The objective of this study was to investigate the feasibility of replacing nitrogen chemical fertilizer with organic soil amendments and determining the optimum planting density based on quality of Persian borage (Echium amoenom Fisch. & Mey.) yield in an ecological system. A split plot arrangement based on a randomized complete block design (RCBD) design with three replications was conducted. Three plant densities (10, 5, and 3 plants m−2) were allocated to the main plots and five different types of organic and chemical fertilizers (compost by 10 t ha−1, vermicompost by 7 t ha−1, cattle manure by 30 t ha−1, chemical nitrogen fertilizer as urea by 180 kg ha−1 and the control) were allocated to the subplots. The results showed that the highest antioxidant capacity (79 mg ml−1) was obtained from the density of 10 plants m−2 and the highest total phenolic content (51 mg gallic acid equivalent g−1 flower dry weight) was observed in the density of 5 plants m−2. Application of compost, vermicompost, cattle manure, and chemical fertilizer increased total phenolic content compared with the control by 51%, 35%, 40%, and 63%, respectively. Application of vermicompost and cattle manure in a density of 3 plants m−2, compared with the control, increased total flavonoid up to 39% and 38%, respectively. The highest total anthocyanin was obtained from the density of 5 plants m−2. Application of vermicompost and cattle manure increased the seed oil content by 10% and 13%, and seed protein content by 34% and 13%, respectively compared with the control. In general, the findings of this research suggest that the application of organic fertilizers and the optimal plant density could result in improved quality and quantity of Persian borage without the hazardous consequences of chemical nitrogen fertilizer in a low-input cropping system.

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