Yarrow (Achillea millefolium L.) is a valuable medicinal and aromatic plant, with its essential oil used in the pharmaceutical, food, and cosmetics industries. However, yarrow and other plants face significant environmental challenges, especially in arid and semiarid climates where water scarcity is a major threat to agricultural productivity. A new study by Farnaz Rezaei-Adl and Abdolah Ghasemi Pirbalouti, along with their colleagues, published in Scientific Reports, investigated how combining a soil amendmentA soil amendment is any material added to the soil to enhance its physical or chemical properties, improving its suitability for plant growth. Biochar is considered a soil amendment as it can improve soil structure, water retention, nutrient availability, and microbial activity.   More of biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More with a foliar spray of chitosan could help yarrow plants tolerate water deficit and improve the quality of their essential oil.

The researchers conducted a two-year experiment in a semiarid climate in Iran, testing different combinations of irrigation levels (optimum, moderate, and severe water deficit), biochar application, and chitosan spraying. The results showed that while water stress alone significantly reduced the biological and flower yields of the yarrow plant, the use of biochar and chitosan helped maintain higher yields. The highest biological yield (9,197.7 kg/ha) and flower yield (1,323.3 kg/ha) were from plants treated with both biochar and chitosan under optimum irrigation. Under severe water stress, the combined treatment still resulted in significantly higher yields compared to untreated plants.

Beyond physical yield, the study focused on the plant’s phytochemical responses. Water stress increases the production of reactive oxygen species in plants, which can cause damage. To counteract this, plants activate antioxidant defense mechanisms. The study found that water stress significantly increased the activity of antioxidant enzymes like catalase, peroxidase, and ascorbate peroxidase, as well as the antioxidant capacity measured by the DPPH method. When biochar and chitosan were applied, these defense mechanisms were further enhanced. For example, the highest DPPH antioxidant capacity (65.38%) was observed in plants treated with both biochar and chitosan under severe water stress.

The most notable findings came from the analysis of the essential oil composition. The researchers found that water stress generally led to a significant increase in the percentage of monoterpenes (such as a-pinene, 1,8-cineole, and borneol) and a decrease in sesquiterpenes (like β-bisabolene and caryophyllene oxide). The combination of biochar and chitosan under severe water stress had the most dramatic effect, increasing the total monoterpene content to 80.77%. This was a remarkable improvement over the untreated plants under optimum irrigation, which had a total monoterpene content of 41.51%. This suggests that the combined application of these two treatments can significantly enhance the quality of yarrow essential oil, making the plant more suitable for industrial applications.

In conclusion, this research highlights a synergistic effect between biochar and chitosan, demonstrating that their combined application can mitigate the negative effects of water stress on yarrow plants. This approach not only helps plants cope with arid conditions by improving growth and biochemical traits, but also significantly enhances the quality of their essential oil by boosting the desirable monoterpene compounds. The study provides a viable strategy for cultivating high-quality yarrow in water-scarce regions and offers a new direction for sustainable agriculture in arid and semiarid climates.

Source: Rezaei-Adl, F., Pirbalouti, A. G., Rahimi, T., Rajabzadeh, F., & Mozafari, H. (2025). Soil-based biochar and foliar-spraying of chitosan enhances the phytochemical traits of yarrow (Achillea millefolium L.) under varying moisture levels. Scientific Reports, 15(30881).