers, with slow-release properties, also contribute to improved crop growth and nutrient efficiency. This study aimed to investigate the effects of different fertilizer sources—chemical, organic, biological, and integrated—on total chlorophyll, nutrient content (N, P, K, Zn, Fe), and yield components of linseed. The objective was to identify sustainable fertilizer regimes that enhance productivity while reducing chemical input.

Materials and Methods
The experiment was conducted in a randomized complete block design with 13 treatments in three replications in the spring and summer of 2013 at the research farm of the Faculty of Agriculture, Yasouj University. The experimental treatments were: T1-control (no fertilizer), T2-application of 90 kg/ha of urea fertilizer, T3-application of 10 tons/ha of vermicompost fertilizer, T4-application of 5 tons/ha of vermicompost fertilizer, T5-application of Barvar1 biofertilizer, T6-application of biofertilizer of nanoparticles of zinc, copper, iron and nitrogen-fixing bacteria, T7-application of 45 kg/ha of urea fertilizer along with 5 tons/ha of vermicompost, T8-application of 45 kg/ha of urea fertilizer along with Barvar1 biofertilizer, T9-application of 45 kg/ha of urea fertilizer along with biofertilizer of nanoparticles of zinc, copper, iron and nitrogen-fixing bacteria, T10-application of 5 tons/ha of vermicompost fertilizer along with biofertilizer of nanoparticles of zinc, copper, iron and nitrogen-fixing bacteria, T11-application of 5 tons per hectare of vermicompost along with Barvar1 biofertilizer, T12-application of 45 kg/ha of urea, 5 tons/ha of vermicompost and Barvar1 biofertilizer, T13-application of 45 kg per hectare of urea, 5 tons per hectare of vermicompost along with biofertilizer of nanoparticles of zinc, copper, iron and nitrogen-fixing bacteria.

Results and Discussion
The results of this study revealed that the application of different fertilizer sources had a significant influence on the growth, nutrient composition, and yield performance of linseed. Among the 13 treatments evaluated, the highest seed yield was recorded in the urea-only treatment (T2), reaching 1120.1 kg/ha. However, several integrated and organic treatments, particularly T13 (45 kg/ha urea + 5 t/ha vermicompost + nano-biofertilizer), T11, and T3 (vermicompost 10 t/ha), produced statistically similar results, indicating that comparable productivity could be achieved with lower chemical inputs when supplemented by organic or biological fertilizers. Total chlorophyll content was notably improved by organic treatments, especially T3, which produced the highest chlorophyll concentration (2.37 mg/g fresh weight). This suggests that vermicompost significantly enhances photosynthetic capacity, likely due to its high levels of organic matter, micronutrients, and beneficial microbial populations that improve soil structure and nutrient availability. Interestingly, T2, T7, and T12 also showed elevated chlorophyll levels, comparable to T3, demonstrating the effectiveness of moderate chemical applications when integrated with organic sources. Nitrogen accumulation in seeds also followed a similar trend, with T2 resulting in the highest nitrogen percentage (3.34%), followed closely by T3 and T13. The efficiency of nano-fertilizers in enhancing nitrogen availability through slow-release mechanisms and increased uptake efficiency may explain these improvements. This observation highlights the physiological advantages conferred by bio- and nano-fertilizers in enhancing nutrient absorption and utilization. Phosphorus content peaked in T10 (5 t/ha vermicompost + nano-fertilizer), but treatments T2, T9, T11, and T13 performed similarly. These findings indicate the crucial role of organic matter and microbial activity in improving phosphorus availability in the rhizosphere. Likewise, potassium content was highest in T13 (5793 mg/kg), reflecting the synergistic effect of integrated nutrient management. Other treatments, including T2, T3, and various combinations, produced similar potassium levels. Micronutrient enhancement was another notable outcome. The highest iron and zinc concentrations were observed in T3, followed closely by T13. This suggests that vermicompost and biofertilizers not only supply micronutrients directly but also improve their bioavailability through mechanisms such as rhizosphere acidification and siderophore production by rhizobacteria. Although T2 yielded the highest oil output per unit area (39.7 g/m²), several other treatments, particularly integrated ones like T13, achieved statistically similar yields. Interestingly, the oil percentage in seeds did not significantly differ across treatments, implying that the increased oil yield was primarily driven by enhanced seed productivity rather than changes in oil concentration. Overall, the combined use of urea with vermicompost and nano-biofertilizers enhanced both quantitative and qualitative traits in linseed, affirming the potential of integrated nutrient management to support high yields, improve seed nutrient density, and promote sustainable production systems. These results suggest that balanced fertilization strategies can optimize productivity while preserving ecological integrity and soil health.
Conclusions
The integrated application of chemical, organic, and biological fertilizers significantly improved yield, chlorophyll content, and nutrient accumulation in linseed. Among the treatments, T13 (45 kg/ha urea + 5 t/ha vermicompost + nano-biofertilizer) is recommended as a sustainable fertilization strategy, offering reduced chemical input without compromising yield or quality.